Municipal Separate Storm Sewer System

Storm water is rain and snow melt that runs off surfaces such as rooftops, paved streets and parking lots that does not percolate into the soil. As water runs off these surfaces, it can pick up pollutants such as: 

  • Animal Waste
  • Fertilizers
  • Oil
  • Pesticides
  • Soil
  • Trash

Storm water can discharge into local streams, creeks, rivers and lakes. In the urban areas of Montana, storm water may go into a storm drain and continue through a storm sewer collection system until it is discharged into a local waterway. Typically, storm water is discharged into water bodies without being treated.

Storm Water Contamination & Illicit Discharges

An illicit discharge is any discharge to a municipal separate storm sewer that is not composed entirely of storm water. Illicit discharges typically refer to storm drain flows during dry periods which contain pollutants and/or pathogens and can be caused by a number of factors such as a sewage disposal system interacting with the storm drain system, accidental spills/dumping, outdoor washing of fueling areas, and non-target landscape irrigation.

Illicit discharges have significant impacts on the natural environment and receiving water body and can contribute to high levels of pollutants to receiving waterbodies, including: 

  • Bacteria
  • Heavy Metals
  • Nutrients
  • Oil and Grease
  • Solvents
  • Toxins
  • Viruses

Pollutant levels from these illicit discharges have been shown in EPA studies to be high enough to significantly degrade receiving water quality and threaten aquatic, wildlife, and human health.

If you observe an illicit discharge or suspect discharge or have general permit requirement questions please send an email to notify us. Cascade County will review all suspect discharges immediately.

Construction Related Storm Drainage

The Montana DEQ regulates discharges of storm water from construction activity through the Montana Pollutant Discharge Elimination System (MPDES) General permit. An authorization under the General Permit for Storm Water Discharges Associated with Construction Activity is required for construction activities that include clearing, excavating, grading, grubbing, or placement/removal of earth material with a total area of one or more acres. Construction projects that disturb an acre or more are required to implement Best Management Practices (BMPs) in order to minimize contamination potential associated with the construction activities.