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AZURE ENVIRONMENTAL August 19, 1996 - - �ti ; �^ ', . i�• �- r AZ145-001.4 Harlan Knoll San Joaquin County Public Health Services 445 N. San Joaquin Street Stockton, California 95201 RE: Proposed Workplan to Conduct Soil Sampling for Soil Treatment Cell Closure Manna Pro Facility, Stockton, California Dear Mr. Knoll: This letter presents a summary of proposed work activities to conduct confirmation soil sampling for soil treatment cell closure at the Manna Pro facility, 4004 South El Dorado Street in Stockton, California. The objective of confirmation soil sampling of the soil treatment cell is to obtain the necessary data to assess residual petroleum hydrocarbon concentrations in treatment cell soil and evaluate options for treatment cell closure. 1.0 BACKGROUND In July 1990 SEMCO, Inc., under contract to WHF Environmental, removed five fuel underground storage tank (USTs) at the Site and excavated hydrocarbon affected soils to a depth of approximately 15-feet below ground surface. Approximately 4,000 cubic yards of hydrocarbon affected soil were removed from the tank excavation and stored on Site. The affected soil was stored on the asphalt based parking area south of the excavation and covered with plastic. The stockpiled soil was sampled and analyzed for total petroleum hydrocarbons as gasoline (TPHg) and diesel (TPHd), and benzene, toluene, ethylbenzene, and xylene (BTEX) compounds. TPHg and BTEX were reportedly not detected in the stockpile samples. Based on the TPHd analytical results, the stockpiled soil was segregated into separate stockpiles. Approximately 1,200 tabic yards were found to be non-detect for TPHd; 1,700 cubic yards contained between 10 mg/kg and 50 mg/kg of TPHd; and 1,100 cubic yards contained between 50 rig/kg and 530 mg/kg of TPHd. In April 1993, the 1,200 cubic yards of stockpiled soil that was characterized as non-detect for petroleum hydrocarbons were used to complete the backfilling of the tank excavation. Soil generated from the installation of a sewer transmission line across the northern portion of the site was also used to backfill the tank excavation. The remaining stockpiled soil was moved to the north end of the site into a 140-foot by 160-foot soil treatment cell. The treatment cell berm was constructed using approximately 200 cubic yards of stockpiled soil containing no greater than 21 mg/kg of TPHd. A 6-inch thick layer of clean sand was spread over the surface of the treatment cell. The sand layer and berm was then covered with a 20-millimeter polyethylene liner. The remaining stockpiled soil (approximately 2,600 cubic yards) was moved into the treatment cell for aeration/bioremediation. 828 Mission Avenue, San Rafael, CA 94901 0 4151485-9740 Fax 4151485-6062