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Work Plan for Groundwater Monitoring Well Installation, Soil Gas and Groundwater Investigation, and Groundwater Monitoring Army Aviation Support Facility Stockton California and the absence of gravels (which can result in drill rod deflection) in the first 20 feet bgs, an adequate seal between formational materials and the drill rod should be formed. Hydrated bentonite may be used to seal the boring at the surface during sample collection. 3.3.2.3 Equilibrium Time During probe emplacement, subsurface conditions are disturbed. To allow for subsurface conditions to equilibrate, leak tests and soil gas sampling will not be conducted for at least 30 minutes following probe installation. 3.3.2.4 Purge Volume Test The purpose of a purge volume test is to ensure stagnant or ambient air is removed from the sampling system and that samples collected are representative of subsurface conditions. This said the ASGI Advisory states a default of three (3) purge volumes should be extracted prior to sampling in the case of sampling soil gas with a SummaTm canister. Soil gas samples are planned to be collected by Summa TM canister. In turn, 3 purge volumes will be evacuated prior to each sample. 3.3.2.5 Shut-in Testing Prior to purging or sampling soil gas, a vacuum (shut-in) test will be performed to check for leaks in the above ground fittings at each location. The assembled above-ground sampling train will be plugged, the lines evacuated to a measured vacuum of about 100 inches of water column (in-H20), or the vacuum created from Summar" canister, and held for approximately one minute. If there is any observable loss of vacuum, the fittings will be adjusted as needed until the vacuum in the above-ground portion of the sample train does not noticeably dissipate. Should continued loss of vacuum occur after adjustments to the sample train and fittings have been made, new tubing, fittings, and SummaTm canister will used and vacuum tested until the target vacuum is achieved. 3.3.2.6 Leak Testing Leakage during soil gas sampling may dilute samples with ambient air and produce results that underestimate actual site concentrations, or contaminate the sample with external contaminants. Leak tests will be conducted to determine whether leakage is present (e.g., the leak check compound is detected and confirmed in the test sample after its application). Leak tests will be conducted for every soil gas sample using a leak-check compound (tracer not associated with site specific contaminants) to confirm that ambient air intrusion is not occurring during sample collection. A liquid tracer compound will be applied to clean rags placed at all locations where ambient air could enter the sampling system or where cross contamination could occur, immediately before sampling. Samples will be analyzed for the tracer gas in addition to VOCs at a fixed-base laboratory. 3.3.2.7 Purge/Sample Flow Rate At the conclusion of the 30-minute period of equilibration, shut-in testing, and leak testing, soil gas will be purged through the samples tubing. A purge rate of 100 to 200 milliliters per minute (mL/min)will be maintained to limit stripping, prevent ambient air from diluting the soil gas samples, and to reduce the variability of purging rates. The low flow purge rate increases the likelihood that representative samples may be collected. The purge/sample rate may be modified based on conditions encountered in individual soil gas probes. Any modified rates will be documented in the soil gas report. OTI E 10