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APR 22 '94 01 : 2SPM MN . FCH - HRZ. WFISTE <br />EG -1006 <br />Sinclair 011 Corporation <br />P.6/16 <br />-2- October 9, 1990 <br />. Reviewing information regarding previous investigations conducted at the site; <br />. Compiling the data and completing this report outlining our proposed CAP. <br />2.0 INITIAL EVALUATION OF REMEDIAL ACTION ALTFRNAT,TVES <br />A file review of existing data was conducted to help estimate the hydrogeologic conditions present <br />beneath the site. Geologic conditions as inferred from soil borings conducted at the site indicate <br />the presence of lacustrine deposits composed of very fine- grained, poorly graded sand overlying <br />glacial till. The sand is in a loose to medium dense condition. The surficial aquifer at the site <br />is the basal lacustrine sediment overlying the glacial till, with groundwater encountered at a depth <br />of 32 to 32.5 feet below grade in the four borings conducted in March. 1990. Subsurface <br />investigations conducted to date do not indicate that soil contamination has migrated to the depth <br />of the groundwater table beneath the site. <br />As noted in the April, 1990 report, petroleum contamination appears to have migrated primarily <br />laterally rather than vertically due to the layered nature of the lacustrine soils in the unsaturated <br />zone. Further downward migration of contaminants should be slow since the site is paved, <br />restricting the infiltration of precipitation in the area of the previously removed tanks. The <br />lateral extent of contamination to the west, north and east is unknown. However, data indicates <br />that contaminant concentrations drop significantly away from the previous tank basin, <br />Based on the existing data, groundwater impacts do not appear to have occurred. Therefore, the <br />CAP will address remediation of contaminated soils only. The remediation will target those soils <br />exhibiting organic vapors over 10 parts per million (ppm). Using PID screening data from the <br />borings as a guide, soils exhibiting these characteristics are estimated to extend over a horizontal <br />area roughly 100 feet (E -W from the vicinity of ST-4 to ST -6) by 90 feet (south edge of tank <br />basin to a point beyond ST -5) see Figure 1]. 'Vertically, the contamination appears to be limited <br />mainly to the zone between 10 to 25 feet below grade. Therefore, a total of approximately <br />135,000 cubic feet (5,000 cubic yards) of soil is targeted for treatment. <br />Page 53 <br />