Stormwater Management

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Let us know your thoughts, complaints or questions on the County’s Stormwater Management Program.

Missoula County is seeking public comment, questions and complaints on stormwater management to help prevent contamination of the Missoula Valley aquifer, the only source of drinking water for all of Missoula’s residents. Stormwater management is crucial for public health, safety, water quality, wildlife habitat and future development.

Small Municipal Separate Storm Sewer system (MS4)

The Federal Environment Protection Agency and Montana Department of Environmental Quality (DEQ) require urbanized areas (populations of 10,000 people or more) to obtain a Municipal Separate Storm Sewer System (MS4) permit to discharge stormwater into state waters.

Missoula County is designated as a Small MS4 and is permitted under the Montana Department of Environmental Quality's MPDES General Permit for Storm Water Discharges with Small Municipal Separate Storm Sewer Systems (MS4). View Missoula County's 2022 NOI to the DEQ.

This permit requires Missoula County to establish a Stormwater Management Program to reduce pollution from stormwater runoff. The program details the stormwater management activities the County performs, including control techniques and practices, systems, designs, good standard engineering practices and other such provisions for controlling water pollutants.

It also must include six specific methods for improving stormwater quality:

  1. Public education and outreach
  2. Public involvement and participation
  3. Illicit discharge detection and elimination
  4. Construction site runoff control
  5. Post-construction runoff control
  6. Pollution prevention and good housekeeping

Missoula County’s current MS4 permit extends through 2027.

Suggestions or Comments

To provide suggestions or comments on the Stormwater Management Program, please fill out the Stormwater Management Program Public Input Form.

To report an illicit discharge, or for questions about stormwater sampling, please contact Kelsie Alling at kalling@missoulacounty.us or 406-258-4968.

Let us know your thoughts, complaints or questions on the County’s Stormwater Management Program.

Missoula County is seeking public comment, questions and complaints on stormwater management to help prevent contamination of the Missoula Valley aquifer, the only source of drinking water for all of Missoula’s residents. Stormwater management is crucial for public health, safety, water quality, wildlife habitat and future development.

Small Municipal Separate Storm Sewer system (MS4)

The Federal Environment Protection Agency and Montana Department of Environmental Quality (DEQ) require urbanized areas (populations of 10,000 people or more) to obtain a Municipal Separate Storm Sewer System (MS4) permit to discharge stormwater into state waters.

Missoula County is designated as a Small MS4 and is permitted under the Montana Department of Environmental Quality's MPDES General Permit for Storm Water Discharges with Small Municipal Separate Storm Sewer Systems (MS4). View Missoula County's 2022 NOI to the DEQ.

This permit requires Missoula County to establish a Stormwater Management Program to reduce pollution from stormwater runoff. The program details the stormwater management activities the County performs, including control techniques and practices, systems, designs, good standard engineering practices and other such provisions for controlling water pollutants.

It also must include six specific methods for improving stormwater quality:

  1. Public education and outreach
  2. Public involvement and participation
  3. Illicit discharge detection and elimination
  4. Construction site runoff control
  5. Post-construction runoff control
  6. Pollution prevention and good housekeeping

Missoula County’s current MS4 permit extends through 2027.

Suggestions or Comments

To provide suggestions or comments on the Stormwater Management Program, please fill out the Stormwater Management Program Public Input Form.

To report an illicit discharge, or for questions about stormwater sampling, please contact Kelsie Alling at kalling@missoulacounty.us or 406-258-4968.

  • Household Chemical Disposal Facility

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    The Household Chemical Disposal Facility was open one day a month in January and February, and then open twice a week from March through October. We also hosted one large HazWaste Day Event in September. We advertise this service to Missoula County homeowners through radio ads, newspaper articles, social media postings, and posting flyers around town. Water Quality District staff also handed out flyers for the facility at an event for Missoula County real estate agents in October.

    As of October 10th, 2025, we have collected over 3,000 gallons of household hazardous waste for responsible disposal and reuse.

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    Event Details:

    • Date: April 19th
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    • Time: 12-4pm

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    Through the Pollution Prevention Program, Water Quality staff conducted individualized outreach with owners and employees at more than 30 industrial facilities. These meetings focused on promoting best management practices such as implementing secondary containment for EPA-regulated substances, maintaining fully stocked spill kits, ensuring proper outdoor storage of potential contaminants, and following responsible fueling procedures to prevent illicit discharges.

  • Informational Flyer

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    Licensed Establishment Team and Water Quality district at Missoula Public Health have partnered together to hand out informational flyers explaining to restaurant staff and owners that grease is considered a water pollutant.

Page last updated: 03 Dec 2025, 11:45 AM