Texas Association of Groundwater Districts

November 30, 2011

Dave O’Rourke, PG, PE

LBG-GUYTON ASSOCIATES

Anthropogenic Groundwater Contamination in Texas Aquifers

Background

• TWDB-sponsored project

• Sister project with “Natural Sources of Groundwater Contamination in Texas” performed by BEG

• Project completed in August 2011

• Mapping and analysis intended for use by RWPGs: Drinking Water-centric

• Potential sources of groundwater contamination from human activity

• Published chemical analytical data for common anthropogenic contaminants

• Volume and treatment cost estimates of affected water

Objectives

Sources of Data

• TCEQ – SWAP Database – Potential Sources of Contamination (PSOCs)

– http://gis3.tceq.state.tx.us/swav/Controller/index.jsp?wtrsrc=

– PWS chemistry data

– Interagency Pesticide Database

• EPA - Underground Injection Control Database

• TWDB - Groundwater Database

• Railroad Commission

• USGS

– NAWQA

– NWIS

• Edwards Aquifer Authority

• Does NOT include contaminant monitoring wells

Groundwater Quality Data

• Chemical Analytical Data

– Public Water Supply (PWS) wells and Irrigation Wells from Interagency Pesticide Database

– Pre-Treatment or mixing; representative of source groundwater

– Non-standard data. Various data sources, sampling periods, detection limits, etc.

– Challenges for volume estimates

Data and Mapping Issues

• Scale, data availability, quality, variability

Contamination Mechanisms

Contamination Mechanisms

PWS Wells

• 12,636 Operational PWS wells in TX

• 5,961 PWS Systems

• WQ Data from 1,292

– Pre-Treatment or mixing; representative of source groundwater

– Non-standard data - Various data sources, sampling periods, detection limits, etc.

Potential Sources of Contamination (PSOCs)

• Business – Gas Stations, Automotive businesses, dry cleaners, etc.

• Industry – Chemical manufacturing, natural resource production,

pipelines, etc.

• Waste Disposal – Landfills, Injection Wells, Wastewater facilities, etc.

• Agriculture – Irrigated lands, CAFOs

PSOCs – Some Statistics

• Business – 55,409 Petroleum Storage Tanks

– 29,987 Automotive Businesses

• Industry – 473,818 Active Oil/Gas Wells

– 619,637 Inactive/Abandoned Oil/Gas Wells

– 187,000 miles of chemical pipeline

• Waste Disposal – 429 Class I UICs

– 39,452 Class II UICs

– 2,520 Abandoned MSW Landfills

– 1,862 Active MSW Landfills

Sample Map Chemical Pipelines, Regions H, I, and D

Sample Map Active O&G Wells, Regions E, F, and J

Sample Map Inactive O&G Wells, Regions E, F, and J

Sample Map Inactive O&G Wells, Regions D, H, and I

Sample Map CAFOs, Regions A, and O

Sample Map Superfund Sites in State

Common Anthropogenic Contaminants

• Hydrocarbons

– BTEX, MTBE

• Lighter than water

• Readily metabolized by native bacteria

• Chlorinated Compounds – PCE, TCE, Disinfection By-products (DBPs)

– Heavier than water, not as easily metabolized

• Pesticides/Herbicides

– Atrazine, Diuron

• Nutrients – Nitrates

TCEQ Groundwater Contamination Cases

Contamination Cases Requiring Public Notification of Private Well Owners

Year Number of Sites

Requiring Notifications

Number of Notifications

2004 24 9,695

2005 10 183

2006 31 423

2007 38 843

2008 42 610

2009 39 419

2010 23 476

Source: TGPC, 2009. 2010 (Draft)

