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,• Mr. Steve Sasson Project 22794-100.001 August 10, 1998 Page 8 characterized 100-cubic-yard quadrant These concentrations appear to be low, based on the excavation sldewall and floor sample analytical results. Using the 140 mg/kg concentration for materials removed from the former tank complex, a volume of 1,050 cubic yards, and a unit weight of 100 pounds per cubic foot for the soil, approximately 400 pounds of TPHD were removed from the complex. The overexcavation of an additional 150 cubic yards from the southwest corner of the UST complex removed an additional mass estimated using the average of concentrations detected 1n floor and sndewall soil samples of approximately 700 pounds of TPHD. This suggests that the overexcavatlon activities conducted at the site removed approximately 1,100 pounds of TPHD. Residual Mass in Soil Isoconcentration maps of the TPHD results in soli at depth intervals of 12 to 20 feet and 20 to 30 feet show the extent of soil impacts (Figures 3 and 4). Average detected concentrations within each contour interval were used in the calculations. The estimated mass in sots is approximately 1,400 pounds of TPHD. The TPHD mass estimate • worksheets are presented in Appendix C Mass in Groundwater TPHD mass in groundwater estimates were prepared from 1991 and 1995 data using both HydroPunch sample and groundwater monitoring well sample results collected during the respective periods. Contoured TPHD concentration data are shown on Figures 5 and 6 The 1995 data include a sltewlde HydroPunch sampling event that covered a greater areal extent than the 1991 HydroPunch sampling Mass evaluation of the 1991 groundwater analytical data suggest that the TPHD mass in the first-encountered water-bearing zone was approximately 108.3 pounds, or approxunately 15 2 gallons The 1995 mass evaluation suggests that the TPHD mass in. the first-encountered water bearing zone was approximately 188.2 pounds or 26.5 gallons. The highest detected 1991 concentration was 160 ppm; 1n contrast the highest detected 1995 concentration was 12 ppm The TPHD mass estimate worksheets are presented in Appendix C. STATISTICAL EVALUATION OF GROUNDWATER RESULTS EMCON performed statistical evaluation of the detected TPHD concentrations to groundwater monitoring well samples. This evaluation utilized the non-parametric Kendall Rank Correlation test method for assessing statistically significant trends. The SAON 1PJZ12794�27941000 ICS-Wfwamer8 Emcon Rev 0.8/10/98