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Working to Restore Nature <br /> In November 1987, the tank cavity was over-excavated to 28 feet below grade in an effort <br /> to remove soil affected by hydrocarbons (LMBE, October 1, 1988). Analytical results of soil <br /> samples collected from the base of the excavation indicated that relatively low <br /> concentrations of gasoline hydrocarbons (0.20 ppm ethylbenzene, 0.020 ppm toluene, and <br /> 3.25 ppm total xylenes) were detected in only one sample, which was collected nearest to <br /> well BH-1/ MW-1 (Table 2). <br /> In duly 1993, RESNA observed drilling of three soil borings and installation of three <br /> monitoring wells (MW-2 through MW-4) in the three borings (RESNA, September 15, <br /> 1993). Results of analyses of soil and water samples indicated that hydrocarbon <br /> concentrations were below laboratory detection limits. Analytical results of soil and <br /> groundwater samples are presented in Table 2 and Table 3. <br /> SITE CONDITIONS <br /> Site GeologX and Hvdrogeology <br /> Sediments encountered beneath the site consist of interbedded silt and gravelly sand. <br /> Groundwater was encountered at approximately 87 feet bsg. The depth to water has varied <br /> from approximately 86 to 88 feet bsg. The direction of groundwater flow has been <br /> ✓ consistently to the southwest with the exception of the first sampling event performed in July <br /> 1993 (RESNA, December 3, 1993 and RESNA, March 14,1993). Plate 3 through Plate 6 <br /> present previous and current groundwater flow. <br /> Residual Hydrocarbons in Soil <br /> Based on cumulative results of the investigation, the majority of soil with residual gasoline <br /> hydrocarbons has been removed and only trace concentrations remain in soil in the vicinity <br /> of the former tank cavity. Soil with gasoline and benzene have been adequately delineated <br /> or removed. Relatively low concentrations of benzene were detected in boring BH-1 at 20 <br /> and 35 feet bsg. Low concentrations of toluene, ethylbenzene, and total xylenes were <br /> detected in boring BH-1 at 35 feet bsg and from the southeast corner of the tank cavity at <br /> 28 feet bsg. Plate 7 and Plate 8 show the extent of residual hydrocarbons quantified as <br /> TPI-Ig and benzene. Plate 9 shows the extent of residual benzene, toluene, ethylbenzene <br /> and xylene. <br /> RESNA calculated the mass of gasoline and benzene, toluene, ethylbenzene, and total <br /> xylene isomers (BTEX) remaining in place beneath the site using the following equations. <br /> 0504gtaW123009.01 3 <br />