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G GEQM.4TRIX Control Board (SWRCB) regarding corrective action at sites where soil and/or groundwater are affected by petroleum hydrocarbons. Specific guidance published by the SWRCB has included"Underground Storage Tank Cleanup Fund Technical Review Guidance Document No. 4" (27 December 1995), which recommended implementation of the Lawrence Livermore National Laboratory (LLNL) 16 October ' 1995 report,"Recommendations to Improve the Cleanup Process for California's Leaking Underground Fuel Tanks (LUFTs)." The LLNL report concluded that intrinsic (naturally-occurring) bioremediation can be as effective as actively-engineered remediation, and they recommended that actively-engineered ' remediation methods be minimized for sites impacted by petroleum hydrocarbons. The LLNL report further stated that, for most low-risk sites, once sources have been removed, soil impacted by petroleum ' hydrocarbons at these sites can be closed in-place without risking further threat to the environment, as the petroleum hydrocarbons will undergo intrinsic bioremediation and degrade naturally with time. Likewise, for groundwater affected by petroleum hydrocarbons at most low-risk sites, the LLNL report ' recommended that monitoring replace actively-engineered corrective action programs. Regional boards and local enforcement agencies, such as the SJCEHD, are evaluating the SWRCB's recommendations and in the coming months will be revising current policies regarding corrective action for sites within ' their jurisdiction. ' Based on a review of the soil and groundwater data collected, we believe that this site should be classified as low risk. The factors considered in ranking the site as low risk are as follows: o the original source for the petroleum hydrocarbons in soil has been removed; o the extent of petroleum hydrocarbon-affected soil is limited and has been defined; ' ! groundwater is shallow and occurs at a depth of about 50 feet bgs beneath the site, and the near- est drinking water supply well is screened from 250 to 530 feet bgs and is located approximately ' 325 feet cross-gradient of the site; • shallow groundwater beneath the site is not likely to be used as a source of drinking water; ' • concentrations of the most mobile petroleum hydrocarbon constituents(BTEX) remaining in soil are low and, of the soil samples collected to date, benzene has been detected in only three soil samples at low concentrations; ' • BTEX have been detected sporadically in groundwater beneath the site at concentrations less than or equal to the maximum contaminant levels (MCLS) established by the California Depart- ment of Toxic Substances Control and published in the California Code of Regulations (Title 22, Division 4, Chapter 15, Article 5.5, Section 64444); • TPH-G has been detected sporadically in groundwater at low concentrations; and • the petroleum hydrocarbons in soil and groundwater beneath the site are expected to remain in place and gradually degrade through natural chemical and biological processes. We recommend that CREMCO seek concurrence from SJCEHD that the site represents a low risk and that an in-place closure would be appropriate for the site. 7 1