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WASTE DISCHARGE REQUIREMENTS -4- RE-MANUFACTURING LTD, RENTAL MACHINERY CO., INC., AND STANLEY S. MOORE CLOSURE OF SURFACE IMPOUNDMENT AS CLASS I LANDFILL SAN JOAQUIN COUNTY 22. A storm drain line discharges about 20 feet to the east of the closed surface impoundment. It carries storm water from the industrial park, and occasionally carries discharges from an on- site chemical company. An open ditch runs from the end of the storm drain line into Mormon Slough. The storm drain and ditch are the eastern boundary of the closure project. WASTE MANAGEMENT UNIT CLOSURE Surface Impoundment 23. The Discharger has removed all hazardous sludges from the surface impoundment; however, contaminated subgrade soils containing hazardous concentrations of waste constituents were left in place. Chapter 15 Section 2582 states in part that if after reasonable attempts to remove such contaminated materials,the Discharger demonstrates that removal of all remaining contamination is unfeasible, then the waste management unit shall be closed as a landfill pursuant to Section 2581. 24. Chapter 15 Section 2581 states in part closed landfills shall be provided with not less than two feet of appropriate materials as a foundation layer for the final cover. In addition, Section 2581 requires closed landfills to be provided with not less than one foot of soil containing no waste or leachate, placed on top of the foundation layer and compacted to attain a permeability of either Ix10-6 cm/sec or less, or equal to the permeability of any bottom liner system or underlying natural geologic materials, whichever is less. Permeability determinations for cover materials are specified in Article 4 and are required to be appended to the closure report. 25. The Discharger's data demonstrate that natural geologic materials between the base of the surface impoundment and ground water may not prevent the impairment of beneficial uses of ground water from the discharge of hazardous wastes to the former surface impoundment. Therefore, the surface impoundment has been capped with 24 inches of compacted clay material, a gravel drainage layer, filter fabric, and overlain by a 12 inch vegetative soil layer. 26. Closure plans specified that the clay cap covering the closed surface impoundment be compacted to a maximum hydraulic conductivity of 1x10-7 cm/sec. Field permeability testing of the clay cap was not performed during the construction period. 27. Suction lysimeters placed below the clay cap were proposed in the approved surface impoundment closure plan to monitor the penetration of liquids through the clay cap. These lysimeters have not been installed below the clay cap. 28. Rock riprap was installed on the northern end of the closed surface impoundment between Mormon Slough and the base of the closed surface impoundment to prevent erosion of the protective clay cap.