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•1 <br /> TABLE 1. SOIL CHEMICAL DATA <br /> Sample Depth TPHG TPHD Benzene Toluene Ethylben Xylene Lead <br /> No ft mg/kg mg/kg ug/kg ug/kg ug/kg ug/kg mg/kg <br /> B- 1 * 12 1 7 ND 6 3 ND ND 1 1 2 9 <br /> E W-1' 7 ND!)iy NDLI,P ND ND/ 0bI N] ND 1 9 <br /> NEC-1* 7 5 ND ND ND N[3-- ND ND 2 3 <br /> N W C-1* 7 PD ND ND ND ND ND 1 2 <br /> SW-1* 7 5 270 ND 420 130 310 800 1 3 <br /> D-1+ 10 450 1 B 200 190 720 1900 3 9 <br /> EW-2+ 10 1 1 1 1 ND ND ND 1 1 2 9 <br /> EW-3+ 10 120 1 3 64 43 170 370 3 0 <br /> SW-2+ 10 24 ND ND 50 88 24 45 <br /> DB-1+ 10 130 ND 260 34 280 310 3 3 <br /> SP-1t - 98 2 1 56 98 160 300 NR <br /> SP-2t - 310 ND 160 740 620 2000 NR <br /> Notes. ND - Not Detected NR - Not Requested mg/kg - milligram per kilogram <br /> ug/I - microgram per liter ug/kg - microgram per kilogram SP - Soil Stockpile <br /> * - sampled Aug 16, 1996 + - sampled Aug 21, 1996 t - sampled Aug 14, 1996 <br /> Discussion <br /> Exploratory boreholes drilled by earlier investigators showed that contamination is <br /> relatively confined to the excavation area, with minimal spreading upon the capillary <br /> fringe Excavation based upon this borehole data revealed contaminants were localized i n <br /> the immediate vicinity of the former tank location Excavation pit and wall samples <br /> laboratory data indicate that only residual concentrations remain Deeper soil sample <br /> data of RESNA showed that contaminant penetration did not extend beyond roughly 12 feet <br /> (see Figure 1) <br /> A relatively slow overall groundwater movement to the north is known from historic <br /> groundwater monitoring data The very flat gradient, together with the very clayey <br /> aquifer strata, appear to have limited dissolved migration of the plume Groundwater <br /> monitoring data shows that the contaminants have remained very low to not detected for <br /> several years <br /> A cross section showing the distribution of contaminants as shown on Detail B, Figure 1 <br /> indicates most were absorbed into the sod in and around the tank pit A calculation of the <br /> estimated contaminant mass prior to excavation showed that 1917 pounds of TPHG and <br /> 3 8 pounds of Benzene were present initially These masses declined to residuals of 6 1 <br /> pounds of TPHG and 0 11 pounds Benzene after excavation as shown on Detail C (see <br /> Appendix A, Calculations) This work together with the tank removals has removed the <br /> sources of sod and groundwater contamination <br /> Page 3 <br />