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U <br /> Level of Significance after Mitigation: <br /> Following implementation of Mitigation Measures 4.2-3a and 4.2-3b, the impact of soil <br /> erosion on proposed post-reclamation slopes would be reduced to a less-than- <br /> significant level. <br /> All Quarry Excavation Alternatives (1. 2,and 3} <br /> Impact 4.2-4 <br /> Capacity of Proposed Processing Basins may be Inadequate <br /> Alternatives 1, 2, and 3 propose the construction and operation of settling basins for- <br /> storage of processing wastewater from the aggregate production plant. Although the <br /> Quarry Excavation Permit application submitted by the proponent indicates that the <br /> processing basins would be constructed below existing grade, the design of the basins is <br /> not provided. If the volume of the basins is not sufficient to contain discharges from the <br /> processing plant and precipitation, overtopping of the basins could result in flooding, <br /> erosion, and sedimentation of adjacent areas (including the mining pits and mining slopes). <br /> This is a significant impact. <br /> Alternative 4: No ProJect <br /> Wastewater processing basins would not be constructed under this alternative and <br /> therefore, potential impacts related to the basins would not occur. <br /> Mitigation Measure 4.2-4a (Alternatives 9, 2, and 3) <br /> Prior to commencement of mining at the project site, the proponent shall submit for <br /> approval by the Development Services. Division, calculations and engineering <br /> drawings prepared by a licensed engineer that demonstrate that the proposed <br /> processing wastewater basins are capable of storing expected wastewater discharge <br /> and precipitation. <br /> Level of Significance after Mitigation: <br /> Following implementation of Mitigation Measure 4.2-4aJ the impact of potential <br /> overtopping of processing wastewater basins would be reduced to a less-than- s <br /> significant level. <br /> All Quarry Excavation Alternatives 1 2 and-3) <br /> Impact 4.2-5 <br /> Decreased Availability of Aggregate Resources <br /> Implementation of Alternatives 1, 2, and 3 would result in the extraction of 29.75 million <br /> tons of aggregate over a 56-year period (0.4$ million tons per year). This extraction would <br /> Draft Environmental Impact Report 4-20 ER-96-3 <br />