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Mr. Doug Ohland -2- 16 June 1993 f + Southwest Hide The background level for salt concentrations needs to be determined. If Southwest Hide intends to leave or use wastes as fill in the pond excavation, then a designated level for salts must be established. Southwest Hide must determine the amount of contaminated soil with salt concentrations above the designated level . Southwest Hide must develop alternatives for disposing of all the wastes, if any, remaining below the surface impoundments. On page 15, the Plan states that the asphaltic concrete surface, which will be used as the cap, is designed to resist cracking under all anticipated traffic and weather conditions and attains a permeability of less than 1 x 10-6 cm/sec. No specific data are used to demonstrate that the asphalt concrete surface was the engineering equivalent to the construction standard stated in Section 2540 of Chapter 15. Also, no cost estimates were included in the closure plan for the closure approach selected or the other approaches not selected. Cost estimates need to be included for the post-closure period which should include the costs identified in the asphalt maintenance schedule. Appendix II of the Plan discusses the permeability testing on the asphalt. The data indicate that the laboratory, after making several adjustments to the sample, was able to get a permeability less than 10-6 cm/sec under laboratory conditions. However, it is not clear whether or not the laboratory conditions are representative of field conditions. Furthermore, actual field permeability may be higher due to varying field conditions. We would expect laboratory results to be on the order of 10' cm/sec or lower to have greater confidence that the field permeabilities were adequate. Since a large portion of the reduction in permeability is due to the pavement fabric being used between the layer of asphalt, more documentation is needed to determine the suitability of the fabric as liner material . What is the thickness of the asphalt cap? Appendix III is supposed to present information that demonstrates that the soils at Southwest Hide have the engineering properties necessary for cover foundation material . The 5 October 1992 letter from Reinard W. Bradley, Consulting Airport Engineer, discusses the use of bituminous surface course mix design (P-401) for an airport apron at Stockton Metropolitan Airport. It is unclear what the relevancy of this information has to do with the use of compacted on-site soils for foundation materials as indicated on page 14. The final approval of the closure of the two surface impoundments will be based on Southwest Hide demonstrating that either all contaminated soils are removed from the site or that the contaminated soils left at the site are not a designated waste and that the proposed closure alternative meets the performance goals of Chapter 15. All information submitted in future reports or the CQA reports must address these issues, otherwise the closure will not be deemed complete. The Closure Plan was submitted without the stamps of the individuals signing off on the document. The signature page must be stamped if the Report is required to be completed under the direction or supervision of a professional engineer or geologist. Please submit a new signature page for the Closure Plan with the appropriate stamp for each person that signs the documents. All