What are Stormwater Utility Credits?

About 50% of stormwater utilities fees are accompanied by partial fee reductions or ‘credits’ offered to residents or property owners in order to incentivize stormwater runoff retention and treatment using various Best Management Practices (BMPs) (Zhao, Fonseca, & Zeerak). The idea is, the less impervious cover you have, the less you are contributing to stormwater pollution, and therefore the lower your stormwater utility fee is. Stormwater utility fee credits typically take the form of Green Stormwater Infrastructure (GSI) implementation, helping to mitigate against the harmful effects of stormwater pollution. GSI uses natural methods to absorb rainfall and runoff and prevent it from running along impervious cover and into storm drains. GSI addresses both stormwater runoff volume and quality, protecting natural waterbodies and preventing infrastructure damage and flooding.

A Breakdown of the Legislative Language

As of July 1st, 2022, House Bill 5506 requires that any established stormwater authority within Connecticut must now provide a credit system with their utility. At a minimum, the stormwater authority in place must offer a partial fee reduction for any property owner who,

  • Has disconnected a percentage of such property’s impervious surfaces from the municipal separate storm sewer system, combined storm sewer system or surface water, and
  • Provides documentation to the satisfaction of the stormwater authority that current stormwater best management practices or other control measures, approved by the stormwater authority, that reduce, retain or treat stormwater onsite are being applied and maintained

What does it mean to disconnect impervious area?

Impervious area is considered to be ‘disconnected’ when, “the appropriate water quality volume has been retained” in compliance with the MS4 permit. As a reminder this means when the first 1” of rainfall (i.e., minimum “Water Quality Volume”), infiltrates into the ground or is otherwise permanently retained on site. Detention does not count. You can retain stormwater on site in many ways as long as it infiltrates the ground or is reused without a surface or storm sewer discharge. In most cases, disconnection will be achieved through common GSI practices or by simply directing runoff to a vegetated area such as a lawn rather than into the stormwater system.

For what property types are credits required for?

Because the legislative language specifies that a fee reduction must be offered for ANY property owner, this means that there either has to be specific credits offered for all property types (res, non-res, commercial, industrial, etc) or there has to be vague credits which all property types can apply for. Virginia has similar legislative language in regards to credits, specifying that,

A locality adopting such a system shall provide for full or partial waivers of charges to any person who installs, operates, and maintains a stormwater management facility (Code of Virgina, § 15.2-2114 (D)).

In order to satisfy these requirements, Waynesboro, VA offers basic stormwater quality and quantity credits that any property owner can apply for. Both credits offer a 10% reduction in fee price if the BMP is approved. This is a great example of basic credits for any property owner.

On the other hand, Alexandria, VA offers separate credits for all property types – Residential, Non-Single Family Residential, Non-Residential (industrial, construction, etc), as well as credits for any property type to apply for.

Are credits required for exceeding stormwater management requirements which are already present?

The legislation also provides stormwater authorities the ability, should they so choose, to provide a credit for any property owner who has installed and is properly maintaining GSI which reduces, retains, or treats stormwater on-site and which exceeds any GSI infrastructure requirements as specified by a designated stormwater permit, DEEP, or a local stormwater ordinance:

  • The stormwater authority may provide a partial fee reduction for any property owner in its district who has installed and is operating and maintaining infrastructure that reduces, retains or treats stormwater onsite, which infrastructure exceeds any requirements for infrastructure that may be applicable to the property 
  • The new Connecticut Stormwater Quality Manual goes further in depth of what it means to receive full recognition and completion of disconnecting an impervious area, either through conversion or disconnection:

    Impervious Area Conversion

    An impervious area conversion is met when, “an existing impervious surface is converted to a pervious vegetated surface and the pre-development infiltration rate and storage capacity of the underlying soils is restored”. This credit is more geared towards construction or industrial development or re-development. The existing impervious surface must be replaced with a pervious vegetated surface and the original soils must tested and adjusted to restore the pre-development infiltration rate and support vegetation.

