City of Eden Prairie Pond Inventory and Maintenance Assessment - - PowerPoint PPT Presentation

Leslie A. Stovring Environmental Coordinator City of Eden Prairie Todd Shoemaker, PE, CFM and Joe Bischoff Wenck Associates, Inc.

City of Eden Prairie Pond Inventory and Maintenance Assessment

Fun Facts about Eden Prairie

• Population of ~62,000
• 12 mi2 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%

developed

• Impaired for

nutrients

Staring Lake

Stormwater System Analysis: Basin Ownership

10 20 30 40 50 60 70 80 90 100 City ROW City Easement Private w/ City Drainage Private Number

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

20 40 60 80 100 120 15-22-B 15-22-C 15-22-D 15-23-A 15-23-C 15-23-D 15-23-E 15-23-F Percent Removal 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)

Next Steps

• Staring Lake
• 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?

Leslie A. Stovring

Environmental Coordinator City of Eden Prairie 952-949-8327 LStovring@edenprairie.org

Todd Shoemaker, PE, CFM

Water Resources Engineer Wenck Associates, Inc. 651-294-4585 tshoemaker@wenck.com