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4. ENyutoNMENTAL ANALYSIS 4.7 GEOLOGY,SOILS,AND SEISNUCrrY quarry slopes. The slope safety element shall contain quant'operation requirements to avoid,to the extent feasible,standard mining activities near the base or at the edge of the proposed 3/4:1 temporary slopes. Mining activities that may occur near slopes could include storage of equipment on the edge or base of slopes, temporary repair of equipment,and construction of haul — roads along the base of temporary slopes. The safety requirements for temporary slopes shall become part of the RMC Pacific Vernalis Quarry safety program and be consistent with San Joaquin County and Stanislaus County quarry excavation regulations,Federal and State — Occupational Safety and Health [Cal-OSHA(Title 8)and OSHA(29 CFR)] Regulations,Mine Safety and Health Administration(30 CFR),and the State Mining and Geology Board regulations for surface mining and reclamation practice(CCR Title 14). Significance after Mitigation: Less-than-significant. _ Impact 4.7.2: Activities related to quarry operations that cause disturbance of surface soils would expose loose soil materials. Exposure of these soils to wind,rain,and concentrated runoff could cause localized erosion that could eventually damage to engineered earthen features. Erosion damage to these features could expose workers injury and equipment to damage. This would be a less-than-significant impact. Project operation will involve a significant amount of earthmoving,stockpiling,road and berm construction,and silt pond grading. Construction of these features would require excavation and replacement of native soils,which in some cases would be placed and compacted on engineered _ slopes(berms,quarry roads)or placed in non-engineered stockpiles. The extent of erosion that could occur varies depending on soil type, slope steepness/stability,vegetation/cover, and weather conditions. Depending on the length of exposure, concentrated wind,rain, and runoff could begin to erode these soils by forming rills(small rivulets caused by runoff)and larger gullies. Erosion of this type removes soils from the earthen feature and deposits it down slope. In some cases, where the rill and gully erosion is allowed to continue over an extended period of time,larger sections of the earthen slope can begin to collapse. Soil collapse could compromise structural integrity if it occurs on berm slopes, slopes supporting roadways,or slopes supporting adjacent structures. Uncontrolled erosion on sloped surfaces adjacent to structures(processing plant and equipment)could cause damage and injury to workers. Rill and gully erosion is usually expected on non-engineered,temporary cut slopes in various locations throughout an active phase of mining. Unless these eroded slopes are supporting structures or are severally eroded and impact an active work area,rill and gully erosion in an open pit quarry typically does not represent a concern for public health and safety. Chapter 9-1415-3(d) (Erosion Control) of the San Joaquin County Development Title, Ordinance for Quarry Excavations(see Regulatory Background section)requires that quarries use erosion control methods such as protective vegetative planting, silt screen dams,or other approved methods necessary to control erosion. These erosion control methods would be installed in areas of the quarry that are especially susceptible to erosion and subjected to uncontrolled runoff. As RMC Pacific Vernalis Quarry Mining and Reclamation Pmjec[ 4.7-22 ESA/203015 V Adm w Draft EIR March 2004