These compounds are present in commonly used industrial solvents and degreasers or are components of gasoline. Methyl tert -butyl ether, a gasoline additive, was the most commonly detected compound. Chloroform was the second most commonly detected compound.
Chloroform is a byproduct of using chlorine as a disinfectant.
Chloroform also is present in septic-system effluent, and it has industrial uses. The presence of VOCs in limestone aquifers in the Great Valley near Harrisburg, Pa., is affected by land use as illustrated by the graph below. Within the urban area, analyses of samples from wells, springs, and a spring-fed stream indicate that contaminated ground water flows from springs into the streams. The frequency of detections of VOCs in urban areas is likely to be a result of the numerous urban sources of VOCs, including spills, leaks from underground tanks, improper disposal, atmospheric deposition, runoff from pavement, and leaking sewerlines. Underground storage tanks that contain gasoline and other fuels can be a source of VOCs in ground water.