A Municipal Separate Storm Sewer System (MS4) consists of a city's stormwater conveyance system including underground pipes, roads with drainage systems, gutters, and ditches.
Infrastructure totals (including City, State, and private assets) in 2019 for the City of Kalispell:
The City of Kalispell is designated as a Small MS4 and is permitted under the Montana Department of Environmental Quality's MPDES General Permit for Storm Water Discharges Associated with Small Municipal Separate Storm Sewer Systems (MS4s).
The Permit requires Kalispell to develop, document, and maintain a Stormwater Management Program (SWMP) (PDF) to reduce the discharge of pollutants from the Small MS4 to the maximum extent practicable.
The goal of the program is to protect and improve local water quality because most stormwater enters local rivers and streams without any treatment.