Storm Water_Content_tmdl

Total Maximum Daily Loads (TMDLs) and Impaired Waters

 

What does the MS4 Permit require for TMDLs and Impaired Waters - Wis Adm Code NR 216.07(10)?

Wis Adm Code NR 216.07(10)

Every two years, Sections 303(d) and 305(b) of the Clean Water Act (CWA) require states to publish a list of all waters not meeting water quality standards and therefore, are considered impaired. While some of these impaired waters are covered by a U.S. EPA-approved TMDL, others are not. However, regardless of TMDL status, if a community with an MS4 permit discharges a pollutant of concern to an impaired water, the MS4 permit contains requirements.

  • If a community with an MS4 Permit discharges a pollutant of concern to an impaired water of the state that is not covered by a US EPA-approved TMDL, the permittee is required to include a written section in its stormwater management program that describes best management practices and control measures it will implement as part of its program to reduce pollutant loading. For example, although many waters are impaired by chloride, currently, chloride is not identified as a pollutant of concern in a U.S. EPA-approved TMDL. However, MS4 permittees discharging to the chloride-impaired water are required to implement actions that work to reduce its chloride loading to the impaired waters. For MS4 permittees, this is typically addressed through its winter road management program because winter deicers (e.g., road salt) are likely the MS4’s primary loading source. However, MS4s may identify other sources of chloride loading and thus, choose to implement a variety of actions. 
  • If a community with an MS4 permit discharges a pollutant of concern to an impaired water of the state that is covered by a US EPA-approved TMDL, the permittee is required to implement actions that demonstrate progress on reducing its pollutant loading. 

Please note, an MS4 permittee may discharge a pollutant of concern to both an impaired water with a US EPA-approved TMDL and, an impaired water without a U.S. EPA-approved TMDL. So, the two points described above may apply to a single MS4 permittee.

MS4 TMDL resources:

  • MS4 TMDL Guidance: Provides several guidance documents for topics such as TMDL modeling, implementation, leaf credit, internally drained areas, and much more.
  • SLAMM and P-8 Modeling: This page provides information on SLAMM and P-8 modeling programs which can be used to predict pollutant loads.

What are TMDLs and impaired waters?

To learn more on TMDLs and impaired waters in Wisconsin, please visit the following links:

To see a list of waters that are included in these TMDLs, please review Impaired Waters tool to find waters with the status code of "Approved TMDL."

TMDL pollutants

Total Suspended Solids (TSS) and Total Phosphorus (TP)

To make progress towards meeting TMDL WLAs, MS4 permittees must implement BMPs to reduce the loading of the identified pollutant of concern.

To make progress on TSS and TP reductions, MS4 permittees may implement a variety of BMPs known to reduce TSS and TP loading. For example, implementing street sweeping and constructing bio-infiltration practices. To demonstrate progress towards reducing TSS and TP, MS4 permittees typically utilize modeling such as WinSLAMM.

Helpful information and resources:

Fecal bacteria

To make progress towards meeting TMDL WLAs, MS4 permittees must implement BMPs to reduce the loading of the identified pollutant of concern.

However, unlike the typical TMDL pollutants of concern (TSS and TP), fecal bacteria WLAs are based on a load reduction curve rather than a mass reduction. For MS4 permittees, this means fecal bacteria loading fluctuates in stormwater runoff. For example, fecal bacteria loading may be higher during high-flow conditions. Additionally, because fecal bacteria loading can drastically change (e.g., a sanitary sewer line may break at an unknown point of time), not only do MS4s need to implement a variety of BMPs to accommodate various flow conditions, MS4s must also continuously evaluate BMPs to implement.

Lastly, because fecal bacteria are a biological organism, MS4s cannot demonstrate progress using a model. Therefore, to demonstrate progress on fecal bacteria reductions, MS4 permittees must implement a variety of BMPs to reduce, with the goal of eliminating, fecal bacteria loading and routinely taking action to identify and eliminate known or potential fecal bacteria sources. For example, eliminating illicit connections; requiring, monitoring, and enforcing proper pet waste management and prohibiting the feeding of wildlife; and disconnecting impervious surface areas to mitigate fecal bacteria build-up and wash-off cycles.

Resources on fecal bacteria pollution in stormwater and different BMPs that could be implemented:

Alternative Compliance Options

Although Adaptive Management (AM) and Water Quality Trading (WQT) are compliance tools utilized by Wastewater permittees, these alternative compliance options are less common for MS4 (stormwater) permittees.

Therefore, any MS4 permittee interested in using AM and WQT for MS4 TMDL compliance should contact its local Department stormwater staff to determine eligibility prior to initiating AM or WQT

Helpful information and resources:

Wisconsin’s Water Quality Trading – Webpage providing overview of WQT, history, implementation, and the difference between WQT and AM. This page also includes the link to guidance for implementing WQT in WPDES permits.

Adaptative Management – Webpage providing an overview of AM, eligibility, plans, and resources. This page also includes the link to the AM Technical Handbook which describes the process, including how to develop a successful AM strategy.