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`- groundwater usage in the area occurs in a much lower aquifer than those shallow lithologic zones contaminated at the site. Intrinsic remediation with monitoring was the final selected alternative in the January 1998 CAP. This technology has been implemented at the site for the past 8 years,and although it has shown signs of ► success,contaminant concentrations have recently leveled offto a point that does not permit site closure. To obtain a more timely goal of site closure,a more aggressive alternative will be necessary. Therefore, W ESTON recommends that the intrinsic remediation with monitoring technology not be considered further. 4.3 Data Gaps Sampling and Low Risk Site Closure In October 1995, the Lawrence Livermore National Laboratory(LLNL) presented its final report, Recommendations to Improve the Cleanup Process for California's Leaking Underground Fuel ► Tanks, to the California Environmental Protection Agency, State Water Resources Control Board (SWRCB). Based on these findings,a letter from Walt Petit,Executive Director ofthe SWRCB,dated December 8, 1995,urged cleanup agencies to proceed aggressively to close low risk soil only cases and ► not to require active remediation oflow risk groundwater cases. As a result,the RWQCB,San Francisco Bay Region,released supplemental instructions for closing low risk soil only cases and managing low risk groundwater impact cases on January 5, 1996. The six criteria required for closure of low risk ► groundwater cases outlined in this document are presented below: ► 1. The leak has been stopped and ongoing sources, including free product, have been removed or remediated. 2. The site has been adequately characterized. 3. The dissolved hydrocarbon plume is not migrating. ► 4. No water wells, deeper drinking water aquifers, surface water, or other sensitive receptors are likely to be impacted. 5. The site presents no significant risk to human heath. ► 6. The site presents no significant risk to the environment. Under this process,the mass of contaminants left at the site can be justified. WESTON feels that the site meets many of these criteria and will qualify for low risk closure;however,data gaps exist that would require additional investigation at the site to present a sound argument to justify low risk closure. These ► data gaps and the low risk site closure criteria they apply to are presented in the following sections. ► 13 r_