Lauren Striegl City of Madison Engineering UPDATE ON CITY OF MADISON S SPECIAL TREATMENT PROJECTS

Transcription

1 Lauren Striegl City of Madison Engineering UPDATE ON CITY OF MADISON S SPECIAL TREATMENT PROJECTS March 15, 2018

2 Starkweather Creek Stormwater Treatment System Removing Phosphorus from Stormwater Runoff Through Coagulant Treatment

3 Why are we doing this? Rock River Basin TMDL Completed in 2011 Madison Stormwater Requirements Phosphorus reduction of ~ 13,000 lbs./yr. 46 % city-wide reduction of TP discharge from current conditions Adaptive Management Madison is a participant in MMSD-led Adaptive Management program, but Madison has committed to reducing 4,900 lbs within City limits Madison

4 Project Site Watershed 5,500 acre watershed 67% urban 33% rural

5 Phase I: Summary of Scope Re-mapping of Starkweather Creek floodway and floodplain near the proposed project site Chemical flocculant testing and selection Testing and monitoring of quarry pond characteristics Hydraulic and hydrologic modeling of the east branch of Starkweather Creek and its watershed Feasibility-level design of a stormwater treatment system

6 Project Concept Coagulant >

7 Background Project Site Fair Oaks Ave. RR Spur Starkweather Park Outlet channel Quarry Pond Lake Mendota Milwaukee St. Tributary East Branch Starkweather Creek Milwaukee St.

8 Pond Configuration Outlet Pump Sta. Pond NWL~ 848 Cut Material Inlet ~ 828 Pond Bottom ~ 825 Fill Material

9 Conceptual Design Plan View 9 Chemical Storage/Controls Bld. Treated Water Return to Creek Diversion Gate 48 diameter pipe (buried) Pump Station Coagulant Mixing Chamber (buried) Treated Water Discharge to Pond Coagulant Settling Pond (NWL 848 ) Pond Outlet

10 Potential TP Reduction 10 Treatment System Performance Raw Water Phosphorus Conc. = mg/l Design maximum flow rate = 100 cfs Annual Treatment Volume ~ 3,500 ac-ft Coagulant Effectiveness = 85% Estimated Annual Phos. Removal = 1,660 lbs/year City of Madison TMDL Phos. Reduction Goal: ~13,000 lbs /yr ~ 13% of TMDL Goal ~34% of City of Madison In-City Goal of 4,900 lbs/yr

11 Estimated Capital Costs Project Components Phase I Site Work Sub-Total: Coag. Treatment System Sub-Total: Construction Sub-Total: Construction Contingency (30%): Const. Sub-Total + Contingency: Design & CRS (20%): $2,417,652 $1,201,520 $3,619,172 $1,085,752 $4,704,924 $940,985 Cost Escalation from 2016 (3%): $141,148 Total Construction Estimate: $5,787,057 Annual Operations and Maintenance Cost: $350,980 Annual Cost/lb of TP Removed: $386

12 Next Steps 12 Continued Public Outreach (ongoing) Land Acquisition (2018) Additional Site Investigations (Post Acquisition ) Wetland delineation Environmental testing Continued DNR / Agency Coordination Permitting Final Design ( ) Construction (2019)

13 Willow Creek Stormwater Treatment System Inline Settling Chamber

14 What Is the Problem? Willow Creek is an urban stream flowing from Campus Drive to University Bay Receives stormwater runoff from watershed of ~1,900 acres of mostly medium density residential and commercial land UW and the City of Madison is concerned with excess sediments and nutrients reaching Lake Mendota Sediment from stormwater runoff has formed a small island in University Bay in Lake Mendota at the outlet of Willow Creek Addressing excess sediments/nutrient loads reaching Lake Mendota from Willow Creek will benefit the UW and the City

15 What Is the Problem? 15 University Bay Willow Creek Lake Mendota Sediment Island Observatory Dr Brown and Caldwell 88th Annual WEFTEC Conference

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17 Three-Phase Solution 17 Phase I capture sediment Largely from City of Madison storm sewer City-led project Phase II restoration of Willow Creek from Phase I project limits to University Bay Includes dredging and remeandering of Willow Creek Phase III dredging of sediment island in University Bay Phases II and III will be headed by UW

18 Project Location 18 Project Area: ~200LF of Willow Creek City of Madison storm sewer outfall Brown and Caldwell 88th Annual WEFTEC Conference

19 Project Concept Inline Settling Basin 19 Flow in (existing box culvert) Sediment settles out, trapped behind weir

20 Design Plan View 20 Regrade channel to 844 (~4 lower than existing) Manhole with sump (for underdrain system) Herrick Install access ramp for Dr maintenance vehicles Weir set at AMSL (Lake Mendota summer max) Re-route secondary box culvert to improve hydraulics

21 Excavation 21 Brown and Caldwell 88th Annual WEFTEC Conference

22 Underdrain System 22 Coarse aggregate drainage stone Geotextile fabric Perforated PVC (6 ) Brown and Caldwell 88th Annual WEFTEC Conference Undercut/clear stone

23 Rebar and Concrete Forming 23 Brown and Caldwell 88th Annual WEFTEC Conference

24 Concrete Pouring 24 Brown and Caldwell 88th Annual WEFTEC Conference

25 Channel Construction 25 Concrete channel Headwall and box culvert

26 Channel at Completion (July 2017) 26

27 Next Steps 27 Boat survey (3/13/18) maximum sediment depth ~3.75 Summer 2018 City of Madison crews will clean concrete channel

28 Questions?