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The total non-cancer hazard associated with potential exposure to CDCs in Site soils and/or groundwater is 0.02, which is below the acceptable threshold for noncancer hazard of 1.o. The calculated potential human health risks associated with vapor intrusion and exposure to Site soils and groundwater are below applicable regulatory thresholds, no further action is recommended with respect to soil vapor, soil or groundwater investigation or remediation. As such,the Site is appropriate for(health) risk-based regulatory closure. 8.o CONCLUSIONS AND RECOMMENDATION In accordance with regulatory guidance, data compilations and evaluations have been conducted to support this Closure Request. These include the following: • Data for soil and groundwater chemistry and groundwater elevations have been compiled and summarized over an extended period of investigations (January 1999 to July 201o). These data are summarized in Tables 1 (soil) and 2-4 (groundwater), in Figure 6 (soil) and Figure 7(groundwater) and Graphs 1-3 (groundwater). • Site investigations conducted over the last to years have led to a comprehensive understanding of Site conditions and those conditions have been summarized in Sections 2.o and 3.0. As demonstrated in these investigation and data summaries, the nature and extent of impacts at the Site and in its vicinity have been adequately characterized. Residual soil impacts are minimal and limited in extent. Similarly, groundwater impacts are relatively low in concentration and the groundwater plume is stable and declining in extent via natural attenuation. • A sensitive receptor survey has been conducted to determine if water supply wells, surface water bodies or other potential receptors are present in areas downgradient of the Site which could be impacted by Site contaminants. As summarized in Section 4.0, no such sensitive receptors are known to be present. • A human health risk assessment has been conducted to quantify and evaluate the potential health risks that residual constituents in soil and vapor intrusion beneath the Site may pose to human health(Section 5.o). The potential risks were found to be below applicable thresholds of concern. The following conclusions are therefore noted: • Extensive remedial (soil removal) actions completed at the Site (CLS, 2oo6) have successfully removed potential sources for further groundwater impacts. • Residual constituent concentrations remaining in groundwater beneath the Site have already reached recommended water quality objectives. • Current levels of petroleum hydrocarbons in Site groundwater, and residual soil impacts remaining above the water table, do not present a significant risk to human health or the environment. • Based on the current concentrations petroleum hydrocarbons onsite, natural attenuation would provide a sufficient mechanism for further contaminant degradation and no additional active remediation is recommended at this time. As such, no further action with respect to site characterization or remediation is warranted, and the Site should be referred for regulatory closure. 11 i