A study was conducted near the Raymark Superfund Site in Stratford, Connecticut to compare results of soil-gas sampling using dedicated vapor probes, a truck-mounted direct-push technique - the Geoprobe Post-Run-Tubing (PRT) system, and a hand-held rotary hammer technique - the AMS Gas Vapor Probe (GVP) kit. A comparison of VOC concentrations using dedicated vapor probes and the GVP sampling kit indicated that the two methods provided similar results. However, at one location, VOC concentrations were significantly higher for dedicated vapor probes indicating potential leakage with the GVP system. VOC concentrations using the PRT system were higher than VOC concentrations using dedicated vapor probes by an average factor of 1.2. This is the same magnitude observed for spatial variability on a scale of 1 m (median of 1.2 and average of 1.3 for 90 sample pairs). However, this effect did not appear to be due to spatial variability which would result in random scatter not a consistent bias as observed. It is also unlikely that extraction volume or sampling sequence caused the observed bias given the results of extraction volume and sample sequence testing. VOC concentrations using the PRT system were also higher than VOC concentrations using the GVP kit by an average factor of 2.4. Similar to the comparison between probe and PRT sampling systems, the effect did not appear to be due to spatial variability, extraction volume, or sequence of sampling. Thus, utilization of the PRT system resulted in observation of higher concentrations of VOCs compared to the GVP kit and dedicated vapor probes. However, variation in concentration was relatively minor when compared to spatial variability on the scale used for comparison testing. Hence for practical purposes, all three sample systems can be considered approximately equivalent.
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