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HomeMy WebLinkAboutITEM VIII. B. April 29 2025 Council Workshop Handouts I:\Engineering\2021 - 2030 Contracts\2024 CONTRACTS\24-24 SW Ord Updates\Administrative\Correspondence\Memo\SW Code Revision Council Memo for Presentation.docx Page 1 of 2 TO: Honorable Mayor and Members of the Common Council FROM: Justin Gierach, Engineering Division Manager / City Engineer DATE: April 25, 2025 RE: Municipal Code Chapter 14: Post-Construction Stormwater Management Ordinance Update Analysis City Engineering Division Staff, in conjunction with Brown and Caldwell, are currently evaluating the pollution control requirements within Municipal Code Chapter 14. This effort is partially funded by a grant from the Wisconsin Department of Natural Resources (WDNR). The resolution authorizing applying for the grant was approved by the Common Council on March 28, 2023 and the Brown and Caldwell agreement associated for this effort was approved on August 28, 2024. The need for this evaluation was originally identified as part of the City of Oshkosh Stormwater Quality Management Plan, November 2022 (Citywide SWMP), which was approved by the Common Council on December 13, 2022. This Citywide SWMP was completed in response to the completion of the Total Maximum Daily Loads for Total Phosphorus and Total Suspended Solids Upper Fox and Wolf Basins, February 2020 (Upper Fox and Wolf TMDL) which was prepared by the WDNR and approved by the Environmental Protection Agency (EPA). The Upper Fox and Wolf TMDL establishes limits, called wasteload allocations, on the amount of Total Phosphorus (TP) and Total Suspended Solids (TSS) that can be discharged into the Fox River, Lake Winnebago, Lake Butte des Morts, and Sawyer Creek by the City’s Municipal Separate Storm Sewer System (MS4). WDNR has provided literature for the general public on what is a TMDL that can be found attached to this memo. The City’s MS4 Permit, which is issued by the WDNR, contains requirements the City must meet to comply with the TMDL. As part of this permit, the City must complete various activities related to the storm sewer system, including making progress towards reducing TSS and TP loads to the levels required by the Upper Fox and Wolf TMDL. I:\Engineering\2021 - 2030 Contracts\2024 CONTRACTS\24-24 SW Ord Updates\Administrative\Correspondence\Memo\SW Code Revision Council Memo for Presentation.docx Page 2 of 2 One of the approaches that was considered in the Citywide SWMP was to incrementally increase TP and TSS reduction requirements associated with the City’s Post-Construction Storm Water Management Code. Several scenarios were evaluated and it was determined that modifying the current code would positively impact TMDL reductions from new development (existing greenfield/no impervious surfaces) and redevelopment (existing impervious surfaces) in the City. Based on that analysis, the Citywide SWMP implementation plan included a recommendation to conduct an additional evaluation of potential code modifications. The City first implemented a Post-Construction Storm Water Management Code in the early 1990’s. That Code only contained a peak flow control (flood control) requirement. The last major code update occurred in 2012, responding to a provision in the City’s MS4 Permit to incorporate WDNR performance standards contained within NR 151 (WDNR’s code for Runoff Management) into the Municipal Code that focused on storm water discharge quality. An Erosion and Sediment Control Code and Illicit Discharge Detection and Elimination Code were also developed in compliance with MS4 Permit requirements. The City of Oshkosh is not the