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3-6 The results of the settlement analyses indicate that the sub grade soils could consolidate up to 2 feet in response to maximum refuse loads, but that the differential settlement of sub grade soils across the planned refuse footprint would be relatively minor (0.36 percent). While the potential for existing refuse to settle continues to exist, since the existing landfill configuration mimics the geometry of the proposed expanded landfill, the differential settlement of existing wastes is expected to be negligible. The settlement analyses of new; wastes indicate that significant settlement can occur. However, assuming a uniform settlement potential for refuse of 25 percent, the minimum landfill final cover slope gradient is calculated to drop from five percent to 3.75 percent. If randomly differential settlement of 22 percent to 28 percent occurs, the calculations indicate that the final cover gradient could range from one percent to six percent in areas where a five percent cover gradient is constructed. 3.4.2 Survey/Settlement Monumentation In order to monitor the future settlement of the Stage 1B partial closure area, a settlement and survey monuments will be installed on the landfill in accordance with 27 CCR, Section 20950 (d). These monuments are proposed to consist of galvanized pipe, two inches in diameter and six inches in length placed in blocks of concrete, 24-inches in diameter by eight inches in depth. A nail and tag will be placed in the center of each monument for identification (see Detail 1 on Figure 6). Two settlement monuments are proposed to be placed on the slope area of the Stage 1B Partial Final Closure area as shown on Figure 2. Permanent perimeter Survey monuments have been placed on undisturbed ground as reference points not subject to settlement as shown on Figure 2. These points are the horizontal and vertical control points for the site aerial topographic survey and will be maintained or replaced, as needed, throughout the post-closure maintenance period. An aerial photographic survey of the site with a maximum contour interval of two feet will be performed and provided to the RWQCB, LEA, and CalRecycle upon completion of closure activities. The settlement monument will be surveyed upon completion of all closure construction activities. Additionally, in accordance with 27 CCR requirements, Forward Landfill Inc. will update the aerial survey of the Stage 1B partial closure area every five years throughout the post-closure maintenance period. An iso-settlement map and report is to be submitted to the RWQCB included as part of the survey information. 3.5 Landfill Slope Stability A slope stability analysis was prepared by GLA in 2005 for the Stage 1A Partial Final Closure construction project. A slope stability analysis is required by 27 CCR, Section 21090 when the closure design includes final slope faces steeper than 3:1 (horizontal to vertical) or a synthetic component in the final cover configuration. The proposed final slopes for the FL Stage 1B Partial Final Closure construction project do not exceed 3:1 and a synthetic component is not proposed, but the slope below the proposed 15-foot wide bench has an inclination of 2:1 (horizontal to vertical). The basic exterior grading for the Stage 1B Partial Final Closure area on the 2:1 slope below the proposed bench has not changed since the 2005 stability analysis was completed. Therefore, the slope stability analysis as prepared for Stage 1A is still valid for the Stage 1B Partial Final Closure. The Stage 1A stability analysis was conducted pursuant to 27 CCR, Section 21750(f)(5) to review the integrity of Forward Landfill Stage 1B Partial Final Closure/Post-Closure Maintenance Plan June 2011 SWT Engineering z:\projects\allied waste\forward\11-1014 partial fnl clsr pin\partial final closure plan document\text\sec 3.doc