Remove Pollutants from Stormwater before They Reach Your Community’s Waterbodies

Stormwater drainage pathways typically end up at a pond, lake, wetland, stream, or river. The health of those water bodies can be protected by removing pollutants from stormwater before it reaches them.

Sure, when an area receives a deluge of rain it’s not surprising that some roadways and parking lots look like the canals of Venice. But if your streets flood and your stormwater system is overwhelmed by anything slightly above a normal rainfall, or you’re noticing a decline in the quality of your community’s lakes or waterways, it may be time to see what’s going on and make plans for repairs or improvements.

Urban stormwater retrofit studies assess a city’s existing stormwater system and provide recommendations for a targeted, prioritized, and measurable action plan. The plan addresses potential quantities of stormwater as well as pollutants, with the goal of reducing their impact on our lakes and rivers. Cities might use this type of study as a resource when developing a capital improvement plan (CIP) or seeking funds to implement stormwater system repairs or improvements. In my work with municipal clients, I typically break the study into three phases:

(1) Desktop Assessment—acquire and assemble data; delineate and characterize the existing system’s pipesheds (i.e., definable areas where all stormwater drains to a single outfall within each area); create a water quality model for the existing conditions; and conduct initial retrofit screening.

(2) Field Assessment—field verify base data and modeling assumptions; field verify initial retrofit screening; identify feasible retrofit locations; select retrofit alternatives; and identify survey needs.

(3) Alternatives Analysis—prepare alternative water quality models; develop opinion of probable costs; coordinate with the city on costs and levels of maintenance; develop 30-year present-day value estimates; and rank alternatives.

Advantages to performing a citywide stormwater retrofit analysis include:

  • Informs MS4–NPDES implementation and reporting
  • Informs CIP planning
  • Produces targeted, prioritized and measurable implementation plan
  • Offers objective, defensible implementation
  • Informs and strengthens stormwater program
  • Is data-driven
  • Offers highest level of accuracy
  • Provides conceptual design elements to inform future designs
  • Can be integrated into a Complete Streets planning effort or program
  • Can be integrated into 2D H and H modeling for drainage alternatives considering grey/green infrastructure
  • Provides powerful, highly competitive grant writing foundation
  • Funding may be available to offset city’s cost of effort

Parlaying the expertise of Widseth Smith Nolting’s water quality, environmental, and GIS professionals, WSN has worked with municipal clients of varying size to complete retrofit studies, secure funding, and design and oversee construction of study recommendations. WSN is currently working with the city of Brainerd on a retrofit study, while I have worked with Baxter, Bemidji, Elk River and Grand Rapids prior to joining WSN. We can assemble a team that brings the specific experience and expertise you need to complete your community’s urban stormwater retrofit study.

For questions about urban stormwater retrofit studies, contact Widseth Smith Nolting’s water quality scientist Lorin Hatch at or 218-316-3625.