ATTACHMENTS 1 Mark Quarles CV 2 Determination of vertical and horizontal pathways of injected fresh wastewater into a

deep saline aquifer (Florida USA) using natural chemical traces Hydrogeology Journal by Walsh Virginia and Price Rene published online February 2010

3 Evaluation of Confining Later Integrity Beneath the South District Wastewater Treatment Plant Miami-Dade Water and Sewer Department Dade County Florida by the Idaho National Engineering and Environmental Laboratory INEEL EXT-01-00046 February 2001

4 NPDES Permit Writerrsquos Manual chapter 8 US EPA EPA-833-B-B-96-003 December 1996

5 Toxicological Profile for Heptachlor and Heptachlor Epoxide chapters 1 and 2 Agency for Toxic Substances and Disease Registry November 2007

6 Tox FAQ Ethylbenzene Agency for Toxic Substances and Disease Registry September 2007

7 Tox FAQ Heptachlor and Heptachlor Epoxide Agency for Toxic Substances and Disease Registry August 2007

8 Tox FAQ Toluene Agency for Toxic Substances and Disease Registry February 2001 9 Tox FAQ Tetrachloroethene Agency for Toxic Substances and Disease Registry

September 1997 10 Tox FAQ Trichloroethylene Agency for Toxic Substances and Disease Registry July

2003 11 Tox FAQ Thallium Agency for Toxic Substances and Disease Registry September

1995 12 Tox FAQ Selenium Agency for Toxic Substances and Disease Registry September

2003 13 Tox FAQ Vinyl Chloride Agency for Toxic Substances and Disease Registry July 2006

MARK A QUARLES PG PROFESSIONAL SUMMARY AND TECHNICAL SPECIALTIES Environmental consultant with approximately 25 years experience in the following coal combustion waste management oil exploration and production waste management hydraulic fracturing for unconventional natural gas hazardous waste management and permitting landfill siting and design utility line environmental assessments hydrogeologic investigations multi-media environmental auditing water and wastewater permitting municipal and industrial stormwater permitting wetland permitting and mitigation reservoir capacity studies and soil groundwater remediation EDUCATION Master of Business Administration Owen Graduate School of Management Vanderbilt University Nashville Tennessee Bachelor of Science Environmental Engineering Technology Western Kentucky University Bowling Green Kentucky PROFESSIONAL EXPERIENCE Global Environmental LLC Nashville Tennessee 2004 to current

Environmental consultant for projects in the United States and South America including as examples reservoir capacity studies public and private utility line permitting municipal stormwater management landfill siting threatened and endangered species groundwater contamination and supply wetland permitting and mitigation surface water contamination and supply and soil contamination

EMPE Inc Nashville Tennessee 1996 to 2001 Project Manager in wide-ranging environmental projects that included as examples stormwater permitting spill prevention and response plans hazardous waste management landfill permitting land development and contaminant fate and transport investigations Managed Fortune 500 industrial client projects throughout the eastern US

SECOR International Inc Franklin Tennessee 1994 to 1996 Senior Engineer Senior Geologist and Project Manager for industrial waste management projects throughout the southeast US that included as examples hydrogeologic investigations and stormwater permitting Managed Fortune 500 industrial client projects throughout the eastern US

RMT Inc Nashville Tennessee 1990 to 1994 Project Engineer and Project Manager for industrial and municipal projects throughout the eastern US for projects that included as examples petroleum underground storage tank removals soil and groundwater remediation landfill siting and design spill prevention and response plans hazardous waste audits industrial stormwater permitting and property transfer assessments

RJN Group Atlanta Georgia and Boston Massachusetts 1987 to 1990 Project Engineer for municipal projects throughout the eastern US for projects that included as examples sanitary sewer hydraulic modeling for drainage basins in excess of 1 million linear feet of conveyance and conducting infiltration and inflow investigations for sanitary sewers

Howard K Bell Consulting Engineers Hopkinsville Kentucky 1985 to 1987 Project Engineer for municipal sanitary sewer water line and landfill design projects in Kentucky

PROFESSIONAL REGISTRATIONS AND CERTIFICATIONS Licensed Professional Geologist (PG) Tennessee Certified Hazardous Materials Manager Masters Level (1993 ndash 2001) Class II Water Pollution Control Operator Massachusetts (1988)

MARK A QUARLES PG PAGE 2 RANGE OF TECHNICAL EXPERIENCE Oil and Gas Exploration and Production Wastes bull Aguida vs ChevronTexaco - Amazon Basin Ecuador

Provided technical support to the plaintiffs related to the first environmental class action lawsuit in South America Ecuadorian judgment resulted in a $10 billion damage against Chevron Work demonstrated that Texacorsquos work in the upper Amazonian jungle of Ecuador did not meet industry standards did not meet practices employed by Texaco from the 1920s through the 1990s and violated international and national water and soil quality standards

bull FECONACO ndash Amazon Basin Peru Provided independent third-party evaluation of crude oil remediation activities of 75 sites in

Block 1AB in the Amazonian jungle occupied by three indigenous groups The work included a) sampling of soil sediment and surface water contamination from present day and legacy operations b) an evaluation on the effectiveness of in-situ bioremediation as the chosen remedial alternative and c) a comparison of cleanup activities relative to Peruvian and US standards

bull Tulane Environmental Law Clinic ndash New Orleans Louisiana Reviewed a draft permit and provided written legal testimony associated with a Draft General

Permit for Discharges from Oil and Gas Exploration Development and Production Facilities The project consisted of comparing proposed effluent limitations to Federal standards comparing sampling parameters to expected exploration and production waste contaminants and recommending additional monitoring schemes that were more reflective of the risks

Coal Combustion Wastes bull Environmental Integrity Project Sierra Club and Earthjusticendash Washington DC

Reviewed historical coal-fired power plant file information and groundwater water monitoring reports for coal combustion waste (CCW) landfills and coal ash impoundments to identify previously undetermined damage cases according to EPA protocol Results were summarized in two co-authored reports Out of Control (February 2010) and In Harms Way (August 2010)

bull Sierra Club - Washington DC Reviewed historical groundwater monitoring reports associated with coal ash landfills and impoundments for 10 coal-fired power plants in Kentucky to identify impacts to groundwater relative to EPA damage case standards

bull Prairie Rivers Network - Champaign Illinois Evaluated Illinois standards for the disposal and beneficial re-use of coal of CCWs compared to national solid waste and surface impoundment disposal standards The project also included an in-depth analysis of material chemical and physical characteristics a summary of site characterization and siting standards and a summary of national damage assessment cases

bull Confidential Client ndash Kingston Tennessee Implemented a surface water monitoring program to determine the lateral extent of 54 million

cubic yards of CCWs that were released to the surface water from a surface impoundment failure at the Tennessee Valley Authority (TVA) Kingston coal-fired power plant

bull Kentucky Waterways Alliance ndash Henderson Kentucky Provided technical review of a draft wastewater discharge permit associated with the proposed

Cash Creek Integrated Gasification Combined Cycle (IGCC) plant and associated landfill At the time only two such plants were operational in the United States The review included a wastewater discharge compliance review of the other plants research into IGCC wastewater and solid waste constituents and a comparison to the proposed discharge criteria

bull Sierra Club ndash Bedford Kentucky Provided technical review of a draft wastewater discharge permit associated with the Trimble

County Generating Station pulverized coal (PC) power plant and flue gas de-sulfurization (FGD) process expansion Research was completed on the characteristics of FGD process and gypsum by-product wastes the leachability of solid wastes the characteristics of PC plant cooling water blowdown metal cleaning wastewater stormwater runoff and coal and limestone pile runoff

MARK A QUARLES PG PAGE 3

the structural integrity of an existing ash surface impoundment proposed for vertical expansion and the technical feasibility of a proposed gypsum disposal surface impoundment

Unconventional Natural Gas and Hydraulic Fracturing bull Shenandoah Valley Network Shenandoah Riverkeeper - Virginia Provided technical review of an application for the first proposed deep shale natural gas well in

Virginia The report evaluated among others the proposed plan for hydraulic fracturing storage of produced waters and flow back protection of groundwater supplies treatment and disposal of wastes and the location relative to the floodplain The applicant decided to rescind their application following submittal of the technical report critical of the proposed well action

bull Sierra Club Washington DC Provided technical comments regarding proposed Tennessee oil and gas regulations with a

particular emphasis on well casing standards fracture chemical disclosure and baseline post drilling monitoring for fracture chemicals and methane intrusion Compared the proposed regulations to API industry standards and other state regulations and provided recommendations for changes

Utility Line Environmental Assessments bull Private Landowner - Livingston Tennessee Served as lead consultant to prevent a proposed Corps of Engineer development Arguments

included identifying deficiencies in the aquatic resources alteration permit the cultural resources survey the stream use classification and the Section 404 application Negotiated alternate route

bull Private Landowner ndash Bowling Green Kentucky Served as lead consultant to provide technical comments to a Draft EA for the construction of a

220-mile electrical powerline Technical legal and financial reporting resulted in stopping the project in its entirety the Public Services Commission revoking the certificate of need (CON) and the Kentucky Attorney General conducting a formal investigation

bull Sumner Trousdale Opposing Pipeline ndash Gallatin Tennessee Served as lead consultant to identify deficiencies in the wetland and aquatic resources alteration

permits for a proposed 30-mile natural gas pipeline to represent the group in public hearings and develop technical arguments for against the proposed pipeline

Reservoir Water Quality and Use Assessments bull Friends of Tims Ford ndash Tims Ford Reservoir - Winchester Tennessee ndash served as lead consultant

to provide comments on Section 10 and Section 26A Regulation permit applications and a Recreational Boating Capacity Study for reservoir-wide community boat docks associated with residential development

bull Honeycomb Homeownerrsquos Association - Guntersville Lake ndash Guntersville Alabama ndash served as lead consultant to provide comments to Section 10 and Section 26A Regulation permit applications for residential developments Completed a detailed assessment of reservoir water quality results relative to designated use standards

bull Murrayrsquos Loch ndash Atlanta Georgia Served as consultant to evaluate the technical merits of a water withdrawal permit and the effects of increased urbanization on stormwater runoff and groundwater recharge Water withdrawal for commercial irrigation purposes resulted in decreased water levels in lakefront property of an adjacent residential neighborhood The permit was appealed to the State Administrative Court

Multi-Media Environmental Permitting bull Nashville Superspeedway USA Inc ndash Lebanon Tennessee

Served as Project Manager for a $125 million superspeedway development The environmental aspects included the requirements to determine the affects of the project on public and private groundwater users stream alterations wetlands endangered plant and animal species air permitting stormwater runoff oil pollution prevention underground injection control and due diligence property assessment

MARK A QUARLES PG PAGE 4 bull Metropolitan Knoxville Airport Authority ndash Knoxville Tennessee

Served as Project Manager for all environmental permitting and compliance activities Activities included spill prevention and response plan development stormwater plan development fuel tank farm design and compliance inspections

bull Various Industrial Clients ndash Tennessee Served as Project Manager for the development of SPCC Plans and SWPP Plans Plans were prepared consistent with the requirements of 40 CFR Part 112 the Tennessee General Permit the EPA Multi-Sector permit and the Tennessee Construction General Permit

Environmental Investigations and Remediation bull USEPA ndash Dickson County Tennessee

Served as Senior Geologist to investigate the occurrence of a cluster of cleft palate cleft lip birth defects in the county relative to the occurrence of trichloroethene in the groundwater and public water supply Reviewed EPA and TDEC regulatory files CDC and Department of Health reports interviewed City County TDEC and EPA officials and interpreted regional karst geologic and hydrogeologic data

bull Harpeth River Watershed Association ndash Franklin Tennessee Served as technical advisor for a review of the environmental investigation report and corrective action plan Contaminants of concern included free product toluene dissolved-phase BTEX constituents dissolved-phase acetone and dissolved-phase chlorinated solvents

bull Natural Resources Defense Council ndash Confidential Location Served as technical advisor for development of a Complaint for Declaratory and Injunctive Relief related to the inappropriate disposal investigation and cleanup of volatile organic compounds in soil groundwater and surface water

bull Confidential Client ndash McMinnville Tennessee Served as Project Manager to identify quantify and remediate the extent of a release of chlorinated solvents in a karst geologic setting Activities included the completion of an interim remedial action a soil gas survey direct push soil borings monitoring wells and well nests dye injection studies streambed sampling and a feasibility analysis

bull Burlington Northern Railroad - Birmingham Alabama Served as a Senior Geologist for an LNAPL investigation The investigation included the installation of temporary piezometers soil borings and permanent groundwater monitoring wells

bull Sunbeam Outdoor Products Inc - Neosho Missouri Developed a Field Sampling and Analysis Plan for the sampling of soils and drummed liquids for a Removal Action required by EPA Region VII Heavy metals and volatile organic compounds were the contaminants of concern in a karst geologic setting

bull United Technologies Automotive Inc - Quincy Michigan Served as Project Manager for groundwater well sampling and the development of an in-situ remedial action for heavy metal contamination

bull United Technologies Automotive Inc - Morganfield Kentucky Served as Project Engineer for a lagoon closure Completed activities for sludge characterization and quantification special waste permitting and closure design for material excavation and site restoration

Solid Waste Disposal bull Meriwether County Landfill Permit Appeal ndash Atlanta Georgia

Served as consultant to evaluate the technical merits of a municipal solid waste disposal permit that had been issued by the Georgia EPD Key technical issues were placement of the landfill adjacent to a public surface water supply typical liner performance and landfill leakage history in Georgia The permit was appealed to the Georgia Administrative Court

bull Various Secondary Aluminum Smelter Waste Landfills - Tennessee Reviewed secondary aluminum smelter waste characterization results landfill designs and associated hydrogeologic investigation reports for two proposed Class II industrial monofill landfill applications and reviewed groundwater monitoring reports associated with three co-mingled municipal solid waste landfills that used dross for intermediate daily cover

MARK A QUARLES PG PAGE 5 bull Various Industrial Landfills - Tennessee

Served as Project Manager for Subtitle D landfill siting and design projects Performed hydrogeologic investigations presented design waivers for site-specific design criteria (when applicable) and developed detailed designs for permitting

bull Various Landfills - Tennessee Served as Project Manager for the design permitting and operation of industrial and municipal solid waste landfills preparation of SWPP Plans quarterly groundwater and gas monitoring reports and hydrogeologic investigation reports

bull Various Municipal Landfills - Kentucky Served as Project Engineer for the design permitting and operation of municipal solid waste landfills

Stormwater Permitting and Compliance bull Tennessee Clean Water Network ndash Knoxville Tennessee

Served as lead consultant for providing technical comments for the draft Knox County Phase II Municipal Separate Storm Sewer System (MS4) permit

bull Various Industrial Clients - Throughout the US Served as Project Manager to obtain permit coverage through the EPA General Permit group permits and individual permits specific to each state Over 125 facilities were permitted

Hazardous Waste Management bull Various Industrial Clients ndash Throughout the US

Served as Project Manager for various projects to evaluate hazardous waste management practices consistent with the rules and regulations established under RCRA

bull Laidlaw Environmental Services Inc ndash Southeastern US Completed SWPP Plans for RCRA treatment storage and disposal facilities

Municipal Wastewater Management bull Various Municipalities ndash Fulton Cobb and Dekalb County Georgia

Served as Project Engineer for sewer modeling and point-source identification Identified sources of infiltration inflow and performed cost evaluations for source removal

bull Various Municipal and Industrial Clients ndash Tennessee Served as Project Engineer to establish beneficial reuse land application programs for wastewater sludge

bull Boston Water and Sewer Commission - Boston Massachusetts Served as Project Engineer for sewer modeling and point-source identification projects of combined and separate sewers up to 15 feet in diameter Identified sources of infiltration inflow and performed cost evaluations for source removal

bull Various Municipal Clients ndash Throughout the US Served as lead technical trainer for the implementation of proprietary software used for automated GIS mapping maintenance scheduling and hydraulic analyses of separate and combined sewers

bull City of Hopkinsville - Hopkinsville Kentucky Served as Project Engineer for water and sewer line expansions and wastewater treatment projects

TECHNICAL PUBLICATIONS AND LECTURES bull Quarles M and William Wilson ldquoUnconventional Natural Gas and its Risk A Tennessee

Perspectiverdquo Appalachian Public Interest Environmental Law Conference Knoxville Tennessee October 2011

bull Quarles M ldquoA Case Study in Karst Hydrogeology and Contaminant Fate and Transportrdquo National Groundwater Association 51st Annual Convention and Exposition December 1999

bull Quarles M and Allen P Lusby ldquoEnhanced Biodegradation of Kerosene-Affected Groundwater and Soilrdquo 1994 Annual Conference of the Academy of Hazardous Materials Managers October 1994

MARK A QUARLES PG PAGE 6 bull Quarles M ldquoNew Tank Performance Standardsrdquo Tennessee Environmental Law Letter July

1993 EXPERT LEGAL TESTIMONY bull Chesney versus Tennessee Valley Authority ndash 2011 US District Court Written testimony

associated with fly and bottom ash sampling waste characterization contaminant fate and transport and contaminant risks compared to US EPA screening levels drinking water standards fish and aquatic life standards and sediment cleanup standards

bull Busch et al versus Dr Carol Couch Atlanta Georgia 2008 State Administrative Court Written and verbal testimony regarding drought restrictive surface water and groundwater use Qualified by the court as an expert in geology hydrogeology and stormwater runoff

bull Darrel Segraves et al versus Dr Carol Couch Atlanta Georgia 2008 State Administrative Court Written and verbal testimony regarding appeal of a municipal solid waste landfill permit Qualified by the court as an expert in geology hydrogeology landfill design pertaining to landfill leakage and stormwater runoff

bull Tulane Environmental Law Clinic 2007 - 2008 Written testimony for numerous draft LDEQ permits and proposed rules

bull Republic of Ecuador and PetroEcuador vs Chevron Texaco Corporation and Texaco Petroleum Company US District Court Southern District of New York 2007 Written testimony regarding environmental investigation protocol

bull Friends of Tims Ford vs Tennessee Valley Authority and Tennessee Department of Environment and Conservation US District Court 2007 Written testimony in support of violations of State and Federal water quality standards reservoir carrying capacity standards and NEPA environmental assessment standards

bull Freddie Howell vs Creative Customs Atlanta Georgia 2007 Technical support regarding litigation associated with stormwater and groundwater flow and their effects on the Howell property

bull Aguida vs ChevronTexaco Lago Agrio Ecuador Court 2006 Written testimony regarding Texacorsquos waste management and standard operating practices in the Ecuadorian concession area relative to industry standards

TRAINING Current Wetland Issues in Tennessee (2007) Professional Liability Education - Contract Review and Revision (2000) Professional Liability Education ndash Mid-Town Developer Case Study Workshop (1999) Professional Liability Education ndash Liability IQ for Environmental Consultants (1998) Liquid Animal Waste Management System Design to NRCS Standards for CAFO (1998) 8-Hour OSHA Health and Safety Refresher Training Hazardous Materials Waste Manager Course University of Alabama (1993) 40-Hour OSHA Health and Safety Training (1990) CONTACT INFORMATION Home telephone 615-352-0471 Mobile telephone 615-504-0956 Email markquarlescomcastnet

Determination of vertical and horizontal pathways of injected freshwastewater into a deep saline aquifer (Florida USA) using naturalchemical tracers

Virginia Walsh amp Reneacute M Price

Abstract Two deep-well injection sites in south FloridaUSA inject an average of 430 million liters per day(MLD) of treated domestic fresh wastewater into a deepsaline aquifer 900m below land surface Elevated levels ofNH3 (highest concentration 939micromol) in the overlyingaquifer above ambient concentrations (concentration lessthan 30micromol) were evidence of the upward migration ofinjected fluids Three pathways were distinguished basedon ammonium chloride and bromide ratios and temper-ature At the South District Wastewater Treatment Plantthe tracer ratios showed that the injectate remainedchemically distinct as it migrated upwards through rapidvertical pathways via density-driven buoyancy Thewarmer injectate (mean 28degC) retained the temperaturesignal as it vertically migrated upwards however thetemperature signal did not persist as the injectate movedhorizontally into the overlying aquifers Once introducedthe injectate moved slowly horizontally through theaquifer and mixed with ambient water At the NorthDistrict Wastewater Treatment Plant data provide strongevidence of a one-time pulse of injectate into theoverlying aquifers due to improper well construction Noevidence of rapid vertical pathways was observed at theNorth District Wastewater Treatment Plant

Keywords Waste disposal Deep well injection Carbonate rocks Confining units Ammonia Temperature USA

Introduction

Deep well injection of treated municipal wastewater intonon-potable aquifers has been used as an alternative todischarge of wastewater to surface waters for manydecades There are 430 permitted municipal wastewaterdeep injection wells in the United States with 163 inFlorida alone (USEPA 2008) These deep aquifers tend tobe saline and the discharge of fresh wastewater into themhas raised concerns of geochemical reactions as a result ofthe mixing of the two waters as well as the buoyanttransport of the wastewater upwards into overlyingaquifers Confined brackish aquifers in Florida have beenused extensively for aquifer storage and recovery (ASR)of potable freshwater (Arthur et al 2001 Renken et al2005) and deeper saline aquifers have been used fordisposal of waste fluids such as oil brines industrial waterand municipal wastewater (Meyer 1989a Meyer 1989b)ASR in Florida has been extensively studied as part of theComprehensive Everglades Restoration Plan (Reese 2002Mirecki 2004 Mirecki 2006) however little research hasbeen published regarding the fate and transport of thetreated wastewater into deep saline aquifers (Meyer1989a Haberfeld 1991 Maliva and Walker 1998Bloetscher et al 2005 Bloetscher and Muniz 2006Maliva et al 2007)

Miami-Dade County Water and Sewer Department(MDWASD) located in southern Florida currently dis-charges 430 million liters per day (MLD) of treateddomestic wastewater into a saline deep aquifer at twolocations in the county Deep well injection has been inuse in Miami-Dade County since the late 1960s Theinjection facilities are located in the north and south of thecounty separated by 44 km (Fig 1) The South DistrictWastewater Treatment Plant (SDWWTP) site was placedinto service in 1983 and is currently permitted for thedisposal of 367 MLD of treated wastewater The NorthDistrict Wastewater Treatment Plant (NDWWTP) site wasplaced into service in 1997 and is permitted for 90 MLD

Received 2 February 2009 Accepted 14 December 2009

copy Springer-Verlag 2010

V Walsh ())Miami-Dade Water and Sewer Department3071 SW 38th Ave Miami FL 33146 USAe-mail walshvmiamidadegov

V WalshDepartment of Earth and EnvironmentFlorida International University11200 SW 8th Street University Park Miami 33199 USA

R M PriceDepartment of Earth and Environment and SoutheastEnvironmental Research CenterFlorida International University11200 SW 8th Street University Park Miami 33199 USA

Hydrogeology Journal DOI 101007s10040-009-0570-8

Both facilities treat domestic wastewater to above second-ary drinking water standards and discharge the treatedwastewater into United States Environmental ProtectionAgency (USEPA) Class I injection wells The treatedwastewater is injected into the Boulder Zone a highlytransmissive interval in the deep saline non-potable LowerFloridan Aquifer The Boulder Zone has been thought to behydrologically separated from overlying aquifers by a335-m-thick confining unit During the installation of addi-tional monitoring wells at the SDWWTP in 1994 ammonia-nitrogen (NH3-N) was detected at 442 m depth in theoverlying aquifer at a concentration of 411 micromoles perliter (micromol) above reported background levels of 29micromol

(BCampECH2M Hill 1977) The detection of NH3ndashN in theaquifers above the Boulder Zone has raised doubts regardingthe efficacy of the confining unit and the resultant waterquality impact to overlying aquifers as these aquifers areused as alternative water supplies via storage of freshwater(ASR) and blending with potable surficial aquifer water

Research has focused on ASR in south Florida (Arthuret al 2001 Reese 2002 Mirecki 2004 Mirecki 2006Reese and Richardson 2008) however few studies havebeen conducted regarding the transport and fate of injectedeffluent into the Boulder Zone and typically these had todo with the relative risk of deep well injection versusocean outfall disposal of municipal waste (Englehardt et

Fig 1 Location of theNDWWTP and the SDWWTPstudy sites

Hydrogeology Journal DOI 101007s10040-009-0570-8

al 2001 USEPA 2003 Bloetscher et al 2005 Bloetscherand Muniz 2006) Recently researchers have studied thetransport mechanisms of the observed migrated injectateand have suggested density-driven buoyant transportmechanism along natural or anthropogenic vertical frac-tures in the lower aquifers (Maliva and Walker 1998McNeill 2000 McNeill 2002 Maliva et al 2007 Walshand Price 2008) The objective of this study was todetermine migration pathways of injected treated waste-water at two facilities in Miami-Dade County Florida(SDWWTP and NDWWTP) using historical time seriesdata and major ion data collected as part of this study Themethodology developed for this study used chloride (Clminus)bromide (Brminus) and NH3 as tracers This methodologyprovided a method for estimating transport pathways andinvolved no additional collection of data other than whatwas typically required under federal and state regulatoryprograms

Natural inorganic tracers have been used extensively inwater resources investigations to trace groundwater flowpaths and calculate mixed water ratios (Langmuir 1997Davis et al 1998 Herczeg and Edmunds 2000) Clminus andBrminus commonly are used as they tend to be conservativeand their ratios may also give information as to the sourceand pathways of water Studies have been conducted insouth Florida (Shinn et al 1994 Paul et al 1997 Corbettet al 2000 Boumlhlke et al 2003) and elsewhere (Kaehlerand Belitz 2003 Clark et al 2004) tracing treatedwastewater in surficial aquifers but NH3 was not used asa tracer as it does not behave conservatively in oxicwaters In this study a novel application of Clminus Brminus andNH3 as conservative tracers of injectate was developed aspart of mixing models to distinguish pathways betweenthe deep aquifers Clminus is a natural anion in the Floridanaquifer system and its principal source is seawater asthere are no evaporite minerals to provide an additionalsource (Sprinkle 1989 Reese 1994) The seawater sourceof Clminus in south Florida is thought to be the result of eitherincomplete flushing of Pleistocene seawater and brackishwater intrusion andor the result of the cyclic flow basedon thermal upwelling of Holocene intruded seawater(Kohout 1965 Sprinkle 1989 Reese 1994) Bromide(Brminus) behaves similar to Clminus in groundwater systems(Davis et al 1998) and in south Florida the source of Brminus

in groundwater is similar to that of Clminus although its naturalabundances are orders of magnitude less than Clminus Theonly source of the NH3 is the injectate and therefore itwas used to trace transport pathways of the injectedwastewater

Geologic and hydrogeologic framework

The Floridan aquifer system (FAS) in southeastern Floridais defined by a vertically continuous sequence of per-meable carbonate rocks of Cenozoic age that are hydrauli-cally connected in varying degrees (Miller 1986) Theaquifer matrix consists of carbonate and dolomitic lime-stones dating from the Paleocene to the Oligocene

epochs Overlying the FAS are the impermeable sedimentsof the late Oligocene to Pliocene age Hawthorn Group a180-m-thick confining layer of clays siltstones and siltylimestones The Hawthorn Group separates the UpperFloridan Aquifer from the late Pliocene and Pleistoceneformations making up the Surficial Aquifer System whichincludes the Biscayne Aquifer in south Florida (Fig 2)The Biscayne Aquifer is an unconfined surficial aquiferand is the major source of potable water in south Florida(Fish and Stewart 1991)

The Floridan Aquifer contains several highly perme-able and less permeable zones with zones of highestpermeabilities typically occurring at or near unconform-ities and usually parallel to the bedding planes (Meyer1989a) Previous studies (Miller 1986 Reese 1994)grouped the Floridan aquifer system into three hydro-stratigraphic units (Fig 2) the Upper Floridan Aquifer(UFA) the Middle Confining Unit (MCU) and the LowerFloridan Aquifer Recently the MCU in south Florida hasbeen divided into the MC1 and MC2 (Fig 2) separatedby the Avon Park permeable layer (Reese and Richardson2008) which in south Florida had previously beenidentified as the Middle Floridan Aquifer The UpperFloridan Aquifer contains relatively fresh water less than10000 mg Lminus1 total dissolved solids (TDS) The LowerFloridan Aquifer consists of seminconfining or leakymicritic limestone and dolomite layers that containgroundwater with compositions approaching seawater(approximately 30000 mg Lminus1 TDS) A dolomite confin-ing unit (DCU) a thin confining unit below the MC2 wascharacterized at the study site by McNeill (McNeill 20002002) This DCU lies above the permeable zone com-monly known as the Boulder Zone within the OldsmarFormation of the Lower Floridan Aquifer The FASoutcrops along the Straits of Florida providing a hydraulicconnection to the sea (Kohout 1965 Miller 1986 Reese1994) Transmissivities in the Upper Florida Aquiferrange from 929 to 23times104m2 dayminus1 (Meyer 1989a Reese1994) while transmissivities in the Boulder Zone rangefrom 297times105m2 dayminus1 to 232times106m2 dayminus1

Site descriptionsThe NDWWTP and the SDWWTP consist of deepinjection wells that penetrate down to approximately855 m The upper 755 m of each well is cased to the topof the Boulder Zone The bottom 100 m of each injectionwell is an open hole in the Boulder Zone Nine suchinjection wells and three multi-zoned and dual-zonedmonitoring wells were constructed between 1977 and1981 at the SDWWTP (Fig 3) The multi-zone test wellBZ cluster (BZ-1 through 4) was constructed in 1977 andconsisted of four telescoping monitoring wells the deepestof which was BZ-4 cased to the top of the Boulder Zonethe shallowest BZ-1 open to the UFA at a depth of 312 mThe remaining monitoring wells were constructed bothat the SDWWTP and NDWWTP using a dual zone designwith an inner steel casing drilled to the deeper intervaland the outer steel casing open to the upper interval For

Hydrogeology Journal DOI 101007s10040-009-0570-8

this report well nomenclature indicates the open intervalof the dual-casing ldquoUrdquo represents the upper monitoringinterval and ldquoLrdquo represents the lower monitoring intervalWells 1 and 2 were dual-cased to monitor water quality inthe UFA (sim300 m) and the lower confining units (sim550 mCH2MHill 1981) In 1994 NH3 was detected aboveambient levels in the confining unit at the BZ well cluster(BZ-2 depth 488 m) and subsequent investigations by theutility found a leak due to corrosion of the casing in thiscluster (MDWASD 1995) The lower three monitoringintervals of the BZ well cluster were plugged in 1995 tostop the upward migration of injectate through the casinghole and the confining unit (488 m) monitoring intervalwas redrilled From 1995ndash1996 nine injection wells and

thirteen dual-zoned monitoring wells were constructed onthe SDWWTP These monitoring wells were cased to theAvon Park Permeable zone (APPZ) and the MC2 withopen holes in the formations approximately 30 m Duringthe construction of the monitoring wells NH3 concen-trations above ambient levels were found throughout thesite Elevated NH3 concentrations were found in thenorthwest corner of the site in the MC1 interval in severalwells but not in the lower MC2 interval of these wellsElevated levels were found in the MC2 interval in thesouth side of the site As a result of the detected NH3 inthe confining units the EPA required purging of the wellsthat showed elevated concentrations NH3 (Starr et al2001) in an attempt to remove the NH3 loading in the

Fig 2 Geologic and hydrogeologic framework of NDWWTP and the SDWWTP modified from Reese and Richardson 2008 Welldiagram on the right shows the number of wells open to the indicated hydrogeologic unit used for this study

Fig 3 Well locations at theSDWWTP

Hydrogeology Journal DOI 101007s10040-009-0570-8

impacted intervals Discontinuous purging of approxi-mately 2100 Lmin commenced from 1997 to 2000 forthe northwest wells (5U 6U 7U 8U 15U and 16U) of theAPPZ interval and the south wells (11L and 12L) of theMC2 (MDWASD 2000)

Injection well construction started at the NDWWTP in1996 Four injection wells were constructed into theBoulder Zone and four dual-zoned monitoring wells wereconstructed to the UFA and the APPZ intervals (Fig 4) In1996 effluent was injected in two completed injectionwells while one injection well was still under constructionresulting in injectate backflowing into an open borehole atan uncased injection well for 5 days Several months afterthe construction of the wells had been completed NH3

concentrations were observed to increase in the APPZinterval of the monitoring wells on site The utility wasrequired to purge the APPZ interval wells for a period of1 year from 2003ndash2004 (MDWASD 2005)

Methodology

Historical data were collected and checked for qualityassurance for the NDWWTP and SDWWTP Data wereavailable from 1983 through 2007 for the SDWWTP and1996ndash2007 for the NDWTP Data studied as part of thisresearch included pressure temperature pH Clminus sulfate(SO4

2minus) NH3 and nitrate (NO3minus) The historical data were

compiled from the utility monthly operating reportsavailable sporadically from 1983 Non-detects that hadbeen entered as a zero value were updated to the detectionlevel of the parameter Summary statistics including meanmedian standard deviation maximum and minimum wereapplied to each of the wellsrsquo time series data to assesswater-quality changes over time and used to compare toambient water quality data at other locations in southFlorida Most water quality for the Floridan Aquifer insouth Florida had been collected as regulatory require-ments which usually included chemical analyses that areused for drinking water quality and therefore did notinclude major ion data Residence time in the Floridan

aquifer system in south Florida is on the order of thousandsof years (Meyer 1989a) and it was assumed that due to thedepth of the aquifer water quality was in equilibrium andthere would be no other cause of perturbations to ambientwater quality other than migration of injectate Time seriesdata that showed large variation over time would indicatenon-equilibrium conditions and therefore not ambientconditions Abrupt changes in water quality and pressurewere observed in the time series data in wells that werepurged in 1997 These changes were not observed in wellsthat were not purged These changes in water quality andpressure were interpreted as being the result of crossconnections developed in the dual zone casings of some ofthe purged wells and review of borehole videos of thesewells taken in 2004 confirmed holes in the casings of thesewells It could not be determined which interval the datacollected from these wells represented after the crossconnections developed therefore data were discardedfrom the historical series analysis based on the month itwas ascertained the cross connection developed and thesummary statistics were recalculated for these wells

Floridan Aquifer water samples were collected at theNDWWTP and SDWWTP during 2006 and 2007 as partof this study for major ions and nitrogen species Thirty-two monitoring wells were sampled at the SDWWTP andwater-quality samples were collected from these wellsfrom the UFA the APPZ and the MC2 At theNDWWTP samples were collected from four monitoringwells representing the UFA and four wells in the APPZTemperature pH dissolved oxygen and conductancewere taken from water samples in the field using an YSI556 MPS The YSI instrument was calibrated per themanufacturerrsquos instructions prior to each sampling eventAll wells were purged for at least 24 h prior to sampling toensure at least three well volumes were evacuated Thewells were sampled through a closed system using a lowflow cell and tygon tubing through a disposable highcapacity 045micromol in-line filter Water samples wereanalyzed for the anions Brminus Clminus Fminus NO3

minus NO2minus and

SO42minus on a DIONEX ion chromatography system

HCO3minus and CO2

minus were analyzed via manual titrationNH3 was analyzed on a LACHAT analyzer 800 withNH4

+ then calculated based on pH and temperature ofthe sample using the NH3 result (Stumm and Morgan1996) Cations (Ca2+ Mg2+ K+ Na+ and Sr2+) wereanalyzed by inductively coupled plasma (ICP)

Results

The mean historical data are summarized in Table 1 forthe SDWWTP and Table 2 for the NDWWTP Dissolvedoxygen NO3

minus and NO2minus had similar results for both the

SDWWTP and NDWWTP sites for the aquifer intervalsNO3

minus concentrations were either detected at very lowconcentrations or below detectable levels NO2

minus levelswere below 1 micromoleL (micromol) for all aquifer intervalsand in the injectate at the NDWWTP and SDWWTP sitesfor the historical time series The injectate had a mean valueFig 4 Well locations at the NDWWTP

Hydrogeology Journal DOI 101007s10040-009-0570-8

Tab

le1

Meanvalues

forhistorical

timeseriesSDWWTP

mblsmetersbelow

land

surface

Geologicform

ation

Hyd

rostratig

raph

icform

ation

WellID

Open

interval

Periodof

record

Tem

pdegC

pHNH3micromol

Clndashmmol

SO42ndashmmol

NO3ndashmicromol

mbls

Pleistocene

Biscayn

eAqu

ifer

Injectate

(S-EFF)

Surface

591

ndash1207

277

66

889

203

109

Und

ifferentiated

Haw

thornAvo

nParkLim

estone

Upp

erFloridan

Aqu

ifer

(UFA

)1U

299ndash

332

983

ndash1207

240

79

1221

32

02

2U29

9ndash311

783

ndash1207

244

79

1321

32

03

3U29

9ndash32

0291

ndash1207

243

79

1023

32

03

BZ1

306ndash

316

783

ndash1207

242

76

1222

31

02

Avo

nPark

Lim

estone

Avo

nParkPermeable

Zon

e(A

PPZ)

13U

451ndash

475

296

ndash1207

239

77

6210

848

03

5U45

4ndash48

4594

ndash1102

241

76

492

108

49

03

6U45

4ndash48

3594

ndash1207

241

76

545

7630

03

7U45

4ndash48

2694

ndash198

245

74

526

738U

454ndash

480

894

ndash602

240

77

216

106

41

02

9U45

4ndash48

4195

ndash1207

239

77

64111

43

02

10U

454ndash

485

296

ndash1207

240

76

3510

542

02

11U

454ndash

484

296

ndash1207

240

76

118

106

43

02

14U

454ndash

480

296

ndash1207

239

74

320

9943

02

15U

454ndash

480

296

ndash1207

231

75

296

106

53

03

16U

454ndash

485

296

ndash1207

231

76

330

109

48

02

12U

456ndash

487

296

ndash204

249

76

100

111

42

02

MiddleCon

fining

Unit(M

C2)

BZ2

481ndash

507

783

ndash1207

254

75

106

133

56

02

2L50

1ndash51

0783

ndash1207

243

74

1219

926

02

4L51

9ndash56

112

91ndash

1207

240

73

1251

019

304

13L

530ndash

562

296

ndash1207

237

75

5550

822

809

3L54

0ndash57

7191

ndash1207

240

73

752

921

910

5L54

6ndash57

6594

ndash1102

239

74

652

821

604

6L54

6ndash57

6594

ndash1005

237

74

3052

622

703

7L55

0ndash57

1694

ndash198

242

71

1053

68L

546ndash

576

894

ndash602

237

74

554

124

804

9L54

6ndash57

3195

ndash1207

234

74

553

422

604

10L

546ndash

576

396

ndash1207

238

76

141

429

204

05

11L

546ndash

576

296

ndash1199

238

76

417

193

93

02

12L

546ndash

576

296

ndash1207

254

74

676

5730

03

15L

546ndash

576

296

ndash104

231

75

1253

125

204

16L

546ndash

576

296

ndash1207

229

74

653

221

904

1L56

1ndash58

7783

ndash1207

238

73

653

923

904

Oldsm

arFormation

Bou

lder

Zon

eLow

erFloridan

Aqu

ifer

BZ4

853

0783ndash894

249

72

634

3

Hydrogeology Journal DOI 101007s10040-009-0570-8

of NO3minus of 379micromol at the NDWWTP and 109micromol

at the SDWWTP for the historical time series Dissolvedoxygen was detected at concentrations less than 10 mg Lminus1

for all aquifer intervals Dissolved oxygen concentrationsfor the injectate at both the NDWWTP and the SDWWTPhad results above 3 mg Lminus1

Historical time series results SDWWTPThe historical period of record data for the freshwaterinjectate samples from the SDWWTP (identified as S-EFF) were available from 1991 through 2007 (Table 1)Temperature ranged from 218 to 311degC with a mean of277degC Mean pH in the historical time series was 66NH3 ranged from 1468ndash18496micromol with a mean of889micromol NH3 varied seasonally and increased with time(Fig 5) Clminus concentrations averaged 2 millimolesL(mmol) with a very small range and standard deviationindicative of the freshwater source of the injectateHistorical data from the SDWWTP for the UFA (wellsBZ1 1U 2U and 3U) were available from 1983 through2007 Temperature averaged 24degC with no significantdifference observed between the wells The range of pHwas from 76 to 82 in the UFA Chloride averagedbetween 21 and 23 mmol while NH3 means rangedbetween 10 and 13micromol The summary statistics for thewater-quality samples collected from the UFA showedconsistent values with no discernable variation over timeHistorical data from wells open to the APPZ at theSDWWTP (wells 5U 6U 7U 8U 9U 10U 11U 12U13U 14U 15U 16U) were available from 1994 through2007 Mean temperatures ranged between 231 and249degC in these wells There was little variation observedin the pH in the APPZ samples but the mean pH of 76was lower than the mean pH in the UFA Almost all of thewells showed variation in NH3 concentrations over timeMean values of NH3 in these wells ranged from 35micromolin well 10U to 545micromol in well 6U Well 6U showed anincreasing trend with time in NH3 that was observed to besimilar to the increasing trend of NH3 in the injectate(Fig 5) The spread between the 5th and 95th percentilewas the greatest in wells 6U and 12U Only wells 9U10U and 13U showed little variation in NH3 over timeMean concentrations of Cl- in wells 6U and 7U were 76and 73 mmol Wells in the MC2 were open to intervalsvarying in depth from 481 to 551 m Mean temperaturevalues ranged from 229 to 242degC in all wells with theexception of a mean value of 254degC in wells BZ2 and12L Mean pH values ranged from 73 to 76 Mean NH3

concentrations showed two groupings Wells BZ2 10L11L and 12L exhibited concentrations of 106 141 417and 676micromol respectively The remainder of the wellsexhibited mean NH3 concentrations of less than 55micromolClminus concentrations for wells 10L 11L and 12L were 429193 and 57 mmol respectively the remainder of the wellshad mean concentrations greater than 508 mmol (excep-tion is BZ-2 whose Clminus concentration of 133 mmolreflects the shallower depth of this well with the openinterval in the lower brackish water zone of the FloridanT

able

2Meanvalues

forhistorical

timeseriesNDWWTP

mblsmetersbelow

land

surface

Geologic

form

ation

Hyd

rostratig

raph

icform

ation

WellID

Open

interval

Period

ofrecord

Tem

ppH

NH3

Cl-

SO42-

NO3-

Revised

period

ofrecord

a

Tem

ppH

NH3

Cl-

SO42-

mbls

degCmicromol

mmol

mmol

micromol

degCmicromol

mmol

mmol

Pleistocene

Biscayn

eAqu

ifer

Injectate

(N-EFF)

Surface

797

ndash1207

284

65

8193

200

05

379

Avo

nPark

Lim

estone

Eocene

Upp

erFloridan

Aqu

ifer

(UFA

)N-1U

354ndash38

5197

ndash1207

231

76

188

737

35

02

N-2U

351ndash38

4396

ndash1207

230

78

177

662

36

21

N-3U

354ndash37

9396

ndash1207

229

78

173

658

36

20

N-4U

354ndash37

9496

ndash1207

231

76

181

684

35

08

Avo

nPark

Permeable

Zon

e(A

PPZ)

N-1L

430ndash46

1496

ndash1207

219

73

2612

3682

328

10

3496ndash797

224

72

193

4617

N-2L

431-

459

396

ndash1207

223

76

1684

3979

156

22

396

ndash898

229

78

177

4557

166

N-3L

430ndash46

0396

ndash1207

222

76

1314

4094

158

10

396

ndash1298

230

77

191

4548

149

N-4L

430ndash46

0496

ndash1207

224

72

1903

3804

152

16

496

ndash1298

223

75

237

4405

Hydrogeology Journal DOI 101007s10040-009-0570-8

Aquifer) Data collected from well 12L were similar todata collected for wells for 6U and 7U These wells hadhigh NH3 concentrations with low Clminus and SO4

minus concen-trations Historical data were available for the BoulderZone interval (well BZ4) from 1983 through 1994 Themean pH and temperature values were 72 and 249degCrespectively Mean NH3 concentration was 634micromol andshowed apparent seasonal variation and increasing trendover time and was similar to the injectate historical timeseries (Fig 5) The mean Clminus concentration was 3 mmolsimilar to the mean Clminus concentration of 2 mmol for theinjectate

Historical time series results NDWWTPThe historical period of record data for freshwaterinjectate samples (N-Eff) at the NDWWTP were availablefrom 2002 through 2007 Temperature ranged from 22 to34degC with a mean of 28degC The mean pH was similar tothe SDWWTP injecate at 65 NH3 ranged from 210ndash3764micromol with a mean of 819micromol and a large standarddeviation indicative of the apparent seasonality similar tothe SDWWTP Clminus concentrations ranged from 08 mmolto 1131 mmol with a mean 20 mmol slightly higher thanthe mean concentration of the SDWWTP injectateHistorical data were available from 1996 through 2007for wells open to the UFA (N-1U N-2U N-3U and N-4U) Mean temperature averaged 23degC in these wellswith no significant difference observed between the wellsMean values of pH ranged from 76 to 78 Clminus meanconcentrations ranged between 662 and 737 mmolsNH3 mean concentrations ranged between 17 to 18micromolConcentrations for the UFAwater-quality samples for theNDWWTP showed consistent values with no discernablevariation over time Historical data were available from1996 through 2007 for wells open to the APPZ (N-1L N-2L N-3L and N-4L) Temperature mean values were

22degC Analysis of historical NH3 data indicates increasingconcentrations of NH3 starting in late 1997 (Fig 6) NH3

concentrations appeared to have reached a peak concen-tration of 408micromol in well N-1L in July 2001 andsteadily declined thereafter to concentrations rangingfrom 200 to 250micromol Wells N-2L N-3L and N-4L showsimilar patterns as well N-1L but with lowered anddelayed peak concentration values NH3 concentrationsare observed to increase scatter after 2003 whichcorresponds to when purging commenced at theNDWWTP Once purging ceased in 2004 NH3 concen-trations in wells varied between 150ndash300micromol The Clminus

mean concentrations ranged from 368 to 409 mmol Clminus

in these wells exhibited variation over time and analysisof the time series indicated that as NH3 concentrationsincreased Clminus concentrations decreased (Fig 6) The timeseries data for the lower wells were revised to removedata after NH3 concentrations were observed to increasein each well in order to determine ambient concentrationsin the APPZ Revised NH3 mean concentrations rangedfrom 18ndash24micromol Clminus mean concentrations ranged from441ndash461 Very little variation was observed in NH3 andClminus mean concentrations after the time series data wereremoved

Major ion data collection resultsMajor ions were collected for this study from 2006ndash2007(Table 3) Data from wells at the SDWWTP site thatexhibited cross connections were removed from thisanalysis Data collected from the SDWWTP UFAexhibited very little variation between wells and weresimilar to the historical time-series data with low cationand anion concentrations For the APPZ wells NH4

+

mean concentrations could be combined into three groupswells 9U 10U and 13U with NH4

+ mean concentrationsof 60 67 and 143micromol respectively wells 14U and 16Uwith 497 and 439micromol and well 6U 823micromol Cation andanion mean concentrations showed a similar grouping asthe NH4

+ concentration grouping with well 6U consis-tently grouping independently and with increasing NH4

+

concentrations correlating to decreasing ion concentra-tions The MC2 mean NH4

+ concentrations could also becombined into three groups well 12L at a mean NH4

+

concentration of 765micromol wells BZ-2 10L and 13LNH4

+ at mean concentrations 176 200 and 108micromolrespectively the remainder wells at NH4

+ concentrationsbelow 10micromol Cation and anion concentrations could becombined in the same 3 groups as the NH4

+ groups withlower ion mean concentrations observed for BZ-2 10Land 13L and much lower ion concentrations observed inwell 12L As with well 6U in the MC1 well 12L in theMC2 consistently grouped independently

The NDWWTP wells open to the UFA (351ndash385 m)exhibited very little variation in field measurements andmean concentrations between wells and were similar tothe historical time series The interval (430ndash461 m) in theAPPZ at the NDWWTP also showed little variation withmean NH4

+ concentrations (215ndash295micromol) and mean

Fig 5 Time series NH3 data from the injectate (black circle) BZ-4(green triangle) and well 6U (red circle) at the SDWWTP site Theapparent seasonal variation observed in the injectate is a result ofincreased flows during the wet season and storm events Theincreasing trends with time correlate to increased injection over timedue to growth in population in Miami-Dade County

Hydrogeology Journal DOI 101007s10040-009-0570-8

concentrations of Clminus (371ndash386 mmol) varying littlebetween wells

Ternary diagramThe typical ClminusBrminus ratio for seawater is about 290 (Daviset al 1998) and most of the ClminusBrminus ratios at both siteswere within that range with no discernable differencesQuite often the addition of a third water-quality membercould enhance the understanding of the data and this wasthe case with using NH4

+ as the third end-member NH4+

Clminus and Brminus data were plotted on a ternary diagram withdata normalized to 100 Typical seawater and freshwaterNH4

+ Clminus and Brminus values after Hem (1985) were alsoplotted for comparison Water quality at the NDWWTPclustered into three distinct groups with two groups basedon depth of the interval sampled and the third the injectate(Fig 7) The ambient aquifer data plot close to seawaterThe injectate data plotted off in the lower left hand cornerdue to the large NH4

+ concentrations At the SDWWTPthree aquifer groupings were observed Ambient well datafrom the MC2 plotted similar to seawater Ambient welldata from the UFA plotted slightly towards freshwaterData from wells that showed elevated NH4

+ plotted in aline towards the injectate with groundwater data from 6Uand 12L plotting very close to the injectate This linerepresents the evolution of the water quality of these wellstowards the injectate water quality and does not show anyevolution of more saline water into the higher intervals inthe aquifer

Mixing end-member modelsEnd-member mixing models of wells 6U 12L and 10Lrepresented the results obtained for all wells at the

SDWWTP (Fig 8) Well 6U and 12L showed theprogressive freshening of water and increasing NH3

concentrations towards the injectate end-member(Fig 8) There was little mixing from the saline end-member towards the brackish end-member in well 6U andalmost all of the mixing was towards the injectate end-member Both 6U and 12L showed large changes inconcentrations from their original end-members over timeWell 10L showed a different pattern than 6U and 12Lwith gradual freshening of the saline water towards theinjectate end-member The mixing was towards the lowerrange of the injectate end-member and there were no largechanges in concentrations of either NH3 or Clminus from thesaline end-member Well N-1L at the NDWWTP end-member mixing model showed a different pattern than theSDWWTP (Fig 9) Clustering of the NH3Cl

minus ratios weredistinguished based on time The NH3Cl

minus ambient ratio canclearly be seen on Fig 9 and lies along the saline end-member As the concentrations of NH3 increased in time tothe peak concentration the NH3Cl

minus ratios showed twodistinct clusters Initially the NH3Cl

minus ratio showed gradualincreasing in NH3 with little change in Clminus from ambientconcentrations There was a rapid change in the NH3Cl

minus

ratio as NH3 reached the peak concentrations Once the peakwas reached the NH3Cl

minus ratios slowly declined in time

Discussion

The Floridan aquifer system was sampled by others atdifferent sites in south Florida and these data aresummarized in Table 4 Wells identified as WWF weremonitoring wells installed as part of the MDWASD ASRsystem west of the NDWWTP and SDWWTP (CH2MHill 1998) The ASR systems were not in use during the

Fig 6 Graph a shows the NH3 data time series for the wells in the APPZ interval at the NDWWTP The dashed lines indicate the purgingtime from 2003 through 2004 NH3 concentrations are observed to increase in well N-1L similar to contaminant breakthrough curves WellN-1L was the closest well to the uncased injection well when injectate backflowed into the APPZ NH3 concentrations for wells N-2LN-3L and N-4L appear to be similar and show a similar increase after 1999 Variability is seen in the data after 2003 Graph b showsClminus concentrations in well N-1L clustered at approximately 300 mmol and an abrupt decrease to less than 300 mmol is seen Clminus

concentrations in wells N-2L N-3L and N-4L are very similar and show a decrease in concentrations after 1999 until 2000 whenconcentrations appear to stabilize Clminus concentrations start to increase slightly and become variable after 2003 All four wells showsimilar concentrations of both NH3 and Cl- after 2004

