Municipal Separate Storm Sewer System (MS4)

MS4 means a Municipal Separate Storm Sewer System, which is a conveyance or a system of conveyances designed to capture stormwater, such as:

  • Curb, gutter, and storm drains
  • Roads with drainage systems
  • Ditches
  • Man-made channels

Small Municipal Separate Storm Sewer System (MS4) Permit

The Montana Department of Environmental Quality (DEQ) regulates discharges of storm water through Montana Pollutant Discharge Elimination System (MPDES) permits. MDT is designated as a Small MS4 and is subject to permitting requirements under DEQ’s MPDES General Permit for Storm Water Discharges Associated with Small MS4s. MDT is currently authorized under the 2010 General Permit to discharge stormwater from the MS4 system in the following urban areas: Billings, Missoula, Great Falls, Butte, Helena, Kalispell, and Bozeman. MDT has submitted an individual permit application, which is currently pending.

Storm Water Management Program (SWMP)

To protect Montana’s surface water resources, MDT implements a statewide Storm Water Management Program (SWMP). MDT’s SWMP describes the program elements and associated best management practices (BMPs) to comply with applicable storm water regulations. This program is intended to reduce the discharge of pollutants from our transportation infrastructure into local surface waters. Components of this program include:

  • Public education to raise awareness of behaviors and activities that impact storm water and to motivate action to reduce pollution;
  • Strategies to involve key target audiences in the development and implementation of the SWMP;
  • Detection and elimination of illicit (i.e., unauthorized) discharges;
  • Reduction of pollutant runoff from construction activities;
  • Control of storm water runoff from new development and redevelopment projects; and
  • Implementation of an operation and maintenance program, including training, that prevents or reduces pollutant runoff from MDT operations.

In accordance with regulatory requirements, MDT’s SWMP is specifically targeted to control storm water pollutant discharges. The SWMP is the formal document that contains the strategies MDT is taking to reduce storm water runoff pollution into Montana’s waterbodies.


MDT’s current SWMP is available online at the following location:

MDT’s SWMP Public Feedback

MDT asks for public input to improve the function of the program and further protect water quality. If you have areas of concern regarding storm water discharges from MDT’s transportation infrastructure and/or suggestions to improve other areas of the program listed above, please complete the Storm Water Management Feedback Form, or email comments to the following address: mdtms4datamanagerXYZmtABCgov.

Alternatively, comments can be mailed to the following physical address:

Montana Department of Transportation
Environmental Services Bureau
Attention: Tom Gocksch, P.E., Environmental Engineering Section Supervisor
2701 Prospect
PO Box 201001
Helena, MT 59620-1001

MDT’s Annual Report

View the annual report highlights of MDT’s storm water program efforts reported to DEQ for the previous year.

View previous years of MDT’s Annual Reports below:
2017 | 2018 | 2019 | 2020 | 2021 | 2022