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---------------- V � A S S O C I A T E S I N C gradient data indicate that groundwater flows to the north and northeast. It is unlikely that Smith Canal has been impacted by petroleum hydrocarbons from the site due to its upgradient location. The closest well to the site is approximately 1,000 feet to the north. There were 22 wells that were revealed in a well survey. None of these wells are located - close enough to the site to be considered potential receptors. 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. BTEX constituents have only been detected in groundwater samples once in 1989, and at concentrations well below their respective maximum contaminant levels (MCLs). Benzene has never been detected in the groundwater above its method detection limit. F_= Detected TPHd concentrations have decreased with distance from monitoring well MW4. The low water solubility of diesel tends to limit its migration. The health risk from diesel when volatile compounds are not present is very low. F >� The groundwater pump test indicated that in 24 hours, after 6,000 gallons of groundwater had been pumped a total of 0.00005 pounds of TPHd had been removed from the €_r!; subsurface. In approximately ten years of constant pumping at the same rate a maximum of 0.18 pounds of TPHd would be extracted. In comparison, ten gallons of product, approximately 68 pounds, had been removed by the skimmer at monitoring well MW4. , r 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. 6_2 Appendix B Check List Appendix B of the Tri-Regional Board's recommendations checklist of required data for site I`I.. closure of USTs has been completed, as appropriate. The checklist is included in this report as Appendix A. 1� 7.4 CONCLUSIONS/RECOMMENDATIONS Findings of our evaluation concluded that the project site does not appear to represent a f significant risk to human health and the environment. Based on the available data, on behalf of F the City of Stockton, ATC formally requests NFA for this site. Upon concurrence by PHS/EHD and the RWQCB, ATC will submit a workplan and permit applications for monitoring well destruction. w:162574-02Sreporlslclosure-smith.doo 8 F::