Hydrogeology Journal DOI 101007s10040-009-0570-8

Tab

le3

Meanfieldparametersandionconcentrations

during

the20

06ndash2

007samplingcompleted

aspartof

thisstud

ymblsmetersbelow

land

surface

Geologic

form

ation

Hyd

rogeolog

icun

itOpen

interval

Well

Temp

pHNH4+

Ca2

+Mg2

+Na+

K+

Sr2+

Cl-

SO42-

HCO3-

Br-

F-

NO3-

NO2-

mbls

IDdegC

micromol

mmol

mmol

mmol

mmol

micromol

mmol

mmol

mmol

micromol

micromol

micromol

micromol

SDWWTP

Pleistocene

Biscayn

eAqu

ifer

Surface

S-EFF

290

67

112

51

03

07

30

430

197

6

Und

ifferentiated

Haw

thornOcala

Lim

estone

toAvo

nPark

Lim

estone

UFA

306ndash31

6BZ1

242

78

61

325

139

213

440

109

11

299ndash33

21U

236

81

61

324

142

224

456

117

01

299ndash32

03U

243

79

61

325

148

284

454

119

41

299ndash311

2U25

379

101

322

143

215

433

143

11

Avo

nPark

Lim

estone

APPZ

454ndash48

49U

238

77

604

1098

399

104

53

169

850

145

4ndash48

510

U24

877

675

1085

212

5112

53

174

451

045

1ndash47

513

U24

477

143

410

883

113

109

54

200

119

21

454ndash48

516

U23

277

439

49

943

7510

25

525

013

51

145

4ndash48

014

U25

075

497

36

662

6570

45

115

801

145

4ndash48

36U

251

75

823

35

872

3245

37

8151

11

MC2

501ndash51

02L

248

75

98

1614

84

147

194

42

305

750

148

1ndash50

7BZ2

241

76

176

511

121

3114

128

64

217

930

154

6ndash57

39L

231

76

311

4445

912

167

550

243

849

211

11

546ndash57

616

L22

975

411

4143

912

175

552

254

800

195

01

540ndash57

73L

241

75

410

4344

012

159

522

233

834

233

51

519ndash56

14L

245

75

711

4041

612

181

492

213

737

234

01

530ndash56

213

L24

275

108

1036

350

1217

446

024

377

531

32

154

6ndash57

610

L24

776

200

830

285

10111

369

233

588

773

054

6ndash57

612

L28

176

765

36

492

3654

45

8735

20

561ndash58

71L

234

75

411

6441

213

161

533

253

834

235

11

NDWWTP

Pleistocene

Biscayn

eAqu

ifer

surface

N-EFF

263

65

505

22

201

616

13

3610

3849

Avo

nPark

Lim

estone

UFA

354ndash38

5N-FA-1U

225

78

173

868

215

573

41

8118

00

135

1ndash38

4N-FA-2U

227

78

133

765

212

166

41

126

179

22

354ndash37

9N-FA-3U

212

79

163

766

213

362

31

115

32

135

4ndash37

9N-FA-4U

208

79

163

769

214

766

41

131

174

11

APPZ

430ndash46

0N-FA-3L

194

75

215

937

423

1121

638

017

365

153

71

243

0ndash46

1N-FA-1L

199

74

231

736

458

1110

038

620

383

942

21

143

0ndash46

0N-FA-4L

192

74

264

937

421

1122

337

119

369

546

32

143

1-45

9N-FA-2L

201

74

295

839

431

1212

538

322

374

848

62

1

Hydrogeology Journal DOI 101007s10040-009-0570-8

time of this study Wells designated as ldquoFPLrdquo were testswells installed into the Floridan aquifer system sim10 kmsouth from the SDWWTP (Dames and Moore 1975Florida Partners 2006) For comparison to the presentstudy the data from these sites were assumed to representambient water-quality concentrations as no injectionactivities had occurred at these sites Wells in this studythat exhibited little variation in the time series data andhad low NH3 concentrations were compared to the datafrom these other sites Although direct comparisons weredifficult due to the varying aquifer open intervals fromwhich these samples were collected some generalizationscan be made NH3 or NH4

+ concentrations from thesewells were below 29micromol Clminus concentrations increasedwith depth of the sampled intervals and were similar inconcentrations to wells in this study of approximately thesame aquifer interval NO3

minus concentrations were below1micromol similar to data collected for this study Based oncomparisons with water quality from these other sites therevised time series water-quality data that had mean NH3

concentrations below 30micromol were assumed to be ambientaquifer water with no influence of injectate All the wellsin the UFA at the SDWWTP were considered ambient andmost of the wells in the MC2 at the SDWWTP wereconsidered ambient with the exception of 10L 11L and12L All of the wells in the APPZ at the SDWWTP hadNH3 concentrations above ambient levels with well 9U thelowest Time series data at the NDWWTP indicated that allof the wells open to the UFAwere considered ambient andthe data from wells open to the APPZ were ambient prior tothe observed increase in NH3 concentrations

Ambient Clminus concentrations from this study showedbrackish transitional and saline zones in the Floridan

aquifer system for the SDWWTP and NDWWTP asdefined by Reese (1994) Although there were only twosample depths at the NDWWTP the top of the saline zoneat the north appears to be higher than at the SDWWTPMean temperatures at the NDWWTP were cooler than atthe SDWWTP with an average of 23degC for both intervalsThe NDWWTP lies closer to the Florida Straits and thecooler temperatures at that site may be due to closerproximity to open seawater Wells that showed a higherconcentration of NH3 at the SDWWTP showed highertemperatures (example Well 12L) whereas at theNDWWTP no change in temperature was noted withincreasing NH3 concentrations

Based on results of this study introduced nitrogen fromthe injectate into the Floridan Aquifer is mostly in theform of NH4

+ This is consistent with eH-pH diagrams fornitrogen (Stumm and Morgan 1996) where in most naturalenvironments any ammoniandashN would have the form ofNH4

+ (Hem 1985) No relationship was observed in thehistorical data or data collected as part of this study betweenNH3 and NO3

minus No change from ambient NO3minus concen-

trations was observed for wells that had elevated NH3

concentrations The reduced form of nitrogen (NH4+) was

not oxidized once introduced in the anoxic aquifer at eithersite and was conserved in the aquifer in this reduced stateAny introduced oxidized form of nitrogen (NO3

minus) from theinjectate that was reduced would result in insignificantchanges in NH4

+ concentrations as NO3minus concentrations

are two to three orders of magnitude less than NH4+ The

elevated concentrations of NH4+ in the Floridan aquifer at

the two sites are interpreted as the result of the upwardmigration of the injectate Once introduced into the aquiferNH4

+ appeared to have behaved conservatively

Fig 7 Ternary diagrams for the NDWWTP and the SDWWTP NH4+ Clndash and Brndash data collected from 2006ndash2007 were normalized to

100 Seawater and freshwater values (Hem 1985) were plotted Ambient water was grouped at the SDWWTP for the MC2 and UFAintervals Ambient MC2 data plot directly with seawater UFA ambient plots towards freshwater reflecting the fresher water quality in theUFA The injectate data plot at the NH4

+ end point indicating the freshwater quality but high NH4+ concentration of the injectate Well data

from the APPZ and MC2 intervals that have NH4+ concentrations above ambient levels plot in a line towards the injectate end point with

data from wells 6U and 12L plotting very close the NH4+ end point Data from the SDWWTP plot into distinct groups based on depth in the

aquifer but no line towards the injectate end point is seen

Hydrogeology Journal DOI 101007s10040-009-0570-8

At least two pathways of injectate were distinguishedbased on the analysis of the natural tracers at theSDWWTP One pathway at the SDWWTP appeared tohave rapid vertical pathways from the Boulder Zone up tothe APPZ with little mixing of ambient waters as itmigrated upward These vertical conduits did not appear

to extend up to the UFA This pathway is identified atwells 6U and 14U in the APPZ and well 12L in the MC2It may be present at well 8U in the APPZ however thedevelopment of cross connection in well 8U compromiseddata interpretation NH4

+ concentrations in these wellswere within the range of injectate NH4

+ concentrations

Fig 8 Graphs on the left areNH3Cl

minus mixing end-membermodels for the APPZ andMC2 intervals at theSDWWTP 6U 12L and 10Lare well identification codesArrows indicate increase intime Hatched red rectangleis injected freshwaterend-member indicating theseasonal range in concentra-tions Cyan square is theAPPZ brackish waterambientwater end-member blue circleis the MC2 saline waterend-member Graphs on theright are NH3 concentrationsover time Solid black lines areconcentrations from each wellsite red line is injected fresh-water concentrations Forwells 6U and 12L the dataplot towards the injectateend-member Little influenceis seen in well 6U from thesaline MC2 end-memberWell 10L shows a differentevolution of water qualitywith data plotting at the salineMC2 end-member and slowlyplotting towards the lower endof the injectate end-member

Fig 9 Graph a is the NH3Clminus mixing end-member model for the APPZ at the NDWWTP for pre-purge data (prior to 2003) for well N-

1L Arrows indicate increase in time Hatched red rectangle is injected freshwater end-member indicating the seasonal range inconcentrations Cyan square is the UFA brackish water ambient water end-member blue circle is the APPZ saline water end-member Thedata plot in separate groupings with the earliest time series plotting around the APPZ saline end-member The second data cluster plottowards the injectate end-member but no evolution towards the injectate end-member is seen as was seen for wells 6U and 12L at theSDWWTP Graph b is the post-purge data plotted for well N-1L Data plot with time back towards the APPZ saline end-member

Hydrogeology Journal DOI 101007s10040-009-0570-8

Clminus concentrations in these wells were also very close toinjectate Clminus concentrations

The mixing models for these wells show a mixingpathway almost directly towards the injectate end-mem-ber with no mixing from the lower MC2 interval observedfor wells 6U and 14U Wells that showed the highestconcentrations of NH3 at the SDWWTP also showedhigher temperatures with the temperature signal of thewarmer injectate observed in well 12L (mean temperatureof 28degC) in the data collected in 2006ndash2007 Well 12L inthe MC2 is much closer to the Boulder Zone than theAPPZ wells and higher injectate temperatures persist intothe MC2 Perhaps due to the longer travel times to theAPPZ the temperature signal was muted but still visible inthe APPZ Ion data for these wells showed freshening ofthe water quality These wells showed a density-drivenbuoyant rapid vertical advective pathway and transport ofthe injectate as a distinct water body with little mixing ofnative waters as it migrated upwards The rapid pathwayscould be the result of construction related events such asdrifting boreholes or the result of structural anomaliessuch as fracturing and karst features that would verticallyconnect aquifers and provide high hydraulic conductivitytransport pathways through confining units Migration ofsaline waters from the Lower to Upper Floridan Aquiferas a result of such structural anomalies have been reportedfor northeastern and central Florida (Flocks et al 2001Spechler 2001) where the Floridan aquifer system liesmuch closer to the surface Upward fluid migration ofinjected fluids in a Palm Beach County Florida deep wellinjection facility had been detected above the confiningzone between the injection zone and the overlayingmonitoring zone and this had been attributed to fractureddolostone comprising the majority of the confining zonestrata (Maliva et al 2007) however no fracturing of theconfining strata at either the NDWWTP or the SDWWTP

has been reported McNeill suggested that as wells locatedon the northwest side of the SDWWTP were cased abovethe DCU in the LFA this would be a possible cause of thebuoyant upward migration of injected fluids through themore permeable units above the DCU through isolatedvertical flow paths bypassing the MC2 (McNeill 20002002)

The second pathway was suggested by the grouping ofwell data observed in wells 15U 16U BZ2 10L and 11LThe well data from this group had no significantcorrelation between NH3 and Clminus The mixing modelsfor these well data showed a slow evolution of waterquality towards the lower average of the injectate end-member with time These wells showed a slight temper-ature increase but no clear temperature signal wasdistinguished in these wells Ion data did not show afreshening of the water quality with little difference seenbetween ambient ion concentrations and concentrationsfrom these wells Other studies (Boumlhlke et al 2006) haveindicated that NH3 transport can be retarded by a factor of3ndash6 in an aquifer with NH3 persisting in an aquifer afterthe more mobile constituents were flushed out if theaquifer remained under suboxic conditions At theSDWWTP it appears that there was still NH3 loadinginto the aquifer via rapid vertical pathways with increas-ing NH3 concentrations over time The data from this wellgrouping may indicate that once NH3 was introduced intoan aquifer interval it traveled horizontally at a muchslower rate with the freshwater injectate substantiallydiluted and not flushed out as freshwater continued tomigrate upwards

Four discrete injectate plumes were delineated at theSDWWTP based on the transport pathways The firstplume (plume 1 in Fig 10) located on the northeast of thesite was associated with the BZ-4 well which provided apathway up into the APPZ until it was plugged This

Table 4 Historical ambient Floridan Aquifer water quality data

Parameter Unit 1Ua WWFb WWFb FPLPW-3c

FPL testwelld

9Ua FPL testwell d

2La 3La FPL testwelld

299ndash332 m

260ndash305 m

260ndash308 m

314ndash380 m

340ndash410 m 454ndash484 m

456ndash517 m 501ndash510 m

530ndash562 m

639ndash701 m

pH 79 80 74 75 77 77 75 75 75 70HCO3

- mmol 00 32 27 33 21 30 26Ca2+ mmol 13 17 37 43 67 78 103 196Mg2+ mmol 27 28 73 101 155 160 434 555Na+ mmol 247 222 746 983 1582 1482 4382 4872K+ mmol 08 08 20 26 38 36 118 97Cl- mmol 223 705 271 821 1043 1794 1939 5216 5923SO4

2- mmol 41 75 69 03 69 47 137 42 226 307NO3

- micromol 03 08 02 02 02 03 02 48 02F- mmol 01 01 01 01 01 01 02 01Si mmol 05 04 02 05 03 03 02Sr2+ micromol 419 776 982 1849 1472 1586Total P micromol 32 71 65 65 32NH4

+ micromol 55 72 610 111 55NH3 micromol 08 294 123

a Data were collected for this study during 2006ndash2007 for wells at the SDWWTPbData from CH2M Hill 1998cData from Florida Partners 2006dData from Dames and Moore 1975

Hydrogeology Journal DOI 101007s10040-009-0570-8

plume slowly migrated to the surrounding areas mainlyvia diffusion as evidenced by slowly increasing NH3

concentrations but no change in Clminus concentrations Thesecond plume was located on the northwest corner of thesite in the APPZ (plume 2) This plume was detected inthe APPZ with no detection of it in the lower MC2indicating a direct pathway to the APPZ bypassing theMC2 This pathway seemed to persist with concentrationsof NH3 increasing with time similar to concentrationlevels of the injectate This plume was a chemicallydistinct water body with little mixing of native watersThe third plume located at well 14U (plume 3) may be adistinct plume but it may also be in connection withplume 2 No monitoring wells of the same interval as well14U are in the vicinity so the extent of this plume couldnot be determined The fourth plume was located on thesouth side of the site in the MC2 (plume 4) All fourplumes appeared to have the same initial transportmechanism up from the Boulder Zone through highhydraulic conductivity pathways with data from plumes2 3 and 4 indicating these pathways still persist

The data collected from the NDWWTP indicate differ-ent transport mechanisms than the SDWWTP Thetemperature signal of the warmer injectate was notobserved in wells with elevated concentrations of NH4

+Water quality showed no evolution towards the injectateplot in the ternary diagram The mixing model showedtwo mixing patterns one towards the injectate end-member before purging and one towards the ambientend-member once purging ceased As observed in the timeseries NH3 data NH3 concentrations were first observedto increase in well N-1L the well that was within 30 m ofthe uncased injection well and concentrations peaked at

341micromol well below the mean NH3 concentration of theinjectate Unlike the increasing NH3 concentrationsobserved at the SDWWTP that are the result of rapidvertical migration pathways once NH3 concentrations atthe NDWWTP peaked they have since decreased withtime All four NDWWTP lower wells have shown verysimilar water quality since 2004 when purging ceased atthe NDWWTP Both the time series analysis and the datacollected as part of this study in 2006 and 2007 appear toindicate a one-time pulse of injectate water into the APPZand this pulse of injectate was still migrating at the timeof this study through the aquifer in the direction ofregional flow There is no geochemical evidence of acontinuing source of NH3 at the NDWWTP however dueto retardation as discussed previously the NH3 plume mayhave persisted a long time in the suboxic aquifer (Boumlhlkeet al 2006)

Conclusions

Chloride bromide and ammonia were used to understandthe pathways and transport mechanisms of injectedwastewater into the deep saline Boulder Zone in theFloridan aquifer system The injectate source was treatedfreshwater with elevated levels of ammonia The waterquality of the injectate was chemically and physicallydistinct from ambient Floridan aquifer system water andthese distinctions were used to determine the possibletransport pathways At the SDWWTP four injectateplumes were identified along with two pathway mecha-nisms density-driven buoyant vertical flow and slowerhorizontal flow At the NDWWTP one plume was

Fig 10 Location of injectate plumes and their depth interval at the SDWWTP The source of the plume centered on the BZ well clusters(plume 1) was plugged in 1995 Plumes 2 3 and 4 are the result of continuing rapid vertical pathways up from the Boulder Zone Theextent of the plumes off site is not known as indicated by the question marks however based on data collected from the site approximateextent of the plumes on the site can be inferred The plume in the MC2 is limited to the southeast of the site The plume located in thenorthwest of the site is located in the APPZ and appears to have bypassed the MC2 The plume from the BZ well cluster appears to belimited to the east of the site The extent of the plume at 14U on site is unknown as there are no wells that monitor the same aquifer intervalin the vicinity of 14U

Hydrogeology Journal DOI 101007s10040-009-0570-8

identified and appeared to be a result of a one-time pulseinjection At the SDWWTP the injectate may first havemigrated upwards through discrete vertical pathways fromthe Boulder Zone to the Middle Confining Unit with thefreshwater injectate migrating upwards through salinewater as a chemically distinct water body The fourplumes identified at the SDWWTP appear to haveoriginated via this pathway Once introduced in the higheraquifer intervals the transport mechanism appeared to bea horizontal flow with mixing of ambient waters Therapid vertical pathways did not appear to extend up to theUFA At the NDWWTP the elevated levels of NH3 inthe lower Middle Confining Unit appeared to be the resultof a construction incident where a pulse of injectate waterbackflowed into an uncased injection well providing apathway to the upper interval Once introduced into theupper aquifer interval the plume slowly migrated with theregional flow within the aquifer No evidence of rapidvertical pathways was observed at the NDWWTP Duringthe course of this study it became clear that purging of thewells had unintended consequences for the SDWWTPCross connections developed in several wells between theupper and lower monitoring zones either during or afterpurging and these cross connections have compromisedwater-quality data in SDWWTP wells 5 6 7 8 11 12and 15 Although it could not be determined from thisstudy these cross connections may provide pathways ofinjectate into layers in the aquifer that had not beenpreviously affected by upward migrating injectate

Acknowledgements This study was funded by the Miami-DadeWater and Sewer Department (MDWASD) The authors greatlyappreciate S Villamil for her invaluable technical expertise andassistance in the field We thank C Powell S Kronheim W Pittand B Goldenberg of MDWASD for their cooperation and Drs ADausman and C Langevin of the US Geological Survey for theirinsightful comments during this research This report was signifi-cantly improved by the thoughtful review of two anonymousreviewers Dr Pricersquos contribution was partially funded by theNational Science Foundation Grant No DBI-0620409 This isSERC contribution 457

References

Arthur JD JB Cowart AA Dabous (2001) Florida Aquifer Storageand Recovery Geochemical Study Year Three Progress ReportOpen File Report 83 Florida Geological Survey TallahasseeFL

BCampECH2M Hill (1977) Drilling and testing of the test-injectionwell for the Miami-Dade Water and Sewer Authority ContractS-153 BCampECH2M Hill Gainesville FL

Bloetscher F Muniz A (2006) Preliminary modeling of class Iinjection wells in southeast Florida Ground Water ProtectionCouncil 2006 Annual Meeting Proceedings Miami FLNovember 2006

Bloetscher F Englehardt JD Chin DA Rose JB Tchobanoglous GAmy VP Gokgoz S (2005) Comparative assessment ofmunicipal wastewater disposal methods in southeast FloridaWater Environ Res 77480ndash490

Boumlhlke JK E Shinn C Reich A Tihansky (2003) Origins andisotopic characteristics of dissolved nitrogen species in groundwater imported domestic water and wastewater in the FloridaKeys US Geological Survey Greater Everglades Science

Program 2002 biennial report US Geol Surv Open-File Rep03-54

Boumlhlke JK Smith RL DN Miller (2006) Ammolonium transportand reaction in contaminated groundwater application ofisotope tracers and isotope fractionation studies Water ResourRes 42 W05411 doi1010292005WR004349

CH2M Hill (1981) Drilling and testing of the 8 injection wells andthe 3 monitoring wells for the South District Regional Waste-water Treatment Plant of the Mimi-Dade Water and SewerAuthority CH2M Hill Englewood CO

CH2M Hill (1998) Engineering report of the construction andtesting of the aquifer storage and recovery (ASR) system at theMDWASD West Wellfield CH2M Hill Englewood CO

Clark JF Bryant Hudson G Lee Davisson M Woodside GHerndon R (2004) Geochemical imaging of flow near anartificial recharge facility Orange County California GroundWater 42167ndash174

Corbett DR Kump L Dillon K Burnett W Chanton J (2000) Fateof wastewater-borne nutrients under low discharge conditions inthe subsurface of the Florida Keys USA Mar Geochem 6999ndash115

Dames and Moore Inc (1975) Floridan aquifer water supplyinvestigation Turkey point Area Miami-Dade County FloridaFlorida Power and Light Miami

Davis SN Whittemore DO Fabryka-Martin J (1998) Uses ofchloridebromide ratios in studies of potable water GroundWater 36338ndash350

Englehardt JD Amy VP Bloetscher F Chinn DA Fleming LEGokgoz S Solo-Gabriele H Rose JB Tchoaboglous G (2001)Comparative assessment of human and ecological impacts formunicipal wastewater disposal methods in southeast Floridadeep wells ocean outfalls and canal discharges University ofMiami Coral Gables FL

Fish JE Stewart M (1991) Hydrogeology of the surficial aquifersystem Dade County Florida US Geol Surv Water ResourInvest Rep 90-4108 50 pp

Flocks JG Kindinger JL Davis JB Swarzenski P (2001) Geo-physical investigations of upward migrating saline water from thelower to upper Floridan Aquifer Central Indian River RegionFlorida In US Geological Survey Karst Interest Group Proceed-ings US Geol Surv Water Resour Invest Rep 01-4011 pp 135ndash140

Florida Lakes Power Partners and Florida Power and LightCompany (2006) Well completion report for Floridan Aquiferwells PW-1 PW-2 and PW-4 FPL Turkey Point ExpansionProject (Unit 5) Homestead FL

Haberfeld JL (1991) Hydrogeology of effluent disposal zonesFloridan aquifer south Florida Ground Water 29186ndash190

Hem JD (1985) Study and interpretation of the chemicalcharacteristics of natural water US Geol Surv Water SupplPap 2254

Herczeg AL WM Edmunds (2000) Inorganic ions as tracers InCook PG Herczeg AL (eds) Environmental tracers in subsur-face hydrology Kluwer Norwell MA pp 31ndash78

Kaehler CA K Belitz (2003) Tracing reclaimed water in MenifeeWinchester and Perris-South ground-water subbasins RiversideCounty California US Geol Surv Water Resour Invest Rep03-4039

Kohout FA (1965) A hypothesis concerning cyclic flow of saltwater related to geothermal heating in the Floridan aquiferTrans NY Acad Sci Ser II 28249ndash271

Langmuir D (1997) Aqueous environmental geochemistry Prentice-Hall Upper Saddle River NJ

Maliva RG CW Walker (1998) Hydrogeology of deep-welldisposal of liquid wastes in southwestern Florida USAHydrogeol J 6(4)538ndash548

Maliva RG Guo W Missimer T (2007) Vertical migration ofmunicipal wastewater in deep injection well systems SouthFlorida USA Hydrogeol J 15(7)1387ndash1396

McNeill DF (2000) Final report a review of upward migration ofeffluent related to subsurface injection at Miami-Dade Waterand Sewer South District Plant McNeill Miami FL

Hydrogeology Journal DOI 101007s10040-009-0570-8

MARK A QUARLES PG PROFESSIONAL SUMMARY AND TECHNICAL SPECIALTIES Environmental consultant with approximately 25 years experience in the following coal combustion waste management oil exploration and production waste management hydraulic fracturing for unconventional natural gas hazardous waste management and permitting landfill siting and design utility line environmental assessments hydrogeologic investigations multi-media environmental auditing water and wastewater permitting municipal and industrial stormwater permitting wetland permitting and mitigation reservoir capacity studies and soil groundwater remediation EDUCATION Master of Business Administration Owen Graduate School of Management Vanderbilt University Nashville Tennessee Bachelor of Science Environmental Engineering Technology Western Kentucky University Bowling Green Kentucky PROFESSIONAL EXPERIENCE Global Environmental LLC Nashville Tennessee 2004 to current

Environmental consultant for projects in the United States and South America including as examples reservoir capacity studies public and private utility line permitting municipal stormwater management landfill siting threatened and endangered species groundwater contamination and supply wetland permitting and mitigation surface water contamination and supply and soil contamination

EMPE Inc Nashville Tennessee 1996 to 2001 Project Manager in wide-ranging environmental projects that included as examples stormwater permitting spill prevention and response plans hazardous waste management landfill permitting land development and contaminant fate and transport investigations Managed Fortune 500 industrial client projects throughout the eastern US

SECOR International Inc Franklin Tennessee 1994 to 1996 Senior Engineer Senior Geologist and Project Manager for industrial waste management projects throughout the southeast US that included as examples hydrogeologic investigations and stormwater permitting Managed Fortune 500 industrial client projects throughout the eastern US

RMT Inc Nashville Tennessee 1990 to 1994 Project Engineer and Project Manager for industrial and municipal projects throughout the eastern US for projects that included as examples petroleum underground storage tank removals soil and groundwater remediation landfill siting and design spill prevention and response plans hazardous waste audits industrial stormwater permitting and property transfer assessments

RJN Group Atlanta Georgia and Boston Massachusetts 1987 to 1990 Project Engineer for municipal projects throughout the eastern US for projects that included as examples sanitary sewer hydraulic modeling for drainage basins in excess of 1 million linear feet of conveyance and conducting infiltration and inflow investigations for sanitary sewers

Howard K Bell Consulting Engineers Hopkinsville Kentucky 1985 to 1987 Project Engineer for municipal sanitary sewer water line and landfill design projects in Kentucky

PROFESSIONAL REGISTRATIONS AND CERTIFICATIONS Licensed Professional Geologist (PG) Tennessee Certified Hazardous Materials Manager Masters Level (1993 ndash 2001) Class II Water Pollution Control Operator Massachusetts (1988)

MARK A QUARLES PG PAGE 2 RANGE OF TECHNICAL EXPERIENCE Oil and Gas Exploration and Production Wastes bull Aguida vs ChevronTexaco - Amazon Basin Ecuador

Provided technical support to the plaintiffs related to the first environmental class action lawsuit in South America Ecuadorian judgment resulted in a $10 billion damage against Chevron Work demonstrated that Texacorsquos work in the upper Amazonian jungle of Ecuador did not meet industry standards did not meet practices employed by Texaco from the 1920s through the 1990s and violated international and national water and soil quality standards

bull FECONACO ndash Amazon Basin Peru Provided independent third-party evaluation of crude oil remediation activities of 75 sites in

Block 1AB in the Amazonian jungle occupied by three indigenous groups The work included a) sampling of soil sediment and surface water contamination from present day and legacy operations b) an evaluation on the effectiveness of in-situ bioremediation as the chosen remedial alternative and c) a comparison of cleanup activities relative to Peruvian and US standards

bull Tulane Environmental Law Clinic ndash New Orleans Louisiana Reviewed a draft permit and provided written legal testimony associated with a Draft General

Permit for Discharges from Oil and Gas Exploration Development and Production Facilities The project consisted of comparing proposed effluent limitations to Federal standards comparing sampling parameters to expected exploration and production waste contaminants and recommending additional monitoring schemes that were more reflective of the risks

Coal Combustion Wastes bull Environmental Integrity Project Sierra Club and Earthjusticendash Washington DC

Reviewed historical coal-fired power plant file information and groundwater water monitoring reports for coal combustion waste (CCW) landfills and coal ash impoundments to identify previously undetermined damage cases according to EPA protocol Results were summarized in two co-authored reports Out of Control (February 2010) and In Harms Way (August 2010)

bull Sierra Club - Washington DC Reviewed historical groundwater monitoring reports associated with coal ash landfills and impoundments for 10 coal-fired power plants in Kentucky to identify impacts to groundwater relative to EPA damage case standards

bull Prairie Rivers Network - Champaign Illinois Evaluated Illinois standards for the disposal and beneficial re-use of coal of CCWs compared to national solid waste and surface impoundment disposal standards The project also included an in-depth analysis of material chemical and physical characteristics a summary of site characterization and siting standards and a summary of national damage assessment cases

bull Confidential Client ndash Kingston Tennessee Implemented a surface water monitoring program to determine the lateral extent of 54 million

cubic yards of CCWs that were released to the surface water from a surface impoundment failure at the Tennessee Valley Authority (TVA) Kingston coal-fired power plant

bull Kentucky Waterways Alliance ndash Henderson Kentucky Provided technical review of a draft wastewater discharge permit associated with the proposed

Cash Creek Integrated Gasification Combined Cycle (IGCC) plant and associated landfill At the time only two such plants were operational in the United States The review included a wastewater discharge compliance review of the other plants research into IGCC wastewater and solid waste constituents and a comparison to the proposed discharge criteria

bull Sierra Club ndash Bedford Kentucky Provided technical review of a draft wastewater discharge permit associated with the Trimble

County Generating Station pulverized coal (PC) power plant and flue gas de-sulfurization (FGD) process expansion Research was completed on the characteristics of FGD process and gypsum by-product wastes the leachability of solid wastes the characteristics of PC plant cooling water blowdown metal cleaning wastewater stormwater runoff and coal and limestone pile runoff

MARK A QUARLES PG PAGE 3

the structural integrity of an existing ash surface impoundment proposed for vertical expansion and the technical feasibility of a proposed gypsum disposal surface impoundment

Unconventional Natural Gas and Hydraulic Fracturing bull Shenandoah Valley Network Shenandoah Riverkeeper - Virginia Provided technical review of an application for the first proposed deep shale natural gas well in

Virginia The report evaluated among others the proposed plan for hydraulic fracturing storage of produced waters and flow back protection of groundwater supplies treatment and disposal of wastes and the location relative to the floodplain The applicant decided to rescind their application following submittal of the technical report critical of the proposed well action

bull Sierra Club Washington DC Provided technical comments regarding proposed Tennessee oil and gas regulations with a

particular emphasis on well casing standards fracture chemical disclosure and baseline post drilling monitoring for fracture chemicals and methane intrusion Compared the proposed regulations to API industry standards and other state regulations and provided recommendations for changes

Utility Line Environmental Assessments bull Private Landowner - Livingston Tennessee Served as lead consultant to prevent a proposed Corps of Engineer development Arguments

included identifying deficiencies in the aquatic resources alteration permit the cultural resources survey the stream use classification and the Section 404 application Negotiated alternate route

bull Private Landowner ndash Bowling Green Kentucky Served as lead consultant to provide technical comments to a Draft EA for the construction of a

220-mile electrical powerline Technical legal and financial reporting resulted in stopping the project in its entirety the Public Services Commission revoking the certificate of need (CON) and the Kentucky Attorney General conducting a formal investigation

bull Sumner Trousdale Opposing Pipeline ndash Gallatin Tennessee Served as lead consultant to identify deficiencies in the wetland and aquatic resources alteration

permits for a proposed 30-mile natural gas pipeline to represent the group in public hearings and develop technical arguments for against the proposed pipeline

Reservoir Water Quality and Use Assessments bull Friends of Tims Ford ndash Tims Ford Reservoir - Winchester Tennessee ndash served as lead consultant

to provide comments on Section 10 and Section 26A Regulation permit applications and a Recreational Boating Capacity Study for reservoir-wide community boat docks associated with residential development

bull Honeycomb Homeownerrsquos Association - Guntersville Lake ndash Guntersville Alabama ndash served as lead consultant to provide comments to Section 10 and Section 26A Regulation permit applications for residential developments Completed a detailed assessment of reservoir water quality results relative to designated use standards

bull Murrayrsquos Loch ndash Atlanta Georgia Served as consultant to evaluate the technical merits of a water withdrawal permit and the effects of increased urbanization on stormwater runoff and groundwater recharge Water withdrawal for commercial irrigation purposes resulted in decreased water levels in lakefront property of an adjacent residential neighborhood The permit was appealed to the State Administrative Court

Multi-Media Environmental Permitting bull Nashville Superspeedway USA Inc ndash Lebanon Tennessee

Served as Project Manager for a $125 million superspeedway development The environmental aspects included the requirements to determine the affects of the project on public and private groundwater users stream alterations wetlands endangered plant and animal species air permitting stormwater runoff oil pollution prevention underground injection control and due diligence property assessment

MARK A QUARLES PG PAGE 4 bull Metropolitan Knoxville Airport Authority ndash Knoxville Tennessee

Served as Project Manager for all environmental permitting and compliance activities Activities included spill prevention and response plan development stormwater plan development fuel tank farm design and compliance inspections

bull Various Industrial Clients ndash Tennessee Served as Project Manager for the development of SPCC Plans and SWPP Plans Plans were prepared consistent with the requirements of 40 CFR Part 112 the Tennessee General Permit the EPA Multi-Sector permit and the Tennessee Construction General Permit

Environmental Investigations and Remediation bull USEPA ndash Dickson County Tennessee

Served as Senior Geologist to investigate the occurrence of a cluster of cleft palate cleft lip birth defects in the county relative to the occurrence of trichloroethene in the groundwater and public water supply Reviewed EPA and TDEC regulatory files CDC and Department of Health reports interviewed City County TDEC and EPA officials and interpreted regional karst geologic and hydrogeologic data

bull Harpeth River Watershed Association ndash Franklin Tennessee Served as technical advisor for a review of the environmental investigation report and corrective action plan Contaminants of concern included free product toluene dissolved-phase BTEX constituents dissolved-phase acetone and dissolved-phase chlorinated solvents

bull Natural Resources Defense Council ndash Confidential Location Served as technical advisor for development of a Complaint for Declaratory and Injunctive Relief related to the inappropriate disposal investigation and cleanup of volatile organic compounds in soil groundwater and surface water

bull Confidential Client ndash McMinnville Tennessee Served as Project Manager to identify quantify and remediate the extent of a release of chlorinated solvents in a karst geologic setting Activities included the completion of an interim remedial action a soil gas survey direct push soil borings monitoring wells and well nests dye injection studies streambed sampling and a feasibility analysis

bull Burlington Northern Railroad - Birmingham Alabama Served as a Senior Geologist for an LNAPL investigation The investigation included the installation of temporary piezometers soil borings and permanent groundwater monitoring wells

bull Sunbeam Outdoor Products Inc - Neosho Missouri Developed a Field Sampling and Analysis Plan for the sampling of soils and drummed liquids for a Removal Action required by EPA Region VII Heavy metals and volatile organic compounds were the contaminants of concern in a karst geologic setting

bull United Technologies Automotive Inc - Quincy Michigan Served as Project Manager for groundwater well sampling and the development of an in-situ remedial action for heavy metal contamination

bull United Technologies Automotive Inc - Morganfield Kentucky Served as Project Engineer for a lagoon closure Completed activities for sludge characterization and quantification special waste permitting and closure design for material excavation and site restoration

Solid Waste Disposal bull Meriwether County Landfill Permit Appeal ndash Atlanta Georgia

Served as consultant to evaluate the technical merits of a municipal solid waste disposal permit that had been issued by the Georgia EPD Key technical issues were placement of the landfill adjacent to a public surface water supply typical liner performance and landfill leakage history in Georgia The permit was appealed to the Georgia Administrative Court

bull Various Secondary Aluminum Smelter Waste Landfills - Tennessee Reviewed secondary aluminum smelter waste characterization results landfill designs and associated hydrogeologic investigation reports for two proposed Class II industrial monofill landfill applications and reviewed groundwater monitoring reports associated with three co-mingled municipal solid waste landfills that used dross for intermediate daily cover

MARK A QUARLES PG PAGE 5 bull Various Industrial Landfills - Tennessee

Served as Project Manager for Subtitle D landfill siting and design projects Performed hydrogeologic investigations presented design waivers for site-specific design criteria (when applicable) and developed detailed designs for permitting

bull Various Landfills - Tennessee Served as Project Manager for the design permitting and operation of industrial and municipal solid waste landfills preparation of SWPP Plans quarterly groundwater and gas monitoring reports and hydrogeologic investigation reports

bull Various Municipal Landfills - Kentucky Served as Project Engineer for the design permitting and operation of municipal solid waste landfills

Stormwater Permitting and Compliance bull Tennessee Clean Water Network ndash Knoxville Tennessee

Served as lead consultant for providing technical comments for the draft Knox County Phase II Municipal Separate Storm Sewer System (MS4) permit

bull Various Industrial Clients - Throughout the US Served as Project Manager to obtain permit coverage through the EPA General Permit group permits and individual permits specific to each state Over 125 facilities were permitted

Hazardous Waste Management bull Various Industrial Clients ndash Throughout the US

Served as Project Manager for various projects to evaluate hazardous waste management practices consistent with the rules and regulations established under RCRA

bull Laidlaw Environmental Services Inc ndash Southeastern US Completed SWPP Plans for RCRA treatment storage and disposal facilities

Municipal Wastewater Management bull Various Municipalities ndash Fulton Cobb and Dekalb County Georgia

Served as Project Engineer for sewer modeling and point-source identification Identified sources of infiltration inflow and performed cost evaluations for source removal

bull Various Municipal and Industrial Clients ndash Tennessee Served as Project Engineer to establish beneficial reuse land application programs for wastewater sludge

bull Boston Water and Sewer Commission - Boston Massachusetts Served as Project Engineer for sewer modeling and point-source identification projects of combined and separate sewers up to 15 feet in diameter Identified sources of infiltration inflow and performed cost evaluations for source removal

bull Various Municipal Clients ndash Throughout the US Served as lead technical trainer for the implementation of proprietary software used for automated GIS mapping maintenance scheduling and hydraulic analyses of separate and combined sewers

bull City of Hopkinsville - Hopkinsville Kentucky Served as Project Engineer for water and sewer line expansions and wastewater treatment projects

TECHNICAL PUBLICATIONS AND LECTURES bull Quarles M and William Wilson ldquoUnconventional Natural Gas and its Risk A Tennessee

Perspectiverdquo Appalachian Public Interest Environmental Law Conference Knoxville Tennessee October 2011

bull Quarles M ldquoA Case Study in Karst Hydrogeology and Contaminant Fate and Transportrdquo National Groundwater Association 51st Annual Convention and Exposition December 1999

bull Quarles M and Allen P Lusby ldquoEnhanced Biodegradation of Kerosene-Affected Groundwater and Soilrdquo 1994 Annual Conference of the Academy of Hazardous Materials Managers October 1994

MARK A QUARLES PG PAGE 6 bull Quarles M ldquoNew Tank Performance Standardsrdquo Tennessee Environmental Law Letter July

1993 EXPERT LEGAL TESTIMONY bull Chesney versus Tennessee Valley Authority ndash 2011 US District Court Written testimony

associated with fly and bottom ash sampling waste characterization contaminant fate and transport and contaminant risks compared to US EPA screening levels drinking water standards fish and aquatic life standards and sediment cleanup standards

bull Busch et al versus Dr Carol Couch Atlanta Georgia 2008 State Administrative Court Written and verbal testimony regarding drought restrictive surface water and groundwater use Qualified by the court as an expert in geology hydrogeology and stormwater runoff

bull Darrel Segraves et al versus Dr Carol Couch Atlanta Georgia 2008 State Administrative Court Written and verbal testimony regarding appeal of a municipal solid waste landfill permit Qualified by the court as an expert in geology hydrogeology landfill design pertaining to landfill leakage and stormwater runoff

bull Tulane Environmental Law Clinic 2007 - 2008 Written testimony for numerous draft LDEQ permits and proposed rules

bull Republic of Ecuador and PetroEcuador vs Chevron Texaco Corporation and Texaco Petroleum Company US District Court Southern District of New York 2007 Written testimony regarding environmental investigation protocol

bull Friends of Tims Ford vs Tennessee Valley Authority and Tennessee Department of Environment and Conservation US District Court 2007 Written testimony in support of violations of State and Federal water quality standards reservoir carrying capacity standards and NEPA environmental assessment standards

bull Freddie Howell vs Creative Customs Atlanta Georgia 2007 Technical support regarding litigation associated with stormwater and groundwater flow and their effects on the Howell property

bull Aguida vs ChevronTexaco Lago Agrio Ecuador Court 2006 Written testimony regarding Texacorsquos waste management and standard operating practices in the Ecuadorian concession area relative to industry standards

TRAINING Current Wetland Issues in Tennessee (2007) Professional Liability Education - Contract Review and Revision (2000) Professional Liability Education ndash Mid-Town Developer Case Study Workshop (1999) Professional Liability Education ndash Liability IQ for Environmental Consultants (1998) Liquid Animal Waste Management System Design to NRCS Standards for CAFO (1998) 8-Hour OSHA Health and Safety Refresher Training Hazardous Materials Waste Manager Course University of Alabama (1993) 40-Hour OSHA Health and Safety Training (1990) CONTACT INFORMATION Home telephone 615-352-0471 Mobile telephone 615-504-0956 Email markquarlescomcastnet

Determination of vertical and horizontal pathways of injected freshwastewater into a deep saline aquifer (Florida USA) using naturalchemical tracers

Virginia Walsh amp Reneacute M Price

Abstract Two deep-well injection sites in south FloridaUSA inject an average of 430 million liters per day(MLD) of treated domestic fresh wastewater into a deepsaline aquifer 900m below land surface Elevated levels ofNH3 (highest concentration 939micromol) in the overlyingaquifer above ambient concentrations (concentration lessthan 30micromol) were evidence of the upward migration ofinjected fluids Three pathways were distinguished basedon ammonium chloride and bromide ratios and temper-ature At the South District Wastewater Treatment Plantthe tracer ratios showed that the injectate remainedchemically distinct as it migrated upwards through rapidvertical pathways via density-driven buoyancy Thewarmer injectate (mean 28degC) retained the temperaturesignal as it vertically migrated upwards however thetemperature signal did not persist as the injectate movedhorizontally into the overlying aquifers Once introducedthe injectate moved slowly horizontally through theaquifer and mixed with ambient water At the NorthDistrict Wastewater Treatment Plant data provide strongevidence of a one-time pulse of injectate into theoverlying aquifers due to improper well construction Noevidence of rapid vertical pathways was observed at theNorth District Wastewater Treatment Plant

Keywords Waste disposal Deep well injection Carbonate rocks Confining units Ammonia Temperature USA

Introduction

Deep well injection of treated municipal wastewater intonon-potable aquifers has been used as an alternative todischarge of wastewater to surface waters for manydecades There are 430 permitted municipal wastewaterdeep injection wells in the United States with 163 inFlorida alone (USEPA 2008) These deep aquifers tend tobe saline and the discharge of fresh wastewater into themhas raised concerns of geochemical reactions as a result ofthe mixing of the two waters as well as the buoyanttransport of the wastewater upwards into overlyingaquifers Confined brackish aquifers in Florida have beenused extensively for aquifer storage and recovery (ASR)of potable freshwater (Arthur et al 2001 Renken et al2005) and deeper saline aquifers have been used fordisposal of waste fluids such as oil brines industrial waterand municipal wastewater (Meyer 1989a Meyer 1989b)ASR in Florida has been extensively studied as part of theComprehensive Everglades Restoration Plan (Reese 2002Mirecki 2004 Mirecki 2006) however little research hasbeen published regarding the fate and transport of thetreated wastewater into deep saline aquifers (Meyer1989a Haberfeld 1991 Maliva and Walker 1998Bloetscher et al 2005 Bloetscher and Muniz 2006Maliva et al 2007)

Miami-Dade County Water and Sewer Department(MDWASD) located in southern Florida currently dis-charges 430 million liters per day (MLD) of treateddomestic wastewater into a saline deep aquifer at twolocations in the county Deep well injection has been inuse in Miami-Dade County since the late 1960s Theinjection facilities are located in the north and south of thecounty separated by 44 km (Fig 1) The South DistrictWastewater Treatment Plant (SDWWTP) site was placedinto service in 1983 and is currently permitted for thedisposal of 367 MLD of treated wastewater The NorthDistrict Wastewater Treatment Plant (NDWWTP) site wasplaced into service in 1997 and is permitted for 90 MLD

Received 2 February 2009 Accepted 14 December 2009

copy Springer-Verlag 2010

V Walsh ())Miami-Dade Water and Sewer Department3071 SW 38th Ave Miami FL 33146 USAe-mail walshvmiamidadegov

V WalshDepartment of Earth and EnvironmentFlorida International University11200 SW 8th Street University Park Miami 33199 USA

R M PriceDepartment of Earth and Environment and SoutheastEnvironmental Research CenterFlorida International University11200 SW 8th Street University Park Miami 33199 USA

Hydrogeology Journal DOI 101007s10040-009-0570-8

Both facilities treat domestic wastewater to above second-ary drinking water standards and discharge the treatedwastewater into United States Environmental ProtectionAgency (USEPA) Class I injection wells The treatedwastewater is injected into the Boulder Zone a highlytransmissive interval in the deep saline non-potable LowerFloridan Aquifer The Boulder Zone has been thought to behydrologically separated from overlying aquifers by a335-m-thick confining unit During the installation of addi-tional monitoring wells at the SDWWTP in 1994 ammonia-nitrogen (NH3-N) was detected at 442 m depth in theoverlying aquifer at a concentration of 411 micromoles perliter (micromol) above reported background levels of 29micromol

(BCampECH2M Hill 1977) The detection of NH3ndashN in theaquifers above the Boulder Zone has raised doubts regardingthe efficacy of the confining unit and the resultant waterquality impact to overlying aquifers as these aquifers areused as alternative water supplies via storage of freshwater(ASR) and blending with potable surficial aquifer water

Research has focused on ASR in south Florida (Arthuret al 2001 Reese 2002 Mirecki 2004 Mirecki 2006Reese and Richardson 2008) however few studies havebeen conducted regarding the transport and fate of injectedeffluent into the Boulder Zone and typically these had todo with the relative risk of deep well injection versusocean outfall disposal of municipal waste (Englehardt et

Fig 1 Location of theNDWWTP and the SDWWTPstudy sites

Hydrogeology Journal DOI 101007s10040-009-0570-8

al 2001 USEPA 2003 Bloetscher et al 2005 Bloetscherand Muniz 2006) Recently researchers have studied thetransport mechanisms of the observed migrated injectateand have suggested density-driven buoyant transportmechanism along natural or anthropogenic vertical frac-tures in the lower aquifers (Maliva and Walker 1998McNeill 2000 McNeill 2002 Maliva et al 2007 Walshand Price 2008) The objective of this study was todetermine migration pathways of injected treated waste-water at two facilities in Miami-Dade County Florida(SDWWTP and NDWWTP) using historical time seriesdata and major ion data collected as part of this study Themethodology developed for this study used chloride (Clminus)bromide (Brminus) and NH3 as tracers This methodologyprovided a method for estimating transport pathways andinvolved no additional collection of data other than whatwas typically required under federal and state regulatoryprograms

Natural inorganic tracers have been used extensively inwater resources investigations to trace groundwater flowpaths and calculate mixed water ratios (Langmuir 1997Davis et al 1998 Herczeg and Edmunds 2000) Clminus andBrminus commonly are used as they tend to be conservativeand their ratios may also give information as to the sourceand pathways of water Studies have been conducted insouth Florida (Shinn et al 1994 Paul et al 1997 Corbettet al 2000 Boumlhlke et al 2003) and elsewhere (Kaehlerand Belitz 2003 Clark et al 2004) tracing treatedwastewater in surficial aquifers but NH3 was not used asa tracer as it does not behave conservatively in oxicwaters In this study a novel application of Clminus Brminus andNH3 as conservative tracers of injectate was developed aspart of mixing models to distinguish pathways betweenthe deep aquifers Clminus is a natural anion in the Floridanaquifer system and its principal source is seawater asthere are no evaporite minerals to provide an additionalsource (Sprinkle 1989 Reese 1994) The seawater sourceof Clminus in south Florida is thought to be the result of eitherincomplete flushing of Pleistocene seawater and brackishwater intrusion andor the result of the cyclic flow basedon thermal upwelling of Holocene intruded seawater(Kohout 1965 Sprinkle 1989 Reese 1994) Bromide(Brminus) behaves similar to Clminus in groundwater systems(Davis et al 1998) and in south Florida the source of Brminus

in groundwater is similar to that of Clminus although its naturalabundances are orders of magnitude less than Clminus Theonly source of the NH3 is the injectate and therefore itwas used to trace transport pathways of the injectedwastewater

Geologic and hydrogeologic framework

The Floridan aquifer system (FAS) in southeastern Floridais defined by a vertically continuous sequence of per-meable carbonate rocks of Cenozoic age that are hydrauli-cally connected in varying degrees (Miller 1986) Theaquifer matrix consists of carbonate and dolomitic lime-stones dating from the Paleocene to the Oligocene

epochs Overlying the FAS are the impermeable sedimentsof the late Oligocene to Pliocene age Hawthorn Group a180-m-thick confining layer of clays siltstones and siltylimestones The Hawthorn Group separates the UpperFloridan Aquifer from the late Pliocene and Pleistoceneformations making up the Surficial Aquifer System whichincludes the Biscayne Aquifer in south Florida (Fig 2)The Biscayne Aquifer is an unconfined surficial aquiferand is the major source of potable water in south Florida(Fish and Stewart 1991)

The Floridan Aquifer contains several highly perme-able and less permeable zones with zones of highestpermeabilities typically occurring at or near unconform-ities and usually parallel to the bedding planes (Meyer1989a) Previous studies (Miller 1986 Reese 1994)grouped the Floridan aquifer system into three hydro-stratigraphic units (Fig 2) the Upper Floridan Aquifer(UFA) the Middle Confining Unit (MCU) and the LowerFloridan Aquifer Recently the MCU in south Florida hasbeen divided into the MC1 and MC2 (Fig 2) separatedby the Avon Park permeable layer (Reese and Richardson2008) which in south Florida had previously beenidentified as the Middle Floridan Aquifer The UpperFloridan Aquifer contains relatively fresh water less than10000 mg Lminus1 total dissolved solids (TDS) The LowerFloridan Aquifer consists of seminconfining or leakymicritic limestone and dolomite layers that containgroundwater with compositions approaching seawater(approximately 30000 mg Lminus1 TDS) A dolomite confin-ing unit (DCU) a thin confining unit below the MC2 wascharacterized at the study site by McNeill (McNeill 20002002) This DCU lies above the permeable zone com-monly known as the Boulder Zone within the OldsmarFormation of the Lower Floridan Aquifer The FASoutcrops along the Straits of Florida providing a hydraulicconnection to the sea (Kohout 1965 Miller 1986 Reese1994) Transmissivities in the Upper Florida Aquiferrange from 929 to 23times104m2 dayminus1 (Meyer 1989a Reese1994) while transmissivities in the Boulder Zone rangefrom 297times105m2 dayminus1 to 232times106m2 dayminus1

Site descriptionsThe NDWWTP and the SDWWTP consist of deepinjection wells that penetrate down to approximately855 m The upper 755 m of each well is cased to the topof the Boulder Zone The bottom 100 m of each injectionwell is an open hole in the Boulder Zone Nine suchinjection wells and three multi-zoned and dual-zonedmonitoring wells were constructed between 1977 and1981 at the SDWWTP (Fig 3) The multi-zone test wellBZ cluster (BZ-1 through 4) was constructed in 1977 andconsisted of four telescoping monitoring wells the deepestof which was BZ-4 cased to the top of the Boulder Zonethe shallowest BZ-1 open to the UFA at a depth of 312 mThe remaining monitoring wells were constructed bothat the SDWWTP and NDWWTP using a dual zone designwith an inner steel casing drilled to the deeper intervaland the outer steel casing open to the upper interval For

