Skip Navigation
Page Background

WPRF Stormwater Remediation Fee Credit Agreement

Anne Arundel County's water resources – its streams, rivers, wetlands, and Chesapeake Bay - play an important role in the quality of life we enjoy. They provide us a sense of place, recreation, support tourism, and are used by industry. These waters, however, are vulnerable to pollution from a wide variety of human activities.  In fact, all of Anne Arundel County's waterways are considered "impaired" because of excessive levels of pollution, largely a result of untreated stormwater runoff.

Land use plays an important role in how pollution ends up in our waterways. Impervious surfaces such as roads, building footprints, parking lots, driveways and other hard surfaces prevent rainfall from seeping into the ground, resulting in the potential for large volumes of stormwater to run off more rapidly and more directly into our local streams and rivers. Pollutants carried with this runoff reduce water quality and negatively impact stream health. Research shows that as the impervious surface area in a watershed increases, the ecological integrity of surrounding streams deteriorates.

The County recognizes that stormwater from public and private property , needs to be treated through the installation and retrofit of stormwater management practices, or best management practices (BMP’s), to help keep our waterways clean and meet Federal and State stormwater pollution mandates.

WPRF Stormwater Remediation Fee Credit Agreement Guidance Document

  • What is the WPRF Stormwater Remediation Fee Credit Agreement?

    The Bureau of Watershed Protection and Restoration established the WPRF Stormwater Remediation Fee Credit Agreement to provide credit to single-family property owners that have installed small-scale stormwater BMP’s on their property.

    The WPRF Stormwater Remediation Fee Credit Agreement is an agreement by and between the property owner and the County, where currently there is no Inspection and Maintenance Agreement for private stormwater management and a County grading permit was not required for the installation practice(s), and the property owner would like to apply for credit for the stormwater practice(s) through the WPRF Credit Program. The agreement would allow single-family property owners to apply for credit towards the WPRF.  The agreement also enables the County to review eligible practices for potential credit.

  • WPRF Credit Program Application Details
    Single-family property owners installing stormwater BMP’s that do not need County grading permit approval (i.e. under 5,000 sq. ft. of disturbance) and do not need an Inspection/Maintenance Agreement for Private Stormwater Management, can enter into the WPRF Credit Agreement as a part of the WPRF Credit Program application process. The below should be submitted as part of your complete application:

       - Completed Single Family Credit Application
       - Completed Single-family Residential Property Stormwater BMP Summary Sheet (included in application)
       - Photographs of BMP And Drainage Area
       - A signed WPRF Credit Agreement

    The County will review and evaluate your completed WPRF Credit Application and supporting documentation within 90 days of receipt.  For more details, visit the WPRF Credit Program page here.
  • Which BMPs are Eligible for a Credit?

    The primary objective of the WPRF Credit Program is to encourage property owners to proactively manage stormwater on their property by incorporating sustainable stormwater management practices that are used to meet or exceed the requirements found in the “2000  Maryland Stormwater Design Manual, Volume I and II” and Supplements. 

    Customers may receive credit for installing and maintaining stormwater BMP’s that limit nutrient loading (primarily phosphorus, nitrogen, and sediment) and decrease the quantity of stormwater entering the County’s waterways. 

    The following examples are typical single-family property stormwater BMP’s, however, other BMP’s may be eligible.

    Stormwater BMPDescription
    Rain GardenA shallow depressed landscaped area with perennials and native vegetation that allows stormwater runoff from impervious surfaces to be filtered.
    Permeable PavementPermeable pavement provides a solid ground surface, structurally strong enough to take heavy loads, like large vehicles, while at the same time they allow water to filter through the surface and reach the underlying soils. Permeable pavers are ideal for patios, sidewalks, and driveways. The voids in the surface of the paving allow water to drain through and infiltrate into the soil below. The underlying in-situ soils should be suitable for infiltration. 
    Rainwater HarvestingRainwater harvesting is a method by which rainwater that falls upon a surface (usually a rooftop) is collected and routed to a storage facility for future use.  To be eligible for credit, rainwater harvesting systems must include not only the cistern, but also a reliable means of using or releasing the captured stormwater e.g., dedicated use.  Rain barrels do not qualify for credit.
    Disconnected Impervious SurfaceDisconnected impervious surface is the practice of directing stormwater runoff from a built-upon area to properly sized, sloped and vegetated pervious surfaces for treatment via infiltration and filtration.  Both roofs and paved areas can be disconnected with slightly differing designs.


