COMPLIANCE INFO_JTD 9/3/2025 - Laserfiche WebLink

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Project No. AU25.1274 | PCPCMP Foothill Sanitary Landfill 4 September 2025 The existing gate at the site entrance will be preserved. Post-closure maintenance of the landfill gas extraction system may require a full-time technician to operate the system. Such personnel would also monitor and maintain the fencing and gates and look for evidence of unauthorized access to the closed facility. 2.4.3 Final Cover and Grading The County is planning to close the landfill using an approved ET final cover system, which is an alternative final cover as allowed in Section 21090(a) of Title 27, California Code of Regulations. This closure method does not include a low hydraulic conductivity barrier layer in the traditional sense. Investigations at the site indicate that there are sufficient soils available to construct the ET cover (JTD Tables 3 and 4, and "Landfill Closure Method Selection Rep ort, Foothill Sanitary Landfill, San Joaquin County, California", September 21, 2004 (revised 3 -17-05)). The top deck is designed with a minimum slope of 6 percent. Side slopes will average about 3.4H:1V and will include 15-foot-wide benches incorporated into the sideslopes every 50 vertical feet. Due to the preliminary nature of the final grading plan the slopes shown on the plan (Figure 6) are inclined at the average slope and do not show the benches. 2.4.4 Slope Stability The stability of the final cover for FSL was reviewed based on the cu rrent final grading plan, the final cover components, and the regulatory requirements under both static and seismic conditions. Title 27 CCR Section 21090(a) states that: "Designs having any slopes steeper than a horizontal to vertical ratio of three to one, or having a geosynthetic component [under paragraph (a)(2)]1, shall have these aspects of their design specifically supported in the slope stability report ... " The proposed maximum slope for FSL is 29% (3.4 to 1), and less than the three to one. Therefore, a slope stability report is not required at this time. However, the County may elect to increase these proposed closure slopes in the future. If so, the County will submit a slope stability report addressing these new slopes as required by the regulations in force at that time. Due to the absence of geosynthetics in the proposed ET final cover, there is no concern that the stability of the final cover is reduced by a geosynthetic component. Class III landfills must be designed to withstand seismic ground motions resulting from the Maximum Probable Earthquake (MPE) at the site. The seismic characterization for the FSL site has been studied and updated several times. Most recently, in 2015, CB&I completed a review of previous slope stability analyses for FSL that included a review of the site’s seismic characterization. The results of the CB&I evaluation indicate the design MPE for the landfill is a moment magnitude 8.1 event on the San Andreas fault, located approximately 84 miles (135 1 Title 27 CCR Section 21090(a)(2) refers to the requirements for the low hydraulic conductivity layer of the final cover.