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4. ENVIRONMENTAL ANALYSIS tr 4.7 GEOLOGY,SOILS,AND SEISMICrrY r 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 quant'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 Measure: No mitigation is required. Impact 4.73: Permanent reclamation slopes could be subjected to excessive soil erosion, resulting in rifling,gullying,debris flows,and berm damage. This would be a less-than- significant impact with mitigation. Upon completion of each mining phase,the steep temporary slopes would be rebuilt by ,s engineered and uniform 2:l(H:V)slopes constructed using the interbedded clay material excavated during mining operations and overburden removed and stockpiled prior to mining. The materials to construct the slopes would be laid down and compacted with heavy equipment at the edge of the pit. The reclamation slopes would be sculpted as one continuous feature extending from the bottom of the pit up approximately 100 vertical feet at a 26 degree slope. The slopes would be hydroseeded to protect the exposed slopes after construction and to promote maximum vegetation growth. Although it is possible that soil erosion of the 2:l(H:V)slopes could occur immediately following hydroseeding, the potential for that erosion to cause damage is minimal because while the compacted surface would promote runoff,the compacted clay materials would �- hinder the removal of soil particles and the eventual formation of rills and gullies. Chapter 9-1415-3(k)(1,2)(Terracing) of the San Joaquin County Development Title, Ordinance for Quarry Excavations(see Regulatory Background section)require that all slopes over 50-feet in height be terraced with a maximum vertical distance between terraces of 50-feet. Terrace or benches are required to be a minimum of 12-feet wide. The Title requires drainage plans with calculations be submitted for approval to San Joaquin Development Services Division for all terraces as part of the Reclamation Plan. Chapter 9-1415-3(k)(6)(Final Slopes)require that final slopes over fifty feet in vertical distance be terraced and have terrace drainage. Minimum final slopes may be 11/2 to I (H:V) if deternrined stable by a site-specific geologic and engineering analysis and while demonstrating that the slope is suitable for the end use and is adequately protected to avoid erosion. San Joaquin County standards are meant to decrease erosion impacts on landscape,and thus reduce the potential for mudslides, landslides, and debris flow. .. The proposed 100 vertical foot, 2:1 (H:V)reclamation slopes configured as in height without terracing,could he subject to erosion hazards and soil collapse more readily than a 50-foot terraced slope due to the length of slope. The potential for surface water to erode soil is partly dependant on the velocity and erosive energy of surface runoff. Although the compacted clay material and vegetation proposed for the reclamation slopes are relatively resistant to erosion, r RMC Pacific vernalis Quwry Mining and Reclamation rrol«t 4.7-23 ESA i 203015 Adm strative Draft Eat March 2004