Impacted Groundwater Summary Atrazine – Most commonly detected compound

PCE – Most commonly detected above PCL

PCL (ug/L) % Wells with

Positive

Detection

% Wells >

PCL

% Analyses with

Positive

Detection

% of Analyses > MCL

Atrazine 3 20.20% 0.45% 27.99% 0.55%

Chloroform 80 13.33% 0.04% 15.92% 0.02%

PCE 5 3.70% 1.37% 15.11% 1.70%

Simazine 4 8.18% 0.00% 14.64% 0.00%

Prometon 400 4.68% 0.00% 10.63% 0.00%

Diazinon 1 4.26% 0.06% 3.17% 0.04%

TCE 5 5.06% 0.44% 3.69% 0.25%

1,1,1-TCA 200 1.88% 0.00% 1.50% 0.00%

2,4-D 70 3.00% 0.07% 2.25% 0.05%

MTBE 13 2.15% 0.25% 1.80% 0.25%

Metolachlor 700 4.60% 0.00% 1.30% 0.00%

Benzene 5 1.76% 0.20% 1.78% 0.23%

Tebuthiuron 1000 5.31% 0.00% 1.20% 0.00%

Carbaryl 40 1.15% 0.00% 1.25% 0.00%

Alachlor 2 0.58% 0.00% 0.40% 0.00%

cis-1,2 DCE 70 0.48% 0.05% 0.45% 0.07%

Diuron 2 1.13% 0.28% 0.99% 0.25%

Maximum 20.20% 1.37% 27.99% 1.70%

Sample Map WQ Results – Atrazine in Groundwater

Sample Map WQ Results – PCE in Groundwater

Sample Map WQ Results – Nitrates in Groundwater

WQ Results – No apparent increasing trends with time

Volume Calculations Part 1, Area

Volume Calculations Part 2, Depth

H = (0.0112*L2)0.5 + b{1-exp[(-L*I)/(K*i*b)]}

Where

H = mixing zone depth (ft)

L = Source length parallel to

flow direction (ft)

I = Infiltration rate (ft/yr)

K = Aquifer hydraulic

conductivity (ft/yr)

i = Hydraulic gradient (ft/ft)

b = Aquifer thickness (ft)

Volume Calculations Conservative Assumptions

• A single lab result that exceeds PCL will tag that location with excedence even if subsequent sampling indicates reduced concentrations

• Lateral areas of contamination likely overestimated due to sparsity of data points

• Vertical mixing depth likely overestimated, often full aquifer thickness

Calculated Volume of Affected Groundwater

Total Calculated Volume = 1.65 Million Acre-feet

Annual TX GW Pumpage ~ 10 million ac-ft

16% of annual pumpage

1.6% of 10 years

pumpage

This estimate is likely

quite conservative.

A more reasonable

estimate may be indicated

by the percentage of

analyses exceeding PCL,

in the 1% range of annual

pumpage.

VOC Treatment Costs

Dependent on influent concentration and treatment volume

• 60 gpm: ~ $2-4/1,000 gallons

• 650 gpm: ~ less than $1/1,000 gallons

Comparison with Other Studies - VOCs

Parameter Data Source

Current Study EAA Study 1 USGS Study 2

Volatile Organic Compounds

Benzene 1.3% 0.7% 2.1%

Toluene 5.5% 3.8% 0.0%

Ethylbenzene 0.6% 1.2% 0.6%

Total Xylenes 1.0% 0.6% 1.7%

MTBE 1.9% 0.7% 12.7%

PCE 18.7% 22.2% 19.5%

TCE 4.5% 6.2% 14.0%

1,1,1-Trichloroethane 1.8% 1.2% 9.5%

cis-1,2-Dichloroethene 0.6% 0.5% 9.5%

Vinyl Chloride 0.3% 0.4% 0.9%

Carbon Tetrachloride 0.2% 0.4% 1.4%

Chloroform 18.1% 18.9% 36.1%

Comparison with Other Studies - Pesticides

Parameter Data Source

Current Study EAA Study 1 USGS Study 2

Pesticides and Herbicides

Atrazine 55.6% 25.8% 29.9%

Simazine 17.3% 15.5% 16.7%

Prometon 13.3% 17.4% 11.3%

Deethylatrazine 39.7% 63.5% 34.4%

Deisopropylatrazine 14.8% No data 13.0%

Diazinon 3.6% 2.8% 0.0%

2,4-D 2.6% 2.7% 0.5%

Carbaryl 1.5% 1.0% 0.5%

Metolachlor 1.7% 1.6% 10.9%

Tebuthiuron 1.5% 0.5% 0.9%

Diuron 1.2% 1.1% 3.3%

Dieldrin 0.1% 0.3% 0.5%

Alachlor 0.6% 0.0% 1.4%

Dinoseb 0.0% 0.0% 0.9%

Acetochlor 0.0% 0.0% 0.5%

PDF Map and Plates Link

http://www.twdb.state.tx.us/publications

/reports/contracted_reports/index.asp

Questions ?