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Ms. Wendy Wyels, SLIC Unit <br /> Central Valley - Regional Water Quality Control Board <br /> September 11, 1997 <br /> Page 2 <br /> Closure Request <br /> Sierra-Pacific is herein requesting that the Regional Water Quality Control Board (RWQCB) issue a closure <br /> letter for the former Cargill facility located at Port Road No.8, Stockton, California. Based on soil and <br /> ground-water sampling, laboratory test results, and information from the scientific literature, we believe that <br /> the former Cargill site no longer poses a significant threat to the waters of California <br /> Soils Test Results - Three limited soil sampling programs were conducted at the site. The first report of <br /> results was submitted to RWQCB on May 29, 1996. The second soil sampling event took place during the <br /> installation of three shallow monitoring wells. The installation report was submitted to RWQCB on <br /> November 15, 1996. Finally, a composite soil sample was collected in February 1997 to characterize <br /> unexcavated soils for possible disposal at Forward Landfill, Manteca. The composite sample work plan was <br /> prepared for Cargill on February 11, 1997. <br /> Demolition of the Cargill facility in April 1997 revealed that about 80 percent of the facility had been paved <br /> with Portland cement and asphaltic concrete. Excavation showed that soils beneath paved areas were <br /> generally clean and dry. The ten-point, composite soil sample was collected in non-paved (potentially <br /> contaminated) areas of the site in February 1997. Laboratory test results from the composite soil sampling <br /> event indicated that soils in these areas contained an average of about 680 mg/kg Total Kjeldahl Nitrogen <br /> (TKN) and 14 mg/kg nitrates (Appendix A). Nitrate (NOO at a concentration of 14 mg/kg is equivalent to <br /> 3.2 mg/kg nitrate as nitrogen (N-NOO. In other words, 99.6 percent of the nitrogen present in shallow soils <br /> at the site is present as organic and ammoniacal nitrogen. Earlier testing further supports that finding. <br /> Ground Water Test Results - Laboratory test results indicate that shallow ground water at the former <br /> Cargill facility contains very low concentrations of molasses-based feed product, and even lower <br /> concentrations of nitrates. Please see the enclosed quarterly monitoring report. <br /> Fate and Transport of Nitrogen Compounds - Field evidence and chemical data suggest that anaerobic <br /> microbial denitrification is taking place beneath the site, and that feed products present in the subsurface <br /> apparently enhance the desired microbial activity. <br /> Saline Ground Water Intrusion - Shallow ground water at the Port of Stockton contains dissolved <br /> minerals, including sodium and magnesium chlorides. Elevated salt concentrations and specific conductance <br /> values appear to be largely caused by the influx of mineralized connate waters into the uppermost aquifers. <br /> Sierra-Pacific has described two distinct sedimentary formations (soil types) in numerous soil borings at the <br /> Port of Stockton (Washington Street and Port Road No. 8 feed product facilities). The deeper formation <br /> consists of uniform, poorly-graded, olive-green, silt with occasional thin beds of bluish-gray smectite clay. <br /> Water samples taken from the olive-green formation contain more dissolved minerals (TDS) than surface <br /> waters. The lower sediments are olive-green due to the presence of ferrous iron cations. Ferrous iron is <br />