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No Further Action Required Request Report US Can—Welty Road September 24,2013 and vertical extent of dissolved hydrocarbons in groundwater as effectively as any active remediation technology. Natural attenuation is a viable technology for weathered heavy-crude oil with low concentrations of BTEX, and where the extents of BTEX and associated TPH plumes in groundwater are generally limited to the area of SPO,as is typically the case at former OVP and TAOC sites. For most of the other technologies evaluated, "the costs to implement the technologies may exceed the value of the land and any improvements." Natural attenuation is generally cost free. The time required for natural attenuation to reduce TPH concentrations below WQOs, and then below background levels, could be lengthy and cannot be reliably estimated. An extended period of time does not pose a concern, as use of the shallow groundwater is unlikely given its likely low yield and poor quality. 15. Provide a discussion (and estimate) of contaminant mass remaining in soil and groundwater versus contaminant mass removed or destroyed by soil excavation or remedial actions. This item is not applicable because active site remediation has not been implemented or recommended. Natural attenuation will continue to reduce the COPC concentrations in soil and groundwater over time, as discussed in item 14. 16. Provide assumptions,parameters, calculations, and the model used in any risk assessments. SAIC calculated an estimated risk and hazard for the HHSE using the equations and assumptions outlined in the PEA Guidance Manual under the residential exposure scenario (the most conservative exposure scenario). The calculated exposure point concentrations for the COPCs are considered protective of a potential resident. See the summary of the HHSE in section 2.1 of this report for details regarding the assumptions,parameters, calculations, and model used in the HHSE(provided as Appendix B.24). 17. Provide assumptions,parameters, calculation, and the model used in fate and transport modeling. Fate and transport modeling has not been performed. 18. Provide a rationale why the conditions remaining at the site will not adversely impact water quality, human health and safety, or other beneficial uses The rationale for NFAR must include a finding about present and future water use, and risks the site may still represent to human health and safety, and water quality. Please see Section 4—Conclusions and Recommendations. 19. Provide a list of technical reports submitted for site assessment, corrective action, confirmation sampling,and closure. A list of references is provided in Section 5. 20.Provide any additional comments supporting site NFAR. See Section 4—Conclusions and Recommendations. 10 SAIE