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(YVATC A S S O C I A T E S I N C L. Criterion 2: Separate phase product has been removed to the extent practicable. Free product has never been detected at this site. Criterion 3: No existing water supply wells, deeper aquifers, surface waters, or other `" receptors are threatened by pollutants remaining in the aquifer. Well MW2, located 70 feet in the downgradient direction, had one detectable concentration of toluene at 0.655 ug/L. This is well below the MCL of 150 ug/L. No other constituents have bee detected in this well nor in well MW3, located crossgradient from the former UST. The HHRA study revealed that the health risk levels for groundwater ingestion were not exceeded at a residential receptor 100 feet from the site. The closest water supply well is located approximately 1,600 feet from the site and the nearest surface water is located approximately 1,700 feet from the site. For the investigation, groundwater wells were installed only in the shallowest aquifer. Well MW 1 was advanced to a depth of 65 feet bgs. The soil sample collected at this depth contained no detectable concentrations. Therefore, the likelihood of pollutants remaining in the aquifer threatening these potential receptors is very low. Criterion 4: The total pollutant mass remaining in the groundwater is decreasing at predicted rates and neither creates, nor threatens to create, a risk to human health and safety or future beneficial use(s) of the aquifer. V The HHRA study revealed that the health risk levels for groundwater ingestion were exceeded for benzene on site. The health risk levels for groundwater ingestion were not exceeded at a residential receptor 100 feet from the site. The HHRA study was based on concentrations of constituents detected in groundwater over the course of the investigation. During the last monitoring event only MTBE was present in the groundwater, all other constituents were reduced to nondetectable levels. Based on depth to groundwater, limited extent of impacted soil and groundwater, results of the HHRA study, and distance to receptors, the subject site does not appear to represent a significant risk to human health and the environment. Human exposure to residual petroleum affected soil is unlikely unless excavation of the soil were to occur. Human exposure to the dissolved groundwater plume is unlikely unless an on-site shallow well is used for drinking water purposes. V 7.2 Appendix B Check List Appendix B of the Tri-Regional Board's recommendations checklist of required data for site closure of USTs has been completed, as appropriate. The checklist is included in this report as Appendix A. w:\62574.05\nportsblosurc-FS3.doc 12 V