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5.ENVIRONMENTAL CHECKLIST MOUNTAIN HOUSE NEIGHBORHOODS K AND L INITIAL STUDY S.HYDROLOGY AND WATER QUALITY surface is reduced or eliminated. Impervious surfaces can increase peak flows in creeks,cause erosion, and result in increased sedimentation in downstream water bodies. Phase II of the NPDES program regulates storm water discharges from small municipal storm water systems (MS4s)and requires that regulated small MS4s obtain coverage under California's General Permit(Order No.2003-0005), Waste Discharge Requirements for Storm Water Discharges from Small _ Municipal Separate Storm Sewer Systems. The Phase Il NPDES program is enforced by the RWQCB.To comply with the Phase II NPDES permit requirements,the Mountain House Community Services District(MHCSD) prepared a Storm Water Management Pian (SWMP)that addresses post- construction storm water management for new development and redevelopment in the Mountain House community(Jacobs, 2008). The proposed drainage system for Neighborhoods K and L is designed to ensure that the initial one-half inch of rainfall runoff(first flush) is drained into the permanent 47.33-acre lake feature in Neighborhood K and the 52.93-acre lake feature in Neighborhood L.The lake features would serve to treat storm water runoff from these neighborhoods prior to discharging to Mountain House Creek. The lake features would help to settle out sediment and particulates from runoff, as well as trace metals, nutrients,and hydrocarbons as these pollutants tend to adhere to soil particles.The lake features would also capture and detain storm water to attenuate peak flows and control erosion.With the proposed project, WQB No. 1 would continue to treat runoff from Neighborhoods B, D, and F. Per the SWMP,the developer would be required to install catch basin inserts in all new catch basins to filter out sediment, hydrocarbons,and chemicals from site runoff. Commercial, industrial, and public facilities that generate runoff that differs in pollutant concentration or content when compared to residential runoff could also be required to implement additional water quality BMPs, depending on the operations proposed at each facility. Commercial and industrial water quality BMPs in Neighborhoods K and L would be determined on a case-by-case basis and approved by the MHCSD in accordance with Phase 11 NPDES requirements (Jacobs, 2008). The SWMP also includes provisions for regular inspections and maintenance of water quality BMPs to ensure proper performance. The MHCSD would be responsible for periodically inspecting the BMPs to determine effectiveness and identify maintenance issues.The lake features would require periodic maintenance, including desilting,vegetation clearing,and trash and debris removal. Maintenance of the lake features and catch basin inserts would be conducted by the MHCSD (Jacobs, 2008). Master Plan Policy 15.7(Implementation Measure[a])states that Mountain House shall implement a SWMP to reduce the discharge of pollutants from the storm sewer system to the maximum extent practicable and protect water quality in the receiving waters. At a minimum, the Master Plan states that the SWMP (9mi 1) 5-112