Laboratory studies and a field demonstration were conducted to determine the ability of the Snap Sampler to recover representative concentrations of several types of inorganic analytes from ground water. Analytes included non-metals, transition metals, alkaline earth metals, alkali metals, and a metalloid. In the laboratory studies, concentrations of analytes in Snap Sampler samples were com-parable with concentrations of the analytes in samples collected from a standpipe (i.e., control samples). For the field demonstration, there were sampling events at the former Pease Air Force Base. Samples taken using a Snap Sampler were compared with samples collected using conventional low-flow purging and sampling and a regenerated cellulose passive diffusion sampler. Based upon statistical analyses, analyte concentrations were found to be equivalent to those in the low-flow samples with one exception -unfiltered iron, where concentrations were significantly higher in the Snap Sampler samples. Differences were most pronounced in samples collected from the two stainless steel wells and from wells with higher turbidity levels. Elevated turbidities may have resulted from installing additional sampling equipment (including the baffle, pump, samplers, and bottom weight) in the well before sampling. We will examine this issue further at our next test site.
Records of selected veils, borings, springs, municipal vater systems, streamflov measurements, and chemical analyses of vater Prepared in cooperation vith the
C014MONWEALTH OF MASSACHUSETTS, WATER RESOURCES COMMISSION
Methods for groundwater sampling have evolved over time. This evolution has been driven by changing theories on how to obtain representative aquifer water samples. Passive sampling is a fairly recent method that relies on the natural flushing capacity of a well to obtain representative samples. The use of diffusion samplers is one method of passive sampling and works well under certain conditions. As part of a 2-year study to determine the temporal variability and trends in concentrations of volatile organic compounds (VOC's) in a large plume (0.5 mi2 area) of contaminated ground water in a glacial-drift aquifer, results of VOC analyses of samples collected with diffusion bag samplers were compared with those of samples collected with other types of samplers. The area of study is the primary source area of the large VOC plume and is located adjacent to a a river that losses flow and recharges the aquifer. The concentrations of VOC's, primarily tetrachloroethylene (PCE), trichloroethylene (TCE), and cw-l,2-dichloroethene (cw-l,2DCE), in samples collected with diffusion samplers show a strong positive linear correlation (root-mean square error of 0.94 and above) with concentrations from purged samples following low-flow sampling procedures. A total of 20 coupled diffusion and peristaltic-pump samples were collected from 7 wells completed in high-permeability glacial-drift. The mean concentration of PCE in the diffusion samples was 1,152 parts per billion (ppb) and the mean from the peristalticpump samples was 1,119 ppb. The standard deviations also were similar. The mean concentrations of TCE were slightly higher in diffusion samples (89.2 ppb) than peristaltic-pump samples (75.4 ppb). The mean concentration of cw-l,2DCE in diffusion samples (95.0 ppb) was virtually identical to the mean in peristaltic-pump samples. Although VOC concentrations changed dramatically at several wells over the sampled period, trends in VOC's detected using diffusion samplers corresponded with trends in VOC's from other lowflow sampling methods. For example, at two wells where coupled diffusion and peristaltic-pump samples were collected, VOC concentrations varied by a half order of magnitude over a two-month period. Although the diffusion sampler was installed and left in the well for the entire period, VOC concentrations in the diffusion sampler at the time of retrieval generally matched those in the instantaneous samples collected with the peristaltic pump on the same day, suggesting relatively rapid equilibration of the diffusion sampler to VOC concentrations in the well. The use of diffusion samplers allowed for the understanding of contaminant transport conditions at the study site because it allowed for an increase in the frequency of sampling without an associated increase in labor cost. For example, spatially variable declines in PCE concentrations were identified over the two-year study that are related to spatial variations in sediment lithology and the location of the plume within the groundwater flow system. Wells screened ...
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.