first municipality to consider ordinance changes modifying TP and TSS reduction requirements for new development and redevelopment. As part of the agreement with Brown and Caldwell, code requirements of other municipalities were reviewed for their pollution reduction requirements and code applicability. Eight (8) municipalities (half of those reviewed) have incorporated TMDL reduction requirements. JER/tlt Enclosures: Definitions WDNR TMDL Literature TMDL Basin Maps Code Revision Scenarios SMP Performance Standards Workshop Presentation –MS4: Municipal Separate Storm Sewer System –Reachshed: Drainage area to a waterbody –SMP: Stormwater Management Practice –SWMP: Stormwater Management Plan –TMDL: Total Maximum Daily Load –The amount of pollution a water body can receive and still meet water quality standards –TP: Total Phosphorus –TSS: Total Suspended Solids Brown and Caldwell 6 Background: Definitions Blue Green Algae – Lake Winnebago (Source: WDNR) Fernau Watershed - North Main Street Wet Detention Basin Total Maximum Daily Load (TMDL) What is a TMDL? A Total Maximum Daily Load (TMDL) is the maximum amount of a pollutant that a body of water can receive while still meeting water quality standards. A waterway that exceeds water quality standards is often no longer suitable for its designated uses, such as wildlife habitat, fishing, or other recreational activities.  Municipal Wastewater  Industrial Wastewater  Stormwater (MS4s)  Naturally occurring from wetlands and forests  Runoff from the landscape TMDL Assessment In order to develop the TMDL and answer the questions above, the watershed is studied to determine the amount of pollution currently entering the waterway from the sources shown in the adjacent figure. Fish and aquatic life Recreation Phosphorus Toxic algae blooms Public health risks Why develop a TMDL? The ultimate goal of a TMDL is to improve water quality by reducing pollutants, such as phosphorus and sediment. To help achieve this, a TMDL answers the following questions: 1. What is the current amount of pollution entering the waterway and how much is each source contributing? 2. How much does pollution need to be reduced in order for each waterway to meet water quality standards? 3. How will the needed pollutant load reductions be achieved for each waterway? A TMDL study and implementation plan provides a strategic framework and prioritizes resources for water quality improvement. Photo credit: Herbert Lange Photo credit: Jim Ziegler Created by Susan Sandford - Wisconsin Department of Natural Resources Bureau of Water Quality Brown and Caldwell 1 Brown and Caldwell 2 Summary of Code Revision Scenarios (4/29/2025) Code Revisions Scenario Summary Scenario TSS Reduction Requirement TP Reduction Requirement New Development Redevelopment New Development Redevelopment Current Code 80% 40% None None Scenario 1 85% 58.4% 57.4% 39.4% Scenario 2 90% 52% 61% 35% Scenario 3 80% 58.4% (Sawyer Cr) 40% (Other Areas) 54% 30% Scenario 4 80% 72.2% 40.5% 40.5% Scenario 5 80% 58.4% 54% 30% –Considered what could be done at site to meet different scenarios –Increased SMP sizes –i.e. larger wet pond –Different SMPs –i.e. Sand filter instead of biofilter Brown and Caldwell 24 Analysis: Code Revisions Potential SMP Performance TPTSSSMP >50%> 80%Wet Pond None80%Biofilter* 35%80%Sand Filter* 35%65%Permeable Pavement* 50%80%Proprietary Filter 15%25%Catch Basin *TSS/TP reductions can be increased with infiltration. SMPs listed are accepted as part of WDNR Technical Standards. April 29, 2025 Common Council Workshop: Municipal Code Ch. 14 Update Agenda 1.Background 2.Analysis of Other Communities 3.Analysis of Code Revisions 4.Next