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Ripon Farm Service Page 3 <br /> 932 Frontage Road March 3, 2010 <br /> Ripon, California 95366 <br /> used to generate the initial calibration and daily calibration check for methods TO-3 and <br /> TO-15 associated with the soil gas samples collected from the Ripon Farm site? <br /> 3. Soil gas samples were not analyzed for TPH-d by method TO-17, an inconsistency with <br /> the approved work plan (EHD letter dated August 27, 2008). TPH-d has historically been <br /> detected at significant concentrations in soil and groundwater collected during previous <br /> investigations at this site. A rational must be provided for deviating from the approved <br /> work plan and not analyzing soil gas samples for TPH-d by method TO-17; it must also be <br /> demonstrated that the reported results are equivalent to those that would have been <br /> provided by method TO-17 and can be relied upon for decision making. <br /> AGE's response did not address these concerns. <br /> Using the Johnson and Ettinger Model, AGE calculated the carcinogenic risk for TPH-g to be <br /> zero, and summation of hazard was calculated to be 1.9E-04, well below the action level of <br /> 1.0. As the data derived by simply dividing the total TPH-g concentration by three to <br /> represent smaller carbon number ranges has not been shown to be valid, the EHD is not <br /> certain that these calculated results reflect the risk posed by the high concentrations of TPH-g <br /> detected in the soil gas samples. For the EHD to proceed with site closure consideration, you <br /> must address the concerns presented in this letter. <br /> Continue the annual sampling schedule by collecting groundwater samples from the <br /> monitoring wells during the second quarter 2010, and analyze the groundwater samples for <br /> MTBE, 1,2-DCA, and TPH-d. if you have any questions concerning this letter, please contact <br /> Vicki McCartney at (209) 468-9852, or by email at vmccartney@sjcehd.com. <br /> Sincerely, <br /> L-�- 6 <br /> Victoria L. McCartney, REHS Nuel C. Henderson, Jr. PG <br /> Senior Registered Environmental Health Specialist Engineering Geologist <br /> c: Mr. William R. Little, PG, Advanced GeoEnvironmental, Inc. 837 Shaw Road, Stockton, <br /> California 95215 <br /> Mr. James L.L. Barton, PG, California Regional Water Quality Control Board Central <br /> Valley Region, 11020 Sun Center Drive, Suite 200, Rancho Cordova, California 95670 <br />