Stormwater BMP Retrofit Policies


While it is increasingly common that new development projects are required to incorporate stormwater BMPs, existing development is still responsible for the majority of poor water quality issues and was not subject to such regulations. Areas that were developed without adequate stormwater controls have ended up with decreased tree canopy cover and extensive imperviousness. The resulting large volumes of rapidly flowing stormwater have caused severe extensive erosion and threatened aquatic habitat. Retrofitting existing development is a critical step in the protection and restoration of water bodies. Stormwater BMPs present an opportunity for private property owners to reduce stormwater runoff and pollution by capturing and infiltrating stormwater on-site. Municipalities have established policies to facilitate the use of stormwater BMPs within their city-wide stormwater management program.

Retrofit Policies

When promoting stormwater BMPs, municipalities can offer several types of incentives or assistance to the public. Incentive programs are an effective way of introducing a new stormwater BMP and allowing the public to become familiar with its applications and benefits before a regulation is possibly established.

  • Subsidies: Subsidies usually offer a certain amount of money per installation or per square foot of the BMP, and is capped at either a maximum amount or a percent of the total cost of the project. The money for such programs comes from stormwater fees collected by the city or general funds. Because stormwater BMPs eliminate runoff before it enters the municipal stormwater system, thus reducing municipal facility cost, size, and maintenance, the public money can be justly spent on private properties. In time, the local market might develop such that the demand for BMP services increases, consequentially lowering the cost of technologies and reducing or eliminating the need for a financial incentives program.
  • Consultations: Providing free consultations to private property owners is a way municipalities can promote stormwater BMPs. Consultations with a municipal or private professionals can help to clear up any misunderstanding or lack of information regarding the applications, cost, maintenance, and benefits of stormwater BMPs.
  • Fee Reduction: Stormwater fee reduction based on the amount of stormwater runoff managed on-site is an incentive for stormwater BMPs that will ensure long term effectiveness. Some municipalities will waive as much as 50-100 percent of the fee, depending on the established storm event criteria. Portland, Oregon offers residential and commercial discount calculators on its Clean River Rewards web site for residents and business owners to estimate the decrease in stormwater fee.
  • Fast Track Permit Review: Philadelphia has established a "Green Project Review" program that reviews the stormwater management portion of a project submittal within five business days for redevelopment projects that have 95 percent or more of the impervious area disconnected from the combined or separate sewer system. Shortening the review time for a submitted permit offers a significant financial incentive for developers.
  • Compliance Assistance: Bremerton, Washington and Portland, Oregon have developed brochures and videos to assist homeowners on the separation of roof drain leaders from the sewer system. The cities offer to do the disconnection work for free, or they will provide reimbursements to property owners who do the work themselves.
  • Using Easements: The space restraints faced by Burnsville, Minnesota led to the launching of a public outreach campaign to involve residents in the city's public right-of-way stormwater management problem. Through grants and city funds, Burnsville built rain gardens on the edge of the private properties of the 85 percent of residents that agreed to help. The rain gardens have reduced runoff by 90 percent and the city is able to maintain the rain gardens through easements.
  • Grants: In effort to protect Lake Michigan, the Milwaukee Metropolitan Sewerage District launched the "Lake Michigan Rain Gardens" initiative, which awards grants to property owners who plant their own rain gardens. The grants are awarded in the form of plants, which are available to recipients at a "two for one" discount. This encourages the use of more plants and reduces impervious surface while improving the appearance of the property. Chicago has also provided $5,000 grants for green roof installations on small-scale commercial and residential properties.
  • Voluntary Programs: The "Mt. Airy Rain Catchers" program is a pilot program being tested in Cincinnati as part of an effort to gauge the effectiveness of incentive programs. Using an auction-based method, private property owners were able to voluntarily bid for the installation of rain gardens or rain barrels on their property, along with the dollar amount they would like to receive in exchange for hosting the new stormwater BMP. The projects would be installed and maintained by the city for three years, free of charge. Projects were awarded based on bids that yielded the largest environmental benefit, a factor determined by comparing the lowest bid amounts with the total imperviousness of the site and the expected cost of installation and maintenance. When a second program was held the following year, most residents did not request monetary compensation but were still interested in participating.
  • Vacant Lot Stabilization: Philadelphia began transforming vacant lots in 1995 by stabilizing the lots with grass, trees, and wood fencing. Community gardens were then created, trees planted, and parks renovated. This effort was funded by a combination of city money and foundation grants. A study by the Wharton School at the University of Pennsylvania found that neighborhoods with higher concentrations of unmanaged vacant lots had property values 18 percent below average, whereas properties adjacent to green lots were found to have an increased value by 30 percent. A maintenance program was established for the upkeep of the lots, which also provides green jobs for community members.
  • Stormwater Offsets: The Maryland Chesapeake and Atlantic Coastal Bays Critical Area 10 percent Rule Guidance Manual allows abandoned or vacant lots to be converted to green lots for the purpose of off-setting the effects of impervious development elsewhere in the watershed that cannot be retrofitted. The green lots, which are to remain a permanent open space, will help balance and restore infiltration rates in the watershed.


  • Milwaukee Metropolitan Sewage District. 2009. Rain Garden Grant Information Accessed December 2009.
  • Thomas R. Schueler and Heather K. Holland, The Importance of Imperviousness: Article 1 from The Practice of Watershed Protection, The Center for Watershed Protection, 2000.
  • Wharton School of Business, University of Pennsylvania. Seeing Green: Study Finds Greening is a Good Investment. 2005.
  • Wisconsin Department of Natural Resources. Impact of Redevelopment on TSS Loads, Runoff Management (PDF, 43K) Accessed December 2009.

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