dave o'rourke, anthropogenic groundwater contamination in texas aquifers
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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 ?