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COUNTIES WITH GROUNDWATER CONTAMINATION FROM NITRATES, PESTICIDES
AND ARSENIC POTENTIALLY FROM AGRICULTURAL ACTIVITIES,
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* nitrate levels exceeding 10 mg/L. In many areas, nitrate levels may be due
to natural factors rather than due to agriculture.
** Counties with arsenic concentrations exceeding the recommended EPA drinking water standard of 0.05 mg/L.
In certain areas, arsenic may be due to naturally-occuring levels rather than agriculture.
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Source: Texas Commission on Environmental Quality, 2002 Draft Texas
Water Quality Inventory (September 2002), 2003; and Texas Groundwater Protection Committee, Joint Groundwater Monitoring and Contamination Report, 2002 (2003),
Table 1.
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Just as they have contaminated surface water, agricultural and forestry activities
have also degraded groundwater quality in Texas. Unauthorized discharges and runoff from Confined Animal Feeding Operations (CAFOs) have been responsible for nitrate
contamination of shallow groundwater. (However, excess nitrate in groundwater can be caused by other sources, such as poorly designed or old septic tanks.) In
2001, the Texas legislature authorized more stringent permit requirements and enforcement action for large dairy farms in the Bosque Watershed area. Currently in
Texas, there are more than 5,000 CAFOs and more than 600 facilities which are large enough to require a state no-discharge wastewater permit.Of these 600, some 50 are required to conduct
groundwater monitoring * These and other agricultural sources are subject to enforcement and inspections by the TCEQ, while smaller sources are generally
inspected by the State Soil and Water Conservation Board. Between FY 1996 and FY 2001, TCEQ inspected between 589 and 1,098 agricultural facilities per year, issued
between 15 and 307 notices of violations, and issued between five and 32 administrative orders. Penalties collected were on average about $5,000 per order *. While most of these administrative orders involved the danger to surface waters, in 1998 contamination of groundwater by a
large CAFO between Tom Green and Runnels counties just outside of San Angelo, led to enforcement action by state environmental authorities.* The
primary causes of agriculture-related groundwater contamination are runoff from CAFOs, pastures, and barnyards;
excessive nitrogen fertilization of cropland; and land-clearing and other agricultural practices that change soil
composition, altering its ability to filter out pollutants. The contamination of groundwater from pesticides and fertilizers
is of greatest concern in the High Plains, the southern rice belt, and the Rio Grande Valley, while contamination from
CAFO runoff is of concern in the Panhandle, North-Central, and East-Central portions of the state.*
Agricultural chemicals such as pesticides and herbicides also are a major concern for groundwater protection. From
1987 to 1990, the Texas Department of Agriculture, which regulates pesticide use, surveyed water wells for pesticide
residues in 11 counties and discovered 75 cases of pesticide-contaminated groundwater. The pesticides found included
arsenic, dicamba, atrazine, and prometon. None of these high levels, however, was determined to be in violation of
state agricultural regulations. In 1996 the department transferred the cases to the TNRCC -- today called the TCEQ --
for further analysis. The agenchy was able to confirm contamination in 6 of the cases. In addition to these data, the
TCEQ has maintained the Interagency Pesticide Database, which compiles the results of sporadic groundwater
monitoring for pesticides statewide. Analyses of some 2,460 samples can be found in this database, indicating some
280 detections of pesticides and confirmed contamination at 33 sites for such pesticides as atrazine (21 sites),
prometon (4), and one detection each of lindane, metolachlor and picloram, 2,4-D, 2,4,5-D, dicamba, diuron and
hetachlor epoxide. In all the TCEQ reported 42 confirmed cases of groundwater contamination related to pesticides *
Other risks to groundwater from agricultural activities include contamination by nitrates and arsenic. High nitrate levels
are sometimes caused by infiltration from fertilizers and animal wastes. Statewide, 24 percent of water wells sampled
through the TWDB ambient monitoring network exceeded the drinking water standard for nitrate, with even higher
percentages in west central and northwest Texas. Animal manure and fertilizer application are the main causes of
agricultural-based high levels of nitrogen and nitrates in groundwater.During the 1990s, some 23 confirmed cases of
elevated arsenic groundwater in Howard and Martin counties near the city of Knott have been attributed to point
sources such as cotton gins, gin waste, gin trash, and hull pits, among other sources.* These high levels of arsenic
were mainly found in wells pumping from the Ogallala Aquifer, which is the major source of drinking and irrigation
water for the Panhandle and High Plains region of Texas. However, it is difficult to distinguish between naturally and agriculture-based arsenic concentrations.
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