This paper reviews both field and laboratory studies that tested or compared the ability of various types of sampling devices to deliver representative ground water samples. Several types of grab samplers, positive displacement devices, and suction‐lift devices were evaluated, Gas‐lift and inertial‐lift pumps were also evaluated. This study found that most of these devices can. under certain circumstances, alter the chemistry of ground water samples, das‐lift pumps, older types of submersible centrifugal pumps, and suction‐lift devices are not recommended when sampling for sensitive constituents such as volatile organics and inorganics, or inorganics that are subject to oxidation/precipitation reactions. In general, of the devices reviewed in this paper, bladder pumps gave the best recovery of sensitive constituents. However, better performance could be achieved for several devices if improved operational guidelines were developed by additional testing, especially at lower flow rates. Clearly, further research is warranted. Future studies should focus on pumping rate, flow control mechanisms, and dedication or decontamination of sampling devices.

Twenty polymeric tubings were filled with a test solution containing eight organic solutes. The test solutions were monitored for losses, indicating that sorption had occurred, and for signs that leaching of organic constituents had occurred. The tubings tested included seven flexible products and eight fluoropolymers. Among the rigid tubings tested, three fluoropolymers (fluorinated ethylene propylene [FEP], FEP‐lined polyethylene, polyvinylidene fluoride) were the least sorptive tubings. However, even these tubings readily sorbed some of the analytes. Among the flexible tubings tested, a fluoroelastomer tubing and a tubing made of a copolymer of vinylidene fluoride and hexafluoropropylene were the least sorptive. Several of the tubings tested leached constituents into the test solution. The polyurethane, polyamide, flexible polyvinyl chloride (PVC), polyester‐lined PVC, and silicone‐modified thermoplastic elastomer tubings were found to leach the most constituents. We were unable to detect any constituents leaching from the polyethylene tubings, the rigid fluoropolymer tubings, and one of the plasticized polypropylene tubings.

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.

A series of laboratory and field studies were conducted to determine the ability of the Snap Sampler to recover representative concentrations of VOC and explosives in ground water. For the laboratory studies, statistical analyses of the data (for each analyte) were conducted to determine if the concentrations of analytes in samples taken with the Snap Sampler were significantly different from known concentrations of the analytes in samples collected from a standpipe (i.e., control samples). For the field studies, concentrations of analytes in samples taken with the Snap Sampler were compared with concentrations of the analytes in samples taken using the EPA's low-flow purging and sampling protocol. Again, statistical analyses were used to determine if there were statistically significant differences between the individual analyte concentrations in these samples. Two field trials were conducted for VOCs and one field trial was conducted for explosives. In the laboratory studies, the Snap Sampler recovered concentrations of VOCs that were comparable to those in the control samples after equilibrating the Snap Sampler for 3 days. Comparable concentrations of explosives were recovered after equilibrating the Snap Sampler for 24 hours. In the field studies, concentrations of VOCs and explosives were comparable to concentrations of these analytes in samples that were collected using low-flow purging and sampling.

This is the second part of a study conducted to determine whether polymeric sampling tubing can affect organic analyte concentrations during a sampling event. In this part of the study, we looked for sorption and desorption of tricholoroethylene (TCE) and leaching of organic constituents in water pumped through five types of polymeric tubing. The materials tested were a rigid fluoropolymer, a flexible fluoropolymer, low‐density polyethylene (LDPE), and two plasticized polypropylene tubings. The effects of tubing length and flow rate were examined. The least sorptive tubings, both initially and at equilibrium, were the fluoropolymers. However, in some instances the LDPE tubing had little effect on TCE concentrations. This was when a slow flow rate was used to sample relatively shallow wells (50 feet [15 m] or less) or when a faster flow rate (1 L/min) was used to sample wells that are less than 500 feet (152 m). Further testing is recommended using more sorptive analytes. Using high performance liquid chromatography (HPLC), we were unable to detect any constituents leaching from any of the tubings used in these studies, even when a slow flow rate was used. However, desorption of sorbed analytes is a concern for all the tubings tested, including the rigid fluoropolymer.

This report examines sorption of low ppb levels of organic solutions by polytetra‐ fluoroethylene (PTFE), rigid polyvinyl chloride (PVC), and stainless steel 304 and 316 well casings. Nineteen organics were selected, including several munitions and chlorinated solvents. Compounds were selected to offer a range of physical properties, such as solubility in water, octanol/water partition coefficient, and molecular structure. When these results were compared with the results from a similar study conducted at ppm levels, the rate and extent of sorption by PTFE and PVC were the same as seen previously for almost all analytes. There were no losses of any compounds associated with stainless steel. At these low levels (ppm and ppb), the rate of diffusion within the polymer (PVC and PTFE) is independent of concentration. Only with PTFE are the rates rapid enough to be of concern when monitoring for some contaminants in ground water. Tetrachloroethylene was the compound PTFE sorbed the most rapidly. The study showed that PVC well casings are suitable for monitoring low levels (ppm and ppb) of organics.

Five relatively newly developed groundwater-sampling devices (the Kabis, HydraSleeve, Discrete Interval, Pneumc-Bailer, and USGS Passive Diffusion Bag [PDB] samplers) were tested to determine their ability to recover representative concentrations of a variety of analytes, including volatile organics, explosives, pesticides, and metals. The first phase of the study included several standpipe experiments with known concentrations of analytes. In the second phase, the devices were used in the field to sample TCE from a deep well and were compared with samples taken using lowflow sampling.We found that the PDB sampler was the easiest device to use but should be used only for selected VOCs. The HydraSleeve and the Kabis Sampler are thief-type samplers that were also relatively easy to use. Although these devices could produce representative concentrations of explosives, pesticides, and metals in the standpipe experiments, they elevated the turbidity in our monitoring well. Therefore, we would recommend that their use be limited to wells where the turbidity is not affected by their use, especially if sampling for metals or the more hydrophobic organic

Four well casing materials — polyvinyl chloride (PVC), polytetrafluoroethylene (PTFE), and stainless steel 304 (SS 304) and 316 (SS 316) — were examined to determine their suitability for monitoring inorganic and organic constituents in well water. The inorganic study used a factorial design to test the effect of concentration of mixed metals (arsenic [As], chromium [Cr], lead [Pb], and cadmium [Cd]), pH, and organic carbon. Sample times were 0.5, 4, 8, 24, and 72 hours. Except for slow loss of Pb, PTFE well casings had no significant effect on the concentration of metals in solution. For the other casings, changes in analyte concentration often exceeded 10 percent in eight hours or less and, thus, could bias analyses of samples taken from wells constructed with these materials. Specifically, PVC casings sorbed Pb and leached Cd; SS 316 casings sorbed As and Pb and leached Cd; and SS 304 casings sorbed As, Cr, and Pb and leached Cd. Both stainless steel casing materials showed markedly poorer performance than the PVC casings. The well casings were also tested for sorption/desorption of 10 organic substances from the following classes: chlorinated alkehes, chlorinated aromatics, nitroaromatics and nitramines. Sample times were 0, 1, 8, 24, and 72 hours, seven days, and six weeks. There were no detectable losses of analytes in any of the sample solutions containing stainless steel well casings. Significant loss of some analytes was observed in sample solutions containing plastic casings, although losses were always more rapid with the PTFE casings than with PVC. Chlorinated organic substances were lost most rapidly. For samples containing PTFE casings, losses of some of these compounds were rapid enough (>10 percent in eight hours) to be of concern for ground water monitoring. Losses of hydrophobic organic constituents in samples containing PTFE casings were correlated with the compound's octanol/water partition coefficient.