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u Detailed construction guidelines for placement of final cover will be developed so that the final cover is completed consistent with the above requirements. 13.2 SETTLEMENT The settlement of refuse fill, characteristic of all landfills, is affected by a variety of factors, including (1) the types and moisture contents of refuse placed, (2) refuse density, (3) consolidation of the refuse under loads imposed by over- lying fill, (4) biological decomposition, and (5) chemical decomposition. The initial refuse density is estimated to be at least 1,200 pounds per cubic yard. Further densification will occur from surcharge loading by successive lifts of refuse. Despite this densification process, refuse settlement after closure is es- timated to range from 15 to 20 percent of the refuse thickness. This estimate is based on the method of preparation, effects of surcharging, estimated settlement during the active life of the landfill operation, refuse composition, and landfill set- tlement experienced at other sites with similar characteristics. The final surface grades are designed to accommodate drainage of the com- pleted landfill after settlement and to minimize erosion of the final cover. To ver- ify the integrity of the final cover, a program of periodic observation and mainte- nance will be instituted. Additionally, two permanent survey control monuments will be established and maintained to provide reference points for future settle- ment measurements. 1 13.3 POSTCLOSURE MAINTENANCE PROGRAM A postclosure maintenance program will be prepared according to CWMB re- quirements and implemented at the landfill upon closure to verify that contain- ment and monitoring facilities retain their integrity. The program will include pro- visions for the routine evaluation of surface drainage control facilities, final vege- tated soil cover areas, ground -water monitoring facilities, and access roads. Cracks in the final cover will be sealed. Any erosion damage, caused by ex- tremely heavy rainfall will be repaired. Temporary berms, ditches, and straw mulch will be used to prevent further erosion damage to soil cover areas until PJ9 9390219A.00W 54 Rev. 0 July 19, 1989