    Impervious Area (Simple) Disconnection

    An impervious area (simple) disconnection is met when “runoff from rooftops, driveways, roads, parking lots, and solar arrays is directed to a qualifying pervious area (QPA) such that the appropriate portion of the water quality volume is dispersed and retained / infiltrated on-site without causing erosion, basement, seepage, or negative impacts to adjacent downgradient properties. The stormwater runoff must be re-directed as sheet flow to the specified pervious area which has met the design criteria as described in the Stormwater Quality Manual. Soil testing is also necessary to test the permeability of the receiving pervious area. For more information on specific stormwater runoff minimum requirements, see Ch. 5.

    Deciding Factors of a Credit

    Credits can come in all shapes and sizes. They can be designed based on BMP use, property type, and total crediting amount. The malleability of credit systems allows it to be shaped to be the best fit for a stormwater utility. The 3 main deciding factors of a credit are the property type, the BMP type / use, and how much the fee will cover. The combinations for how to design your credit are endless, so it is best to mold them based on the enabling legislation, the established stormwater utility, and the makeup of the community.

    The most common examples of property types addressed by credits are residential and non-residential. There are also credits which can be offered for educational facilities. Here is a breakdown of common set ups for each property type:


    While not as common as credits for non-residential properties, residential credits can offer great incentives to boost impervious cover disconnection and fee reductions for any residents who many not be as apt to pay a new utility fee. It is important to evaluate your stormwater utility fee and ensure that any residential credits which area provided create a push towards GSI implementation that actively reduces stormwater pollution all while no creating a loss of profit with the fee. In a study performed in 2014 evaluating the hydrologic and economic efficacy of stormwater utility credit programs in the US for residential properties, it was found that of the examined utilities, the ones which had minimum treatment requirements provided “a higher reduction in runoff than constituted in the discount” while other utilities experienced a higher discount for a fraction of the reduction in runoff (Kertesz, et al 2014).

    Most often, residential credits provide a percentage for fee reduction or an amount in billing units in return for the implementation and maintenance of GSI on the property. Rain gardens, rain barrels, cisterns, permeable pavements, and green roofs are all common examples of qualified implementations:


    Residential properties can earn a credit of 0.5 Stormwater Billing Unit (SBU) for every whole increment of 600 sq. ft. of impervious area treated, up to a maximum of 0.5 SBU for properties with less than 1800 sq. ft. of impervious area, and 1.0 SBU for properties with 1800 or more square feet of impervious area… Credits are available to residential properties that treat impervious area with the following structural controls: cisterns, dry wells, modified French drains, permeable pavers and rain gardens (Stormwater Credit Manual; Portland, ME).


    To receive a 25% credit, at least 25% of the property’s total on-site impervious surface area must drain to the rain garden. In order to receive a 50% credit, at least 50% of the on-site impervious surface area, including rooftops, must drain to the rain garden (Stormwater Utility Fee Credit Manual for Residential; Harrisonburg, VA).


    50 percent of the property’s roof area must be connected to rain barrels or other storage devices that provide at least 50 gallons of storage per downspout…. Must drain in no less than 24 hours and no more than four days after each rainfall event. Overflows from storage must be directed to appropriate outlets or areas and away from neighboring properties, sidewalks, steep slopes or retaining walls (Single Family Residential Property Credit Manual; Richmond, VA).


    While these are typical residential credits, there are a variety of non-structural BMP options. For example, Alexandria, VA offers residential credits for ‘No Fertilizer’ pledging and native tree planting, while Senoia, GA offers septic tank maintenance and natural land conservation residential credits.

    In order to maximize stormwater pollution reduction without a profit loss on the fee, most cities and towns place a cap on the amount of credits a residential property can receive. This is calculated based on impervious area size, peak flow of a storm, and the ability of a BMP to retain stormwater runoff. Cost of stormwater management and administration expenses must also be taken into consideration when deciding on credit caps. However caps are not required and there is no one correct cap to use. For example,  Roswell, GA’s approach offers 100% reduction for the first year of a residential credit for rain barrels, which is reduced to 25% for the following years.


    Non-Residential properties include properties such as facilities and buildings, industrial facilities, and developments. These properties are often split into two categories: credits which address stormwater quality and credits which address stormwater quantity.

