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Environmental Impacts of the Proposed Changes to the Original Project Addendum to the City of Pleasanton Downtown Specific Plan Final Environmental Impact Report 45 5.8 Hydrology, Drainage, and Water Quality Impacts Identified in the Certified Final EIR The Final EIR concluded that the DSP would not violate water quality standards or waste discharge requirements as development facilitated by the DSP would be required to comply with the region’s NPDES permit, which includes preparation of a stormwater pollution prevention plan (SWPPP) if applicable, and would also be required to comply with stormwater and erosion control standards outlined in the PMC. Impacts would be less than significant. The Final EIR includes an analysis of groundwater supply and determined that development facilitated by the DSP would draw have a groundwater demand of 21 acre-feet per year (AFY), which represents 0.6 percent of the City’s reasonably available volume of groundwater. Additionally, the Final EIR determined that because the DSP area is already largely built out, development and redevelopment facilitated by the DSP would not increase the total impervious surface area of the DSP area and would not substantially interfere with groundwater recharge. Development would be required to comply with several regional and local programs pertaining to stormwater runoff and groundwater recharge, including the Alameda Countywide C.3 Stormwater Technical Guidance, the Municipal Regional NPDES Permit, the Construction General Permit, and Statewide General Waste Discharge Requirements for sanitary sewer flows. With compliance with existing federal, state, and local programs, the Final EIR concludes that the DSP would not result in substantial decreases in groundwater supply or substantial interference with groundwater recharge and impacts would be less than significant. Because the DSP area is already largely built out, the Final EIR determined that development facilitated by the DSP would not substantially alter the drainage pattern of the DSP area, including through the alteration of a stream or river. Individual projects would be required to develop and implement a SWPPP with erosion, stormwater control, and sediment control BMPs as required by the Construction General Permit to manage erosion, siltation, and flooding impacts during construction, in operation. If projects facilitated by the DSP result in a net increase in impervious area or are larger than one acre, they would be required to implement hydromodification management BMPs. The Final EIR concludes that compliance with state, regional, and local programs and regulations, development facilitated by the DSP would not result in substantial alterations to the existing drainage pattern of the DSP area and would not result in substantial erosion, siltation, or flooding. Impacts would be less than significant. The Final EIR determined that development facilitated by the DSP would not substantially degrade water quality. Existing local ordinances in the PMC and DSP policies would minimize and control sources of water pollutants, and impacts related to substantial degradation of water quality would be less than significant. The Final EIR concludes that because only a small portion of the DSP area is within a designated flood zone (areas adjacent to Arroyo del Valle), development facilitated by the DSP would not impede or redirect flood flows. Further, Policies LD-P.61, LD-P.62, and LD-P.63 would ensure conservation of the Arroyo Del Valle through design and best management practices. PMC Section 9.14.090 prohibits development within 20 feet of the top of a watercourse bank without a permit, which would minimize risks associated with flood hazards and redirection of flood flows. Similarly, because the DSP area is not proximate to the ocean or a large body of water subject to seiche, impacts related to inundation would be less than significant.