USGS:  Science for a changing world


U.S. Department of the Interior

U.S. Geological Survey
Water Resources Division
4821 Quail Crest Place
Lawrence, Kansas 66049-3839

March 13, 1996 ------------------------------- Contact: John Stamer (913) 832-3517


A recent article by the U.S. Geological Survey (USGS), U.S. Department of the Interior, indicates that the herbicides atrazine, alachlor, and cyanazine were likely to have implications for managing public water supplies in the Midwest, where most of the corn, soybean, and sorghum production in the Nation occurs. Public water utilities that withdraw supplies from either surface water or groundwater from alluvial aquifers adjacent to streams that receive runoff from cropland would most likely be affected.

The U.S. Environmental Protection Agency requires that utilities sample finished (treated) water supplies at least four times (quarterly) per year to monitor the occurrence of selected pesticides. According to John K. Stamer, Hydrologist and author, "Annual average cyanazine concentrations in Midwest water supplies could exceed the Health Advisory Level of 1.0 microgram per liter, established by the U.S. Environmental Protection Agency, whether sampled on a quarterly or monthly basis under most hydrologic conditions. However, annual average atrazine and alachlor concentrations are more likely to exceed their respective Maximum Contaminant Levels of 3.0 and 2.0 micrograms per liter on the basis of quarterly sampling rather than monthly sampling." Conventional water-treatment processes such as coagulation, sand filtration, and chlorination are ineffective in removing these herbicides from finished drinking water. Stamer emphasized that "the drinking-water regulations and criteria are based on annual averages and that one or more samples that exceeded the value of regulation or criterion do not necessarily indicate noncompliance." Concentrations of the three herbicides were generally larger in the spring and summer and smaller in the fall and winter.

Results are based on water samples collected for 1 year from the Platte River near its confluence with the Missouri River in Nebraska when hydrologic conditions were relatively dry during spring and near normal for the year. The drainage area upstream of this site is similar to many agricultural areas in the Midwest.

The article, "Water Supply Implications of Herbicide Sampling," written by John K. Stamer is published in the February 1996 issue of the Journal American Water Works Association (volume 88, number 2). Reprints can be viewed at U.S. Geological Survey District Offices in Lincoln, Nebraska, and Lawrence, Kansas. A limited number of reprints of the article are available upon written request to John K. Stamer, Hydrologist, U.S. Geological Survey, 4821 Quail Crest Place, Lawrence, KS 66049-3839.

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