Agenda - Public Works Committee - 03/20/2012

Home

Outlet Pipe Size 100-Year HWL Estimated Cost Existing 865.5 N/A 15" 865.4 $1 6,264 18" 865.1 $31,566 24" 864.3 $45,381 148 Lane Description As shown on Exhibit 1, a low area exists south of 148 Lane. A 15" outlet pipe drains the low area north and then east to DNR Wetland 658W. The invert of the outlet pipe is at elevation 862.3 and the bottom of the low area is at elevation 859.8. Water in the low area has to rise 2.5 feet prior to discharging. The water below the outlet infiltrates into the soil, which may take days depending on the condition of the soil. The existing 100 -year high water level (HWL) for the low area is 865.5. As shown on Exhibit 2, a drainage easement exists in the rear of Lots 2 through 5, Block 2 of Ramsey Comrnons 2 Addition. Alternatives The following alternatives address the water elevation in the existing low area. Alternative 1 In this alternative, a new outlet pipe would be installed between Lot 1 of Ramsey Commons 2 Addition and Lot 2 of Sunny Ponds, as shown on Exhibit 3. It was assumed that the existing outlet pipe to the north would be removed. By installing an outlet pipe in this location, the invert of the outlet pipe can be lowered from 862.3 to 861.6. The following table summarizes the 100 -year HWL's and estimated costs for each outlet pipe: * The existing pipe being connected to in Germanium Street is a 15" diamter. Installing the 18" and 24" outlets will require the removal and replacement of this pipe to match the size of the pipe being installed. Tables 1 through 3 include the individual costs for this alternative. Alternative 2 In this alternative, a new outlet pipe would be installed between Lots 2 and 3 of Sunny Ponds, as shown on Exhibit 4. It was assumed that the existing outlet pipe to the north would be removed. By installing an outlet pipe in this location, the invert of the outlet pipe can be lowered from 862.3 to 861.4. This alternative would require additional grading and the acquisition of a permanent easement on the property south of Ramsey Commons 2 Addition and west of Sunny Ponds. The following table summarizes the 100 -year HWL's and estimated costs for each outlet pipe: