More cities in Montana are being classified as Municipal Separate Storm Sewer (“MS4”) cities for purposes of storm water regulations under EPA and MTDEQ. Under the federal law, MS4 cities are required to use best management practices to reduce pollution from storm water runoff.  MTDEQ is responsible for issuing general permits to the MS4 cities. In past years MTDEQ was more aggressive than the EPA BMP standards and required additional burdens such as monitoring and sampling of water quality in storm water runoff. Though this initially only affected the larger Montana cities, the history of the MS4 designation has been to reach down into lower populated cities.  Originally in 1990, only cities with populations over 100,000 were affected. By 1999, it potentially affected municipalities with 1,000 people or more. The MLCT and affected cities agree with protecting water quality and using BMPs for storm water management. What we do not agree with is having to do sampling and monitoring that is of no benefit. Sampling for the sake of sampling is an idle act.

The concern is that MTDEQ may interpret “state waters” (75-5-104(34), MCA) to include storm water retention and detention ponds, which are the BMP’s means for trapping pollutants before reaching bona fide state waters. This interpretation would require retention and detention ponds, constructed as BMPs for storm water, to have water quality compliance similar to lakes and rivers.

Such an interpretation has resulted in difficulties conducting water main flushing, fire hydrant testing, water main repair and maintenance (non-storm water discharges). That interpretation combined with the first 1/2″ treatment requirement in the current discharge permit has also raised questions about whether it is permissible for storm water leaving a site to enter the MS4 at all, and thus detention or retention ponds and basins, before the first 1/2″ of water is treated.

MTDEQ has established working groups with the MS4 cities to reach a mutually satisfactory resolution on these issues.  This process is still on-going and will take more time and work to resolve the differences.


MLCT extends its appreciation to MTDEQ for its efforts having a working group to work toward resolution of BMP requirements for mitigation for storm water quality.  The MLCT will consult with and work with DEQ if legislative changes may be needed for effective implementation of BMPs in a cost-effective and reasonable manner. The MLCT will monitor legislation and regulatory action dealing with storm water quality and MS4 regulations.