Hydrogeology Journal DOI 101007s10040-009-0570-8

this report well nomenclature indicates the open intervalof the dual-casing ldquoUrdquo represents the upper monitoringinterval and ldquoLrdquo represents the lower monitoring intervalWells 1 and 2 were dual-cased to monitor water quality inthe UFA (sim300 m) and the lower confining units (sim550 mCH2MHill 1981) In 1994 NH3 was detected aboveambient levels in the confining unit at the BZ well cluster(BZ-2 depth 488 m) and subsequent investigations by theutility found a leak due to corrosion of the casing in thiscluster (MDWASD 1995) The lower three monitoringintervals of the BZ well cluster were plugged in 1995 tostop the upward migration of injectate through the casinghole and the confining unit (488 m) monitoring intervalwas redrilled From 1995ndash1996 nine injection wells and

thirteen dual-zoned monitoring wells were constructed onthe SDWWTP These monitoring wells were cased to theAvon Park Permeable zone (APPZ) and the MC2 withopen holes in the formations approximately 30 m Duringthe construction of the monitoring wells NH3 concen-trations above ambient levels were found throughout thesite Elevated NH3 concentrations were found in thenorthwest corner of the site in the MC1 interval in severalwells but not in the lower MC2 interval of these wellsElevated levels were found in the MC2 interval in thesouth side of the site As a result of the detected NH3 inthe confining units the EPA required purging of the wellsthat showed elevated concentrations NH3 (Starr et al2001) in an attempt to remove the NH3 loading in the

Fig 2 Geologic and hydrogeologic framework of NDWWTP and the SDWWTP modified from Reese and Richardson 2008 Welldiagram on the right shows the number of wells open to the indicated hydrogeologic unit used for this study

Fig 3 Well locations at theSDWWTP

Hydrogeology Journal DOI 101007s10040-009-0570-8

impacted intervals Discontinuous purging of approxi-mately 2100 Lmin commenced from 1997 to 2000 forthe northwest wells (5U 6U 7U 8U 15U and 16U) of theAPPZ interval and the south wells (11L and 12L) of theMC2 (MDWASD 2000)

Injection well construction started at the NDWWTP in1996 Four injection wells were constructed into theBoulder Zone and four dual-zoned monitoring wells wereconstructed to the UFA and the APPZ intervals (Fig 4) In1996 effluent was injected in two completed injectionwells while one injection well was still under constructionresulting in injectate backflowing into an open borehole atan uncased injection well for 5 days Several months afterthe construction of the wells had been completed NH3

concentrations were observed to increase in the APPZinterval of the monitoring wells on site The utility wasrequired to purge the APPZ interval wells for a period of1 year from 2003ndash2004 (MDWASD 2005)

Methodology

Historical data were collected and checked for qualityassurance for the NDWWTP and SDWWTP Data wereavailable from 1983 through 2007 for the SDWWTP and1996ndash2007 for the NDWTP Data studied as part of thisresearch included pressure temperature pH Clminus sulfate(SO4

2minus) NH3 and nitrate (NO3minus) The historical data were

compiled from the utility monthly operating reportsavailable sporadically from 1983 Non-detects that hadbeen entered as a zero value were updated to the detectionlevel of the parameter Summary statistics including meanmedian standard deviation maximum and minimum wereapplied to each of the wellsrsquo time series data to assesswater-quality changes over time and used to compare toambient water quality data at other locations in southFlorida Most water quality for the Floridan Aquifer insouth Florida had been collected as regulatory require-ments which usually included chemical analyses that areused for drinking water quality and therefore did notinclude major ion data Residence time in the Floridan

aquifer system in south Florida is on the order of thousandsof years (Meyer 1989a) and it was assumed that due to thedepth of the aquifer water quality was in equilibrium andthere would be no other cause of perturbations to ambientwater quality other than migration of injectate Time seriesdata that showed large variation over time would indicatenon-equilibrium conditions and therefore not ambientconditions Abrupt changes in water quality and pressurewere observed in the time series data in wells that werepurged in 1997 These changes were not observed in wellsthat were not purged These changes in water quality andpressure were interpreted as being the result of crossconnections developed in the dual zone casings of some ofthe purged wells and review of borehole videos of thesewells taken in 2004 confirmed holes in the casings of thesewells It could not be determined which interval the datacollected from these wells represented after the crossconnections developed therefore data were discardedfrom the historical series analysis based on the month itwas ascertained the cross connection developed and thesummary statistics were recalculated for these wells

Floridan Aquifer water samples were collected at theNDWWTP and SDWWTP during 2006 and 2007 as partof this study for major ions and nitrogen species Thirty-two monitoring wells were sampled at the SDWWTP andwater-quality samples were collected from these wellsfrom the UFA the APPZ and the MC2 At theNDWWTP samples were collected from four monitoringwells representing the UFA and four wells in the APPZTemperature pH dissolved oxygen and conductancewere taken from water samples in the field using an YSI556 MPS The YSI instrument was calibrated per themanufacturerrsquos instructions prior to each sampling eventAll wells were purged for at least 24 h prior to sampling toensure at least three well volumes were evacuated Thewells were sampled through a closed system using a lowflow cell and tygon tubing through a disposable highcapacity 045micromol in-line filter Water samples wereanalyzed for the anions Brminus Clminus Fminus NO3

minus NO2minus and

SO42minus on a DIONEX ion chromatography system

HCO3minus and CO2

minus were analyzed via manual titrationNH3 was analyzed on a LACHAT analyzer 800 withNH4

+ then calculated based on pH and temperature ofthe sample using the NH3 result (Stumm and Morgan1996) Cations (Ca2+ Mg2+ K+ Na+ and Sr2+) wereanalyzed by inductively coupled plasma (ICP)

Results

The mean historical data are summarized in Table 1 forthe SDWWTP and Table 2 for the NDWWTP Dissolvedoxygen NO3

minus and NO2minus had similar results for both the

SDWWTP and NDWWTP sites for the aquifer intervalsNO3

minus concentrations were either detected at very lowconcentrations or below detectable levels NO2

minus levelswere below 1 micromoleL (micromol) for all aquifer intervalsand in the injectate at the NDWWTP and SDWWTP sitesfor the historical time series The injectate had a mean valueFig 4 Well locations at the NDWWTP

Hydrogeology Journal DOI 101007s10040-009-0570-8

Tab

le1

Meanvalues

forhistorical

timeseriesSDWWTP

mblsmetersbelow

land

surface

Geologicform

ation

Hyd

rostratig

raph

icform

ation

WellID

Open

interval

Periodof

record

Tem

pdegC

pHNH3micromol

Clndashmmol

SO42ndashmmol

NO3ndashmicromol

mbls

Pleistocene

Biscayn

eAqu

ifer

Injectate

(S-EFF)

Surface

591

ndash1207

277

66

889

203

109

Und

ifferentiated

Haw

thornAvo

nParkLim

estone

Upp

erFloridan

Aqu

ifer

(UFA

)1U

299ndash

332

983

ndash1207

240

79

1221

32

02

2U29

9ndash311

783

ndash1207

244

79

1321

32

03

3U29

9ndash32

0291

ndash1207

243

79

1023

32

03

BZ1

306ndash

316

783

ndash1207

242

76

1222

31

02

Avo

nPark

Lim

estone

Avo

nParkPermeable

Zon

e(A

PPZ)

13U

451ndash

475

296

ndash1207

239

77

6210

848

03

5U45

4ndash48

4594

ndash1102

241

76

492

108

49

03

6U45

4ndash48

3594

ndash1207

241

76

545

7630

03

7U45

4ndash48

2694

ndash198

245

74

526

738U

454ndash

480

894

ndash602

240

77

216

106

41

02

9U45

4ndash48

4195

ndash1207

239

77

64111

43

02

10U

454ndash

485

296

ndash1207

240

76

3510

542

02

11U

454ndash

484

296

ndash1207

240

76

118

106

43

02

14U

454ndash

480

296

ndash1207

239

74

320

9943

02

15U

454ndash

480

296

ndash1207

231

75

296

106

53

03

16U

454ndash

485

296

ndash1207

231

76

330

109

48

02

12U

456ndash

487

296

ndash204

249

76

100

111

42

02

MiddleCon

fining

Unit(M

C2)

BZ2

481ndash

507

783

ndash1207

254

75

106

133

56

02

2L50

1ndash51

0783

ndash1207

243

74

1219

926

02

4L51

9ndash56

112

91ndash

1207

240

73

1251

019

304

13L

530ndash

562

296

ndash1207

237

75

5550

822

809

3L54

0ndash57

7191

ndash1207

240

73

752

921

910

5L54

6ndash57

6594

ndash1102

239

74

652

821

604

6L54

6ndash57

6594

ndash1005

237

74

3052

622

703

7L55

0ndash57

1694

ndash198

242

71

1053

68L

546ndash

576

894

ndash602

237

74

554

124

804

9L54

6ndash57

3195

ndash1207

234

74

553

422

604

10L

546ndash

576

396

ndash1207

238

76

141

429

204

05

11L

546ndash

576

296

ndash1199

238

76

417

193

93

02

12L

546ndash

576

296

ndash1207

254

74

676

5730

03

15L

546ndash

576

296

ndash104

231

75

1253

125

204

16L

546ndash

576

296

ndash1207

229

74

653

221

904

1L56

1ndash58

7783

ndash1207

238

73

653

923

904

Oldsm

arFormation

Bou

lder

Zon

eLow

erFloridan

Aqu

ifer

BZ4

853

0783ndash894

249

72

634

3

Hydrogeology Journal DOI 101007s10040-009-0570-8

of NO3minus of 379micromol at the NDWWTP and 109micromol

at the SDWWTP for the historical time series Dissolvedoxygen was detected at concentrations less than 10 mg Lminus1

for all aquifer intervals Dissolved oxygen concentrationsfor the injectate at both the NDWWTP and the SDWWTPhad results above 3 mg Lminus1

Historical time series results SDWWTPThe historical period of record data for the freshwaterinjectate samples from the SDWWTP (identified as S-EFF) were available from 1991 through 2007 (Table 1)Temperature ranged from 218 to 311degC with a mean of277degC Mean pH in the historical time series was 66NH3 ranged from 1468ndash18496micromol with a mean of889micromol NH3 varied seasonally and increased with time(Fig 5) Clminus concentrations averaged 2 millimolesL(mmol) with a very small range and standard deviationindicative of the freshwater source of the injectateHistorical data from the SDWWTP for the UFA (wellsBZ1 1U 2U and 3U) were available from 1983 through2007 Temperature averaged 24degC with no significantdifference observed between the wells The range of pHwas from 76 to 82 in the UFA Chloride averagedbetween 21 and 23 mmol while NH3 means rangedbetween 10 and 13micromol The summary statistics for thewater-quality samples collected from the UFA showedconsistent values with no discernable variation over timeHistorical data from wells open to the APPZ at theSDWWTP (wells 5U 6U 7U 8U 9U 10U 11U 12U13U 14U 15U 16U) were available from 1994 through2007 Mean temperatures ranged between 231 and249degC in these wells There was little variation observedin the pH in the APPZ samples but the mean pH of 76was lower than the mean pH in the UFA Almost all of thewells showed variation in NH3 concentrations over timeMean values of NH3 in these wells ranged from 35micromolin well 10U to 545micromol in well 6U Well 6U showed anincreasing trend with time in NH3 that was observed to besimilar to the increasing trend of NH3 in the injectate(Fig 5) The spread between the 5th and 95th percentilewas the greatest in wells 6U and 12U Only wells 9U10U and 13U showed little variation in NH3 over timeMean concentrations of Cl- in wells 6U and 7U were 76and 73 mmol Wells in the MC2 were open to intervalsvarying in depth from 481 to 551 m Mean temperaturevalues ranged from 229 to 242degC in all wells with theexception of a mean value of 254degC in wells BZ2 and12L Mean pH values ranged from 73 to 76 Mean NH3

concentrations showed two groupings Wells BZ2 10L11L and 12L exhibited concentrations of 106 141 417and 676micromol respectively The remainder of the wellsexhibited mean NH3 concentrations of less than 55micromolClminus concentrations for wells 10L 11L and 12L were 429193 and 57 mmol respectively the remainder of the wellshad mean concentrations greater than 508 mmol (excep-tion is BZ-2 whose Clminus concentration of 133 mmolreflects the shallower depth of this well with the openinterval in the lower brackish water zone of the FloridanT

able

2Meanvalues

forhistorical

timeseriesNDWWTP

mblsmetersbelow

land

surface

Geologic

form

ation

Hyd

rostratig

raph

icform

ation

WellID

Open

interval

Period

ofrecord

Tem

ppH

NH3

Cl-

SO42-

NO3-

Revised

period

ofrecord

a

Tem

ppH

NH3

Cl-

SO42-

mbls

degCmicromol

mmol

mmol

micromol

degCmicromol

mmol

mmol

Pleistocene

Biscayn

eAqu

ifer

Injectate

(N-EFF)

Surface

797

ndash1207

284

65

8193

200

05

379

Avo

nPark

Lim

estone

Eocene

Upp

erFloridan

Aqu

ifer

(UFA

)N-1U

354ndash38

5197

ndash1207

231

76

188

737

35

02

N-2U

351ndash38

4396

ndash1207

230

78

177

662

36

21

N-3U

354ndash37

9396

ndash1207

229

78

173

658

36

20

N-4U

354ndash37

9496

ndash1207

231

76

181

684

35

08

Avo

nPark

Permeable

Zon

e(A

PPZ)

N-1L

430ndash46

1496

ndash1207

219

73

2612

3682

328

10

3496ndash797

224

72

193

4617

N-2L

431-

459

396

ndash1207

223

76

1684

3979

156

22

396

ndash898

229

78

177

4557

166

N-3L

430ndash46

0396

ndash1207

222

76

1314

4094

158

10

396

ndash1298

230

77

191

4548

149

N-4L

430ndash46

0496

ndash1207

224

72

1903

3804

152

16

496

ndash1298

223

75

237

4405

Hydrogeology Journal DOI 101007s10040-009-0570-8

Aquifer) Data collected from well 12L were similar todata collected for wells for 6U and 7U These wells hadhigh NH3 concentrations with low Clminus and SO4

minus concen-trations Historical data were available for the BoulderZone interval (well BZ4) from 1983 through 1994 Themean pH and temperature values were 72 and 249degCrespectively Mean NH3 concentration was 634micromol andshowed apparent seasonal variation and increasing trendover time and was similar to the injectate historical timeseries (Fig 5) The mean Clminus concentration was 3 mmolsimilar to the mean Clminus concentration of 2 mmol for theinjectate

Historical time series results NDWWTPThe historical period of record data for freshwaterinjectate samples (N-Eff) at the NDWWTP were availablefrom 2002 through 2007 Temperature ranged from 22 to34degC with a mean of 28degC The mean pH was similar tothe SDWWTP injecate at 65 NH3 ranged from 210ndash3764micromol with a mean of 819micromol and a large standarddeviation indicative of the apparent seasonality similar tothe SDWWTP Clminus concentrations ranged from 08 mmolto 1131 mmol with a mean 20 mmol slightly higher thanthe mean concentration of the SDWWTP injectateHistorical data were available from 1996 through 2007for wells open to the UFA (N-1U N-2U N-3U and N-4U) Mean temperature averaged 23degC in these wellswith no significant difference observed between the wellsMean values of pH ranged from 76 to 78 Clminus meanconcentrations ranged between 662 and 737 mmolsNH3 mean concentrations ranged between 17 to 18micromolConcentrations for the UFAwater-quality samples for theNDWWTP showed consistent values with no discernablevariation over time Historical data were available from1996 through 2007 for wells open to the APPZ (N-1L N-2L N-3L and N-4L) Temperature mean values were

22degC Analysis of historical NH3 data indicates increasingconcentrations of NH3 starting in late 1997 (Fig 6) NH3

concentrations appeared to have reached a peak concen-tration of 408micromol in well N-1L in July 2001 andsteadily declined thereafter to concentrations rangingfrom 200 to 250micromol Wells N-2L N-3L and N-4L showsimilar patterns as well N-1L but with lowered anddelayed peak concentration values NH3 concentrationsare observed to increase scatter after 2003 whichcorresponds to when purging commenced at theNDWWTP Once purging ceased in 2004 NH3 concen-trations in wells varied between 150ndash300micromol The Clminus

mean concentrations ranged from 368 to 409 mmol Clminus

in these wells exhibited variation over time and analysisof the time series indicated that as NH3 concentrationsincreased Clminus concentrations decreased (Fig 6) The timeseries data for the lower wells were revised to removedata after NH3 concentrations were observed to increasein each well in order to determine ambient concentrationsin the APPZ Revised NH3 mean concentrations rangedfrom 18ndash24micromol Clminus mean concentrations ranged from441ndash461 Very little variation was observed in NH3 andClminus mean concentrations after the time series data wereremoved

Major ion data collection resultsMajor ions were collected for this study from 2006ndash2007(Table 3) Data from wells at the SDWWTP site thatexhibited cross connections were removed from thisanalysis Data collected from the SDWWTP UFAexhibited very little variation between wells and weresimilar to the historical time-series data with low cationand anion concentrations For the APPZ wells NH4

+

mean concentrations could be combined into three groupswells 9U 10U and 13U with NH4

+ mean concentrationsof 60 67 and 143micromol respectively wells 14U and 16Uwith 497 and 439micromol and well 6U 823micromol Cation andanion mean concentrations showed a similar grouping asthe NH4

+ concentration grouping with well 6U consis-tently grouping independently and with increasing NH4

+

concentrations correlating to decreasing ion concentra-tions The MC2 mean NH4

+ concentrations could also becombined into three groups well 12L at a mean NH4

+

concentration of 765micromol wells BZ-2 10L and 13LNH4

+ at mean concentrations 176 200 and 108micromolrespectively the remainder wells at NH4

+ concentrationsbelow 10micromol Cation and anion concentrations could becombined in the same 3 groups as the NH4

+ groups withlower ion mean concentrations observed for BZ-2 10Land 13L and much lower ion concentrations observed inwell 12L As with well 6U in the MC1 well 12L in theMC2 consistently grouped independently

The NDWWTP wells open to the UFA (351ndash385 m)exhibited very little variation in field measurements andmean concentrations between wells and were similar tothe historical time series The interval (430ndash461 m) in theAPPZ at the NDWWTP also showed little variation withmean NH4

+ concentrations (215ndash295micromol) and mean

Fig 5 Time series NH3 data from the injectate (black circle) BZ-4(green triangle) and well 6U (red circle) at the SDWWTP site Theapparent seasonal variation observed in the injectate is a result ofincreased flows during the wet season and storm events Theincreasing trends with time correlate to increased injection over timedue to growth in population in Miami-Dade County

Hydrogeology Journal DOI 101007s10040-009-0570-8

concentrations of Clminus (371ndash386 mmol) varying littlebetween wells

Ternary diagramThe typical ClminusBrminus ratio for seawater is about 290 (Daviset al 1998) and most of the ClminusBrminus ratios at both siteswere within that range with no discernable differencesQuite often the addition of a third water-quality membercould enhance the understanding of the data and this wasthe case with using NH4

+ as the third end-member NH4+

Clminus and Brminus data were plotted on a ternary diagram withdata normalized to 100 Typical seawater and freshwaterNH4

+ Clminus and Brminus values after Hem (1985) were alsoplotted for comparison Water quality at the NDWWTPclustered into three distinct groups with two groups basedon depth of the interval sampled and the third the injectate(Fig 7) The ambient aquifer data plot close to seawaterThe injectate data plotted off in the lower left hand cornerdue to the large NH4

+ concentrations At the SDWWTPthree aquifer groupings were observed Ambient well datafrom the MC2 plotted similar to seawater Ambient welldata from the UFA plotted slightly towards freshwaterData from wells that showed elevated NH4

+ plotted in aline towards the injectate with groundwater data from 6Uand 12L plotting very close to the injectate This linerepresents the evolution of the water quality of these wellstowards the injectate water quality and does not show anyevolution of more saline water into the higher intervals inthe aquifer

Mixing end-member modelsEnd-member mixing models of wells 6U 12L and 10Lrepresented the results obtained for all wells at the

SDWWTP (Fig 8) Well 6U and 12L showed theprogressive freshening of water and increasing NH3

concentrations towards the injectate end-member(Fig 8) There was little mixing from the saline end-member towards the brackish end-member in well 6U andalmost all of the mixing was towards the injectate end-member Both 6U and 12L showed large changes inconcentrations from their original end-members over timeWell 10L showed a different pattern than 6U and 12Lwith gradual freshening of the saline water towards theinjectate end-member The mixing was towards the lowerrange of the injectate end-member and there were no largechanges in concentrations of either NH3 or Clminus from thesaline end-member Well N-1L at the NDWWTP end-member mixing model showed a different pattern than theSDWWTP (Fig 9) Clustering of the NH3Cl

minus ratios weredistinguished based on time The NH3Cl

minus ambient ratio canclearly be seen on Fig 9 and lies along the saline end-member As the concentrations of NH3 increased in time tothe peak concentration the NH3Cl

minus ratios showed twodistinct clusters Initially the NH3Cl

minus ratio showed gradualincreasing in NH3 with little change in Clminus from ambientconcentrations There was a rapid change in the NH3Cl

minus

ratio as NH3 reached the peak concentrations Once the peakwas reached the NH3Cl

minus ratios slowly declined in time

Discussion

The Floridan aquifer system was sampled by others atdifferent sites in south Florida and these data aresummarized in Table 4 Wells identified as WWF weremonitoring wells installed as part of the MDWASD ASRsystem west of the NDWWTP and SDWWTP (CH2MHill 1998) The ASR systems were not in use during the

Fig 6 Graph a shows the NH3 data time series for the wells in the APPZ interval at the NDWWTP The dashed lines indicate the purgingtime from 2003 through 2004 NH3 concentrations are observed to increase in well N-1L similar to contaminant breakthrough curves WellN-1L was the closest well to the uncased injection well when injectate backflowed into the APPZ NH3 concentrations for wells N-2LN-3L and N-4L appear to be similar and show a similar increase after 1999 Variability is seen in the data after 2003 Graph b showsClminus concentrations in well N-1L clustered at approximately 300 mmol and an abrupt decrease to less than 300 mmol is seen Clminus

concentrations in wells N-2L N-3L and N-4L are very similar and show a decrease in concentrations after 1999 until 2000 whenconcentrations appear to stabilize Clminus concentrations start to increase slightly and become variable after 2003 All four wells showsimilar concentrations of both NH3 and Cl- after 2004

Hydrogeology Journal DOI 101007s10040-009-0570-8

Tab

le3

Meanfieldparametersandionconcentrations

during

the20

06ndash2

007samplingcompleted

aspartof

thisstud

ymblsmetersbelow

land

surface

Geologic

form

ation

Hyd

rogeolog

icun

itOpen

interval

Well

Temp

pHNH4+

Ca2

+Mg2

+Na+

K+

Sr2+

Cl-

SO42-

HCO3-

Br-

F-

NO3-

NO2-

mbls

IDdegC

micromol

mmol

mmol

mmol

mmol

micromol

mmol

mmol

mmol

micromol

micromol

micromol

micromol

SDWWTP

Pleistocene

Biscayn

eAqu

ifer

Surface

S-EFF

290

67

112

51

03

07

30

430

197

6

Und

ifferentiated

Haw

thornOcala

Lim

estone

toAvo

nPark

Lim

estone

UFA

306ndash31

6BZ1

242

78

61

325

139

213

440

109

11

299ndash33

21U

236

81

61

324

142

224

456

117

01

299ndash32

03U

243

79

61

325

148

284

454

119

41

299ndash311

2U25

379

101

322

143

215

433

143

11

Avo

nPark

Lim

estone

APPZ

454ndash48

49U

238

77

604

1098

399

104

53

169

850

145

4ndash48

510

U24

877

675

1085

212

5112

53

174

451

045

1ndash47

513

U24

477

143

410

883

113

109

54

200

119

21

454ndash48

516

U23

277

439

49

943

7510

25

525

013

51

145

4ndash48

014

U25

075

497

36

662

6570

45

115

801

145

4ndash48

36U

251

75

823

35

872

3245

37

8151

11

MC2

501ndash51

02L

248

75

98

1614

84

147

194

42

305

750

148

1ndash50

7BZ2

241

76

176

511

121

3114

128

64

217

930

154

6ndash57

39L

231

76

311

4445

912

167

550

243

849

211

11

546ndash57

616

L22

975

411

4143

912

175

552

254

800

195

01

540ndash57

73L

241

75

410

4344

012

159

522

233

834

233

51

519ndash56

14L

245

75

711

4041

612

181

492

213

737

234

01

530ndash56

213

L24

275

108

1036

350

1217

446

024

377

531

32

154

6ndash57

610

L24

776

200

830

285

10111

369

233

588

773

054

6ndash57

612

L28

176

765

36

492

3654

45

8735

20

561ndash58

71L

234

75

411

6441

213

161

533

253

834

235

11

NDWWTP

Pleistocene

Biscayn

eAqu

ifer

surface

N-EFF

263

65

505

22

201

616

13

3610

3849

Avo

nPark

Lim

estone

UFA

354ndash38

5N-FA-1U

225

78

173

868

215

573

41

8118

00

135

1ndash38

4N-FA-2U

227

78

133

765

212

166

41

126

179

22

354ndash37

9N-FA-3U

212

79

163

766

213

362

31

115

32

135

4ndash37

9N-FA-4U

208

79

163

769

214

766

41

131

174

11

APPZ

430ndash46

0N-FA-3L

194

75

215

937

423

1121

638

017

365

153

71

243

0ndash46

1N-FA-1L

199

74

231

736

458

1110

038

620

383

942

21

143

0ndash46

0N-FA-4L

192

74

264

937

421

1122

337

119

369

546

32

143

1-45

9N-FA-2L

201

74

295

839

431

1212

538

322

374

848

62

1

Hydrogeology Journal DOI 101007s10040-009-0570-8

time of this study Wells designated as ldquoFPLrdquo were testswells installed into the Floridan aquifer system sim10 kmsouth from the SDWWTP (Dames and Moore 1975Florida Partners 2006) For comparison to the presentstudy the data from these sites were assumed to representambient water-quality concentrations as no injectionactivities had occurred at these sites Wells in this studythat exhibited little variation in the time series data andhad low NH3 concentrations were compared to the datafrom these other sites Although direct comparisons weredifficult due to the varying aquifer open intervals fromwhich these samples were collected some generalizationscan be made NH3 or NH4

+ concentrations from thesewells were below 29micromol Clminus concentrations increasedwith depth of the sampled intervals and were similar inconcentrations to wells in this study of approximately thesame aquifer interval NO3

minus concentrations were below1micromol similar to data collected for this study Based oncomparisons with water quality from these other sites therevised time series water-quality data that had mean NH3

concentrations below 30micromol were assumed to be ambientaquifer water with no influence of injectate All the wellsin the UFA at the SDWWTP were considered ambient andmost of the wells in the MC2 at the SDWWTP wereconsidered ambient with the exception of 10L 11L and12L All of the wells in the APPZ at the SDWWTP hadNH3 concentrations above ambient levels with well 9U thelowest Time series data at the NDWWTP indicated that allof the wells open to the UFAwere considered ambient andthe data from wells open to the APPZ were ambient prior tothe observed increase in NH3 concentrations

Ambient Clminus concentrations from this study showedbrackish transitional and saline zones in the Floridan

aquifer system for the SDWWTP and NDWWTP asdefined by Reese (1994) Although there were only twosample depths at the NDWWTP the top of the saline zoneat the north appears to be higher than at the SDWWTPMean temperatures at the NDWWTP were cooler than atthe SDWWTP with an average of 23degC for both intervalsThe NDWWTP lies closer to the Florida Straits and thecooler temperatures at that site may be due to closerproximity to open seawater Wells that showed a higherconcentration of NH3 at the SDWWTP showed highertemperatures (example Well 12L) whereas at theNDWWTP no change in temperature was noted withincreasing NH3 concentrations

Based on results of this study introduced nitrogen fromthe injectate into the Floridan Aquifer is mostly in theform of NH4

+ This is consistent with eH-pH diagrams fornitrogen (Stumm and Morgan 1996) where in most naturalenvironments any ammoniandashN would have the form ofNH4

+ (Hem 1985) No relationship was observed in thehistorical data or data collected as part of this study betweenNH3 and NO3

minus No change from ambient NO3minus concen-

trations was observed for wells that had elevated NH3

concentrations The reduced form of nitrogen (NH4+) was

not oxidized once introduced in the anoxic aquifer at eithersite and was conserved in the aquifer in this reduced stateAny introduced oxidized form of nitrogen (NO3

minus) from theinjectate that was reduced would result in insignificantchanges in NH4

+ concentrations as NO3minus concentrations

are two to three orders of magnitude less than NH4+ The

elevated concentrations of NH4+ in the Floridan aquifer at

the two sites are interpreted as the result of the upwardmigration of the injectate Once introduced into the aquiferNH4

+ appeared to have behaved conservatively

Fig 7 Ternary diagrams for the NDWWTP and the SDWWTP NH4+ Clndash and Brndash data collected from 2006ndash2007 were normalized to

100 Seawater and freshwater values (Hem 1985) were plotted Ambient water was grouped at the SDWWTP for the MC2 and UFAintervals Ambient MC2 data plot directly with seawater UFA ambient plots towards freshwater reflecting the fresher water quality in theUFA The injectate data plot at the NH4

+ end point indicating the freshwater quality but high NH4+ concentration of the injectate Well data

from the APPZ and MC2 intervals that have NH4+ concentrations above ambient levels plot in a line towards the injectate end point with

data from wells 6U and 12L plotting very close the NH4+ end point Data from the SDWWTP plot into distinct groups based on depth in the

aquifer but no line towards the injectate end point is seen

Hydrogeology Journal DOI 101007s10040-009-0570-8

At least two pathways of injectate were distinguishedbased on the analysis of the natural tracers at theSDWWTP One pathway at the SDWWTP appeared tohave rapid vertical pathways from the Boulder Zone up tothe APPZ with little mixing of ambient waters as itmigrated upward These vertical conduits did not appear

to extend up to the UFA This pathway is identified atwells 6U and 14U in the APPZ and well 12L in the MC2It may be present at well 8U in the APPZ however thedevelopment of cross connection in well 8U compromiseddata interpretation NH4

+ concentrations in these wellswere within the range of injectate NH4

+ concentrations

Fig 8 Graphs on the left areNH3Cl

minus mixing end-membermodels for the APPZ andMC2 intervals at theSDWWTP 6U 12L and 10Lare well identification codesArrows indicate increase intime Hatched red rectangleis injected freshwaterend-member indicating theseasonal range in concentra-tions Cyan square is theAPPZ brackish waterambientwater end-member blue circleis the MC2 saline waterend-member Graphs on theright are NH3 concentrationsover time Solid black lines areconcentrations from each wellsite red line is injected fresh-water concentrations Forwells 6U and 12L the dataplot towards the injectateend-member Little influenceis seen in well 6U from thesaline MC2 end-memberWell 10L shows a differentevolution of water qualitywith data plotting at the salineMC2 end-member and slowlyplotting towards the lower endof the injectate end-member

Fig 9 Graph a is the NH3Clminus mixing end-member model for the APPZ at the NDWWTP for pre-purge data (prior to 2003) for well N-

1L Arrows indicate increase in time Hatched red rectangle is injected freshwater end-member indicating the seasonal range inconcentrations Cyan square is the UFA brackish water ambient water end-member blue circle is the APPZ saline water end-member Thedata plot in separate groupings with the earliest time series plotting around the APPZ saline end-member The second data cluster plottowards the injectate end-member but no evolution towards the injectate end-member is seen as was seen for wells 6U and 12L at theSDWWTP Graph b is the post-purge data plotted for well N-1L Data plot with time back towards the APPZ saline end-member

Hydrogeology Journal DOI 101007s10040-009-0570-8

Clminus concentrations in these wells were also very close toinjectate Clminus concentrations

The mixing models for these wells show a mixingpathway almost directly towards the injectate end-mem-ber with no mixing from the lower MC2 interval observedfor wells 6U and 14U Wells that showed the highestconcentrations of NH3 at the SDWWTP also showedhigher temperatures with the temperature signal of thewarmer injectate observed in well 12L (mean temperatureof 28degC) in the data collected in 2006ndash2007 Well 12L inthe MC2 is much closer to the Boulder Zone than theAPPZ wells and higher injectate temperatures persist intothe MC2 Perhaps due to the longer travel times to theAPPZ the temperature signal was muted but still visible inthe APPZ Ion data for these wells showed freshening ofthe water quality These wells showed a density-drivenbuoyant rapid vertical advective pathway and transport ofthe injectate as a distinct water body with little mixing ofnative waters as it migrated upwards The rapid pathwayscould be the result of construction related events such asdrifting boreholes or the result of structural anomaliessuch as fracturing and karst features that would verticallyconnect aquifers and provide high hydraulic conductivitytransport pathways through confining units Migration ofsaline waters from the Lower to Upper Floridan Aquiferas a result of such structural anomalies have been reportedfor northeastern and central Florida (Flocks et al 2001Spechler 2001) where the Floridan aquifer system liesmuch closer to the surface Upward fluid migration ofinjected fluids in a Palm Beach County Florida deep wellinjection facility had been detected above the confiningzone between the injection zone and the overlayingmonitoring zone and this had been attributed to fractureddolostone comprising the majority of the confining zonestrata (Maliva et al 2007) however no fracturing of theconfining strata at either the NDWWTP or the SDWWTP

has been reported McNeill suggested that as wells locatedon the northwest side of the SDWWTP were cased abovethe DCU in the LFA this would be a possible cause of thebuoyant upward migration of injected fluids through themore permeable units above the DCU through isolatedvertical flow paths bypassing the MC2 (McNeill 20002002)

The second pathway was suggested by the grouping ofwell data observed in wells 15U 16U BZ2 10L and 11LThe well data from this group had no significantcorrelation between NH3 and Clminus The mixing modelsfor these well data showed a slow evolution of waterquality towards the lower average of the injectate end-member with time These wells showed a slight temper-ature increase but no clear temperature signal wasdistinguished in these wells Ion data did not show afreshening of the water quality with little difference seenbetween ambient ion concentrations and concentrationsfrom these wells Other studies (Boumlhlke et al 2006) haveindicated that NH3 transport can be retarded by a factor of3ndash6 in an aquifer with NH3 persisting in an aquifer afterthe more mobile constituents were flushed out if theaquifer remained under suboxic conditions At theSDWWTP it appears that there was still NH3 loadinginto the aquifer via rapid vertical pathways with increas-ing NH3 concentrations over time The data from this wellgrouping may indicate that once NH3 was introduced intoan aquifer interval it traveled horizontally at a muchslower rate with the freshwater injectate substantiallydiluted and not flushed out as freshwater continued tomigrate upwards

Four discrete injectate plumes were delineated at theSDWWTP based on the transport pathways The firstplume (plume 1 in Fig 10) located on the northeast of thesite was associated with the BZ-4 well which provided apathway up into the APPZ until it was plugged This

Table 4 Historical ambient Floridan Aquifer water quality data

Parameter Unit 1Ua WWFb WWFb FPLPW-3c

FPL testwelld

9Ua FPL testwell d

2La 3La FPL testwelld

299ndash332 m

260ndash305 m

260ndash308 m

314ndash380 m

340ndash410 m 454ndash484 m

456ndash517 m 501ndash510 m

530ndash562 m

639ndash701 m

pH 79 80 74 75 77 77 75 75 75 70HCO3

- mmol 00 32 27 33 21 30 26Ca2+ mmol 13 17 37 43 67 78 103 196Mg2+ mmol 27 28 73 101 155 160 434 555Na+ mmol 247 222 746 983 1582 1482 4382 4872K+ mmol 08 08 20 26 38 36 118 97Cl- mmol 223 705 271 821 1043 1794 1939 5216 5923SO4

2- mmol 41 75 69 03 69 47 137 42 226 307NO3

- micromol 03 08 02 02 02 03 02 48 02F- mmol 01 01 01 01 01 01 02 01Si mmol 05 04 02 05 03 03 02Sr2+ micromol 419 776 982 1849 1472 1586Total P micromol 32 71 65 65 32NH4

+ micromol 55 72 610 111 55NH3 micromol 08 294 123

a Data were collected for this study during 2006ndash2007 for wells at the SDWWTPbData from CH2M Hill 1998cData from Florida Partners 2006dData from Dames and Moore 1975

Hydrogeology Journal DOI 101007s10040-009-0570-8

plume slowly migrated to the surrounding areas mainlyvia diffusion as evidenced by slowly increasing NH3

concentrations but no change in Clminus concentrations Thesecond plume was located on the northwest corner of thesite in the APPZ (plume 2) This plume was detected inthe APPZ with no detection of it in the lower MC2indicating a direct pathway to the APPZ bypassing theMC2 This pathway seemed to persist with concentrationsof NH3 increasing with time similar to concentrationlevels of the injectate This plume was a chemicallydistinct water body with little mixing of native watersThe third plume located at well 14U (plume 3) may be adistinct plume but it may also be in connection withplume 2 No monitoring wells of the same interval as well14U are in the vicinity so the extent of this plume couldnot be determined The fourth plume was located on thesouth side of the site in the MC2 (plume 4) All fourplumes appeared to have the same initial transportmechanism up from the Boulder Zone through highhydraulic conductivity pathways with data from plumes2 3 and 4 indicating these pathways still persist

The data collected from the NDWWTP indicate differ-ent transport mechanisms than the SDWWTP Thetemperature signal of the warmer injectate was notobserved in wells with elevated concentrations of NH4

+Water quality showed no evolution towards the injectateplot in the ternary diagram The mixing model showedtwo mixing patterns one towards the injectate end-member before purging and one towards the ambientend-member once purging ceased As observed in the timeseries NH3 data NH3 concentrations were first observedto increase in well N-1L the well that was within 30 m ofthe uncased injection well and concentrations peaked at

341micromol well below the mean NH3 concentration of theinjectate Unlike the increasing NH3 concentrationsobserved at the SDWWTP that are the result of rapidvertical migration pathways once NH3 concentrations atthe NDWWTP peaked they have since decreased withtime All four NDWWTP lower wells have shown verysimilar water quality since 2004 when purging ceased atthe NDWWTP Both the time series analysis and the datacollected as part of this study in 2006 and 2007 appear toindicate a one-time pulse of injectate water into the APPZand this pulse of injectate was still migrating at the timeof this study through the aquifer in the direction ofregional flow There is no geochemical evidence of acontinuing source of NH3 at the NDWWTP however dueto retardation as discussed previously the NH3 plume mayhave persisted a long time in the suboxic aquifer (Boumlhlkeet al 2006)

Conclusions

Chloride bromide and ammonia were used to understandthe pathways and transport mechanisms of injectedwastewater into the deep saline Boulder Zone in theFloridan aquifer system The injectate source was treatedfreshwater with elevated levels of ammonia The waterquality of the injectate was chemically and physicallydistinct from ambient Floridan aquifer system water andthese distinctions were used to determine the possibletransport pathways At the SDWWTP four injectateplumes were identified along with two pathway mecha-nisms density-driven buoyant vertical flow and slowerhorizontal flow At the NDWWTP one plume was

Fig 10 Location of injectate plumes and their depth interval at the SDWWTP The source of the plume centered on the BZ well clusters(plume 1) was plugged in 1995 Plumes 2 3 and 4 are the result of continuing rapid vertical pathways up from the Boulder Zone Theextent of the plumes off site is not known as indicated by the question marks however based on data collected from the site approximateextent of the plumes on the site can be inferred The plume in the MC2 is limited to the southeast of the site The plume located in thenorthwest of the site is located in the APPZ and appears to have bypassed the MC2 The plume from the BZ well cluster appears to belimited to the east of the site The extent of the plume at 14U on site is unknown as there are no wells that monitor the same aquifer intervalin the vicinity of 14U

Hydrogeology Journal DOI 101007s10040-009-0570-8

identified and appeared to be a result of a one-time pulseinjection At the SDWWTP the injectate may first havemigrated upwards through discrete vertical pathways fromthe Boulder Zone to the Middle Confining Unit with thefreshwater injectate migrating upwards through salinewater as a chemically distinct water body The fourplumes identified at the SDWWTP appear to haveoriginated via this pathway Once introduced in the higheraquifer intervals the transport mechanism appeared to bea horizontal flow with mixing of ambient waters Therapid vertical pathways did not appear to extend up to theUFA At the NDWWTP the elevated levels of NH3 inthe lower Middle Confining Unit appeared to be the resultof a construction incident where a pulse of injectate waterbackflowed into an uncased injection well providing apathway to the upper interval Once introduced into theupper aquifer interval the plume slowly migrated with theregional flow within the aquifer No evidence of rapidvertical pathways was observed at the NDWWTP Duringthe course of this study it became clear that purging of thewells had unintended consequences for the SDWWTPCross connections developed in several wells between theupper and lower monitoring zones either during or afterpurging and these cross connections have compromisedwater-quality data in SDWWTP wells 5 6 7 8 11 12and 15 Although it could not be determined from thisstudy these cross connections may provide pathways ofinjectate into layers in the aquifer that had not beenpreviously affected by upward migrating injectate

Acknowledgements This study was funded by the Miami-DadeWater and Sewer Department (MDWASD) The authors greatlyappreciate S Villamil for her invaluable technical expertise andassistance in the field We thank C Powell S Kronheim W Pittand B Goldenberg of MDWASD for their cooperation and Drs ADausman and C Langevin of the US Geological Survey for theirinsightful comments during this research This report was signifi-cantly improved by the thoughtful review of two anonymousreviewers Dr Pricersquos contribution was partially funded by theNational Science Foundation Grant No DBI-0620409 This isSERC contribution 457

References

Arthur JD JB Cowart AA Dabous (2001) Florida Aquifer Storageand Recovery Geochemical Study Year Three Progress ReportOpen File Report 83 Florida Geological Survey TallahasseeFL

BCampECH2M Hill (1977) Drilling and testing of the test-injectionwell for the Miami-Dade Water and Sewer Authority ContractS-153 BCampECH2M Hill Gainesville FL

Bloetscher F Muniz A (2006) Preliminary modeling of class Iinjection wells in southeast Florida Ground Water ProtectionCouncil 2006 Annual Meeting Proceedings Miami FLNovember 2006

Bloetscher F Englehardt JD Chin DA Rose JB Tchobanoglous GAmy VP Gokgoz S (2005) Comparative assessment ofmunicipal wastewater disposal methods in southeast FloridaWater Environ Res 77480ndash490

Boumlhlke JK E Shinn C Reich A Tihansky (2003) Origins andisotopic characteristics of dissolved nitrogen species in groundwater imported domestic water and wastewater in the FloridaKeys US Geological Survey Greater Everglades Science

Program 2002 biennial report US Geol Surv Open-File Rep03-54

Boumlhlke JK Smith RL DN Miller (2006) Ammolonium transportand reaction in contaminated groundwater application ofisotope tracers and isotope fractionation studies Water ResourRes 42 W05411 doi1010292005WR004349

CH2M Hill (1981) Drilling and testing of the 8 injection wells andthe 3 monitoring wells for the South District Regional Waste-water Treatment Plant of the Mimi-Dade Water and SewerAuthority CH2M Hill Englewood CO

CH2M Hill (1998) Engineering report of the construction andtesting of the aquifer storage and recovery (ASR) system at theMDWASD West Wellfield CH2M Hill Englewood CO

Clark JF Bryant Hudson G Lee Davisson M Woodside GHerndon R (2004) Geochemical imaging of flow near anartificial recharge facility Orange County California GroundWater 42167ndash174

Corbett DR Kump L Dillon K Burnett W Chanton J (2000) Fateof wastewater-borne nutrients under low discharge conditions inthe subsurface of the Florida Keys USA Mar Geochem 6999ndash115

Dames and Moore Inc (1975) Floridan aquifer water supplyinvestigation Turkey point Area Miami-Dade County FloridaFlorida Power and Light Miami

Davis SN Whittemore DO Fabryka-Martin J (1998) Uses ofchloridebromide ratios in studies of potable water GroundWater 36338ndash350

Englehardt JD Amy VP Bloetscher F Chinn DA Fleming LEGokgoz S Solo-Gabriele H Rose JB Tchoaboglous G (2001)Comparative assessment of human and ecological impacts formunicipal wastewater disposal methods in southeast Floridadeep wells ocean outfalls and canal discharges University ofMiami Coral Gables FL

Fish JE Stewart M (1991) Hydrogeology of the surficial aquifersystem Dade County Florida US Geol Surv Water ResourInvest Rep 90-4108 50 pp

Flocks JG Kindinger JL Davis JB Swarzenski P (2001) Geo-physical investigations of upward migrating saline water from thelower to upper Floridan Aquifer Central Indian River RegionFlorida In US Geological Survey Karst Interest Group Proceed-ings US Geol Surv Water Resour Invest Rep 01-4011 pp 135ndash140

Florida Lakes Power Partners and Florida Power and LightCompany (2006) Well completion report for Floridan Aquiferwells PW-1 PW-2 and PW-4 FPL Turkey Point ExpansionProject (Unit 5) Homestead FL

Haberfeld JL (1991) Hydrogeology of effluent disposal zonesFloridan aquifer south Florida Ground Water 29186ndash190

Hem JD (1985) Study and interpretation of the chemicalcharacteristics of natural water US Geol Surv Water SupplPap 2254

Herczeg AL WM Edmunds (2000) Inorganic ions as tracers InCook PG Herczeg AL (eds) Environmental tracers in subsur-face hydrology Kluwer Norwell MA pp 31ndash78

Kaehler CA K Belitz (2003) Tracing reclaimed water in MenifeeWinchester and Perris-South ground-water subbasins RiversideCounty California US Geol Surv Water Resour Invest Rep03-4039

Kohout FA (1965) A hypothesis concerning cyclic flow of saltwater related to geothermal heating in the Floridan aquiferTrans NY Acad Sci Ser II 28249ndash271

Langmuir D (1997) Aqueous environmental geochemistry Prentice-Hall Upper Saddle River NJ

Maliva RG CW Walker (1998) Hydrogeology of deep-welldisposal of liquid wastes in southwestern Florida USAHydrogeol J 6(4)538ndash548

Maliva RG Guo W Missimer T (2007) Vertical migration ofmunicipal wastewater in deep injection well systems SouthFlorida USA Hydrogeol J 15(7)1387ndash1396

McNeill DF (2000) Final report a review of upward migration ofeffluent related to subsurface injection at Miami-Dade Waterand Sewer South District Plant McNeill Miami FL

Hydrogeology Journal DOI 101007s10040-009-0570-8

MARK A QUARLES PG PAGE 2 RANGE OF TECHNICAL EXPERIENCE Oil and Gas Exploration and Production Wastes bull Aguida vs ChevronTexaco - Amazon Basin Ecuador

Provided technical support to the plaintiffs related to the first environmental class action lawsuit in South America Ecuadorian judgment resulted in a $10 billion damage against Chevron Work demonstrated that Texacorsquos work in the upper Amazonian jungle of Ecuador did not meet industry standards did not meet practices employed by Texaco from the 1920s through the 1990s and violated international and national water and soil quality standards

bull FECONACO ndash Amazon Basin Peru Provided independent third-party evaluation of crude oil remediation activities of 75 sites in

Block 1AB in the Amazonian jungle occupied by three indigenous groups The work included a) sampling of soil sediment and surface water contamination from present day and legacy operations b) an evaluation on the effectiveness of in-situ bioremediation as the chosen remedial alternative and c) a comparison of cleanup activities relative to Peruvian and US standards

bull Tulane Environmental Law Clinic ndash New Orleans Louisiana Reviewed a draft permit and provided written legal testimony associated with a Draft General

Permit for Discharges from Oil and Gas Exploration Development and Production Facilities The project consisted of comparing proposed effluent limitations to Federal standards comparing sampling parameters to expected exploration and production waste contaminants and recommending additional monitoring schemes that were more reflective of the risks

Coal Combustion Wastes bull Environmental Integrity Project Sierra Club and Earthjusticendash Washington DC

Reviewed historical coal-fired power plant file information and groundwater water monitoring reports for coal combustion waste (CCW) landfills and coal ash impoundments to identify previously undetermined damage cases according to EPA protocol Results were summarized in two co-authored reports Out of Control (February 2010) and In Harms Way (August 2010)

bull Sierra Club - Washington DC Reviewed historical groundwater monitoring reports associated with coal ash landfills and impoundments for 10 coal-fired power plants in Kentucky to identify impacts to groundwater relative to EPA damage case standards

bull Prairie Rivers Network - Champaign Illinois Evaluated Illinois standards for the disposal and beneficial re-use of coal of CCWs compared to national solid waste and surface impoundment disposal standards The project also included an in-depth analysis of material chemical and physical characteristics a summary of site characterization and siting standards and a summary of national damage assessment cases

bull Confidential Client ndash Kingston Tennessee Implemented a surface water monitoring program to determine the lateral extent of 54 million

cubic yards of CCWs that were released to the surface water from a surface impoundment failure at the Tennessee Valley Authority (TVA) Kingston coal-fired power plant

bull Kentucky Waterways Alliance ndash Henderson Kentucky Provided technical review of a draft wastewater discharge permit associated with the proposed

Cash Creek Integrated Gasification Combined Cycle (IGCC) plant and associated landfill At the time only two such plants were operational in the United States The review included a wastewater discharge compliance review of the other plants research into IGCC wastewater and solid waste constituents and a comparison to the proposed discharge criteria

bull Sierra Club ndash Bedford Kentucky Provided technical review of a draft wastewater discharge permit associated with the Trimble

County Generating Station pulverized coal (PC) power plant and flue gas de-sulfurization (FGD) process expansion Research was completed on the characteristics of FGD process and gypsum by-product wastes the leachability of solid wastes the characteristics of PC plant cooling water blowdown metal cleaning wastewater stormwater runoff and coal and limestone pile runoff

MARK A QUARLES PG PAGE 3

the structural integrity of an existing ash surface impoundment proposed for vertical expansion and the technical feasibility of a proposed gypsum disposal surface impoundment

Unconventional Natural Gas and Hydraulic Fracturing bull Shenandoah Valley Network Shenandoah Riverkeeper - Virginia Provided technical review of an application for the first proposed deep shale natural gas well in

Virginia The report evaluated among others the proposed plan for hydraulic fracturing storage of produced waters and flow back protection of groundwater supplies treatment and disposal of wastes and the location relative to the floodplain The applicant decided to rescind their application following submittal of the technical report critical of the proposed well action

bull Sierra Club Washington DC Provided technical comments regarding proposed Tennessee oil and gas regulations with a

particular emphasis on well casing standards fracture chemical disclosure and baseline post drilling monitoring for fracture chemicals and methane intrusion Compared the proposed regulations to API industry standards and other state regulations and provided recommendations for changes

Utility Line Environmental Assessments bull Private Landowner - Livingston Tennessee Served as lead consultant to prevent a proposed Corps of Engineer development Arguments

included identifying deficiencies in the aquatic resources alteration permit the cultural resources survey the stream use classification and the Section 404 application Negotiated alternate route

bull Private Landowner ndash Bowling Green Kentucky Served as lead consultant to provide technical comments to a Draft EA for the construction of a

220-mile electrical powerline Technical legal and financial reporting resulted in stopping the project in its entirety the Public Services Commission revoking the certificate of need (CON) and the Kentucky Attorney General conducting a formal investigation

bull Sumner Trousdale Opposing Pipeline ndash Gallatin Tennessee Served as lead consultant to identify deficiencies in the wetland and aquatic resources alteration

permits for a proposed 30-mile natural gas pipeline to represent the group in public hearings and develop technical arguments for against the proposed pipeline

Reservoir Water Quality and Use Assessments bull Friends of Tims Ford ndash Tims Ford Reservoir - Winchester Tennessee ndash served as lead consultant

to provide comments on Section 10 and Section 26A Regulation permit applications and a Recreational Boating Capacity Study for reservoir-wide community boat docks associated with residential development

bull Honeycomb Homeownerrsquos Association - Guntersville Lake ndash Guntersville Alabama ndash served as lead consultant to provide comments to Section 10 and Section 26A Regulation permit applications for residential developments Completed a detailed assessment of reservoir water quality results relative to designated use standards

bull Murrayrsquos Loch ndash Atlanta Georgia Served as consultant to evaluate the technical merits of a water withdrawal permit and the effects of increased urbanization on stormwater runoff and groundwater recharge Water withdrawal for commercial irrigation purposes resulted in decreased water levels in lakefront property of an adjacent residential neighborhood The permit was appealed to the State Administrative Court

Multi-Media Environmental Permitting bull Nashville Superspeedway USA Inc ndash Lebanon Tennessee

Served as Project Manager for a $125 million superspeedway development The environmental aspects included the requirements to determine the affects of the project on public and private groundwater users stream alterations wetlands endangered plant and animal species air permitting stormwater runoff oil pollution prevention underground injection control and due diligence property assessment

MARK A QUARLES PG PAGE 4 bull Metropolitan Knoxville Airport Authority ndash Knoxville Tennessee

