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Ms Laurie Cotulla April 29, 1992 Page 5 i BCC's 1987 Investigation In May 1987, BCC supervised the drilling of seven soil boreholes (AS-1 through AS-7) at the site (see Figure 2) BCC's June 10, 1987, PAR details the results of this investigation The boreholes were advanced to a depth of approximately 10 feet below the bgs and two soil samples were collected from each borehole (one from approximately 5 feet and one from approximately 10 feet) At the tune of thas investigation the static groundwater was 11 to 13 feet bgs The results of this investigation indicated that hydrocarbons were present in the soil with the highest concentrations on the eastern side of the site Soil samples collected from the western portion of the site did not contain detectable hydrocarbon concentrations or contained only minor hydrocarbon concentrations None of the samples collected from 5 feet bgs contained detectable concentrations of hydrocarbons This indicates that the hydrocarbons in the soil were limited to the capillary fringe and are probably residual hydrocarbons from the groundwater Product Recovery Tank Removal, 1991 On September 23, 1991, BCC conducted soil sampling dunng the removal of one product recovery tank and installation of one waste oil tank BCC's January 13, 1992,letter report details the results of this sampling The recovery tank was located near the location of the groundwater extraction well and the waste oil tank has been installed on the west side of the station building The results of this sampling indicate that hydrocarbon affected soil is present in the recovery tank area and to a lessor extent in the waste . oil tank area The most likely source of these hydrocarbons is the former underground storage tanks (removed in 1984) Soil Vapor Extraction Pilot Test Results On February 24, 1992, BCC performed a series of vapor extraction pilot tests at the site The purpose of these tests was to gather information to determine the feasibility of designing a soil vapor extraction and remediation system at ARCO Station 2133 The data collected provides for the evaluation of (1) the relationship between volumetric flow rates and extracted well vacuum, (2) the area of influence that a tested vapor well has on surrounding subsurface soil in the vadose zone,and(3)the concentrations of gasoline-based hydrocarbons,chlorinated solvents,and organic lead in the extracted soil vapor A letter describing the test methodology and requesting permission to perform the test was submitted to the APCD on January 27, 1992 A verbal approval was granted by the APCD to perform the test Written approval to perform the test was received in a February 14, 1992 letter A copy of BCC's January 27 letter and APCD's February 14 response letter are included with this plan as Appendix A During the test, vapors were extracted from the soil through three vapor wells at the Site using a five-horsepower air extraction blower Two 55-gallon containers of granular activated carbon (GAC) were used to filter hydrocarbon compounds from the extracted vapors The GAC units were connected in series on the effluent of the vapor extraction apparatus to prevent hydrocarbon compounds from escaping to the atmosphere Vapors were extracted from groundwater monitoring wells E-3, E-5, E-10, and E-11 (see Figure 2) Brown and Caldwell 6747uzFLP0xTs6747-0aiTR Consultants