To determine whether ground-water contamination has occurred or remediation efforts have been effective, it is necessary to collect ground-water samples in such a way that the samples are representative of ground-water conditions. Unfortunately, formation of stagnant water within conventional monitoring wells requires that these wells be purged prior to sampling, a procedure that may introduce significant bias into the determination of concentrations of sensitive constituents such as volatile organic compounds (VOCs). The use of in situ ground-water sampling devices, which minimize or eliminate the need for well purging, may help alleviate some of the difficulties associated with sampling ground-water at hazardous waste sites. In the study, several ground-water sampling devices, including two in situ systems, were field-tested to determine their capability for yielding representative VOC data. Sampling devices included a bladder pump, a bladder pump below an inflatable packer, a bailer, a bailer with a bottom-emptying device, an in situ Westbay MP System, two in situ BAT devices, and a prototype BAT well probe. The devices were field-tested at a site contaminated by a VOC plume, and the comparison was based on the ability of the devices to recover representative concentrations of the VOCs. The results of the study indicate that the tested in situ devices may eliminate the need for well purging prior to sample collection and that the resulting samples are at least as representative as those collected with a bladder pump in a conventional monitoring well.

"PB91-181776." "This study was conducted in cooperation with Water Resources Center, Desert Research Institute, Las Vegas, Nevada"--Cover. "Cooperative Agreement CR 812713-01"--Cover. "May 1991." "EPA 600-4-90-028." Includes bibliographical references (pages 52-54). Print reproduction.