fractured bedrock characterization and effective remedy selection in region 4 · 2013-05-11 ·...

FRACTURED BEDROCK CHARACTERISATION AND

EFFECTIVE REMEDY SELECTION IN REGION 4

BEN BENTKOWSKI, P.G. EPA REGION 4

11/2/2010 EPA Region 4 Perspective 1

Presentation Outline Region 4’s area with Fractured Bedrock Aquifers

Examples of three kinds of aquifers Fractured Metamorphic

Fractured Igneous

Fractured Sedimentary

Characterization and Remediation Five Federal Facilities Four Non-Federal Facilities

Summary and Conclusions



Fractured Metamorphic Rock

Lawrenceville, GA


Fractured Igneous Rock

Fractured Sedimentary Rock

West Trenton, NJ

Manchester, TN



Air Force Plant No. 6 - Marietta, GA Fractured Metamorphic Rock - Piedmont

Site Map


Airplane Assembly since WWII

Multiple Solvent Releases

Detailed Characterization

Groundwater contamination in saprolite, partially weathered rock (PWR) (together considered the overburden aquifer) and bedrock (BR)

Dissolved Phase and DNAPL

Most recent report – (third) Annual Corrective Action Effectiveness Report - RCRA




Characterization included: Bedrock cores and thin section analysis (gneiss v. schist)

Borehole geophysics PWR aquifer test - one connected anisotropic aquifer

but with differing properties Site-wide water level gauging and gradient analysis

suggesting less flow in BR Extensive soil and groundwater sampling Conceptual Site Model development

1011/2/2010 EPA Region 4 Perspective


Hydrogeology Conceptual Site Model

DNAPL Conceptual Site Model


Air Force Plant No. 6 - Marietta, GA Fractured Metamorphic Rock - Piedmont Conceptual Site Model


Air Force Plant No. 6 - Marietta, GA Fractured Metamorphic Rock - Piedmont TCE in the

Overburden Aquifer


Air Force Plant No. 6 - Marietta, GA Fractured Metamorphic Rock - Piedmont TCE in the

Bedrock Aquifer



REMEDIAL TECHNOLOGIES SELECTED Air Sparge/Soil Vapor Extraction in Overburden Aquifer

and Vadose Zone

In-Situ Chemical Oxidation in Overburden Aquifer

Microbiological Enhancement with Microbes

Permeable Reactive Barrier

Monitored Natural Attenuation

Land Use Controls



GOALS: Reduce Mass Flux and Offsite Migration & Facilitate MNA

This is happening but offsite investigation handled by different contractor

TIMEFRAME: Estimated for Overburden, not for Bedrock aquifer

NOTE: No treatment of DNAPL in the fractured bedrock

“It is important to emphasize that the presence of residual DNAPL does not impact the conclusions of the RA (risk assessment) and the recommendations for site risk management.” Final Corrective Action Plan, p. 2-5


Alabama Army Ammunition Plant - Childersburg, AL Fractured Sedimentary Rock

Located 40 miles southeast of Birmingham, AL

Operated 1941 -1945 manufacturing TNT, DNT

Approximately 5,000 acres

Standby 1946 – 1973 and declared excess

Property no longer owned by Army

CERCLA investigations started in the 1980s

Source Control - 120,000 cubic yard soil incineration 1994-97

2010 - Final Soils ROD

Groundwater RI completed 2010



•Broad expanse of Knox Formation, carbonates

•Thrust sheets evidence tectonic activity resulting in significant fractures

•Adjacent to Coosa River whose course is fracture controlled


MAIN MANUFACTURING AND STORAGE AREA

Investigated with traditionalbiased/ hotspotm ethodsbutdid notprovide acceptable groundwatercharacterization



