Total Maximum Daily Load (TMDL) Wasteload Allocations (WLAs) approved by the U.S. Environmental Protection Agency (EPA) prior to the November 16, 2020 issuance date of the MS4 (Municipal Separate Storm Sewer System) General Permit (permit) must be addressed by permittees in their Stormwater Pollution Prevention Program (SWPPP) Document, which includes the TMDL Application Form. The Clean Water Act requires the Minnesota Pollution Control Agency (MPCA) to include, in all National Pollutant Discharge Elimination System (NPDES) permits, discharge requirements that are consistent with requirements established in TMDLs. The permit requires applicants to submit information at the time of application on applicable WLAs and document how they will make progress on performance-based WLAs (bacteria, chloride, temperature), demonstrate they are currently meeting their numerical WLAs (oxygen demand, nitrate, total phosphorus or total suspended solids), or develop a compliance schedule for those numerical WLAs that are not being met.
Wasteload allocations are allowable loads from regulated or future regulated sources in TMDLs. They are expressed as a load (i.e. pounds per day, kilograms per year, etc.) in TMDLs. They may also be expressed as a percent reduction in pollutant loading from existing conditions. The MPCA’s Stormwater Program believes the percent reduction, when provided in the TMDL report, is a useful expression of the information for implementation and planning because it provides an estimate on the magnitude of pollutant loading reduction needed for regulated entities to meet their assigned WLA(s) from the baseline year.
WLAs for MS4 sources are either individual or categorical. Individual WLAs provide a single load for each Permittee, whereas categorical WLAs group multiple Permittees into one load that collectively must be achieved by all contributing sources. Regardless of the type of WLA, the information required to be submitted at the time of application is the same.
It is important to note watershed boundaries define TMDL study areas, while MS4 permits apply to a political boundary or jurisdiction. Further, WLAs apply only to the area that drains to the receiving water defined in the TMDL report. Therefore, it is possible that only a portion of a regulated entity’s area will be within the TMDL study area. Credit for pollutant removal from best management practices (BMPs) can only be applied to the treatment applied to stormwater runoff generated within the TMDL study area for a particular WLA; however, BMPs often treat water generated both inside and outside the study area.
A single TMDL project may contain multiple wasteload allocations for a single MS4. This can occur in the following situations:
The term “applicable WLA” is used in the MS4 General Permit and is considered to be any wasteload allocation assigned to a regulated MS4 that is
The permit conditions apply only to those TMDLs approved prior to the November 16, 2020 issuance date of the General Permit and are the only WLAs that must be addressed in the SWPPP Document. MPCA created the 2020 Municipal stormwater permit TMDL WLAs list which is a spreadsheet that contains WLA information for all TMDLs approved prior to the effective date of the General Permit. Each line on the spreadsheet represents a different WLA. This spreadsheet also has a tab which lists the TMDL project webpage for each WLA. The information found on the TMDL project webpages and linked reports can provide helpful information to MS4s.
In addition to the 2020 Municipal stormwater permit TMDL WLAs list, the MPCA created custom TMDL Application forms for each permittee, which need to be completed in order to comply with MS4 general permit. The link to the 2020 MS4 General Permit TMDL Application forms is found here. Guidance for completing the forms is located here.
Public entities that own or operate an MS4 are required to develop and implement a stormwater pollution prevention program (SWPPP) to reduce the discharge of pollutants from their storm sewer system, to the maximum extent practicable. The regulated entity must also identify best management practices (BMPs) they will implement to reduce pollution from reaching impaired waters covered by a total maximum daily load (TMDL) study. The following has been updated to reflect the TMDL related SWPPP requirements for the 2020 permit.
Bacteria: For each applicable WLA where a reduction in pollutant loading is required for bacteria,
The MPCA and partners have developed a form that can be used to fulfill this requirement. Permittees are not required to use it, but they must have a method to inventory and prioritize reduction activities. Guidance for meeting bacteria requirements is located here.
Chloride: If the permittee has an applicable waste load allocation (WLA) where a reduction in pollutant loading is required for chloride,
The permittee may use the Agency's Smart Salting Assessment Tool or other available resources and methods to complete this assessment. The permittee must document the assessment. Guidance for meeting chloride requirements is located here.
Temperature: If the permittee has an applicable waste load allocation (WLA) where a reduction in pollutant loading is required for temperature,
Guidance for meeting temperature requirements is located here.
Oxygen demand, nitrate, TSS, TP: If the applicant is claiming to meet an applicable WLA where a reduction in pollutant loading is required for oxygen demand, nitrate, TSS, or TP, the applicant must provide documentation to demonstrate the applicable WLA is being met. At a minimum, the applicant must provide the following information:
This requirement is met by completing the TMDL application form. Guidance for completing the TMDL application form is here.
For each applicable WLA not met for oxygen demand, nitrate, total suspended solids (TSS), and total phosphorus (TP), at the time of application, a compliance schedule is required. Compliance schedules can be developed to include multiple WLAs and shall include
This requirement is met by completing the TMDL application form.
The compliance schedule must demonstrate that progress toward reducing pollutant loads will be achieved within the permit cycle. Per federal rule, dates and reporting on implementation of the interim milestones must be at least annual.
Reductions in pollutant loading are achieved by implementing Best Management Practices (BMPs). When selecting BMPs to include in a compliance schedule, the applicant should consider the following:
The applicant will include BMPs they plan to implement over the five-year permit term in the Compliance Schedule section of the TMDL Application form associated with the SWPPP Document. BMPs are often applicable to multiple WLAs and can reduce the contribution of multiple pollutants. For example, volume control practices are likely applicable to both nutrient and sediment WLAs. MPCA recommends selecting BMPs that address multiple WLAs when possible.
It should be noted target dates that extend beyond the five-year permit term are expected for WLAs requiring a significant reduction in pollutant loading from an MS4.
For permittees with best management practices in place, they may be meeting their applicable WLAs. This can be demonstrated through modeling exercises. Refer to Overview of models used to meet MS4 TMDL permit requirements for more information.
Please see Guidance for completing the TMDL reporting form.