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1 Working To Restore Nature Addendum One to Remedial Action Plan March 1, 1993 Coca-Cola Former Distribution Facility, Stockton, California 5400601 Fourth Quarter 1992 groundwater monitoring are reported under separate cover (RESNA, February 1993), and the results of laboratory analyses of groundwater samples, and depth ' to water measurements are presented in Tables A-3 and A-4. In November 1992, a soil vapor extraction test was conducted at the subject site on the eight ' existing vapor extraction wells (RESNA,January 1993). Laboratory analyses of air samples indicated that TPHg vapor concentrations ranged from 33 mg/m3 (near nondetectable ) in well VEW-5, to 19,000 mg/m3 in well VEW-4 This concentration range is considered to be low to moderate. Test flows ranged from 26.2 cubic feet per minute (cfm) to 109 cfm at applied vacuums of 10 to 100-inches of water column. Some of the results of the vapor extraction test are summarized in Tables A-5 and A-6 in Appendix A. Soil vapor extraction was determined to be a viable alternative for remediation of TPH and P g BTEX impacted soil at the site. It was recommended that the vapor extraction system would bring three vapor wells on line: VEW-2, VEW-3, and VEW-7. The estimated effective radius of influence for this proposed vapor extraction system was adequate to cover the area of concern, which was previously estimated from laboratory analyses of soil boring samples. The proposed design flows were 75 cf n per well, for a total of 225 cfrn, at a design wellhead vacuum of 60-inches of water column. The most conservative estimated ' time of operation of the proposed vapor extraction system was 12 to 15 months or less, before extracted petroleum hydrocarbon vapors would become consistently nondetectable. ' DESCRIPTION OF PROPOSED SOIL REMEDIATION SYSTEM The purpose of the proposed vapor extraction system (VES) is to remediate hydrocarbon- impacted soils beneath the subject site to hydrocarbon levels acceptable to the regulatory agencies involved in the closure of the site; and also to treat the soil in order to reduce the leaching of petroleum hydrocarbons into the groundwater. After the VES has operated for ' several months, the effectiveness of the proposed VES to remediate sods beneath the subject site to hydrocarbon concentrations acceptable to the regulatory agencies will be reassessed Additional vapor extraction wells, if necessary, may then be installed to remediate hydrocarbon impacted soils Immacted Area of Concern 1 Based on the results of previous subsurface investigations (USTEC, June and November 1990, and September 1991), the area of concern for petroleum hydrocarbon impacted soil is shown in Plate 4. The area of concern is limited to an approximately 20 foot radius surrounding the former underground gasoline storage tank, and down to a depth of about ' 3