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Modeling Results <br />TSS Removal <br />(lb/yr) <br />TP Removal <br />(lb/yr) <br />Ditch 100-yr HWL <br />HWL Decrease (ft) <br />5,688 <br />19.75 <br />891.30 <br />0.85 <br />The results above are based on the P8 modeling for this project. The IESF is <br />proposed primarily for water quality benefits, as proposed it would have a negligible <br />impact on floodplain volumes and water levels and therefore, they were unchanged <br />from Concept 3. As shown in the results, this concept would greatly increase TSS <br />and TP removals while taking up a relatively small footprint within the overall project <br />area. Combined with Concept 3, TP removals are near 20 pounds per year. <br />9.2 Construction r-stimate <br />As with Concept 3, excavation costs still dominate the estimated project. Earthwork <br />quantities are slightly increased with the proposed IESF, but its volume is much less <br />than the other wetland basins. Other major costs include the specialized iron - <br />enhanced filter media and replacement of storm sewer. The total estimated concept <br />cost, including a 20 percent cost contingency, is $601,000. Again, this construction <br />estimate does not include potential recreational improvements such as a boardwalk <br />or trail. Refer to the budget table at the end of this section for the base construction <br />cost line item breakdown. <br />Monitoring and maintenance of the site's natural resources will be key to <br />establishing a diverse, native plant community. Site maintenance includes a <br />minimum of two site visits (spring and fall) for five years to conduct mowing and <br />herbicide spot treatments, and supplemental seeding during one of the <br />recommended five years. The cost of maintenance for five years as described is <br />$34,380. Monitoring the vegetation each year would provide the City with an <br />adaptive management approach to maintenance. The cost of monitoring one time per <br />year for five years is $8,500. <br />Current design standards assume an approximate 10-year lifespan for effective <br />pollutant capture of an IESF BMP. This lifespan can be extended with filter media <br />replacement. The estimated cost of replacement is $45,000. This includes costs for <br />removal of old media, installation of new iron -enhanced sand, and a 20 percent <br />contingency. <br />Shenandoah Improvements Feasibility Report <br />City of Lino Lakes, MN <br />WSB Project No. 018901-000 <br />Page 18 <br />