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4.7 Geology,Soils,and Seismicity r materials to construct the slopes would be laid down, watered, and compacted in 6-inch lifts with heavy equipment. 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. According to its Reclamation Plan (November 2003), "the applicant would prepare a Revegetation Plan based upon mitigations agreed upon during the permitting process to _ address soil amendments,erosion control, seed mix, planting, irrigation, and test plots."The revegetation practices developed by the applicant must be consistent with performance standards for regrading, backfilling,revegetation, and drainage, as set forth in California Code of Division 2, Chapter, Subchapter 1, Sections 3704 to 3706. Although it is possible that soil erosion of the 2:1(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. ., The proposed 100-vertical-foot,2:1 (H:V)reclamation slopes constructed without terracing could he subject to erosion hazards and soil collapse more readily than a 100-foot slope with a 50-foot terraced midslope because of the greater length of uninterrupted slope. The potential for surface water to erode soil is partly dependant on the velocity and erosive energy of surface runoff.This is greater for longer lengths of slopes not interrupted by a midslope terrace. However, the compacted clay material and vegetation proposed for the reclamation slopes are relatively resistant to erosion; the revegetated slopes would reduce the velocity of the surface water flows that could initiate rill erosion, gully erosion, and debris flows. The applicant has not proposed terracing for 100-foot-high, 2:1 (H:V)final reclamation slopes, and as discussed above,this is not consistent with Chapter 9-1415-3(k)(1) (Terracing)of the San Joaquin County Development Title,Ordinance for Quarry Excavations (see Regulatory W Background section). It is unknown at this time whether the applicant could apply to San Joaquin County for a variance to construct the proposed slopes. If the applicant does apply for a variance ` to the slope ordinance, it would likely be required to demonstrate that the slope would remain stable to avoid erosion in the proposed configuration. Information reviewed for this EIR indicates that the applicant has based its proposal for non-terraced slopes on the success of 2:1 (H:V) slopes at other RMC Pacific Vernalis Quarry mining sites, including Huck Quarry in San Joaquin County. Implementing the erosion control plan as proposed by the applicant in its Reclamation Plan, which includes revegetation,drainage,and monitoring practices consistent with the provisions required by the California Code of Regulations(CCR Title 14) and the Counties of San Joaquin and Stanislaus, would reduce the potential for long-term,damaging erosion and would ensure that impacts related to post-mining erosion would remain less than significant. r Mitigation: No mitigation is required. RMC Pacific Vernalis Quarry Mining and Reclamation Project 4.7-21 ESA 1203015 Draft Environmental Impact Report May 2006 r