Volatile Organic Compounds in Ground Water – 15 Years of Research by the U.S. Geological Survey

During the past 15 years (1994-2008), the National Water-Quality Assessment Program (NAWQA) of the U.S. Geological Survey has collected or compiled data on volatile organic compounds (VOCs) in ground water from across the United States. Detailed analyses of these data have revealed many important findings and implications for ground-water quality at a national scale. VOCs have been detected in ground water from aquifers throughout the Nation. Although prevalent in ground water, the concentrations of most detected VOCs were relatively low and few exceeded human-health benchmarks.

The most frequently detected VOCs in ground water were trihalomethanes such as chloroform and solvents such as perchloroethene and trichloroethene. The gasoline oxygenate methyl tert-butyl ether (MTBE) was also frequently detected. Mixtures were a common mode of occurrence of VOCs in ground water. Public-supply wells had higher occurrence of VOCs compared to domestic-supply wells and also had more frequent occurrence of VOC concentrations that exceed a human-health benchmark. Various sources may be responsible for VOC contamination of ground water but the most likely include point sources such as hazardous waste sites, leaking storage tanks, and septic systems as well as non-point-source influences from urban development. Properties of the unsaturated zone and aquifer redox conditions also affect the concentrations of VOCs in ground water.

The findings indicate that aquifers may be more vulnerable to VOCs than anticipated and ground-water managers may need to consider proactive measures to protect ground water for future use. Findings from the NAWQA Program also aid in developing appropriate risk-assessment and exposure studies for VOCs in ground water and alert government agencies of the need to screen high-production volume chemicals for their environmental and toxic properties prior to widespread use.