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i <br /> L <br /> Sec. 9-1415.3(k)(5) Temporaly cut Slopes @t Setback Lines. Temporary cut slopes (i.e., <br /> t f for limited periods of time, slopes that are in the process of extraction <br /> prior to being backfilled) at setback lines-shall not exceed one (1) foot <br /> horizontal to one (1) foot.vertical; except that temporary cut slopes at <br /> F setback lines to a maximum of one half 112 of a foot horizontal <br /> ( ) to <br /> one (1) foot vertical may be maintained if site-specific geologic and <br /> engineering analysis demonstrate through a slope stability analysis <br /> • that the proposed temporary ry cut lopes will have a minimum slope <br /> stability factor of safety as required in Section 9-1415.3(k)(4). <br /> .:However,- in -the event that there are existing structures on the <br /> adjacentro e <br /> p p rtY (or the immediate potential for structures on the - <br /> adjacent property), the excavation shall at no time be closer to the <br /> property line than a line projected on a slope of one (1) to one (1) <br /> from the property line to the toe of the slope. <br /> The temporary cut slopes for the project are proposed one-third (113) of a foot horizontal <br /> to one (1)foot vertical (113:1)with 15-foot wide benches every 34 feet of slope height. The <br /> slopes between the benches would be steeper than the maximum slope steepness allowed <br /> for by the standard. The average slope steepness of the cut slopes would be three-quarter <br /> ~ (314) of a foot horizontal to one (1) vertical (314:1), steeper than the general requirement <br /> { of the standard (1:1). The slopes were evaluated in the slope stability analysis, prepared <br /> } for the proposed project. The factors of safety values for surficial failure of the slopes <br /> between the benches ranged from 1.3 to 2.2 under static conditions and 1.1 to 1.8 under <br /> seismic conditions. Deeper seated failures (involving-the.entire benched slope) for the <br /> temporary cut slopes had a factor of safety of 1.3 for static conditions and 1.0 to 1.1 under <br /> seismic conditions. Therefore, the proposed temporary cut slopes do not meet the general <br /> 3 <br /> requirements of the standard (1:1 slopes) or the requirements for factors of safety <br /> presented in Section 9-1415.3(k)(4). The potential impact of slope design is addressed by <br /> Mitigation Measures 4.2-2a, 4.2-2b, and 4.2-2c. <br /> Sec. 9-1415.3(k)(6) Final Slopes. Final cut and/or fill slopes shall not exceed two (2) feet <br /> horizontal to one (1) foot vertical, except as specified below: <br /> 4 <br /> (A) Final slopes to a maximum of one and one-half (1 112) feet <br /> horizontal to one (1) foot vertical maybe maintained when <br /> site-specific geologic and engineering analysis demonstrate <br /> through a slope stability analysis that the proposed slopes will <br /> r have a minimum slope stability factor of safety as required in <br /> Section 9-1415.2(k)(4), while demonstrating suitability for the <br /> proposed end use and protecting against erosion (by means <br /> of revegetation or other methods approved by development <br /> Services Division). <br /> (B) Final slopes to a maximum of one (1) horizontal foot to one (1) <br /> foot vertical may be maintained underwater(beginning five (5) <br /> feet below the lowest water table-on the property experienced <br /> Draft Environmental Impact Report 7 ER-96-3 <br /> t <br />