AWWA WQTC62521

As part of the National Water-Quality Assessment (NAWQA) Program, the U.S Geological Survey (USGS) is conducting Source-Water Quality Assessments (SWQAs) to characterize the occurrence and concentrations of anthropogenic organic compounds in groundwater withdrawn from selected aquifers used for water supply. SWQAs are intended to complement existing drinking water monitoring required by Federal, State, and local programs, which focus primarily on post-treatment compliance monitoring. In the first year, samples of source or raw water collected from about 15 production wells in each of 11 study areas across the United States were analyzed for about 270 anthropogenic organic compounds that include pesticides, pesticide degradates, polycyclic aromatic hydrocarbons, and volatile organic compounds (VOCs). Detection- frequency and concentration criteria developed from the results of these analyses were used to select a subset of the initial 163 wells for sampling during the second year of the study. During the second year, samples of source water from 69 wells and of the corresponding finished water were analyzed to characterize the extent to which compounds detected in source water are detected in finished water. Preliminary findings from the first year of sampling indicate that the five most frequently detected compounds were the pesticides metolachlor, deethylatrazine, and atrazine with detection frequencies of 52, 42, and 37 percent, respectively, and maximum concentrations of 3.6, 0.3, and 0.4 micrograms per liter, respectively; the pesticide degradate alachlor ethane sulfonic acid, with a detection frequency of 33 percent and a maximum concentration of 0.6 micrograms per liter; and the VOC trichloromethane, with a detection frequency of 47 percent and a maximum concentration of 13.5 micrograms per liter. About 45 percent of the constituents analyzed for were detected at least once. Results from the second year of sampling, which focuses on comparing concentrations of anthropogenic organic compounds in source water to concentrations in finished water, will enable NAWQA researchers to ascertain which compounds frequently found in source water are entering the communities' distributions systems and the concentrations at which they occur. Includes abstract only.