Updating the Minnesota Stormwater Inspection and Maintenance Resource Guide

UPDATES: November 2025 | Volume 20, Issue 3

Contributed by Andy Erickson, John Gulliver, and Peter Weiss

Stormwater best management practices (BMPs) or stormwater control measures (SCMs) operate at their greatest efficiency when properly maintained. In most fully functioning applications, SCMs are designed to provide specific pollutant removal efficiency. Most are designed to capture and treat the first inch of runoff for water quality, to settle and retain particles of sediment, and retain or remove dissolved substances for a specific contributing sub-watershed. As it fills with debris and sediment, the SCM’s efficiency decreases to the point of being non-functioning unless it is properly maintained. The goal is to provide proper maintenance at a proper frequency in order to maintain the most cost-effective balance between total lifecycle cost and SCM performance.

The Challenge

Stormwater control measures require a substantial commitment to maintenance, including regular inspections and assessments. Existing regulations require governmental units to develop a systematic approach for on-going inspection and maintenance to ensure that they are achieving their desired treatment goals. A lack of maintenance will lead to a decrease in SCM performance and will often result in expensive rehabilitation or rebuild. 

In 2009, SRF Consulting produced a maintenance guide for the Local Road Research Board (LRRB) (Marti, et al. 2009). It addressed local Minnesota government inspection and maintenance activities for various categories of SCMs. In 2023 the LRRB commissioned the University of Minnesota St. Anthony Falls Laboratory to update this guide to reflect new best practices. The updated guide is a supplement to the Minnesota Stormwater Manual (MPCA 2023) and will help you plan for recommended long-term maintenance activities. 

What We Did

We expanded the scope to include visual inspection, capacity testing and synthetic runoff testing in addition to maintenance (Figures 1 - 4), with guidelines as to which is appropriate for each situation.  In addition to stormwater ponds, sedimentation chambers, infiltration practices, filtration practices and biofiltration practices, we also included floating treatment wetlands, sand filter amendments to capture dissolved constituents, full-depth permeable pavement, stormwater harvesting with case studies, and a chapter on meeting stormwater management objectives by targeted pollutant. Finally, we included the results of a survey on the factors that frequently caused deterioration of the stormwater treatment practice and typical maintenance costs and their range. The appendices have inspection checklists that are PDF fillable forms, intended as a resource so that users can edit, copy, and amend for their needs.  The appendices also have typical maintenance activities related to action items identified in the inspection checklists.

What We Found

As shown in Figure 5, Erickson et al. (2010) breaks maintenance activities into three categories: routine, non-routine, and major. Routine maintenance occurs frequently (e.g., once per year or more) on a regular schedule, and is typically less time and/or labor intensive per site visit than the other categories. Examples of routine maintenance are visual inspection, mowing grass, raking the surface of a sand filter, litter and trash removal, and weeding.

Non-routine maintenance is less frequent than routine maintenance, irregular (i.e., only as needed, not scheduled) and is more time and labor intensive per site visit than routine maintenance. Examples of non-routine maintenance include structural repairs, sediment removal, and partial rehabilitation of the practice. 

Major maintenance actions are rare, very time and labor intensive, and include actions such as replacing an entire media bed in a filtration practice, full rehabilitation of the practice, or total reconstruction.

The frequency of any maintenance activity, regardless of its level on the maintenance pyramid, depends on a vast array of variables including type and characteristics of the particular practice, watershed size, land use and soil characteristics, type and number of trees nearby, amount of construction in the watershed, and rainfall patterns and amounts. While maintenance schedules should be determined for each individual practice, typically, routine maintenance occurs from 2-4 times per year with more frequent maintenance sometimes being necessary, such as in the first year following construction. 

The first step in optimizing life-cycle costs of a SCM is its assessment to determine if it needs maintenance. Assessment is the evaluation of the practice to determine if it is functioning as desired. Thus, all maintenance plans and budgets should include the regular assessment and corresponding resources for the assessment of SCMs. There are various levels of assessment that span a wide range of difficulty and cost. Erickson et al. (2013) list four levels of assessment, in increasing levels of time and cost, as 1) visual inspection, 2) capacity testing, 3) synthetic runoff testing, and 4) monitoring.

These levels range from simple visual inspection and documentation that may take 30 minutes to 1 hour per site and inspection to monitoring of natural runoff events that may last for months or years. Thus, the construction of any stormwater treatment practice must be accompanied by an assessment and maintenance plan with a corresponding budget to support the plan for as long as the practice is to remain in service. More details about conducting any of the four levels of assessment and about recommended maintenance activities for specific stormwater treatment practices are provided by Erickson et al. (2013).

What you can do

If you are managing the maintenance of stormwater treatment facilities, these guidelines are made for your use as a resource and implementation tool.  The fillable PDF forms may prove useful, as well as the list of maintenance activities related to action items identified in the inspection forms.  An understanding of the treatment processes utilized by SCMs can also prove useful in diagnosing performance challenges in your stormwater treatment practice.  A short identification of these processes is included in the inspection and maintenance guideline.

Due to the multitude of variables involved, optimizing the total life-cycle costs of a SCM may never be perfect. With regular assessment and maintenance, however, the effective life of an SCM can be extended and the costs associated with maintenance minimized. The updated Minnesota Stormwater Inspection and Maintenance Resource Guide is designed to help you choose the proper assessment tools and the corresponding maintenance activities that are best suited for your SCMs and, thereby, optimize life-cycle costs to the greatest extent possible.

To access the full guide, please visit: Erickson, AJ, Gulliver, JS, and Weiss, PT. (2024). "Stormwater BMP Inspection and Maintenance Resource Guide." MnDOT Report no. MN 2024-09. https://www.cts.umn.edu/publications/report/stormwater-bmp-inspection-and-maintenance-resource-guide and https://researchprojects.dot.state.mn.us/projectpages/pages/projectDetails.jsf?id=28083&type=CONTRACT Minneapolis, MN, June 2024.

References

• Erickson, A.J., J.S. Gulliver, J.H. Kang, P.T. Weiss, and C.B. Wilson, 2010. Maintenance of Stormwater Treatment Practices, Journal of Contemporary Water Research and Education, 146, pp. 75-82.
• Erickson, A.J., P.T. Weiss and J.S. Gulliver, 2013. Optimizing Stormwater Treatment Practices: A Handbook of Assessment and Maintenance, Springer, New York, NY.
• Marti, M., J. Giese and L. Goddard. 2009. Stormwater Maintenance BMP Resource Guide. Minnesota Department of Transportation Report No. MN/RC – 2009RIC12. St. Paul, MN. http://www.lrrb.org/PDF/2009RIC12.pdf
• MPCA (Minnesota Pollution Control Agency). 2023. Minnesota Stormwater Manual. https://stormwater.pca.state.mn.us/