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Former Unocal Station No 0187 February 14, 1995 encountered at approximately 40 feet bgs, but this sandy clay was underlain again by clay to approximately 57 feet bgs, where clayey sand was again encountered Clayey gravel was encountered to a depth of approximately 14 feet bgs in exploratory soil boring U-G This material is imported fill placed in the former UST excavation Brick and the fragments encountered in Borings U-A and U-D and other man-made debris encountered during UST and product line removal indicate the uppermost ten to twelve feet of soil beneath the site is fill material Groundwater was most recently (November 17, 1994) measured at depths ranging from 47 48 to 47 91 feet bgs. Based on these data, shallow groundwater beneath the subject site appears to flow north at a gradient of 0 004 (MPDS, 1994a) Previous monitoring data (August 9, 1994) indicates that groundwater may also flow toward the west (MPDS, 1994b) PROPOSED SCOPE OF WORK To further assess the vertical and horizontal distribution of residual petroleum hydrocarbons remaining in the soil in the vicinity of borings U-C and U-D and the original USTs, GSI • proposes to drill three onsite soil borings (U-N, U-O, and U-P) to groundwater, approximately 45 feet bgs The locations of the proposed soil borings are shown on the Site Plan (Figure 2) Borings U-N and U-O are situated to provide assessment of the lateral extent of hydrocarbon impacted soil to the north and northwest Delineation of lateral hydrocarbon impact has been achieved to the west and southwest (boring U-J and well U-2) Boring U-P will be drilled adjacent to the location of boring U-C to assess the vertical extent of hydrocarbon impact beneath the original UST excavation To further assess the lateral extent of hydrocarbon-impacted groundwater beneath the subject site, GSI proposes to install three onsite groundwater monitoring wells (U-4 through U-6) along the northern and western property boundaries at the locations shown on the Site Plan (Figure 2) These wells are situated downgradient of the original USTs and former dispenser island D-4 The wells will be installed to approximately 55 feet bgs, approximately 10 feet into the shallow groundwater To assess the lateral extent of hydrocarbon-impacted groundwater upgradient of the original USTs and evaluate the possibility of offsite sources of hydrocarbons, GSI proposes to install two offsite groundwater monitoring wells Well U-7 will be located south of the site across East Miner Avenue, and Well U-8 will be situated east of the site across California Street The locations of the proposed offsite monitoring wells are shown on the Extended Site Plan (Figure 3) In addition, a limited Phase I assessment of the properties immediately upgradient of the subject site will be performed to assess potential offsite sources of petroleum hydrocarbons 482704-1 4 GeoStrategies Inc.