MPDES Permits for Storm Water Discharges

Stormwater Construction and Sage Grouse Habitat 

Activities within designated sage grouse habitats require consultation with the Montana Sage Grouse Habitat Conservation Program. The DEQ Sage Grouse Advisory is also a source of information.

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

Storm water can discharge into local streams, creeks, rivers, lakes, or other water bodies. Additionally, in the urban areas of Montana, it 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.

Additionally, impervious surfaces in developed areas can increase the quantity of peak flows of runoff because the ability for storm water to infiltrate is greatly reduced. These peak flows can cause hydrologic impacts such as scoured streambed channels, in-stream sedimentation and loss of habitat. Finally, mass loads of pollutants in storm water can be very significant due to the volume of runoff discharges.

Impacts of Storm water

  • Human Health: In general, untreated storm water is unsafe. It can contain toxic metals, organic compounds, bacteria, and viruses. Untreated storm water is not safe for people to drink and is not recommended for swimming.
  • Drinking Water: Untreated storm water discharging to the ground could contaminate aquifers that are used for drinking water.
  • Degraded Water Quality: Virtually all of our creeks, streams, and rivers are harmed by storm water pollution. Storm water is a leading contributor to water quality pollution in waterways throughout Montana.
  • Impaired Habitat: Storm water harms and pollutes streams that provide habitat for fish and wildlife. Alterations to the watershed, such as building homes and other structures and clearing away trees and shrubs, are the leading causes for storm water pollution.

Storm Water General Permits

The Water Protection Bureau issues permit authorizations for storm water discharges associated with the following types of activities:

Storm Water Associated with Construction Activity

General permit coverage is required for construction activities that include clearing, grading, grubbing, excavation, or other earth disturbing activities that disturb one or more acres and discharge storm water to state surface waters or to a storm sewer system that discharges to a state surface water.

NOTE: Construction dewatering permits are HERE.

Storm Water Associated with Industrial Activity

General permit coverage is required for facilities conducting industrial activities that discharge storm water to state surface waters or to a storm sewer system that discharges to a state surface water. Industrial activities covered by this permit are determined by the facility’s standard industrial classification (SIC) code.

Storm Water Small Municipal Separate Storm Sewer System

General permit coverage is required for small municipalities, including non-traditional Small Municipal Separate Storm Sewer Systems (MS4s), such as governmental facilities and public campuses, that discharge storm water through a separate storm sewer system to state surface water.


Go To Facts

Click the logo to go to FACTS, the Water Protection Bureau’s online system to apply for and manage wastewater and stormwater discharge permits. All permits, individual surface and groundwater as well as general permits, are included in the system.