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Ms Mary Meays Project 0805-109 01 August 15, 1994 Page 2 SITE GEOLOGY Based on previous soil characterization sediments underlying the site appear to consist primarily of silt with some clay and silt with fine- to medium-grained sand The interpreted subsurface conditions are shown on geologic cross-section A-A' and section B-B' (see Figures 3 and 4, respectively) The trace of the geologic cross-sections is included on Figure 2 VAPOR EXTRACTION TEST On March 3, 1992, the previous consultant conducted a soil vapor extraction test (SVET) to evaluate the feasibility of using soil vapor extraction to remediate vadose zone soil at the site Appendix A contains a copy of the previous consultant's SVET report. The previous consultant utilized the vacuum and distance measurements obtained during the SVET to estimate an effective radius of influence for the site. The previous consultant estimate that a wellhead flow rate of 80 cubic feet per minute (cfm) will result in an effective radius of influence of approximately 30 feet for one vapor extraction well • PRELIMINARY EVALUATION OF REMEDIAL ALTERNATIVES Based on the size of the site, the extent and concentrations of the hydrocarbons in soil, the minima impact to groundwater, and the type of soil present at the site, in situ bioremediation, chemical neutralization, and slurry wall containment are not technically or economically feasible remedial options The following feasible options are presented Soil Remediation Excavation Vadose soil with residual hydrocarbons occurs in the vicinity of the underground storage tanks (USTs) and extends toward the southern dispenser island Capillary fringe soil 1s affected Excavation as a remedial alternative will require removal of the USTs If this alternative is selected, soil removed by excavation cannot be treated on site due to lack of available space and site constraints, therefore, the soil must be hauled to an appropriate landfill for treatment and disposal Additionally, because petroleum hydrocarbons were detected in soil samples collected to groundwater (approximately 40 feet below surface grade) near the USTs, it is not feasible to excavate all petroleum hydrocarbons impacted due to excavation equipment limitations SAC/pj"8OW8051090 1bm-94 mam 4