2003 - 2009 GW Investigation •Bedrock Focus •Fracture Trace Analysis •Resistivity Surveys •Focused Drilling for bedrock wells

on fractures/conduits •18 of 19 drilled on fractures

•Central facility v. exit pathway wells •Thermal survey along river confirmed exit points •To complete RI, characterization approach required focus on

the fractured nature bedrock •With source removed, bedrock GW now demonstrated to be

relatively minor problem 11/2/2010 EPA Region 4 Perspective 19


Redstone Arsenal - Huntsville, AL Fractured Sedimentary Rock

38,300 acres just west of Huntsville, AL

1,841 acre Marshall Space Flight Center within Redstone Arsenal property

158 active IRP sites, 20 surface media OUs, 13 GW investigation areas

Finalized on NPL in 1994

COCs – solvents, metals, pesticides, perchlorate & chemical weapons material

Karst hydrogeology with fractured bedrock influence



Structural setting –horst and graben

Dipping limestones

Thermal imaging of springs

Coring, hydro-physics, flute wells

Complicated groundwater chemistry with salt water and natural oil at depth


Local Conceptual Hydrogeologic Model

Area-wide ConceptualHydrogeologicalM odel

Figures from MSFC reports 11/2/2010 EPA Region 4 Perspective 22


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schkaem per,October,2010

0 650 1,300 2,600 3,900 5,200 Feet ±

Map showing TCE Plum e and

W ells with Groundwater > 1% Effective Solubility

overlayed with the Interpreted Faults based on Seism icLines

RSA -146

11/2/2010 EPA Region 4 Perspective M ap by KayW i

Explanation

!C W ells with Effective Solubility > 1%

Seism icFaultLines

2009 TCE GroundwaterPlum e

Concentration (ug/L)

1 -10

10 -100

100 -1,000

1,000 -10,000

10,000 -100,000

>100,000

23


Oak Ridge Reservation, Oak Ridge, TN Anniston Army Depot, Anniston, AL Fractured Sedimentary Rock

Very large, very complex sites in Valley and Ridge

Hydrogeology is a blend of fractured due to tectonic activity and karst due to carbonates

Both facilities have performed source control/removals and interim actions for receptor protection

Neither have final groundwater remedies for their largest releases


J. P. Stevens Facility- Upstate South Carolina Fractured Metamorphic Rock – Piedmont with Igneous Intrusions

Source Area (Tank Farm)

Overall, much smaller scale of release & remedial action BUT uses broad range of characterization techniques

COCs – Benzene, Chlorobenzene Cis-1,2-DCE, Vinyl Chloride


CHARACTERIZATION and FINDINGS Regional recon and outcrop mapping – site at edge of thrust

sheet

Lineament studies and rose diagrams

Trenching perpendicular to creek and structural dip – detailed logging

Found series of intrusive dikes in soil/saprolite Used structural information to predict anisotropy and

design aquifer characterization




Membrane Interface Probe used in Source Areas

Cored bedrock with packer and analytical tests on fracture features

Bedrock aquifer test – 60 GPM with minimal drawdown (14 GPM Steady State P&T)

Capture zone analysis using simplified three layer model

Ozone sparging source control/treatment

Groundwater recovery system – plume migration control



GW Flow direction

Baseline conditions

After 90 and 200 days

Ozone Air Sparge Progress


Why was Ozone Sparging Successful at J.P. Stevens?

Sparge and multi-level injection points enhance shape of area of influence Monitoring of indicator parameters (ORP, DO)

substantiated ozone was impacting groundwater Good interconnection between saprolite and bedrock Multiple depths of injection and monitoring Well-designed pilot study Length of monitoring before, during, and after Spacing of monitoring points



Hitachai - Greenville, SC Fractured Metamorphic Rock

Release of 12,000+ lbs of TCE

This remedial action employed In-Situ Thermal Desorption in soils and shallow bedrock

14 Heater wells (~90’ bls) 10 Heater vacuum points (~95’

bls)

