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GEOMATRIX 6.0 COMPARISON TO REGULATORY CRITERIA AND RECOMMENDATIONS FOR SITE CLOSURE According to the Consistent Technical Approach, the lack of detectable concentrations of petroleum constituents in groundwater would classify the site as a"Soil Case,"in which any t potential risks associated with residual petroleum in soil would be evaluated by the Local Agency(i.e.,the SJCPHS). However, due to the"detections" of constituents in temporary well ' TW-2 at concentrations slightly greater than WQOs and the presence of a sheen in TW-2, site conditions will be evaluated as a"Groundwater Case" according to the October 1996 revision of"Appendix B Tri-Regional Board Staff Recommendations for Preliminary Investigation a Evaluation of Underground Tank Site" issued by the RWQCB—Region 5 and referred to herein a"Appendix B" (RWQCB, 1996). Appendix B describes certain criteria for defining"Low Risk" cases and presents management strategies for cleanup decisions at petroleum impacted ' sites. Using this guidance, appropriate further action can be determined by comparing site conditions to four measurable criteria. Based on the results of the soil and groundwater assessment, we recommend that no further action is necessary at the site with regard to residual petroleum present in the subsurface, and agency closure be granted. This is based on a ' favorable comparison of site conditions at the Surland Homes Property to the four criteria for the "Criteria for Low Risk Groundwater Designation," as described below. ' Criterion 1: Contaminants remaining in the vadose zone must not reverse or threaten to reverse the mass reduction rate of ground water pollutants discussed in #4 below. ' There are no detectable dissolved petroleum constituents in groundwater ("groundwater pollutants") and the beneficial use is not impacted. Residual petroleum is present in the vadose zone and below the water table; however, this material will not"reverse the mass reduction rate of groundwater pollutants" or ' add petroleum mass to groundwater because it is comprised of highly weathered crude oil (greater than 50 years old) that does not contain significant ' concentrations of soluble petroleum constituents. This is exhibited by the lack of detectable concentrations of soluble petroleum constituents in groundwater samples collected from wells downgradient of petroleum-affected soil. \\sf3\deptdam\Dm_Safe\4780.01\ctsrrpt.dm 6