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City of Arden Hills - Indian Oaks Area Downstream Drainage Review <br />March 12, 2018 <br />Page 7 <br /> <br /> <br />Building a legacy – your legacy. <br />Equal Opportunity Employer | wsbeng.com <br /> <br />Figure 5. Colleen Wetland 100-yr Highwater Level <br /> <br /> <br /> <br />Anticipated Costs <br />A feasibility level Opinion of Probable Construction Costs was prepared as part of this drainage study for <br />the 18” and 21”/24” option. The environmental review of the Colleen Wetland has not been completed at <br />this time. It should be anticipated that purchasing wetland credits or wetland mitigation will likely be <br />necessary for encroachment from the trail improvements. A line item estimate for phase 2 improvement <br />costs is provided in Attachment C. A phase 1 construction cost estimate was not prepared since the cost <br />difference is expected to only include the pipe costs. Orifice plates for phase 1 construction are included <br />in the estimate. This estimate does not include any potential private utility adjustments. The 18” and <br />21”/24” options are estimated to have a total cost approximately $229,000 and $252,000. <br /> <br />The phase 2 construction may have wetland impacts pending environmental review and design grading. <br />We anticipate a wetland mitigation credits to cost around $4000 to $7000. <br /> <br />V. RECOMMENDATIONS <br /> <br />While lowering the IOC Wetland outlet provides additional flood protection, restricting peak flow rates to at <br />or below existing conditions does not provide freeboard below the low opening elevation of the home at <br />1416 Indian Oak Court. Based on the findings of this drainage review and evaluation of potential <br />downstream improvements and costs we offer the following recommendations: <br />