  • The Stormwater BMP Summary Sheet asks for "Water Quality Volume" or WQv. What is WQv?
    The Water Quality Volume (denoted as the WQv) is the storage needed to capture and treat the runoff from 90% of the average annual rainfall. In numerical terms, it is equivalent to an inch of rainfall multiplied by the volumetric runoff coefficient (Rv) and site area.
  • How is WQv Calculated?
    There are two primary methods that can be used to determine the volume of runoff from a given design storm: the Simple Method (Schueler, 1987) and the discrete SCS Curve Number Method (NRCS, 1986). Both of these methods are intended for use at the scale of a single drainage area.   Anne Arundel County recommends using the Simple Method but either method is acceptable.  

    The following equation can be used to determine the storage volume, WQv (in square feet of storage):

    WQv = (3630 * RD * Rv * A)

    Where: WQv = Volume of runoff that must be controlled for the design storm (ft3)

    RD = Design storm rainfall depth (in) ( use 1.0” in Anne Arundel County)

    A = Drainage area (ac) ; One acre = 43,560 Sq.ft 

    RV = (0.05 +0.9 * IA)

    Where: RV = Runoff coefficient [storm runoff (in)/storm rainfall (in)], unitless

    IA = Impervious fraction [impervious portion of drainage area (ac)/ drainage area (ac)], unitless. 

  • How is water quality volume used to determine the amount of credit provided?
    In general, the amount of credit is dependent on the amount of impervious area being treated in relation to the total amount of impervious area on the property and also the water quality volume treated in relation to the 1” water quality volume. By Law, the maximum credit for any property is 50% of the WPRF. The calculation is as follows:

    Total Credits = (impervious area treated/total impervious area) * 0.5 (i.e. maximum credit of 50%)

    Here is an example:

    A resident has installed a 500 sq. ft. rain garden designed for treating 1" water quality volume for 500 sq. ft. of impervious area. The property has 2,000 sq. ft. of impervious area and is currently charged a WPRF of $89.25 annually.  As the rain garden is designed to treat the full 1" water quality volume the credit is calculated as follows:

    (500/2000)*0.5 = .125 or 12.5%

    Since the current WPRF for the property is $89.25 the amount of credit is calculated as:

    $89.25*0.125= $11.16; Therefore, the new WPRF for this property is $78.09.
  • How is the credit determined for different sized projects?
    The amount of credit is dependent on the amount of impervious area being treated in relation to the total amount of impervious area on the property and also the water quality volume treated in relation to the 1” water quality volume. 
    ExampleTotal Impervious Area (Sq. ft.)Impervious Area Treated (Sq. ft.)1Credit Calculation (Max. of 50% of WPRF)Credit ReductionFinal Fee
    Residential - WPRF = $89.252,5002,500(2500/2500)*0.5 = 0.50$89.25*0.5 = $42.50$89.25 - $42.50 = $42.50
    Residential - WPRF = $178.505,0002,500(2500/5000)*0.5 = 0.25$178.50*0.25 = $44.63$178.50 - $44.63= $133.87
    Residential - WPRF = $89.252,000500(500/2000)*0.5 = 0.125$89.25*0.125 = $11.16$89.25 - $11.16 = $78.09
    Residential - WPRF = $35.702,000500(500/2000)*0.5 = 0.125 $35.70*0.125 = $4.46$35.70 - $4.46 = $31.24

    1 Assumes BMP provides full WQv (i.e. 1 inch) treatment.  Credit is lowered proportionally to the actual WQv treated in relation to the full WQv.