VOLATILE ORGANIC COMPOUNDS IN THE NATION'S GROUND WATER AND DRINKING-WATER SUPPLY WELLS

Volatile organic compounds (VOCs) are produced in large volumes and are associated with a myriad of products, such as plastics, adhesives, paints, gasoline, fumigants, refrigerants, and drycleaning fluids. Widespread and long-term use of VOCs and their ability to persist and migrate in ground water raise questions about possible adverse effects on the environment, including drinking-water quality. A long-term survey by the National Water-Quality Assessment Program of the United States Geological Survey provides the most comprehensive national analysis to date of the occurrence of VOCs in ground water, based on results from sampling between 1985 and 2002. Among the major findings are that VOCs were detected in most aquifers throughout the Nation, and were not limited to a few specific aquifers or regions. VOCs were not detected, however, in many of the nearly 3,500 sampled wells; for example, about 80 percent had no detections above a threshold of 0.2 part per billion. The most frequently detected VOCs were chloroform, the solvents perchloroethene and trichloroethene, and the gasoline oxygenate methyl tert-butyl ether; 13 of the 55 compounds included in the assessment were not detected at all. A separate analysis of untreated ground-water samples from drinking-water supply wells showed that VOCs were detected in domestic well samples (14 percent) and public well samples (26 percent). Less than 3 percent of samples of ground water from domestic and public wells had concentrations greater than Federal drinking-water standards.