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Soil Vapor Sampling SOP Page 7 of 11 Stantec Rev. 1.0 Apr 2019 could indicate that soil intruded during the push or that the expendable point was lost during the push. Driller Precautions The drilling contractor must ensure regular checks and cleaning of the PRT tip threads and seats. 0-rings must be changed daily. If the sample cannot be collected immediately, the end of the tubing should be capped with a stainless- steel Swagelok® cap. Upon completion of the soil vapor probe installations, subsurface conditions should be allowed to equilibrate for a minimum of 30-minutes before soil vapor samples are collected. 8.0 VAPOR SAMPLE COLLECTION 8.1 PERMEABILITY TESTING If there is a potential for low flow conditions due to soil lithology permeability may be assessed quantitatively by connecting a vacuum gauge to the implant tubing (as close as possible to surface seal). A pump and flow-meter equipped with rotameter are then used to withdraw soil gas at a measured rate. If a flow rate of approximately 100 mL/min with an applied vacuum of less than 100 inches water column (in. w.c.) cannot be sustained for 2 to 3 minutes, low flow conditions exist. An alternate procedure for sample collection under low-flow conditions may include collection of a smaller aliquot of soil gas followed by a period of time for the vacuum to dissipate (dependent of gas permeability of soils around sand pack). The process is repeated until approximately 800 mL of soil gas is collected in the 1-liter Summa®canister. 8.2 Leak Testing Leakage of atmospheric air into the sampling equipment during sample collection can compromise sample integrity and dilute measured soil vapor concentrations, possibly to the point that the concentration is below the method reporting limit (i.e., a false negative). Contaminants in ambient air can also enter the sampling system and be detected in the sample from a non-contaminated sampling implant (i.e., a false positive). Air leakage can occur at the land surface into the implant and, less likely, through loose fittings in the aboveground sampling equipment. Leak testing must be performed at every vapor monitoring well location each time a soil vapor sample is collected. To avoid leaks, the connections, fittings, and other parts associated with the sampling equipment will be checked to verify that they tightly fit. To test for leaks, two methods will be used. The first method involves performing a vacuum test (shut-in test) on the aboveground sampling equipment (e.g., valves, lines and fittings) as follows: THIS INFORMATION FOR AUTHORIZED COMPANY USE ONLY STANTEC CONSULTING