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1 Emergency Remediation- 2480 Tracy Blvd., Tracy, CA. • Page 12 contaminated. The total volume of soil from all sources that was set aside for treatment ' amounted to some 600 cu. yds. (loose measure). The contaminated soil from the basement excavation and wash-water-recycling tank pit was initially stockpiled on plastic sheeting spread over the ground along the eastern boundary of the site. This was done so that cross-contamination of the uncontaminated surficial soil would be avoided until the results from the analyses of the soil samples recovered from the basement excavation were available, the concentration of components of gasoline that it contained was known, and an appropriate method for treating the contaminated spoil selected. Groundwater Pumping The submersible pump that had previously been installed in the dewatering sump was used to lower the groundwater table sufficient to permit completion of the basement excavation. Pumping began on April 8, 1996 at a rate of 10 gpm (gallons per minute). The contaminated water discharged from the pump was directed into mobile 20,000-gallon storage tanks (Baker tanks), where it was held prior to treatment. A full description of the groundwater treatment system is presented in the next section of this report. 1 As a cone of depression formed in the water table, the rate of pumping required to maintain the bottom of the excavation dry steadily diminished. The necessary pumping rate decreased futher as the sequential stages of the work to excavate for and construct the basement were completed and the maximum depth of the open excavation was reduced. Pumping of contaminated groundwater was stopped on April 24, 1996, by which time the basement slab had been placed and cured and the rate of discharge from the sump pump had been adjusted downward to less than 2.5 gpm. On April 26, 1996, the elevation of the floor of the completed basement structure was surveyed and determined to be at 20.36 MSL, which is approximately 6.5 ft. beneath the ground surface. On the same day, the elevation of the groundwater table was 19.16 ft. MSL or 1.20 ft. beneath the top of the basement floor slab. By May 2, 1996, when it was next measured, the elevation of the water table had fallen slightly to 19.14 ft., which is approximately 6.6 in. below the bottom of the 8 in.-thick foundation slab. Additional samples of groundwater were taken from the sampling port in the riser from the submersible pump on April 14 and May 2, 1996. These, which were sequentially identified as samples WATER 3 and WATER 4, contained 990 ppb and 300 ppb, respectively, of total petroleum hydrocarbons quantified as gasoline. The reduction in hydrocarbon concentrations in those samples, compared to that found in the first sample taken from the sump on April 3, 1996, reflects the soil and groundwater remediation effected by the extraction of groundwater from the close proximity of the basement