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Raymond Investment Corporation Page 2 <br /> 730 Channel Street May 12,2009 <br /> Stockton, California 95202 <br /> • The average groundwater gradient is toward the northeast and the rate of flow during the last five <br /> years was calculated to be approximately sixty-six feet per year. <br /> • Soil beneath the surface has been identified predominately as clay and clay mixtures with a sand <br /> "layer" identified at approximately thirty feet bsg. <br /> • Impacted soil vapor is concentrated below the concrete that covers the ground surface and <br /> extends from approximately six to sixteen feet bsg. (Condor had previously calculated the <br /> summation of risk for soil gas for all constituents of concern to be 5.1E-08, and the hazard to be <br /> 9.3E-02,both well below the action levels.) <br /> • Sensitive receptors include a medical clinic within five-hundred feet and cross-gradient of the <br /> site, and childcare centers, schools, parks, two inactive municipal wells, and four apparently <br /> inactive domestic wells more than one-thousand feet from the site. <br /> Based on this information the EHD believes additional investigation is needed to delineate the vertical <br /> and lateral extent of groundwater contamination at the identified source of contamination and down- <br /> gradient northeast of the source area. This includes investigating soil and groundwater beneath the <br /> building located northeast of the source and may possibly warrant collecting soil gas samples near the <br /> building. Also, soil contamination in the vadose zone needs to be addressed. For this, a feasibility study <br /> is needed to identify a remedial technology, or combination of technologies, capable of mitigating <br /> petroleum hydrocarbon contamination in the soil near soil boring SB-7 and monitoring well MW-4. <br /> Submit a work plan to delineate the groundwater plume and a feasibility study to address soil <br /> contamination in the vadose zone to the EHD by August 4, 2009. If you have any questions regarding <br /> this letter,please contact Vicki McCartney at(209)468-9852, or by email at vmccartney@sjcehd.com. <br /> Sincerely, <br /> Victoria L. McCartney, RENS Nuel C. Henderson, Jr.,PG <br /> Senior Registered Environmental Health S ecialist Engineering Geologist <br /> c: Mr. Bill A. Cook III, PG, Condor Earth Technologies, Incorporated, 188 Frank West Circle, Suite 1, <br /> Stockton, California 95206 <br /> Mr. James L.L. Barton, PG, California Regional Water Quality Control Board Central Valley Region, <br /> 11020 Sun Center Drive, Suite 200,Rancho Cordova, California 95670 <br /> I <br />