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• MF�lru� Working to Restore Nature In November 1987, the tank cavity was over-excavated to 28 feet below grade in an effort to remove soil affected by hydrocarbons (LMBE, October 1, 1988) Analytical results of soil samples collected from the base of the excavation indicated that relatively low concentrations of gasoline hydrocarbons (0 20 ppm ethylbenzene, 0 020 ppm toluene, and 3.25 ppm total xylenes) were detected in only one sample, which was collected nearest to well BH-1/ MW-1 (Table 2) In July 1993, RESNA observed drilling of three soil borings and installation of three monitonng wells (MW-2 through MW-4) in the three borings (RESNA, September 15, 1993) Results of analyses of soil and water samples indicated that hydrocarbon lid concentrations were below laboratory detection limits Analytical results of soil and groundwater samples are presented in Table 2 and Table 3 SITE CONDITIONS 1� Site Geology and Hydrogeology Sediments encountered beneath the site consist of interbedded silt and gravelly sand We constructed a geologic cross section A-A'(Plate 3) to show our interpretation of the stratigraphy beneath the site, the cross section shows the geology beneath the site in the west-east direction During drilling, our geologist collected soil samples at approximately 5-foot intervals Samples were identified using visual and manual methods and classified using the Unified Soil Classification System (Appendix A), descriptions of the materials encountered are presented in the Logs of Boring (Appendix A) Details on the construction of the wells are shown on the Logs of Borings (Appendix A) Groundwater was encountered at approximately 87 feet bsg The depth to water has varied from approximately 86 to 88 feet bsg The direction of groundwater flow has been consistently to the southwest with the exception of the first sampling event performed in July 1993 (RESNA, December 3, 1993 and RESNA, March 14,1993) Plate 4 through Plate 7 present previous and current groundwater flow Residual Hydrocarbons in Soil Based on cumulative results of the investigation (Appendix B), the majority of soil with residual gasoline hydrocarbons has been removed and only trace concentrations remain in soil in the vicinity of the former tank cavity. Soil with gasoline and benzene have been adequately delineated or removed Relatively low concentrations of benzene were detected in boring BH-1 at 20 and 35 feet bsg Low concentrations of toluene, ethylbenzene, and total xylene were detected in boring BH-1 at 35 feet bsg and from the southeast corner of • S05o9gc&k/12_ o9 of 3