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The placement of bonngs SB2 and SB3 in the northwest end of the overexcavation was to confirm WHF's conclusion that contamination was limited to that area Soil samples from SB2 and SB3 contained very low levels of TPHg, ethylbenzene, and xylenes Soil samples collected from MW3 and MW 1 approximately 25 feet north and northwest of SB2 contained no detectable Iconcentrations of TPHg, TPHd, or BTEX ' Based on the confirmation floor and wall soil samples collected by WHY and the soil samples tcollected from borings SB2, SB3, MlW1, MW2, and MW3, there is estimated to be approximately 220 cubic yards of residually contaminated soil along the west and north sidewalls of the overexcavation Calculations are shown in Appendix E The contaminated soil is approximately 15 to 18 feet below ground surface Some natural biodegradation of impacted soil has occured since the last soil sample was collected on October 10, 1994 4_4 Assessment of Groundwater Contamination Soil borings MW 1, MW2, and MW3 were subsequently completed as groundwater monitoring wells to assess the possibility of groundwater contarmnation beneath the site, and to provide measurement points for the determination of groundwater flow direction and hydraulic gradient 1 Each well was constructed with 2-inch PVC casing The screened interval of each well was positioned from approximately five feet above to 15 feet below the encountered water table to allow for seasonal water level fluctuations The screen slot size is 0 020-inch Well construction diagrams are depicted on the bonnglwell logs contained in Appendix D The wells were developed, monitored and sampled on October 14, 1994 Samples were placed on ice and transported under chain-of-custody documentation to Argon Laboratories The water samples were analyzed for BTEX, TPHg, and TPHd Groundwater analytical results are summarized in Table 2 IThe monitoring wells have been monitored intermittently since their installations Wells MW2 and MW3, the downgradient wells, have never contained detectable concentrations of petroleum hydrocarbons during their four quarters of monitoring Well MWl has contained petroleum hydrocarbons only once(benzene at 3 5 parts per billion(ppb), July 1995)in four sampling events 445 Remedial Actions 1 4.5.1 Stockpiled Soil Remediation A passive approach was used to remediate the stockpiled soil The confirmation soil samples from the overexcavation contained maximum concentrations of TPHg at 1,100 parts per million(ppm), benzene at 24 ppm,toluene at 120 ppm, ethylbenzene at 120 ppm, and xylenes at 27 ppm These samples were collected between July 7 and July 12, 1993, when the soil was stockpiled The soil was then allowed to aerate and petroleum hydrocarbon constituents allowed to naturally biodegrade Confirmation samples w 1943371clos=dw 4 • Sian 1