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MOUNTAIN HOUSE PROPOSED ALTAMONT HEIGHTS TENTATIVE MAP 4. ENVIRONMENTAL CHECKLIST 4.8 HYDROLOGY AND WATER QUALITY During construction of the proposed project, grading operations would result in the removal of vegetation and topsoil and create the potential for erosion of on-site soils and off-site siltation. The project applicant would have to comply with the Phase I National Pollutant Discharge Elimination System(NPDES)permit program. Under the program,developers of projects that disturb five acres or more of land are required prepare a SWPPP to implement BMPs to reduce the off-site impacts of sediment-laden runoff(EDAW, 2005b). In addition, MHMP Policies 4.2.2(x) and(b) requires control of runoff, erosion, and sedimentation during grading. MHMP Policy 6.8.3(b) requires that adequate efforts be made to control or eliminate soil erosion and sedimentation associated with construction activities. Upon completion of construction of the proposed project, existing WQB No.1 would treat storm water runoff from the proposed project prior to discharge to Mountain House Creek and Old River. WQB No. 1 would settle out sediment and particulates from runoff,as well as trace metals,nutrients and hydrocarbons,as these pollutants tend to adhere to soil particles (EDAW, 2005b). MHMP Policy 15.7 (Implementation [a]) states that Mountain House(i.e., the MHCSD) shall implement a long-terra Storm Water Management Plan(SWMP)to reduce the discharge of pollutants from the storm drain system to the maximum extent practicable and protect water quality in the receiving waters. At a minimum, the MHMP states that the SWMP shall include the following elements: (1)public education and outreach on storm water impacts; (2)public involvement/participation; (3)illicit discharge detection and elimination; (4)construction site storm water runoff control; (5)post-construction storm water management; and(6)pollution prevention/good housekeeping for municipal operations. West Yost and Associates prepared a SWMP for the MHCSD in April 2001. The SWMP identifies a list of water quality BMPs and provides recommendations for the MHCSD's storm water quality ordinance. A storm water quality ordinance has not been adopted by the MHCSD,but will be when the State of California designates the Mountain House Community as a Phase II MS4 area(Machado Chiclets, 2006). MS4 is the State Water Resources Control Board's designation for municipal separate storm sewer systems. Phase II applies to small municipalities with populations less than 100,000. Mitigation Measures With implementation of the mitigation measures and policies cited above,there would be no violation of any water quality standards or waste discharge requirements. The impact of the proposed project would be less than significant. No additional mitigation measures are required. b) Substantially deplete groundwater supplies or interfere substantially with groundwater recharge such that there would be a net deficit in aquifer volume or a lowering of the local groundwater table level(e.g., the production rate of pre-existing nearby wells would drop to a level which would not support existing land uses or planned uses for which permits have been granted)? No groundwater would be used for the proposed project's water supply, so the project would not substantially deplete groundwater supplies. The Initial Study for the SPIIIEIR states that 4-43