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ARCADIS Ms. Kathryn Dominic <br /> 26 November 2008 <br /> Please verify when the confirmation sampling will be performed and provide the <br /> results to this office within 30 days of receipt of the laboratory data. <br /> ARCADIS Response: ARCADIS resampled wells MW-08A, MW-17A, <br /> MW-11 BR, MW-146, MW-15B, MW-16B, MW-01C, and MW-15C for TEPHd in <br /> September 2008. TEPHd was not detected in the September 2008 groundwater <br /> samples from these wells and therefore, the March 2008 detections are <br /> unconfirmed. The cause of the TEPHd detections in the March 2008 data is not <br /> known. The laboratory report of the analytical results is attached. <br /> Comment 3 <br /> Appendix A presents TEPH as diesel using the silica gel cleanup method. As stated <br /> in our 22 April 2008 letter, the Regional Water Board does not accept the silica gel <br /> cleanup method for delineating TEPH as diesel, particularly for those sites that have <br /> weathered petroleum plumes and free product. Even though the silica gel analytical <br /> method discriminates non-hydrocarbon related polar compounds, it also removes <br /> diesel degradation by-products that still must be accounted for in the investigation <br /> and cleanup. In the future, please use EPA Method 8015M to delineate the <br /> dissolved-phase diesel at this site. <br /> ARCADIS Response: As requested, during the March 2008 sampling event, <br /> ARCADIS analyzed the samples for TEPHd using Method 8015M without silica <br /> gel cleanup. We understand the RWQCB's position regarding use of the silica <br /> gel cleanup method for TEPHd analysis. However, in the March 2008 sampling <br /> event and in future events, ARCADIS may have samples analyzed using the <br /> silica gel cleanup for comparison purposes only. EPA Method 8015M data <br /> (without silica gel cleanup)will be used to delineate the dissolved phase diesel at <br /> the site in the figures and main text of the reports. <br /> Imagine the result Page: <br /> GNRCADIS_DatalProjects-ActivelUnion Pacific RailroaMRC709-Tracy YardtCorres-Regulatory@00&11-26 Response to RWOCB 9-1601tr-Response to conments_11 26 o6.doc 4/5 <br />