During mining operations, a series of benches may be excavated in a slope provided that the excavations are made in compliance with the requirements of the State Mine Safety Orders (California Code of Regulations, Title 8, Subchapter 17). The vertical height and slope of the benches constructed for permanent reclaimed slopes shall not exceed maximum standards for the specific soil types presented in the California Code of Regulations, Title 8, Article 6. In general, vertical cutslopes between benches shall not exceed four (4') feet in height in topsoil and overburden sediments. Benching shall be allowed in cohesive soil (clay, sandy or silty clay, clayey silt) only. Slopes above the elevation of groundwater (determined at the time of the excavation by the level of exposed water in the excavation) that exceed the maximum vertical height shall be excavated and maintained at slopes not steeper than 2:1 (horizontal:vertical). Slopes located five (5') feet or less below the average summer low ground-water level shall not be steeper than 2:1 (horizontal:vertical). Slopes located more than five (5') feet below the average summer low groundwater level shall not be steeper than 1: 1 (horizontal to vertical).
Vertical cutslopes in excess of four (4') feet in height may be approved for the development of special habitat (e.g., bank swallows) if a site-specific slope stability analysis, performed by a licensed engineer, indicates that the slope does not exceed critical height for the on-site soil conditions. Projects proposing such slopes shall submit a long-term maintenance plan to ensure that the function of the slopes as habitat is met.
(§ 1, Ord. 1190, eff. September 5, 1996; as amended by Ord. 1518, eff. February 13, 2020)