2 Recovery wells (~45-76’ bls) recovered 72,000 gallons of

water during operation before water became steam Therm alTreatm entArea

33’x76’x90’deep PW R at55’


Hitachai Greenville, SC Fractured Metamorphic Rock

BEFORE AFTER Note: treatment zone only 2,500 ft2


Hitachai Greenville, SC Fractured Metamorphic Rock Removed about 12,000 lbs TCE (~5 months operation)

Met treatment goals for vadose zone soil

Goal was 60 ug/kg TCE

Attained 13.41 ug/kg TCE (UCL) Overall soil (vadose and subaqueous) 17.05 ug/kg TCE

Initial reductions of 75% to 99% of TCE in groundwater

Rebound noted (DNAPL; Fractures, Relic Fractures, Back-Diffusion)

Longer treatment period required for more bedrock improvement

Progress towards but not the Final Remedy

Fractured Metamorphic Bedrock

Historical solvent release managed with shallow SVE and ozone treatment in nearby springs – interim remedy

Ongoing investigation focused on facility and generally shallower portions of bedrock aquifer

Private deep bedrock drinking water supply wells contaminated up to 1 mile away

Detailed geological mapping by State Geologic Survey

Detailed hydrogeological characterization by USGS


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Explanation

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4 90

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0 235 470 940 1,410 1,880 Feet

Figure byKay W ischkaem per,O ctober,201,M illsGap Rd.

11/2/2010 EPA Region 4 Perspective 36 0

Fractured Metamorphic Bedrock

Historical site understanding focused investigation topographically downgradient and shallower

Employed sophisticated characterization techniques to understand possible connections between solvent releases and contaminated private drinking wells

Deepest contaminated well discovered to date - 700’ deep

Recent characterization work will guide future work with a much improved conceptual site model. However, it does not represent an easy path forward.



Actual Example of Poor Characterization Fractured Rock – North Carolina Piedmont

One well with 50’ open hole completion in bedrock with DNAPL solvents

Two analytical data points -1 set of three diffusion bag samplers and 1 sample collected 6 months later by low flow purge

Proposed one well pilot study - Enhanced Reductive Dechlorination


Actual Example of Poor Characterization Fractured Rock – North Carolina Piedmont

Just a Few of the Problems with This Approach

Contamination not delineated

No surveys to identify fractured zones

No other proposed monitoring wells

Pilot Study would invalidate the use of this one well as a monitoring location

No demonstration of how this well relates to the rest of the site or how this test would benefit the rest of the site


SUMMARY EPA Region 4 Perspective

FEDERAL FACILITIES Large facilities, Large number of releases, Large volume of

releases

Applying a wide range of increasingly sophisticated characterization technologies

Performing source removal, source control and receptor protection

Final groundwater remedies - uncommon

Deep fractured bedrock remediation - no final answer YET


SUMMARY EPA Region 4 Perspective

Non-Federal Facilities Smaller facilities and smaller releases

Also applying a wide range of increasingly sophisticated characterization technologies

Appear to have made more progress Smaller problems, smaller solutions different motivation - Industry v. Federal

Deep fractured bedrock remediation – no final answer YET


CONCLUSIONS This Hydrogeologist’s Perspective

Last 20 years have made great advances in types and sophistication of characterization. Focus on flow zones and geophysics/sensors

Biggest number of unresolved sites have dissolved or DNAPL solvents in fractured bedrock.

At a basic level, it still a question of really understanding the nature and extent of the contamination and how that affects the selection of an effective remedy.

CONCLUSIONS This Hydrogeologist’s Perspective

Good progress on remediating saprolite and partially weathered bedrock

Fractured Bedrock and Solvents No cure for this problem yet

Difficult and expensive to characterize flow pathways at depth

Back diffusion and time (cost) to remediate – biggest impediments

Ultimate Goal The MCLCONCENTRATION

∞


fractured bedrock characterization and effective remedy selection in region 4 · 2013-05-11 ·...

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