SITE INFORMATION AND CORRESPONDENCE

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CLOSURE PLAN FOR RE-MANUFACTURING SURFACE IMPOUNDMENT, STOCKTON, SAN JOAQUIN COUNTY The Closure Plan submitted by Kleinfelder dated December 14 , 1990 , was determined to be inadequate by Board staff. In over- view, the Plan proposed closure of the impoundment with no fur- ther excavation, backfilling with native soils and capping with asphalt. The Closure Plan will be revised to propose a more accurate determination of background lead concentrations and additional excavation to background to achieve "clean closure" pursuant to Section 2582 , Chapter 15 , Division 3 , Title 23 , California Code of Regulations. Confirmation samples will in- clude other detected constituents which were observed during previous sampling. Lead will be used as an indicator parameter for initial determination of extent of contamination and proposed excavation. Additional samples have been collected from the impoundment walls on the north and east sides of the pond and analyzed for total lead. Results will be compared to background sample concentra- tions and presented in the revised Closure Plan. Most of the comments provided by staff on the Kleinfelder Closure Plan were specific to the proposed closure-in-place approach. Since clean closure of the surface impoundment is now being proposed, comments will only be addressed as applicable. Once the volume of the waste is identified, treatment and dispos- al alternatives will be evaluated. The most likely option is excavation with disposal at Class I and II landfills, as applica- ble. Preliminary negotiations have been conducted with both Chem Waste Management-Kettleman Hills Facility and Forward, Inc. Solid Waste Disposal Site. For purposes of closure of the surface impoundment pursuant to TPCA, clean closure to background levels is proposed, with back- ground being established as discussed above . If subsequent investigation determines that other sources unrelated to opera- tion of the surface impoundment have resulted in an unacceptable level of contamination in the area and the background levels themselves require remediation, the remaining soils in the sur- face impoundment will be addressed with the contamination of the area. It would be inequitable to require cleanup of the surface impoundment at this time to levels below the current background levels even though they may not be naturally occurring. This is particularly true considering that the elevated lead in the area may not be due to site activities, but due to historical activi- ties throughout the entire Stockton area. Elevated concentra- tions onsite may be due to previous placement of dredged material from Mormon Slough. 4