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4.Environmental Analysis 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, concentration of runoff,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, including surface grading to direct water away from the slopes and storm water collection systems, would be installed in areas of the quarry that are especially susceptible to erosion and subjected to uncontrolled runoff. As part of the project, surface drainage in the mining area will be directed to open mining pits, — directed by berms,ditches, and pipes to minimize erosion and sedimentation.The Title also requires the quarry to prepare and implement an erosion and sediment control plan that must be approved by Development Services Division and become part of the reclamation plan. These — measures would ensure that uncontrolled erosion and sedimentation are managed appropriately to minimize damage to exposed engineered and non-engineered slopes within the quarry and that _ impacts associated with erosion remain less than significant. Mitigation: No mitigation is required. — Impact 4.7.3: Permanent reclamation slopes could be subjected to excessive soil erosion, resulting in Ailing,gullying,debris flows,and berm damage. This would be a less-than- significant impact given the project's erosion control plan. — Upon completion of each mining phase, the steep temporary slopes would be rebuilt by engineered and uniform 2:l(H:V) slopes constructed using the unusable interbedded clay material — excavated during mining operations and overburden removed and stockpiled prior to mining. The RMC Pacific Vernalis Quarry Mining and Reclamation Proiect 4.7-20 ESA/203015 Draft Environmental Impact Report May 2006