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Mr. Jeffrey Wong <br /> Environmental Health <br /> San Joaquin County <br /> March 8, 2024 <br /> Advancement of Soil Borings and Soil and Groundwater Sampling <br /> Fifteen soil borings (SB-1 through SB-15)will be advanced to evaluate subsurface conditions within the vicinity of <br /> the site features discussed above. The proposed boring locations are shown on Figure 1. The soil boring <br /> locations will be pre-cleared using a hand auger tool for the first five feet. Soil borings will then be advanced via <br /> use of a direct-push drilling unit to the desired total depth. Soil cores will be collected into acetate liners and <br /> retrieved for logging and classification. One soil sample will be collected for analysis from each boring. The <br /> sample selected for analysis will be determined in the field based on the results of field screenings using a <br /> photoionization detector, visual/olfactory observations, or at a depth just above the observed water table. The final <br /> depth of each boring will not exceed 15 feet below the ground surface. Unused soil cuttings will be placed in a 55- <br /> gallon drum for characterization and off-site disposal. <br /> A previous investigation performed by others at the Site indicated that groundwater was potentially present at <br /> depths of 5-10 feet below ground surface. Four of the proposed soil borings (SB-6, SB-9, SB-11, and SB-13) are <br /> proposed to be completed as temporary monitoring wells for the purposes of collecting direct groundwater <br /> samples for laboratory analysis. The grab samples will be collected using a bailer or peristaltic pump with a limited <br /> amount of purging. Purge water generated during these activities will be placed in a 55-gallon drum for <br /> characterization and off-site disposal. <br /> Upon completion of grab groundwater sampling, the temporary well screen and riser will be removed. All boring <br /> locations will be backfilled with a slurry grout to the surface and restored to match existing grade and condition <br /> (e.g., asphalt or concrete), under the oversight of the San Joaquin County Health Department inspector. <br /> Laboratory Analyses <br /> Soil and groundwater samples will be collected into appropriate laboratory supplied containers and will be <br /> transported to a California-certified laboratory in ice-chilled coolers and under strict chain-of-custody protocols for <br /> requisite analyses. All soil samples will be submitted for analysis for total petroleum hydrocarbons diesel range <br /> organics (TPH-DRO), TPH gasoline range organics (TPH-GRO), volatile organic compounds (VOCs) and <br /> polyaromatic hydrocarbons. Select samples collected near the used oil UST and oil/water separators will also be <br /> analyzed for one or more additional analysis including polychlorinated biphenyls and total (CAM 17) metals. <br /> Groundwater samples will be analyzed for TPH-DRO, TPH-GRO and VOCs. <br /> Quality Assurance/Quality Control (QA/QC)samples will also be collected to include submission of a trip blank <br /> sample for VOCs, blind duplicate, field/equipment blank, and a matrix spike/matrix spike duplicate for each <br /> analysis performed. <br /> Soil Vapor Sampling <br /> Soil vapor samples are proposed to be collected adjacent to the two fuel dispenser locations (SV-6 and SV-7), <br /> and at one location near the used oil UST (SV-8; Figure 1). Soil vapor samples will be collected at least 48-hours <br /> after drilling a small diameter hole in the concrete pad adjacent to each dispenser and installing a soil vapor <br /> probe. Each soil gas probe will be installed above the water table and properly abandoned after sample collection. <br /> Soil vapor samples will be collected into summa canisters and analyzed for VOCs by the United States <br /> Environmental Protection Agency (EPA)test method TO-15. <br /> www.arcadis.com 2/3 <br /> Draft Lathrop CA Phase II_Work Plan <br />