Served as Project Manager for all environmental permitting and compliance activities Activities included spill prevention and response plan development stormwater plan development fuel tank farm design and compliance inspections

bull Various Industrial Clients ndash Tennessee Served as Project Manager for the development of SPCC Plans and SWPP Plans Plans were prepared consistent with the requirements of 40 CFR Part 112 the Tennessee General Permit the EPA Multi-Sector permit and the Tennessee Construction General Permit

Environmental Investigations and Remediation bull USEPA ndash Dickson County Tennessee

Served as Senior Geologist to investigate the occurrence of a cluster of cleft palate cleft lip birth defects in the county relative to the occurrence of trichloroethene in the groundwater and public water supply Reviewed EPA and TDEC regulatory files CDC and Department of Health reports interviewed City County TDEC and EPA officials and interpreted regional karst geologic and hydrogeologic data

bull Harpeth River Watershed Association ndash Franklin Tennessee Served as technical advisor for a review of the environmental investigation report and corrective action plan Contaminants of concern included free product toluene dissolved-phase BTEX constituents dissolved-phase acetone and dissolved-phase chlorinated solvents

bull Natural Resources Defense Council ndash Confidential Location Served as technical advisor for development of a Complaint for Declaratory and Injunctive Relief related to the inappropriate disposal investigation and cleanup of volatile organic compounds in soil groundwater and surface water

bull Confidential Client ndash McMinnville Tennessee Served as Project Manager to identify quantify and remediate the extent of a release of chlorinated solvents in a karst geologic setting Activities included the completion of an interim remedial action a soil gas survey direct push soil borings monitoring wells and well nests dye injection studies streambed sampling and a feasibility analysis

bull Burlington Northern Railroad - Birmingham Alabama Served as a Senior Geologist for an LNAPL investigation The investigation included the installation of temporary piezometers soil borings and permanent groundwater monitoring wells

bull Sunbeam Outdoor Products Inc - Neosho Missouri Developed a Field Sampling and Analysis Plan for the sampling of soils and drummed liquids for a Removal Action required by EPA Region VII Heavy metals and volatile organic compounds were the contaminants of concern in a karst geologic setting

bull United Technologies Automotive Inc - Quincy Michigan Served as Project Manager for groundwater well sampling and the development of an in-situ remedial action for heavy metal contamination

bull United Technologies Automotive Inc - Morganfield Kentucky Served as Project Engineer for a lagoon closure Completed activities for sludge characterization and quantification special waste permitting and closure design for material excavation and site restoration

Solid Waste Disposal bull Meriwether County Landfill Permit Appeal ndash Atlanta Georgia

Served as consultant to evaluate the technical merits of a municipal solid waste disposal permit that had been issued by the Georgia EPD Key technical issues were placement of the landfill adjacent to a public surface water supply typical liner performance and landfill leakage history in Georgia The permit was appealed to the Georgia Administrative Court

bull Various Secondary Aluminum Smelter Waste Landfills - Tennessee Reviewed secondary aluminum smelter waste characterization results landfill designs and associated hydrogeologic investigation reports for two proposed Class II industrial monofill landfill applications and reviewed groundwater monitoring reports associated with three co-mingled municipal solid waste landfills that used dross for intermediate daily cover

MARK A QUARLES PG PAGE 5 bull Various Industrial Landfills - Tennessee

Served as Project Manager for Subtitle D landfill siting and design projects Performed hydrogeologic investigations presented design waivers for site-specific design criteria (when applicable) and developed detailed designs for permitting

bull Various Landfills - Tennessee Served as Project Manager for the design permitting and operation of industrial and municipal solid waste landfills preparation of SWPP Plans quarterly groundwater and gas monitoring reports and hydrogeologic investigation reports

bull Various Municipal Landfills - Kentucky Served as Project Engineer for the design permitting and operation of municipal solid waste landfills

Stormwater Permitting and Compliance bull Tennessee Clean Water Network ndash Knoxville Tennessee

Served as lead consultant for providing technical comments for the draft Knox County Phase II Municipal Separate Storm Sewer System (MS4) permit

bull Various Industrial Clients - Throughout the US Served as Project Manager to obtain permit coverage through the EPA General Permit group permits and individual permits specific to each state Over 125 facilities were permitted

Hazardous Waste Management bull Various Industrial Clients ndash Throughout the US

Served as Project Manager for various projects to evaluate hazardous waste management practices consistent with the rules and regulations established under RCRA

bull Laidlaw Environmental Services Inc ndash Southeastern US Completed SWPP Plans for RCRA treatment storage and disposal facilities

Municipal Wastewater Management bull Various Municipalities ndash Fulton Cobb and Dekalb County Georgia

Served as Project Engineer for sewer modeling and point-source identification Identified sources of infiltration inflow and performed cost evaluations for source removal

bull Various Municipal and Industrial Clients ndash Tennessee Served as Project Engineer to establish beneficial reuse land application programs for wastewater sludge

bull Boston Water and Sewer Commission - Boston Massachusetts Served as Project Engineer for sewer modeling and point-source identification projects of combined and separate sewers up to 15 feet in diameter Identified sources of infiltration inflow and performed cost evaluations for source removal

bull Various Municipal Clients ndash Throughout the US Served as lead technical trainer for the implementation of proprietary software used for automated GIS mapping maintenance scheduling and hydraulic analyses of separate and combined sewers

bull City of Hopkinsville - Hopkinsville Kentucky Served as Project Engineer for water and sewer line expansions and wastewater treatment projects

TECHNICAL PUBLICATIONS AND LECTURES bull Quarles M and William Wilson ldquoUnconventional Natural Gas and its Risk A Tennessee

Perspectiverdquo Appalachian Public Interest Environmental Law Conference Knoxville Tennessee October 2011

bull Quarles M ldquoA Case Study in Karst Hydrogeology and Contaminant Fate and Transportrdquo National Groundwater Association 51st Annual Convention and Exposition December 1999

bull Quarles M and Allen P Lusby ldquoEnhanced Biodegradation of Kerosene-Affected Groundwater and Soilrdquo 1994 Annual Conference of the Academy of Hazardous Materials Managers October 1994

MARK A QUARLES PG PAGE 6 bull Quarles M ldquoNew Tank Performance Standardsrdquo Tennessee Environmental Law Letter July

1993 EXPERT LEGAL TESTIMONY bull Chesney versus Tennessee Valley Authority ndash 2011 US District Court Written testimony

associated with fly and bottom ash sampling waste characterization contaminant fate and transport and contaminant risks compared to US EPA screening levels drinking water standards fish and aquatic life standards and sediment cleanup standards

bull Busch et al versus Dr Carol Couch Atlanta Georgia 2008 State Administrative Court Written and verbal testimony regarding drought restrictive surface water and groundwater use Qualified by the court as an expert in geology hydrogeology and stormwater runoff

bull Darrel Segraves et al versus Dr Carol Couch Atlanta Georgia 2008 State Administrative Court Written and verbal testimony regarding appeal of a municipal solid waste landfill permit Qualified by the court as an expert in geology hydrogeology landfill design pertaining to landfill leakage and stormwater runoff

bull Tulane Environmental Law Clinic 2007 - 2008 Written testimony for numerous draft LDEQ permits and proposed rules

bull Republic of Ecuador and PetroEcuador vs Chevron Texaco Corporation and Texaco Petroleum Company US District Court Southern District of New York 2007 Written testimony regarding environmental investigation protocol

bull Friends of Tims Ford vs Tennessee Valley Authority and Tennessee Department of Environment and Conservation US District Court 2007 Written testimony in support of violations of State and Federal water quality standards reservoir carrying capacity standards and NEPA environmental assessment standards

bull Freddie Howell vs Creative Customs Atlanta Georgia 2007 Technical support regarding litigation associated with stormwater and groundwater flow and their effects on the Howell property

bull Aguida vs ChevronTexaco Lago Agrio Ecuador Court 2006 Written testimony regarding Texacorsquos waste management and standard operating practices in the Ecuadorian concession area relative to industry standards

TRAINING Current Wetland Issues in Tennessee (2007) Professional Liability Education - Contract Review and Revision (2000) Professional Liability Education ndash Mid-Town Developer Case Study Workshop (1999) Professional Liability Education ndash Liability IQ for Environmental Consultants (1998) Liquid Animal Waste Management System Design to NRCS Standards for CAFO (1998) 8-Hour OSHA Health and Safety Refresher Training Hazardous Materials Waste Manager Course University of Alabama (1993) 40-Hour OSHA Health and Safety Training (1990) CONTACT INFORMATION Home telephone 615-352-0471 Mobile telephone 615-504-0956 Email markquarlescomcastnet

Determination of vertical and horizontal pathways of injected freshwastewater into a deep saline aquifer (Florida USA) using naturalchemical tracers

Virginia Walsh amp Reneacute M Price

Abstract Two deep-well injection sites in south FloridaUSA inject an average of 430 million liters per day(MLD) of treated domestic fresh wastewater into a deepsaline aquifer 900m below land surface Elevated levels ofNH3 (highest concentration 939micromol) in the overlyingaquifer above ambient concentrations (concentration lessthan 30micromol) were evidence of the upward migration ofinjected fluids Three pathways were distinguished basedon ammonium chloride and bromide ratios and temper-ature At the South District Wastewater Treatment Plantthe tracer ratios showed that the injectate remainedchemically distinct as it migrated upwards through rapidvertical pathways via density-driven buoyancy Thewarmer injectate (mean 28degC) retained the temperaturesignal as it vertically migrated upwards however thetemperature signal did not persist as the injectate movedhorizontally into the overlying aquifers Once introducedthe injectate moved slowly horizontally through theaquifer and mixed with ambient water At the NorthDistrict Wastewater Treatment Plant data provide strongevidence of a one-time pulse of injectate into theoverlying aquifers due to improper well construction Noevidence of rapid vertical pathways was observed at theNorth District Wastewater Treatment Plant

Keywords Waste disposal Deep well injection Carbonate rocks Confining units Ammonia Temperature USA

Introduction

Deep well injection of treated municipal wastewater intonon-potable aquifers has been used as an alternative todischarge of wastewater to surface waters for manydecades There are 430 permitted municipal wastewaterdeep injection wells in the United States with 163 inFlorida alone (USEPA 2008) These deep aquifers tend tobe saline and the discharge of fresh wastewater into themhas raised concerns of geochemical reactions as a result ofthe mixing of the two waters as well as the buoyanttransport of the wastewater upwards into overlyingaquifers Confined brackish aquifers in Florida have beenused extensively for aquifer storage and recovery (ASR)of potable freshwater (Arthur et al 2001 Renken et al2005) and deeper saline aquifers have been used fordisposal of waste fluids such as oil brines industrial waterand municipal wastewater (Meyer 1989a Meyer 1989b)ASR in Florida has been extensively studied as part of theComprehensive Everglades Restoration Plan (Reese 2002Mirecki 2004 Mirecki 2006) however little research hasbeen published regarding the fate and transport of thetreated wastewater into deep saline aquifers (Meyer1989a Haberfeld 1991 Maliva and Walker 1998Bloetscher et al 2005 Bloetscher and Muniz 2006Maliva et al 2007)

Miami-Dade County Water and Sewer Department(MDWASD) located in southern Florida currently dis-charges 430 million liters per day (MLD) of treateddomestic wastewater into a saline deep aquifer at twolocations in the county Deep well injection has been inuse in Miami-Dade County since the late 1960s Theinjection facilities are located in the north and south of thecounty separated by 44 km (Fig 1) The South DistrictWastewater Treatment Plant (SDWWTP) site was placedinto service in 1983 and is currently permitted for thedisposal of 367 MLD of treated wastewater The NorthDistrict Wastewater Treatment Plant (NDWWTP) site wasplaced into service in 1997 and is permitted for 90 MLD

Received 2 February 2009 Accepted 14 December 2009

copy Springer-Verlag 2010

V Walsh ())Miami-Dade Water and Sewer Department3071 SW 38th Ave Miami FL 33146 USAe-mail walshvmiamidadegov

V WalshDepartment of Earth and EnvironmentFlorida International University11200 SW 8th Street University Park Miami 33199 USA

R M PriceDepartment of Earth and Environment and SoutheastEnvironmental Research CenterFlorida International University11200 SW 8th Street University Park Miami 33199 USA

Hydrogeology Journal DOI 101007s10040-009-0570-8

Both facilities treat domestic wastewater to above second-ary drinking water standards and discharge the treatedwastewater into United States Environmental ProtectionAgency (USEPA) Class I injection wells The treatedwastewater is injected into the Boulder Zone a highlytransmissive interval in the deep saline non-potable LowerFloridan Aquifer The Boulder Zone has been thought to behydrologically separated from overlying aquifers by a335-m-thick confining unit During the installation of addi-tional monitoring wells at the SDWWTP in 1994 ammonia-nitrogen (NH3-N) was detected at 442 m depth in theoverlying aquifer at a concentration of 411 micromoles perliter (micromol) above reported background levels of 29micromol

(BCampECH2M Hill 1977) The detection of NH3ndashN in theaquifers above the Boulder Zone has raised doubts regardingthe efficacy of the confining unit and the resultant waterquality impact to overlying aquifers as these aquifers areused as alternative water supplies via storage of freshwater(ASR) and blending with potable surficial aquifer water

Research has focused on ASR in south Florida (Arthuret al 2001 Reese 2002 Mirecki 2004 Mirecki 2006Reese and Richardson 2008) however few studies havebeen conducted regarding the transport and fate of injectedeffluent into the Boulder Zone and typically these had todo with the relative risk of deep well injection versusocean outfall disposal of municipal waste (Englehardt et

Fig 1 Location of theNDWWTP and the SDWWTPstudy sites

Hydrogeology Journal DOI 101007s10040-009-0570-8

al 2001 USEPA 2003 Bloetscher et al 2005 Bloetscherand Muniz 2006) Recently researchers have studied thetransport mechanisms of the observed migrated injectateand have suggested density-driven buoyant transportmechanism along natural or anthropogenic vertical frac-tures in the lower aquifers (Maliva and Walker 1998McNeill 2000 McNeill 2002 Maliva et al 2007 Walshand Price 2008) The objective of this study was todetermine migration pathways of injected treated waste-water at two facilities in Miami-Dade County Florida(SDWWTP and NDWWTP) using historical time seriesdata and major ion data collected as part of this study Themethodology developed for this study used chloride (Clminus)bromide (Brminus) and NH3 as tracers This methodologyprovided a method for estimating transport pathways andinvolved no additional collection of data other than whatwas typically required under federal and state regulatoryprograms

Natural inorganic tracers have been used extensively inwater resources investigations to trace groundwater flowpaths and calculate mixed water ratios (Langmuir 1997Davis et al 1998 Herczeg and Edmunds 2000) Clminus andBrminus commonly are used as they tend to be conservativeand their ratios may also give information as to the sourceand pathways of water Studies have been conducted insouth Florida (Shinn et al 1994 Paul et al 1997 Corbettet al 2000 Boumlhlke et al 2003) and elsewhere (Kaehlerand Belitz 2003 Clark et al 2004) tracing treatedwastewater in surficial aquifers but NH3 was not used asa tracer as it does not behave conservatively in oxicwaters In this study a novel application of Clminus Brminus andNH3 as conservative tracers of injectate was developed aspart of mixing models to distinguish pathways betweenthe deep aquifers Clminus is a natural anion in the Floridanaquifer system and its principal source is seawater asthere are no evaporite minerals to provide an additionalsource (Sprinkle 1989 Reese 1994) The seawater sourceof Clminus in south Florida is thought to be the result of eitherincomplete flushing of Pleistocene seawater and brackishwater intrusion andor the result of the cyclic flow basedon thermal upwelling of Holocene intruded seawater(Kohout 1965 Sprinkle 1989 Reese 1994) Bromide(Brminus) behaves similar to Clminus in groundwater systems(Davis et al 1998) and in south Florida the source of Brminus

in groundwater is similar to that of Clminus although its naturalabundances are orders of magnitude less than Clminus Theonly source of the NH3 is the injectate and therefore itwas used to trace transport pathways of the injectedwastewater

Geologic and hydrogeologic framework

The Floridan aquifer system (FAS) in southeastern Floridais defined by a vertically continuous sequence of per-meable carbonate rocks of Cenozoic age that are hydrauli-cally connected in varying degrees (Miller 1986) Theaquifer matrix consists of carbonate and dolomitic lime-stones dating from the Paleocene to the Oligocene

epochs Overlying the FAS are the impermeable sedimentsof the late Oligocene to Pliocene age Hawthorn Group a180-m-thick confining layer of clays siltstones and siltylimestones The Hawthorn Group separates the UpperFloridan Aquifer from the late Pliocene and Pleistoceneformations making up the Surficial Aquifer System whichincludes the Biscayne Aquifer in south Florida (Fig 2)The Biscayne Aquifer is an unconfined surficial aquiferand is the major source of potable water in south Florida(Fish and Stewart 1991)

The Floridan Aquifer contains several highly perme-able and less permeable zones with zones of highestpermeabilities typically occurring at or near unconform-ities and usually parallel to the bedding planes (Meyer1989a) Previous studies (Miller 1986 Reese 1994)grouped the Floridan aquifer system into three hydro-stratigraphic units (Fig 2) the Upper Floridan Aquifer(UFA) the Middle Confining Unit (MCU) and the LowerFloridan Aquifer Recently the MCU in south Florida hasbeen divided into the MC1 and MC2 (Fig 2) separatedby the Avon Park permeable layer (Reese and Richardson2008) which in south Florida had previously beenidentified as the Middle Floridan Aquifer The UpperFloridan Aquifer contains relatively fresh water less than10000 mg Lminus1 total dissolved solids (TDS) The LowerFloridan Aquifer consists of seminconfining or leakymicritic limestone and dolomite layers that containgroundwater with compositions approaching seawater(approximately 30000 mg Lminus1 TDS) A dolomite confin-ing unit (DCU) a thin confining unit below the MC2 wascharacterized at the study site by McNeill (McNeill 20002002) This DCU lies above the permeable zone com-monly known as the Boulder Zone within the OldsmarFormation of the Lower Floridan Aquifer The FASoutcrops along the Straits of Florida providing a hydraulicconnection to the sea (Kohout 1965 Miller 1986 Reese1994) Transmissivities in the Upper Florida Aquiferrange from 929 to 23times104m2 dayminus1 (Meyer 1989a Reese1994) while transmissivities in the Boulder Zone rangefrom 297times105m2 dayminus1 to 232times106m2 dayminus1

Site descriptionsThe NDWWTP and the SDWWTP consist of deepinjection wells that penetrate down to approximately855 m The upper 755 m of each well is cased to the topof the Boulder Zone The bottom 100 m of each injectionwell is an open hole in the Boulder Zone Nine suchinjection wells and three multi-zoned and dual-zonedmonitoring wells were constructed between 1977 and1981 at the SDWWTP (Fig 3) The multi-zone test wellBZ cluster (BZ-1 through 4) was constructed in 1977 andconsisted of four telescoping monitoring wells the deepestof which was BZ-4 cased to the top of the Boulder Zonethe shallowest BZ-1 open to the UFA at a depth of 312 mThe remaining monitoring wells were constructed bothat the SDWWTP and NDWWTP using a dual zone designwith an inner steel casing drilled to the deeper intervaland the outer steel casing open to the upper interval For

Hydrogeology Journal DOI 101007s10040-009-0570-8

this report well nomenclature indicates the open intervalof the dual-casing ldquoUrdquo represents the upper monitoringinterval and ldquoLrdquo represents the lower monitoring intervalWells 1 and 2 were dual-cased to monitor water quality inthe UFA (sim300 m) and the lower confining units (sim550 mCH2MHill 1981) In 1994 NH3 was detected aboveambient levels in the confining unit at the BZ well cluster(BZ-2 depth 488 m) and subsequent investigations by theutility found a leak due to corrosion of the casing in thiscluster (MDWASD 1995) The lower three monitoringintervals of the BZ well cluster were plugged in 1995 tostop the upward migration of injectate through the casinghole and the confining unit (488 m) monitoring intervalwas redrilled From 1995ndash1996 nine injection wells and

thirteen dual-zoned monitoring wells were constructed onthe SDWWTP These monitoring wells were cased to theAvon Park Permeable zone (APPZ) and the MC2 withopen holes in the formations approximately 30 m Duringthe construction of the monitoring wells NH3 concen-trations above ambient levels were found throughout thesite Elevated NH3 concentrations were found in thenorthwest corner of the site in the MC1 interval in severalwells but not in the lower MC2 interval of these wellsElevated levels were found in the MC2 interval in thesouth side of the site As a result of the detected NH3 inthe confining units the EPA required purging of the wellsthat showed elevated concentrations NH3 (Starr et al2001) in an attempt to remove the NH3 loading in the

Fig 2 Geologic and hydrogeologic framework of NDWWTP and the SDWWTP modified from Reese and Richardson 2008 Welldiagram on the right shows the number of wells open to the indicated hydrogeologic unit used for this study

Fig 3 Well locations at theSDWWTP

Hydrogeology Journal DOI 101007s10040-009-0570-8

impacted intervals Discontinuous purging of approxi-mately 2100 Lmin commenced from 1997 to 2000 forthe northwest wells (5U 6U 7U 8U 15U and 16U) of theAPPZ interval and the south wells (11L and 12L) of theMC2 (MDWASD 2000)

Injection well construction started at the NDWWTP in1996 Four injection wells were constructed into theBoulder Zone and four dual-zoned monitoring wells wereconstructed to the UFA and the APPZ intervals (Fig 4) In1996 effluent was injected in two completed injectionwells while one injection well was still under constructionresulting in injectate backflowing into an open borehole atan uncased injection well for 5 days Several months afterthe construction of the wells had been completed NH3

concentrations were observed to increase in the APPZinterval of the monitoring wells on site The utility wasrequired to purge the APPZ interval wells for a period of1 year from 2003ndash2004 (MDWASD 2005)

Methodology

Historical data were collected and checked for qualityassurance for the NDWWTP and SDWWTP Data wereavailable from 1983 through 2007 for the SDWWTP and1996ndash2007 for the NDWTP Data studied as part of thisresearch included pressure temperature pH Clminus sulfate(SO4

2minus) NH3 and nitrate (NO3minus) The historical data were

compiled from the utility monthly operating reportsavailable sporadically from 1983 Non-detects that hadbeen entered as a zero value were updated to the detectionlevel of the parameter Summary statistics including meanmedian standard deviation maximum and minimum wereapplied to each of the wellsrsquo time series data to assesswater-quality changes over time and used to compare toambient water quality data at other locations in southFlorida Most water quality for the Floridan Aquifer insouth Florida had been collected as regulatory require-ments which usually included chemical analyses that areused for drinking water quality and therefore did notinclude major ion data Residence time in the Floridan

aquifer system in south Florida is on the order of thousandsof years (Meyer 1989a) and it was assumed that due to thedepth of the aquifer water quality was in equilibrium andthere would be no other cause of perturbations to ambientwater quality other than migration of injectate Time seriesdata that showed large variation over time would indicatenon-equilibrium conditions and therefore not ambientconditions Abrupt changes in water quality and pressurewere observed in the time series data in wells that werepurged in 1997 These changes were not observed in wellsthat were not purged These changes in water quality andpressure were interpreted as being the result of crossconnections developed in the dual zone casings of some ofthe purged wells and review of borehole videos of thesewells taken in 2004 confirmed holes in the casings of thesewells It could not be determined which interval the datacollected from these wells represented after the crossconnections developed therefore data were discardedfrom the historical series analysis based on the month itwas ascertained the cross connection developed and thesummary statistics were recalculated for these wells

Floridan Aquifer water samples were collected at theNDWWTP and SDWWTP during 2006 and 2007 as partof this study for major ions and nitrogen species Thirty-two monitoring wells were sampled at the SDWWTP andwater-quality samples were collected from these wellsfrom the UFA the APPZ and the MC2 At theNDWWTP samples were collected from four monitoringwells representing the UFA and four wells in the APPZTemperature pH dissolved oxygen and conductancewere taken from water samples in the field using an YSI556 MPS The YSI instrument was calibrated per themanufacturerrsquos instructions prior to each sampling eventAll wells were purged for at least 24 h prior to sampling toensure at least three well volumes were evacuated Thewells were sampled through a closed system using a lowflow cell and tygon tubing through a disposable highcapacity 045micromol in-line filter Water samples wereanalyzed for the anions Brminus Clminus Fminus NO3

minus NO2minus and

SO42minus on a DIONEX ion chromatography system

HCO3minus and CO2

minus were analyzed via manual titrationNH3 was analyzed on a LACHAT analyzer 800 withNH4

+ then calculated based on pH and temperature ofthe sample using the NH3 result (Stumm and Morgan1996) Cations (Ca2+ Mg2+ K+ Na+ and Sr2+) wereanalyzed by inductively coupled plasma (ICP)

Results

The mean historical data are summarized in Table 1 forthe SDWWTP and Table 2 for the NDWWTP Dissolvedoxygen NO3

minus and NO2minus had similar results for both the

SDWWTP and NDWWTP sites for the aquifer intervalsNO3

minus concentrations were either detected at very lowconcentrations or below detectable levels NO2

minus levelswere below 1 micromoleL (micromol) for all aquifer intervalsand in the injectate at the NDWWTP and SDWWTP sitesfor the historical time series The injectate had a mean valueFig 4 Well locations at the NDWWTP

Hydrogeology Journal DOI 101007s10040-009-0570-8

Tab

le1

Meanvalues

forhistorical

timeseriesSDWWTP

mblsmetersbelow

land

surface

Geologicform

ation

Hyd

rostratig

raph

icform

ation

WellID

Open

interval

Periodof

record

Tem

pdegC

pHNH3micromol

Clndashmmol

SO42ndashmmol

NO3ndashmicromol

mbls

Pleistocene

Biscayn

eAqu

ifer

Injectate

(S-EFF)

Surface

591

ndash1207

277

66

889

203

109

Und

ifferentiated

Haw

thornAvo

nParkLim

estone

Upp

erFloridan

Aqu

ifer

(UFA

)1U

299ndash

332

983

ndash1207

240

79

1221

32

02

2U29

9ndash311

783

ndash1207

244

79

1321

32

03

3U29

9ndash32

0291

ndash1207

243

79

1023

32

03

BZ1

306ndash

316

783

ndash1207

242

76

1222

31

02

Avo

nPark

Lim

estone

Avo

nParkPermeable

Zon

e(A

PPZ)

13U

451ndash

475

296

ndash1207

239

77

6210

848

03

5U45

4ndash48

4594

ndash1102

241

76

492

108

49

03

6U45

4ndash48

3594

ndash1207

241

76

545

7630

03

7U45

4ndash48

2694

ndash198

245

74

526

738U

454ndash

480

894

ndash602

240

77

216

106

41

02

9U45

4ndash48

4195

ndash1207

239

77

64111

43

02

10U

454ndash

485

296

ndash1207

240

76

3510

542

02

11U

454ndash

484

296

ndash1207

240

76

118

106

43

02

14U

454ndash

480

296

ndash1207

239

74

320

9943

02

15U

454ndash

480

296

ndash1207

231

75

296

106

53

03

16U

454ndash

485

296

ndash1207

231

76

330

109

48

02

12U

456ndash

487

296

ndash204

249

76

100

111

42

02

MiddleCon

fining

Unit(M

C2)

BZ2

481ndash

507

783

ndash1207

254

75

106

133

56

02

2L50

1ndash51

0783

ndash1207

243

74

1219

926

02

4L51

9ndash56

112

91ndash

1207

240

73

1251

019

304

13L

530ndash

562

296

ndash1207

237

75

5550

822

809

3L54

0ndash57

7191

ndash1207

240

73

752

921

910

5L54

6ndash57

6594

ndash1102

239

74

652

821

604

6L54

6ndash57

6594

ndash1005

237

74

3052

622

703

7L55

0ndash57

1694

ndash198

242

71

1053

68L

546ndash

576

894

ndash602

237

74

554

124

804

9L54

6ndash57

3195

ndash1207

234

74

553

422

604

10L

546ndash

576

396

ndash1207

238

76

141

429

204

05

11L

546ndash

576

296

ndash1199

238

76

417

193

93

02

12L

546ndash

576

296

ndash1207

254

74

676

5730

03

15L

546ndash

576

296

ndash104

231

75

1253

125

204

16L

546ndash

576

296

ndash1207

229

74

653

221

904

1L56

1ndash58

7783

ndash1207

238

73

653

923

904

Oldsm

arFormation

Bou

lder

Zon

eLow

erFloridan

Aqu

ifer

BZ4

853

0783ndash894

249

72

634

3

Hydrogeology Journal DOI 101007s10040-009-0570-8

of NO3minus of 379micromol at the NDWWTP and 109micromol

at the SDWWTP for the historical time series Dissolvedoxygen was detected at concentrations less than 10 mg Lminus1

for all aquifer intervals Dissolved oxygen concentrationsfor the injectate at both the NDWWTP and the SDWWTPhad results above 3 mg Lminus1

Historical time series results SDWWTPThe historical period of record data for the freshwaterinjectate samples from the SDWWTP (identified as S-EFF) were available from 1991 through 2007 (Table 1)Temperature ranged from 218 to 311degC with a mean of277degC Mean pH in the historical time series was 66NH3 ranged from 1468ndash18496micromol with a mean of889micromol NH3 varied seasonally and increased with time(Fig 5) Clminus concentrations averaged 2 millimolesL(mmol) with a very small range and standard deviationindicative of the freshwater source of the injectateHistorical data from the SDWWTP for the UFA (wellsBZ1 1U 2U and 3U) were available from 1983 through2007 Temperature averaged 24degC with no significantdifference observed between the wells The range of pHwas from 76 to 82 in the UFA Chloride averagedbetween 21 and 23 mmol while NH3 means rangedbetween 10 and 13micromol The summary statistics for thewater-quality samples collected from the UFA showedconsistent values with no discernable variation over timeHistorical data from wells open to the APPZ at theSDWWTP (wells 5U 6U 7U 8U 9U 10U 11U 12U13U 14U 15U 16U) were available from 1994 through2007 Mean temperatures ranged between 231 and249degC in these wells There was little variation observedin the pH in the APPZ samples but the mean pH of 76was lower than the mean pH in the UFA Almost all of thewells showed variation in NH3 concentrations over timeMean values of NH3 in these wells ranged from 35micromolin well 10U to 545micromol in well 6U Well 6U showed anincreasing trend with time in NH3 that was observed to besimilar to the increasing trend of NH3 in the injectate(Fig 5) The spread between the 5th and 95th percentilewas the greatest in wells 6U and 12U Only wells 9U10U and 13U showed little variation in NH3 over timeMean concentrations of Cl- in wells 6U and 7U were 76and 73 mmol Wells in the MC2 were open to intervalsvarying in depth from 481 to 551 m Mean temperaturevalues ranged from 229 to 242degC in all wells with theexception of a mean value of 254degC in wells BZ2 and12L Mean pH values ranged from 73 to 76 Mean NH3

concentrations showed two groupings Wells BZ2 10L11L and 12L exhibited concentrations of 106 141 417and 676micromol respectively The remainder of the wellsexhibited mean NH3 concentrations of less than 55micromolClminus concentrations for wells 10L 11L and 12L were 429193 and 57 mmol respectively the remainder of the wellshad mean concentrations greater than 508 mmol (excep-tion is BZ-2 whose Clminus concentration of 133 mmolreflects the shallower depth of this well with the openinterval in the lower brackish water zone of the FloridanT

able

2Meanvalues

forhistorical

timeseriesNDWWTP

mblsmetersbelow

land

surface

Geologic

form

ation

Hyd

rostratig

raph

icform

ation

WellID

Open

interval

Period

ofrecord

Tem

ppH

NH3

Cl-

SO42-

NO3-

Revised

period

ofrecord

a

Tem

ppH

NH3

Cl-

SO42-

mbls

degCmicromol

mmol

mmol

micromol

degCmicromol

mmol

mmol

Pleistocene

Biscayn

eAqu

ifer

Injectate

(N-EFF)

Surface

797

ndash1207

284

65

8193

200

05

379

Avo

nPark

Lim

estone

Eocene

Upp

erFloridan

Aqu

ifer

(UFA

)N-1U

354ndash38

5197

ndash1207

231

76

188

737

35

02

N-2U

351ndash38

4396

ndash1207

230

78

177

662

36

21

N-3U

354ndash37

9396

ndash1207

229

78

173

658

36

20

N-4U

354ndash37

9496

ndash1207

231

76

181

684

35

08

Avo

nPark

Permeable

Zon

e(A

PPZ)

N-1L

430ndash46

1496

ndash1207

219

73

2612

3682

328

10

3496ndash797

224

72

193

4617

N-2L

431-

459

396

ndash1207

223

76

1684

3979

156

22

396

ndash898

229

78

177

4557

166

N-3L

430ndash46

0396

ndash1207

222

76

1314

4094

158

10

396

ndash1298

230

77

191

4548

149

N-4L

430ndash46

0496

ndash1207

224

72

1903

3804

152

16

496

ndash1298

223

75

237

4405

Hydrogeology Journal DOI 101007s10040-009-0570-8

Aquifer) Data collected from well 12L were similar todata collected for wells for 6U and 7U These wells hadhigh NH3 concentrations with low Clminus and SO4

minus concen-trations Historical data were available for the BoulderZone interval (well BZ4) from 1983 through 1994 Themean pH and temperature values were 72 and 249degCrespectively Mean NH3 concentration was 634micromol andshowed apparent seasonal variation and increasing trendover time and was similar to the injectate historical timeseries (Fig 5) The mean Clminus concentration was 3 mmolsimilar to the mean Clminus concentration of 2 mmol for theinjectate

Historical time series results NDWWTPThe historical period of record data for freshwaterinjectate samples (N-Eff) at the NDWWTP were availablefrom 2002 through 2007 Temperature ranged from 22 to34degC with a mean of 28degC The mean pH was similar tothe SDWWTP injecate at 65 NH3 ranged from 210ndash3764micromol with a mean of 819micromol and a large standarddeviation indicative of the apparent seasonality similar tothe SDWWTP Clminus concentrations ranged from 08 mmolto 1131 mmol with a mean 20 mmol slightly higher thanthe mean concentration of the SDWWTP injectateHistorical data were available from 1996 through 2007for wells open to the UFA (N-1U N-2U N-3U and N-4U) Mean temperature averaged 23degC in these wellswith no significant difference observed between the wellsMean values of pH ranged from 76 to 78 Clminus meanconcentrations ranged between 662 and 737 mmolsNH3 mean concentrations ranged between 17 to 18micromolConcentrations for the UFAwater-quality samples for theNDWWTP showed consistent values with no discernablevariation over time Historical data were available from1996 through 2007 for wells open to the APPZ (N-1L N-2L N-3L and N-4L) Temperature mean values were

22degC Analysis of historical NH3 data indicates increasingconcentrations of NH3 starting in late 1997 (Fig 6) NH3

concentrations appeared to have reached a peak concen-tration of 408micromol in well N-1L in July 2001 andsteadily declined thereafter to concentrations rangingfrom 200 to 250micromol Wells N-2L N-3L and N-4L showsimilar patterns as well N-1L but with lowered anddelayed peak concentration values NH3 concentrationsare observed to increase scatter after 2003 whichcorresponds to when purging commenced at theNDWWTP Once purging ceased in 2004 NH3 concen-trations in wells varied between 150ndash300micromol The Clminus

mean concentrations ranged from 368 to 409 mmol Clminus

in these wells exhibited variation over time and analysisof the time series indicated that as NH3 concentrationsincreased Clminus concentrations decreased (Fig 6) The timeseries data for the lower wells were revised to removedata after NH3 concentrations were observed to increasein each well in order to determine ambient concentrationsin the APPZ Revised NH3 mean concentrations rangedfrom 18ndash24micromol Clminus mean concentrations ranged from441ndash461 Very little variation was observed in NH3 andClminus mean concentrations after the time series data wereremoved

Major ion data collection resultsMajor ions were collected for this study from 2006ndash2007(Table 3) Data from wells at the SDWWTP site thatexhibited cross connections were removed from thisanalysis Data collected from the SDWWTP UFAexhibited very little variation between wells and weresimilar to the historical time-series data with low cationand anion concentrations For the APPZ wells NH4

+

mean concentrations could be combined into three groupswells 9U 10U and 13U with NH4

+ mean concentrationsof 60 67 and 143micromol respectively wells 14U and 16Uwith 497 and 439micromol and well 6U 823micromol Cation andanion mean concentrations showed a similar grouping asthe NH4

+ concentration grouping with well 6U consis-tently grouping independently and with increasing NH4

+

concentrations correlating to decreasing ion concentra-tions The MC2 mean NH4

+ concentrations could also becombined into three groups well 12L at a mean NH4

+

concentration of 765micromol wells BZ-2 10L and 13LNH4

+ at mean concentrations 176 200 and 108micromolrespectively the remainder wells at NH4

+ concentrationsbelow 10micromol Cation and anion concentrations could becombined in the same 3 groups as the NH4

+ groups withlower ion mean concentrations observed for BZ-2 10Land 13L and much lower ion concentrations observed inwell 12L As with well 6U in the MC1 well 12L in theMC2 consistently grouped independently

The NDWWTP wells open to the UFA (351ndash385 m)exhibited very little variation in field measurements andmean concentrations between wells and were similar tothe historical time series The interval (430ndash461 m) in theAPPZ at the NDWWTP also showed little variation withmean NH4

+ concentrations (215ndash295micromol) and mean

Fig 5 Time series NH3 data from the injectate (black circle) BZ-4(green triangle) and well 6U (red circle) at the SDWWTP site Theapparent seasonal variation observed in the injectate is a result ofincreased flows during the wet season and storm events Theincreasing trends with time correlate to increased injection over timedue to growth in population in Miami-Dade County

Hydrogeology Journal DOI 101007s10040-009-0570-8

concentrations of Clminus (371ndash386 mmol) varying littlebetween wells

Ternary diagramThe typical ClminusBrminus ratio for seawater is about 290 (Daviset al 1998) and most of the ClminusBrminus ratios at both siteswere within that range with no discernable differencesQuite often the addition of a third water-quality membercould enhance the understanding of the data and this wasthe case with using NH4

+ as the third end-member NH4+

Clminus and Brminus data were plotted on a ternary diagram withdata normalized to 100 Typical seawater and freshwaterNH4

+ Clminus and Brminus values after Hem (1985) were alsoplotted for comparison Water quality at the NDWWTPclustered into three distinct groups with two groups basedon depth of the interval sampled and the third the injectate(Fig 7) The ambient aquifer data plot close to seawaterThe injectate data plotted off in the lower left hand cornerdue to the large NH4

+ concentrations At the SDWWTPthree aquifer groupings were observed Ambient well datafrom the MC2 plotted similar to seawater Ambient welldata from the UFA plotted slightly towards freshwaterData from wells that showed elevated NH4

+ plotted in aline towards the injectate with groundwater data from 6Uand 12L plotting very close to the injectate This linerepresents the evolution of the water quality of these wellstowards the injectate water quality and does not show anyevolution of more saline water into the higher intervals inthe aquifer

Mixing end-member modelsEnd-member mixing models of wells 6U 12L and 10Lrepresented the results obtained for all wells at the

SDWWTP (Fig 8) Well 6U and 12L showed theprogressive freshening of water and increasing NH3

concentrations towards the injectate end-member(Fig 8) There was little mixing from the saline end-member towards the brackish end-member in well 6U andalmost all of the mixing was towards the injectate end-member Both 6U and 12L showed large changes inconcentrations from their original end-members over timeWell 10L showed a different pattern than 6U and 12Lwith gradual freshening of the saline water towards theinjectate end-member The mixing was towards the lowerrange of the injectate end-member and there were no largechanges in concentrations of either NH3 or Clminus from thesaline end-member Well N-1L at the NDWWTP end-member mixing model showed a different pattern than theSDWWTP (Fig 9) Clustering of the NH3Cl

minus ratios weredistinguished based on time The NH3Cl

minus ambient ratio canclearly be seen on Fig 9 and lies along the saline end-member As the concentrations of NH3 increased in time tothe peak concentration the NH3Cl

minus ratios showed twodistinct clusters Initially the NH3Cl

minus ratio showed gradualincreasing in NH3 with little change in Clminus from ambientconcentrations There was a rapid change in the NH3Cl

minus

ratio as NH3 reached the peak concentrations Once the peakwas reached the NH3Cl

minus ratios slowly declined in time

Discussion

The Floridan aquifer system was sampled by others atdifferent sites in south Florida and these data aresummarized in Table 4 Wells identified as WWF weremonitoring wells installed as part of the MDWASD ASRsystem west of the NDWWTP and SDWWTP (CH2MHill 1998) The ASR systems were not in use during the

Fig 6 Graph a shows the NH3 data time series for the wells in the APPZ interval at the NDWWTP The dashed lines indicate the purgingtime from 2003 through 2004 NH3 concentrations are observed to increase in well N-1L similar to contaminant breakthrough curves WellN-1L was the closest well to the uncased injection well when injectate backflowed into the APPZ NH3 concentrations for wells N-2LN-3L and N-4L appear to be similar and show a similar increase after 1999 Variability is seen in the data after 2003 Graph b showsClminus concentrations in well N-1L clustered at approximately 300 mmol and an abrupt decrease to less than 300 mmol is seen Clminus

concentrations in wells N-2L N-3L and N-4L are very similar and show a decrease in concentrations after 1999 until 2000 whenconcentrations appear to stabilize Clminus concentrations start to increase slightly and become variable after 2003 All four wells showsimilar concentrations of both NH3 and Cl- after 2004

Hydrogeology Journal DOI 101007s10040-009-0570-8

Tab

le3

Meanfieldparametersandionconcentrations

during

the20

06ndash2

007samplingcompleted

aspartof

thisstud

ymblsmetersbelow

land

surface

Geologic

form

ation

Hyd

rogeolog

icun

itOpen

interval

Well

Temp

pHNH4+

Ca2

+Mg2

+Na+

K+

Sr2+

Cl-

SO42-

HCO3-

Br-

F-

NO3-

NO2-

mbls

IDdegC

micromol

mmol

mmol

mmol

mmol

micromol

mmol

mmol

mmol

micromol

micromol

micromol

micromol

SDWWTP

Pleistocene

Biscayn

eAqu

ifer

Surface

S-EFF

290

67

112

51

03

07

30

430

197

6

Und

ifferentiated

Haw

thornOcala

Lim

estone

toAvo

nPark

Lim

estone

UFA

306ndash31

6BZ1

242

78

61

325

139

213

440

109

11

299ndash33

21U

236

81

61

324

142

224

456

117

01

299ndash32

03U

243

79

61

325

148

284

454

119

41

299ndash311

2U25

379

101

322

143

215

433

143

11

Avo

nPark

Lim

estone

APPZ

454ndash48

49U

238

77

604

1098

399

104

53

169

850

145

4ndash48

510

U24

877

675

1085

212

5112

53

174

451

045

1ndash47

513

U24

477

143

410

883

113

109

54

200

119

21

454ndash48

516

U23

277

439

49

943

7510

25

525

013

51

145

4ndash48

014

U25

075

497

36

662

6570

45

115

801

145

4ndash48

36U

251

75

823

35

872

3245

37

8151

11

MC2

501ndash51

02L

248

75

98

1614

84

147

194

42

305

750

148

1ndash50

7BZ2

241

76

176

511

121

3114

128

64

217

930

154

6ndash57

39L

231

76

311

4445

912

167

550

243

849

211

11

546ndash57

616

L22

975

411

4143

912

175

552

254

800

195

01

540ndash57

73L

241

75

410

4344

012

159

522

233

834

233

51

519ndash56

14L

245

75

711

4041

612

181

492

213

737

234

01

530ndash56

213

L24

275

108

1036

350

1217

446

024

377

531

32

154

6ndash57

610

L24

776

200

830

285

10111

369

233

588

773

054

6ndash57

612

L28

176

765

36

492

3654

45

8735

20

561ndash58

71L

234

75

411

6441

213

161

533

253

834

235

11

NDWWTP

Pleistocene

Biscayn

eAqu

ifer

surface

N-EFF

263

65

505

22

201

616

13

3610

3849

Avo

nPark

Lim

estone

UFA

354ndash38

5N-FA-1U

225

78

173

868

215

573

41

8118

00

135

1ndash38

4N-FA-2U

227

78

133

765

212

166

41

126

179

22

354ndash37

9N-FA-3U

212

79

163

766

213

362

31

115

32

135

4ndash37

9N-FA-4U

208

79

163

769

214

766

41

131

174

11

APPZ

430ndash46

0N-FA-3L

194

75

215

937

423

1121

638

017

365

153

71

243

0ndash46

1N-FA-1L

199

74

231

736

458

1110

038

620

383

942

21

143

0ndash46

0N-FA-4L

192

74

264

937

421

1122

337

119

369

546

32

143

1-45

9N-FA-2L

201

74

295

839

431

1212

538

322

374

848

62

1

Hydrogeology Journal DOI 101007s10040-009-0570-8

time of this study Wells designated as ldquoFPLrdquo were testswells installed into the Floridan aquifer system sim10 kmsouth from the SDWWTP (Dames and Moore 1975Florida Partners 2006) For comparison to the presentstudy the data from these sites were assumed to representambient water-quality concentrations as no injectionactivities had occurred at these sites Wells in this studythat exhibited little variation in the time series data andhad low NH3 concentrations were compared to the datafrom these other sites Although direct comparisons weredifficult due to the varying aquifer open intervals fromwhich these samples were collected some generalizationscan be made NH3 or NH4

+ concentrations from thesewells were below 29micromol Clminus concentrations increasedwith depth of the sampled intervals and were similar inconcentrations to wells in this study of approximately thesame aquifer interval NO3

minus concentrations were below1micromol similar to data collected for this study Based oncomparisons with water quality from these other sites therevised time series water-quality data that had mean NH3

concentrations below 30micromol were assumed to be ambientaquifer water with no influence of injectate All the wellsin the UFA at the SDWWTP were considered ambient andmost of the wells in the MC2 at the SDWWTP wereconsidered ambient with the exception of 10L 11L and12L All of the wells in the APPZ at the SDWWTP hadNH3 concentrations above ambient levels with well 9U thelowest Time series data at the NDWWTP indicated that allof the wells open to the UFAwere considered ambient andthe data from wells open to the APPZ were ambient prior tothe observed increase in NH3 concentrations

Ambient Clminus concentrations from this study showedbrackish transitional and saline zones in the Floridan

aquifer system for the SDWWTP and NDWWTP asdefined by Reese (1994) Although there were only twosample depths at the NDWWTP the top of the saline zoneat the north appears to be higher than at the SDWWTPMean temperatures at the NDWWTP were cooler than atthe SDWWTP with an average of 23degC for both intervalsThe NDWWTP lies closer to the Florida Straits and thecooler temperatures at that site may be due to closerproximity to open seawater Wells that showed a higherconcentration of NH3 at the SDWWTP showed highertemperatures (example Well 12L) whereas at theNDWWTP no change in temperature was noted withincreasing NH3 concentrations

Based on results of this study introduced nitrogen fromthe injectate into the Floridan Aquifer is mostly in theform of NH4

+ This is consistent with eH-pH diagrams fornitrogen (Stumm and Morgan 1996) where in most naturalenvironments any ammoniandashN would have the form ofNH4

+ (Hem 1985) No relationship was observed in thehistorical data or data collected as part of this study betweenNH3 and NO3

minus No change from ambient NO3minus concen-

trations was observed for wells that had elevated NH3

concentrations The reduced form of nitrogen (NH4+) was

not oxidized once introduced in the anoxic aquifer at eithersite and was conserved in the aquifer in this reduced stateAny introduced oxidized form of nitrogen (NO3

minus) from theinjectate that was reduced would result in insignificantchanges in NH4

+ concentrations as NO3minus concentrations

are two to three orders of magnitude less than NH4+ The

elevated concentrations of NH4+ in the Floridan aquifer at

the two sites are interpreted as the result of the upwardmigration of the injectate Once introduced into the aquiferNH4

+ appeared to have behaved conservatively

Fig 7 Ternary diagrams for the NDWWTP and the SDWWTP NH4+ Clndash and Brndash data collected from 2006ndash2007 were normalized to

100 Seawater and freshwater values (Hem 1985) were plotted Ambient water was grouped at the SDWWTP for the MC2 and UFAintervals Ambient MC2 data plot directly with seawater UFA ambient plots towards freshwater reflecting the fresher water quality in theUFA The injectate data plot at the NH4

+ end point indicating the freshwater quality but high NH4+ concentration of the injectate Well data

from the APPZ and MC2 intervals that have NH4+ concentrations above ambient levels plot in a line towards the injectate end point with

data from wells 6U and 12L plotting very close the NH4+ end point Data from the SDWWTP plot into distinct groups based on depth in the

aquifer but no line towards the injectate end point is seen

Hydrogeology Journal DOI 101007s10040-009-0570-8

At least two pathways of injectate were distinguishedbased on the analysis of the natural tracers at theSDWWTP One pathway at the SDWWTP appeared tohave rapid vertical pathways from the Boulder Zone up tothe APPZ with little mixing of ambient waters as itmigrated upward These vertical conduits did not appear

to extend up to the UFA This pathway is identified atwells 6U and 14U in the APPZ and well 12L in the MC2It may be present at well 8U in the APPZ however thedevelopment of cross connection in well 8U compromiseddata interpretation NH4

+ concentrations in these wellswere within the range of injectate NH4

+ concentrations

Fig 8 Graphs on the left areNH3Cl

minus mixing end-membermodels for the APPZ andMC2 intervals at theSDWWTP 6U 12L and 10Lare well identification codesArrows indicate increase intime Hatched red rectangleis injected freshwaterend-member indicating theseasonal range in concentra-tions Cyan square is theAPPZ brackish waterambientwater end-member blue circleis the MC2 saline waterend-member Graphs on theright are NH3 concentrationsover time Solid black lines areconcentrations from each wellsite red line is injected fresh-water concentrations Forwells 6U and 12L the dataplot towards the injectateend-member Little influenceis seen in well 6U from thesaline MC2 end-memberWell 10L shows a differentevolution of water qualitywith data plotting at the salineMC2 end-member and slowlyplotting towards the lower endof the injectate end-member

Fig 9 Graph a is the NH3Clminus mixing end-member model for the APPZ at the NDWWTP for pre-purge data (prior to 2003) for well N-

1L Arrows indicate increase in time Hatched red rectangle is injected freshwater end-member indicating the seasonal range inconcentrations Cyan square is the UFA brackish water ambient water end-member blue circle is the APPZ saline water end-member Thedata plot in separate groupings with the earliest time series plotting around the APPZ saline end-member The second data cluster plottowards the injectate end-member but no evolution towards the injectate end-member is seen as was seen for wells 6U and 12L at theSDWWTP Graph b is the post-purge data plotted for well N-1L Data plot with time back towards the APPZ saline end-member

Hydrogeology Journal DOI 101007s10040-009-0570-8

Clminus concentrations in these wells were also very close toinjectate Clminus concentrations

The mixing models for these wells show a mixingpathway almost directly towards the injectate end-mem-ber with no mixing from the lower MC2 interval observedfor wells 6U and 14U Wells that showed the highestconcentrations of NH3 at the SDWWTP also showedhigher temperatures with the temperature signal of thewarmer injectate observed in well 12L (mean temperatureof 28degC) in the data collected in 2006ndash2007 Well 12L inthe MC2 is much closer to the Boulder Zone than theAPPZ wells and higher injectate temperatures persist intothe MC2 Perhaps due to the longer travel times to theAPPZ the temperature signal was muted but still visible inthe APPZ Ion data for these wells showed freshening ofthe water quality These wells showed a density-drivenbuoyant rapid vertical advective pathway and transport ofthe injectate as a distinct water body with little mixing ofnative waters as it migrated upwards The rapid pathwayscould be the result of construction related events such asdrifting boreholes or the result of structural anomaliessuch as fracturing and karst features that would verticallyconnect aquifers and provide high hydraulic conductivitytransport pathways through confining units Migration ofsaline waters from the Lower to Upper Floridan Aquiferas a result of such structural anomalies have been reportedfor northeastern and central Florida (Flocks et al 2001Spechler 2001) where the Floridan aquifer system liesmuch closer to the surface Upward fluid migration ofinjected fluids in a Palm Beach County Florida deep wellinjection facility had been detected above the confiningzone between the injection zone and the overlayingmonitoring zone and this had been attributed to fractureddolostone comprising the majority of the confining zonestrata (Maliva et al 2007) however no fracturing of theconfining strata at either the NDWWTP or the SDWWTP

has been reported McNeill suggested that as wells locatedon the northwest side of the SDWWTP were cased abovethe DCU in the LFA this would be a possible cause of thebuoyant upward migration of injected fluids through themore permeable units above the DCU through isolatedvertical flow paths bypassing the MC2 (McNeill 20002002)

