05-05-25 - Council Work Session Agenda

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" " Modeling Results TSS Removal (lb/yr) TP Removal (lb/yr) Ditch 100-yr HWL HWL Decrease (ft) 1,297 8.37 891.30 0.85 The results above are based on the P8 and InfoSWMM modeling for this project. The proposed wetland basins provided water quality improvements in accordance with their footprint and volume, TSS and TP removals shown are increases over existing modeled pollutant removals. The drop in ditch high water level is also a function of basin volume. As such, Concept 3 shows the slightly decreased benefits compared to Concept 2, but they are still significant. 8.2 Construction Estimate Excavation costs still dominate the estimate project total under this concept, but less so than Concept 2. 12,500 cubic yards of excavation are proposed, but this would be slightly offset with the proposed embankment volumes to fill in the old ditch channel. Earthwork estimates account for about 70 percent of total improvement costs. The total estimated concept cost, including a 20 percent cost contingency, is $455,350. It should be noted the construction estimate does not include potential recreational improvements such as a boardwalk or trail. Monitoring and maintenance of the site's natural resources will be key to establishing a diverse, native plant community. Site maintenance includes a minimum of two site visits (spring and fall) for five years to conduct mowing and herbicide spot treatments, and supplemental seeding during one of the recommended five years. The cost of maintenance for five years as described is $34,380. Monitoring the vegetation each year would provide the City with an adaptive management approach to maintenance. The cost of monitoring one time per year for five years is $8,500. Construction Cost - Option 3 Description Units Contract Quantity Unit Price Total Price Comments MOBILIZATION LS 1 $30,000 $30,000 —10%oftotal budget COMMON EXCAVATION C Y 12500 $17.50 $218,750 Essentially all cut and removal from site COMMON EMBANKMENT CY 600 $17.50 $10,500 Fill old channel RANDOM RIPRAP CL III C Y 20 $120.00 $2,400 For inlets 12" RCP L F 240 $90 $21,600 Based on OneOffice 12" RCP APRON EACH 5.00 $1,500 $7,500 Based on OneOffice FLAP GATE/DUCKBILL VALVE EACH 4.00 $3,000 $12,000 Based on OneOffice, no duckbill estimate STABILIZED CONSTRUCTION ENTRANCE EACH 1.00 $1,500 $1,500 Likely off Arrowhead Or SILT FENCE L F 400 $3.50 $1,400 Need around grading + 40'to double up at culvert outlet EROSION CONTROL BLANKET SY 9500 $3 $28,500 Placed on all pond slopes (top contour area - bottom contour area) SEEDING ACRE 3.6 $2,000 $7,200 Assume seeding occurs within full limits of disturbance plus over access route SEED MIX 25-151 LB 55 $10 $550 Seeding over access road and old channel, 120 Ib/ac SEED MIX 34-261 LB 100 $75 $7,500 Seeding wetland/pond/channel areas, 31.5lb/ac LIVE STAKES EACH 210 $3 1 $544 iStabilization along erosive edge of realigned ditch 1.5" CAL TREE - BALLED AND BURLAPPED TREE 55 $400 1 $22,000 113asedon OneOffice SHRUB - 5 GAL POT SHRB 100 $75 1 $7,500 1 Based on OneOffice 5 YEAR MON ITORI NG/MAI NTENANCE LS 1 $42,880 1 $42,880 201/o Contingency $75,889 Total: 1 $455,333 Shenandoah Improvements Feasibility Report City of Lino Lakes, MN WSB Project No. 018901-000 Page 15