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M. Scott Mansholt - 2 - 14 June 2007 <br /> Mountain House Site #1 <br /> methods used evaluated a particular sample for carbon ranges and as such the results <br /> represent a certain degree of overlap between the method(s) selected for a particular analysis. <br /> According to the analytical data review, the chromatogram patterns are consistent with TPHc, <br /> based on the broad range of carbon chains noted, i.e., for TPHc (CIO- C36), TPHd (CIO- C28) <br /> and for TPHg (C6- CIO). <br /> SAIC concluded that based on the absence of BTEX compounds, and the broad range of <br /> carbon chains noted consistent with TPHc, the elevated concentrations of crude oil at the site <br /> are the likely source of elevated petroleum hydrocarbon compounds concentrations in soil and <br /> groundwater. Based on SAIC's clarifications for the TPHg detection, items needing <br /> clarification have been adequately addressed and further investigation or characterization is <br /> not required. <br /> Regional Water Board staff concurred in our 26 March 2007 response to Chevron that the <br /> affected soil and groundwater had been adequately delineated and is limited with approximate <br /> dimensions of 150-feet by 200-feet; affected groundwater generally coincides with the outline <br /> of affected soil. <br /> Both the affected soil and groundwater occurs within the Byron Road and Union Pacific <br /> Railroad (UPRR) right-of-way, primarily beneath Byron Road, the UPRR tracks, and the <br /> existing pipelines located next to the tracks. It is very unlikely that future commercial/industrial <br /> or residential development will occur on this site. Thus, exposure to affected soil or <br /> groundwater should not occur. <br /> Regional Water Board staff concurred that removal of impacted soil generally is not feasible <br /> given that the majority lies beneath Byron Road, the railroad, Mountain House Creek, and <br /> other pipelines. Current land use for the site within the right-of-way will likely remain <br /> unchanged and continue for the Byron Road roadway, ingress/egress needs, the UPRR <br /> railroad tracks, and for the active pipelines. <br /> According to the field investigative data and information, and SAIC's response to comments, <br /> and with the provision that the information provided was accurate and representative of site <br /> conditions, Chevron may prepare a request of no further action determination. Chevron's <br /> request should be in accordance with Central Valley Regional Water Quality Control Board's <br /> 16 April 2004 update to Appendix B of the Tri-Regional Board Staff Recommendations for <br /> Preliminary Investigation and Evaluation of Underground Tank Sites -- No Further Action <br /> Requests, Section 6.5 NFAR for Cases Exceeding Water Quality Objectives. <br /> The no further action request should include the SMP and a description of the process for <br /> recording an Environmental Restriction that outlines the petroleum-impacted soil and <br /> groundwater conditions. <br /> If existing, additional, or previously unidentified chemical constituents at the site cause or <br /> threaten to cause pollution or nuisance or are found to pose a threat to public health or water <br /> quality, then 1) nothing in this determination is intended or shall be construed to limit or <br />