The second pathway was suggested by the grouping ofwell data observed in wells 15U 16U BZ2 10L and 11LThe well data from this group had no significantcorrelation between NH3 and Clminus The mixing modelsfor these well data showed a slow evolution of waterquality towards the lower average of the injectate end-member with time These wells showed a slight temper-ature increase but no clear temperature signal wasdistinguished in these wells Ion data did not show afreshening of the water quality with little difference seenbetween ambient ion concentrations and concentrationsfrom these wells Other studies (Boumlhlke et al 2006) haveindicated that NH3 transport can be retarded by a factor of3ndash6 in an aquifer with NH3 persisting in an aquifer afterthe more mobile constituents were flushed out if theaquifer remained under suboxic conditions At theSDWWTP it appears that there was still NH3 loadinginto the aquifer via rapid vertical pathways with increas-ing NH3 concentrations over time The data from this wellgrouping may indicate that once NH3 was introduced intoan aquifer interval it traveled horizontally at a muchslower rate with the freshwater injectate substantiallydiluted and not flushed out as freshwater continued tomigrate upwards

Four discrete injectate plumes were delineated at theSDWWTP based on the transport pathways The firstplume (plume 1 in Fig 10) located on the northeast of thesite was associated with the BZ-4 well which provided apathway up into the APPZ until it was plugged This

Table 4 Historical ambient Floridan Aquifer water quality data

Parameter Unit 1Ua WWFb WWFb FPLPW-3c

FPL testwelld

9Ua FPL testwell d

2La 3La FPL testwelld

299ndash332 m

260ndash305 m

260ndash308 m

314ndash380 m

340ndash410 m 454ndash484 m

456ndash517 m 501ndash510 m

530ndash562 m

639ndash701 m

pH 79 80 74 75 77 77 75 75 75 70HCO3

- mmol 00 32 27 33 21 30 26Ca2+ mmol 13 17 37 43 67 78 103 196Mg2+ mmol 27 28 73 101 155 160 434 555Na+ mmol 247 222 746 983 1582 1482 4382 4872K+ mmol 08 08 20 26 38 36 118 97Cl- mmol 223 705 271 821 1043 1794 1939 5216 5923SO4

2- mmol 41 75 69 03 69 47 137 42 226 307NO3

- micromol 03 08 02 02 02 03 02 48 02F- mmol 01 01 01 01 01 01 02 01Si mmol 05 04 02 05 03 03 02Sr2+ micromol 419 776 982 1849 1472 1586Total P micromol 32 71 65 65 32NH4

+ micromol 55 72 610 111 55NH3 micromol 08 294 123

a Data were collected for this study during 2006ndash2007 for wells at the SDWWTPbData from CH2M Hill 1998cData from Florida Partners 2006dData from Dames and Moore 1975

Hydrogeology Journal DOI 101007s10040-009-0570-8

plume slowly migrated to the surrounding areas mainlyvia diffusion as evidenced by slowly increasing NH3

concentrations but no change in Clminus concentrations Thesecond plume was located on the northwest corner of thesite in the APPZ (plume 2) This plume was detected inthe APPZ with no detection of it in the lower MC2indicating a direct pathway to the APPZ bypassing theMC2 This pathway seemed to persist with concentrationsof NH3 increasing with time similar to concentrationlevels of the injectate This plume was a chemicallydistinct water body with little mixing of native watersThe third plume located at well 14U (plume 3) may be adistinct plume but it may also be in connection withplume 2 No monitoring wells of the same interval as well14U are in the vicinity so the extent of this plume couldnot be determined The fourth plume was located on thesouth side of the site in the MC2 (plume 4) All fourplumes appeared to have the same initial transportmechanism up from the Boulder Zone through highhydraulic conductivity pathways with data from plumes2 3 and 4 indicating these pathways still persist

The data collected from the NDWWTP indicate differ-ent transport mechanisms than the SDWWTP Thetemperature signal of the warmer injectate was notobserved in wells with elevated concentrations of NH4

+Water quality showed no evolution towards the injectateplot in the ternary diagram The mixing model showedtwo mixing patterns one towards the injectate end-member before purging and one towards the ambientend-member once purging ceased As observed in the timeseries NH3 data NH3 concentrations were first observedto increase in well N-1L the well that was within 30 m ofthe uncased injection well and concentrations peaked at

341micromol well below the mean NH3 concentration of theinjectate Unlike the increasing NH3 concentrationsobserved at the SDWWTP that are the result of rapidvertical migration pathways once NH3 concentrations atthe NDWWTP peaked they have since decreased withtime All four NDWWTP lower wells have shown verysimilar water quality since 2004 when purging ceased atthe NDWWTP Both the time series analysis and the datacollected as part of this study in 2006 and 2007 appear toindicate a one-time pulse of injectate water into the APPZand this pulse of injectate was still migrating at the timeof this study through the aquifer in the direction ofregional flow There is no geochemical evidence of acontinuing source of NH3 at the NDWWTP however dueto retardation as discussed previously the NH3 plume mayhave persisted a long time in the suboxic aquifer (Boumlhlkeet al 2006)

Conclusions

Chloride bromide and ammonia were used to understandthe pathways and transport mechanisms of injectedwastewater into the deep saline Boulder Zone in theFloridan aquifer system The injectate source was treatedfreshwater with elevated levels of ammonia The waterquality of the injectate was chemically and physicallydistinct from ambient Floridan aquifer system water andthese distinctions were used to determine the possibletransport pathways At the SDWWTP four injectateplumes were identified along with two pathway mecha-nisms density-driven buoyant vertical flow and slowerhorizontal flow At the NDWWTP one plume was

Fig 10 Location of injectate plumes and their depth interval at the SDWWTP The source of the plume centered on the BZ well clusters(plume 1) was plugged in 1995 Plumes 2 3 and 4 are the result of continuing rapid vertical pathways up from the Boulder Zone Theextent of the plumes off site is not known as indicated by the question marks however based on data collected from the site approximateextent of the plumes on the site can be inferred The plume in the MC2 is limited to the southeast of the site The plume located in thenorthwest of the site is located in the APPZ and appears to have bypassed the MC2 The plume from the BZ well cluster appears to belimited to the east of the site The extent of the plume at 14U on site is unknown as there are no wells that monitor the same aquifer intervalin the vicinity of 14U

Hydrogeology Journal DOI 101007s10040-009-0570-8

identified and appeared to be a result of a one-time pulseinjection At the SDWWTP the injectate may first havemigrated upwards through discrete vertical pathways fromthe Boulder Zone to the Middle Confining Unit with thefreshwater injectate migrating upwards through salinewater as a chemically distinct water body The fourplumes identified at the SDWWTP appear to haveoriginated via this pathway Once introduced in the higheraquifer intervals the transport mechanism appeared to bea horizontal flow with mixing of ambient waters Therapid vertical pathways did not appear to extend up to theUFA At the NDWWTP the elevated levels of NH3 inthe lower Middle Confining Unit appeared to be the resultof a construction incident where a pulse of injectate waterbackflowed into an uncased injection well providing apathway to the upper interval Once introduced into theupper aquifer interval the plume slowly migrated with theregional flow within the aquifer No evidence of rapidvertical pathways was observed at the NDWWTP Duringthe course of this study it became clear that purging of thewells had unintended consequences for the SDWWTPCross connections developed in several wells between theupper and lower monitoring zones either during or afterpurging and these cross connections have compromisedwater-quality data in SDWWTP wells 5 6 7 8 11 12and 15 Although it could not be determined from thisstudy these cross connections may provide pathways ofinjectate into layers in the aquifer that had not beenpreviously affected by upward migrating injectate

Acknowledgements This study was funded by the Miami-DadeWater and Sewer Department (MDWASD) The authors greatlyappreciate S Villamil for her invaluable technical expertise andassistance in the field We thank C Powell S Kronheim W Pittand B Goldenberg of MDWASD for their cooperation and Drs ADausman and C Langevin of the US Geological Survey for theirinsightful comments during this research This report was signifi-cantly improved by the thoughtful review of two anonymousreviewers Dr Pricersquos contribution was partially funded by theNational Science Foundation Grant No DBI-0620409 This isSERC contribution 457

References

Arthur JD JB Cowart AA Dabous (2001) Florida Aquifer Storageand Recovery Geochemical Study Year Three Progress ReportOpen File Report 83 Florida Geological Survey TallahasseeFL

BCampECH2M Hill (1977) Drilling and testing of the test-injectionwell for the Miami-Dade Water and Sewer Authority ContractS-153 BCampECH2M Hill Gainesville FL

Bloetscher F Muniz A (2006) Preliminary modeling of class Iinjection wells in southeast Florida Ground Water ProtectionCouncil 2006 Annual Meeting Proceedings Miami FLNovember 2006

Bloetscher F Englehardt JD Chin DA Rose JB Tchobanoglous GAmy VP Gokgoz S (2005) Comparative assessment ofmunicipal wastewater disposal methods in southeast FloridaWater Environ Res 77480ndash490

Boumlhlke JK E Shinn C Reich A Tihansky (2003) Origins andisotopic characteristics of dissolved nitrogen species in groundwater imported domestic water and wastewater in the FloridaKeys US Geological Survey Greater Everglades Science

Program 2002 biennial report US Geol Surv Open-File Rep03-54

Boumlhlke JK Smith RL DN Miller (2006) Ammolonium transportand reaction in contaminated groundwater application ofisotope tracers and isotope fractionation studies Water ResourRes 42 W05411 doi1010292005WR004349

CH2M Hill (1981) Drilling and testing of the 8 injection wells andthe 3 monitoring wells for the South District Regional Waste-water Treatment Plant of the Mimi-Dade Water and SewerAuthority CH2M Hill Englewood CO

CH2M Hill (1998) Engineering report of the construction andtesting of the aquifer storage and recovery (ASR) system at theMDWASD West Wellfield CH2M Hill Englewood CO

Clark JF Bryant Hudson G Lee Davisson M Woodside GHerndon R (2004) Geochemical imaging of flow near anartificial recharge facility Orange County California GroundWater 42167ndash174

Corbett DR Kump L Dillon K Burnett W Chanton J (2000) Fateof wastewater-borne nutrients under low discharge conditions inthe subsurface of the Florida Keys USA Mar Geochem 6999ndash115

Dames and Moore Inc (1975) Floridan aquifer water supplyinvestigation Turkey point Area Miami-Dade County FloridaFlorida Power and Light Miami

Davis SN Whittemore DO Fabryka-Martin J (1998) Uses ofchloridebromide ratios in studies of potable water GroundWater 36338ndash350

Englehardt JD Amy VP Bloetscher F Chinn DA Fleming LEGokgoz S Solo-Gabriele H Rose JB Tchoaboglous G (2001)Comparative assessment of human and ecological impacts formunicipal wastewater disposal methods in southeast Floridadeep wells ocean outfalls and canal discharges University ofMiami Coral Gables FL

Fish JE Stewart M (1991) Hydrogeology of the surficial aquifersystem Dade County Florida US Geol Surv Water ResourInvest Rep 90-4108 50 pp

Flocks JG Kindinger JL Davis JB Swarzenski P (2001) Geo-physical investigations of upward migrating saline water from thelower to upper Floridan Aquifer Central Indian River RegionFlorida In US Geological Survey Karst Interest Group Proceed-ings US Geol Surv Water Resour Invest Rep 01-4011 pp 135ndash140

Florida Lakes Power Partners and Florida Power and LightCompany (2006) Well completion report for Floridan Aquiferwells PW-1 PW-2 and PW-4 FPL Turkey Point ExpansionProject (Unit 5) Homestead FL

Haberfeld JL (1991) Hydrogeology of effluent disposal zonesFloridan aquifer south Florida Ground Water 29186ndash190

Hem JD (1985) Study and interpretation of the chemicalcharacteristics of natural water US Geol Surv Water SupplPap 2254

Herczeg AL WM Edmunds (2000) Inorganic ions as tracers InCook PG Herczeg AL (eds) Environmental tracers in subsur-face hydrology Kluwer Norwell MA pp 31ndash78

Kaehler CA K Belitz (2003) Tracing reclaimed water in MenifeeWinchester and Perris-South ground-water subbasins RiversideCounty California US Geol Surv Water Resour Invest Rep03-4039

Kohout FA (1965) A hypothesis concerning cyclic flow of saltwater related to geothermal heating in the Floridan aquiferTrans NY Acad Sci Ser II 28249ndash271

Langmuir D (1997) Aqueous environmental geochemistry Prentice-Hall Upper Saddle River NJ

Maliva RG CW Walker (1998) Hydrogeology of deep-welldisposal of liquid wastes in southwestern Florida USAHydrogeol J 6(4)538ndash548

Maliva RG Guo W Missimer T (2007) Vertical migration ofmunicipal wastewater in deep injection well systems SouthFlorida USA Hydrogeol J 15(7)1387ndash1396

McNeill DF (2000) Final report a review of upward migration ofeffluent related to subsurface injection at Miami-Dade Waterand Sewer South District Plant McNeill Miami FL

Hydrogeology Journal DOI 101007s10040-009-0570-8

MARK A QUARLES PG PAGE 3

the structural integrity of an existing ash surface impoundment proposed for vertical expansion and the technical feasibility of a proposed gypsum disposal surface impoundment

Unconventional Natural Gas and Hydraulic Fracturing bull Shenandoah Valley Network Shenandoah Riverkeeper - Virginia Provided technical review of an application for the first proposed deep shale natural gas well in

Virginia The report evaluated among others the proposed plan for hydraulic fracturing storage of produced waters and flow back protection of groundwater supplies treatment and disposal of wastes and the location relative to the floodplain The applicant decided to rescind their application following submittal of the technical report critical of the proposed well action

bull Sierra Club Washington DC Provided technical comments regarding proposed Tennessee oil and gas regulations with a

particular emphasis on well casing standards fracture chemical disclosure and baseline post drilling monitoring for fracture chemicals and methane intrusion Compared the proposed regulations to API industry standards and other state regulations and provided recommendations for changes

Utility Line Environmental Assessments bull Private Landowner - Livingston Tennessee Served as lead consultant to prevent a proposed Corps of Engineer development Arguments

included identifying deficiencies in the aquatic resources alteration permit the cultural resources survey the stream use classification and the Section 404 application Negotiated alternate route

bull Private Landowner ndash Bowling Green Kentucky Served as lead consultant to provide technical comments to a Draft EA for the construction of a

220-mile electrical powerline Technical legal and financial reporting resulted in stopping the project in its entirety the Public Services Commission revoking the certificate of need (CON) and the Kentucky Attorney General conducting a formal investigation

bull Sumner Trousdale Opposing Pipeline ndash Gallatin Tennessee Served as lead consultant to identify deficiencies in the wetland and aquatic resources alteration

permits for a proposed 30-mile natural gas pipeline to represent the group in public hearings and develop technical arguments for against the proposed pipeline

Reservoir Water Quality and Use Assessments bull Friends of Tims Ford ndash Tims Ford Reservoir - Winchester Tennessee ndash served as lead consultant

to provide comments on Section 10 and Section 26A Regulation permit applications and a Recreational Boating Capacity Study for reservoir-wide community boat docks associated with residential development

bull Honeycomb Homeownerrsquos Association - Guntersville Lake ndash Guntersville Alabama ndash served as lead consultant to provide comments to Section 10 and Section 26A Regulation permit applications for residential developments Completed a detailed assessment of reservoir water quality results relative to designated use standards

bull Murrayrsquos Loch ndash Atlanta Georgia Served as consultant to evaluate the technical merits of a water withdrawal permit and the effects of increased urbanization on stormwater runoff and groundwater recharge Water withdrawal for commercial irrigation purposes resulted in decreased water levels in lakefront property of an adjacent residential neighborhood The permit was appealed to the State Administrative Court

Multi-Media Environmental Permitting bull Nashville Superspeedway USA Inc ndash Lebanon Tennessee

Served as Project Manager for a $125 million superspeedway development The environmental aspects included the requirements to determine the affects of the project on public and private groundwater users stream alterations wetlands endangered plant and animal species air permitting stormwater runoff oil pollution prevention underground injection control and due diligence property assessment

MARK A QUARLES PG PAGE 4 bull Metropolitan Knoxville Airport Authority ndash Knoxville Tennessee

Served as Project Manager for all environmental permitting and compliance activities Activities included spill prevention and response plan development stormwater plan development fuel tank farm design and compliance inspections

bull Various Industrial Clients ndash Tennessee Served as Project Manager for the development of SPCC Plans and SWPP Plans Plans were prepared consistent with the requirements of 40 CFR Part 112 the Tennessee General Permit the EPA Multi-Sector permit and the Tennessee Construction General Permit

Environmental Investigations and Remediation bull USEPA ndash Dickson County Tennessee

Served as Senior Geologist to investigate the occurrence of a cluster of cleft palate cleft lip birth defects in the county relative to the occurrence of trichloroethene in the groundwater and public water supply Reviewed EPA and TDEC regulatory files CDC and Department of Health reports interviewed City County TDEC and EPA officials and interpreted regional karst geologic and hydrogeologic data

bull Harpeth River Watershed Association ndash Franklin Tennessee Served as technical advisor for a review of the environmental investigation report and corrective action plan Contaminants of concern included free product toluene dissolved-phase BTEX constituents dissolved-phase acetone and dissolved-phase chlorinated solvents

bull Natural Resources Defense Council ndash Confidential Location Served as technical advisor for development of a Complaint for Declaratory and Injunctive Relief related to the inappropriate disposal investigation and cleanup of volatile organic compounds in soil groundwater and surface water

bull Confidential Client ndash McMinnville Tennessee Served as Project Manager to identify quantify and remediate the extent of a release of chlorinated solvents in a karst geologic setting Activities included the completion of an interim remedial action a soil gas survey direct push soil borings monitoring wells and well nests dye injection studies streambed sampling and a feasibility analysis

bull Burlington Northern Railroad - Birmingham Alabama Served as a Senior Geologist for an LNAPL investigation The investigation included the installation of temporary piezometers soil borings and permanent groundwater monitoring wells

bull Sunbeam Outdoor Products Inc - Neosho Missouri Developed a Field Sampling and Analysis Plan for the sampling of soils and drummed liquids for a Removal Action required by EPA Region VII Heavy metals and volatile organic compounds were the contaminants of concern in a karst geologic setting

bull United Technologies Automotive Inc - Quincy Michigan Served as Project Manager for groundwater well sampling and the development of an in-situ remedial action for heavy metal contamination

bull United Technologies Automotive Inc - Morganfield Kentucky Served as Project Engineer for a lagoon closure Completed activities for sludge characterization and quantification special waste permitting and closure design for material excavation and site restoration

Solid Waste Disposal bull Meriwether County Landfill Permit Appeal ndash Atlanta Georgia

Served as consultant to evaluate the technical merits of a municipal solid waste disposal permit that had been issued by the Georgia EPD Key technical issues were placement of the landfill adjacent to a public surface water supply typical liner performance and landfill leakage history in Georgia The permit was appealed to the Georgia Administrative Court

bull Various Secondary Aluminum Smelter Waste Landfills - Tennessee Reviewed secondary aluminum smelter waste characterization results landfill designs and associated hydrogeologic investigation reports for two proposed Class II industrial monofill landfill applications and reviewed groundwater monitoring reports associated with three co-mingled municipal solid waste landfills that used dross for intermediate daily cover

MARK A QUARLES PG PAGE 5 bull Various Industrial Landfills - Tennessee

Served as Project Manager for Subtitle D landfill siting and design projects Performed hydrogeologic investigations presented design waivers for site-specific design criteria (when applicable) and developed detailed designs for permitting

bull Various Landfills - Tennessee Served as Project Manager for the design permitting and operation of industrial and municipal solid waste landfills preparation of SWPP Plans quarterly groundwater and gas monitoring reports and hydrogeologic investigation reports

bull Various Municipal Landfills - Kentucky Served as Project Engineer for the design permitting and operation of municipal solid waste landfills

Stormwater Permitting and Compliance bull Tennessee Clean Water Network ndash Knoxville Tennessee

Served as lead consultant for providing technical comments for the draft Knox County Phase II Municipal Separate Storm Sewer System (MS4) permit

bull Various Industrial Clients - Throughout the US Served as Project Manager to obtain permit coverage through the EPA General Permit group permits and individual permits specific to each state Over 125 facilities were permitted

Hazardous Waste Management bull Various Industrial Clients ndash Throughout the US

Served as Project Manager for various projects to evaluate hazardous waste management practices consistent with the rules and regulations established under RCRA

bull Laidlaw Environmental Services Inc ndash Southeastern US Completed SWPP Plans for RCRA treatment storage and disposal facilities

Municipal Wastewater Management bull Various Municipalities ndash Fulton Cobb and Dekalb County Georgia

Served as Project Engineer for sewer modeling and point-source identification Identified sources of infiltration inflow and performed cost evaluations for source removal

bull Various Municipal and Industrial Clients ndash Tennessee Served as Project Engineer to establish beneficial reuse land application programs for wastewater sludge

bull Boston Water and Sewer Commission - Boston Massachusetts Served as Project Engineer for sewer modeling and point-source identification projects of combined and separate sewers up to 15 feet in diameter Identified sources of infiltration inflow and performed cost evaluations for source removal

bull Various Municipal Clients ndash Throughout the US Served as lead technical trainer for the implementation of proprietary software used for automated GIS mapping maintenance scheduling and hydraulic analyses of separate and combined sewers

bull City of Hopkinsville - Hopkinsville Kentucky Served as Project Engineer for water and sewer line expansions and wastewater treatment projects

TECHNICAL PUBLICATIONS AND LECTURES bull Quarles M and William Wilson ldquoUnconventional Natural Gas and its Risk A Tennessee

Perspectiverdquo Appalachian Public Interest Environmental Law Conference Knoxville Tennessee October 2011

bull Quarles M ldquoA Case Study in Karst Hydrogeology and Contaminant Fate and Transportrdquo National Groundwater Association 51st Annual Convention and Exposition December 1999

bull Quarles M and Allen P Lusby ldquoEnhanced Biodegradation of Kerosene-Affected Groundwater and Soilrdquo 1994 Annual Conference of the Academy of Hazardous Materials Managers October 1994

MARK A QUARLES PG PAGE 6 bull Quarles M ldquoNew Tank Performance Standardsrdquo Tennessee Environmental Law Letter July

1993 EXPERT LEGAL TESTIMONY bull Chesney versus Tennessee Valley Authority ndash 2011 US District Court Written testimony

associated with fly and bottom ash sampling waste characterization contaminant fate and transport and contaminant risks compared to US EPA screening levels drinking water standards fish and aquatic life standards and sediment cleanup standards

bull Busch et al versus Dr Carol Couch Atlanta Georgia 2008 State Administrative Court Written and verbal testimony regarding drought restrictive surface water and groundwater use Qualified by the court as an expert in geology hydrogeology and stormwater runoff

bull Darrel Segraves et al versus Dr Carol Couch Atlanta Georgia 2008 State Administrative Court Written and verbal testimony regarding appeal of a municipal solid waste landfill permit Qualified by the court as an expert in geology hydrogeology landfill design pertaining to landfill leakage and stormwater runoff

bull Tulane Environmental Law Clinic 2007 - 2008 Written testimony for numerous draft LDEQ permits and proposed rules

bull Republic of Ecuador and PetroEcuador vs Chevron Texaco Corporation and Texaco Petroleum Company US District Court Southern District of New York 2007 Written testimony regarding environmental investigation protocol

bull Friends of Tims Ford vs Tennessee Valley Authority and Tennessee Department of Environment and Conservation US District Court 2007 Written testimony in support of violations of State and Federal water quality standards reservoir carrying capacity standards and NEPA environmental assessment standards

bull Freddie Howell vs Creative Customs Atlanta Georgia 2007 Technical support regarding litigation associated with stormwater and groundwater flow and their effects on the Howell property

bull Aguida vs ChevronTexaco Lago Agrio Ecuador Court 2006 Written testimony regarding Texacorsquos waste management and standard operating practices in the Ecuadorian concession area relative to industry standards

TRAINING Current Wetland Issues in Tennessee (2007) Professional Liability Education - Contract Review and Revision (2000) Professional Liability Education ndash Mid-Town Developer Case Study Workshop (1999) Professional Liability Education ndash Liability IQ for Environmental Consultants (1998) Liquid Animal Waste Management System Design to NRCS Standards for CAFO (1998) 8-Hour OSHA Health and Safety Refresher Training Hazardous Materials Waste Manager Course University of Alabama (1993) 40-Hour OSHA Health and Safety Training (1990) CONTACT INFORMATION Home telephone 615-352-0471 Mobile telephone 615-504-0956 Email markquarlescomcastnet

Determination of vertical and horizontal pathways of injected freshwastewater into a deep saline aquifer (Florida USA) using naturalchemical tracers

Virginia Walsh amp Reneacute M Price

Abstract Two deep-well injection sites in south FloridaUSA inject an average of 430 million liters per day(MLD) of treated domestic fresh wastewater into a deepsaline aquifer 900m below land surface Elevated levels ofNH3 (highest concentration 939micromol) in the overlyingaquifer above ambient concentrations (concentration lessthan 30micromol) were evidence of the upward migration ofinjected fluids Three pathways were distinguished basedon ammonium chloride and bromide ratios and temper-ature At the South District Wastewater Treatment Plantthe tracer ratios showed that the injectate remainedchemically distinct as it migrated upwards through rapidvertical pathways via density-driven buoyancy Thewarmer injectate (mean 28degC) retained the temperaturesignal as it vertically migrated upwards however thetemperature signal did not persist as the injectate movedhorizontally into the overlying aquifers Once introducedthe injectate moved slowly horizontally through theaquifer and mixed with ambient water At the NorthDistrict Wastewater Treatment Plant data provide strongevidence of a one-time pulse of injectate into theoverlying aquifers due to improper well construction Noevidence of rapid vertical pathways was observed at theNorth District Wastewater Treatment Plant

Keywords Waste disposal Deep well injection Carbonate rocks Confining units Ammonia Temperature USA

Introduction

Deep well injection of treated municipal wastewater intonon-potable aquifers has been used as an alternative todischarge of wastewater to surface waters for manydecades There are 430 permitted municipal wastewaterdeep injection wells in the United States with 163 inFlorida alone (USEPA 2008) These deep aquifers tend tobe saline and the discharge of fresh wastewater into themhas raised concerns of geochemical reactions as a result ofthe mixing of the two waters as well as the buoyanttransport of the wastewater upwards into overlyingaquifers Confined brackish aquifers in Florida have beenused extensively for aquifer storage and recovery (ASR)of potable freshwater (Arthur et al 2001 Renken et al2005) and deeper saline aquifers have been used fordisposal of waste fluids such as oil brines industrial waterand municipal wastewater (Meyer 1989a Meyer 1989b)ASR in Florida has been extensively studied as part of theComprehensive Everglades Restoration Plan (Reese 2002Mirecki 2004 Mirecki 2006) however little research hasbeen published regarding the fate and transport of thetreated wastewater into deep saline aquifers (Meyer1989a Haberfeld 1991 Maliva and Walker 1998Bloetscher et al 2005 Bloetscher and Muniz 2006Maliva et al 2007)

Miami-Dade County Water and Sewer Department(MDWASD) located in southern Florida currently dis-charges 430 million liters per day (MLD) of treateddomestic wastewater into a saline deep aquifer at twolocations in the county Deep well injection has been inuse in Miami-Dade County since the late 1960s Theinjection facilities are located in the north and south of thecounty separated by 44 km (Fig 1) The South DistrictWastewater Treatment Plant (SDWWTP) site was placedinto service in 1983 and is currently permitted for thedisposal of 367 MLD of treated wastewater The NorthDistrict Wastewater Treatment Plant (NDWWTP) site wasplaced into service in 1997 and is permitted for 90 MLD

Received 2 February 2009 Accepted 14 December 2009

copy Springer-Verlag 2010

V Walsh ())Miami-Dade Water and Sewer Department3071 SW 38th Ave Miami FL 33146 USAe-mail walshvmiamidadegov

V WalshDepartment of Earth and EnvironmentFlorida International University11200 SW 8th Street University Park Miami 33199 USA

R M PriceDepartment of Earth and Environment and SoutheastEnvironmental Research CenterFlorida International University11200 SW 8th Street University Park Miami 33199 USA

Hydrogeology Journal DOI 101007s10040-009-0570-8

Both facilities treat domestic wastewater to above second-ary drinking water standards and discharge the treatedwastewater into United States Environmental ProtectionAgency (USEPA) Class I injection wells The treatedwastewater is injected into the Boulder Zone a highlytransmissive interval in the deep saline non-potable LowerFloridan Aquifer The Boulder Zone has been thought to behydrologically separated from overlying aquifers by a335-m-thick confining unit During the installation of addi-tional monitoring wells at the SDWWTP in 1994 ammonia-nitrogen (NH3-N) was detected at 442 m depth in theoverlying aquifer at a concentration of 411 micromoles perliter (micromol) above reported background levels of 29micromol

(BCampECH2M Hill 1977) The detection of NH3ndashN in theaquifers above the Boulder Zone has raised doubts regardingthe efficacy of the confining unit and the resultant waterquality impact to overlying aquifers as these aquifers areused as alternative water supplies via storage of freshwater(ASR) and blending with potable surficial aquifer water

Research has focused on ASR in south Florida (Arthuret al 2001 Reese 2002 Mirecki 2004 Mirecki 2006Reese and Richardson 2008) however few studies havebeen conducted regarding the transport and fate of injectedeffluent into the Boulder Zone and typically these had todo with the relative risk of deep well injection versusocean outfall disposal of municipal waste (Englehardt et

Fig 1 Location of theNDWWTP and the SDWWTPstudy sites

Hydrogeology Journal DOI 101007s10040-009-0570-8

al 2001 USEPA 2003 Bloetscher et al 2005 Bloetscherand Muniz 2006) Recently researchers have studied thetransport mechanisms of the observed migrated injectateand have suggested density-driven buoyant transportmechanism along natural or anthropogenic vertical frac-tures in the lower aquifers (Maliva and Walker 1998McNeill 2000 McNeill 2002 Maliva et al 2007 Walshand Price 2008) The objective of this study was todetermine migration pathways of injected treated waste-water at two facilities in Miami-Dade County Florida(SDWWTP and NDWWTP) using historical time seriesdata and major ion data collected as part of this study Themethodology developed for this study used chloride (Clminus)bromide (Brminus) and NH3 as tracers This methodologyprovided a method for estimating transport pathways andinvolved no additional collection of data other than whatwas typically required under federal and state regulatoryprograms

Natural inorganic tracers have been used extensively inwater resources investigations to trace groundwater flowpaths and calculate mixed water ratios (Langmuir 1997Davis et al 1998 Herczeg and Edmunds 2000) Clminus andBrminus commonly are used as they tend to be conservativeand their ratios may also give information as to the sourceand pathways of water Studies have been conducted insouth Florida (Shinn et al 1994 Paul et al 1997 Corbettet al 2000 Boumlhlke et al 2003) and elsewhere (Kaehlerand Belitz 2003 Clark et al 2004) tracing treatedwastewater in surficial aquifers but NH3 was not used asa tracer as it does not behave conservatively in oxicwaters In this study a novel application of Clminus Brminus andNH3 as conservative tracers of injectate was developed aspart of mixing models to distinguish pathways betweenthe deep aquifers Clminus is a natural anion in the Floridanaquifer system and its principal source is seawater asthere are no evaporite minerals to provide an additionalsource (Sprinkle 1989 Reese 1994) The seawater sourceof Clminus in south Florida is thought to be the result of eitherincomplete flushing of Pleistocene seawater and brackishwater intrusion andor the result of the cyclic flow basedon thermal upwelling of Holocene intruded seawater(Kohout 1965 Sprinkle 1989 Reese 1994) Bromide(Brminus) behaves similar to Clminus in groundwater systems(Davis et al 1998) and in south Florida the source of Brminus

in groundwater is similar to that of Clminus although its naturalabundances are orders of magnitude less than Clminus Theonly source of the NH3 is the injectate and therefore itwas used to trace transport pathways of the injectedwastewater

Geologic and hydrogeologic framework

The Floridan aquifer system (FAS) in southeastern Floridais defined by a vertically continuous sequence of per-meable carbonate rocks of Cenozoic age that are hydrauli-cally connected in varying degrees (Miller 1986) Theaquifer matrix consists of carbonate and dolomitic lime-stones dating from the Paleocene to the Oligocene

epochs Overlying the FAS are the impermeable sedimentsof the late Oligocene to Pliocene age Hawthorn Group a180-m-thick confining layer of clays siltstones and siltylimestones The Hawthorn Group separates the UpperFloridan Aquifer from the late Pliocene and Pleistoceneformations making up the Surficial Aquifer System whichincludes the Biscayne Aquifer in south Florida (Fig 2)The Biscayne Aquifer is an unconfined surficial aquiferand is the major source of potable water in south Florida(Fish and Stewart 1991)

The Floridan Aquifer contains several highly perme-able and less permeable zones with zones of highestpermeabilities typically occurring at or near unconform-ities and usually parallel to the bedding planes (Meyer1989a) Previous studies (Miller 1986 Reese 1994)grouped the Floridan aquifer system into three hydro-stratigraphic units (Fig 2) the Upper Floridan Aquifer(UFA) the Middle Confining Unit (MCU) and the LowerFloridan Aquifer Recently the MCU in south Florida hasbeen divided into the MC1 and MC2 (Fig 2) separatedby the Avon Park permeable layer (Reese and Richardson2008) which in south Florida had previously beenidentified as the Middle Floridan Aquifer The UpperFloridan Aquifer contains relatively fresh water less than10000 mg Lminus1 total dissolved solids (TDS) The LowerFloridan Aquifer consists of seminconfining or leakymicritic limestone and dolomite layers that containgroundwater with compositions approaching seawater(approximately 30000 mg Lminus1 TDS) A dolomite confin-ing unit (DCU) a thin confining unit below the MC2 wascharacterized at the study site by McNeill (McNeill 20002002) This DCU lies above the permeable zone com-monly known as the Boulder Zone within the OldsmarFormation of the Lower Floridan Aquifer The FASoutcrops along the Straits of Florida providing a hydraulicconnection to the sea (Kohout 1965 Miller 1986 Reese1994) Transmissivities in the Upper Florida Aquiferrange from 929 to 23times104m2 dayminus1 (Meyer 1989a Reese1994) while transmissivities in the Boulder Zone rangefrom 297times105m2 dayminus1 to 232times106m2 dayminus1

Site descriptionsThe NDWWTP and the SDWWTP consist of deepinjection wells that penetrate down to approximately855 m The upper 755 m of each well is cased to the topof the Boulder Zone The bottom 100 m of each injectionwell is an open hole in the Boulder Zone Nine suchinjection wells and three multi-zoned and dual-zonedmonitoring wells were constructed between 1977 and1981 at the SDWWTP (Fig 3) The multi-zone test wellBZ cluster (BZ-1 through 4) was constructed in 1977 andconsisted of four telescoping monitoring wells the deepestof which was BZ-4 cased to the top of the Boulder Zonethe shallowest BZ-1 open to the UFA at a depth of 312 mThe remaining monitoring wells were constructed bothat the SDWWTP and NDWWTP using a dual zone designwith an inner steel casing drilled to the deeper intervaland the outer steel casing open to the upper interval For

Hydrogeology Journal DOI 101007s10040-009-0570-8

this report well nomenclature indicates the open intervalof the dual-casing ldquoUrdquo represents the upper monitoringinterval and ldquoLrdquo represents the lower monitoring intervalWells 1 and 2 were dual-cased to monitor water quality inthe UFA (sim300 m) and the lower confining units (sim550 mCH2MHill 1981) In 1994 NH3 was detected aboveambient levels in the confining unit at the BZ well cluster(BZ-2 depth 488 m) and subsequent investigations by theutility found a leak due to corrosion of the casing in thiscluster (MDWASD 1995) The lower three monitoringintervals of the BZ well cluster were plugged in 1995 tostop the upward migration of injectate through the casinghole and the confining unit (488 m) monitoring intervalwas redrilled From 1995ndash1996 nine injection wells and

thirteen dual-zoned monitoring wells were constructed onthe SDWWTP These monitoring wells were cased to theAvon Park Permeable zone (APPZ) and the MC2 withopen holes in the formations approximately 30 m Duringthe construction of the monitoring wells NH3 concen-trations above ambient levels were found throughout thesite Elevated NH3 concentrations were found in thenorthwest corner of the site in the MC1 interval in severalwells but not in the lower MC2 interval of these wellsElevated levels were found in the MC2 interval in thesouth side of the site As a result of the detected NH3 inthe confining units the EPA required purging of the wellsthat showed elevated concentrations NH3 (Starr et al2001) in an attempt to remove the NH3 loading in the

Fig 2 Geologic and hydrogeologic framework of NDWWTP and the SDWWTP modified from Reese and Richardson 2008 Welldiagram on the right shows the number of wells open to the indicated hydrogeologic unit used for this study

Fig 3 Well locations at theSDWWTP

Hydrogeology Journal DOI 101007s10040-009-0570-8

impacted intervals Discontinuous purging of approxi-mately 2100 Lmin commenced from 1997 to 2000 forthe northwest wells (5U 6U 7U 8U 15U and 16U) of theAPPZ interval and the south wells (11L and 12L) of theMC2 (MDWASD 2000)

Injection well construction started at the NDWWTP in1996 Four injection wells were constructed into theBoulder Zone and four dual-zoned monitoring wells wereconstructed to the UFA and the APPZ intervals (Fig 4) In1996 effluent was injected in two completed injectionwells while one injection well was still under constructionresulting in injectate backflowing into an open borehole atan uncased injection well for 5 days Several months afterthe construction of the wells had been completed NH3

concentrations were observed to increase in the APPZinterval of the monitoring wells on site The utility wasrequired to purge the APPZ interval wells for a period of1 year from 2003ndash2004 (MDWASD 2005)

Methodology

Historical data were collected and checked for qualityassurance for the NDWWTP and SDWWTP Data wereavailable from 1983 through 2007 for the SDWWTP and1996ndash2007 for the NDWTP Data studied as part of thisresearch included pressure temperature pH Clminus sulfate(SO4

2minus) NH3 and nitrate (NO3minus) The historical data were

compiled from the utility monthly operating reportsavailable sporadically from 1983 Non-detects that hadbeen entered as a zero value were updated to the detectionlevel of the parameter Summary statistics including meanmedian standard deviation maximum and minimum wereapplied to each of the wellsrsquo time series data to assesswater-quality changes over time and used to compare toambient water quality data at other locations in southFlorida Most water quality for the Floridan Aquifer insouth Florida had been collected as regulatory require-ments which usually included chemical analyses that areused for drinking water quality and therefore did notinclude major ion data Residence time in the Floridan

aquifer system in south Florida is on the order of thousandsof years (Meyer 1989a) and it was assumed that due to thedepth of the aquifer water quality was in equilibrium andthere would be no other cause of perturbations to ambientwater quality other than migration of injectate Time seriesdata that showed large variation over time would indicatenon-equilibrium conditions and therefore not ambientconditions Abrupt changes in water quality and pressurewere observed in the time series data in wells that werepurged in 1997 These changes were not observed in wellsthat were not purged These changes in water quality andpressure were interpreted as being the result of crossconnections developed in the dual zone casings of some ofthe purged wells and review of borehole videos of thesewells taken in 2004 confirmed holes in the casings of thesewells It could not be determined which interval the datacollected from these wells represented after the crossconnections developed therefore data were discardedfrom the historical series analysis based on the month itwas ascertained the cross connection developed and thesummary statistics were recalculated for these wells

Floridan Aquifer water samples were collected at theNDWWTP and SDWWTP during 2006 and 2007 as partof this study for major ions and nitrogen species Thirty-two monitoring wells were sampled at the SDWWTP andwater-quality samples were collected from these wellsfrom the UFA the APPZ and the MC2 At theNDWWTP samples were collected from four monitoringwells representing the UFA and four wells in the APPZTemperature pH dissolved oxygen and conductancewere taken from water samples in the field using an YSI556 MPS The YSI instrument was calibrated per themanufacturerrsquos instructions prior to each sampling eventAll wells were purged for at least 24 h prior to sampling toensure at least three well volumes were evacuated Thewells were sampled through a closed system using a lowflow cell and tygon tubing through a disposable highcapacity 045micromol in-line filter Water samples wereanalyzed for the anions Brminus Clminus Fminus NO3

minus NO2minus and

SO42minus on a DIONEX ion chromatography system

HCO3minus and CO2

minus were analyzed via manual titrationNH3 was analyzed on a LACHAT analyzer 800 withNH4

+ then calculated based on pH and temperature ofthe sample using the NH3 result (Stumm and Morgan1996) Cations (Ca2+ Mg2+ K+ Na+ and Sr2+) wereanalyzed by inductively coupled plasma (ICP)

Results

The mean historical data are summarized in Table 1 forthe SDWWTP and Table 2 for the NDWWTP Dissolvedoxygen NO3

minus and NO2minus had similar results for both the

SDWWTP and NDWWTP sites for the aquifer intervalsNO3

minus concentrations were either detected at very lowconcentrations or below detectable levels NO2

minus levelswere below 1 micromoleL (micromol) for all aquifer intervalsand in the injectate at the NDWWTP and SDWWTP sitesfor the historical time series The injectate had a mean valueFig 4 Well locations at the NDWWTP

Hydrogeology Journal DOI 101007s10040-009-0570-8

Tab

le1

Meanvalues

forhistorical

timeseriesSDWWTP

mblsmetersbelow

land

surface

Geologicform

ation

Hyd

rostratig

raph

icform

ation

WellID

Open

interval

Periodof

record

Tem

pdegC

pHNH3micromol

Clndashmmol

SO42ndashmmol

NO3ndashmicromol

mbls

Pleistocene

Biscayn

eAqu

ifer

Injectate

(S-EFF)

Surface

591

ndash1207

277

66

889

203

109

Und

ifferentiated

Haw

thornAvo

nParkLim

estone

Upp

erFloridan

Aqu

ifer

(UFA

)1U

299ndash

332

983

ndash1207

240

79

1221

32

02

2U29

9ndash311

783

ndash1207

244

79

1321

32

03

3U29

9ndash32

0291

ndash1207

243

79

1023

32

03

BZ1

306ndash

316

783

ndash1207

242

76

1222

31

02

Avo

nPark

Lim

estone

Avo

nParkPermeable

Zon

e(A

PPZ)

13U

451ndash

475

296

ndash1207

239

77

6210

848

03

5U45

4ndash48

4594

ndash1102

241

76

492

108

49

03

6U45

4ndash48

3594

ndash1207

241

76

545

7630

03

7U45

4ndash48

2694

ndash198

245

74

526

738U

454ndash

480

894

ndash602

240

77

216

106

41

02

9U45

4ndash48

4195

ndash1207

239

77

64111

43

02

10U

454ndash

485

296

ndash1207

240

76

3510

542

02

11U

454ndash

484

296

ndash1207

240

76

118

106

43

02

14U

454ndash

480

296

ndash1207

239

74

320

9943

02

15U

454ndash

480

296

ndash1207

231

75

296

106

53

03

16U

454ndash

485

296

ndash1207

231

76

330

109

48

02

12U

456ndash

487

296

ndash204

249

76

100

111

42

02

MiddleCon

fining

Unit(M

C2)

BZ2

481ndash

507

783

ndash1207

254

75

106

133

56

02

2L50

1ndash51

0783

ndash1207

243

74

1219

926

02

4L51

9ndash56

112

91ndash

1207

240

73

1251

019

304

13L

530ndash

562

296

ndash1207

237

75

5550

822

809

3L54

0ndash57

7191

ndash1207

240

73

752

921

910

5L54

6ndash57

6594

ndash1102

239

74

652

821

604

6L54

6ndash57

6594

ndash1005

237

74

3052

622

703

7L55

0ndash57

1694

ndash198

242

71

1053

68L

546ndash

576

894

ndash602

237

74

554

124

804

9L54

6ndash57

3195

ndash1207

234

74

553

422

604

10L

546ndash

576

396

ndash1207

238

76

141

429

204

05

11L

546ndash

576

296

ndash1199

238

76

417

193

93

02

12L

546ndash

576

296

ndash1207

254

74

676

5730

03

15L

546ndash

576

296

ndash104

231

75

1253

125

204

16L

546ndash

576

296

ndash1207

229

74

653

221

904

1L56

1ndash58

7783

ndash1207

238

73

653

923

904

Oldsm

arFormation

Bou

lder

Zon

eLow

erFloridan

Aqu

ifer

BZ4

853

0783ndash894

249

72

634

3

Hydrogeology Journal DOI 101007s10040-009-0570-8

of NO3minus of 379micromol at the NDWWTP and 109micromol

at the SDWWTP for the historical time series Dissolvedoxygen was detected at concentrations less than 10 mg Lminus1

for all aquifer intervals Dissolved oxygen concentrationsfor the injectate at both the NDWWTP and the SDWWTPhad results above 3 mg Lminus1

Historical time series results SDWWTPThe historical period of record data for the freshwaterinjectate samples from the SDWWTP (identified as S-EFF) were available from 1991 through 2007 (Table 1)Temperature ranged from 218 to 311degC with a mean of277degC Mean pH in the historical time series was 66NH3 ranged from 1468ndash18496micromol with a mean of889micromol NH3 varied seasonally and increased with time(Fig 5) Clminus concentrations averaged 2 millimolesL(mmol) with a very small range and standard deviationindicative of the freshwater source of the injectateHistorical data from the SDWWTP for the UFA (wellsBZ1 1U 2U and 3U) were available from 1983 through2007 Temperature averaged 24degC with no significantdifference observed between the wells The range of pHwas from 76 to 82 in the UFA Chloride averagedbetween 21 and 23 mmol while NH3 means rangedbetween 10 and 13micromol The summary statistics for thewater-quality samples collected from the UFA showedconsistent values with no discernable variation over timeHistorical data from wells open to the APPZ at theSDWWTP (wells 5U 6U 7U 8U 9U 10U 11U 12U13U 14U 15U 16U) were available from 1994 through2007 Mean temperatures ranged between 231 and249degC in these wells There was little variation observedin the pH in the APPZ samples but the mean pH of 76was lower than the mean pH in the UFA Almost all of thewells showed variation in NH3 concentrations over timeMean values of NH3 in these wells ranged from 35micromolin well 10U to 545micromol in well 6U Well 6U showed anincreasing trend with time in NH3 that was observed to besimilar to the increasing trend of NH3 in the injectate(Fig 5) The spread between the 5th and 95th percentilewas the greatest in wells 6U and 12U Only wells 9U10U and 13U showed little variation in NH3 over timeMean concentrations of Cl- in wells 6U and 7U were 76and 73 mmol Wells in the MC2 were open to intervalsvarying in depth from 481 to 551 m Mean temperaturevalues ranged from 229 to 242degC in all wells with theexception of a mean value of 254degC in wells BZ2 and12L Mean pH values ranged from 73 to 76 Mean NH3

concentrations showed two groupings Wells BZ2 10L11L and 12L exhibited concentrations of 106 141 417and 676micromol respectively The remainder of the wellsexhibited mean NH3 concentrations of less than 55micromolClminus concentrations for wells 10L 11L and 12L were 429193 and 57 mmol respectively the remainder of the wellshad mean concentrations greater than 508 mmol (excep-tion is BZ-2 whose Clminus concentration of 133 mmolreflects the shallower depth of this well with the openinterval in the lower brackish water zone of the FloridanT

able

2Meanvalues

forhistorical

timeseriesNDWWTP

mblsmetersbelow

land

surface

Geologic

form

ation

Hyd

rostratig

raph

icform

ation

WellID

Open

interval

Period

ofrecord

Tem

ppH

NH3

Cl-

SO42-

NO3-

Revised

period

ofrecord

a

Tem

ppH

NH3

Cl-

SO42-

mbls

degCmicromol

mmol

mmol

micromol

degCmicromol

mmol

mmol

Pleistocene

Biscayn

eAqu

ifer

Injectate

(N-EFF)

Surface

797

ndash1207

284

65

8193

200

05

379

Avo

nPark

Lim

estone

Eocene

Upp

erFloridan

Aqu

ifer

(UFA

)N-1U

354ndash38

5197

ndash1207

231

76

188

737

35

02

N-2U

351ndash38

4396

ndash1207

230

78

177

662

36

21

N-3U

354ndash37

9396

ndash1207

229

78

173

658

36

20

N-4U

354ndash37

9496

ndash1207

231

76

181

684

35

08

Avo

nPark

Permeable

Zon

e(A

PPZ)

N-1L

430ndash46

1496

ndash1207

219

73

2612

3682

328

10

3496ndash797

224

72

193

4617

N-2L

431-

459

396

ndash1207

223

76

1684

3979

156

22

396

ndash898

229

78

177

4557

166

N-3L

430ndash46

0396

ndash1207

222

76

1314

4094

158

10

396

ndash1298

230

77

191

4548

149

N-4L

430ndash46

0496

ndash1207

224

72

1903

3804

152

16

496

ndash1298

223

75

237

4405

Hydrogeology Journal DOI 101007s10040-009-0570-8

Aquifer) Data collected from well 12L were similar todata collected for wells for 6U and 7U These wells hadhigh NH3 concentrations with low Clminus and SO4

minus concen-trations Historical data were available for the BoulderZone interval (well BZ4) from 1983 through 1994 Themean pH and temperature values were 72 and 249degCrespectively Mean NH3 concentration was 634micromol andshowed apparent seasonal variation and increasing trendover time and was similar to the injectate historical timeseries (Fig 5) The mean Clminus concentration was 3 mmolsimilar to the mean Clminus concentration of 2 mmol for theinjectate

Historical time series results NDWWTPThe historical period of record data for freshwaterinjectate samples (N-Eff) at the NDWWTP were availablefrom 2002 through 2007 Temperature ranged from 22 to34degC with a mean of 28degC The mean pH was similar tothe SDWWTP injecate at 65 NH3 ranged from 210ndash3764micromol with a mean of 819micromol and a large standarddeviation indicative of the apparent seasonality similar tothe SDWWTP Clminus concentrations ranged from 08 mmolto 1131 mmol with a mean 20 mmol slightly higher thanthe mean concentration of the SDWWTP injectateHistorical data were available from 1996 through 2007for wells open to the UFA (N-1U N-2U N-3U and N-4U) Mean temperature averaged 23degC in these wellswith no significant difference observed between the wellsMean values of pH ranged from 76 to 78 Clminus meanconcentrations ranged between 662 and 737 mmolsNH3 mean concentrations ranged between 17 to 18micromolConcentrations for the UFAwater-quality samples for theNDWWTP showed consistent values with no discernablevariation over time Historical data were available from1996 through 2007 for wells open to the APPZ (N-1L N-2L N-3L and N-4L) Temperature mean values were

22degC Analysis of historical NH3 data indicates increasingconcentrations of NH3 starting in late 1997 (Fig 6) NH3

concentrations appeared to have reached a peak concen-tration of 408micromol in well N-1L in July 2001 andsteadily declined thereafter to concentrations rangingfrom 200 to 250micromol Wells N-2L N-3L and N-4L showsimilar patterns as well N-1L but with lowered anddelayed peak concentration values NH3 concentrationsare observed to increase scatter after 2003 whichcorresponds to when purging commenced at theNDWWTP Once purging ceased in 2004 NH3 concen-trations in wells varied between 150ndash300micromol The Clminus

mean concentrations ranged from 368 to 409 mmol Clminus

in these wells exhibited variation over time and analysisof the time series indicated that as NH3 concentrationsincreased Clminus concentrations decreased (Fig 6) The timeseries data for the lower wells were revised to removedata after NH3 concentrations were observed to increasein each well in order to determine ambient concentrationsin the APPZ Revised NH3 mean concentrations rangedfrom 18ndash24micromol Clminus mean concentrations ranged from441ndash461 Very little variation was observed in NH3 andClminus mean concentrations after the time series data wereremoved

Major ion data collection resultsMajor ions were collected for this study from 2006ndash2007(Table 3) Data from wells at the SDWWTP site thatexhibited cross connections were removed from thisanalysis Data collected from the SDWWTP UFAexhibited very little variation between wells and weresimilar to the historical time-series data with low cationand anion concentrations For the APPZ wells NH4

+

mean concentrations could be combined into three groupswells 9U 10U and 13U with NH4

+ mean concentrationsof 60 67 and 143micromol respectively wells 14U and 16Uwith 497 and 439micromol and well 6U 823micromol Cation andanion mean concentrations showed a similar grouping asthe NH4

