SFPUC 2001 Alameda Watershed Management Plan

XII. SUMMARY OF COMMMENTS AND RESPONSESB. SUMMARY OF COMMENTS AND RESPONSESvalley.” (Luhdorff and Scalmanini Consulting Engineers, 1993). As the comments of AlamedaCreek Alliance point out, the Bookman-Edmonston report does note that the depth to water tablemay have been increased by mining. It should also be noted that both previously mentionedreports support the use of the slurry cutoff walls. Cutoff walls in the Mission Valley RockCompany pits seem to have prevented most inflow from the Creek through the shallow alluviuminto the pits. The shallow alluvium is the primary aquifer in this area. The deeper Livermoreformation is more dense and has lower transmissivity. These facts explain the Luhdorff andScalmanini observation that “…once the upper alluvium has been cut off from groundwaterinflow [by the installation of a cutoff wall], excavation to 140 feet has been possible with limiteddewatering.”Although CEQA does not require analysis of a project’s possible impacts on future environmentalrestoration projects, the possibility of impacts cannot be ruled out due to the potential for changedconditions in the future (e.g., the re-establishment of an anadromous run of steelhead trout inAlameda Creek). In addition, possible impacts cannot be ruled out due to the lack ofcomprehensive groundwater information and/or absence of specific information about futuremining proposals south of I-680. Future installation of cutoff walls at the expanded pits maydivert groundwater from the creek system around the pits, although further study is neededregarding site-specific groundwater flow patterns and the need for and/or effectiveness ofbentonite cutoff walls. Although any groundwater flow entering the expanded pits mayultimately be returned to the creek via pumping, there may be impacts associated with the timingand quality of water returned to the creek. For example, subsurface percolation of water from thecreek (likely water released from SFPUC reservoirs for this purpose) during the spring outmigrationperiod for steelhead smolts could adversely affect the species by reducing availableflow in the creek during that period. Therefore, because of the concern about potential futureimpacts to Alameda Creek and its resources, the following text revisions have been made toDEIR pages III.D-29 through III.D-30:Changes to Gravel Mining OperationsThe Management Plan would allow continuation of mining activities in the SunolValley (Policy WA37) as well as consideration of amending the existing miningpermits to expand mining south of I-680, either in depth or in both depth and area, ormodifications in the timing and sequence of mining and mining reclamation north ofI-680 (Actions sun1, sun2a/2b). As described previously under Setting, Section 1.6,Gravel Mining, mining operations have historically affected hydrologic and waterquality conditions in the Sunol Valley. These impacts are currently being addressedthrough conditions of approval for the operating permits and lease requirements forSMP-32, SMP-30, and SMP-24. However, implementation of Actions sun1 andsun2a/2b could result in modifications of existing mining permits that could result inpotentially significant effects on water quality and groundwater.As described earlier in this document, actions proposed in the Alameda WatershedManagement Plan for mining north of I-680 would take place substantially inNOP 96.223E: Alameda Watershed Management Plan C&R.45 ESA / 930385