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John and Margaret Marci Property S"`' 17 October 2008 <br /> 2969 Loomis Road Page 3 of 3 <br /> Stockton, California 95205 <br /> GTI concluded from the DPE pilot test that the technology is a potential remedial <br /> method for the site, focusing on the vacuum extraction portion of the method as a <br /> means of introducing additional oxygen to soil gas and groundwater to stimulate <br /> the biological breakdown of the hydrocarbon contaminants. The results of the test <br /> were interesting to the EHD as they appear to indicate that the EHD should <br /> reconsider its earlier rejection of soil vapor extraction (SVE) as a potential remedial <br /> technology applicable to your site and contaminants. <br /> The EHD notes that when monitoring soil gas in the observation wells during the <br /> bioventing pilot test, the procedure was modified from purging three well volumes <br /> of soil gas from the wells to one well volume prior to sampling because the <br /> hydrocarbon vapor concentrations were so high as to pose a risk of saturating the <br /> meter sensors. Also, during the DPE pilot test, the propane fuel feed to the <br /> treatment system had to be cut back to reduce the operating temperature of the <br /> thermal oxidizer from 1900° F to 1500° F; GTI attributed the excess 400° F to <br /> burning of the hydrocarbons in the extracted soil gas. These observations lead the <br /> EHD to believe that a significant hydrocarbon mass may be recovered through <br /> either SVE or DPE. As the TPHg and TPHd concentrations in the extracted soil <br /> gas were not assessed, the EHD recommends further pilot studies of SVE and/or <br /> DPE to assess the total contaminant recovery rate and sustainability. Provide the <br /> EHD a response to these comments or a work plan for further pilot test(s) as <br /> discussed above no tater than 15 December 2008. <br /> If you have any questions, please contact Vicki McCartney at (209) 468-9852 or by <br /> email at vmccartney(a)_sicehd.com. <br /> Sincerely, <br /> Victoria L. McCartney, REHS Nuel C. Henderson, Jr., PG <br /> Senior Registered Environmental Engineering Geologist <br /> Health Specialist <br /> C: Mr. Reza Ghanbari, Geological Technics Inc., 1101 7 1 Street, Modesto, California 95354 <br /> Mr. James Barton, PG, California Regional Water Quality Control Board Central Valley Region, <br /> 11020 Sun Center Drive, Suite 200, Rancho Cordova, California 95670 <br /> Bioventing Pilot Test Comment Letter 1008.doc <br />