| This report evaluates the applicability of diffusion sampling for monitoring VOC concentrations in ground water collected from monitoring wells on the Massachusetts Military Reservation. The applicability of the diffusion-sampling method is measured by the utility of the method to detect concentrations of VOCs similar to those obtained by the pumped-sampling method. VOC concentrations in samples collected by the diffusion- and pumped-sampling methods are compared with each other; and in cases where the concentrations did not match, bias in the diffusion-sampling method is assessed. Comparisons are made between well, diffusion-sampler, aquifer, and geochemical characteristics, and the degree of agreement of the sampling methods. These comparisons add to the current understanding of diffusion samplers by examining how the samplers work in wells with short screens (2-5 ft long). This study was done cooperatively by the U.S. Geological Survey (USGS) and the Air Force Center for Environmental Excellence (AFCEE). Ground-water samples from 89 monitoring wells were collected from July 1999 through December 2002. |