ARCHIVED REPORTS_1993_1 - Laserfiche WebLink

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H. Project Description • number of vehicles utilizing the site per day and per week;and • log of special occurrences. CLOSURE Once a landfill has reached its capacity,it would be formally closed to protect public health and the environment from the wastes contained in the landfill (CCR Title 14, Section 17760). Typically closure involves installation of a final cover over the landfill. Closure often occurs in phases as portions of a landfill reach capacity. The final cover or cap of the proposed landfill expansion would be constructed in compliance with State guidelines in effect at the time of closure of the landfill. The preliminary design of the cap consists of a 24-inch foundation layer, 12-inch compacted material layer with a permeability of 1 x 10-6 cm/sec,and 12-inch vegetative/top soil layer, as shown in Figure 11.4. The final cover is designed to route as much rainfall as possible off the site to minimize leachate generation and reduce the potential for odors and gas emissions. The final vegetative cover must provide maximum coverage and tolerate site conditions with minimum maintenance. According to California regulations,the roots must not penetrate the barrier layer of a soil cover,limiting the root depth of the vegetation for soil covers. The expansion areas would use a geomembrane cover which is not nearly as susceptible to degradation by roots. An additional advantage of the geomembrane cover is protection of the vegetative cover from landfill gas. Establishment and maintenance of the vegetative cover is particularly critical in the first year of closure. The minimum slope on the closed landfill would be five percent and the maximum slope would be 25 percent(4 horizontal:I vertical)on the sides of the landfill. The proposed final grading of the site is shown in Figure II.6. Perimeter drainage ditches,benching,and revegetation would be used to minimize erosion of the cover. The estimated final cover annual soil erosion for the landfill is approximately 27 tons per year. It is estimated that this would result in approximately 20 cubic yards per year deposited in the surface water detention pond. II.34