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AFK-05-99 14:14 From:WOODWARD CLYDE + T-1ZZ P0510 Jab-542 `N./ 1%./ at 500 feet bgs. Currently 37 percent of the water supply for the California Water Service Company is derived from groundwater. The survey will be conducted in conjunction with Caltrans staff in the Stockton office. We propose to review public well records maintained by the Department of Water Resources and local water agencies and conduct a door-to-door survey of landowners within 500 feet of Shop 10. Task 2-Vertical Delineation;of Petroleum Hydrocarbons in Groundwater The CVRWQCB requested that the vertical delineation of hydrocarbons in groundwater be evaluated for the Shop 10 site. Water saturated soil samples have been collected and analyzed for petroleum hydrocarbons during the installation of the vapor extraction wells in 1996. The highest concentrations were detected to approximately 40 feet bgs and then decrease to nondetect levels. The saturated soil samples are a measure of two phases, the adsorbed phase and the liquid phase. To further delineate the vertical distribution of petroleum hydrocarbons in groundwater, the Kabis discrete groundwater sampler is proposed to monitor petroleum hydrocarbons concentration vertically within two monitoring wells where petroleum hydrocarbons have been detected. Monitoring wells MW-13 (screened frorn 65 to 90 feet; groundwater was located at 49') and VM-2 (screener! from 60 to 80 feet bgs; groundwater was located at 50') are proposed to be used for discrete sampling. Both wells are four inch diameter PVC wells that are located in areas where petroleum hydrocarbons have been historically detected in groundwater. Groundwater samples are proposed to be collected in the 4-inch wells within 2 feet of the top of the wafer table (to emulare standard groundwater sample collection using a bailer), at 10 feet below the top of the water table, and at 15 to 20 feet below the top of the water table (if possible). Groundwater will not be purged from the well prior to sample collection. Rather, the objective will be to collect undisturbed samples (to the extent possible) at three sample depths. The Kabis Sampler is capable of collecting up to three 40-milliliter aliquots per sample depth in a 4-inch diameter well and one 40-milliliter aiiquat per sample depth in a 2-inch diamctcr well. Literature on the Kabis Sampler is attached to this workplan. C.wwu4u"w/wrkpin2.doc