Design & Drawings

Best Practice Storm Water Infrastructure Designs

The 2017 Montana Post-Construction Storm Water BMP Design Guidance Manual provides information to Design Professionals, Contractors, Project Owners, Operators, and Interested Citizens. See Section 1.2 for which chapters are relevant to you. The EPA provides tools to help calculate storm water capital and long-term maintenance costs of individual Best Management Practices (BMPs) and Low Impact Development (LID) techniques.

Economic Impact of Pollution Prevention

Ultimately, cleaner water reduces risk to economies and each Missoula resident can help. Yet, design and engineer teams build the foundation for a longer-term impact to reduce a site's pollution from entering our already impaired Missoula waterways. See this EPA fact-sheet on how designing for storm water can save money, with examples across the nation.

According to the EPA, Green Infrastructure can save communities money on water treatment, infrastruc Opens in new window

Design For Construction

Traditional construction practices may cause errors in your site's storm water designs. Avoid the most common errors with this EPA-recommended LID Construction Guide.

Within City of Missoula limits, construction activities should meet the STD-650 SWPPP Minimum Standard Requirements and expect site inspection frequencies as stated within. If your construction requires a SWPPP permit, see these instructions. The owner/operator must ensure post-construction storm water management on their property, and these designs must be included in the SWPPP permit to Montana DEQ.

Design For Soil & Drainage

Sites with steep slopes or impermeable soils may not provide suitable drainage for dry-wells. Know what percentage of clay or other impermeable soil layers are located in your subwatershed. Water from uphill drains and collects at the bottom of your subwatershed, meaning if impermeable soils are uphill or within your site, then your site's substrate may become quickly saturated and other infrastructure solutions may be required to deal with any single precipitation and run-off event. Storm water in these areas may require additional mains and pre-treatment prior to discharge.

Storm Water Standard Drawings

All projects must be designed by a qualified professional and will be assessed on an individual basis. To help you get started, the City of Missoula provides standard drawings for common storm water facilities. If you have trouble finding a standard drawing or would like to request a standard drawing created for a particular facility, please contact the Storm Water Division. Commonly asked for Missoula Standard Drawings include:

  • Standard Symbols & Abbreviations STD-SYM;
  • Storm Sewer Manhole Cover STD-300B;
  • Standard Manhole Ring & Dustpan STD-300D;
  • Sanitary & Storm Sewer Manhole STD-301 page 1, page 2, page 3, and page 4;
  • Standard 8' Precast Sump (Dry-well) STD-302;
  • Storm Sewer Manhole Cover STD-300B;
  • Oil & Sand Interceptor STD-313 for large volume projects (Development Services Engineering Utility Inspectors can identify if you have a large project);
  • Fats, Oils, Grease, and Garbage (FOGG) Interceptor STD-314 for large volume projects (Development Services Engineering Utility Inspectors can identify if you have a large project);
  • External Ejector Pump Standard STD-320;
  • Temporary Access to Construction Sites STD-408; and
  • Typical Grading and Drainage Site Plan for One- and Two-Family Dwellings STD-512.
  • A Single PDF including all Storm Water Standard Drawings from STD-600a to STD-690, including:
    • Curb Inlet STD-603;
    • Storm Water Management Curb Opening Into Boulevard STD-625;
    • Storm Water Management Curb Opening Through Sidewalk Section STD-626;
    • Storm Water Management Typical Rain Garden -- Parking Lot STD-627;
    • Storm Water Management Subsurface Infiltration Chamber Boulevard Installation STD-628; and
    • Storm Water Management Subsurface Infiltration With Pretreatment STD-629.

More questions on which designs will be accepted can be directed to Development Services at (406) 552-6630.

If you have construction project complaints or suspect illicit discharge, report online anonymously. To reach the general spill hotline during business hours call 406-258-4890, or, for after hours dispatch call 911. Missoula County's MVWQD responds to all illicit discharge complaints.