Steps –MS4 Permit from DNR requires City to comply with the TMDL –Update Council regarding the Municipal Code Ch. 14 Updates project –Get input from Council on analysis and recommendations Brown and Caldwell 3 Why are we here? –City Engineering Division, with Brown and Caldwell (BC), is evaluating changes to Municipal Code Chapter 14 –Changes focused on stormwater pollution reduction requirements –Will include other minor revisions –Partially funded by WDNR Grant –3/28/2023: Grant application authorized by Common Council –8/28/2024: BC Contract approved by Common Council Brown and Caldwell 4 Background –Flooding incidents since 1990 –Presidential Disaster Declarations –1990, 1993, 2001, 2004, 2008 –Other Incidents –1996, 1999 (2), 2000, 2010, 2012 –Source: Winnebago County Hazard Mitigation Plan –Project will not modify peak flow control requirements targeted at flood reduction Brown and Caldwell 5 Background: Flooding –MS4: Municipal Separate Storm Sewer System –Reachshed: Drainage area to a waterbody –SMP: Stormwater Management Practice –SWMP: Stormwater Management Plan –TMDL: Total Maximum Daily Load –The amount of pollution a water body can receive and still meet water quality standards –TP: Total Phosphorus –TSS: Total Suspended Solids Brown and Caldwell 6 Background: Definitions Blue Green Algae –Lake Winnebago (Source: WDNR) Fernau Watershed -North Main Street Wet Detention Basin –City’s storm sewer system is regulated by WDNR Municipal Separate Storm Sewer System (MS4) General Permit –Initial permit issued in 2007 –5-year permit cycle –Last issued in 2019, waiting for updated permit –TMDL was prepared by WDNR and approved by US EPA (2020) –Requirements for City associated with TMDL is incorporated into MS4 Permit –City must make progress towards TMDL requirements Brown and Caldwell 7 Background: MS4 Permit –City Municipal Code governing stormwater management –Established in the early 1990’s (as Chapter 24) –Peak flow control requirements only –Last major revision in 2012 (became Chapter 14) –Added pollution control (TSS reduction) requirements –Minor updates in 2014 and 2023 Brown and Caldwell 8 Background: Chapter 14 –Current Pollution Control Requirements –Redevelopment: 40% TSS reduction –New Development: 80% TSS reduction –Applies to sites with more than 20,000 ft2 of impervious surface Brown and Caldwell 9 Background: Chapter 14 Biofilter at City Hall Parking Lot Catch basins in 9th Avenue –Upper Fox and Wolf River TMDL –Established limits for TP and TSS –Considers agricultural, industrial, stormwater, and wastewater sources Brown and Caldwell 10 Background: TMDL –Established limits the City’s storm sewer system can discharge to: –Fox River –Lake Winnebago –Lake Butte Des Morts –Sawyer Creek –Established limits for the City’s wastewater treatment plant Brown and Caldwell 11 Background: TMDL –Requirements Brown and Caldwell 12 Background: TMDL TMDL Reach Required TSS Reduction Required TP Reduction Sawyer Creek 58.4%85.6% Lake Butte des Morts 20.0%85.6% Fox River 20.0%85.6% Lake Winnebago 20.0%85.6% Neenah Slough (Lower Fox River TMDL)52.0%40.5% –November 2022: Most Recent Citywide SWMP completed –Established City’s current TSS & TP control levels Reachshed TMDL Target TSS Load Reduction % “With Controls” TSS Reduction % TMDL Target TP Load Reduction % “With Controls” TP Reduction % Upper Fox/Wolf TMDL Sawyer Creek 58.4%28.7%85.6%20.9% Lake Butte des Morts 20%23.2%85.6%18.3% Fox River 20%38.3%85.6%28.6% Lake Winnebago 20%30.8%85.6%24.8% Lower Fox River TMDL Neenah Slough 52%0%40.5%0% Brown and Caldwell 13 Background: Citywide SWMP –Considered how City can reduce TSS and TP –Potential SMPs –Wet Detention Ponds –Biofilters –Rain Gardens –Enhanced Settling for Wet Ponds –Revisions to Chapter 14 –Increased requirements for new development and redevelopment Brown and Caldwell 14 Background: Citywide SWMP –Considered Revisions to Chapter 14 –Evaluated Citywide impact of future development –Current code & 2 scenarios –Evaluated site specific impact to 3 past developments –Included added evaluation in implementation plan Brown and Caldwell 15 Background: Citywide SWMP Implementation Plan Element Scheduled Year(s) Research / integrate additional existing Non-Regional SMPs 2023 (recent sites) 2024-2025 (older sites) Additional evaluation of Municipal Code Modifications 2023-2024 Build WinSLAMM models for Southwest Industrial Park ponds 2026 Additional leaf management evaluation 2027 Preliminary design study of enhanced settling 2028-2029 Citywide SWMP Update –evaluate new technology and alternative compliance options (i.e. trading) 2030-2032 –Scope of Work –Look at what other municipalities are doing. –Evaluate additional scenarios. –Consider how changes could impact development sites. –Communicate with stakeholders. Brown and Caldwell 16 Analysis: Current Project –State Requirements –Wisconsin Administrative Code NR 151 –Runoff Management –Redevelopment: 40% TSS Reduction –New Development: 80% TSS Reduction –Other municipalities were reviewed to determine if higher requirements were implemented Brown and Caldwell 17 Analysis: Other Municipal Code Requirements –Local Ordinance Requires TMDL Reductions (TSS & TP control) –Appleton –Menasha –Neenah –Calumet County –Fox Crossing –Grand Chute –Kaukauna –Outagamie County –Local Ordinance Requires NR 151 Reductions (TSS control) –Town of Algoma –Eau Claire* –Fond du Lac –Green Bay –Janesville –La Crosse* –Wausau –Winnebago County Brown and Caldwell 18 Analysis: Other Municipal Code Requirements *Municipality not within a TMDL area Other Communities Code Requirements Brown and Caldwell 19 City Reachshed New Development Redevelopment TSS TP TSS TP Appleton Lake Winnebago 80%85.6%40%85.6% Fox River 80%40.5%72.2%40.5% Bear Creek 84%85.6%84%85.6% Garners Creek 80%68.6%59.9%68.6% Mud Creek 80%48.2%42.8%48.2% Apple/Duck Creeks 80%40.5%52%40.5% Neenah Lake Winnebago 80%-40%- Neenah Slough 80%41%52%41% Fox River 80%41%72%41% Menasha Lake Winnebago 80%60%40%30% Lower Fox River 80%41%72%41% –Specific pollution reduction requirements from selected communities with TMDL reduction requirements –Criteria –Progress toward TMDL –Feasible for sites to meet targets –Consider Cost Brown and Caldwell 20 Analysis: Code Revisions –Pollution reduction scenarios considered –Developed scenarios based on TMDL, SMP effectiveness, and nearby community requirements Brown and Caldwell 21 Analysis: Code Revisions Code Revisions Scenario Summary Scenario TSS Reduction Requirement TP Reduction Requirement New Development Redevelopment New Development Redevelopment Current Code 80%40%None None Scenario 1 85%58.4%57.4%39.4% Scenario 2 90%52%61%35% Scenario 3 80%58.4% (Sawyer Cr) 40% (Other Areas)54%30% Scenario 4 80% 72.2% 40.5% 40.5% Scenario 5 80%58.4%54%30% –MS4 Permit requires continual progress each permit term towards TMDL numeric standards –Assessing Progress Towards TMDL –Considered Citywide Impact of Code Changes –Used a 30-year planning horizon –Projected rate of development based on past –Would not fully comply with TMDL targets under any scenario –Amount of anticipated new development and re-development happening over the next 30-years is limited –Additional SMPs will have to be designed and installed by the City to treat existing development Brown and Caldwell 22 Analysis: Code Revisions –Redevelopment Sites