+ concentration grouping with well 6U consis-tently grouping independently and with increasing NH4

+

concentrations correlating to decreasing ion concentra-tions The MC2 mean NH4

+ concentrations could also becombined into three groups well 12L at a mean NH4

+

concentration of 765micromol wells BZ-2 10L and 13LNH4

+ at mean concentrations 176 200 and 108micromolrespectively the remainder wells at NH4

+ concentrationsbelow 10micromol Cation and anion concentrations could becombined in the same 3 groups as the NH4

+ groups withlower ion mean concentrations observed for BZ-2 10Land 13L and much lower ion concentrations observed inwell 12L As with well 6U in the MC1 well 12L in theMC2 consistently grouped independently

The NDWWTP wells open to the UFA (351ndash385 m)exhibited very little variation in field measurements andmean concentrations between wells and were similar tothe historical time series The interval (430ndash461 m) in theAPPZ at the NDWWTP also showed little variation withmean NH4

+ concentrations (215ndash295micromol) and mean

Fig 5 Time series NH3 data from the injectate (black circle) BZ-4(green triangle) and well 6U (red circle) at the SDWWTP site Theapparent seasonal variation observed in the injectate is a result ofincreased flows during the wet season and storm events Theincreasing trends with time correlate to increased injection over timedue to growth in population in Miami-Dade County

Hydrogeology Journal DOI 101007s10040-009-0570-8

concentrations of Clminus (371ndash386 mmol) varying littlebetween wells

Ternary diagramThe typical ClminusBrminus ratio for seawater is about 290 (Daviset al 1998) and most of the ClminusBrminus ratios at both siteswere within that range with no discernable differencesQuite often the addition of a third water-quality membercould enhance the understanding of the data and this wasthe case with using NH4

+ as the third end-member NH4+

Clminus and Brminus data were plotted on a ternary diagram withdata normalized to 100 Typical seawater and freshwaterNH4

+ Clminus and Brminus values after Hem (1985) were alsoplotted for comparison Water quality at the NDWWTPclustered into three distinct groups with two groups basedon depth of the interval sampled and the third the injectate(Fig 7) The ambient aquifer data plot close to seawaterThe injectate data plotted off in the lower left hand cornerdue to the large NH4

+ concentrations At the SDWWTPthree aquifer groupings were observed Ambient well datafrom the MC2 plotted similar to seawater Ambient welldata from the UFA plotted slightly towards freshwaterData from wells that showed elevated NH4

+ plotted in aline towards the injectate with groundwater data from 6Uand 12L plotting very close to the injectate This linerepresents the evolution of the water quality of these wellstowards the injectate water quality and does not show anyevolution of more saline water into the higher intervals inthe aquifer

Mixing end-member modelsEnd-member mixing models of wells 6U 12L and 10Lrepresented the results obtained for all wells at the

SDWWTP (Fig 8) Well 6U and 12L showed theprogressive freshening of water and increasing NH3

concentrations towards the injectate end-member(Fig 8) There was little mixing from the saline end-member towards the brackish end-member in well 6U andalmost all of the mixing was towards the injectate end-member Both 6U and 12L showed large changes inconcentrations from their original end-members over timeWell 10L showed a different pattern than 6U and 12Lwith gradual freshening of the saline water towards theinjectate end-member The mixing was towards the lowerrange of the injectate end-member and there were no largechanges in concentrations of either NH3 or Clminus from thesaline end-member Well N-1L at the NDWWTP end-member mixing model showed a different pattern than theSDWWTP (Fig 9) Clustering of the NH3Cl

minus ratios weredistinguished based on time The NH3Cl

minus ambient ratio canclearly be seen on Fig 9 and lies along the saline end-member As the concentrations of NH3 increased in time tothe peak concentration the NH3Cl

minus ratios showed twodistinct clusters Initially the NH3Cl

minus ratio showed gradualincreasing in NH3 with little change in Clminus from ambientconcentrations There was a rapid change in the NH3Cl

minus

ratio as NH3 reached the peak concentrations Once the peakwas reached the NH3Cl

minus ratios slowly declined in time

Discussion

The Floridan aquifer system was sampled by others atdifferent sites in south Florida and these data aresummarized in Table 4 Wells identified as WWF weremonitoring wells installed as part of the MDWASD ASRsystem west of the NDWWTP and SDWWTP (CH2MHill 1998) The ASR systems were not in use during the

Fig 6 Graph a shows the NH3 data time series for the wells in the APPZ interval at the NDWWTP The dashed lines indicate the purgingtime from 2003 through 2004 NH3 concentrations are observed to increase in well N-1L similar to contaminant breakthrough curves WellN-1L was the closest well to the uncased injection well when injectate backflowed into the APPZ NH3 concentrations for wells N-2LN-3L and N-4L appear to be similar and show a similar increase after 1999 Variability is seen in the data after 2003 Graph b showsClminus concentrations in well N-1L clustered at approximately 300 mmol and an abrupt decrease to less than 300 mmol is seen Clminus

concentrations in wells N-2L N-3L and N-4L are very similar and show a decrease in concentrations after 1999 until 2000 whenconcentrations appear to stabilize Clminus concentrations start to increase slightly and become variable after 2003 All four wells showsimilar concentrations of both NH3 and Cl- after 2004

Hydrogeology Journal DOI 101007s10040-009-0570-8

Tab

le3

Meanfieldparametersandionconcentrations

during

the20

06ndash2

007samplingcompleted

aspartof

thisstud

ymblsmetersbelow

land

surface

Geologic

form

ation

Hyd

rogeolog

icun

itOpen

interval

Well

Temp

pHNH4+

Ca2

+Mg2

+Na+

K+

Sr2+

Cl-

SO42-

HCO3-

Br-

F-

NO3-

NO2-

mbls

IDdegC

micromol

mmol

mmol

mmol

mmol

micromol

mmol

mmol

mmol

micromol

micromol

micromol

micromol

SDWWTP

Pleistocene

Biscayn

eAqu

ifer

Surface

S-EFF

290

67

112

51

03

07

30

430

197

6

Und

ifferentiated

Haw

thornOcala

Lim

estone

toAvo

nPark

Lim

estone

UFA

306ndash31

6BZ1

242

78

61

325

139

213

440

109

11

299ndash33

21U

236

81

61

324

142

224

456

117

01

299ndash32

03U

243

79

61

325

148

284

454

119

41

299ndash311

2U25

379

101

322

143

215

433

143

11

Avo

nPark

Lim

estone

APPZ

454ndash48

49U

238

77

604

1098

399

104

53

169

850

145

4ndash48

510

U24

877

675

1085

212

5112

53

174

451

045

1ndash47

513

U24

477

143

410

883

113

109

54

200

119

21

454ndash48

516

U23

277

439

49

943

7510

25

525

013

51

145

4ndash48

014

U25

075

497

36

662

6570

45

115

801

145

4ndash48

36U

251

75

823

35

872

3245

37

8151

11

MC2

501ndash51

02L

248

75

98

1614

84

147

194

42

305

750

148

1ndash50

7BZ2

241

76

176

511

121

3114

128

64

217

930

154

6ndash57

39L

231

76

311

4445

912

167

550

243

849

211

11

546ndash57

616

L22

975

411

4143

912

175

552

254

800

195

01

540ndash57

73L

241

75

410

4344

012

159

522

233

834

233

51

519ndash56

14L

245

75

711

4041

612

181

492

213

737

234

01

530ndash56

213

L24

275

108

1036

350

1217

446

024

377

531

32

154

6ndash57

610

L24

776

200

830

285

10111

369

233

588

773

054

6ndash57

612

L28

176

765

36

492

3654

45

8735

20

561ndash58

71L

234

75

411

6441

213

161

533

253

834

235

11

NDWWTP

Pleistocene

Biscayn

eAqu

ifer

surface

N-EFF

263

65

505

22

201

616

13

3610

3849

Avo

nPark

Lim

estone

UFA

354ndash38

5N-FA-1U

225

78

173

868

215

573

41

8118

00

135

1ndash38

4N-FA-2U

227

78

133

765

212

166

41

126

179

22

354ndash37

9N-FA-3U

212

79

163

766

213

362

31

115

32

135

4ndash37

9N-FA-4U

208

79

163

769

214

766

41

131

174

11

APPZ

430ndash46

0N-FA-3L

194

75

215

937

423

1121

638

017

365

153

71

243

0ndash46

1N-FA-1L

199

74

231

736

458

1110

038

620

383

942

21

143

0ndash46

0N-FA-4L

192

74

264

937

421

1122

337

119

369

546

32

143

1-45

9N-FA-2L

201

74

295

839

431

1212

538

322

374

848

62

1

Hydrogeology Journal DOI 101007s10040-009-0570-8

time of this study Wells designated as ldquoFPLrdquo were testswells installed into the Floridan aquifer system sim10 kmsouth from the SDWWTP (Dames and Moore 1975Florida Partners 2006) For comparison to the presentstudy the data from these sites were assumed to representambient water-quality concentrations as no injectionactivities had occurred at these sites Wells in this studythat exhibited little variation in the time series data andhad low NH3 concentrations were compared to the datafrom these other sites Although direct comparisons weredifficult due to the varying aquifer open intervals fromwhich these samples were collected some generalizationscan be made NH3 or NH4

+ concentrations from thesewells were below 29micromol Clminus concentrations increasedwith depth of the sampled intervals and were similar inconcentrations to wells in this study of approximately thesame aquifer interval NO3

minus concentrations were below1micromol similar to data collected for this study Based oncomparisons with water quality from these other sites therevised time series water-quality data that had mean NH3

concentrations below 30micromol were assumed to be ambientaquifer water with no influence of injectate All the wellsin the UFA at the SDWWTP were considered ambient andmost of the wells in the MC2 at the SDWWTP wereconsidered ambient with the exception of 10L 11L and12L All of the wells in the APPZ at the SDWWTP hadNH3 concentrations above ambient levels with well 9U thelowest Time series data at the NDWWTP indicated that allof the wells open to the UFAwere considered ambient andthe data from wells open to the APPZ were ambient prior tothe observed increase in NH3 concentrations

Ambient Clminus concentrations from this study showedbrackish transitional and saline zones in the Floridan

aquifer system for the SDWWTP and NDWWTP asdefined by Reese (1994) Although there were only twosample depths at the NDWWTP the top of the saline zoneat the north appears to be higher than at the SDWWTPMean temperatures at the NDWWTP were cooler than atthe SDWWTP with an average of 23degC for both intervalsThe NDWWTP lies closer to the Florida Straits and thecooler temperatures at that site may be due to closerproximity to open seawater Wells that showed a higherconcentration of NH3 at the SDWWTP showed highertemperatures (example Well 12L) whereas at theNDWWTP no change in temperature was noted withincreasing NH3 concentrations

Based on results of this study introduced nitrogen fromthe injectate into the Floridan Aquifer is mostly in theform of NH4

+ This is consistent with eH-pH diagrams fornitrogen (Stumm and Morgan 1996) where in most naturalenvironments any ammoniandashN would have the form ofNH4

+ (Hem 1985) No relationship was observed in thehistorical data or data collected as part of this study betweenNH3 and NO3

minus No change from ambient NO3minus concen-

trations was observed for wells that had elevated NH3

concentrations The reduced form of nitrogen (NH4+) was

not oxidized once introduced in the anoxic aquifer at eithersite and was conserved in the aquifer in this reduced stateAny introduced oxidized form of nitrogen (NO3

minus) from theinjectate that was reduced would result in insignificantchanges in NH4

+ concentrations as NO3minus concentrations

are two to three orders of magnitude less than NH4+ The

elevated concentrations of NH4+ in the Floridan aquifer at

the two sites are interpreted as the result of the upwardmigration of the injectate Once introduced into the aquiferNH4

+ appeared to have behaved conservatively

Fig 7 Ternary diagrams for the NDWWTP and the SDWWTP NH4+ Clndash and Brndash data collected from 2006ndash2007 were normalized to

100 Seawater and freshwater values (Hem 1985) were plotted Ambient water was grouped at the SDWWTP for the MC2 and UFAintervals Ambient MC2 data plot directly with seawater UFA ambient plots towards freshwater reflecting the fresher water quality in theUFA The injectate data plot at the NH4

+ end point indicating the freshwater quality but high NH4+ concentration of the injectate Well data

from the APPZ and MC2 intervals that have NH4+ concentrations above ambient levels plot in a line towards the injectate end point with

data from wells 6U and 12L plotting very close the NH4+ end point Data from the SDWWTP plot into distinct groups based on depth in the

aquifer but no line towards the injectate end point is seen

Hydrogeology Journal DOI 101007s10040-009-0570-8

At least two pathways of injectate were distinguishedbased on the analysis of the natural tracers at theSDWWTP One pathway at the SDWWTP appeared tohave rapid vertical pathways from the Boulder Zone up tothe APPZ with little mixing of ambient waters as itmigrated upward These vertical conduits did not appear

to extend up to the UFA This pathway is identified atwells 6U and 14U in the APPZ and well 12L in the MC2It may be present at well 8U in the APPZ however thedevelopment of cross connection in well 8U compromiseddata interpretation NH4

+ concentrations in these wellswere within the range of injectate NH4

+ concentrations

Fig 8 Graphs on the left areNH3Cl

minus mixing end-membermodels for the APPZ andMC2 intervals at theSDWWTP 6U 12L and 10Lare well identification codesArrows indicate increase intime Hatched red rectangleis injected freshwaterend-member indicating theseasonal range in concentra-tions Cyan square is theAPPZ brackish waterambientwater end-member blue circleis the MC2 saline waterend-member Graphs on theright are NH3 concentrationsover time Solid black lines areconcentrations from each wellsite red line is injected fresh-water concentrations Forwells 6U and 12L the dataplot towards the injectateend-member Little influenceis seen in well 6U from thesaline MC2 end-memberWell 10L shows a differentevolution of water qualitywith data plotting at the salineMC2 end-member and slowlyplotting towards the lower endof the injectate end-member

Fig 9 Graph a is the NH3Clminus mixing end-member model for the APPZ at the NDWWTP for pre-purge data (prior to 2003) for well N-

1L Arrows indicate increase in time Hatched red rectangle is injected freshwater end-member indicating the seasonal range inconcentrations Cyan square is the UFA brackish water ambient water end-member blue circle is the APPZ saline water end-member Thedata plot in separate groupings with the earliest time series plotting around the APPZ saline end-member The second data cluster plottowards the injectate end-member but no evolution towards the injectate end-member is seen as was seen for wells 6U and 12L at theSDWWTP Graph b is the post-purge data plotted for well N-1L Data plot with time back towards the APPZ saline end-member

Hydrogeology Journal DOI 101007s10040-009-0570-8

Clminus concentrations in these wells were also very close toinjectate Clminus concentrations

The mixing models for these wells show a mixingpathway almost directly towards the injectate end-mem-ber with no mixing from the lower MC2 interval observedfor wells 6U and 14U Wells that showed the highestconcentrations of NH3 at the SDWWTP also showedhigher temperatures with the temperature signal of thewarmer injectate observed in well 12L (mean temperatureof 28degC) in the data collected in 2006ndash2007 Well 12L inthe MC2 is much closer to the Boulder Zone than theAPPZ wells and higher injectate temperatures persist intothe MC2 Perhaps due to the longer travel times to theAPPZ the temperature signal was muted but still visible inthe APPZ Ion data for these wells showed freshening ofthe water quality These wells showed a density-drivenbuoyant rapid vertical advective pathway and transport ofthe injectate as a distinct water body with little mixing ofnative waters as it migrated upwards The rapid pathwayscould be the result of construction related events such asdrifting boreholes or the result of structural anomaliessuch as fracturing and karst features that would verticallyconnect aquifers and provide high hydraulic conductivitytransport pathways through confining units Migration ofsaline waters from the Lower to Upper Floridan Aquiferas a result of such structural anomalies have been reportedfor northeastern and central Florida (Flocks et al 2001Spechler 2001) where the Floridan aquifer system liesmuch closer to the surface Upward fluid migration ofinjected fluids in a Palm Beach County Florida deep wellinjection facility had been detected above the confiningzone between the injection zone and the overlayingmonitoring zone and this had been attributed to fractureddolostone comprising the majority of the confining zonestrata (Maliva et al 2007) however no fracturing of theconfining strata at either the NDWWTP or the SDWWTP

has been reported McNeill suggested that as wells locatedon the northwest side of the SDWWTP were cased abovethe DCU in the LFA this would be a possible cause of thebuoyant upward migration of injected fluids through themore permeable units above the DCU through isolatedvertical flow paths bypassing the MC2 (McNeill 20002002)

The second pathway was suggested by the grouping ofwell data observed in wells 15U 16U BZ2 10L and 11LThe well data from this group had no significantcorrelation between NH3 and Clminus The mixing modelsfor these well data showed a slow evolution of waterquality towards the lower average of the injectate end-member with time These wells showed a slight temper-ature increase but no clear temperature signal wasdistinguished in these wells Ion data did not show afreshening of the water quality with little difference seenbetween ambient ion concentrations and concentrationsfrom these wells Other studies (Boumlhlke et al 2006) haveindicated that NH3 transport can be retarded by a factor of3ndash6 in an aquifer with NH3 persisting in an aquifer afterthe more mobile constituents were flushed out if theaquifer remained under suboxic conditions At theSDWWTP it appears that there was still NH3 loadinginto the aquifer via rapid vertical pathways with increas-ing NH3 concentrations over time The data from this wellgrouping may indicate that once NH3 was introduced intoan aquifer interval it traveled horizontally at a muchslower rate with the freshwater injectate substantiallydiluted and not flushed out as freshwater continued tomigrate upwards

Four discrete injectate plumes were delineated at theSDWWTP based on the transport pathways The firstplume (plume 1 in Fig 10) located on the northeast of thesite was associated with the BZ-4 well which provided apathway up into the APPZ until it was plugged This

Table 4 Historical ambient Floridan Aquifer water quality data

Parameter Unit 1Ua WWFb WWFb FPLPW-3c

FPL testwelld

9Ua FPL testwell d

2La 3La FPL testwelld

299ndash332 m

260ndash305 m

260ndash308 m

314ndash380 m

340ndash410 m 454ndash484 m

456ndash517 m 501ndash510 m

530ndash562 m

639ndash701 m

pH 79 80 74 75 77 77 75 75 75 70HCO3

- mmol 00 32 27 33 21 30 26Ca2+ mmol 13 17 37 43 67 78 103 196Mg2+ mmol 27 28 73 101 155 160 434 555Na+ mmol 247 222 746 983 1582 1482 4382 4872K+ mmol 08 08 20 26 38 36 118 97Cl- mmol 223 705 271 821 1043 1794 1939 5216 5923SO4

2- mmol 41 75 69 03 69 47 137 42 226 307NO3

- micromol 03 08 02 02 02 03 02 48 02F- mmol 01 01 01 01 01 01 02 01Si mmol 05 04 02 05 03 03 02Sr2+ micromol 419 776 982 1849 1472 1586Total P micromol 32 71 65 65 32NH4

+ micromol 55 72 610 111 55NH3 micromol 08 294 123

a Data were collected for this study during 2006ndash2007 for wells at the SDWWTPbData from CH2M Hill 1998cData from Florida Partners 2006dData from Dames and Moore 1975

Hydrogeology Journal DOI 101007s10040-009-0570-8

plume slowly migrated to the surrounding areas mainlyvia diffusion as evidenced by slowly increasing NH3

concentrations but no change in Clminus concentrations Thesecond plume was located on the northwest corner of thesite in the APPZ (plume 2) This plume was detected inthe APPZ with no detection of it in the lower MC2indicating a direct pathway to the APPZ bypassing theMC2 This pathway seemed to persist with concentrationsof NH3 increasing with time similar to concentrationlevels of the injectate This plume was a chemicallydistinct water body with little mixing of native watersThe third plume located at well 14U (plume 3) may be adistinct plume but it may also be in connection withplume 2 No monitoring wells of the same interval as well14U are in the vicinity so the extent of this plume couldnot be determined The fourth plume was located on thesouth side of the site in the MC2 (plume 4) All fourplumes appeared to have the same initial transportmechanism up from the Boulder Zone through highhydraulic conductivity pathways with data from plumes2 3 and 4 indicating these pathways still persist

The data collected from the NDWWTP indicate differ-ent transport mechanisms than the SDWWTP Thetemperature signal of the warmer injectate was notobserved in wells with elevated concentrations of NH4

+Water quality showed no evolution towards the injectateplot in the ternary diagram The mixing model showedtwo mixing patterns one towards the injectate end-member before purging and one towards the ambientend-member once purging ceased As observed in the timeseries NH3 data NH3 concentrations were first observedto increase in well N-1L the well that was within 30 m ofthe uncased injection well and concentrations peaked at

341micromol well below the mean NH3 concentration of theinjectate Unlike the increasing NH3 concentrationsobserved at the SDWWTP that are the result of rapidvertical migration pathways once NH3 concentrations atthe NDWWTP peaked they have since decreased withtime All four NDWWTP lower wells have shown verysimilar water quality since 2004 when purging ceased atthe NDWWTP Both the time series analysis and the datacollected as part of this study in 2006 and 2007 appear toindicate a one-time pulse of injectate water into the APPZand this pulse of injectate was still migrating at the timeof this study through the aquifer in the direction ofregional flow There is no geochemical evidence of acontinuing source of NH3 at the NDWWTP however dueto retardation as discussed previously the NH3 plume mayhave persisted a long time in the suboxic aquifer (Boumlhlkeet al 2006)

Conclusions

Chloride bromide and ammonia were used to understandthe pathways and transport mechanisms of injectedwastewater into the deep saline Boulder Zone in theFloridan aquifer system The injectate source was treatedfreshwater with elevated levels of ammonia The waterquality of the injectate was chemically and physicallydistinct from ambient Floridan aquifer system water andthese distinctions were used to determine the possibletransport pathways At the SDWWTP four injectateplumes were identified along with two pathway mecha-nisms density-driven buoyant vertical flow and slowerhorizontal flow At the NDWWTP one plume was

Fig 10 Location of injectate plumes and their depth interval at the SDWWTP The source of the plume centered on the BZ well clusters(plume 1) was plugged in 1995 Plumes 2 3 and 4 are the result of continuing rapid vertical pathways up from the Boulder Zone Theextent of the plumes off site is not known as indicated by the question marks however based on data collected from the site approximateextent of the plumes on the site can be inferred The plume in the MC2 is limited to the southeast of the site The plume located in thenorthwest of the site is located in the APPZ and appears to have bypassed the MC2 The plume from the BZ well cluster appears to belimited to the east of the site The extent of the plume at 14U on site is unknown as there are no wells that monitor the same aquifer intervalin the vicinity of 14U

Hydrogeology Journal DOI 101007s10040-009-0570-8

identified and appeared to be a result of a one-time pulseinjection At the SDWWTP the injectate may first havemigrated upwards through discrete vertical pathways fromthe Boulder Zone to the Middle Confining Unit with thefreshwater injectate migrating upwards through salinewater as a chemically distinct water body The fourplumes identified at the SDWWTP appear to haveoriginated via this pathway Once introduced in the higheraquifer intervals the transport mechanism appeared to bea horizontal flow with mixing of ambient waters Therapid vertical pathways did not appear to extend up to theUFA At the NDWWTP the elevated levels of NH3 inthe lower Middle Confining Unit appeared to be the resultof a construction incident where a pulse of injectate waterbackflowed into an uncased injection well providing apathway to the upper interval Once introduced into theupper aquifer interval the plume slowly migrated with theregional flow within the aquifer No evidence of rapidvertical pathways was observed at the NDWWTP Duringthe course of this study it became clear that purging of thewells had unintended consequences for the SDWWTPCross connections developed in several wells between theupper and lower monitoring zones either during or afterpurging and these cross connections have compromisedwater-quality data in SDWWTP wells 5 6 7 8 11 12and 15 Although it could not be determined from thisstudy these cross connections may provide pathways ofinjectate into layers in the aquifer that had not beenpreviously affected by upward migrating injectate

Acknowledgements This study was funded by the Miami-DadeWater and Sewer Department (MDWASD) The authors greatlyappreciate S Villamil for her invaluable technical expertise andassistance in the field We thank C Powell S Kronheim W Pittand B Goldenberg of MDWASD for their cooperation and Drs ADausman and C Langevin of the US Geological Survey for theirinsightful comments during this research This report was signifi-cantly improved by the thoughtful review of two anonymousreviewers Dr Pricersquos contribution was partially funded by theNational Science Foundation Grant No DBI-0620409 This isSERC contribution 457

References

Arthur JD JB Cowart AA Dabous (2001) Florida Aquifer Storageand Recovery Geochemical Study Year Three Progress ReportOpen File Report 83 Florida Geological Survey TallahasseeFL

BCampECH2M Hill (1977) Drilling and testing of the test-injectionwell for the Miami-Dade Water and Sewer Authority ContractS-153 BCampECH2M Hill Gainesville FL

Bloetscher F Muniz A (2006) Preliminary modeling of class Iinjection wells in southeast Florida Ground Water ProtectionCouncil 2006 Annual Meeting Proceedings Miami FLNovember 2006

Bloetscher F Englehardt JD Chin DA Rose JB Tchobanoglous GAmy VP Gokgoz S (2005) Comparative assessment ofmunicipal wastewater disposal methods in southeast FloridaWater Environ Res 77480ndash490

Boumlhlke JK E Shinn C Reich A Tihansky (2003) Origins andisotopic characteristics of dissolved nitrogen species in groundwater imported domestic water and wastewater in the FloridaKeys US Geological Survey Greater Everglades Science

Program 2002 biennial report US Geol Surv Open-File Rep03-54

Boumlhlke JK Smith RL DN Miller (2006) Ammolonium transportand reaction in contaminated groundwater application ofisotope tracers and isotope fractionation studies Water ResourRes 42 W05411 doi1010292005WR004349

CH2M Hill (1981) Drilling and testing of the 8 injection wells andthe 3 monitoring wells for the South District Regional Waste-water Treatment Plant of the Mimi-Dade Water and SewerAuthority CH2M Hill Englewood CO

CH2M Hill (1998) Engineering report of the construction andtesting of the aquifer storage and recovery (ASR) system at theMDWASD West Wellfield CH2M Hill Englewood CO

Clark JF Bryant Hudson G Lee Davisson M Woodside GHerndon R (2004) Geochemical imaging of flow near anartificial recharge facility Orange County California GroundWater 42167ndash174

Corbett DR Kump L Dillon K Burnett W Chanton J (2000) Fateof wastewater-borne nutrients under low discharge conditions inthe subsurface of the Florida Keys USA Mar Geochem 6999ndash115

Dames and Moore Inc (1975) Floridan aquifer water supplyinvestigation Turkey point Area Miami-Dade County FloridaFlorida Power and Light Miami

Davis SN Whittemore DO Fabryka-Martin J (1998) Uses ofchloridebromide ratios in studies of potable water GroundWater 36338ndash350

Englehardt JD Amy VP Bloetscher F Chinn DA Fleming LEGokgoz S Solo-Gabriele H Rose JB Tchoaboglous G (2001)Comparative assessment of human and ecological impacts formunicipal wastewater disposal methods in southeast Floridadeep wells ocean outfalls and canal discharges University ofMiami Coral Gables FL

Fish JE Stewart M (1991) Hydrogeology of the surficial aquifersystem Dade County Florida US Geol Surv Water ResourInvest Rep 90-4108 50 pp

Flocks JG Kindinger JL Davis JB Swarzenski P (2001) Geo-physical investigations of upward migrating saline water from thelower to upper Floridan Aquifer Central Indian River RegionFlorida In US Geological Survey Karst Interest Group Proceed-ings US Geol Surv Water Resour Invest Rep 01-4011 pp 135ndash140

Florida Lakes Power Partners and Florida Power and LightCompany (2006) Well completion report for Floridan Aquiferwells PW-1 PW-2 and PW-4 FPL Turkey Point ExpansionProject (Unit 5) Homestead FL

Haberfeld JL (1991) Hydrogeology of effluent disposal zonesFloridan aquifer south Florida Ground Water 29186ndash190

Hem JD (1985) Study and interpretation of the chemicalcharacteristics of natural water US Geol Surv Water SupplPap 2254

Herczeg AL WM Edmunds (2000) Inorganic ions as tracers InCook PG Herczeg AL (eds) Environmental tracers in subsur-face hydrology Kluwer Norwell MA pp 31ndash78

Kaehler CA K Belitz (2003) Tracing reclaimed water in MenifeeWinchester and Perris-South ground-water subbasins RiversideCounty California US Geol Surv Water Resour Invest Rep03-4039

Kohout FA (1965) A hypothesis concerning cyclic flow of saltwater related to geothermal heating in the Floridan aquiferTrans NY Acad Sci Ser II 28249ndash271

Langmuir D (1997) Aqueous environmental geochemistry Prentice-Hall Upper Saddle River NJ

Maliva RG CW Walker (1998) Hydrogeology of deep-welldisposal of liquid wastes in southwestern Florida USAHydrogeol J 6(4)538ndash548

Maliva RG Guo W Missimer T (2007) Vertical migration ofmunicipal wastewater in deep injection well systems SouthFlorida USA Hydrogeol J 15(7)1387ndash1396

McNeill DF (2000) Final report a review of upward migration ofeffluent related to subsurface injection at Miami-Dade Waterand Sewer South District Plant McNeill Miami FL

Hydrogeology Journal DOI 101007s10040-009-0570-8

MARK A QUARLES PG PAGE 4 bull Metropolitan Knoxville Airport Authority ndash Knoxville Tennessee

Served as Project Manager for all environmental permitting and compliance activities Activities included spill prevention and response plan development stormwater plan development fuel tank farm design and compliance inspections

bull Various Industrial Clients ndash Tennessee Served as Project Manager for the development of SPCC Plans and SWPP Plans Plans were prepared consistent with the requirements of 40 CFR Part 112 the Tennessee General Permit the EPA Multi-Sector permit and the Tennessee Construction General Permit

Environmental Investigations and Remediation bull USEPA ndash Dickson County Tennessee

Served as Senior Geologist to investigate the occurrence of a cluster of cleft palate cleft lip birth defects in the county relative to the occurrence of trichloroethene in the groundwater and public water supply Reviewed EPA and TDEC regulatory files CDC and Department of Health reports interviewed City County TDEC and EPA officials and interpreted regional karst geologic and hydrogeologic data

bull Harpeth River Watershed Association ndash Franklin Tennessee Served as technical advisor for a review of the environmental investigation report and corrective action plan Contaminants of concern included free product toluene dissolved-phase BTEX constituents dissolved-phase acetone and dissolved-phase chlorinated solvents

bull Natural Resources Defense Council ndash Confidential Location Served as technical advisor for development of a Complaint for Declaratory and Injunctive Relief related to the inappropriate disposal investigation and cleanup of volatile organic compounds in soil groundwater and surface water

bull Confidential Client ndash McMinnville Tennessee Served as Project Manager to identify quantify and remediate the extent of a release of chlorinated solvents in a karst geologic setting Activities included the completion of an interim remedial action a soil gas survey direct push soil borings monitoring wells and well nests dye injection studies streambed sampling and a feasibility analysis

bull Burlington Northern Railroad - Birmingham Alabama Served as a Senior Geologist for an LNAPL investigation The investigation included the installation of temporary piezometers soil borings and permanent groundwater monitoring wells

bull Sunbeam Outdoor Products Inc - Neosho Missouri Developed a Field Sampling and Analysis Plan for the sampling of soils and drummed liquids for a Removal Action required by EPA Region VII Heavy metals and volatile organic compounds were the contaminants of concern in a karst geologic setting

bull United Technologies Automotive Inc - Quincy Michigan Served as Project Manager for groundwater well sampling and the development of an in-situ remedial action for heavy metal contamination

bull United Technologies Automotive Inc - Morganfield Kentucky Served as Project Engineer for a lagoon closure Completed activities for sludge characterization and quantification special waste permitting and closure design for material excavation and site restoration

Solid Waste Disposal bull Meriwether County Landfill Permit Appeal ndash Atlanta Georgia

Served as consultant to evaluate the technical merits of a municipal solid waste disposal permit that had been issued by the Georgia EPD Key technical issues were placement of the landfill adjacent to a public surface water supply typical liner performance and landfill leakage history in Georgia The permit was appealed to the Georgia Administrative Court

bull Various Secondary Aluminum Smelter Waste Landfills - Tennessee Reviewed secondary aluminum smelter waste characterization results landfill designs and associated hydrogeologic investigation reports for two proposed Class II industrial monofill landfill applications and reviewed groundwater monitoring reports associated with three co-mingled municipal solid waste landfills that used dross for intermediate daily cover

MARK A QUARLES PG PAGE 5 bull Various Industrial Landfills - Tennessee

Served as Project Manager for Subtitle D landfill siting and design projects Performed hydrogeologic investigations presented design waivers for site-specific design criteria (when applicable) and developed detailed designs for permitting

bull Various Landfills - Tennessee Served as Project Manager for the design permitting and operation of industrial and municipal solid waste landfills preparation of SWPP Plans quarterly groundwater and gas monitoring reports and hydrogeologic investigation reports

bull Various Municipal Landfills - Kentucky Served as Project Engineer for the design permitting and operation of municipal solid waste landfills

Stormwater Permitting and Compliance bull Tennessee Clean Water Network ndash Knoxville Tennessee

Served as lead consultant for providing technical comments for the draft Knox County Phase II Municipal Separate Storm Sewer System (MS4) permit

bull Various Industrial Clients - Throughout the US Served as Project Manager to obtain permit coverage through the EPA General Permit group permits and individual permits specific to each state Over 125 facilities were permitted

Hazardous Waste Management bull Various Industrial Clients ndash Throughout the US

Served as Project Manager for various projects to evaluate hazardous waste management practices consistent with the rules and regulations established under RCRA

bull Laidlaw Environmental Services Inc ndash Southeastern US Completed SWPP Plans for RCRA treatment storage and disposal facilities

Municipal Wastewater Management bull Various Municipalities ndash Fulton Cobb and Dekalb County Georgia

Served as Project Engineer for sewer modeling and point-source identification Identified sources of infiltration inflow and performed cost evaluations for source removal

bull Various Municipal and Industrial Clients ndash Tennessee Served as Project Engineer to establish beneficial reuse land application programs for wastewater sludge

bull Boston Water and Sewer Commission - Boston Massachusetts Served as Project Engineer for sewer modeling and point-source identification projects of combined and separate sewers up to 15 feet in diameter Identified sources of infiltration inflow and performed cost evaluations for source removal

bull Various Municipal Clients ndash Throughout the US Served as lead technical trainer for the implementation of proprietary software used for automated GIS mapping maintenance scheduling and hydraulic analyses of separate and combined sewers

bull City of Hopkinsville - Hopkinsville Kentucky Served as Project Engineer for water and sewer line expansions and wastewater treatment projects

TECHNICAL PUBLICATIONS AND LECTURES bull Quarles M and William Wilson ldquoUnconventional Natural Gas and its Risk A Tennessee

Perspectiverdquo Appalachian Public Interest Environmental Law Conference Knoxville Tennessee October 2011

bull Quarles M ldquoA Case Study in Karst Hydrogeology and Contaminant Fate and Transportrdquo National Groundwater Association 51st Annual Convention and Exposition December 1999

bull Quarles M and Allen P Lusby ldquoEnhanced Biodegradation of Kerosene-Affected Groundwater and Soilrdquo 1994 Annual Conference of the Academy of Hazardous Materials Managers October 1994

MARK A QUARLES PG PAGE 6 bull Quarles M ldquoNew Tank Performance Standardsrdquo Tennessee Environmental Law Letter July

1993 EXPERT LEGAL TESTIMONY bull Chesney versus Tennessee Valley Authority ndash 2011 US District Court Written testimony

associated with fly and bottom ash sampling waste characterization contaminant fate and transport and contaminant risks compared to US EPA screening levels drinking water standards fish and aquatic life standards and sediment cleanup standards

bull Busch et al versus Dr Carol Couch Atlanta Georgia 2008 State Administrative Court Written and verbal testimony regarding drought restrictive surface water and groundwater use Qualified by the court as an expert in geology hydrogeology and stormwater runoff

bull Darrel Segraves et al versus Dr Carol Couch Atlanta Georgia 2008 State Administrative Court Written and verbal testimony regarding appeal of a municipal solid waste landfill permit Qualified by the court as an expert in geology hydrogeology landfill design pertaining to landfill leakage and stormwater runoff

bull Tulane Environmental Law Clinic 2007 - 2008 Written testimony for numerous draft LDEQ permits and proposed rules

bull Republic of Ecuador and PetroEcuador vs Chevron Texaco Corporation and Texaco Petroleum Company US District Court Southern District of New York 2007 Written testimony regarding environmental investigation protocol

bull Friends of Tims Ford vs Tennessee Valley Authority and Tennessee Department of Environment and Conservation US District Court 2007 Written testimony in support of violations of State and Federal water quality standards reservoir carrying capacity standards and NEPA environmental assessment standards

bull Freddie Howell vs Creative Customs Atlanta Georgia 2007 Technical support regarding litigation associated with stormwater and groundwater flow and their effects on the Howell property

bull Aguida vs ChevronTexaco Lago Agrio Ecuador Court 2006 Written testimony regarding Texacorsquos waste management and standard operating practices in the Ecuadorian concession area relative to industry standards

TRAINING Current Wetland Issues in Tennessee (2007) Professional Liability Education - Contract Review and Revision (2000) Professional Liability Education ndash Mid-Town Developer Case Study Workshop (1999) Professional Liability Education ndash Liability IQ for Environmental Consultants (1998) Liquid Animal Waste Management System Design to NRCS Standards for CAFO (1998) 8-Hour OSHA Health and Safety Refresher Training Hazardous Materials Waste Manager Course University of Alabama (1993) 40-Hour OSHA Health and Safety Training (1990) CONTACT INFORMATION Home telephone 615-352-0471 Mobile telephone 615-504-0956 Email markquarlescomcastnet

Determination of vertical and horizontal pathways of injected freshwastewater into a deep saline aquifer (Florida USA) using naturalchemical tracers

Virginia Walsh amp Reneacute M Price

Abstract Two deep-well injection sites in south FloridaUSA inject an average of 430 million liters per day(MLD) of treated domestic fresh wastewater into a deepsaline aquifer 900m below land surface Elevated levels ofNH3 (highest concentration 939micromol) in the overlyingaquifer above ambient concentrations (concentration lessthan 30micromol) were evidence of the upward migration ofinjected fluids Three pathways were distinguished basedon ammonium chloride and bromide ratios and temper-ature At the South District Wastewater Treatment Plantthe tracer ratios showed that the injectate remainedchemically distinct as it migrated upwards through rapidvertical pathways via density-driven buoyancy Thewarmer injectate (mean 28degC) retained the temperaturesignal as it vertically migrated upwards however thetemperature signal did not persist as the injectate movedhorizontally into the overlying aquifers Once introducedthe injectate moved slowly horizontally through theaquifer and mixed with ambient water At the NorthDistrict Wastewater Treatment Plant data provide strongevidence of a one-time pulse of injectate into theoverlying aquifers due to improper well construction Noevidence of rapid vertical pathways was observed at theNorth District Wastewater Treatment Plant

Keywords Waste disposal Deep well injection Carbonate rocks Confining units Ammonia Temperature USA

Introduction

Deep well injection of treated municipal wastewater intonon-potable aquifers has been used as an alternative todischarge of wastewater to surface waters for manydecades There are 430 permitted municipal wastewaterdeep injection wells in the United States with 163 inFlorida alone (USEPA 2008) These deep aquifers tend tobe saline and the discharge of fresh wastewater into themhas raised concerns of geochemical reactions as a result ofthe mixing of the two waters as well as the buoyanttransport of the wastewater upwards into overlyingaquifers Confined brackish aquifers in Florida have beenused extensively for aquifer storage and recovery (ASR)of potable freshwater (Arthur et al 2001 Renken et al2005) and deeper saline aquifers have been used fordisposal of waste fluids such as oil brines industrial waterand municipal wastewater (Meyer 1989a Meyer 1989b)ASR in Florida has been extensively studied as part of theComprehensive Everglades Restoration Plan (Reese 2002Mirecki 2004 Mirecki 2006) however little research hasbeen published regarding the fate and transport of thetreated wastewater into deep saline aquifers (Meyer1989a Haberfeld 1991 Maliva and Walker 1998Bloetscher et al 2005 Bloetscher and Muniz 2006Maliva et al 2007)

Miami-Dade County Water and Sewer Department(MDWASD) located in southern Florida currently dis-charges 430 million liters per day (MLD) of treateddomestic wastewater into a saline deep aquifer at twolocations in the county Deep well injection has been inuse in Miami-Dade County since the late 1960s Theinjection facilities are located in the north and south of thecounty separated by 44 km (Fig 1) The South DistrictWastewater Treatment Plant (SDWWTP) site was placedinto service in 1983 and is currently permitted for thedisposal of 367 MLD of treated wastewater The NorthDistrict Wastewater Treatment Plant (NDWWTP) site wasplaced into service in 1997 and is permitted for 90 MLD

Received 2 February 2009 Accepted 14 December 2009

copy Springer-Verlag 2010

V Walsh ())Miami-Dade Water and Sewer Department3071 SW 38th Ave Miami FL 33146 USAe-mail walshvmiamidadegov

V WalshDepartment of Earth and EnvironmentFlorida International University11200 SW 8th Street University Park Miami 33199 USA

R M PriceDepartment of Earth and Environment and SoutheastEnvironmental Research CenterFlorida International University11200 SW 8th Street University Park Miami 33199 USA

Hydrogeology Journal DOI 101007s10040-009-0570-8

Both facilities treat domestic wastewater to above second-ary drinking water standards and discharge the treatedwastewater into United States Environmental ProtectionAgency (USEPA) Class I injection wells The treatedwastewater is injected into the Boulder Zone a highlytransmissive interval in the deep saline non-potable LowerFloridan Aquifer The Boulder Zone has been thought to behydrologically separated from overlying aquifers by a335-m-thick confining unit During the installation of addi-tional monitoring wells at the SDWWTP in 1994 ammonia-nitrogen (NH3-N) was detected at 442 m depth in theoverlying aquifer at a concentration of 411 micromoles perliter (micromol) above reported background levels of 29micromol

(BCampECH2M Hill 1977) The detection of NH3ndashN in theaquifers above the Boulder Zone has raised doubts regardingthe efficacy of the confining unit and the resultant waterquality impact to overlying aquifers as these aquifers areused as alternative water supplies via storage of freshwater(ASR) and blending with potable surficial aquifer water

Research has focused on ASR in south Florida (Arthuret al 2001 Reese 2002 Mirecki 2004 Mirecki 2006Reese and Richardson 2008) however few studies havebeen conducted regarding the transport and fate of injectedeffluent into the Boulder Zone and typically these had todo with the relative risk of deep well injection versusocean outfall disposal of municipal waste (Englehardt et

Fig 1 Location of theNDWWTP and the SDWWTPstudy sites

Hydrogeology Journal DOI 101007s10040-009-0570-8

al 2001 USEPA 2003 Bloetscher et al 2005 Bloetscherand Muniz 2006) Recently researchers have studied thetransport mechanisms of the observed migrated injectateand have suggested density-driven buoyant transportmechanism along natural or anthropogenic vertical frac-tures in the lower aquifers (Maliva and Walker 1998McNeill 2000 McNeill 2002 Maliva et al 2007 Walshand Price 2008) The objective of this study was todetermine migration pathways of injected treated waste-water at two facilities in Miami-Dade County Florida(SDWWTP and NDWWTP) using historical time seriesdata and major ion data collected as part of this study Themethodology developed for this study used chloride (Clminus)bromide (Brminus) and NH3 as tracers This methodologyprovided a method for estimating transport pathways andinvolved no additional collection of data other than whatwas typically required under federal and state regulatoryprograms

Natural inorganic tracers have been used extensively inwater resources investigations to trace groundwater flowpaths and calculate mixed water ratios (Langmuir 1997Davis et al 1998 Herczeg and Edmunds 2000) Clminus andBrminus commonly are used as they tend to be conservativeand their ratios may also give information as to the sourceand pathways of water Studies have been conducted insouth Florida (Shinn et al 1994 Paul et al 1997 Corbettet al 2000 Boumlhlke et al 2003) and elsewhere (Kaehlerand Belitz 2003 Clark et al 2004) tracing treatedwastewater in surficial aquifers but NH3 was not used asa tracer as it does not behave conservatively in oxicwaters In this study a novel application of Clminus Brminus andNH3 as conservative tracers of injectate was developed aspart of mixing models to distinguish pathways betweenthe deep aquifers Clminus is a natural anion in the Floridanaquifer system and its principal source is seawater asthere are no evaporite minerals to provide an additionalsource (Sprinkle 1989 Reese 1994) The seawater sourceof Clminus in south Florida is thought to be the result of eitherincomplete flushing of Pleistocene seawater and brackishwater intrusion andor the result of the cyclic flow basedon thermal upwelling of Holocene intruded seawater(Kohout 1965 Sprinkle 1989 Reese 1994) Bromide(Brminus) behaves similar to Clminus in groundwater systems(Davis et al 1998) and in south Florida the source of Brminus

in groundwater is similar to that of Clminus although its naturalabundances are orders of magnitude less than Clminus Theonly source of the NH3 is the injectate and therefore itwas used to trace transport pathways of the injectedwastewater

Geologic and hydrogeologic framework

The Floridan aquifer system (FAS) in southeastern Floridais defined by a vertically continuous sequence of per-meable carbonate rocks of Cenozoic age that are hydrauli-cally connected in varying degrees (Miller 1986) Theaquifer matrix consists of carbonate and dolomitic lime-stones dating from the Paleocene to the Oligocene

epochs Overlying the FAS are the impermeable sedimentsof the late Oligocene to Pliocene age Hawthorn Group a180-m-thick confining layer of clays siltstones and siltylimestones The Hawthorn Group separates the UpperFloridan Aquifer from the late Pliocene and Pleistoceneformations making up the Surficial Aquifer System whichincludes the Biscayne Aquifer in south Florida (Fig 2)The Biscayne Aquifer is an unconfined surficial aquiferand is the major source of potable water in south Florida(Fish and Stewart 1991)

The Floridan Aquifer contains several highly perme-able and less permeable zones with zones of highestpermeabilities typically occurring at or near unconform-ities and usually parallel to the bedding planes (Meyer1989a) Previous studies (Miller 1986 Reese 1994)grouped the Floridan aquifer system into three hydro-stratigraphic units (Fig 2) the Upper Floridan Aquifer(UFA) the Middle Confining Unit (MCU) and the LowerFloridan Aquifer Recently the MCU in south Florida hasbeen divided into the MC1 and MC2 (Fig 2) separatedby the Avon Park permeable layer (Reese and Richardson2008) which in south Florida had previously beenidentified as the Middle Floridan Aquifer The UpperFloridan Aquifer contains relatively fresh water less than10000 mg Lminus1 total dissolved solids (TDS) The LowerFloridan Aquifer consists of seminconfining or leakymicritic limestone and dolomite layers that containgroundwater with compositions approaching seawater(approximately 30000 mg Lminus1 TDS) A dolomite confin-ing unit (DCU) a thin confining unit below the MC2 wascharacterized at the study site by McNeill (McNeill 20002002) This DCU lies above the permeable zone com-monly known as the Boulder Zone within the OldsmarFormation of the Lower Floridan Aquifer The FASoutcrops along the Straits of Florida providing a hydraulicconnection to the sea (Kohout 1965 Miller 1986 Reese1994) Transmissivities in the Upper Florida Aquiferrange from 929 to 23times104m2 dayminus1 (Meyer 1989a Reese1994) while transmissivities in the Boulder Zone rangefrom 297times105m2 dayminus1 to 232times106m2 dayminus1

Site descriptionsThe NDWWTP and the SDWWTP consist of deepinjection wells that penetrate down to approximately855 m The upper 755 m of each well is cased to the topof the Boulder Zone The bottom 100 m of each injectionwell is an open hole in the Boulder Zone Nine suchinjection wells and three multi-zoned and dual-zonedmonitoring wells were constructed between 1977 and1981 at the SDWWTP (Fig 3) The multi-zone test wellBZ cluster (BZ-1 through 4) was constructed in 1977 andconsisted of four telescoping monitoring wells the deepestof which was BZ-4 cased to the top of the Boulder Zonethe shallowest BZ-1 open to the UFA at a depth of 312 mThe remaining monitoring wells were constructed bothat the SDWWTP and NDWWTP using a dual zone designwith an inner steel casing drilled to the deeper intervaland the outer steel casing open to the upper interval For

Hydrogeology Journal DOI 101007s10040-009-0570-8

this report well nomenclature indicates the open intervalof the dual-casing ldquoUrdquo represents the upper monitoringinterval and ldquoLrdquo represents the lower monitoring intervalWells 1 and 2 were dual-cased to monitor water quality inthe UFA (sim300 m) and the lower confining units (sim550 mCH2MHill 1981) In 1994 NH3 was detected aboveambient levels in the confining unit at the BZ well cluster(BZ-2 depth 488 m) and subsequent investigations by theutility found a leak due to corrosion of the casing in thiscluster (MDWASD 1995) The lower three monitoringintervals of the BZ well cluster were plugged in 1995 tostop the upward migration of injectate through the casinghole and the confining unit (488 m) monitoring intervalwas redrilled From 1995ndash1996 nine injection wells and

thirteen dual-zoned monitoring wells were constructed onthe SDWWTP These monitoring wells were cased to theAvon Park Permeable zone (APPZ) and the MC2 withopen holes in the formations approximately 30 m Duringthe construction of the monitoring wells NH3 concen-trations above ambient levels were found throughout thesite Elevated NH3 concentrations were found in thenorthwest corner of the site in the MC1 interval in severalwells but not in the lower MC2 interval of these wellsElevated levels were found in the MC2 interval in thesouth side of the site As a result of the detected NH3 inthe confining units the EPA required purging of the wellsthat showed elevated concentrations NH3 (Starr et al2001) in an attempt to remove the NH3 loading in the

Fig 2 Geologic and hydrogeologic framework of NDWWTP and the SDWWTP modified from Reese and Richardson 2008 Welldiagram on the right shows the number of wells open to the indicated hydrogeologic unit used for this study

Fig 3 Well locations at theSDWWTP

Hydrogeology Journal DOI 101007s10040-009-0570-8

impacted intervals Discontinuous purging of approxi-mately 2100 Lmin commenced from 1997 to 2000 forthe northwest wells (5U 6U 7U 8U 15U and 16U) of theAPPZ interval and the south wells (11L and 12L) of theMC2 (MDWASD 2000)

Injection well construction started at the NDWWTP in1996 Four injection wells were constructed into theBoulder Zone and four dual-zoned monitoring wells wereconstructed to the UFA and the APPZ intervals (Fig 4) In1996 effluent was injected in two completed injectionwells while one injection well was still under constructionresulting in injectate backflowing into an open borehole atan uncased injection well for 5 days Several months afterthe construction of the wells had been completed NH3

concentrations were observed to increase in the APPZinterval of the monitoring wells on site The utility wasrequired to purge the APPZ interval wells for a period of1 year from 2003ndash2004 (MDWASD 2005)

Methodology

Historical data were collected and checked for qualityassurance for the NDWWTP and SDWWTP Data wereavailable from 1983 through 2007 for the SDWWTP and1996ndash2007 for the NDWTP Data studied as part of thisresearch included pressure temperature pH Clminus sulfate(SO4

2minus) NH3 and nitrate (NO3minus) The historical data were

compiled from the utility monthly operating reportsavailable sporadically from 1983 Non-detects that hadbeen entered as a zero value were updated to the detectionlevel of the parameter Summary statistics including meanmedian standard deviation maximum and minimum wereapplied to each of the wellsrsquo time series data to assesswater-quality changes over time and used to compare toambient water quality data at other locations in southFlorida Most water quality for the Floridan Aquifer insouth Florida had been collected as regulatory require-ments which usually included chemical analyses that areused for drinking water quality and therefore did notinclude major ion data Residence time in the Floridan

aquifer system in south Florida is on the order of thousandsof years (Meyer 1989a) and it was assumed that due to thedepth of the aquifer water quality was in equilibrium andthere would be no other cause of perturbations to ambientwater quality other than migration of injectate Time seriesdata that showed large variation over time would indicatenon-equilibrium conditions and therefore not ambientconditions Abrupt changes in water quality and pressurewere observed in the time series data in wells that werepurged in 1997 These changes were not observed in wellsthat were not purged These changes in water quality andpressure were interpreted as being the result of crossconnections developed in the dual zone casings of some ofthe purged wells and review of borehole videos of thesewells taken in 2004 confirmed holes in the casings of thesewells It could not be determined which interval the datacollected from these wells represented after the crossconnections developed therefore data were discardedfrom the historical series analysis based on the month itwas ascertained the cross connection developed and thesummary statistics were recalculated for these wells

