Design & Drawings

Best Practice Stormwater Infrastructure Designs

The 2017 Montana Post-Construction Stormwater 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. Stormwater Utility design criteria is available in the City of Missoula Stormwater Specifications and Design Standards.

Stormwater 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 stormwater 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 Stormwater Division. 

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

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 the EPA website for stormwater design and it's potential cost savings, with examples across the nation.

WaterWorld Magazine, a resource serving engineers, managers, and consultants in the water/wastewater industry worldwide.  See their article titled Stormwater Management Guide, which addresses many of the most commonly asked questions about how to best manage stormwater and protect water quality.

"Designing a project site to maintain its normal stormwater flows and reduce pollutants after development is essential. The right plan prevents flooding, habitat degradation, erosion, and pollution in our waterways. Whether your project is a re-development, new development, or an urban retrofit, there are a variety of tools and techniques that can be used to meet water protection programs and regulations." WaterWorld, Stormwater Management Guide

Design For Construction

Traditional construction practices may cause errors in your site’s stormwater 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 stormwater 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. Stormwater in these areas may require additional mains and pre-treatment prior to discharge.

To better understand how soil & drainage design can effect the water quality of our watersheds, please see the following helpful reports:

Stormwater Management in Areas of Shallow Groundwater

Stormwater Infiltration Contamination

Impacts on Mountain Basin Groundwater Recharge

The Missoula Valley Water Quality District (MVWQD), a division within the Missoula City-County Health Department, responds to illicit discharges.

If you would like to report an illicit discharge or have a stormwater construction site concern you may use the online reporting form or call 406-258-4890 during regular business hours or for an after-hours matter, please call 911.