Total Maximum Daily Load (TMDL) Wasteload Allocations (WLAs) approved by the U.S. Environmental Protection Agency (EPA) prior to the effective date of the MS4 General Permit (permit) must be addressed by Permittees in their Stormwater Pollution Prevention Program (SWPPP) Document. 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 indicate how they will make progress toward achieving those WLAs over the current five-year permit term. Applicants must include long term strategies for meeting WLAs that will not be fully achieved in the current permit term and target dates for fully achieving all WLAs.
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 from existing conditions. 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 information on the effectiveness of Best Management Practices (BMPs) is often expressed as a percent of pollutant removed.
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 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 means any wasteload allocation assigned to a regulated MS4 in an EPA-approved TMDL. The permit conditions apply only to those TMDLs approved prior to the effective date of the General Permit and are the only WLAs that must be addressed in the SWPPP Document. MPCA created a spreadsheet containing WLA information for all TMDLs approved prior to the effective date of the General Permit. The spreadsheet is located on the MS4 Permit Program website. Each line on the spreadsheet represents a different WLA, and all that are assigned to an MS4 must be included in the SWPPP Document. The information that must be included, at a minimum, in the SWPPP Document is as follows:
For each applicable WLA not met at the time of application, a compliance schedule is required. Compliance schedules can be developed to include multiple WLAs associated with a TMDL project and shall include:
For each applicable WLA the permittee is reasonably confident is being met at the time of application, the permittee must provide the following documentation:
For each WLA not being met at the time of application, a compliance schedule must be included in the SWPPP Document. The compliance schedule must demonstrate that progress toward reducing pollutant loads will be achieved within the permit cycle. Multiple WLAs can be combined and referenced by TMDL project name to consolidate the compliance schedule. Compliance schedules must contain annual interim milestones, dates for implementation of each milestone, a strategy for ongoing implementation, and a target date for achieving each WLA. Interim milestones may be expressed in the form of BMPs, implementation of BMPs, or progress in the implementation of BMPs. Per federal rule, dates and reporting on implementation of the interim milestones must be at least annual. MPCA recommends applicants align reporting on compliance schedules with the MS4 General Permit Annual Report.
Reductions in pollutant loading are achieved by implementing Best Management Practices (BMPs). When selecting BMPs to include as interim milestones, the applicant should consider the following:
The applicant will include BMPs they plan to implement over the current five-year permit term in the Compliance Schedule section of 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 turbidity WLAs. MPCA recommends WLAs included in the same TMDL Project be grouped together and BMPs selected that address multiple WLAs when possible. MPCA also recommends BMP identification numbers be included at the time of application as they are a required component of pond inventories and annual reporting. BMP IDs should be unique and can be developed using any numeric naming convention useful to the Permitte (e.g. POND-0362). A long term strategy and target date must also be included in the compliance schedule that describes the approach the Permittee will take to continue to recognize reductions in loading from their MS4 until all WLAs are being met. Incorporating pollution prevention strategies that reduce or eliminate pollution at its source can be an effective approach when developing long term strategies. This may include a general timeframe developed as part of the TMDL report or TMDL Implementation Plan, or a schedule the Permittee finds more appropriate. To incorporate this into the SWPPP Document, include a short narrative statement describing a general approach the Permittee will take to continue implementation of BMPs, making progress toward the ultimate achievement of all WLAs. It should be noted target dates that extend beyond the current five-year permit term are expected for WLAs requiring a significant reduction in pollutant loading from an MS4. In subsequent permitting cycles, the target date can be refined to more accurately reflect full implementation of BMPs to achieve the WLAs.
Please see Guidance for completing the TMDL reporting form.