AN EVALUATION OF SOIL-GAS SURVEYING FOR H2S FOR LOCATING SUBSURFACE HYDROCARBON CONTAMINATION

A soil-gas survey was conducted at a gasoline service station and a fo rmer fire training facility to determine if surveying for hydrogen sul fide could be useful in locating nonaqueous phase hydrocarbon fuel in the subsurface. Relative to total organic vapor, oxygen, and carbon di oxide distributions, detectable hydrogen sulfide concentrations were m uch more restricted to the suspected source vicinity at both sites. Ap preciable levels of soil-gas hydrogen sulfide, up to 600 Vppb, were ob served in areas characterized by anaerobic or microaerophilic conditio ns having bulk oxygen levels below 4 percent. Based on the hydrogen su lfide distribution, nonaqueous phase hydrocarbon fuel was located at e ach site. These results suggest that soil-gas surveying for hydrogen s ulfide may help locate mobile or residual gasoline and other nonaqueou s phase hydrocarbons in the subsurface.