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3` MWIS"MME w 1 �`1 Department of Mater Ri„sources. The closest Well to the site is due east of the site on E1 Dorado Street. The approximate locations of known water wells within a one-mile radius of the site are plotted on Figure 3. Previous investigations at the facility show that the unsaturated soils beneath much of the site consist primarily of clays (CL/CH) from surface toapproximately 26 feet below grade with a zone of elastic silt (MH) and clay (CL) to a depth of 36 feet, the maximum depth of the unsaturated zone. However, in the central portion of the site, roughly coincident with the area of the former tank excavation, the site is comprised largely of sands. A portion of this material may be Fill from off-site, placed in the excavation to a depths of approximately 12 feet below grade. From approximately 12 to gra feet below grade, the native material is largely sand as indicated by the logs from borings SB3, SB4, SB4, VP1 and VP2. The saturated zone from approximately 35 feet to at least 50 feet below grade is comprised of intercalated clays, silts and sands. This zone appears to be under some degree of confinement and is clearly separated hydraulically from the nearby surface water (deep water channel). Current depth to groundwater at the site is approximately 35 .feet below grade. Groundwater gradient at the site is toward the north - northeast at 0.005 feet per foot or 26 feet per mile (Figure S). 4.0 SUMMARY OF PR%"JXOUS INVESTIGATIONS Previous assessments at the facility have included 1) ERM West (September 1989), 2) Kleir.felder, . litc. (May and .lune, 1990), 3) Leedshill-Herkenhoff, Inc. (October 1990), and 4) RESNA Industries (May, 1991). These assessments have identified a petroleum hydrocarbon plume associated with the previously excavated product storage tanks at the facility. In September 1989, ERM - West of Sacramento, California, conducted a Phase I Environmental site Assessment which included a site visit and a survey of surrounding land uses. - A second phase of investigation included a soil gas survey around the former storage tank area and pump islands by Kleinfelder, Inc. Soil.- gas samples were collected from 15 locations et the site and analyzed for total hydrocarbons, and benzene, toluene, ethylbenzene and xylenes by gas chromatography. Findings from this investigation determined that petroleum hydrocarbon concentrations were detected in soil-gas from the area where_._the former_..tanks_._had_._.been-_excavated.--.-- -.-_...-------- --_---- -------- ---..---- Petroleum hydrocarbons were also detected in soil-gas samples up to 6f) feet west and 50 feet southeast of the tank excavation and adjacent to the underground piping which leads from the tank area to the easterly. pump island. A detailed summary of findings can be found in Kleinfelder's Soil-Gas and Storage Tank Assessment report dated .0'une .14, 1990. Veber Polut Property - 475 _ _ - - H20R"791.TLP - 2 - 4