The following are some frequently asked questions on how to fill out the TMDL Annual Reporting form for Municipal Separate Storm Sewer System (MS4) permittees for the 2013 General Permit. Additional information on this reporting requirement is available here.

  • Could we submit a single report for all permittees in a given TMDL project area that share a categorical WLA?

Because the MS4 permit focuses on individually-owned MS4s, each permittee must report on their implementation activities separate from other permittees. If a single report exists that summarizes information for multiple permittees, a permittee can copy information concerning their MS4 from that report into the TMDL Annual Report form.

  • What if multiple MS4 permittees collaborate to implement BMPs? Can more than one MS4 claim Category 1 credit for a BMP?

We encourage permittees to collaborate on BMPs when it results in more efficient stormwater management. It is for this reason that we developed different reporting categories. The actual reduction in pollutant loading can only occur within a specific MS4. The permittee that owns this MS4 therefore reports the reduction on their TMDL form. This is Category 1 reporting. To acknowledge contributions to the pollutant reduction, other permittees claim a Category 2 credit, which indicates they contributed to the pollutant reduction even though the reduction does not occur in their MS4.

If multiple permittees claimed the same pollutant reduction, that would result in inaccurate estimates of pollutant reduction. Also, if a pollutant reduction was divided among permittees based on their contribution, that would inaccurately indicate where the actual reduction occurred.


Permittees in TMDL X study area (outlined in blue) have a categorical WLA of 40 lbs/day (allowable load) and estimated existing loading to be 60 lbs/day. These four permittees collaborated to implement a BMP/s that reduce loading to 30 lbs/day. Since this BMP is located in City A’s jurisdiction and is reducing the pollutant discharged from their conveyance, they will claim a 30 lb reduction in Category 1. City B, C, and D will claim ‘1’ in Category 2.


  • If multiple permittees work together to implement a BMP in my MS4 and the total pounds reduced by the BMP exceed the WLA required reduction, should I only claim enough pounds to meet the WLA?

No. Claim the entire load reduction. We are interested in total pounds reduced by BMPs regardless of where those reductions are occurring. Other permittees will take Category 2 credits for the BMP.

  • How do I know when my WLA is met?

The individual permittee makes this determination. The determination may be based on multiple criteria, such as estimates of load reductions that have been achieved; the number of BMPs implemented, water quality in the receiving water, and so on. When a permittee determines they are meeting their WLA, they may tell us in their SWPPP submittal.

  • How do I decide who “owns” a BMP for the BMP-activities tab (column L)?

For the purposes of this reporting form:

Any practice that reduces pollutants prior to your outfalls, from conveyance systems owned by YOU, is a practice that you “own” regardless of who paid for it and who maintains it. If a BMP has been installed within your jurisdictional boundary, it is most likely owned by you. Water leaving one MS4s jurisdiction should be viewed as leaving through an outfall.

Coordinate with your local partners to create consistency in reporting. If you decide to claim ownership of a BMP this year, that will be your BMP to report in perpetuity.

  • Who should take category 1 vs category 2 credit on the Cumulative Reductions tab when there is a collaboration?

The MPCA stormwater program views both types of credit equally in terms of making progress and permit compliance. Category 1 credit can only be taken for BMPs constructed within your jurisdiction. When jurisdiction overlaps, a non-traditional MS4 (ex. county, watershed district, or correctional facility) defer to the City or Township unless the BMP is constructed within the conveyance system of the non-traditional MS4.



BMP 1: The watershed district can take category 1 credit. City A, B, and/or C can take category 2 credit if there is a partnership agreement in place. If BMP 1 happened to be outside the urbanized area, no MS4 would take credit for the BMP.

BMP 2: City A can take category 1 credit. The watershed district, City B, and/or C can take category 2 credit if there is a partnership agreement in place.

BMP 3: City B can take category 1 credit. The watershed district, City A, and/or C can take category 2 credit if there is a partnership agreement in place.

BMP 4: No MS4 can take credit in either category for this BMP because it is constructed outside the TMDL study area.

This page was last edited on 24 December 2020, at 17:00.


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