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8.d1 Bliss Addition Stormwater PlanningBliss Addition Stormwater Planning Scandia City Council November 19th, 2019 Tim Olson, PE, CFM Water Resources Project Manager Bolton & Menk, Inc. Big Marine Lake Bliss Addition Study Background and Goals •Improve water quality in Big Marine Lake •High quality, deep water resource •Minimally improving trend for total phosphorus •328 shoreland parcels •Mitigate routine surface flooding in Bliss Addition •39-acre residential area •Degrading roadside ditches •Lost infiltration capacity •Steep slopes Public Engagement •April 16 –2019: First public meeting, presented drainage maps. •August 20, 2019: Second public meeting, presented preliminary best management practices. Management Areas •North and South Management Areas •Roadside ditches and culverts •Perennial stream •No current treatment Modified Infiltration Ditches •Excavate 30”, sand/bioretention media •6” perforated underdrain and control valve •Native plants Bioinfiltration Basin (Rain Garden) •Depressed area, sand/bioretention media •Larger footprint than infiltration ditch •6” perforated underdrain and control valve •Native plants Heavy Sediment/Gross Solids Treatment •Concrete paver bottom •Riprap armored side slopes •Slotted filter weir North Management Area •Bioinfiltration basin, catch basin on north end of Larkspur/192nd •Sediment/solids capture area •New 8” outlet to redirect surface flow to wetland •New storm outlet, regrade street to direct flow away from driveways 1 2 3 4 South Management Area •Bioinfiltration basin, outlet to wetland •New catch basin across 189th to north, enhanced infiltration ditches 5 6 Project Results •Increase small storm retention by 6,111 cubic feet •Reduce total phosphorus by 9.9 lbs per year •Reduce total suspend solids by 1,531 lbs per year •Improve stormwater conveyance •North Management Area ~ $330,000 •South Management Area ~ 103,000 Preliminary Cost Estimates Thank you! Questions? Discussion.