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Weldon Church Property Page 2 <br /> 104 West Beverly Place June 14, 2011 <br /> Tracy, California 95376 <br /> Environmental Protection Agency, page 14, recommends that the default attenuation factors <br /> in Table 2 be used along with the maximum detected soil gas concentration for preliminary <br /> screening evaluations. Also, it appears that the average concentration of benzene was not <br /> converted from ug/m3 to milligrams per cubic meter (mg/ m) when entering the <br /> concentration into the Johnson and Ettinger Model. <br /> r y 50 <br /> Please submit a technical justification,. supported by the authoritative guidance, for the <br /> methodology used to enter the average soil gas concentration of benzene into the Johnson <br /> and Ettinger Model to determine the potential risk posed by soil gas intrusion into the <br /> structure at your site, or recalculate the health risk using the highest soil gas concentration <br /> detected for benzene (240 ug/m3) and report the results to the EHD within 60 days of the <br /> date of this letter. Also collect soil gas samples from soil vapor sampling points V-4 and V-5 <br /> after the rainy season has ended and report the potential health risk posed by soil gas <br /> intrusion into the structure from these two locations. If groundwater is encountered during <br /> the collection of soil gas samples, groundwater grab samples should be collected and <br /> analyzed for TPH-g; benzene, toluene, ethylbenzene, and total xylenes (BTEX); and 1,2- <br /> dichloroethane (1,2-DCA). This is in accordance with the DTSC guidance document. <br /> If you have any questions concerning this letter, please contact Vicki McCartney at (209) <br /> 468-9852, or by email at vmccartney@sjcehd.com. <br /> Sincerely, <br /> Victoria L. McCartney, REHS Nuel C., Henderson, Jr., PG <br /> Senior Registered Environmental Health S ecialist Engineering Geologist <br /> c: Mr. Brian Millman, 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 /> Frank and Bette A. Grande Family LP, Post Office Box 1076, Tracy, California 95378 <br />