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Chris Ceausu January 30, 2015 <br /> White Arrow Page 2 of 2 <br /> 2402 S. California St. <br /> Stockton, CA 95206 <br /> concentrations toward the northeast from B-10A, but the concentration trend appears to be <br /> favorable. <br /> The plume of MORO-impacted soil is not well delineated; the highest concentration detected, 1,900 <br /> milligrams per kilogram (mg/kg) occurs at 5 feet bsg in B-10A and is not delineated toward the <br /> northeast, over an angle of approximately 155 degrees from the point of highest known <br /> concentration. A requirement for case closure is defining the boundaries of the plume, referred to as <br /> plume delineation. To complete the plume delineation, at least one sampling point, preferably two, <br /> northeast of B-10A is needed. Please submit a short work plan addendum to delineate MORO and <br /> DRO in soil toward the northeast from boring B-10A. <br /> The EHD erred in thinking that soil samples had been previously analyzed for semivolatile organic <br /> compounds (SVOCs) as shown in the EHD directive letter dated 21 August 2014; however no <br /> samples had been analyzed for SVOCs, which is part of the sampling protocol for waste oil <br /> underground storage tanks (USTs) or tanks of unknown use. Please resample B10A at 5 feet bsg <br /> and B5 at 10 feet bsg locations and analyze those samples only for SVOCs by EPA Method 8270C <br /> to complete the analytical suite for waste oil or unknown tank cases. <br /> The scope of investigation thus'far has to been to obtain reduce uncertainties associated with <br /> known and potential contaminants in soil, which the EHD considers the directed activities above will <br /> accomplish. If it is desired to reduce uncertainties associated with groundwater, the EHD <br /> recommends obtaining a groundwater sample for laboratory analysis of DRO and MORO, and <br /> volatile organic compounds. The EHD reviewed three monitored sites around the subject site and <br /> has inferred that groundwater may be encountered at approximately 30 feet bsg and that the flow <br /> direction is toward the east. If a groundwater sample is to be obtained, the EHD recommends <br /> utilizing a boring east or northeast of B-1 OA to obtain the sample. <br /> If you have questions or comments regarding this letter, please contact Nuel Henderson at (209) <br /> 468-3436 or by email at nhenderson(cDsicehd.com. <br /> Sincerely, tllsra'/esser, <br /> Nuel C. Henderson, Jr., PG A rienne REHS <br /> Engineering Geologist Program Coordinator <br /> CC: Misty Vazquez Ponce, PE, Partner Engineering and Science, Inc., 2154 Torrance Blvd., Ste. <br /> 200, Torrance, CA 90501 <br />