Update the City’s WinSLAMM Model for TMDL Purposes

Background Information:

In 2008, the City of Fitchburg completed storm water quality modeling efforts within the City’s MS4 permitted boundary to address the control and management of storm water. The plan included analyzing the City-wide non-point source pollution using WinSLAMM to evaluate base (“no controls”) and existing (“with controls”) pollutant loadings. The Wisconsin Department of Natural Resources (WDNR) concurred that the City was exceeding the required 20 percent Total Suspended Solids (TSS) removal requirement from the baseline conditions and was therefore in compliance with NR 151 regulations.

In 2011, the Rock River TMDL was approved by US Environmental Protection Agency (EPA), with three TMDL reachsheds with pollutant loading limits in the City’s MS4 permitted boundary: Lake Wingra (Reach 64), Nine Springs Creek (Reach 65), and Swan Creek (Reach 66). For more information on MS4 requirements for co-permittees subject to the Rock River TMDL, see the City’s MS4 Permit.

In 2014, MSA completed storm water quality modeling for the Nine Springs Creek (Reach 65) reachshed; however, final TMDL modeling guidance from the DNR became available in October 2014 after the project was complete. The updated storm water modeling found the City was not in compliance with the required TMDL reductions at the time, and the modeling incorporated several potential BMPs to work towards pollutant load removal compliance within the reachshed. Results are summarized in the Nine Springs Watershed Master Plan.

MSA completed the City’s most recent WinSLAMM model. We will rely on a recommendation from the Consultant on whether it is more efficient to use this model as a starting point, or to create a new model from scratch, given changes in DNR’s guidance regarding modeling. We also have a desire to take credit for privately owned and maintained stormwater facilities in our model.

Project Description:

The City of Fitchburg is seeking assistance with updating the water quality modelling for Reaches 64, 65, and 66, and to identify necessary efforts for compliance with the Rock River TMDL regulations. This project will include updating/preparing WinSLAMM models to establish existing “no controls” loads, “with controls” loads, and future loads after implementation of potential future stormwater control practices (for both TSS and total phosphorous).

The consultant will identify future stormwater control practices, determine load reductions achieved, prepare cost estimates for the proposed control practices, prepare a cost-load reduction comparison for each practice, and help the City prepare an implementation schedule (with the goal of meeting full TMDL compliance within the City’s boundary rather than relying on Yahara WINS and the approved Adaptive Management Plan).

In addition, the project will include updating the City’s Stormwater and Erosion Control ordinance with the goal of meeting TMDL requirements.

After completion of this project, the WinSLAMM model will be a “living document” which the City desires to update in-house to reflect future developments.

These services will be provided in the calendar year 2022.

The City currently meets the MS4 (NR 151) requirements, so this project will only focus on the TMDL requirements.

We anticipate receiving a DNR Planning Grant for this project. The grant application was prepared for the City by AECOM.