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UWork Plan for Additional Groundwater Investigation Quik Stop Market No. 132 3555 West Hammer Lane Stockton,California f ' Task 3. Advance Borings and Perform Sampling and Analysis In order to further delineate the vertical and lateral extent of petroleum hydrocarbon impacted soil and groundwater related to the site, borings are proposed at five down-gradient locations at the �] intersection of West Hammer Lane and Mariners Drive as shown on Figure 3. Based on review of �I the site geology, it appears that a second water bearing zone may exist beneath the site at approximately 20 to 30 feet bgs. In order to further delineate the extent of petroleum hydrocarbon impacted soil and groundwater within this water bearing zone, four borings will be completed to an approximate depth of 25 feet below grade surface (bgs). In addition, a fifth boring will be completed to 20 feet below the deepest known drilling depth a the site per the request of the San EEEL..�Srr Joaquin County Environmental Health Division in order to further delineate the vertical extent of petroleum hydrocarbon impacted soil and groundwater beneath the site. The proposed deep boring will be completed to a maximum drilling depth of approximately 50 feet bgs, and will be completed downgradient from the monitoring well containing the maximum known MTBE concentration. The proposed boring may be terminated at a shallower depth if a competent fine-grained unit with a rI thickness of five feet or more is encountered during drilling activities. This will be done to minimize the possibility of cross-contaminating a deeper aquifer. The proposed locations are based on the established southerly to southeasterly groundwater gradient at the site, and the historic concentrations of MTBE in the existing site groundwater monitoring wells. The boreholes will be drilled by a drilling contractor with a current C-57 license. All project work will be performed under the direction of a California Registered Geologist. Soil and groundwater grab samples will be obtained at each of these locations and will be analyzed by a California-certified laboratory for TPH-g by EPA Method 8015M, BTEX by EPA Method 8020, and MTBE and other fuel oxygenates by EPA Method 8260. The borehole locations will be marked and cleared for under ground utilities prior to drilling. The borings will be advanced with a direct push sampler, or equivalent. The rods and sampling equipment will be steam cleaned prior to commencing each boring. Continuous soil cores will be obtained by pushing a direct push sampler with acrylic liners into the subsurface. The soil (1.3{ core will be screened with a photo ionization detector (PID) for evidence of petroleum hydrocarbon vapors. The field geologist will prepare a log of the subsurface conditions, and soil p' samples will be classified in accordance with the Unified Soil Classification System (USCS). �y One or more.soil samples will be selected from each boring from the vadose zone for laboratory analysis. Upon retrieval, a 6-inch section of the soil core liner will be cut at the selected p' sampling depth. The ends of the 6-inch tube containing the soil to be tested will be covered with �1 aluminum foil, capped with plastic end-caps, and taped shut. The tubes will then be labeled and placed in an iced cooler for transportation to the laboratory. Each boring will be advanced to a depth sufficient to allow water to collect in the boring. Groundwater samples will be collected by installing a temporary well in each boring, and bailing groundwater samples. The temporary wells will be constructed of 1-inch diameter schedule 40 APLEASANTON\Ad.,n T.kWe ina\QuikSmp)WORKPLAN(Gi pmbc).d.c 4