    Water quality management focuses on GSI BMPs which absorbs stormwater to remove pollutants from impervious cover before they reach nearby waterways and improve runoff quality. These BMPs are typically on a much larger scale for non-residential properties. Some examples might include bioretention areas, vegetated buffers, and wet ponds. Water quantity refers to runoff reduction BMPs focused on reducing the amount of peak flow. This typically includes detention basins. Similar to residential properties, most of the non-residential credits have a cap on the amount of credit which can be received. Non-residential credits amounts are typically granted in proportion to the amount of impervious area being treated for water quality and or quantity. Some credits also specify minimum requirements as well. Here are a few examples:


    In addition to a runoff volume equal to 1.0 inch of rainfall on all impervious area, they must treat 0.4 inches of rainfall on the drainage area that is landscaped (Stormwater Credit Manual; Portland, ME).


    BMPs must be able to provide a minimum of 75% reduction in Total Suspended Solids on annual basis (Water Quality BMPs Credit; Normal, IL).


    “Storage to match peak flow for the pre-development conditions for the post-development sites for the 2, 5, 25, and 50-year storm events. Facility must also be capable for safely passing the 100-year storm event” (Detention Credit; Augusta, GA).


    As seen in the examples above, measurements of stormwater quality and quantity can be measured in various ways, such as amount (in), percentage, or compared to flow of storm events. Storm events are used to describe the chance of how much rain within a 24-hr period will fall dependent on your location. Another possible way of measuring the productivity of a BMP is through the focus on a specific impairment. For example, Bellingham, MA, addresses their main impairment of phosphorous in local waters by requiring that credits only be granted to GSI implementations which create a reduction in phosphorous. The credit grants $500 per pound of phosphorous reduced a year.

    Educational Credit:

    Stormwater utilities can also provide credits to educational facilities which incorporate approved stormwater education into their teaching. This credit does not work in the same way as a residential or non-residential credit as it does not involve the implementation of GSI. This credit works in the form of cost-reduction, meaning it simply reduces the cost of the fee, often though not always, for every student who is educated on stormwater pollution. For example, Normal, IL offers $2.50 for every 3rd grader taught per year. Augusta, GA created four tiers of education and has a range of the reduction cost for each participant from $10 to $50. However, South Burlington, VT simply offers a 10% credit for educational facilities.

    Credit Process


    The process for credits typically requires an application from property owners for the specific credit or credits they believe they qualify for. It is typical for property owners to have to apply each year for the same credit to ensure proper maintenance of the BMP and proper stormwater management. It is also typical that the credit be attached to the person, not the property. Therefore, if a person leaves their property and it goes into a new name, the new owner of the property will have to apply for all of the credits which the property qualifies for. Credit timelines vary from no expiration so long as applications are approved and the BMP is proven to be properly maintained to having a certain time cap on how long a property can have a credit for. See an example application from Salem.


    Inspections are crucial to ensuring long term maintenance and care of the BMPs. Most utilities have a baseline inspection when approving the credit but also have the right to inspect the property at any time:

    By receiving a Stormwater Utility Credit, the property owner is providing the Town or its designees with authorization to inspect the facility for operation and proper maintenance… the Town has access to the site for inspection, maintenance, preservation of stormwater runoff conveyance, infiltration, and detention areas and facilities (Stormwater Utility Credit Manual; Millis, MA).


    A right-of-entry or easement, as applicable, must be granted to the Town in order for the town to review and approve the credit application, and to perform occasional visual inspections. Right-of-entry is granted via the applicant’s or property or parcel owner’s signature on the credit application (Stormwater User Fee Credit Manual; St. Albans, VT).


    Inspections ensure that BMPs are working efficiently, and credits are being properly earned. Any improper maintenance of BMPs can be addressed during these. Typically, a period of time is set aside for any changes to be made by the property owner. If the problem persists or is not dealt with, the credit can be revoked.


    Appeals give the offer of having one’s property be re-evaluated on how much impervious cover they are contributing to stormwater runoff. If a property owner applies for an appeal, it would require an in-person visit to ensure the fee they pay is correct based on their impervious cover. Ithaca, NY has a separate application for appeals.


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