1. Texas Association of Groundwater
Districts
Anthropogenic Groundwater
Contamination in Texas Aquifers
November 30, 2011
Dave O’Rourke, PG, PE
LBG-GUYTON ASSOCIATES

2. Background
• TWDB-sponsored project
• Sister project with “Natural Sources of
Groundwater Contamination in Texas”
performed by BEG
• Project completed in August 2011

3. Objectives
• 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

4. 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

5. 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

6. Data and Mapping Issues
• Scale, data availability, quality, variability

7. Contamination Mechanisms

8. Contamination Mechanisms

9. 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.

10. 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

11. 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

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

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

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

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

16. Sample Map
CAFOs, Regions A, and O

17. Sample Map
Superfund Sites in State

18. 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

19. TCEQ Groundwater Contamination Cases

20. Contamination Cases Requiring Public
Notification of Private Well Owners
Number of Sites
Number of
Year Requiring
Notifications
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)

21. Impacted Groundwater Summary
Atrazine – Most commonly detected compound
PCE – Most commonly detected above PCL
PCL (ug/L) % Wells with % Wells > % Analyses with % of Analyses > MCL
Positive PCL Positive
Detection Detection
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%

22. Sample Map WQ Results – Atrazine in Groundwater

23. Sample Map WQ Results – PCE in Groundwater

24. Sample Map WQ Results – Nitrates in Groundwater

25. WQ Results – No apparent increasing
trends with time

26. Volume Calculations
Part 1, Area

27. 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)

28. 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

29. Calculated Volume of Affected Groundwater
Total Calculated Volume = 1.65 Million Acre-feet
16% of annual pumpage
Annual TX GW Pumpage ~ 10 million ac-ft 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.

30. 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

31. Comparison with Other Studies - VOCs
Data Source
Parameter 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%

32. Comparison with Other Studies -
Pesticides
Data Source
Parameter
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%

33. PDF Map and Plates Link
http://www.twdb.state.tx.us/publications
/reports/contracted_reports/index.asp

34. Questions ?