Occurrence and distribution of volatile organic compounds in drinking water supplied by community water systems in the Northeast and Mid-Atlantic regions of the United States, 1993-98

Data on volatile organic compounds (VOCs) in drinking water supplied by community water systems (CWSs) are available for 12 Northeast and Mid-Atlantic States from 1993-98. The data are from 2,110 CWSs representing a 20 percent random selection of the total 10,749 active CWSs in the region. The data were collected for compliance monitoring under the Safe Drinking Water Act from both surface-and ground-water sources and largely represent samples of finished drinking water collected prior to distribution. Overall, 39 percent of the 2,110 randomly selected CWSs reported a detection of one or more VOCs at or above 1.0 μg/L (micrograms per liter).

Although differences in analytical coverage complicate comparisons, in the 1,543 CWSs with THM data at or above 1.0 μg/L, 42 percent reported an occurrence of one or more THMs. The common detection of THMs in finished drinking water probably is related to their formation through the chlorination of drinking-water supplies. Comparatively, solvents, the next most frequently detected VOC group, were reported in 9.8 percent of 2,097 CWSs with solvent data at or above 1.0 μg/L, and gasoline components were detected in 9.0 percent of 2,098 CWSs with data at or above 1.0 μg/L.

Individually, the THMs—chloroform, bromodichloromethane, chlorodibromomethane, and bromoform—were the most frequently detected VOCs ranging from 33 to 8 percent. The most frequently detected non-THM compound was methyl tert-butyl ether, which was identified in 8 percent of CWSs. Of the 2,110 randomly selected CWSs, 6 percent had at least one sample with one or more VOCs with a concentration above a Maximum Contaminant Level, Health Advisory, or Drinking-Water Advisory.

VOCs were more frequently detected in drinking water from systems that are supplied by surface-water sources, or both surface-and ground-water sources, than in systems that are supplied exclusively by ground water, and from systems serving very large and large populations (serving