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Geospte& consultants less than 5% of the minimum shroud concentration, consistent with recommendations in the Advisory (DTSC 2015). 4.2.5.4 Purge and Sampling Rate Prior to sampling, air will be purged from each soil vapor probe to remove stagnant or ambient air and collect samples that are representative of subsurface conditions. A minimum of three casing volumes will be purged prior to sampling, consistent with recommendations in the Advisory. Purge volumes will be calculated based on the volume of the void space in the tubing plus an estimate of the void space in the sand filter pack of each soil gas probe. The probes will be purged by drawing soil gas from the formation using a lung box to fill a I-liter(L) TedlarTM bag. The purged soil vapor will be screened in the field using a PID, multi- gas detector, and a helium detector. The purge volume for each sample location will be recorded. Soil vapor will be purged from each location at an approximate flow rate of 200 milliliters per minute(mUmin). 4.2.5.5 Soil Vapor Sample Collection After completion of shut-in testing, leak testing, and purging, soil vapor samples will be collected through dedicated NylaflowTM tubing attached to each probe with airtight fittings into I-L SummaTM canisters. Soil vapor samples will be collected until the vacuum on the SummaTM canister decreases from 30 inches of mercury to approximately 5 inches of mercury. Duplicate samples will be collected at a frequency of 10% of the number of primary samples with a"tee"-fitting that splits the soil vapor sample between to two canisters. 4.2.6 Sample Labeling,Handling, and Analysis Soil, groundwater, and soil gas samples will be labeled, handled, and analyzed as presented below. 4.2.6.1 Sample Identification and Handling Each soil, soil vapor, and grab groundwater sample will be assigned a unique alphanumeric identifier. The identifier will be formatted as "Project Identifier-Location-Matrix-Depth-Date" using the following information: • The project designator will be "817B,"to denote Port of Stockton UST-817B site. • The location will correspond to sample locations shown in Table 1. • The matrix will correspond to the media type sampled from, abbreviated"SS" for soil, "GW" for groundwater, and"SV" for soil vapor. • The depth will indicate the sample depth in feet bgs. • Date of collection will be in the form of YYYYMMDD. Investigation Work Plan—UST 817B 10 December 2024