City Council Meeting Date: November 12, 2024
To: Mayor and City Council
City Administrator
From: James McDermott, Water Quality Technician
Sean Simonson, Engineering Manager
David E. Bennett, Public Works Director/City Engineer
Title
Consider Resolution adopting the Waste Load Allocation Implementation Plan.
Body
Action Requested:
The Northfield City Council approves the attached Resolution adopting the Waste Load Allocation Implementation Plan.
Summary Report:
In the Fall of 2021, the City of Northfield was authorized for coverage under the updated Municipal Separate Storm Sewer System (MS4) General Permit by the Minnesota Pollution Control Agency (MPCA). Along with authorization under this new permit, the City of Northfield received new Waste Load Allocations (WLAs) from the Cannon River Watershed and Restoration Protection Strategies (WRAPS) Report. With the addition and evaluation of the new and existing WLAs, a study was commissioned to identify ways the City of Northfield can continue to reduce storm water pollution and identify strategies that will assist in meeting WLAs over the next several years.
Based on current understanding, the long-term goal will be for the City of Northfield to attain a 45 percent reduction from the existing discharge total phosphorous (TP) loading rate from the overall drainage area. This goal is subject to change as the MPCA adjusts WLAs to account for current water quality conditions. A 45 percent reduction from the existing TP load reduction rate would correspond with approximately 20 pounds of additional TP loading that the city would need to successively reduce on an annualized basis.
The City hired Barr Engineering Co. (Barr) to develop a Waste Load Allocation Implementation Plan (Attachment #2) and adaptive tool that supports the plan and can be used for future modeling scenarios. This Plan is intended to play an active role in supporting the city’s Strategic Initiatives, Climate Action Goals, and relate with the city’s geographic information system (GIS) and 2020 Surface Water Model. Some of the key recommendations related to potential future actions are listed below.
1. Street sweeping-potential for 300-pound TP reduction by increasing street sweeping frequency in priority pipesheds, with emphasis in the spring and fall
2. Street reclamation and overlay projects-potential for 100-pound TP reduction by implementing structural BMPs in priority pipesheds
3. Agricultural sources-potential for at least 700-pound TP reduction from structural BMPs implemented with future development
4. Streambank and bed erosion-sources of erosion are unknown currently; it is recommended that the city inventory (and/or use new LiDAR data), and subsequently stabilize erosion
5. Chemical treatment of Spring Creek flow-potential for at least 500-pound TP reduction from this tributary; it is recommended that the city survey/verify existing TP load reductions that could be realized from alum treatment (plant or aerial lake application).
Alternative Options:
The City Council could decide not to approve the Plan, however an alternative plan would need to be developed.
Financial Impacts:
The recommendations in the report will be considered and evaluated with future City Capital Improvement Plans.
Tentative Timelines:
Staff will reference this implementation plan in future improvement projects.