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' Final Remedial Plan - Geweke 2 January 1992 Page 6 of 15 Based upon the mostly sandy soil type and the volatile nature of the hydrocarbon contaminants, an in-situ vacuum extraction appears to be the preferred method of mitigation. Although we do not anticipate to encounter a free-floating product layer at this site, the proposed vacuum extraction system has proven itself to remediate a minor layer of volatile free-floating product as well . A destruction rate of greater than. 90% of hydrocarbon is expected throughout the entire cleanup duration. This destruction rate of hydrocarbons is better than that of an average and well-tuned car engine, representing' a negligible health risk factor. Based upon the above mentioned criteria, we believe that this proposed cleanup ' method represents the most effective method, both in cost and in operation. Since August 1991, GeoAudit has been working on a vacuum extraction ' project at a site in Stockton. A permit to operate the vacuum extraction system for various locations in San Joaquin County is currently being reviewed by the San. Joaquin County -- Air Pollution Control District (APCD) . Based upon recent conversations with the APCD, the permit should be issued shortly. ' 3 . 2 . VACUUM EXTRACTION METHOD AND EQUIPMENT DESCRIPTION The plan calls for vapor extraction from a group of extraction ' wells in the location of the former dispenser. The wells, which will be installed to a total depth of 70 feet, are designed to facilitate extraction from practically the entire casing. Prior to ' installation of the extraction wells, a limited soil-gas survey is recommended to determine the most strategic placement of the wells. The detailed work plan on the soil-gas survey and well installation is covered under Sections 3 . 7 . 1. and 3 .7 . 2 . , respectively. The vacuum extraction is performed using an Environmental Techniques - Vapor Extraction and Treatment System - Vaclean 1000 ' (ET Vaclean 1000) . A various location permit for this unit from the APCD is pending and is projected to be available for this project. in order to maximize the efficiency of the treatment, a 24-hour ' operation is planned. This system is designed to remove volatile organic/ hydrocarbon compounds from the voids of contaminated soil, both in-situ and on the surface (post excavation) . The system consists of a vacuum blower and an internal combustion engine. The vacuum blower is connected to a vapor recovery well, which is established in the center of the contaminated zone (Figure ' 2 - Site Plan) . Under the suction force of the blower, air displacement towards the vapor recovery well(s) takes place. The