Abstract

A Remedial Investigation/Feasibility Study (RI/FS) of Operable Unit 3 at Hill Air Force Base is currently being conducted by James M. Montgomery Consulting Engineers, Inc. (JMM). As part of the site characterization phase of the RI, JMM conducted a soil-gas screening survey and a ground-water sampling and analysis program in the Industrial Waste Treatment Plant (IWTP) area during the summer and fall of 1988. The soil-gas survey consisted of sampling and analysis of 69 soil gas sampling probes which were analyzed in the field using a portable gas chromatograph. The target volatile organic compounds (VOCs) used in the soil-gas survey were benzene, toluene, 1,1-dichloroethene, trichloroethene, and tetrachloroethene. The groundwater sampling program consisted of sampling and laboratory analysis of ground water obtained from twelve monitoring wells located in the vicinity of the IWTP and the same general area encompassed by the soil-gas survey.

This paper presents a comparison between the VOCs detected in the soil-gas measurements with those detected in the ground water sampled from the same area. While in general there is some correlation between the VOC concentrations measured in the soil gas versus that in the ground water, there is very little agreement between the concentrations measured in the two media when compared on a point by point basis. Reasons for the lack of agreement between the two data sets includes (1) the presence of a clay lens which acts as a barrier to diffusion of VOCs between the water table and the ground surface, and (2) the presence of near-surface VOC source areas which affect VOC concentrations in soil gas.