Jump to Navigation

Maintenance of Stormwater BMPs: Frequency, effort, and cost

November-December 2008 issue, The Stormwater Newsletter
By Joo-Hyon Kang, Peter T. Weiss, John S Gulliver, Bruce C. Wilson

Although many resources are available to aid in the design and construction of most structural stormwater best management practices (BMPs), few guides exist pertaining to their operation and maintenance. Historically, it seems as though a “build ’em and walk” approach has been commonplace. However, increasing focus upon mass balances, numeric goal setting, and total maximum daily loads (TMDLs) now requires that much more emphasis be placed upon BMP operation and maintenance for permitting and reporting requirements—for example, for the National Pollutant Discharge Elimination System (NPDES) municipal separate storm sewer system (MS4) permit program, and as a part of stormwater pollution prevention plan (SWPPP) reporting.

Typically, we think of structural stormwater BMP operation for optimizing (1) the removal of pollutants and (2) the reduction of runoff volumes/rates via the management of stormwater networks or treatment trains. BMP maintenance is the purposeful management of a BMP to maintain a desired level of performance and efficiency. Maintenance consists of short-term (routine or more frequent), long-term (non-routine or less frequent), and major (rare) actions (Figure 1).

Stormwater BMPs have a lifecycle from their creation (design and construction) through operative stages (functional or not) that is largely dictated by operation and maintenance (O&M) actions. As maintenance involves a significant amount of resources (personnel, equipment, materials, sediment disposal expense, etc.), the more we learn about BMP operation, the more likely we are to maintain optimal performance and improve cost efficiencies. The purpose of this article is to advance short- and long-term maintenance considerations to develop more realistic O&M plans. To do this, we have used a combination of a national literature search for maintenance costs coupled with a detailed municipal public works survey.

Minnesota BMP Maintenance Survey
The statewide survey of Minnesota Municipal Public Works managers to define maintenance needs and guidelines was conducted by the University of Minnesota and partly funded by the Minnesota Pollution Control Agency. Previously, the University of Minnesota produced a manual, Assessment and Maintenance of Stormwater Best Management Practices, which includes source reduction and four levels of assessment (from visual to state-of-the-art monitoring). The manual is available online at www.pca.state.mn.us/water/stormwater/stormwater-research.html or wrc.umn.edu/outreach/stormwater/bmpassessment/index.html.

The specific goals of the survey were to identify and inventory stormwater BMP maintenance in Minnesota. Survey questionnaires focusing on the following questions were sent to 106 cities; we received 27 responses, for a slightly higher than 25% response rate.

How many BMPs are in your watershed?
How often are your BMPs inspected?
What is the average staff-hours spent per routine inspection/maintenance?
How complex is the maintenance of your BMPs?
Which factors most frequently cause the performance deterioration of your BMPs?
What are the costs for non-routine maintenance activities?

We attempted to make the survey as simple as possible, requesting information for typical response ranges of common BMPs. Although the number of respondents was relatively low, we believe that the results will help refine operation and maintenance needs.

Inspection Frequency and Staff-Hours. The required frequency of stormwater BMP maintenance actions and the associated required staff-hours are two key parameters that are necessary to reasonably budget and schedule inspection and maintenance. Frequency and staff-hours vary according to BMP design, climate conditions, accessibility of the BMP, and maintenance strategies of the BMP operators. As part of the survey, cities were asked to provide information regarding their frequency of routine maintenance actions for various kinds of BMPs.
For entire article, please see website.