Evaluated –Ceape / Otter Parking Lot* –Field Operations Facility* –Freddy’s Oshkosh** –New Development Sites Evaluated –The Wit Apartment Complex* –Valley Veterinary Hospital** Brown and Caldwell 23 Analysis: Code Revisions Permeable Pavement at Ceape/Otter Parking Lot Biofilter at Field Operations Facility *Site evaluated as part of Citywide SWMP. **Site evaluated as part of current project. –Considered what could be done at site to meet different scenarios –Increased SMP sizes –i.e. larger wet pond –Different SMPs –i.e. Sand filter instead of biofilter Brown and Caldwell 24 Analysis: Code Revisions Potential SMP Performance SMP TSS TP Wet Pond > 80%>50% Biofilter*80%None Sand Filter*80%35% Permeable Pavement*65%35% Proprietary Filter 80%50% Catch Basin 25%15% *TSS/TP reductions can be increased with infiltration. SMPs listed are accepted as part of WDNR Technical Standards. –Does existing site design meet code scenarios? Redevelopment Site (current TSS / TP reductions) Would Updated Municipal Code be Met? (Redevelopment) Scenario 1 (58.4% TSS / 39.4% TP) Scenario 2 (52% TSS / 35% TP) Scenario 3 (58.4% TSS / 30% TP) Scenario 4 (72.2% TSS / 40.5% TP) Scenario 5 (58.4% TSS / 30% TP) Ceape/Otter Parking* (63.2% TSS / 34.7% TP) Partial (TSS only) Partial (TSS only)Yes No Yes Field Operations* (56.8% TSS / 23.1% TP)No Partial (TSS only)No No No Freddy’s Oshkosh** (42.9% TSS / 36.3% TP)No Partial (TP only) Partial (TP only)No Partial (TP only) Brown and Caldwell 25 Analysis: Code Revisions *Site evaluated as part of Citywide SWMP. **Site evaluated as part of current project. New Development Site (current TSS / TP reductions) Would Updated Municipal Code be Met? (New Development) Scenario 1 (85% TSS / 57.4% TP) Scenario 2 (90% TSS / 61% TP) Scenario 3 (80% TSS / 54% TP) Scenario 4 (80% TSS / 40.5% TP) Scenario 5 (80% TSS / 54% TP) The Wit Apartments* (85.5% TSS / 62.7% TP)Yes Partial (TP only)Yes Yes Yes Valley Vet. Hospital** (80.0% TSS / 35.0% TP)No No Partial (TSS only) Partial (TSS only) Partial (TSS only) –Is it feasible to meet scenarios? –Evaluated potential site changes that could be used to meet an updated municipal code Redevelopment Site Could Updated Municipal Code be Met? (Redevelopment) Scenario 1 (58.4% TSS / 39.4% TP) Scenario 2 (52% TSS / 35% TP) Scenario 3 (58.4% TSS / 30% TP) Scenario 4 (72.2% TSS / 40.5% TP) Scenario 5 (58.4% TSS / 30% TP) Ceape/Otter Parking*Yes Yes Yes No Yes Field Operations Facility*Yes Yes Yes No Yes Freddy’s Oshkosh**Yes Yes Yes Yes Yes Brown and Caldwell 26 Analysis: Site Revisions *Site evaluated as part of Citywide SWMP. **Site evaluated as part of current project. New Development Site Could Updated Municipal Code be Met? (New Development) Scenario 1 (85% TSS / 57.4% TP) Scenario 2 (90% TSS / 61% TP) Scenario 3 (80% TSS / 54% TP) Scenario 4 (80% TSS / 40.5% TP) Scenario 5 (80% TSS / 54% TP) The Wit Apartment Complex* Yes Yes Yes Yes Yes Valley Veterinary Hospital** Partial (TSS only)No Yes Yes Yes Brown and Caldwell 27 Potential Site Impacts: Freddy’s Oshkosh Alternative TSS Load Reduction (%) TP Load Reduction (%) Is Municipal Code Met? Current Scenario 1 Scenario 2 Scenario 3 Scenario 4 Scenario 5 TSS (40%) TP (N/A) TSS (58.4%) TP (39.4%) TSS (52%) TP (35%) TSS (58.4%) TP (30%) TSS (72.2%) TP (40.5%) TSS (58.4%) TP (30%) Site Design 42.9%36.3%Yes N/A No No No Yes No Yes No No No Yes Alt. 1 53.7%42.3%Yes N/A No Yes Yes Yes No Yes No Yes No Yes Alt. 2 58.6%35.8%Yes N/A Yes No Yes Yes Yes Yes No No Yes Yes Alt. 3 72.5%57.2%Yes N/A Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Alt. 4 66.1%49.0%Yes N/A Yes Yes Yes Yes Yes Yes No Yes Yes Yes Alt. 5 64.9%72.2%Yes N/A Yes Yes Yes Yes