Laserfiche WebLink
No Further Action Required Request Report <br /> Mountain House Development Site#6 September 15,2011 <br /> Central Valley soils. The evaluation also found that threats to water quality, human health, and <br /> ' the environment are essentially the same whether free product is actively removed or not, <br /> because in each case, significant percentages of free product will remain. SAIC and Geomatrix <br /> concluded that all of the remedial technologies—with the exception of excavation at some <br /> sites—are ineffective, not easily implemented, and/or disproportionately costly in comparison to <br /> benefits. <br /> Unlike removal technologies, natural attenuation—coupled with a soil and groundwater <br /> management plan—is a viable approach for the Site. Natural attenuation will degrade the <br /> residual crude oil and limit the lateral and vertical extent of dissolved hydrocarbons in <br /> groundwater as well as any active remediation technology. Natural attenuation is a viable <br /> technology for weathered heavy crude oil with low concentrations of BTEX, and the extents of <br /> BTEX and associated TPH plumes in groundwater are generally limited to the area of SPO. The <br /> effectiveness, implementability, and cost-effectiveness of natural attenuation are summarized <br /> ' below. For most of the other technologies evaluated, "the costs to implement the technologies <br /> 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 and likely <br /> ' low yield. <br /> 15. 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 Item 14 response. <br /> 16. Provide assumptions,parameters, calculations and the model used in any risk assessments <br /> SAIC calculated an estimated risk and hazard for the HHSE using the equations and assumptions <br /> outlined in the PEA Guidance Manual under the future resident exposure scenario (the most <br /> conservative exposure scenario). Groundwater at the Site does not appear to be useable for <br /> drinking-water purposes; as the possibility of exposure to potential residents is unlikely, an <br /> evaluation of constituents in groundwater was not necessary and was not performed. The <br /> exposure routes evaluated quantitatively under the residential scenario were incidental ingestion <br /> and dermal contact with soil, inhalation of wind-blown dust for non-volatile constituents, and <br /> inhalation of volatile chemical vapors from soil. <br /> The calculated EPCs for the COPCs are considered protective of a potential resident. See the <br /> entire report included as Appendix A.23 for details regarding the assumptions, parameters, <br /> calculations, and model used in 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 /> 10 <br /> -SAIC <br />