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City of Arden Hills - Indian Oaks Area Downstream Drainage Review March 12, 2018 Page 8 Building a legacy – your legacy. Equal Opportunity Employer | wsbeng.com - Implement the 21”/24” option described in Section IV for phase 1 and 2 construction. o This option provides a high water level in the IOC Wetland of approximately 1 foot from the low opening of the home 1416 Indian Oak Court and 0.5-foot freeboard from the Indian Oaks Court roadway. o HDPE pipe can be installed within the drainage easement between Indian Oaks Court and Colleen Avenue to minimize equipment use between homes. o This option costs roughly $23,000 more than the 18” option and results in additional freeboard. - Orifice plates will be necessary inside manholes to temporary reduce peak discharge rates until downstream improvements to accommodate the rate increase can occur. - Advanced the design of phase 2 and construct the improvements to provide flood protection as soon as feasible. VI. NEXT STEPS If the City of Arden Hills wishes to pursue the phased approach described in this memorandum, the following tasks will need to be completed: - Adjust the 2018 PMP Project (Phase 1) construction documents to reflect the desired downstream improvements option. - Environmental review and wetland delineation of the Colleen Wetland and drainage channel. - Complete a design-level survey of the trail improvements area - Refine the existing and proposed condition stormwater models and analysis with an advanced design and detailed topographic survey data. - Coordination with Rice Creek Watershed District including preliminary meetings and permitting - Easement Acquisition Coordination (If necessary) - Final phase 2 design and construction document preparation. Please let WSB know if you have any questions or would like to sit down to discuss further.