SFPUC 2001 Alameda Watershed Management Plan

XII. SUMMARY OF COMMMENTS AND RESPONSESB. SUMMARY OF COMMENTS AND RESPONSESaccordance with limits and mitigations set forth in the conditions of approval forAlameda County’s SMP-32. The Management Plan incorporates SMP-32 conditionsof approval and proposes modification in the timing and sequencing of mining(extendingshortening the completion date for water storage pits) and miningreclamation. These modifications may require amendment of the existing permit butwould not bring about any new water quality impacts beyond those disclosed andmitigated in the EIR prepared for SMP-32. Alameda County’s conditions ofapproval for SMP-32 include controls for drainage, erosion, and sedimentation thatmitigate proposed related mining impacts to a less than significant level. Given thechange of timing and sequence of mining under the Management Plan, impactswould take place over a longer period of time.Extending the area of mining south of I-680 could affect both surface water and thegroundwater system. A larger pit would require redirecting the drainage around theexpanded perimeter and would require construction of associated drainage controlsfor the runoff that would eventually flow to Alameda Creek. There would be anegligible decrease in the volume of runoff from the perimeter of the pit to the creek,with the associated slight increase directly entering the mining pit. Similar toexisting conditions, runoff directly entering the mining pit would likely either bedirected for mining process water or discharged to Alameda Creek in compliancewith any discharge permits. On a program level, continued implementation ofrequired drainage, erosion, and sedimentation controls, as required by the conditionsof approval for SMP-30 and SMP-24, as well as compliance with regulatorydischarge permits, would reduce any impact associated with runoff draining toAlameda Creek to a less than significant level.Increasing the area of mining south of I-680 would also require installation ofbentonite cutoff walls in the upper 50 feet of the expanded perimeter of the miningpits, where appropriate, in compliance with existing permit and lease conditions.In some locations, the fault trace along Calaveras Road acts as an impermeablebarrier to groundwater, precluding the need for a cutoff wall along the easternlimit of the mining pits in that area. Bentonite cutoff walls at the Mission ValleyRock Company SMP-24 area have been effective in diverting groundwater flowaround the pits and in maintaining the overall flow of groundwater to theAlameda Creek channel. Similar to the SMP-24 existing mining pits, theinstallation of bentonite cutoff walls along the north, west, and south sides of inthe expanded pits cwould be expected to prevent the flow of shallow groundwaterinto the pits and protect, thereby maintaining the groundwater flow to the AlamedaCreek channel and within the groundwater system. Therefore, on a program level,the expanded pits would not result in significant changes to the existing groundwatersystem.If groundwater were present, extending the depth of mining in existing mining pits(Actions sun2a and sun2b) could further alter groundwater flow patterns within theNOP 96.223E: Alameda Watershed Management Plan C&R.46 ESA / 930385