Floridan Aquifer water samples were collected at theNDWWTP and SDWWTP during 2006 and 2007 as partof this study for major ions and nitrogen species Thirty-two monitoring wells were sampled at the SDWWTP andwater-quality samples were collected from these wellsfrom the UFA the APPZ and the MC2 At theNDWWTP samples were collected from four monitoringwells representing the UFA and four wells in the APPZTemperature pH dissolved oxygen and conductancewere taken from water samples in the field using an YSI556 MPS The YSI instrument was calibrated per themanufacturerrsquos instructions prior to each sampling eventAll wells were purged for at least 24 h prior to sampling toensure at least three well volumes were evacuated Thewells were sampled through a closed system using a lowflow cell and tygon tubing through a disposable highcapacity 045micromol in-line filter Water samples wereanalyzed for the anions Brminus Clminus Fminus NO3

minus NO2minus and

SO42minus on a DIONEX ion chromatography system

HCO3minus and CO2

minus were analyzed via manual titrationNH3 was analyzed on a LACHAT analyzer 800 withNH4

+ then calculated based on pH and temperature ofthe sample using the NH3 result (Stumm and Morgan1996) Cations (Ca2+ Mg2+ K+ Na+ and Sr2+) wereanalyzed by inductively coupled plasma (ICP)

Results

The mean historical data are summarized in Table 1 forthe SDWWTP and Table 2 for the NDWWTP Dissolvedoxygen NO3

minus and NO2minus had similar results for both the

SDWWTP and NDWWTP sites for the aquifer intervalsNO3

minus concentrations were either detected at very lowconcentrations or below detectable levels NO2

minus levelswere below 1 micromoleL (micromol) for all aquifer intervalsand in the injectate at the NDWWTP and SDWWTP sitesfor the historical time series The injectate had a mean valueFig 4 Well locations at the NDWWTP

Hydrogeology Journal DOI 101007s10040-009-0570-8

Tab

le1

Meanvalues

forhistorical

timeseriesSDWWTP

mblsmetersbelow

land

surface

Geologicform

ation

Hyd

rostratig

raph

icform

ation

WellID

Open

interval

Periodof

record

Tem

pdegC

pHNH3micromol

Clndashmmol

SO42ndashmmol

NO3ndashmicromol

mbls

Pleistocene

Biscayn

eAqu

ifer

Injectate

(S-EFF)

Surface

591

ndash1207

277

66

889

203

109

Und

ifferentiated

Haw

thornAvo

nParkLim

estone

Upp

erFloridan

Aqu

ifer

(UFA

)1U

299ndash

332

983

ndash1207

240

79

1221

32

02

2U29

9ndash311

783

ndash1207

244

79

1321

32

03

3U29

9ndash32

0291

ndash1207

243

79

1023

32

03

BZ1

306ndash

316

783

ndash1207

242

76

1222

31

02

Avo

nPark

Lim

estone

Avo

nParkPermeable

Zon

e(A

PPZ)

13U

451ndash

475

296

ndash1207

239

77

6210

848

03

5U45

4ndash48

4594

ndash1102

241

76

492

108

49

03

6U45

4ndash48

3594

ndash1207

241

76

545

7630

03

7U45

4ndash48

2694

ndash198

245

74

526

738U

454ndash

480

894

ndash602

240

77

216

106

41

02

9U45

4ndash48

4195

ndash1207

239

77

64111

43

02

10U

454ndash

485

296

ndash1207

240

76

3510

542

02

11U

454ndash

484

296

ndash1207

240

76

118

106

43

02

14U

454ndash

480

296

ndash1207

239

74

320

9943

02

15U

454ndash

480

296

ndash1207

231

75

296

106

53

03

16U

454ndash

485

296

ndash1207

231

76

330

109

48

02

12U

456ndash

487

296

ndash204

249

76

100

111

42

02

MiddleCon

fining

Unit(M

C2)

BZ2

481ndash

507

783

ndash1207

254

75

106

133

56

02

2L50

1ndash51

0783

ndash1207

243

74

1219

926

02

4L51

9ndash56

112

91ndash

1207

240

73

1251

019

304

13L

530ndash

562

296

ndash1207

237

75

5550

822

809

3L54

0ndash57

7191

ndash1207

240

73

752

921

910

5L54

6ndash57

6594

ndash1102

239

74

652

821

604

6L54

6ndash57

6594

ndash1005

237

74

3052

622

703

7L55

0ndash57

1694

ndash198

242

71

1053

68L

546ndash

576

894

ndash602

237

74

554

124

804

9L54

6ndash57

3195

ndash1207

234

74

553

422

604

10L

546ndash

576

396

ndash1207

238

76

141

429

204

05

11L

546ndash

576

296

ndash1199

238

76

417

193

93

02

12L

546ndash

576

296

ndash1207

254

74

676

5730

03

15L

546ndash

576

296

ndash104

231

75

1253

125

204

16L

546ndash

576

296

ndash1207

229

74

653

221

904

1L56

1ndash58

7783

ndash1207

238

73

653

923

904

Oldsm

arFormation

Bou

lder

Zon

eLow

erFloridan

Aqu

ifer

BZ4

853

0783ndash894

249

72

634

3

Hydrogeology Journal DOI 101007s10040-009-0570-8

of NO3minus of 379micromol at the NDWWTP and 109micromol

at the SDWWTP for the historical time series Dissolvedoxygen was detected at concentrations less than 10 mg Lminus1

for all aquifer intervals Dissolved oxygen concentrationsfor the injectate at both the NDWWTP and the SDWWTPhad results above 3 mg Lminus1

Historical time series results SDWWTPThe historical period of record data for the freshwaterinjectate samples from the SDWWTP (identified as S-EFF) were available from 1991 through 2007 (Table 1)Temperature ranged from 218 to 311degC with a mean of277degC Mean pH in the historical time series was 66NH3 ranged from 1468ndash18496micromol with a mean of889micromol NH3 varied seasonally and increased with time(Fig 5) Clminus concentrations averaged 2 millimolesL(mmol) with a very small range and standard deviationindicative of the freshwater source of the injectateHistorical data from the SDWWTP for the UFA (wellsBZ1 1U 2U and 3U) were available from 1983 through2007 Temperature averaged 24degC with no significantdifference observed between the wells The range of pHwas from 76 to 82 in the UFA Chloride averagedbetween 21 and 23 mmol while NH3 means rangedbetween 10 and 13micromol The summary statistics for thewater-quality samples collected from the UFA showedconsistent values with no discernable variation over timeHistorical data from wells open to the APPZ at theSDWWTP (wells 5U 6U 7U 8U 9U 10U 11U 12U13U 14U 15U 16U) were available from 1994 through2007 Mean temperatures ranged between 231 and249degC in these wells There was little variation observedin the pH in the APPZ samples but the mean pH of 76was lower than the mean pH in the UFA Almost all of thewells showed variation in NH3 concentrations over timeMean values of NH3 in these wells ranged from 35micromolin well 10U to 545micromol in well 6U Well 6U showed anincreasing trend with time in NH3 that was observed to besimilar to the increasing trend of NH3 in the injectate(Fig 5) The spread between the 5th and 95th percentilewas the greatest in wells 6U and 12U Only wells 9U10U and 13U showed little variation in NH3 over timeMean concentrations of Cl- in wells 6U and 7U were 76and 73 mmol Wells in the MC2 were open to intervalsvarying in depth from 481 to 551 m Mean temperaturevalues ranged from 229 to 242degC in all wells with theexception of a mean value of 254degC in wells BZ2 and12L Mean pH values ranged from 73 to 76 Mean NH3

concentrations showed two groupings Wells BZ2 10L11L and 12L exhibited concentrations of 106 141 417and 676micromol respectively The remainder of the wellsexhibited mean NH3 concentrations of less than 55micromolClminus concentrations for wells 10L 11L and 12L were 429193 and 57 mmol respectively the remainder of the wellshad mean concentrations greater than 508 mmol (excep-tion is BZ-2 whose Clminus concentration of 133 mmolreflects the shallower depth of this well with the openinterval in the lower brackish water zone of the FloridanT

able

2Meanvalues

forhistorical

timeseriesNDWWTP

mblsmetersbelow

land

surface

Geologic

form

ation

Hyd

rostratig

raph

icform

ation

WellID

Open

interval

Period

ofrecord

Tem

ppH

NH3

Cl-

SO42-

NO3-

Revised

period

ofrecord

a

Tem

ppH

NH3

Cl-

SO42-

mbls

degCmicromol

mmol

mmol

micromol

degCmicromol

mmol

mmol

Pleistocene

Biscayn

eAqu

ifer

Injectate

(N-EFF)

Surface

797

ndash1207

284

65

8193

200

05

379

Avo

nPark

Lim

estone

Eocene

Upp

erFloridan

Aqu

ifer

(UFA

)N-1U

354ndash38

5197

ndash1207

231

76

188

737

35

02

N-2U

351ndash38

4396

ndash1207

230

78

177

662

36

21

N-3U

354ndash37

9396

ndash1207

229

78

173

658

36

20

N-4U

354ndash37

9496

ndash1207

231

76

181

684

35

08

Avo

nPark

Permeable

Zon

e(A

PPZ)

N-1L

430ndash46

1496

ndash1207

219

73

2612

3682

328

10

3496ndash797

224

72

193

4617

N-2L

431-

459

396

ndash1207

223

76

1684

3979

156

22

396

ndash898

229

78

177

4557

166

N-3L

430ndash46

0396

ndash1207

222

76

1314

4094

158

10

396

ndash1298

230

77

191

4548

149

N-4L

430ndash46

0496

ndash1207

224

72

1903

3804

152

16

496

ndash1298

223

75

237

4405

Hydrogeology Journal DOI 101007s10040-009-0570-8

Aquifer) Data collected from well 12L were similar todata collected for wells for 6U and 7U These wells hadhigh NH3 concentrations with low Clminus and SO4

minus concen-trations Historical data were available for the BoulderZone interval (well BZ4) from 1983 through 1994 Themean pH and temperature values were 72 and 249degCrespectively Mean NH3 concentration was 634micromol andshowed apparent seasonal variation and increasing trendover time and was similar to the injectate historical timeseries (Fig 5) The mean Clminus concentration was 3 mmolsimilar to the mean Clminus concentration of 2 mmol for theinjectate

Historical time series results NDWWTPThe historical period of record data for freshwaterinjectate samples (N-Eff) at the NDWWTP were availablefrom 2002 through 2007 Temperature ranged from 22 to34degC with a mean of 28degC The mean pH was similar tothe SDWWTP injecate at 65 NH3 ranged from 210ndash3764micromol with a mean of 819micromol and a large standarddeviation indicative of the apparent seasonality similar tothe SDWWTP Clminus concentrations ranged from 08 mmolto 1131 mmol with a mean 20 mmol slightly higher thanthe mean concentration of the SDWWTP injectateHistorical data were available from 1996 through 2007for wells open to the UFA (N-1U N-2U N-3U and N-4U) Mean temperature averaged 23degC in these wellswith no significant difference observed between the wellsMean values of pH ranged from 76 to 78 Clminus meanconcentrations ranged between 662 and 737 mmolsNH3 mean concentrations ranged between 17 to 18micromolConcentrations for the UFAwater-quality samples for theNDWWTP showed consistent values with no discernablevariation over time Historical data were available from1996 through 2007 for wells open to the APPZ (N-1L N-2L N-3L and N-4L) Temperature mean values were

22degC Analysis of historical NH3 data indicates increasingconcentrations of NH3 starting in late 1997 (Fig 6) NH3

concentrations appeared to have reached a peak concen-tration of 408micromol in well N-1L in July 2001 andsteadily declined thereafter to concentrations rangingfrom 200 to 250micromol Wells N-2L N-3L and N-4L showsimilar patterns as well N-1L but with lowered anddelayed peak concentration values NH3 concentrationsare observed to increase scatter after 2003 whichcorresponds to when purging commenced at theNDWWTP Once purging ceased in 2004 NH3 concen-trations in wells varied between 150ndash300micromol The Clminus

mean concentrations ranged from 368 to 409 mmol Clminus

in these wells exhibited variation over time and analysisof the time series indicated that as NH3 concentrationsincreased Clminus concentrations decreased (Fig 6) The timeseries data for the lower wells were revised to removedata after NH3 concentrations were observed to increasein each well in order to determine ambient concentrationsin the APPZ Revised NH3 mean concentrations rangedfrom 18ndash24micromol Clminus mean concentrations ranged from441ndash461 Very little variation was observed in NH3 andClminus mean concentrations after the time series data wereremoved

Major ion data collection resultsMajor ions were collected for this study from 2006ndash2007(Table 3) Data from wells at the SDWWTP site thatexhibited cross connections were removed from thisanalysis Data collected from the SDWWTP UFAexhibited very little variation between wells and weresimilar to the historical time-series data with low cationand anion concentrations For the APPZ wells NH4

+

mean concentrations could be combined into three groupswells 9U 10U and 13U with NH4

+ mean concentrationsof 60 67 and 143micromol respectively wells 14U and 16Uwith 497 and 439micromol and well 6U 823micromol Cation andanion mean concentrations showed a similar grouping asthe NH4

+ concentration grouping with well 6U consis-tently grouping independently and with increasing NH4

+

concentrations correlating to decreasing ion concentra-tions The MC2 mean NH4

+ concentrations could also becombined into three groups well 12L at a mean NH4

+

concentration of 765micromol wells BZ-2 10L and 13LNH4

+ at mean concentrations 176 200 and 108micromolrespectively the remainder wells at NH4

+ concentrationsbelow 10micromol Cation and anion concentrations could becombined in the same 3 groups as the NH4

+ groups withlower ion mean concentrations observed for BZ-2 10Land 13L and much lower ion concentrations observed inwell 12L As with well 6U in the MC1 well 12L in theMC2 consistently grouped independently

The NDWWTP wells open to the UFA (351ndash385 m)exhibited very little variation in field measurements andmean concentrations between wells and were similar tothe historical time series The interval (430ndash461 m) in theAPPZ at the NDWWTP also showed little variation withmean NH4

+ concentrations (215ndash295micromol) and mean

Fig 5 Time series NH3 data from the injectate (black circle) BZ-4(green triangle) and well 6U (red circle) at the SDWWTP site Theapparent seasonal variation observed in the injectate is a result ofincreased flows during the wet season and storm events Theincreasing trends with time correlate to increased injection over timedue to growth in population in Miami-Dade County

Hydrogeology Journal DOI 101007s10040-009-0570-8

concentrations of Clminus (371ndash386 mmol) varying littlebetween wells

Ternary diagramThe typical ClminusBrminus ratio for seawater is about 290 (Daviset al 1998) and most of the ClminusBrminus ratios at both siteswere within that range with no discernable differencesQuite often the addition of a third water-quality membercould enhance the understanding of the data and this wasthe case with using NH4

+ as the third end-member NH4+

Clminus and Brminus data were plotted on a ternary diagram withdata normalized to 100 Typical seawater and freshwaterNH4

+ Clminus and Brminus values after Hem (1985) were alsoplotted for comparison Water quality at the NDWWTPclustered into three distinct groups with two groups basedon depth of the interval sampled and the third the injectate(Fig 7) The ambient aquifer data plot close to seawaterThe injectate data plotted off in the lower left hand cornerdue to the large NH4

+ concentrations At the SDWWTPthree aquifer groupings were observed Ambient well datafrom the MC2 plotted similar to seawater Ambient welldata from the UFA plotted slightly towards freshwaterData from wells that showed elevated NH4

+ plotted in aline towards the injectate with groundwater data from 6Uand 12L plotting very close to the injectate This linerepresents the evolution of the water quality of these wellstowards the injectate water quality and does not show anyevolution of more saline water into the higher intervals inthe aquifer

Mixing end-member modelsEnd-member mixing models of wells 6U 12L and 10Lrepresented the results obtained for all wells at the

SDWWTP (Fig 8) Well 6U and 12L showed theprogressive freshening of water and increasing NH3

concentrations towards the injectate end-member(Fig 8) There was little mixing from the saline end-member towards the brackish end-member in well 6U andalmost all of the mixing was towards the injectate end-member Both 6U and 12L showed large changes inconcentrations from their original end-members over timeWell 10L showed a different pattern than 6U and 12Lwith gradual freshening of the saline water towards theinjectate end-member The mixing was towards the lowerrange of the injectate end-member and there were no largechanges in concentrations of either NH3 or Clminus from thesaline end-member Well N-1L at the NDWWTP end-member mixing model showed a different pattern than theSDWWTP (Fig 9) Clustering of the NH3Cl

minus ratios weredistinguished based on time The NH3Cl

minus ambient ratio canclearly be seen on Fig 9 and lies along the saline end-member As the concentrations of NH3 increased in time tothe peak concentration the NH3Cl

minus ratios showed twodistinct clusters Initially the NH3Cl

minus ratio showed gradualincreasing in NH3 with little change in Clminus from ambientconcentrations There was a rapid change in the NH3Cl

minus

ratio as NH3 reached the peak concentrations Once the peakwas reached the NH3Cl

minus ratios slowly declined in time

Discussion

The Floridan aquifer system was sampled by others atdifferent sites in south Florida and these data aresummarized in Table 4 Wells identified as WWF weremonitoring wells installed as part of the MDWASD ASRsystem west of the NDWWTP and SDWWTP (CH2MHill 1998) The ASR systems were not in use during the

Fig 6 Graph a shows the NH3 data time series for the wells in the APPZ interval at the NDWWTP The dashed lines indicate the purgingtime from 2003 through 2004 NH3 concentrations are observed to increase in well N-1L similar to contaminant breakthrough curves WellN-1L was the closest well to the uncased injection well when injectate backflowed into the APPZ NH3 concentrations for wells N-2LN-3L and N-4L appear to be similar and show a similar increase after 1999 Variability is seen in the data after 2003 Graph b showsClminus concentrations in well N-1L clustered at approximately 300 mmol and an abrupt decrease to less than 300 mmol is seen Clminus

concentrations in wells N-2L N-3L and N-4L are very similar and show a decrease in concentrations after 1999 until 2000 whenconcentrations appear to stabilize Clminus concentrations start to increase slightly and become variable after 2003 All four wells showsimilar concentrations of both NH3 and Cl- after 2004

Hydrogeology Journal DOI 101007s10040-009-0570-8

Tab

le3

Meanfieldparametersandionconcentrations

during

the20

06ndash2

007samplingcompleted

aspartof

thisstud

ymblsmetersbelow

land

surface

Geologic

form

ation

Hyd

rogeolog

icun

itOpen

interval

Well

Temp

pHNH4+

Ca2

+Mg2

+Na+

K+

Sr2+

Cl-

SO42-

HCO3-

Br-

F-

NO3-

NO2-

mbls

IDdegC

micromol

mmol

mmol

mmol

mmol

micromol

mmol

mmol

mmol

micromol

micromol

micromol

micromol

SDWWTP

Pleistocene

Biscayn

eAqu

ifer

Surface

S-EFF

290

67

112

51

03

07

30

430

197

6

Und

ifferentiated

Haw

thornOcala

Lim

estone

toAvo

nPark

Lim

estone

UFA

306ndash31

6BZ1

242

78

61

325

139

213

440

109

11

299ndash33

21U

236

81

61

324

142

224

456

117

01

299ndash32

03U

243

79

61

325

148

284

454

119

41

299ndash311

2U25

379

101

322

143

215

433

143

11

Avo

nPark

Lim

estone

APPZ

454ndash48

49U

238

77

604

1098

399

104

53

169

850

145

4ndash48

510

U24

877

675

1085

212

5112

53

174

451

045

1ndash47

513

U24

477

143

410

883

113

109

54

200

119

21

454ndash48

516

U23

277

439

49

943

7510

25

525

013

51

145

4ndash48

014

U25

075

497

36

662

6570

45

115

801

145

4ndash48

36U

251

75

823

35

872

3245

37

8151

11

MC2

501ndash51

02L

248

75

98

1614

84

147

194

42

305

750

148

1ndash50

7BZ2

241

76

176

511

121

3114

128

64

217

930

154

6ndash57

39L

231

76

311

4445

912

167

550

243

849

211

11

546ndash57

616

L22

975

411

4143

912

175

552

254

800

195

01

540ndash57

73L

241

75

410

4344

012

159

522

233

834

233

51

519ndash56

14L

245

75

711

4041

612

181

492

213

737

234

01

530ndash56

213

L24

275

108

1036

350

1217

446

024

377

531

32

154

6ndash57

610

L24

776

200

830

285

10111

369

233

588

773

054

6ndash57

612

L28

176

765

36

492

3654

45

8735

20

561ndash58

71L

234

75

411

6441

213

161

533

253

834

235

11

NDWWTP

Pleistocene

Biscayn

eAqu

ifer

surface

N-EFF

263

65

505

22

201

616

13

3610

3849

Avo

nPark

Lim

estone

UFA

354ndash38

5N-FA-1U

225

78

173

868

215

573

41

8118

00

135

1ndash38

4N-FA-2U

227

78

133

765

212

166

41

126

179

22

354ndash37

9N-FA-3U

212

79

163

766

213

362

31

115

32

135

4ndash37

9N-FA-4U

208

79

163

769

214

766

41

131

174

11

APPZ

430ndash46

0N-FA-3L

194

75

215

937

423

1121

638

017

365

153

71

243

0ndash46

1N-FA-1L

199

74

231

736

458

1110

038

620

383

942

21

143

0ndash46

0N-FA-4L

192

74

264

937

421

1122

337

119

369

546

32

143

1-45

9N-FA-2L

201

74

295

839

431

1212

538

322

374

848

62

1

Hydrogeology Journal DOI 101007s10040-009-0570-8

time of this study Wells designated as ldquoFPLrdquo were testswells installed into the Floridan aquifer system sim10 kmsouth from the SDWWTP (Dames and Moore 1975Florida Partners 2006) For comparison to the presentstudy the data from these sites were assumed to representambient water-quality concentrations as no injectionactivities had occurred at these sites Wells in this studythat exhibited little variation in the time series data andhad low NH3 concentrations were compared to the datafrom these other sites Although direct comparisons weredifficult due to the varying aquifer open intervals fromwhich these samples were collected some generalizationscan be made NH3 or NH4

+ concentrations from thesewells were below 29micromol Clminus concentrations increasedwith depth of the sampled intervals and were similar inconcentrations to wells in this study of approximately thesame aquifer interval NO3

minus concentrations were below1micromol similar to data collected for this study Based oncomparisons with water quality from these other sites therevised time series water-quality data that had mean NH3

concentrations below 30micromol were assumed to be ambientaquifer water with no influence of injectate All the wellsin the UFA at the SDWWTP were considered ambient andmost of the wells in the MC2 at the SDWWTP wereconsidered ambient with the exception of 10L 11L and12L All of the wells in the APPZ at the SDWWTP hadNH3 concentrations above ambient levels with well 9U thelowest Time series data at the NDWWTP indicated that allof the wells open to the UFAwere considered ambient andthe data from wells open to the APPZ were ambient prior tothe observed increase in NH3 concentrations

Ambient Clminus concentrations from this study showedbrackish transitional and saline zones in the Floridan

aquifer system for the SDWWTP and NDWWTP asdefined by Reese (1994) Although there were only twosample depths at the NDWWTP the top of the saline zoneat the north appears to be higher than at the SDWWTPMean temperatures at the NDWWTP were cooler than atthe SDWWTP with an average of 23degC for both intervalsThe NDWWTP lies closer to the Florida Straits and thecooler temperatures at that site may be due to closerproximity to open seawater Wells that showed a higherconcentration of NH3 at the SDWWTP showed highertemperatures (example Well 12L) whereas at theNDWWTP no change in temperature was noted withincreasing NH3 concentrations

Based on results of this study introduced nitrogen fromthe injectate into the Floridan Aquifer is mostly in theform of NH4

+ This is consistent with eH-pH diagrams fornitrogen (Stumm and Morgan 1996) where in most naturalenvironments any ammoniandashN would have the form ofNH4

+ (Hem 1985) No relationship was observed in thehistorical data or data collected as part of this study betweenNH3 and NO3

minus No change from ambient NO3minus concen-

trations was observed for wells that had elevated NH3

concentrations The reduced form of nitrogen (NH4+) was

not oxidized once introduced in the anoxic aquifer at eithersite and was conserved in the aquifer in this reduced stateAny introduced oxidized form of nitrogen (NO3

minus) from theinjectate that was reduced would result in insignificantchanges in NH4

+ concentrations as NO3minus concentrations

are two to three orders of magnitude less than NH4+ The

elevated concentrations of NH4+ in the Floridan aquifer at

the two sites are interpreted as the result of the upwardmigration of the injectate Once introduced into the aquiferNH4

+ appeared to have behaved conservatively

Fig 7 Ternary diagrams for the NDWWTP and the SDWWTP NH4+ Clndash and Brndash data collected from 2006ndash2007 were normalized to

100 Seawater and freshwater values (Hem 1985) were plotted Ambient water was grouped at the SDWWTP for the MC2 and UFAintervals Ambient MC2 data plot directly with seawater UFA ambient plots towards freshwater reflecting the fresher water quality in theUFA The injectate data plot at the NH4

+ end point indicating the freshwater quality but high NH4+ concentration of the injectate Well data

from the APPZ and MC2 intervals that have NH4+ concentrations above ambient levels plot in a line towards the injectate end point with

data from wells 6U and 12L plotting very close the NH4+ end point Data from the SDWWTP plot into distinct groups based on depth in the

aquifer but no line towards the injectate end point is seen

Hydrogeology Journal DOI 101007s10040-009-0570-8

At least two pathways of injectate were distinguishedbased on the analysis of the natural tracers at theSDWWTP One pathway at the SDWWTP appeared tohave rapid vertical pathways from the Boulder Zone up tothe APPZ with little mixing of ambient waters as itmigrated upward These vertical conduits did not appear

to extend up to the UFA This pathway is identified atwells 6U and 14U in the APPZ and well 12L in the MC2It may be present at well 8U in the APPZ however thedevelopment of cross connection in well 8U compromiseddata interpretation NH4

+ concentrations in these wellswere within the range of injectate NH4

+ concentrations

Fig 8 Graphs on the left areNH3Cl

minus mixing end-membermodels for the APPZ andMC2 intervals at theSDWWTP 6U 12L and 10Lare well identification codesArrows indicate increase intime Hatched red rectangleis injected freshwaterend-member indicating theseasonal range in concentra-tions Cyan square is theAPPZ brackish waterambientwater end-member blue circleis the MC2 saline waterend-member Graphs on theright are NH3 concentrationsover time Solid black lines areconcentrations from each wellsite red line is injected fresh-water concentrations Forwells 6U and 12L the dataplot towards the injectateend-member Little influenceis seen in well 6U from thesaline MC2 end-memberWell 10L shows a differentevolution of water qualitywith data plotting at the salineMC2 end-member and slowlyplotting towards the lower endof the injectate end-member

Fig 9 Graph a is the NH3Clminus mixing end-member model for the APPZ at the NDWWTP for pre-purge data (prior to 2003) for well N-

1L Arrows indicate increase in time Hatched red rectangle is injected freshwater end-member indicating the seasonal range inconcentrations Cyan square is the UFA brackish water ambient water end-member blue circle is the APPZ saline water end-member Thedata plot in separate groupings with the earliest time series plotting around the APPZ saline end-member The second data cluster plottowards the injectate end-member but no evolution towards the injectate end-member is seen as was seen for wells 6U and 12L at theSDWWTP Graph b is the post-purge data plotted for well N-1L Data plot with time back towards the APPZ saline end-member

Hydrogeology Journal DOI 101007s10040-009-0570-8

Clminus concentrations in these wells were also very close toinjectate Clminus concentrations

The mixing models for these wells show a mixingpathway almost directly towards the injectate end-mem-ber with no mixing from the lower MC2 interval observedfor wells 6U and 14U Wells that showed the highestconcentrations of NH3 at the SDWWTP also showedhigher temperatures with the temperature signal of thewarmer injectate observed in well 12L (mean temperatureof 28degC) in the data collected in 2006ndash2007 Well 12L inthe MC2 is much closer to the Boulder Zone than theAPPZ wells and higher injectate temperatures persist intothe MC2 Perhaps due to the longer travel times to theAPPZ the temperature signal was muted but still visible inthe APPZ Ion data for these wells showed freshening ofthe water quality These wells showed a density-drivenbuoyant rapid vertical advective pathway and transport ofthe injectate as a distinct water body with little mixing ofnative waters as it migrated upwards The rapid pathwayscould be the result of construction related events such asdrifting boreholes or the result of structural anomaliessuch as fracturing and karst features that would verticallyconnect aquifers and provide high hydraulic conductivitytransport pathways through confining units Migration ofsaline waters from the Lower to Upper Floridan Aquiferas a result of such structural anomalies have been reportedfor northeastern and central Florida (Flocks et al 2001Spechler 2001) where the Floridan aquifer system liesmuch closer to the surface Upward fluid migration ofinjected fluids in a Palm Beach County Florida deep wellinjection facility had been detected above the confiningzone between the injection zone and the overlayingmonitoring zone and this had been attributed to fractureddolostone comprising the majority of the confining zonestrata (Maliva et al 2007) however no fracturing of theconfining strata at either the NDWWTP or the SDWWTP

has been reported McNeill suggested that as wells locatedon the northwest side of the SDWWTP were cased abovethe DCU in the LFA this would be a possible cause of thebuoyant upward migration of injected fluids through themore permeable units above the DCU through isolatedvertical flow paths bypassing the MC2 (McNeill 20002002)

The second pathway was suggested by the grouping ofwell data observed in wells 15U 16U BZ2 10L and 11LThe well data from this group had no significantcorrelation between NH3 and Clminus The mixing modelsfor these well data showed a slow evolution of waterquality towards the lower average of the injectate end-member with time These wells showed a slight temper-ature increase but no clear temperature signal wasdistinguished in these wells Ion data did not show afreshening of the water quality with little difference seenbetween ambient ion concentrations and concentrationsfrom these wells Other studies (Boumlhlke et al 2006) haveindicated that NH3 transport can be retarded by a factor of3ndash6 in an aquifer with NH3 persisting in an aquifer afterthe more mobile constituents were flushed out if theaquifer remained under suboxic conditions At theSDWWTP it appears that there was still NH3 loadinginto the aquifer via rapid vertical pathways with increas-ing NH3 concentrations over time The data from this wellgrouping may indicate that once NH3 was introduced intoan aquifer interval it traveled horizontally at a muchslower rate with the freshwater injectate substantiallydiluted and not flushed out as freshwater continued tomigrate upwards

Four discrete injectate plumes were delineated at theSDWWTP based on the transport pathways The firstplume (plume 1 in Fig 10) located on the northeast of thesite was associated with the BZ-4 well which provided apathway up into the APPZ until it was plugged This

Table 4 Historical ambient Floridan Aquifer water quality data

Parameter Unit 1Ua WWFb WWFb FPLPW-3c

FPL testwelld

9Ua FPL testwell d

2La 3La FPL testwelld

299ndash332 m

260ndash305 m

260ndash308 m

314ndash380 m

340ndash410 m 454ndash484 m

456ndash517 m 501ndash510 m

530ndash562 m

639ndash701 m

pH 79 80 74 75 77 77 75 75 75 70HCO3

- mmol 00 32 27 33 21 30 26Ca2+ mmol 13 17 37 43 67 78 103 196Mg2+ mmol 27 28 73 101 155 160 434 555Na+ mmol 247 222 746 983 1582 1482 4382 4872K+ mmol 08 08 20 26 38 36 118 97Cl- mmol 223 705 271 821 1043 1794 1939 5216 5923SO4

2- mmol 41 75 69 03 69 47 137 42 226 307NO3

- micromol 03 08 02 02 02 03 02 48 02F- mmol 01 01 01 01 01 01 02 01Si mmol 05 04 02 05 03 03 02Sr2+ micromol 419 776 982 1849 1472 1586Total P micromol 32 71 65 65 32NH4

+ micromol 55 72 610 111 55NH3 micromol 08 294 123

a Data were collected for this study during 2006ndash2007 for wells at the SDWWTPbData from CH2M Hill 1998cData from Florida Partners 2006dData from Dames and Moore 1975

Hydrogeology Journal DOI 101007s10040-009-0570-8

plume slowly migrated to the surrounding areas mainlyvia diffusion as evidenced by slowly increasing NH3

concentrations but no change in Clminus concentrations Thesecond plume was located on the northwest corner of thesite in the APPZ (plume 2) This plume was detected inthe APPZ with no detection of it in the lower MC2indicating a direct pathway to the APPZ bypassing theMC2 This pathway seemed to persist with concentrationsof NH3 increasing with time similar to concentrationlevels of the injectate This plume was a chemicallydistinct water body with little mixing of native watersThe third plume located at well 14U (plume 3) may be adistinct plume but it may also be in connection withplume 2 No monitoring wells of the same interval as well14U are in the vicinity so the extent of this plume couldnot be determined The fourth plume was located on thesouth side of the site in the MC2 (plume 4) All fourplumes appeared to have the same initial transportmechanism up from the Boulder Zone through highhydraulic conductivity pathways with data from plumes2 3 and 4 indicating these pathways still persist

The data collected from the NDWWTP indicate differ-ent transport mechanisms than the SDWWTP Thetemperature signal of the warmer injectate was notobserved in wells with elevated concentrations of NH4

+Water quality showed no evolution towards the injectateplot in the ternary diagram The mixing model showedtwo mixing patterns one towards the injectate end-member before purging and one towards the ambientend-member once purging ceased As observed in the timeseries NH3 data NH3 concentrations were first observedto increase in well N-1L the well that was within 30 m ofthe uncased injection well and concentrations peaked at

341micromol well below the mean NH3 concentration of theinjectate Unlike the increasing NH3 concentrationsobserved at the SDWWTP that are the result of rapidvertical migration pathways once NH3 concentrations atthe NDWWTP peaked they have since decreased withtime All four NDWWTP lower wells have shown verysimilar water quality since 2004 when purging ceased atthe NDWWTP Both the time series analysis and the datacollected as part of this study in 2006 and 2007 appear toindicate a one-time pulse of injectate water into the APPZand this pulse of injectate was still migrating at the timeof this study through the aquifer in the direction ofregional flow There is no geochemical evidence of acontinuing source of NH3 at the NDWWTP however dueto retardation as discussed previously the NH3 plume mayhave persisted a long time in the suboxic aquifer (Boumlhlkeet al 2006)

Conclusions

Chloride bromide and ammonia were used to understandthe pathways and transport mechanisms of injectedwastewater into the deep saline Boulder Zone in theFloridan aquifer system The injectate source was treatedfreshwater with elevated levels of ammonia The waterquality of the injectate was chemically and physicallydistinct from ambient Floridan aquifer system water andthese distinctions were used to determine the possibletransport pathways At the SDWWTP four injectateplumes were identified along with two pathway mecha-nisms density-driven buoyant vertical flow and slowerhorizontal flow At the NDWWTP one plume was

Fig 10 Location of injectate plumes and their depth interval at the SDWWTP The source of the plume centered on the BZ well clusters(plume 1) was plugged in 1995 Plumes 2 3 and 4 are the result of continuing rapid vertical pathways up from the Boulder Zone Theextent of the plumes off site is not known as indicated by the question marks however based on data collected from the site approximateextent of the plumes on the site can be inferred The plume in the MC2 is limited to the southeast of the site The plume located in thenorthwest of the site is located in the APPZ and appears to have bypassed the MC2 The plume from the BZ well cluster appears to belimited to the east of the site The extent of the plume at 14U on site is unknown as there are no wells that monitor the same aquifer intervalin the vicinity of 14U

Hydrogeology Journal DOI 101007s10040-009-0570-8

identified and appeared to be a result of a one-time pulseinjection At the SDWWTP the injectate may first havemigrated upwards through discrete vertical pathways fromthe Boulder Zone to the Middle Confining Unit with thefreshwater injectate migrating upwards through salinewater as a chemically distinct water body The fourplumes identified at the SDWWTP appear to haveoriginated via this pathway Once introduced in the higheraquifer intervals the transport mechanism appeared to bea horizontal flow with mixing of ambient waters Therapid vertical pathways did not appear to extend up to theUFA At the NDWWTP the elevated levels of NH3 inthe lower Middle Confining Unit appeared to be the resultof a construction incident where a pulse of injectate waterbackflowed into an uncased injection well providing apathway to the upper interval Once introduced into theupper aquifer interval the plume slowly migrated with theregional flow within the aquifer No evidence of rapidvertical pathways was observed at the NDWWTP Duringthe course of this study it became clear that purging of thewells had unintended consequences for the SDWWTPCross connections developed in several wells between theupper and lower monitoring zones either during or afterpurging and these cross connections have compromisedwater-quality data in SDWWTP wells 5 6 7 8 11 12and 15 Although it could not be determined from thisstudy these cross connections may provide pathways ofinjectate into layers in the aquifer that had not beenpreviously affected by upward migrating injectate

Acknowledgements This study was funded by the Miami-DadeWater and Sewer Department (MDWASD) The authors greatlyappreciate S Villamil for her invaluable technical expertise andassistance in the field We thank C Powell S Kronheim W Pittand B Goldenberg of MDWASD for their cooperation and Drs ADausman and C Langevin of the US Geological Survey for theirinsightful comments during this research This report was signifi-cantly improved by the thoughtful review of two anonymousreviewers Dr Pricersquos contribution was partially funded by theNational Science Foundation Grant No DBI-0620409 This isSERC contribution 457

References

Arthur JD JB Cowart AA Dabous (2001) Florida Aquifer Storageand Recovery Geochemical Study Year Three Progress ReportOpen File Report 83 Florida Geological Survey TallahasseeFL

BCampECH2M Hill (1977) Drilling and testing of the test-injectionwell for the Miami-Dade Water and Sewer Authority ContractS-153 BCampECH2M Hill Gainesville FL

Bloetscher F Muniz A (2006) Preliminary modeling of class Iinjection wells in southeast Florida Ground Water ProtectionCouncil 2006 Annual Meeting Proceedings Miami FLNovember 2006

Bloetscher F Englehardt JD Chin DA Rose JB Tchobanoglous GAmy VP Gokgoz S (2005) Comparative assessment ofmunicipal wastewater disposal methods in southeast FloridaWater Environ Res 77480ndash490

Boumlhlke JK E Shinn C Reich A Tihansky (2003) Origins andisotopic characteristics of dissolved nitrogen species in groundwater imported domestic water and wastewater in the FloridaKeys US Geological Survey Greater Everglades Science

Program 2002 biennial report US Geol Surv Open-File Rep03-54

Boumlhlke JK Smith RL DN Miller (2006) Ammolonium transportand reaction in contaminated groundwater application ofisotope tracers and isotope fractionation studies Water ResourRes 42 W05411 doi1010292005WR004349

CH2M Hill (1981) Drilling and testing of the 8 injection wells andthe 3 monitoring wells for the South District Regional Waste-water Treatment Plant of the Mimi-Dade Water and SewerAuthority CH2M Hill Englewood CO

CH2M Hill (1998) Engineering report of the construction andtesting of the aquifer storage and recovery (ASR) system at theMDWASD West Wellfield CH2M Hill Englewood CO

Clark JF Bryant Hudson G Lee Davisson M Woodside GHerndon R (2004) Geochemical imaging of flow near anartificial recharge facility Orange County California GroundWater 42167ndash174

Corbett DR Kump L Dillon K Burnett W Chanton J (2000) Fateof wastewater-borne nutrients under low discharge conditions inthe subsurface of the Florida Keys USA Mar Geochem 6999ndash115

Dames and Moore Inc (1975) Floridan aquifer water supplyinvestigation Turkey point Area Miami-Dade County FloridaFlorida Power and Light Miami

Davis SN Whittemore DO Fabryka-Martin J (1998) Uses ofchloridebromide ratios in studies of potable water GroundWater 36338ndash350

Englehardt JD Amy VP Bloetscher F Chinn DA Fleming LEGokgoz S Solo-Gabriele H Rose JB Tchoaboglous G (2001)Comparative assessment of human and ecological impacts formunicipal wastewater disposal methods in southeast Floridadeep wells ocean outfalls and canal discharges University ofMiami Coral Gables FL

Fish JE Stewart M (1991) Hydrogeology of the surficial aquifersystem Dade County Florida US Geol Surv Water ResourInvest Rep 90-4108 50 pp

Flocks JG Kindinger JL Davis JB Swarzenski P (2001) Geo-physical investigations of upward migrating saline water from thelower to upper Floridan Aquifer Central Indian River RegionFlorida In US Geological Survey Karst Interest Group Proceed-ings US Geol Surv Water Resour Invest Rep 01-4011 pp 135ndash140

Florida Lakes Power Partners and Florida Power and LightCompany (2006) Well completion report for Floridan Aquiferwells PW-1 PW-2 and PW-4 FPL Turkey Point ExpansionProject (Unit 5) Homestead FL

Haberfeld JL (1991) Hydrogeology of effluent disposal zonesFloridan aquifer south Florida Ground Water 29186ndash190

Hem JD (1985) Study and interpretation of the chemicalcharacteristics of natural water US Geol Surv Water SupplPap 2254

Herczeg AL WM Edmunds (2000) Inorganic ions as tracers InCook PG Herczeg AL (eds) Environmental tracers in subsur-face hydrology Kluwer Norwell MA pp 31ndash78

Kaehler CA K Belitz (2003) Tracing reclaimed water in MenifeeWinchester and Perris-South ground-water subbasins RiversideCounty California US Geol Surv Water Resour Invest Rep03-4039

Kohout FA (1965) A hypothesis concerning cyclic flow of saltwater related to geothermal heating in the Floridan aquiferTrans NY Acad Sci Ser II 28249ndash271

Langmuir D (1997) Aqueous environmental geochemistry Prentice-Hall Upper Saddle River NJ

Maliva RG CW Walker (1998) Hydrogeology of deep-welldisposal of liquid wastes in southwestern Florida USAHydrogeol J 6(4)538ndash548

Maliva RG Guo W Missimer T (2007) Vertical migration ofmunicipal wastewater in deep injection well systems SouthFlorida USA Hydrogeol J 15(7)1387ndash1396

McNeill DF (2000) Final report a review of upward migration ofeffluent related to subsurface injection at Miami-Dade Waterand Sewer South District Plant McNeill Miami FL

Hydrogeology Journal DOI 101007s10040-009-0570-8

MARK A QUARLES PG PAGE 5 bull Various Industrial Landfills - Tennessee

Served as Project Manager for Subtitle D landfill siting and design projects Performed hydrogeologic investigations presented design waivers for site-specific design criteria (when applicable) and developed detailed designs for permitting

bull Various Landfills - Tennessee Served as Project Manager for the design permitting and operation of industrial and municipal solid waste landfills preparation of SWPP Plans quarterly groundwater and gas monitoring reports and hydrogeologic investigation reports

bull Various Municipal Landfills - Kentucky Served as Project Engineer for the design permitting and operation of municipal solid waste landfills

Stormwater Permitting and Compliance bull Tennessee Clean Water Network ndash Knoxville Tennessee

Served as lead consultant for providing technical comments for the draft Knox County Phase II Municipal Separate Storm Sewer System (MS4) permit

bull Various Industrial Clients - Throughout the US Served as Project Manager to obtain permit coverage through the EPA General Permit group permits and individual permits specific to each state Over 125 facilities were permitted

Hazardous Waste Management bull Various Industrial Clients ndash Throughout the US

Served as Project Manager for various projects to evaluate hazardous waste management practices consistent with the rules and regulations established under RCRA

bull Laidlaw Environmental Services Inc ndash Southeastern US Completed SWPP Plans for RCRA treatment storage and disposal facilities

Municipal Wastewater Management bull Various Municipalities ndash Fulton Cobb and Dekalb County Georgia

Served as Project Engineer for sewer modeling and point-source identification Identified sources of infiltration inflow and performed cost evaluations for source removal

bull Various Municipal and Industrial Clients ndash Tennessee Served as Project Engineer to establish beneficial reuse land application programs for wastewater sludge

bull Boston Water and Sewer Commission - Boston Massachusetts Served as Project Engineer for sewer modeling and point-source identification projects of combined and separate sewers up to 15 feet in diameter Identified sources of infiltration inflow and performed cost evaluations for source removal

bull Various Municipal Clients ndash Throughout the US Served as lead technical trainer for the implementation of proprietary software used for automated GIS mapping maintenance scheduling and hydraulic analyses of separate and combined sewers

bull City of Hopkinsville - Hopkinsville Kentucky Served as Project Engineer for water and sewer line expansions and wastewater treatment projects

TECHNICAL PUBLICATIONS AND LECTURES bull Quarles M and William Wilson ldquoUnconventional Natural Gas and its Risk A Tennessee

Perspectiverdquo Appalachian Public Interest Environmental Law Conference Knoxville Tennessee October 2011

bull Quarles M ldquoA Case Study in Karst Hydrogeology and Contaminant Fate and Transportrdquo National Groundwater Association 51st Annual Convention and Exposition December 1999

bull Quarles M and Allen P Lusby ldquoEnhanced Biodegradation of Kerosene-Affected Groundwater and Soilrdquo 1994 Annual Conference of the Academy of Hazardous Materials Managers October 1994

MARK A QUARLES PG PAGE 6 bull Quarles M ldquoNew Tank Performance Standardsrdquo Tennessee Environmental Law Letter July

1993 EXPERT LEGAL TESTIMONY bull Chesney versus Tennessee Valley Authority ndash 2011 US District Court Written testimony

associated with fly and bottom ash sampling waste characterization contaminant fate and transport and contaminant risks compared to US EPA screening levels drinking water standards fish and aquatic life standards and sediment cleanup standards

bull Busch et al versus Dr Carol Couch Atlanta Georgia 2008 State Administrative Court Written and verbal testimony regarding drought restrictive surface water and groundwater use Qualified by the court as an expert in geology hydrogeology and stormwater runoff

bull Darrel Segraves et al versus Dr Carol Couch Atlanta Georgia 2008 State Administrative Court Written and verbal testimony regarding appeal of a municipal solid waste landfill permit Qualified by the court as an expert in geology hydrogeology landfill design pertaining to landfill leakage and stormwater runoff

bull Tulane Environmental Law Clinic 2007 - 2008 Written testimony for numerous draft LDEQ permits and proposed rules

bull Republic of Ecuador and PetroEcuador vs Chevron Texaco Corporation and Texaco Petroleum Company US District Court Southern District of New York 2007 Written testimony regarding environmental investigation protocol

bull Friends of Tims Ford vs Tennessee Valley Authority and Tennessee Department of Environment and Conservation US District Court 2007 Written testimony in support of violations of State and Federal water quality standards reservoir carrying capacity standards and NEPA environmental assessment standards

bull Freddie Howell vs Creative Customs Atlanta Georgia 2007 Technical support regarding litigation associated with stormwater and groundwater flow and their effects on the Howell property

bull Aguida vs ChevronTexaco Lago Agrio Ecuador Court 2006 Written testimony regarding Texacorsquos waste management and standard operating practices in the Ecuadorian concession area relative to industry standards

TRAINING Current Wetland Issues in Tennessee (2007) Professional Liability Education - Contract Review and Revision (2000) Professional Liability Education ndash Mid-Town Developer Case Study Workshop (1999) Professional Liability Education ndash Liability IQ for Environmental Consultants (1998) Liquid Animal Waste Management System Design to NRCS Standards for CAFO (1998) 8-Hour OSHA Health and Safety Refresher Training Hazardous Materials Waste Manager Course University of Alabama (1993) 40-Hour OSHA Health and Safety Training (1990) CONTACT INFORMATION Home telephone 615-352-0471 Mobile telephone 615-504-0956 Email markquarlescomcastnet

Determination of vertical and horizontal pathways of injected freshwastewater into a deep saline aquifer (Florida USA) using naturalchemical tracers

Virginia Walsh amp Reneacute M Price

Abstract Two deep-well injection sites in south FloridaUSA inject an average of 430 million liters per day(MLD) of treated domestic fresh wastewater into a deepsaline aquifer 900m below land surface Elevated levels ofNH3 (highest concentration 939micromol) in the overlyingaquifer above ambient concentrations (concentration lessthan 30micromol) were evidence of the upward migration ofinjected fluids Three pathways were distinguished basedon ammonium chloride and bromide ratios and temper-ature At the South District Wastewater Treatment Plantthe tracer ratios showed that the injectate remainedchemically distinct as it migrated upwards through rapidvertical pathways via density-driven buoyancy Thewarmer injectate (mean 28degC) retained the temperaturesignal as it vertically migrated upwards however thetemperature signal did not persist as the injectate movedhorizontally into the overlying aquifers Once introducedthe injectate moved slowly horizontally through theaquifer and mixed with ambient water At the NorthDistrict Wastewater Treatment Plant data provide strongevidence of a one-time pulse of injectate into theoverlying aquifers due to improper well construction Noevidence of rapid vertical pathways was observed at theNorth District Wastewater Treatment Plant

Keywords Waste disposal Deep well injection Carbonate rocks Confining units Ammonia Temperature USA

Introduction

Deep well injection of treated municipal wastewater intonon-potable aquifers has been used as an alternative todischarge of wastewater to surface waters for manydecades There are 430 permitted municipal wastewaterdeep injection wells in the United States with 163 inFlorida alone (USEPA 2008) These deep aquifers tend tobe saline and the discharge of fresh wastewater into themhas raised concerns of geochemical reactions as a result ofthe mixing of the two waters as well as the buoyanttransport of the wastewater upwards into overlyingaquifers Confined brackish aquifers in Florida have beenused extensively for aquifer storage and recovery (ASR)of potable freshwater (Arthur et al 2001 Renken et al2005) and deeper saline aquifers have been used fordisposal of waste fluids such as oil brines industrial waterand municipal wastewater (Meyer 1989a Meyer 1989b)ASR in Florida has been extensively studied as part of theComprehensive Everglades Restoration Plan (Reese 2002Mirecki 2004 Mirecki 2006) however little research hasbeen published regarding the fate and transport of thetreated wastewater into deep saline aquifers (Meyer1989a Haberfeld 1991 Maliva and Walker 1998Bloetscher et al 2005 Bloetscher and Muniz 2006Maliva et al 2007)

Miami-Dade County Water and Sewer Department(MDWASD) located in southern Florida currently dis-charges 430 million liters per day (MLD) of treateddomestic wastewater into a saline deep aquifer at twolocations in the county Deep well injection has been inuse in Miami-Dade County since the late 1960s Theinjection facilities are located in the north and south of thecounty separated by 44 km (Fig 1) The South DistrictWastewater Treatment Plant (SDWWTP) site was placedinto service in 1983 and is currently permitted for thedisposal of 367 MLD of treated wastewater The NorthDistrict Wastewater Treatment Plant (NDWWTP) site wasplaced into service in 1997 and is permitted for 90 MLD

Received 2 February 2009 Accepted 14 December 2009

copy Springer-Verlag 2010

V Walsh ())Miami-Dade Water and Sewer Department3071 SW 38th Ave Miami FL 33146 USAe-mail walshvmiamidadegov

V WalshDepartment of Earth and EnvironmentFlorida International University11200 SW 8th Street University Park Miami 33199 USA

R M PriceDepartment of Earth and Environment and SoutheastEnvironmental Research CenterFlorida International University11200 SW 8th Street University Park Miami 33199 USA

Hydrogeology Journal DOI 101007s10040-009-0570-8

Both facilities treat domestic wastewater to above second-ary drinking water standards and discharge the treatedwastewater into United States Environmental ProtectionAgency (USEPA) Class I injection wells The treatedwastewater is injected into the Boulder Zone a highlytransmissive interval in the deep saline non-potable LowerFloridan Aquifer The Boulder Zone has been thought to behydrologically separated from overlying aquifers by a335-m-thick confining unit During the installation of addi-tional monitoring wells at the SDWWTP in 1994 ammonia-nitrogen (NH3-N) was detected at 442 m depth in theoverlying aquifer at a concentration of 411 micromoles perliter (micromol) above reported background levels of 29micromol

(BCampECH2M Hill 1977) The detection of NH3ndashN in theaquifers above the Boulder Zone has raised doubts regardingthe efficacy of the confining unit and the resultant waterquality impact to overlying aquifers as these aquifers areused as alternative water supplies via storage of freshwater(ASR) and blending with potable surficial aquifer water

