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Implementation 15.3(c).Each segment of the storm drainage system shall be designed as needed to provide protection for each phase of development. Storm Drainage and Flood Protection(Section 15.4) ► Policy 15.4(a).Pipes and/or open channels shall be designed with 100-year flood capacity to a point of terminal discharge. Policy 15.4(b).Open-channels shall be designed to minimize erosion. ► Policy 15.4(c). Sediment generated by grading or construction activities shall be subject to BMPs before discharge to creeks,ditches, and Old River. _ Policy 15.4(d).Trunk line pipes(72-inch and larger), detention basins, and major open channels shall be designed and constructed to transport the 100-year volumetric flow rate. Policy 15.4(e).Trunk-line pipes shall be designed for gravity-flow conditions. ► Policy 15.40. Open-channels shall be designed and constructed to meet the most conservative freeboard requirements of federal, state,or county standards. ► Policy 15.4(g).Erosion shall be minimized by designing and constructing open channels to convey storm- water runoff at or below the allowable maximum velocity. ► Policy 15.4(1).The ultimate point of terminal discharge for all drainage shall be Old River.Future flows shall _ be metered to pre-development rates. Mountain House Creek Improvements(Section 15.6) ► Policy 15.6(d).Mountain House Creek shall be designed to minimize erosion. Phasing and Costs(Section 15.11) — ► Section 15.11.2 (Operations and Maintenance). Storm-drainage and flood-protection facilities will be maintained by the MHCSD. A channel-maintenance plan shall be prepared before the submittal of the first development permit and shall include a program to monitor sedimentation buildout for Mountain House Creek and drainage channels. Maintenance costs have been incorporated in the fiscal analysis presented in the PFP. Final EIR for the Mountain House Master Plan and Specific Plan 1 1994 (Mitigation Measures) The following drainage mitigation measures from the Final EIR for the Mountain House Master Plan and Specific Plan I are applicable to the proposed project. ► Mitigation Measure 4.74(Preliminary Soils Report).The soils report required for each subdivision shall identify the seasonal high groundwater level at the site of any detention/retention basins proposed as part of the stormwater management system.The report shall provide recommendations for appropriate design elevations for the detention/retention basins that would avoid saturation or partial filling by groundwater.The report shall - specifically address the potential for increased groundwater levels caused by removal or disruption of existing subsurface drains.The report will provide recommendations for subsurface drains for all newly constructed structures or facilities.These recommendations shall include provisions for routing and disposal of drain discharges that will not result in adverse flooding or saturation hazards in other areas of the project site. EDAW College Park at Mountain House Speedic Plan III Draft EIR Drainage 4.7-8 San Joaquin County