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i collected on December 4, 1994 and April 9, 1996 contained no detectable concentrations of TPHg, TPHd, or BTEX 4.5.2 Groundwater Remediation In July 1993, a discrete water sample was collected from the excavation pit Prior to sample collection, 7,500 gallons of water was pumped from the excavation into an onsite storage tank and a sample was collected from the storage tank The samples were placed on ice and transported under chain-of- custody, to Argon Laboratories The samples were analyzed for TPHg, TPHd, and BTEX The pit sample contained TPHg at concentrations of 1,800 ppb, benzene at concentrations of 140 ppb,toluene at concentrations of 97 ppb, ethylbenzene at concentrations of 5 0 ppb, and xylenes at concentrations ' of 240 ppb The sample from the storage tank contained no detectable concentrations of TPHg, TPHd, or BTEX Analytical results are summarized in Table 3 Due to the relatively low levels of dissolved petroleum hydrocarbons detected in the groundwater, active groundwater remediation was not initiated at the site Natural biodegradation of petroleum ' constituents was monitored by conducting groundwater monitoring and sampling activities Since groundwater monitoring was mitiated, TPHg, TPHd, and BTEX have not been detectable in wells MW2 and MW3 Well MW 1 contained benzene at concentrations of 3 5 (ppb)on July 3, 1995 5.0 EXISTING CONDITIONS 5_1 Soil Conditions Soils encountered beneath the project site consist primarily of interbedded morganmc micaceous silty ' sands and clayey, sandy silts This is typical of the valley fill deposits in the region A notable bed of cross-bedded fluvial sand is continuous throughout the site from a depth of 8 0 to 12 5 feet It is an unconsolidated, clean,loose,well-sorted sand that caves easily Confirmation soil bonngs were advanced following soil remediation activities at the site Soil samples collected during the installation of wells MWI through MW3 contained no detectable concentrations of TPHg, TPHd, or BTEX Low levels of TPHg and/or ethylbenzene and xylenes were detected at 16 feet below ground surface in borings SB2 and SB3, located west of the former excavation 5.2 Groundwater Conditions Shallow groundwater beneath the site is encountered at approximately 15 feet below grade and generally flows to the west with a gradient of 0 001 ft/ft The groundwater gradient measured on March 22, 1996 is depicted on Figure 3 Results from the most recent groundwater samphng event indicate that TPHg, TPHd, and BTEX are below method detection limits in wells MW 1 through MW3 These results are consistent with historical data(Table 2) rw 1943371closuro doc 5' . SWFU 1