Research has focused on ASR in south Florida (Arthuret al 2001 Reese 2002 Mirecki 2004 Mirecki 2006Reese and Richardson 2008) however few studies havebeen conducted regarding the transport and fate of injectedeffluent into the Boulder Zone and typically these had todo with the relative risk of deep well injection versusocean outfall disposal of municipal waste (Englehardt et

Fig 1 Location of theNDWWTP and the SDWWTPstudy sites

Hydrogeology Journal DOI 101007s10040-009-0570-8

al 2001 USEPA 2003 Bloetscher et al 2005 Bloetscherand Muniz 2006) Recently researchers have studied thetransport mechanisms of the observed migrated injectateand have suggested density-driven buoyant transportmechanism along natural or anthropogenic vertical frac-tures in the lower aquifers (Maliva and Walker 1998McNeill 2000 McNeill 2002 Maliva et al 2007 Walshand Price 2008) The objective of this study was todetermine migration pathways of injected treated waste-water at two facilities in Miami-Dade County Florida(SDWWTP and NDWWTP) using historical time seriesdata and major ion data collected as part of this study Themethodology developed for this study used chloride (Clminus)bromide (Brminus) and NH3 as tracers This methodologyprovided a method for estimating transport pathways andinvolved no additional collection of data other than whatwas typically required under federal and state regulatoryprograms

Natural inorganic tracers have been used extensively inwater resources investigations to trace groundwater flowpaths and calculate mixed water ratios (Langmuir 1997Davis et al 1998 Herczeg and Edmunds 2000) Clminus andBrminus commonly are used as they tend to be conservativeand their ratios may also give information as to the sourceand pathways of water Studies have been conducted insouth Florida (Shinn et al 1994 Paul et al 1997 Corbettet al 2000 Boumlhlke et al 2003) and elsewhere (Kaehlerand Belitz 2003 Clark et al 2004) tracing treatedwastewater in surficial aquifers but NH3 was not used asa tracer as it does not behave conservatively in oxicwaters In this study a novel application of Clminus Brminus andNH3 as conservative tracers of injectate was developed aspart of mixing models to distinguish pathways betweenthe deep aquifers Clminus is a natural anion in the Floridanaquifer system and its principal source is seawater asthere are no evaporite minerals to provide an additionalsource (Sprinkle 1989 Reese 1994) The seawater sourceof Clminus in south Florida is thought to be the result of eitherincomplete flushing of Pleistocene seawater and brackishwater intrusion andor the result of the cyclic flow basedon thermal upwelling of Holocene intruded seawater(Kohout 1965 Sprinkle 1989 Reese 1994) Bromide(Brminus) behaves similar to Clminus in groundwater systems(Davis et al 1998) and in south Florida the source of Brminus

in groundwater is similar to that of Clminus although its naturalabundances are orders of magnitude less than Clminus Theonly source of the NH3 is the injectate and therefore itwas used to trace transport pathways of the injectedwastewater

Geologic and hydrogeologic framework

The Floridan aquifer system (FAS) in southeastern Floridais defined by a vertically continuous sequence of per-meable carbonate rocks of Cenozoic age that are hydrauli-cally connected in varying degrees (Miller 1986) Theaquifer matrix consists of carbonate and dolomitic lime-stones dating from the Paleocene to the Oligocene

epochs Overlying the FAS are the impermeable sedimentsof the late Oligocene to Pliocene age Hawthorn Group a180-m-thick confining layer of clays siltstones and siltylimestones The Hawthorn Group separates the UpperFloridan Aquifer from the late Pliocene and Pleistoceneformations making up the Surficial Aquifer System whichincludes the Biscayne Aquifer in south Florida (Fig 2)The Biscayne Aquifer is an unconfined surficial aquiferand is the major source of potable water in south Florida(Fish and Stewart 1991)

The Floridan Aquifer contains several highly perme-able and less permeable zones with zones of highestpermeabilities typically occurring at or near unconform-ities and usually parallel to the bedding planes (Meyer1989a) Previous studies (Miller 1986 Reese 1994)grouped the Floridan aquifer system into three hydro-stratigraphic units (Fig 2) the Upper Floridan Aquifer(UFA) the Middle Confining Unit (MCU) and the LowerFloridan Aquifer Recently the MCU in south Florida hasbeen divided into the MC1 and MC2 (Fig 2) separatedby the Avon Park permeable layer (Reese and Richardson2008) which in south Florida had previously beenidentified as the Middle Floridan Aquifer The UpperFloridan Aquifer contains relatively fresh water less than10000 mg Lminus1 total dissolved solids (TDS) The LowerFloridan Aquifer consists of seminconfining or leakymicritic limestone and dolomite layers that containgroundwater with compositions approaching seawater(approximately 30000 mg Lminus1 TDS) A dolomite confin-ing unit (DCU) a thin confining unit below the MC2 wascharacterized at the study site by McNeill (McNeill 20002002) This DCU lies above the permeable zone com-monly known as the Boulder Zone within the OldsmarFormation of the Lower Floridan Aquifer The FASoutcrops along the Straits of Florida providing a hydraulicconnection to the sea (Kohout 1965 Miller 1986 Reese1994) Transmissivities in the Upper Florida Aquiferrange from 929 to 23times104m2 dayminus1 (Meyer 1989a Reese1994) while transmissivities in the Boulder Zone rangefrom 297times105m2 dayminus1 to 232times106m2 dayminus1

Site descriptionsThe NDWWTP and the SDWWTP consist of deepinjection wells that penetrate down to approximately855 m The upper 755 m of each well is cased to the topof the Boulder Zone The bottom 100 m of each injectionwell is an open hole in the Boulder Zone Nine suchinjection wells and three multi-zoned and dual-zonedmonitoring wells were constructed between 1977 and1981 at the SDWWTP (Fig 3) The multi-zone test wellBZ cluster (BZ-1 through 4) was constructed in 1977 andconsisted of four telescoping monitoring wells the deepestof which was BZ-4 cased to the top of the Boulder Zonethe shallowest BZ-1 open to the UFA at a depth of 312 mThe remaining monitoring wells were constructed bothat the SDWWTP and NDWWTP using a dual zone designwith an inner steel casing drilled to the deeper intervaland the outer steel casing open to the upper interval For

Hydrogeology Journal DOI 101007s10040-009-0570-8

this report well nomenclature indicates the open intervalof the dual-casing ldquoUrdquo represents the upper monitoringinterval and ldquoLrdquo represents the lower monitoring intervalWells 1 and 2 were dual-cased to monitor water quality inthe UFA (sim300 m) and the lower confining units (sim550 mCH2MHill 1981) In 1994 NH3 was detected aboveambient levels in the confining unit at the BZ well cluster(BZ-2 depth 488 m) and subsequent investigations by theutility found a leak due to corrosion of the casing in thiscluster (MDWASD 1995) The lower three monitoringintervals of the BZ well cluster were plugged in 1995 tostop the upward migration of injectate through the casinghole and the confining unit (488 m) monitoring intervalwas redrilled From 1995ndash1996 nine injection wells and

thirteen dual-zoned monitoring wells were constructed onthe SDWWTP These monitoring wells were cased to theAvon Park Permeable zone (APPZ) and the MC2 withopen holes in the formations approximately 30 m Duringthe construction of the monitoring wells NH3 concen-trations above ambient levels were found throughout thesite Elevated NH3 concentrations were found in thenorthwest corner of the site in the MC1 interval in severalwells but not in the lower MC2 interval of these wellsElevated levels were found in the MC2 interval in thesouth side of the site As a result of the detected NH3 inthe confining units the EPA required purging of the wellsthat showed elevated concentrations NH3 (Starr et al2001) in an attempt to remove the NH3 loading in the

Fig 2 Geologic and hydrogeologic framework of NDWWTP and the SDWWTP modified from Reese and Richardson 2008 Welldiagram on the right shows the number of wells open to the indicated hydrogeologic unit used for this study

Fig 3 Well locations at theSDWWTP

Hydrogeology Journal DOI 101007s10040-009-0570-8

impacted intervals Discontinuous purging of approxi-mately 2100 Lmin commenced from 1997 to 2000 forthe northwest wells (5U 6U 7U 8U 15U and 16U) of theAPPZ interval and the south wells (11L and 12L) of theMC2 (MDWASD 2000)

Injection well construction started at the NDWWTP in1996 Four injection wells were constructed into theBoulder Zone and four dual-zoned monitoring wells wereconstructed to the UFA and the APPZ intervals (Fig 4) In1996 effluent was injected in two completed injectionwells while one injection well was still under constructionresulting in injectate backflowing into an open borehole atan uncased injection well for 5 days Several months afterthe construction of the wells had been completed NH3

concentrations were observed to increase in the APPZinterval of the monitoring wells on site The utility wasrequired to purge the APPZ interval wells for a period of1 year from 2003ndash2004 (MDWASD 2005)

Methodology

Historical data were collected and checked for qualityassurance for the NDWWTP and SDWWTP Data wereavailable from 1983 through 2007 for the SDWWTP and1996ndash2007 for the NDWTP Data studied as part of thisresearch included pressure temperature pH Clminus sulfate(SO4

2minus) NH3 and nitrate (NO3minus) The historical data were

compiled from the utility monthly operating reportsavailable sporadically from 1983 Non-detects that hadbeen entered as a zero value were updated to the detectionlevel of the parameter Summary statistics including meanmedian standard deviation maximum and minimum wereapplied to each of the wellsrsquo time series data to assesswater-quality changes over time and used to compare toambient water quality data at other locations in southFlorida Most water quality for the Floridan Aquifer insouth Florida had been collected as regulatory require-ments which usually included chemical analyses that areused for drinking water quality and therefore did notinclude major ion data Residence time in the Floridan

aquifer system in south Florida is on the order of thousandsof years (Meyer 1989a) and it was assumed that due to thedepth of the aquifer water quality was in equilibrium andthere would be no other cause of perturbations to ambientwater quality other than migration of injectate Time seriesdata that showed large variation over time would indicatenon-equilibrium conditions and therefore not ambientconditions Abrupt changes in water quality and pressurewere observed in the time series data in wells that werepurged in 1997 These changes were not observed in wellsthat were not purged These changes in water quality andpressure were interpreted as being the result of crossconnections developed in the dual zone casings of some ofthe purged wells and review of borehole videos of thesewells taken in 2004 confirmed holes in the casings of thesewells It could not be determined which interval the datacollected from these wells represented after the crossconnections developed therefore data were discardedfrom the historical series analysis based on the month itwas ascertained the cross connection developed and thesummary statistics were recalculated for these wells

Floridan Aquifer water samples were collected at theNDWWTP and SDWWTP during 2006 and 2007 as partof this study for major ions and nitrogen species Thirty-two monitoring wells were sampled at the SDWWTP andwater-quality samples were collected from these wellsfrom the UFA the APPZ and the MC2 At theNDWWTP samples were collected from four monitoringwells representing the UFA and four wells in the APPZTemperature pH dissolved oxygen and conductancewere taken from water samples in the field using an YSI556 MPS The YSI instrument was calibrated per themanufacturerrsquos instructions prior to each sampling eventAll wells were purged for at least 24 h prior to sampling toensure at least three well volumes were evacuated Thewells were sampled through a closed system using a lowflow cell and tygon tubing through a disposable highcapacity 045micromol in-line filter Water samples wereanalyzed for the anions Brminus Clminus Fminus NO3

minus NO2minus and

SO42minus on a DIONEX ion chromatography system

HCO3minus and CO2

minus were analyzed via manual titrationNH3 was analyzed on a LACHAT analyzer 800 withNH4

+ then calculated based on pH and temperature ofthe sample using the NH3 result (Stumm and Morgan1996) Cations (Ca2+ Mg2+ K+ Na+ and Sr2+) wereanalyzed by inductively coupled plasma (ICP)

Results

The mean historical data are summarized in Table 1 forthe SDWWTP and Table 2 for the NDWWTP Dissolvedoxygen NO3

minus and NO2minus had similar results for both the

SDWWTP and NDWWTP sites for the aquifer intervalsNO3

minus concentrations were either detected at very lowconcentrations or below detectable levels NO2

minus levelswere below 1 micromoleL (micromol) for all aquifer intervalsand in the injectate at the NDWWTP and SDWWTP sitesfor the historical time series The injectate had a mean valueFig 4 Well locations at the NDWWTP

Hydrogeology Journal DOI 101007s10040-009-0570-8

Tab

le1

Meanvalues

forhistorical

timeseriesSDWWTP

mblsmetersbelow

land

surface

Geologicform

ation

Hyd

rostratig

raph

icform

ation

WellID

Open

interval

Periodof

record

Tem

pdegC

pHNH3micromol

Clndashmmol

SO42ndashmmol

NO3ndashmicromol

mbls

Pleistocene

Biscayn

eAqu

ifer

Injectate

(S-EFF)

Surface

591

ndash1207

277

66

889

203

109

Und

ifferentiated

Haw

thornAvo

nParkLim

estone

Upp

erFloridan

Aqu

ifer

(UFA

)1U

299ndash

332

983

ndash1207

240

79

1221

32

02

2U29

9ndash311

783

ndash1207

244

79

1321

32

03

3U29

9ndash32

0291

ndash1207

243

79

1023

32

03

BZ1

306ndash

316

783

ndash1207

242

76

1222

31

02

Avo

nPark

Lim

estone

Avo

nParkPermeable

Zon

e(A

PPZ)

13U

451ndash

475

296

ndash1207

239

77

6210

848

03

5U45

4ndash48

4594

ndash1102

241

76

492

108

49

03

6U45

4ndash48

3594

ndash1207

241

76

545

7630

03

7U45

4ndash48

2694

ndash198

245

74

526

738U

454ndash

480

894

ndash602

240

77

216

106

41

02

9U45

4ndash48

4195

ndash1207

239

77

64111

43

02

10U

454ndash

485

296

ndash1207

240

76

3510

542

02

11U

454ndash

484

296

ndash1207

240

76

118

106

43

02

14U

454ndash

480

296

ndash1207

239

74

320

9943

02

15U

454ndash

480

296

ndash1207

231

75

296

106

53

03

16U

454ndash

485

296

ndash1207

231

76

330

109

48

02

12U

456ndash

487

296

ndash204

249

76

100

111

42

02

MiddleCon

fining

Unit(M

C2)

BZ2

481ndash

507

783

ndash1207

254

75

106

133

56

02

2L50

1ndash51

0783

ndash1207

243

74

1219

926

02

4L51

9ndash56

112

91ndash

1207

240

73

1251

019

304

13L

530ndash

562

296

ndash1207

237

75

5550

822

809

3L54

0ndash57

7191

ndash1207

240

73

752

921

910

5L54

6ndash57

6594

ndash1102

239

74

652

821

604

6L54

6ndash57

6594

ndash1005

237

74

3052

622

703

7L55

0ndash57

1694

ndash198

242

71

1053

68L

546ndash

576

894

ndash602

237

74

554

124

804

9L54

6ndash57

3195

ndash1207

234

74

553

422

604

10L

546ndash

576

396

ndash1207

238

76

141

429

204

05

11L

546ndash

576

296

ndash1199

238

76

417

193

93

02

12L

546ndash

576

296

ndash1207

254

74

676

5730

03

15L

546ndash

576

296

ndash104

231

75

1253

125

204

16L

546ndash

576

296

ndash1207

229

74

653

221

904

1L56

1ndash58

7783

ndash1207

238

73

653

923

904

Oldsm

arFormation

Bou

lder

Zon

eLow

erFloridan

Aqu

ifer

BZ4

853

0783ndash894

249

72

634

3

Hydrogeology Journal DOI 101007s10040-009-0570-8

of NO3minus of 379micromol at the NDWWTP and 109micromol

at the SDWWTP for the historical time series Dissolvedoxygen was detected at concentrations less than 10 mg Lminus1

for all aquifer intervals Dissolved oxygen concentrationsfor the injectate at both the NDWWTP and the SDWWTPhad results above 3 mg Lminus1

Historical time series results SDWWTPThe historical period of record data for the freshwaterinjectate samples from the SDWWTP (identified as S-EFF) were available from 1991 through 2007 (Table 1)Temperature ranged from 218 to 311degC with a mean of277degC Mean pH in the historical time series was 66NH3 ranged from 1468ndash18496micromol with a mean of889micromol NH3 varied seasonally and increased with time(Fig 5) Clminus concentrations averaged 2 millimolesL(mmol) with a very small range and standard deviationindicative of the freshwater source of the injectateHistorical data from the SDWWTP for the UFA (wellsBZ1 1U 2U and 3U) were available from 1983 through2007 Temperature averaged 24degC with no significantdifference observed between the wells The range of pHwas from 76 to 82 in the UFA Chloride averagedbetween 21 and 23 mmol while NH3 means rangedbetween 10 and 13micromol The summary statistics for thewater-quality samples collected from the UFA showedconsistent values with no discernable variation over timeHistorical data from wells open to the APPZ at theSDWWTP (wells 5U 6U 7U 8U 9U 10U 11U 12U13U 14U 15U 16U) were available from 1994 through2007 Mean temperatures ranged between 231 and249degC in these wells There was little variation observedin the pH in the APPZ samples but the mean pH of 76was lower than the mean pH in the UFA Almost all of thewells showed variation in NH3 concentrations over timeMean values of NH3 in these wells ranged from 35micromolin well 10U to 545micromol in well 6U Well 6U showed anincreasing trend with time in NH3 that was observed to besimilar to the increasing trend of NH3 in the injectate(Fig 5) The spread between the 5th and 95th percentilewas the greatest in wells 6U and 12U Only wells 9U10U and 13U showed little variation in NH3 over timeMean concentrations of Cl- in wells 6U and 7U were 76and 73 mmol Wells in the MC2 were open to intervalsvarying in depth from 481 to 551 m Mean temperaturevalues ranged from 229 to 242degC in all wells with theexception of a mean value of 254degC in wells BZ2 and12L Mean pH values ranged from 73 to 76 Mean NH3

concentrations showed two groupings Wells BZ2 10L11L and 12L exhibited concentrations of 106 141 417and 676micromol respectively The remainder of the wellsexhibited mean NH3 concentrations of less than 55micromolClminus concentrations for wells 10L 11L and 12L were 429193 and 57 mmol respectively the remainder of the wellshad mean concentrations greater than 508 mmol (excep-tion is BZ-2 whose Clminus concentration of 133 mmolreflects the shallower depth of this well with the openinterval in the lower brackish water zone of the FloridanT

able

2Meanvalues

forhistorical

timeseriesNDWWTP

mblsmetersbelow

land

surface

Geologic

form

ation

Hyd

rostratig

raph

icform

ation

WellID

Open

interval

Period

ofrecord

Tem

ppH

NH3

Cl-

SO42-

NO3-

Revised

period

ofrecord

a

Tem

ppH

NH3

Cl-

SO42-

mbls

degCmicromol

mmol

mmol

micromol

degCmicromol

mmol

mmol

Pleistocene

Biscayn

eAqu

ifer

Injectate

(N-EFF)

Surface

797

ndash1207

284

65

8193

200

05

379

Avo

nPark

Lim

estone

Eocene

Upp

erFloridan

Aqu

ifer

(UFA

)N-1U

354ndash38

5197

ndash1207

231

76

188

737

35

02

N-2U

351ndash38

4396

ndash1207

230

78

177

662

36

21

N-3U

354ndash37

9396

ndash1207

229

78

173

658

36

20

N-4U

354ndash37

9496

ndash1207

231

76

181

684

35

08

Avo

nPark

Permeable

Zon

e(A

PPZ)

N-1L

430ndash46

1496

ndash1207

219

73

2612

3682

328

10

3496ndash797

224

72

193

4617

N-2L

431-

459

396

ndash1207

223

76

1684

3979

156

22

396

ndash898

229

78

177

4557

166

N-3L

430ndash46

0396

ndash1207

222

76

1314

4094

158

10

396

ndash1298

230

77

191

4548

149

N-4L

430ndash46

0496

ndash1207

224

72

1903

3804

152

16

496

ndash1298

223

75

237

4405

Hydrogeology Journal DOI 101007s10040-009-0570-8

Aquifer) Data collected from well 12L were similar todata collected for wells for 6U and 7U These wells hadhigh NH3 concentrations with low Clminus and SO4

minus concen-trations Historical data were available for the BoulderZone interval (well BZ4) from 1983 through 1994 Themean pH and temperature values were 72 and 249degCrespectively Mean NH3 concentration was 634micromol andshowed apparent seasonal variation and increasing trendover time and was similar to the injectate historical timeseries (Fig 5) The mean Clminus concentration was 3 mmolsimilar to the mean Clminus concentration of 2 mmol for theinjectate

Historical time series results NDWWTPThe historical period of record data for freshwaterinjectate samples (N-Eff) at the NDWWTP were availablefrom 2002 through 2007 Temperature ranged from 22 to34degC with a mean of 28degC The mean pH was similar tothe SDWWTP injecate at 65 NH3 ranged from 210ndash3764micromol with a mean of 819micromol and a large standarddeviation indicative of the apparent seasonality similar tothe SDWWTP Clminus concentrations ranged from 08 mmolto 1131 mmol with a mean 20 mmol slightly higher thanthe mean concentration of the SDWWTP injectateHistorical data were available from 1996 through 2007for wells open to the UFA (N-1U N-2U N-3U and N-4U) Mean temperature averaged 23degC in these wellswith no significant difference observed between the wellsMean values of pH ranged from 76 to 78 Clminus meanconcentrations ranged between 662 and 737 mmolsNH3 mean concentrations ranged between 17 to 18micromolConcentrations for the UFAwater-quality samples for theNDWWTP showed consistent values with no discernablevariation over time Historical data were available from1996 through 2007 for wells open to the APPZ (N-1L N-2L N-3L and N-4L) Temperature mean values were

22degC Analysis of historical NH3 data indicates increasingconcentrations of NH3 starting in late 1997 (Fig 6) NH3

concentrations appeared to have reached a peak concen-tration of 408micromol in well N-1L in July 2001 andsteadily declined thereafter to concentrations rangingfrom 200 to 250micromol Wells N-2L N-3L and N-4L showsimilar patterns as well N-1L but with lowered anddelayed peak concentration values NH3 concentrationsare observed to increase scatter after 2003 whichcorresponds to when purging commenced at theNDWWTP Once purging ceased in 2004 NH3 concen-trations in wells varied between 150ndash300micromol The Clminus

mean concentrations ranged from 368 to 409 mmol Clminus

in these wells exhibited variation over time and analysisof the time series indicated that as NH3 concentrationsincreased Clminus concentrations decreased (Fig 6) The timeseries data for the lower wells were revised to removedata after NH3 concentrations were observed to increasein each well in order to determine ambient concentrationsin the APPZ Revised NH3 mean concentrations rangedfrom 18ndash24micromol Clminus mean concentrations ranged from441ndash461 Very little variation was observed in NH3 andClminus mean concentrations after the time series data wereremoved

Major ion data collection resultsMajor ions were collected for this study from 2006ndash2007(Table 3) Data from wells at the SDWWTP site thatexhibited cross connections were removed from thisanalysis Data collected from the SDWWTP UFAexhibited very little variation between wells and weresimilar to the historical time-series data with low cationand anion concentrations For the APPZ wells NH4

+

mean concentrations could be combined into three groupswells 9U 10U and 13U with NH4

+ mean concentrationsof 60 67 and 143micromol respectively wells 14U and 16Uwith 497 and 439micromol and well 6U 823micromol Cation andanion mean concentrations showed a similar grouping asthe NH4

+ concentration grouping with well 6U consis-tently grouping independently and with increasing NH4

+

concentrations correlating to decreasing ion concentra-tions The MC2 mean NH4

+ concentrations could also becombined into three groups well 12L at a mean NH4

+

concentration of 765micromol wells BZ-2 10L and 13LNH4

+ at mean concentrations 176 200 and 108micromolrespectively the remainder wells at NH4

+ concentrationsbelow 10micromol Cation and anion concentrations could becombined in the same 3 groups as the NH4

+ groups withlower ion mean concentrations observed for BZ-2 10Land 13L and much lower ion concentrations observed inwell 12L As with well 6U in the MC1 well 12L in theMC2 consistently grouped independently

The NDWWTP wells open to the UFA (351ndash385 m)exhibited very little variation in field measurements andmean concentrations between wells and were similar tothe historical time series The interval (430ndash461 m) in theAPPZ at the NDWWTP also showed little variation withmean NH4

+ concentrations (215ndash295micromol) and mean

Fig 5 Time series NH3 data from the injectate (black circle) BZ-4(green triangle) and well 6U (red circle) at the SDWWTP site Theapparent seasonal variation observed in the injectate is a result ofincreased flows during the wet season and storm events Theincreasing trends with time correlate to increased injection over timedue to growth in population in Miami-Dade County

Hydrogeology Journal DOI 101007s10040-009-0570-8

concentrations of Clminus (371ndash386 mmol) varying littlebetween wells

Ternary diagramThe typical ClminusBrminus ratio for seawater is about 290 (Daviset al 1998) and most of the ClminusBrminus ratios at both siteswere within that range with no discernable differencesQuite often the addition of a third water-quality membercould enhance the understanding of the data and this wasthe case with using NH4

+ as the third end-member NH4+

Clminus and Brminus data were plotted on a ternary diagram withdata normalized to 100 Typical seawater and freshwaterNH4

+ Clminus and Brminus values after Hem (1985) were alsoplotted for comparison Water quality at the NDWWTPclustered into three distinct groups with two groups basedon depth of the interval sampled and the third the injectate(Fig 7) The ambient aquifer data plot close to seawaterThe injectate data plotted off in the lower left hand cornerdue to the large NH4

+ concentrations At the SDWWTPthree aquifer groupings were observed Ambient well datafrom the MC2 plotted similar to seawater Ambient welldata from the UFA plotted slightly towards freshwaterData from wells that showed elevated NH4

+ plotted in aline towards the injectate with groundwater data from 6Uand 12L plotting very close to the injectate This linerepresents the evolution of the water quality of these wellstowards the injectate water quality and does not show anyevolution of more saline water into the higher intervals inthe aquifer

Mixing end-member modelsEnd-member mixing models of wells 6U 12L and 10Lrepresented the results obtained for all wells at the

SDWWTP (Fig 8) Well 6U and 12L showed theprogressive freshening of water and increasing NH3

concentrations towards the injectate end-member(Fig 8) There was little mixing from the saline end-member towards the brackish end-member in well 6U andalmost all of the mixing was towards the injectate end-member Both 6U and 12L showed large changes inconcentrations from their original end-members over timeWell 10L showed a different pattern than 6U and 12Lwith gradual freshening of the saline water towards theinjectate end-member The mixing was towards the lowerrange of the injectate end-member and there were no largechanges in concentrations of either NH3 or Clminus from thesaline end-member Well N-1L at the NDWWTP end-member mixing model showed a different pattern than theSDWWTP (Fig 9) Clustering of the NH3Cl

minus ratios weredistinguished based on time The NH3Cl

minus ambient ratio canclearly be seen on Fig 9 and lies along the saline end-member As the concentrations of NH3 increased in time tothe peak concentration the NH3Cl

minus ratios showed twodistinct clusters Initially the NH3Cl

minus ratio showed gradualincreasing in NH3 with little change in Clminus from ambientconcentrations There was a rapid change in the NH3Cl

minus

ratio as NH3 reached the peak concentrations Once the peakwas reached the NH3Cl

minus ratios slowly declined in time

Discussion

The Floridan aquifer system was sampled by others atdifferent sites in south Florida and these data aresummarized in Table 4 Wells identified as WWF weremonitoring wells installed as part of the MDWASD ASRsystem west of the NDWWTP and SDWWTP (CH2MHill 1998) The ASR systems were not in use during the

Fig 6 Graph a shows the NH3 data time series for the wells in the APPZ interval at the NDWWTP The dashed lines indicate the purgingtime from 2003 through 2004 NH3 concentrations are observed to increase in well N-1L similar to contaminant breakthrough curves WellN-1L was the closest well to the uncased injection well when injectate backflowed into the APPZ NH3 concentrations for wells N-2LN-3L and N-4L appear to be similar and show a similar increase after 1999 Variability is seen in the data after 2003 Graph b showsClminus concentrations in well N-1L clustered at approximately 300 mmol and an abrupt decrease to less than 300 mmol is seen Clminus

concentrations in wells N-2L N-3L and N-4L are very similar and show a decrease in concentrations after 1999 until 2000 whenconcentrations appear to stabilize Clminus concentrations start to increase slightly and become variable after 2003 All four wells showsimilar concentrations of both NH3 and Cl- after 2004

Hydrogeology Journal DOI 101007s10040-009-0570-8

Tab

le3

Meanfieldparametersandionconcentrations

during

the20

06ndash2

007samplingcompleted

aspartof

thisstud

ymblsmetersbelow

land

surface

Geologic

form

ation

Hyd

rogeolog

icun

itOpen

interval

Well

Temp

pHNH4+

Ca2

+Mg2

+Na+

K+

Sr2+

Cl-

SO42-

HCO3-

Br-

F-

NO3-

NO2-

mbls

IDdegC

micromol

mmol

mmol

mmol

mmol

micromol

mmol

mmol

mmol

micromol

micromol

micromol

micromol

SDWWTP

Pleistocene

Biscayn

eAqu

ifer

Surface

S-EFF

290

67

112

51

03

07

30

430

197

6

Und

ifferentiated

Haw

thornOcala

Lim

estone

toAvo

nPark

Lim

estone

UFA

306ndash31

6BZ1

242

78

61

325

139

213

440

109

11

299ndash33

21U

236

81

61

324

142

224

456

117

01

299ndash32

03U

243

79

61

325

148

284

454

119

41

299ndash311

2U25

379

101

322

143

215

433

143

11

Avo

nPark

Lim

estone

APPZ

454ndash48

49U

238

77

604

1098

399

104

53

169

850

145

4ndash48

510

U24

877

675

1085

212

5112

53

174

451

045

1ndash47

513

U24

477

143

410

883

113

109

54

200

119

21

454ndash48

516

U23

277

439

49

943

7510

25

525

013

51

145

4ndash48

014

U25

075

497

36

662

6570

45

115

801

145

4ndash48

36U

251

75

823

35

872

3245

37

8151

11

MC2

501ndash51

02L

248

75

98

1614

84

147

194

42

305

750

148

1ndash50

7BZ2

241

76

176

511

121

3114

128

64

217

930

154

6ndash57

39L

231

76

311

4445

912

167

550

243

849

211

11

546ndash57

616

L22

975

411

4143

912

175

552

254

800

195

01

540ndash57

73L

241

75

410

4344

012

159

522

233

834

233

51

519ndash56

14L

245

75

711

4041

612

181

492

213

737

234

01

530ndash56

213

L24

275

108

1036

350

1217

446

024

377

531

32

154

6ndash57

610

L24

776

200

830

285

10111

369

233

588

773

054

6ndash57

612

L28

176

765

36

492

3654

45

8735

20

561ndash58

71L

234

75

411

6441

213

161

533

253

834

235

11

NDWWTP

Pleistocene

Biscayn

eAqu

ifer

surface

N-EFF

263

65

505

22

201

616

13

3610

3849

Avo

nPark

Lim

estone

UFA

354ndash38

5N-FA-1U

225

78

173

868

215

573

41

8118

00

135

1ndash38

4N-FA-2U

227

78

133

765

212

166

41

126

179

22

354ndash37

9N-FA-3U

212

79

163

766

213

362

31

115

32

135

4ndash37

9N-FA-4U

208

79

163

769

214

766

41

131

174

11

APPZ

430ndash46

0N-FA-3L

194

75

215

937

423

1121

638

017

365

153

71

243

0ndash46

1N-FA-1L

199

74

231

736

458

1110

038

620

383

942

21

143

0ndash46

0N-FA-4L

192

74

264

937

421

1122

337

119

369

546

32

143

1-45

9N-FA-2L

201

74

295

839

431

1212

538

322

374

848

62

1

Hydrogeology Journal DOI 101007s10040-009-0570-8

time of this study Wells designated as ldquoFPLrdquo were testswells installed into the Floridan aquifer system sim10 kmsouth from the SDWWTP (Dames and Moore 1975Florida Partners 2006) For comparison to the presentstudy the data from these sites were assumed to representambient water-quality concentrations as no injectionactivities had occurred at these sites Wells in this studythat exhibited little variation in the time series data andhad low NH3 concentrations were compared to the datafrom these other sites Although direct comparisons weredifficult due to the varying aquifer open intervals fromwhich these samples were collected some generalizationscan be made NH3 or NH4

+ concentrations from thesewells were below 29micromol Clminus concentrations increasedwith depth of the sampled intervals and were similar inconcentrations to wells in this study of approximately thesame aquifer interval NO3

minus concentrations were below1micromol similar to data collected for this study Based oncomparisons with water quality from these other sites therevised time series water-quality data that had mean NH3

concentrations below 30micromol were assumed to be ambientaquifer water with no influence of injectate All the wellsin the UFA at the SDWWTP were considered ambient andmost of the wells in the MC2 at the SDWWTP wereconsidered ambient with the exception of 10L 11L and12L All of the wells in the APPZ at the SDWWTP hadNH3 concentrations above ambient levels with well 9U thelowest Time series data at the NDWWTP indicated that allof the wells open to the UFAwere considered ambient andthe data from wells open to the APPZ were ambient prior tothe observed increase in NH3 concentrations

Ambient Clminus concentrations from this study showedbrackish transitional and saline zones in the Floridan

aquifer system for the SDWWTP and NDWWTP asdefined by Reese (1994) Although there were only twosample depths at the NDWWTP the top of the saline zoneat the north appears to be higher than at the SDWWTPMean temperatures at the NDWWTP were cooler than atthe SDWWTP with an average of 23degC for both intervalsThe NDWWTP lies closer to the Florida Straits and thecooler temperatures at that site may be due to closerproximity to open seawater Wells that showed a higherconcentration of NH3 at the SDWWTP showed highertemperatures (example Well 12L) whereas at theNDWWTP no change in temperature was noted withincreasing NH3 concentrations

Based on results of this study introduced nitrogen fromthe injectate into the Floridan Aquifer is mostly in theform of NH4

+ This is consistent with eH-pH diagrams fornitrogen (Stumm and Morgan 1996) where in most naturalenvironments any ammoniandashN would have the form ofNH4

+ (Hem 1985) No relationship was observed in thehistorical data or data collected as part of this study betweenNH3 and NO3

minus No change from ambient NO3minus concen-

trations was observed for wells that had elevated NH3

concentrations The reduced form of nitrogen (NH4+) was

not oxidized once introduced in the anoxic aquifer at eithersite and was conserved in the aquifer in this reduced stateAny introduced oxidized form of nitrogen (NO3

minus) from theinjectate that was reduced would result in insignificantchanges in NH4

+ concentrations as NO3minus concentrations

are two to three orders of magnitude less than NH4+ The

elevated concentrations of NH4+ in the Floridan aquifer at

the two sites are interpreted as the result of the upwardmigration of the injectate Once introduced into the aquiferNH4

+ appeared to have behaved conservatively

Fig 7 Ternary diagrams for the NDWWTP and the SDWWTP NH4+ Clndash and Brndash data collected from 2006ndash2007 were normalized to

100 Seawater and freshwater values (Hem 1985) were plotted Ambient water was grouped at the SDWWTP for the MC2 and UFAintervals Ambient MC2 data plot directly with seawater UFA ambient plots towards freshwater reflecting the fresher water quality in theUFA The injectate data plot at the NH4

+ end point indicating the freshwater quality but high NH4+ concentration of the injectate Well data

from the APPZ and MC2 intervals that have NH4+ concentrations above ambient levels plot in a line towards the injectate end point with

data from wells 6U and 12L plotting very close the NH4+ end point Data from the SDWWTP plot into distinct groups based on depth in the

aquifer but no line towards the injectate end point is seen

Hydrogeology Journal DOI 101007s10040-009-0570-8

At least two pathways of injectate were distinguishedbased on the analysis of the natural tracers at theSDWWTP One pathway at the SDWWTP appeared tohave rapid vertical pathways from the Boulder Zone up tothe APPZ with little mixing of ambient waters as itmigrated upward These vertical conduits did not appear

to extend up to the UFA This pathway is identified atwells 6U and 14U in the APPZ and well 12L in the MC2It may be present at well 8U in the APPZ however thedevelopment of cross connection in well 8U compromiseddata interpretation NH4

+ concentrations in these wellswere within the range of injectate NH4

+ concentrations

Fig 8 Graphs on the left areNH3Cl

minus mixing end-membermodels for the APPZ andMC2 intervals at theSDWWTP 6U 12L and 10Lare well identification codesArrows indicate increase intime Hatched red rectangleis injected freshwaterend-member indicating theseasonal range in concentra-tions Cyan square is theAPPZ brackish waterambientwater end-member blue circleis the MC2 saline waterend-member Graphs on theright are NH3 concentrationsover time Solid black lines areconcentrations from each wellsite red line is injected fresh-water concentrations Forwells 6U and 12L the dataplot towards the injectateend-member Little influenceis seen in well 6U from thesaline MC2 end-memberWell 10L shows a differentevolution of water qualitywith data plotting at the salineMC2 end-member and slowlyplotting towards the lower endof the injectate end-member

Fig 9 Graph a is the NH3Clminus mixing end-member model for the APPZ at the NDWWTP for pre-purge data (prior to 2003) for well N-

1L Arrows indicate increase in time Hatched red rectangle is injected freshwater end-member indicating the seasonal range inconcentrations Cyan square is the UFA brackish water ambient water end-member blue circle is the APPZ saline water end-member Thedata plot in separate groupings with the earliest time series plotting around the APPZ saline end-member The second data cluster plottowards the injectate end-member but no evolution towards the injectate end-member is seen as was seen for wells 6U and 12L at theSDWWTP Graph b is the post-purge data plotted for well N-1L Data plot with time back towards the APPZ saline end-member

Hydrogeology Journal DOI 101007s10040-009-0570-8

Clminus concentrations in these wells were also very close toinjectate Clminus concentrations

The mixing models for these wells show a mixingpathway almost directly towards the injectate end-mem-ber with no mixing from the lower MC2 interval observedfor wells 6U and 14U Wells that showed the highestconcentrations of NH3 at the SDWWTP also showedhigher temperatures with the temperature signal of thewarmer injectate observed in well 12L (mean temperatureof 28degC) in the data collected in 2006ndash2007 Well 12L inthe MC2 is much closer to the Boulder Zone than theAPPZ wells and higher injectate temperatures persist intothe MC2 Perhaps due to the longer travel times to theAPPZ the temperature signal was muted but still visible inthe APPZ Ion data for these wells showed freshening ofthe water quality These wells showed a density-drivenbuoyant rapid vertical advective pathway and transport ofthe injectate as a distinct water body with little mixing ofnative waters as it migrated upwards The rapid pathwayscould be the result of construction related events such asdrifting boreholes or the result of structural anomaliessuch as fracturing and karst features that would verticallyconnect aquifers and provide high hydraulic conductivitytransport pathways through confining units Migration ofsaline waters from the Lower to Upper Floridan Aquiferas a result of such structural anomalies have been reportedfor northeastern and central Florida (Flocks et al 2001Spechler 2001) where the Floridan aquifer system liesmuch closer to the surface Upward fluid migration ofinjected fluids in a Palm Beach County Florida deep wellinjection facility had been detected above the confiningzone between the injection zone and the overlayingmonitoring zone and this had been attributed to fractureddolostone comprising the majority of the confining zonestrata (Maliva et al 2007) however no fracturing of theconfining strata at either the NDWWTP or the SDWWTP

has been reported McNeill suggested that as wells locatedon the northwest side of the SDWWTP were cased abovethe DCU in the LFA this would be a possible cause of thebuoyant upward migration of injected fluids through themore permeable units above the DCU through isolatedvertical flow paths bypassing the MC2 (McNeill 20002002)

The second pathway was suggested by the grouping ofwell data observed in wells 15U 16U BZ2 10L and 11LThe well data from this group had no significantcorrelation between NH3 and Clminus The mixing modelsfor these well data showed a slow evolution of waterquality towards the lower average of the injectate end-member with time These wells showed a slight temper-ature increase but no clear temperature signal wasdistinguished in these wells Ion data did not show afreshening of the water quality with little difference seenbetween ambient ion concentrations and concentrationsfrom these wells Other studies (Boumlhlke et al 2006) haveindicated that NH3 transport can be retarded by a factor of3ndash6 in an aquifer with NH3 persisting in an aquifer afterthe more mobile constituents were flushed out if theaquifer remained under suboxic conditions At theSDWWTP it appears that there was still NH3 loadinginto the aquifer via rapid vertical pathways with increas-ing NH3 concentrations over time The data from this wellgrouping may indicate that once NH3 was introduced intoan aquifer interval it traveled horizontally at a muchslower rate with the freshwater injectate substantiallydiluted and not flushed out as freshwater continued tomigrate upwards

Four discrete injectate plumes were delineated at theSDWWTP based on the transport pathways The firstplume (plume 1 in Fig 10) located on the northeast of thesite was associated with the BZ-4 well which provided apathway up into the APPZ until it was plugged This

Table 4 Historical ambient Floridan Aquifer water quality data

Parameter Unit 1Ua WWFb WWFb FPLPW-3c

FPL testwelld

9Ua FPL testwell d

2La 3La FPL testwelld

299ndash332 m

260ndash305 m

260ndash308 m

314ndash380 m

340ndash410 m 454ndash484 m

456ndash517 m 501ndash510 m

530ndash562 m

639ndash701 m

pH 79 80 74 75 77 77 75 75 75 70HCO3

- mmol 00 32 27 33 21 30 26Ca2+ mmol 13 17 37 43 67 78 103 196Mg2+ mmol 27 28 73 101 155 160 434 555Na+ mmol 247 222 746 983 1582 1482 4382 4872K+ mmol 08 08 20 26 38 36 118 97Cl- mmol 223 705 271 821 1043 1794 1939 5216 5923SO4

2- mmol 41 75 69 03 69 47 137 42 226 307NO3

- micromol 03 08 02 02 02 03 02 48 02F- mmol 01 01 01 01 01 01 02 01Si mmol 05 04 02 05 03 03 02Sr2+ micromol 419 776 982 1849 1472 1586Total P micromol 32 71 65 65 32NH4

+ micromol 55 72 610 111 55NH3 micromol 08 294 123

a Data were collected for this study during 2006ndash2007 for wells at the SDWWTPbData from CH2M Hill 1998cData from Florida Partners 2006dData from Dames and Moore 1975

Hydrogeology Journal DOI 101007s10040-009-0570-8

plume slowly migrated to the surrounding areas mainlyvia diffusion as evidenced by slowly increasing NH3

concentrations but no change in Clminus concentrations Thesecond plume was located on the northwest corner of thesite in the APPZ (plume 2) This plume was detected inthe APPZ with no detection of it in the lower MC2indicating a direct pathway to the APPZ bypassing theMC2 This pathway seemed to persist with concentrationsof NH3 increasing with time similar to concentrationlevels of the injectate This plume was a chemicallydistinct water body with little mixing of native watersThe third plume located at well 14U (plume 3) may be adistinct plume but it may also be in connection withplume 2 No monitoring wells of the same interval as well14U are in the vicinity so the extent of this plume couldnot be determined The fourth plume was located on thesouth side of the site in the MC2 (plume 4) All fourplumes appeared to have the same initial transportmechanism up from the Boulder Zone through highhydraulic conductivity pathways with data from plumes2 3 and 4 indicating these pathways still persist

The data collected from the NDWWTP indicate differ-ent transport mechanisms than the SDWWTP Thetemperature signal of the warmer injectate was notobserved in wells with elevated concentrations of NH4

+Water quality showed no evolution towards the injectateplot in the ternary diagram The mixing model showedtwo mixing patterns one towards the injectate end-member before purging and one towards the ambientend-member once purging ceased As observed in the timeseries NH3 data NH3 concentrations were first observedto increase in well N-1L the well that was within 30 m ofthe uncased injection well and concentrations peaked at

341micromol well below the mean NH3 concentration of theinjectate Unlike the increasing NH3 concentrationsobserved at the SDWWTP that are the result of rapidvertical migration pathways once NH3 concentrations atthe NDWWTP peaked they have since decreased withtime All four NDWWTP lower wells have shown verysimilar water quality since 2004 when purging ceased atthe NDWWTP Both the time series analysis and the datacollected as part of this study in 2006 and 2007 appear toindicate a one-time pulse of injectate water into the APPZand this pulse of injectate was still migrating at the timeof this study through the aquifer in the direction ofregional flow There is no geochemical evidence of acontinuing source of NH3 at the NDWWTP however dueto retardation as discussed previously the NH3 plume mayhave persisted a long time in the suboxic aquifer (Boumlhlkeet al 2006)

Conclusions

Chloride bromide and ammonia were used to understandthe pathways and transport mechanisms of injectedwastewater into the deep saline Boulder Zone in theFloridan aquifer system The injectate source was treatedfreshwater with elevated levels of ammonia The waterquality of the injectate was chemically and physicallydistinct from ambient Floridan aquifer system water andthese distinctions were used to determine the possibletransport pathways At the SDWWTP four injectateplumes were identified along with two pathway mecha-nisms density-driven buoyant vertical flow and slowerhorizontal flow At the NDWWTP one plume was

Fig 10 Location of injectate plumes and their depth interval at the SDWWTP The source of the plume centered on the BZ well clusters(plume 1) was plugged in 1995 Plumes 2 3 and 4 are the result of continuing rapid vertical pathways up from the Boulder Zone Theextent of the plumes off site is not known as indicated by the question marks however based on data collected from the site approximateextent of the plumes on the site can be inferred The plume in the MC2 is limited to the southeast of the site The plume located in thenorthwest of the site is located in the APPZ and appears to have bypassed the MC2 The plume from the BZ well cluster appears to belimited to the east of the site The extent of the plume at 14U on site is unknown as there are no wells that monitor the same aquifer intervalin the vicinity of 14U

Hydrogeology Journal DOI 101007s10040-009-0570-8

identified and appeared to be a result of a one-time pulseinjection At the SDWWTP the injectate may first havemigrated upwards through discrete vertical pathways fromthe Boulder Zone to the Middle Confining Unit with thefreshwater injectate migrating upwards through salinewater as a chemically distinct water body The fourplumes identified at the SDWWTP appear to haveoriginated via this pathway Once introduced in the higheraquifer intervals the transport mechanism appeared to bea horizontal flow with mixing of ambient waters Therapid vertical pathways did not appear to extend up to theUFA At the NDWWTP the elevated levels of NH3 inthe lower Middle Confining Unit appeared to be the resultof a construction incident where a pulse of injectate waterbackflowed into an uncased injection well providing apathway to the upper interval Once introduced into theupper aquifer interval the plume slowly migrated with theregional flow within the aquifer No evidence of rapidvertical pathways was observed at the NDWWTP Duringthe course of this study it became clear that purging of thewells had unintended consequences for the SDWWTPCross connections developed in several wells between theupper and lower monitoring zones either during or afterpurging and these cross connections have compromisedwater-quality data in SDWWTP wells 5 6 7 8 11 12and 15 Although it could not be determined from thisstudy these cross connections may provide pathways ofinjectate into layers in the aquifer that had not beenpreviously affected by upward migrating injectate

Acknowledgements This study was funded by the Miami-DadeWater and Sewer Department (MDWASD) The authors greatlyappreciate S Villamil for her invaluable technical expertise andassistance in the field We thank C Powell S Kronheim W Pittand B Goldenberg of MDWASD for their cooperation and Drs ADausman and C Langevin of the US Geological Survey for theirinsightful comments during this research This report was signifi-cantly improved by the thoughtful review of two anonymousreviewers Dr Pricersquos contribution was partially funded by theNational Science Foundation Grant No DBI-0620409 This isSERC contribution 457

References

Arthur JD JB Cowart AA Dabous (2001) Florida Aquifer Storageand Recovery Geochemical Study Year Three Progress ReportOpen File Report 83 Florida Geological Survey TallahasseeFL

BCampECH2M Hill (1977) Drilling and testing of the test-injectionwell for the Miami-Dade Water and Sewer Authority ContractS-153 BCampECH2M Hill Gainesville FL

Bloetscher F Muniz A (2006) Preliminary modeling of class Iinjection wells in southeast Florida Ground Water ProtectionCouncil 2006 Annual Meeting Proceedings Miami FLNovember 2006

Bloetscher F Englehardt JD Chin DA Rose JB Tchobanoglous GAmy VP Gokgoz S (2005) Comparative assessment ofmunicipal wastewater disposal methods in southeast FloridaWater Environ Res 77480ndash490

Boumlhlke JK E Shinn C Reich A Tihansky (2003) Origins andisotopic characteristics of dissolved nitrogen species in groundwater imported domestic water and wastewater in the FloridaKeys US Geological Survey Greater Everglades Science

Program 2002 biennial report US Geol Surv Open-File Rep03-54

Boumlhlke JK Smith RL DN Miller (2006) Ammolonium transportand reaction in contaminated groundwater application ofisotope tracers and isotope fractionation studies Water ResourRes 42 W05411 doi1010292005WR004349

CH2M Hill (1981) Drilling and testing of the 8 injection wells andthe 3 monitoring wells for the South District Regional Waste-water Treatment Plant of the Mimi-Dade Water and SewerAuthority CH2M Hill Englewood CO

CH2M Hill (1998) Engineering report of the construction andtesting of the aquifer storage and recovery (ASR) system at theMDWASD West Wellfield CH2M Hill Englewood CO

Clark JF Bryant Hudson G Lee Davisson M Woodside GHerndon R (2004) Geochemical imaging of flow near anartificial recharge facility Orange County California GroundWater 42167ndash174

Corbett DR Kump L Dillon K Burnett W Chanton J (2000) Fateof wastewater-borne nutrients under low discharge conditions inthe subsurface of the Florida Keys USA Mar Geochem 6999ndash115

Dames and Moore Inc (1975) Floridan aquifer water supplyinvestigation Turkey point Area Miami-Dade County FloridaFlorida Power and Light Miami

Davis SN Whittemore DO Fabryka-Martin J (1998) Uses ofchloridebromide ratios in studies of potable water GroundWater 36338ndash350

Englehardt JD Amy VP Bloetscher F Chinn DA Fleming LEGokgoz S Solo-Gabriele H Rose JB Tchoaboglous G (2001)Comparative assessment of human and ecological impacts formunicipal wastewater disposal methods in southeast Floridadeep wells ocean outfalls and canal discharges University ofMiami Coral Gables FL

Fish JE Stewart M (1991) Hydrogeology of the surficial aquifersystem Dade County Florida US Geol Surv Water ResourInvest Rep 90-4108 50 pp

Flocks JG Kindinger JL Davis JB Swarzenski P (2001) Geo-physical investigations of upward migrating saline water from thelower to upper Floridan Aquifer Central Indian River RegionFlorida In US Geological Survey Karst Interest Group Proceed-ings US Geol Surv Water Resour Invest Rep 01-4011 pp 135ndash140

Florida Lakes Power Partners and Florida Power and LightCompany (2006) Well completion report for Floridan Aquiferwells PW-1 PW-2 and PW-4 FPL Turkey Point ExpansionProject (Unit 5) Homestead FL

Haberfeld JL (1991) Hydrogeology of effluent disposal zonesFloridan aquifer south Florida Ground Water 29186ndash190

Hem JD (1985) Study and interpretation of the chemicalcharacteristics of natural water US Geol Surv Water SupplPap 2254

Herczeg AL WM Edmunds (2000) Inorganic ions as tracers InCook PG Herczeg AL (eds) Environmental tracers in subsur-face hydrology Kluwer Norwell MA pp 31ndash78

Kaehler CA K Belitz (2003) Tracing reclaimed water in MenifeeWinchester and Perris-South ground-water subbasins RiversideCounty California US Geol Surv Water Resour Invest Rep03-4039

Kohout FA (1965) A hypothesis concerning cyclic flow of saltwater related to geothermal heating in the Floridan aquiferTrans NY Acad Sci Ser II 28249ndash271

Langmuir D (1997) Aqueous environmental geochemistry Prentice-Hall Upper Saddle River NJ

Maliva RG CW Walker (1998) Hydrogeology of deep-welldisposal of liquid wastes in southwestern Florida USAHydrogeol J 6(4)538ndash548

Maliva RG Guo W Missimer T (2007) Vertical migration ofmunicipal wastewater in deep injection well systems SouthFlorida USA Hydrogeol J 15(7)1387ndash1396

McNeill DF (2000) Final report a review of upward migration ofeffluent related to subsurface injection at Miami-Dade Waterand Sewer South District Plant McNeill Miami FL

Hydrogeology Journal DOI 101007s10040-009-0570-8