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Figures 4 and 5 are maps depicting the Estimated Downgradient Decline of Benzene on ff: July 7, 1995 and January 22, 1997. The maps, requested by Mr. Sasson, were constructed by establishing the decline rate noted in the 30 feet of horizontal distance between MW-6 and hydropunch HP-9. Possible contours were plotted downgradient at 30-foot intervals over distances between 200 and 250 feet. A south-to-north cross- section between selected wells and hydropunches is included as Figure 6; the line-of- section is drawn on Figures 4 and 5. A possible contaminant path emanating from the former tank pit is drawn on Figure 5. Assignment of Low-Risk Status The Soil and Groundwater Remedial Action Plan (W.W. Irwin, Inc.; December 29, 1995) was prepared following the issue of the Pro'ect Status Report of Groundwater Monitoring for the fourth quarter of the year on October 31, 1995. The options considered for remediation were: • the use of five bioventing wells and the existing monitoring wells with a blower system to inject air into the subsurface, with a pilot program and frequent samplings; • intrinsic remediation, to consist of no action other than groundwater monitoring. After the publication of Recommendations. to Improve the Cleanup Process for California's Leaking Underground Fuel Tanks (Lawrence Livermore National Laboratory, October 16, 1995), the SJCEHD concluded that the site had attained low-risk status. With this decision, only intrinsic remediation with quarterly monitoring has been rr required. Background levels are expected to be attained with the passage of time as the residual fuel degrades. It is this writer's opinion that the costly continuance of any monitoring program for a heretofore indefinite period cannot enhance or accelerate this natural process. With the exception of the five monitoring wells on the site, the water table is not readily accessible from the surface. A file survey was conducted by W.W. Irwin, Inc. personnel on December 15, 1994 at the SJCEHD to identify any production wells within 2000 feet of the site. No known public or private water wells are operated by the City of Stockton, California Water Service Company, or private citizens within 2000 feet of the site. The nearest water well was identified one mile to the northeast adjacent to a ramp at Benjamin Holt Drive and Interstate 5 (see Figure 1); the identification number of the well and perforated interval of the well are not known. Village West Marina receives publicly- supplied water. There are no known sensitive receptors within the reachable influence of the small plume. Fourteen-Mile Slough is not at risk because it is the upgradient, sea-level source of the groundwater underlying the site. DAYNE L. FRARY,GEOLOGIST 0897-012-2 3