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ADVISORY- ACTIVE SOIL GAS INVESTIGATIONS <br />5.1.1 Syringes <br />Syringes should be checked for leaks before each use by closing the exit valve and <br />attempting to force ambient air through the needle. Gas-tight glass syringes with Teflon® <br />seals are preferred. Glass syringes should be leak tested periodically to verify integrity <br />with age. <br />Plastic syringes should not be used because of the potential interaction with some <br />target analytes. <br />5.1.2 Passivated Stainless Steel Canisters <br />Passivated stainless steel canisters need a flow regulator and vacuum gauge when <br />sampling soil gas. If the canister is not fitted with a permanent vacuum gauge, a field <br />vacuum gauge should be attached between the flow regulator and the canister inlet <br />during sampling. To prevent stripping, connections should be initially hand-tightened. To <br />verify the integrity of the seal on the steel canisters during transit, pressure readings <br />should be collected during the canister's journey. The stationary laboratory should <br />record the pressure when the canisters leave the laboratory and record it again on <br />receipt of the canisters. Likewise, the field crew should record the pressure upon start <br />and completion of the sampling. Typically, canisters are returned to the stationary <br />laboratory with a slight vacuum (two to four inches of mercury). These pressure <br />measurements should be included in the laboratory's analytical report as a mechanism <br />to verify the integrity of the sample. <br />Pressure measurements should be collected using a calibrated pressure gauge, using <br />the same gauge at the laboratory and in the field. Field crews should only rely on <br />canister-dedicated pressure gauges if the gauges are calibrated and working properly. <br />Canister-dedicated gauges tend to be inaccurate due to overuse. <br />Note that for passivated stainless steel canisters, storage pressure and humidity in a <br />canister are also important factors that determine analyte recovery. Additionally, <br />mercaptans, dimethyl acetal and bis-[chloromonnethyl] ether at low concentrations are <br />not suitable for collection in passivated canisters pursuant to a study by Brymer and <br />others (1996). <br />5.1.3 Polymer Gas Sampling Bags or Glass Bulbs <br />Samples in polymer gas sampling bags or glass bulbs should be analyzed within six <br />hours after collection. Appendix B discusses the merits of collecting samples in polymer <br />gas sampling bags. <br />Surrogates do not need to be added to polymer gas sampling bags because surrogate <br />recovery levels cannot be precisely calculated since the volume of soil gas collected in <br />a polymer gas sampling bag cannot be measured precisely. Thus, adding surrogates to <br />polymer gas sampling bags is unnecessary. <br />Samples collected in glass bulbs should have surrogates added within 15 minutes of <br />collection and the samples analyzed within six hours after collection. <br />July 2015 25