Decision tools for stormwater infiltration

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This site was recently updated and is undergoing development. Anticipated completion date is July, 2015.

This page provides information for determining the feasibility of infiltrating stormwater at a site.

The Minimal Impact Design Standards (MIDS) design sequence flowchart can be used to make decisions about the feasibility of infiltrating stormwater at a site. Although the flowchart focuses on MIDS performance goals, it can be adapted to help determine if infiltration restrictions exist at a site. Potential constraints to infiltration, with links to the MIDS flowchart and other guidance in this manual, are shown below.

• Are there constraints due to lack of available right-of-way, off-site drainage and/or rate control requirements?
• Are there zoning and land use requirements that constrain infiltration?
• Is the site located in a DWSMA, wellhead protection area or within 200 feet of a drinking water well? Also see guidance on wellhead protection.
• Are there existing or proposed structures or infrastructure that constrain infiltration?
• Is karst present on the site? Also see guidance on sites with karst.
• Is shallow groundwater or shallow bedrock present on site? Also see guidance for sites with shallow groundwater or shallow bedrock.
• Is there presence of contaminated soils and/or groundwater, or hotspot runoff? Also see guidance for sites with contaminated soils or groundwater or potential stormwater hotspots.
• Are there very low infiltrating soils (<0.2 inches per hour) on site? Also see guidance for sites with soils having low infiltration capacity.
• Are there very high infiltrating soils (more than 8 inches per hour)?
• Are there adverse surface water hydrologic impacts from infiltration practices (e.g. impacting perched wetland)?
• Also see guidance on setback distances

In addition to the above questions, the sizing and design information in this manual can be used to determine the amount of infiltration feasible at a site. See sizing information in the various design sections of this manual. The MIDS calculator may also be used to calculate infiltration volumes based on BMP sizing information.

Guidance for determining the feasibility of infiltrating stormwater has been developed for locations outside Minnesota. Examples can be found through a simple Google search on stormwater infiltration guidance.

Caution: Caution must be exercised in applying guidance from other locations to Minnesota since regulations may differ.

Two examples that may be useful are indicated below.

• Wisconsin Site Evaluation for Stormwater Infiltration
• Strategies/Guidance for Managing Stormwater: Infiltration vs. Surface Water Discharge. Clark, S., Baker, K., Lalor, M., Mikula, J., and Burkhardt, C. (2005). Impacts of Global Climate Change: pp. 1-12. doi: 10.1061/40792(173)228.