For our friends in the MS4 communities, hopefully, you completed the Year 1 requirements to meet the June 30, 2019 deadline. This included, among other things, completion of a Stormwater Management Plan (SWMP), Illicit Discharge and Detection Elimination (IDDE) Plan, outfall ranking and prioritization for subsequent outfall investigations, construction site runoff control procedures, a schedule for catch basin cleaning, a schedule for street sweeping, written winter road maintenance procedures, distribute two targeted messages (depending on the community), and develop a Chloride Reduction Plan. So, what’s next?

MS4 communities must continue to work on/update the stormwater system mapping. This includes key elements and features of the stormwater conveyance system, structural Best Management Practices (BMPs), open channels, etc. 2003 MS4 communities have two years (until June 30, 2020) to complete the update of the stormwater system mapping. New MS4 communities as of the 2017 MS4 have 3 years (until June 30, 2021) in which to complete the mapping of their stormwater system. As part of this effort, the initial catchment delineations should be refined as well. Systematic investigation of problem catchments, or high-priority catchments if there are no problem catchments, is to be started. A written catchment investigation procedure must be developed by December 31, 2019.

The investigation of problem and high-priority outfalls starts with a field inspection during dry weather. If dry-weather flow is observed, then further screening is required to determine if there may potentially be illicit discharges present. This can be done using field test kits; however, screening for bacteria requires laboratory testing. The results of the screening will determine whether additional investigation is required to determine sources of illicit discharges. The outfall ranking and prioritization will also be updated accordingly.

Stormwater outfall concrete pipe with water draining out of itGood housekeeping procedures must be developed for permittee-owned facilities, including: develop inventory of all permittee-owned facilities; develop O&M procedures for municipal activities; develop O&M procedures to reduce/minimize/eliminate discharge of pollutants; develop and implement Stormwater Pollution Prevention Plan (SWPPP) for municipally-owned facilities such as maintenance garages, public works yards, salt sheds, transfer stations and other areas where pollutants are exposed to stormwater; and cover salt storage areas. Are you having fun yet?

Public Education and Outreach activities must be continued during Year 2. This involves distributing two targeted messages.

Permittees lucky enough to have discharges to waters with an approved Total Maximum Daily Load (TMDL) have additional activities to complete during Year 2 as well. Permittees subject to an approved TMDL for chlorides must begin implementation of their Chloride Reduction Plan. Permittees subject to an approved bacteria and pathogen TMDL must disseminate public education materials and work on implementation of their IDDE plan. Permittees subject to a phosphorus TMDL must have a legal analysis of their Lake Phosphorus Control Plan (LPCP) completed.

Permittees with discharges to impaired waters without an approved TMDL would be well advised to begin planning for future MS4 permit obligations as well. Impairments to waters without an approved TMDL include: nitrogen, phosphorus, bacteria or pathogens, chloride, total suspended solids, metals, and oil and grease. Did you know that leaf litter contributes phosphorus and nitrogen to stormwater runoff?

Did I mention that the Year 1 annual report must be completed and submitted by the EPA-extended date of September 30, 2019? The reporting period for Year 1 is from May 1, 2018 to June 30, 2019. The reporting period is from July 1 to June 30 for all subsequent years. The EPA has developed a template based on the 2017 MS4 permit that can be used for the annual report. The template can be found here.

The Hoyle, Tanner team of experts is available to assist you as needed with MS4 permit compliance. If you have questions, please contact Michael Trainque ( or Heidi Marshall ( at Hoyle, Tanner & Associates, Inc.


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