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Fate and Transport of Pesticides in the Ground Water Systems of Southwest Georgia, 1993–2005

U.S. Geological Survey, 3039 Amwiler Road, Suite 130, Atlanta, GA 30360-2824

^* Corresponding author (msdalton{at}usgs.gov).

Received for publication March 30, 2007. Modern agricultural practices in the United States have resulted in nearly unrivaled efficiency and productivity. Unfortunately, there is also the potential for release of these compounds to the environment and consequent adverse affects on wildlife and human populations. Since 1993, the National Water-Quality Assessment (NAWQA) program of the U.S. Geological Survey has evaluated water quality in agricultural areas to address these concerns. The objective of this study is to evaluate trends in pesticide concentrations from 1993–2005 in the surficial and Upper Floridan aquifers of southwest Georgia using pesticide and pesticide degradate data collected for the NAWQA program. There were six compounds—five herbicides and one degradate—that were detected in more than 20% of samples: atrazine, deethylatrazine (DEA), metolachlor, alachlor, floumeturon, and tebuthiuron. Of the 128 wells sampled during the study, only eight wells had pesticide concentrations that either increased (7) or decreased (1) on a decadal time scale. Most of the significant trends were increasing concentrations of pesticides in older water; median pesticide concentrations did not differ between the surficial and Upper Floridan aquifers from 1993 and 2005. Deethylatrazine, in the Upper Floridan aquifer, was the only compound that had a significant change (increase) in concentration during the study. The limited number of wells with increases in pesticide concentrations suggest that ground-water sources of these compounds are not increasing in concentration over the time scale represented in this study.

Abbreviations: ACFB, Apalachicola–Chattahoochee–Flint River Basin • CI, cycle I (1993–2001) • CII, cycle II (2001–2005) • CFCs, chlorofluorocarbons • CFC-11, trichlorofluoromethane • CFC-12, dichlorodifluoromethane • CFC-113, trichlorotrifluoroethane • DEA, deethylatrazine • GAFL, Georgia–Florida Coastal Plain drainages • UFA, Upper Floridan aquifer • LT-MDL, long-term method detection level • MCL, USEPA maximum contaminant level • NAWQA, National Water Quality Assessment Program • UFA, Upper Floridan aquifer • USEPA, U.S. Environmental Protection Agency • USGS, U.S. Geological Survey