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4.7.4 IMPACT ANALYSIS ANALYSIS METHODOLOGY The analysis of drainage is based on existing information gathered from previously prepared documents that address stormwater drainage for the whole Mountain House community,including the Mountain House New Community Master Plan,Final Environmental Impact Report for Mountain House Master Plan and Specific Plan I,Mountain House Stormwater Master Drainage Plan, and College Park at Mountain House New Community Speck Plan III. Analysis of stormwater drainage specific to the project site is based on technical analysis prepared by the project sponsor's engineer(MacKay& Somps)which provides details about drainage improvements proposed with implementation of the proposed project. IMPACTS AND MITIGATION MEASURES The Initial Study(IS)found that the proposed project would not housing or structures in a 100-year flood hazard area because the project site is not located within a 100-year flood hazard area as mapped in the MHMP or on a FEMA Flood Insurance Rate Map.In addition, the IS found that the proposed project would not be subject to a seiche,tsunami,or mudflow because the project site is not located near any large water bodies,including the ocean,and because the project site is not located adjacent to or downstream of the primary drainage of the Mountain House Creek watershed where any mudflows would be generated. Therefore,in accordance with Section 15063(b)(1)(C) of the State CEQA Guidelines,the potential for the proposed project to place housing or structures in flood hazard areas and be subject to a seiche,mudflow,or tsunami are not evaluated further in this EIR. See the IS(Appendix D of this Draft EIR)for further discussion. IMPACT Drainage—Increased Erosion or Sedimentation. Development of the proposed project could atter the 4.7-1 existing drainage pattem of the site or area in a manner that could result in substantial erosion and sedimentation during project construction and operation. Compliance with MHMP policies, MHMP mitigation measures, and Phase 1 and 11 NPDES permit requirements,including the preparation and implementation of a SWPPP that outlines BMPs to be followed to minimize erosion and sedimentation, would avoid substantial erosion and sedimentation during project construction and operation. No adverse effects on the capacity and performance of the storm-drain system would occur.A less-than-significant impact would occur. Project construction activities would include earth-moving and grading activities that would affect the existing drainage pattern at the project site,temporarily remove existing vegetative cover,include stockpiled soils,and create the potential for erosion and sedimentation of on-site soils during construction.However,MHMP Policies 42.2(a) and(b)require that runoff, erosion,and sedimentation be controlled 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,MHMP Policy 15.4(c)requires that sediment generated by grading or construction activities be subject to BMPs before discharge to creeks,ditches,and Old River.Also, state regulations (Phase I �. and II NPDES permit requirements)are in place that require the preparation and implementation of a SWPPP, including the implementation of BMPs during construction that are designed to avoid substantial erosion and sedimentation.Compliance with these and other applicable erosion and sediment-control requirements would result in a less-than-significant impact. Project operation would include landscape maintenance and other activities that could result in substantial on-site erosion sedimentation.This, in turn,could lead to adverse effects on the capacity and performance of the storm- drain system In addition, flow-through runoff from upstream of the College Park project site could carry with it sediment that could lead to adverse effects on the storm-drain system.MHMP Section 15.11.2 requires that storm drainage and flood-protection facilities be maintained by MHCSD, and that a channel maintenance plan be �- prepared by MHCSD to include a program to monitor sedimentation buildout for Mountain House Creek and drainage channels.Mitigation Measure 4.7-2(b)in the Delta College EIR requires that, after construction,all drainage facilities shall be inspected on a yearly basis for accumulated sediment, and if sediment has accumulated, College Park at Mountain House Specific Plan III Draft EIR EDAW San Joaquin County 4.7.11 Drainage