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01ARWATER G R O U P I N C approximately 200 feet north of the site A domestic water well is located in the northern portion of the site (Figure 2) The well was installed in approximately 1987 ' and is screened from 165 to 185 feet below grade The bentonite sanitary seal for the well extends to a depth of 100 feet below grade Water from the well is currently not used for drinking, although it is used for bathing and other domestic sanitary purposes Water samples collected from it have historically been free of detectable levels of gasoline hydrocarbons The building on-site is currently used as the Ruiz Grocery Store, and was used in the past as a gasoline station The gasoline station operated two 1000-gallon underground storage tanks (USTs), plumbed to one dispenser island Both unleaded and leaded gasoline were stored in the USTs The USTs were removed in February 1988 1.3 Previous Investigations In late 1991, Delta Environmental Consultants supervised the installation of three monitoring wells (MW-1 through MW-3) Groundwater was present at a depth of approximately 10 feet below grade, and flow was toward the northeast Separate phase hydrocarbons (SPH) have been detected intermittently in wells MW-1 and MW-2, however, water samples collected from well MW-3 and the domestic well were free of gasoline hydrocarbons Between October 1993 and July 1994, RESNA industries Inc (RESNA) supervised the drilling of six soil borings (HP-1 through HP-6), and the installation of four additional monitoring wells (MW-4 through MW-7) and three vapor wells (VW-1 through VW-3) Sediments encountered beneath the site consisted primarily of interbedded silts and silty sands with lesser amounts of isolated clay beds to a depth of 26 5 feet below grade, the maximum depth explored Groundwater was present at a depth of approximately 12 feet below grade and flow was toward the northwest Soil samples collected from perimeter borings (HP-1 through HP-6 and MW-4 through MW-7) did not contain detectable levels of gasoline hydrocarbons, and thus delineated the vertical and horizontal extent of vadose zone contamination Water samples collected from the new wells were also free of detectable levels of gasoline hydrocarbons, and therefore also delineated the extent of contamination in the shallow water bearing zone Both soil and groundwater contamination appeared to be centered within an approximate 60 foot radius of the former UST pits Results of this phase of investigation were presented in RESNA's summary letter report dated September 2, 1994 Groundwater has historically fluctuated between 10 and 17 feet below grade, and flow has varied from the northwest to northeast at hydraulic gradients from approximately 0 001 to 0 004 D-107 PAR RAP � 2 February 21, 1996