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Rob <br /> From: "Djuth,Gerald@Waterboards"<Gerald.Djuth@waterboards.ca.gov> <br /> Date: Wednesday,January 02,2013 5:57 PM <br /> To: "Ijaz S.Jamall"<ijamall@riskbaseddecisions.com> <br /> Cc: "Kent Calfee"<KCalfee@calfeelaw.com>; "Teri Stout"<tstout@riskbaseddecisions.com>; "Rob Pexton" <br /> <rpexton@riskbaseddecisions.com>;"Tex Lu"<texlu@riskbaseddecisions.com> <br /> Subject: RE:2005 Navy Drive,Stockton-Workplan for Supplemental Investigation <br /> Ijaz- <br /> Staff of the Regional Water Quality Control Board have reviewed the 2 January 2012 Workplan for Supplemental <br /> Investigation for 2005 Navy Drive in Stockton (Workplan). The Workplan proposes further investigations to <br /> determine if DCE found in site groundwater originated from site activities or from an off-site source. The <br /> Workplan proposes a multi-depth soil gas survey around the former tank location and wash rack at the Site, <br /> followed by possibility two or more rounds of grab groundwater sampling. <br /> The Workplan proposes initially sampling nine soil gas locations mostly around a former tank site and wash <br /> rack. The Workplan text proposes nine initial grab groundwater samples,followed by an additional seven <br /> locations if the initial samples suggest an off-site source for a total of 16 samples. Regional Board staff note <br /> that Figure 6 shows at least 27 grab groundwater locations. Therefore,the text and figure need to be revised to <br /> be consistent. <br /> The Workplan also presents a discussion on Contaminant Fate and Transport, arguing that because DCE is often <br /> seen as a breakdown product of PCE/TCE, and because these chemicals were not detect in site groundwater the <br /> DCE must have come from off-site. Regional Board staff acknowledge that DCE is often a breakdown product of <br /> PCE/TCE, however, staff experience has seen DCE used as product by itself. DCE is commonly used as a solvent <br /> for waxes, and it may have been present in products used in the site wash rack. Therefore, staff cannot draw <br /> any conclusions regarding the source of the groundwater contamination based on the absence of PCE and/or <br /> TCE in the groundwater. <br /> Staff concur with the Workplan, in general. However, staff prefer to see an expanded soil gas survey with data <br /> points at the assumed upgradient, downgradient and lateral site boundaries in addition to the proposed <br /> locations around the wash rack. Locations for grab groundwater samples could then be determined after <br /> examining the soil gas data, possibly reducing the number of samples needed to define the extent of <br /> groundwater contamination. Therefore,the Workplan is approved on the condition that the soil gas survey be <br /> expanded to sample locations at upgradient, downgradient and lateral site boundaries, and the data presented <br /> to Regional Board staff along with proposed groundwater sampling locations for staff approval prior to obtaining <br /> groundwater samples. <br /> If you have any questions regarding this correspondence, please respond to this email or call me at 916-464- <br /> 4677. <br /> Gerald J Djuth, PE,CEG <br /> Central Valley Regional Water Quality Control Board <br /> Chief, Federal/Private Site Cleanup <br /> 11020 Sun Center Drive#200 <br /> Rancho Cordova,CA 95670 <br /> (916)464-4677 <br /> From: Ijaz S. Jamall [mailto:ijamall@riskbaseddecisions.com] <br /> Sent: Wednesday,January 02, 2013 3:24 PM <br /> To: Djuth, Gerald@Waterboards <br /> 1/16/2013 <br />