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7.0 CLOSURE AND POSTCLOSURE MAINTENANCE PLAN All closure and postclosure maintenance activities for the site will conform to an approved closure and postclosure maintenance plan. The plan will be prepared in accordance with RWQCB and recently adopted CWMB requirements. The RWQCB and the CWMB will be notified at least 180 days before beginning any partial or final closure activities, and within 30 days after their completion. All closure activities will be observed and documented by a registered civil engineer or a certified engineering geologist. Closure activities will be documented in a written report. This section describes the proposed closure and postclosure maintenance plan for the site. The NCSL's closure schedule is dependent both on the site's service life and on the level of module activity. Because the site will be filled on a one module at -a - time basis, the entire site's closure depends upon the time required to complete closure of individual modules. It is estimated that within 2 years of the last mod- ule's completion, the entire site will be closed. Based on this estimate, the site service life of 36 years (see Section 5.2), and the proposed starting date in late 1990, site closure should be completed by 2029. Final landfill slopes will be constructed no steeper than 12 percent. Minimum fi- nal surface slopes of 3 percent (after settlement) will be used to provide sufficient slope for surface -water runoff. Drainage swales will be constructed and main- tained at a minimum 2 percent slope to divert surface drainage away from cov- ered wastes. The completed landfill will be covered with at least 4.5 feet of cover material con- sisting of the following: • A minimum 24 -inch foundation layer of compacted soil placed over waste fill A minimum 12 -inch layer of clayey soil compacted to achieve a hy- draulic conductivity of 1 x 10-6 cm/sec or less, placed over the foundation layer PJ9 9390218A.00W 65 Rev. 0 July 20, 1989