Anthropogenic Organic Compounds in Source and Finished Water from Community Water System Wells in Western and Central Connecticut, 2002-2004

A water-quality assessment by the U.S. Geological Survey (USGS) determined the occurrence of anthropogenic (manmade) organic compounds (AOCs) in water from 15 community water system (CWS) wells and associated finished drinking water. The study, which focused on water from the unconfined glacial stratified aquifer in western and central Connecticut, was conducted as part of the USGS National Water-Quality Assessment Program (NAWQA) Source Water-Quality Assessment (SWQA) project and included analysis of water samples for 88 volatile organic compounds (VOCs), 120 pesticides, and 50 other anthropogenic organic compounds (OAOCs).

During Phase I of the study, 25 AOCs were detected (12 VOCs, 10 pesticides, and 3 OAOCs) in source-water samples collected from 15 CWS wells sampled once from October 2002 to May 2003. Although concentrations generally were low (less than 1 microgram per liter), four compounds were detected at higher concentrations in ground water from four wells. The most frequently occurring AOCs were detected in more than half of the samples and included chloroform (87 percent), methyl tert-butyl ether (MTBE, 80 percent), 1,1,1-trichloroethane (67 percent), atrazine (60 percent), deethylatrazine (60 percent), perchloroethene (PCE, 53 percent), and simazine (53 percent). Trichloroethene (TCE) was detected in 47 percent of samples. Samples generally contained a mixture of compounds ranging from 2 to 19 detected compounds, with an average of 8 detected compounds per sample.

During Phase II of the study, 42 AOCs were detected in source-water samples collected from 10 resampled CWS wells or their associated finished water. Trihalomethanes accounted for most of the VOCs detections with all concentrations less than 1 microgram per liter. Chloroform, the most frequently detected VOC, was found in all source-water and all finished-water samples. As with the Phase I samples, other frequently detected VOCs included MTBE, and the solvents 1,1,1-trichloroethane, PCE, and TCE. Triazine herbicides and their degradation products accounted for most of the detected pesticides.