SITE INFORMATION AND CORRESPONDENCE

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I Ms. Laurie Cotulla .1 fi September 23, 1992 Page 3 The presence of dissolved hydrocarbons in the groundwater is well documented at this site and the groundwater extraction system in place is effectively halting the migration of the hydrocarbons. Items 5 and 6 The results of the soil sampling beneath the former product recovery tank and the new waste oil tank indicate that hydrocarbons are present in the soil in these locations. These areas are within the characterized area of the site. ARCO has revised the number of vapor extraction wells proposed for the site and these areas will be remediated with the currently proposed vapor extraction system. Figure 1 presents the revised number and locations of soil vapor extraction wells proposed for this site. Item 7 This statement by the County is unclear. Since the groundwater table has dropped significantly since monitoring wells E-2 through E-12 were installed in 1984, it would be impossible to define the dissolved hydrocarbon plume at 1984 water levels. ARCO has graphically shown the estimated extent of dissolved hydrocarbons in the groundwater in each of the first two quarterly reports for 1992. Item 8 The EMCON borehole logs of wells E-1 (no longer exists) through E-12 do indeed indicate the presence of hydrocarbon odor in some of the boreholes. However, odors were not noted in wells E-7, E-8, E-10, or E-12. Hydrocarbon odors were noted only at the groundwater surface in wells E-3 (faint), E-4, E-5, E-9, and E-11. The other wells (E-1, E-2, and E-6) are well within the proposed remediation area. As stated in item 6, ARCO is proposing a number of soil vapor extraction wells in addition to the five wells presented in BCC's April 29, 1992, Final Remediation Plan (FRP). This proposed system should effectively remediate the hydrocarbon-affected soil at this site. Confirmation sampling will be conducted when the system has operated for a period of time. The County has accepted the FRP for both soil and groundwater as they are written. ARCO is proposing a soil vapor extraction system that is above and beyond the system proposed in the FRP. Based on the information contained in this letter, it is not necessary to conduct further characterization investigation, and further work at the site should be remediation—not further characterization. We request that the County rescind the request for a work plan for soil characterization. If this is not acceptable to the County, ARCO is requesting that a meeting be scheduled immediately among you, ARCO, BCC, and Gordon Boggs of the California Regional Water Quality Control Board, Central Valley Region, to discuss these issues. Brown and Caldwell 6746\C0RRESP6746-08.1_3 Consultants