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MOUNTAIN HOUSE NEIGHBORHOOD"F"PROJECT INITIAL STUDY The development of the project would substantially alter drainage patterns on the project site during and after construction. Construction of the project would entail large areas of grading which would result in removal of on-site soil cover and exposed bare soil to forces of rainfall runoff and erosion. Projects disturbing more than five acres of land during construction are required to file a Notice of Intent(NOI) with the Regional Water Quality Control Board to be covered under the State National Pollutant Discharge Elimination System(NPDES)General Construction Permit for discharges of storm water associated with construction activity. A developer must propose control measures that are consistent with the State General Permit. A Storm Water Pollution Prevention Plan(SWPPP)must be developed and implemented for each site covered by the general permit. A SWPPP should include Best Management Practices (BMPs)designed to reduce potential impacts to surface water quality through the construction and life of the project. The permit for the Mountain House wastewater treatment plant issued by the Regional Water Quality Control Board has Waste Discharge Requirements(WDRs)established which specify final effluent water quality criteria. The WDRs are designed to protect human health and the environment based on the proposed disposal method or use of the water. After project construction, an underground storm drain system would collect and convey runoff into Mountain House Creek. The Neighborhood"F"plan includes a first flush water quality basin north of Byron Road. This drainage system would concentrate storm water at specific points along or adjacent to the stream channel. This concentrated discharge, if unprotected, would cause erosion and/or siltation. The Neighborhood"F"drainage plan calls for energy dissipaters and erosion protection on many of the proposed facilities. Condition of Approval HYDRO-3:Implementation of thefollowing measures would reduce construction-related erosion and sedimentation impacts to less-than-significant levels: • The project grading plan shall include an approved drainage and erosion control plan to minimize the impacts from erosion and sedimentation during grading. This plan shall conform to all standards adopted by San Joaquin County or Mountain House Community Services District This plan shall include procedures such as: (1) restricting grading as mandated by the Regional Water Quality Control Board; (2)protecting all finished graded slopes from erosion using such techniques as slope benching, erosion control matting, and hydroseeding; (3)protecting downstream storm drainage inlets from sedimentation;and (4)use of silt fencing to retain sediment on the project site- • Prior to site earthmoving and grading activities, sedimentation basins shall be developed in order to retain sediment on-site as required by the Regional Water Quality Control Board. The sedimentation basins can either be created as temporary basins, or the planned project sediment basins can be constructed and put on-line prior to earthmoving activities. Appropriate sedimentation basins shall be part of the approved drainage and erosion control plan described above. • After construction is completed, all drainage culverts shall be inspected for accumulated sediment. If sediment accumulation has occurred, these drainage structures shall be cleared of debris and sediment • A precise Winterization Plan shall be developed by the project engineer and shall be approved by the County Engineer and/or the Mountain House Community Services District prior to issuance of grading or building permits. The Winterization Plan shall identify specific locations where on-site water erosion is a threat, and shall identify specific cvoeswcuNnIAL MUDY+1NAL1 mwsRMY•PARn.00c(7/22=) 97 V.J. HYDROLOGY AND WATER QUALITY