Yes Yes No Yes Yes Yes –Site Design: 6 –4’ dia catch basins with sumps & grass swale –Alternative 1: 6 -10’ dia catch basins with sumps & grass swale –Alternative 2: 2 –800 sq ft underground detention areas (no catch basins or swales) –Alternative 3: 2 permeable pavement areas (2,500 sq ft and 3,000 sq ft; 0.5 in/hr infiltration rate) –Alternative 4: 2 –400 sq ft sand filters (2 –4’ dia catch basins and grass swale remain) –Alternative 5: Proprietary filter Brown and Caldwell 28 Potential Site Impacts: Freddy’s Oshkosh Alternative SMPs Estimated Construction Cost Estimated Annual Maintenance Cost Estimated Non-Routine Maintenance Cost Total Annualized Cost Site Design 6 -Catch Basins (4' dia), Grass Swale $35,600 $400 N/A $2,100 Alt. 1 10' dia Catch Basins, Grass Swale $150,000 $1,400 N/A $8,400 Alt. 2 2 -800 sq ft Underground Detention Area $192,000 $400 $4,400 $9,800 Alt. 3 2,500 & 3,000 sq ft Permeable Pavement Areas $207,800 $200 $12,375 $13,700 Alt. 4 2 -400 sq ft Sand Filters, Grass Swale, 2 -Catch Basins (4' dia)$43,900 $2,000 $17,800 $5,400 Alt. 5 Proprietary Filter $42,400 $3,300 N/A $5,300 –All SMPs: 4% Interest rate, 50-year lifespan –Catch Basins: Annual cleaning –Permeable Pavement: Annual site inspection, cleaning every 3-years, resealing every 5-year –Proprietary Filter: Annual cleaning & filter replacement –Sand Filter: Annual inspection & minor maintenance, rehabilitation every 20-years –Underground Detention: Annual inspection, sediment removal every 15- years Brown and Caldwell 29 Potential Site Impacts: Valley Veterinary Hospital Alternative TSS Load Reduction (%) TP Load Reduction (%) Is Municipal Code Met? Current Scenario 1 Scenario 2 Scenario 3 Scenario 4 Scenario 5 TSS (80%) TP (N/A) TSS (85%) TP (57.4%) TSS (90%) TP (61%) TSS (80%) TP (54%) TSS (80%) TP (40.5%) TSS (80%) TP (54%) Site Design 80.0%35.0%Yes N/A No No No No Yes No Yes No Yes No Alt. 1 86.6%57.1%Yes N/A Yes No No No Yes Yes Yes Yes Yes Yes Alt. 2 80.5%60.2%Yes N/A No Yes No No Yes Yes Yes Yes Yes Yes –Site Design: Sand filter with clay liner (no infiltration) –Alternative 1: Sand filter with infiltration rate of 0.24 in/hr (same footprint as designed sand filter) –Alternative 2: Wet detention basin in place of biofilter (3-inch orifice outlet, 0.05 acre permanent pool) Brown and Caldwell 30 Potential Site Impacts: Valley Veterinary Hospital Alternative SMPs Estimated Construction Cost Estimated Annual Maintenance Cost Estimated Non-Routine Maintenance Cost Total Annualized Cost Site Design Sand Filter $92,600 $845 $30,200 $7,400 Alt. 1 Over-excavated Sand Filter $103,300 $845 $51,500 $9,500 Alt. 2 Wet Pond $87,600 $800 $16,000 $5,800 –All SMPs: 4% Interest rate, 50-year lifespan –Sand Filter: Annual inspection & minor maintenance, rehabilitation every 20-years (assumes replacement of top half of sand media) –Wet Pond: Site inspection & minor maintenance, dredging every 35-years 1.Site specific conditions can limit potential SMPs that are applicable 2.Peak flow control requirements often result in site exceeding current TSS reduction targets 3.Impact of infiltration (even at low rates) can be significant 4.Cost impacted by variety of factors 5.Higher reduction requirements will lead to more maximum extent practicable requests Brown and Caldwell 31 Analysis: Takeaways –Pending direction from Common Council –Which scenario would you like us to move forward with? –Next Steps Proposed –Sustainability Advisory Board Recommendations –Plan Commission Recommendations –Revise Code Language –Council Approval of Code Updates –Complete by End of 2025 (Grant Deadline) Brown and Caldwell 32 Next Steps –Questions? Thank you. Brown and Caldwell 34