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No Further Action Required Request Report <br /> Tracy Byron Road-Tracy,Califomia December 1,2011 <br /> below. For most of the other technologies evaluated,"the costs to implement the technologies <br /> I may exceed the value of the land and any improvements." Natural attenuation is generally cost <br /> free. <br /> The time required for natural attenuation to reduce the COPC concentrations below WQOs and <br /> background levels cannot be known with much certainty. An extended period of time does not <br /> pose a concern, as use of the shallow groundwater is unlikely given its poor quality due naturally <br /> occurring high TDS concentrations and likely low yield. <br /> ' IS. Provide a discussion (and estimate)of contaminant mass remaining in soil and <br /> groundwater versus contaminant mass removed or destroyed by soil excavation or <br /> remedial actions. <br /> This item is not applicable because active site remediation has not been implemented or <br /> recommended. Natural attenuation will continue to reduce the constituent concentrations in soil <br /> and groundwater over time, as discussed in the response to Item 14. <br /> 16. Provide assumptions,parameters,calculations and the model used in any risk assessments. <br /> For the HHSE, SAIC calculated an estimated risk and hazard using the equations and <br /> assumptions outlined in the PEA Guidance Manual under the residential exposure scenario(the <br /> most conservative exposure scenario). The evaluation of risk associated with soil exposure <br /> pathways was limited to the upper 10 feet of on-site soils, consistent with the on-site residential <br /> land-use scenario described in the PEA Guidance Manual and with the proposed use of the Site. <br /> The exposure routes evaluated quantitatively were incidental ingestion of soil and dermal contact <br /> with soil, inhalation of wind-blown dust for non-volatile constituents, and inhalation of chemical <br /> vapors from soils. <br /> SAIC calculated exposure point concentrations for the COPCs in the HHSE and determined that <br /> ' there is not a significant risk to potential residents. See the summaries in section 2.1 and <br /> Appendix B.4 for details regarding the assumptions,parameters, calculations, and model used in <br /> the HHSE. <br /> 17. Provide assumptions,parameters, calculation, and the model used in fate and transport <br /> modeling. <br /> Fate and transport modeling has not been performed. <br /> 18. Provide a rationale why the conditions remaining at the site will not adversely impact <br /> water quality, human health, and safety,or other beneficial uses. The rationale for NFAR <br /> must include a finding about present and future water use, and risks the site may still <br /> represent to human health and safety, and water quality. <br /> Please see Section 4, Conclusions and Recommendations. <br /> 19. Provide a list of technical reports submitted for site assessment, corrective action, <br /> confirmation sampling,and closure. <br /> A list of references is provided in Section 5. <br /> 20. Provide any additional comments supporting site NFAR. <br /> See Section 4, Conclusions and Recommendations. <br /> 9 <br /> SAIL <br />