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Former Cheaper Store Number 37 Page 2 <br /> 15 Grant Line Road August 5, 2011 <br /> Tracy, California 95376 <br /> By letter dated 01 April 2011, the EHD had directed ATC to provide the locations for additional <br /> proposed soil borings ATC `had proposed and the technical justification to support the <br /> necessity for the additional characterization of impacted soil if the evaluation of soil gas <br /> concentrations indicated a significant vapor intrusion problem. Although ATC has not <br /> addressed the potential health risk posed by the high TPH-g concentrations detected in soil <br /> gas, results from the Johnson .and Ettinger model do indicate that human health does not <br /> appear to be at risk from the soil gas concentrations. Although ATC has not provided the <br /> number and locations of the proposed borings to the EHD, ATC did state that additional <br /> source area characterization appeared warranted to "evaluate the residual impact to vadose <br /> zone soil including the capillary fringe" and update mass calculations. Based on the most <br /> current sampling event'completed on 14 March 2011, methyl tertiary-butyl ether (MTBE) was <br /> detected in groundwater samples collected from monitoring wells MW-1, MW-5, and MW-8 at <br /> concentrations of 3.3 micrograms per liter (Ng/L), 2.5 pg/L and 1.0 pg/L, respectively. Tertiary- <br /> butyl alcohol (TBA) was the only other contaminant detected in groundwater from MW-5 at 13 <br /> pg/L. These groundwater and soil gas results-do not appear to justify further,assessment <br /> work at this site. The EHD suggests that the previously submitted residual mass estimate be <br /> updated, incorporating soil data recently collected at this site, and that the results be <br /> submitted in the closure summary report. <br /> If you have any questions concerning this letter, please contact Vicki McCartney at (209) 468- <br /> 9852, or by e-mail at vmccartney(a)sicehd.com. <br /> Sincerely, <br /> Victoria L. McCartney, REHS Nuel C. Henderson, Jr., PG <br /> Registered Environmental Health S7ialrist Engineering Geologist <br /> c: Mr. Nathan Christman, PG, ATC Associates Incorporated, 1117 Lone Palm Avenue, Suite <br /> 201, Modesto, California 95351 <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 />