City of Eden Prairie Pond Inventory and Maintenance Assessment Leslie A. Stovring Environmental Coordinator City of Eden Prairie Todd Shoemaker, PE, CFM and Joe Bischoff Wenck Associates, Inc.
Fun Facts about Eden Prairie • Population of ~62,000 • 12 mi 2 in area • >1,000 water bodies currently in inventory (private and public) • Significant development from 1980 to 2000 • 2013 Stormwater Utility budget = ~$1.4M • 2014 Stormwater Utility budget = ~ $1.6M
Project Drivers • Phase II NPDES MS4 permit holder • Schedule of Compliance • Jan. 12, 2009 – Notice of Intent • Jan. 28, 2010 – Final Schedule of Compliance • Inventory of ALL stormwater treatment BMPs • Most lakes listed as impaired for nutrients • Project Coordination with Watershed District • Light Rail Transit corridor • Want to maintain stormwater ponds cost- effectively • 2013 MS4 stormwater permit requirements
Project Goals • Create streamlined approach to: • Verify basin performance • Prioritize inspections • Prioritize maintenance needs • Quantify impact on receiving water bodies • Is current water quality treatment adequate? • If not, where can improvements be made? • Would the improvements impact the receiving water?
Priorities, Priorities, Priorities • Why prioritize? • Fiscal limitations • Limited resources • Large number of water resources in the City • What to prioritize for? • “Biggest Bang for the Buck” • Per project • Per budget cycle
Approach • Start with a pilot watershed – ensure approach replicable throughout city • GIS to quantify basins and target inspections • Drainage watershed • Design elevations • Assess sediment accumulation in ponds vs. design • P8 – urban water quality model • Evaluate if resource is protected • BATHTUB model – In-Lake / Lake response analysis
Budget Status • Phase I (Staring Lake) • 172 basins • Phase II (Neill / Eden Lakes) • 26 basins • Phase III (Red Rock / Duck Lakes) • 74 basins • Phase IV (Lower Riley Creek) • Estimated 75 basins • Cost Phase I – Phase III = $399,662 • Total est. cost through Phase IV = $486,914 • Cost Per Basin = ~$1,400 (plus city intern)
Phase Locations
Stormwater System Analysis • Review EP basin inventory using GIS (ArcView) and LiDAR (2-foot topography) • Constructed ponds • Stormwater wetlands / wetlands • Mitigation wetlands • Creek segments • Ditches / Swales • Infiltration BMPs • Exclude basins that do not receive runoff from City property, ROW or drainage easements
Staring Lake (2010-2011) • 11,200 acre watershed • 159 acre lake / 15 foot max. depth • Surveyed 172 of 237 basins • Over 90% Staring developed Lake • Impaired for nutrients
Stormwater System Analysis: Basin Ownership 100 90 80 70 60 Number 50 40 30 20 10 0 City ROW City Easement Private w/ City Drainage Private
Basin Analysis Methods • Sedimentation survey • Calculate ratio of NURP volume provided to NURP volume required • Why NURP? • Design guidelines for ponds since mid- 1980’s • Runoff from 2.5-inch rainfall • Generally results in 80-90% TSS removal and 50-60% TP removal • Estimate TSS and TP removal using model trials • Use ArcView 3D Analyst to calculate volumes from our survey points
Basin Analysis: Field Survey
Basin Analysis: Data Collection
Basin Analysis: GIS 3D Analyst
Basin Analysis: Estimated Pollutant Removal • Estimated using P8 computer model • 10 acre drainage area • 38% impervious (single family residential) • Pervious Curve Number = 74 • NURP Vol = (Imp Area)*(2.5”/12”)*(0.9) = 0.71 AF • 4 ft average depth with 3:1 side slope • Six trials • 125%, 100%, 75%, 50%, 25%, 10% of NURP volume provided in permanent pool volume • Also evaluated commercial land use with similar results
Basin Analysis: Field Survey Results 120 100 80 Percent Removal 60 40 20 0 15-22-B 15-22-C 15-22-D 15-23-A 15-23-C 15-23-D 15-23-E 15-23-F Pond ID % TSS Removal % TP Removal
Results – Staring Lake Survey • Sediment accumulation ranged from 0-53% of pond capacity (5 ponds >50%) • Of the 172 ponds surveyed: • 86 did not meet NURP guidelines • Of the 86, 11 would not meet NURP guidelines if restored to design condition • 22 rated as high priority for maintenance • Maintenance correlated well with undersized basins • Approximately $1.2 million for all identified projects • $34,000 per pound of phosphorus removed • Does not include lab testing, wetland mitigation, land acquisition, disposal of contaminated sediment
Phase II / III Results • Eden / Neill Lakes • High – 3 ponds / $280,000 • Medium – 2 ponds / $264,000 • Duck / Red Rock Lakes • High – 4 ponds / $590,000 • Medium – 5 ponds / $485,000 • 14.2 pounds / year of TP reduction • (10.8 lbs. for Duck Lake) • Provides 10.8 pounds reduction in TP for Duck Lake • 14.4 pounds required • No reductions required for Red Rock Lake (meets state standards currently)
• Staring Lake Next Steps • Completed two pond dredging and expansion projects in 2012 • Pond dredging 2013-14 (Olympic Hills) • Iron-enhanced sand filter 2013-14 • Purgatory Creek Park Management Plan • Creek stabilization projects (2) – 2013 • City’s stormwater utility budget increased 15% in 2014 to include the new maintenance recommendations and increased project needs • 14% 2015 • 12% 2016-17 • 10% 2018-19
Next Phases / Projects • Phase IV field survey to be completed this spring (Riley Creek) • 50 water bodies (36 constructed / 14 wetlands) • 11 Riley Creek segments – assessed inlets / outlets • Phase V – Mitchell Lake to start in 2014 • Estimate 45 ponds / wetlands • Will incorporate lake management goals (RPBCWD)
Other Plans • Local Water Management Plan Update – 2013-14 • Creek inventory and assessment , including a creek restoration and improvement plan • HydroCAD Update • Funding assessment • Database / GIS review • Website review • Will incorporate Wetland Plan Update • Stormwater Permit Update • Facilities Inventory / IDDE Plan • Town Center Stormwater Study
Inventory Schedule Inventory split over 11 years • 2010-2011 – Staring Lake • Report completed and submitted to MPCA • 2011 – Neill and Eden Lakes (Town Center) • 2012 – Duck and Red Rock Lakes • 2013 – Lower Riley Creek (no lake) • 2014 – Mitchell Lake • 2015 – Purgatory Creek (no lake) • 2016 – Round Lake • 2017 – Grass and Rice Lakes (Minnesota River) • 2018 – Riley and Rice Marsh Lakes • 2019 – Anderson and Smetana Lakes • 2020 – Bryant and Birch Island Lakes • 2021 – Areas Missed / What’s Next?
Conclusions • Approach fulfills MS4 requirements • GIS does facilitate targeted inspections • Have identified a number of retrofitting opportunities (LID practices) • Resources need to be evaluated to ensure dollars used effectively • Staring Lake would not meet state water quality standards even with all projects being completed • All projects = 36 lb./yr. additional phosphorus removal • 2,800 lb./yr. reduction needed to meet state water quality standards • Cost increases seen due to PAH contamination (Polycyclic Aromatic Hydrocarbons)
Questions? Todd Shoemaker, PE, CFM Leslie A. Stovring Water Resources Engineer Environmental Coordinator Wenck Associates, Inc. City of Eden Prairie 651-294-4585 952-949-8327 tshoemaker@wenck.com LStovring@edenprairie.org
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