COMPLIANCE INFO_JTD 9/3/2025 - Laserfiche WebLink

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Project No. AU25.1274 | PCPCMP Foothill Sanitary Landfill 5 September 2025 kilometers) from the site. This seismic event is estimated to result in median horizontal peak ground acceleration (PGA) of 0.054g for "rock" subgrade conditions, which is a re latively low acceleration. The CB&I evaluation found that global slopes of 3.4 to 1 were stable (JTD Appendix L) as reflected in the proposed final grading plan. The calculated yield acceleration is 0.14g for the critical slope. The yield acceleration is more than twice the design PGA of 0.054g, indicating that seismic displacement is not likely. The FSL final cover is sufficiently stable given the relatively flat final grades, low se ismic acceleration, and the use of soil only in the final cover. A detaile d stability analysis is, therefore, not necessary. However, stability analyses will be evaluated as part of the design of each cell of the landfill, because interim conditions may be more critical than the final landfill condition. Construction of the final cover and associated drainage structures will be certified by a qualified third party. During construction, the final cap will undergo continuous testing and inspection. This testing and inspection will conform to procedures set forth in an approved Construction Quality Assurance (CQA) Plan that will be developed and included in the final closure plan. The CQA Plan will conform to the requirements of Title 27 Sections 20323 and 20324. 2.4.5 Drainage and Erosion Control Closure drainage controls include the use of grass-lined drainage swales and slope benches to downchutes that direct runoff to the toe of the landfill. From there, the water will flow into a series of large perimeter drainage ditches (12 feet wide) that will discharge to one of six sto rm water detention basins (Appendix A Figure 1). Being detention basins, water will be allowed to fill the basins and then discharged to offsite natural drainage courses. The purpose of the detention basins is to attenuate peak flows off site and to control sedi ment via the particle settlement that can occur in the basins (Appendix A). Final drainage elements such as culverts, downdrains, concrete channels, etc. will be constructed during closure construction and are included in the closure cost estimate. The Shaw 2010 drainage design was reviewed to assess whether it was still applicable. Our review indicates rainfall intensities have actually decreased slightly since the Shaw analysis was completed. Therefore, their design should be more than sufficient. Also, Shaw used a peak design flow of 200 cubic feet per second (cfs) for the main perimeter channel. The actual peak flow in that channel is estimated to be 158 cfs, which is roughly 80 percent of the design flow. Erosion control of the final cover will be achieved through maintenance of vegetation on the surface of the landfill cap and ongoing repair of erosion damage, if any. An analysis of estimated soil loss due to erosion using the Revised Universal Soil Loss Equation (RUSLE2 software issued by the Natural Resources Conservation Service) was recently completed. The modeling assumed that the FSL, when closed, is covered with ET cover soils. This assessment indicated that the estimated soil loss would be approximately 1.7 tons per acre per year which is a reasonable