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For non-residential parcels

You can estimate the surface water management fee and discounts for a non-residential parcel by using the SWM fee calculator.

To promote the reduction or mitigation of impervious surface -- the main contributor to surface water runoff and its adverse effects (such as water quality degradation, erosion, flooding, and sedimentation), several discounts, credits, and cost-share opportunities are available to owners of developed parcels. These are briefly described below and explained in detail in a procedures document titled, SWM Fee Protocols.You can also contact a surface water customer service representative by calling 206-477-4800.

Runoff mitigation discounts

Your parcel may qualify for one of the two runoff mitigation discounts described below. To learn more about these or to request this type of discount, contact the Stormwater Services Section at 206-477-4811.

Stormwater facility discount

If you operate or bring into operation one or more stormwater flow control or water quality treatment facilities approved by King County or functioning to the performance level required by King County standards, you may be eligible to have your fee reduced. Qualifying residential parcels will receive a discount equal to half the residential fee, or $75.50 in 2013 and $85.75 in 2014. All facilities are either inspected by County engineering staff or are sent a self-certification package. Documentation of maintenance by one of these methods is necessary to qualify for the discount.
For non-residential parcels, the King County Council adopted a new discount program that has replaced the 2012 program. The intent is to reward property owners whose runoff is managed using stormwater control or treatment facilities or best management practices. The discount is contingent on completion of any required inspection and maintenance of these facilities or management practices and parcel compliance with King County code. Qualifying facilities and practices can be found in the King County Surface Water Design Manual.

A key feature of the new non-residential discount program is a tiered system of percentage discounts that can add up to a maximum 90 percent discount. The purpose is to give credit for various levels or types of stormwater controls that mitigate the runoff from developed surfaces on the parcel. Briefly, the percentage discounts are as follows:

  1. A maximum 20 percent discount is given for flow control facilities that meet any current or previous King County standard for design of such facilities. Any other qualifying discounts listed below are in addition to this discount.
  2. A maximum 20 percent discount is given for flow control facilities that meet modern design standards, that is, standards adopted in the 1990 or later versions of the King County Surface Water Design Manual. This discount is in addition to any other qualifying discounts in this list.
  3. A maximum 20 percent discount is given for flow control best management practices or infiltration facilities meeting County standards that use existing pervious areas on the parcel (lawns, low areas, etc.) to absorb, retain, or disperse runoff onsite so its discharge to the surface water system is minimized. This discount is in addition to any other qualifying discounts in this list.
  4. A maximum 20 percent discount is given for County standard water quality treatment facilities (or equivalent) that remove pollutants from runoff prior to discharge to the surface water system or to groundwater. This discount is in addition to any other qualifying discounts in this list.
  5. A maximum 10 percent discount is given to parcels in which stormwater discharges are regulated under a National Pollutant Discharge Elimination System (NPDES) stormwater permit issued by the state. This discount is in addition to any other qualifying discounts in this list.

The first four stackable discounts are prorated to the amount of the parcel's impervious surface that is served by the stormwater control eligible for discount. The table below specifies the amount of proration:

Percentage of Parcel's Impervious Surface Served by a Facility Discount Amount
4% to <20% 4%
20% to <30% 8%
30% to <40% 12%
40% to <50% 16%
50% to 100% 20%

The NPDES permit discount is not prorated and will be applied if the majority of the parcel's impervious surface (greater than 50 percent) drains to the discharge point or points covered under the permit. Please call 206-296-1900 to determine whether you qualify for this discount.

With regard to the above table, note that King County does not yet have the impervious surface-served information for every parcel. This information will be collected in 2013 and 2014 as King County inspects these parcels. In the meantime where we don’t have the actual information, we will assume that each stormwater facility or best management practice known to exist on a parcel serves 100 percent of the parcel’s impervious surface. Because of this assumption, please be aware that your parcel’s surface water management fee discount in 2013 may be reduced in future years when the above proration is applied.

65-10 discount

Your fee assessment may qualify for a discount if your property is at least 65 percent forested or native condition, has no more than 10 percent effective impervious area, and uses best management practices for dispersing and infiltrating runoff from the non-effective impervious surface are implemented. King County will need to verify the parcel conditions. In some cases, technical information such as a topographic survey may be required. Other conditions may apply and at least one site visit will be required for approval. Qualifying residential parcels will receive a discount equal to half the residential fee, or $75.50 in 2013 and $85.75 in 2014. Qualifying non-residential parcels will receive a discount of 80 percent of the SWM fee. This discount may not be combined with other runoff mitigation discounts.

    Example of the 65-10 discount applied to a 10-acre forested site:

    Total site is 10 acres.

    At least 6.5 acres remain forested, leaving 3.5 acres of land for development or impervious surface.

    Total effective impervious area (EIA) must be less than or equal to 10% (43,550 s.f.).

    Total actual impervious area (AIA) may range up to 20% (87,100 s.f.), depending on the ability of the site to “fully disperse” runoff from the AIA.

    The discounted fee for a single-family residence is $75.50 in 2013 and $85.75 in 2014.

    The discounted fee for a non-single family residential parcel is 80%.

    Example diagram: 65-10 SWM discount rate
    Using the diagram above, the SWM fee for this parcel before applying the 65-10 discount in 2013 would be $3,638.90 (rate class 3: $363.89 per acre X 10 acres). After receiving the 65-10 discount, the SWM fee in 2013 would be $727.78 ($3,638.90 x .20), reducing the fee by $2,911.12.

    In 2014, the SWM fee before applying the 65-10 discount would be $4,133.80 (rate class 3: $413.38 per acre x 10 acres). After receiving the 65-10 discount, the SWM fee in 2014 would be $826.76 ($4,133.80 x .20), reducing the fee by $3,307.04.

Impervious surface cost share and credit program

As an incentive to reduce impervious surface, King County is making funds available for sharing the costs of converting impervious surface to (1) native-vegetated landscape, (2) compost-amended lawn, or (3) grassed, modular-grid pavement. To qualify, a plot plan and description of the proposed conversion must be submitted to County engineering staff who will work with you to develop your plan. Fifty percent of costs up to $20,000 will be reimbursed after the conversion is complete and inspected.

In addition, reducing your impervious surface could potentially increase your fee discount or possibly place you into a lower rate category and reduce your fee. Only non-residential properties are eligible. The cost-sharing program is available on a first come, first served basis until annual appropriations are expended. To learn more about this program, contact the Stormwater Services Section at 206-477-4811 or refer to the SWM Fee Protocols.

Open space discount

If your property were to be classified as "open space", "agriculture", or "timber" and enrolled in the Current Use Taxation Program, or if your development rights were to be sold, you could be eligible for a fee reduction. Both residential and non-residential properties are eligible. Please visit our current use taxation page or transfer of development rights program site for more information about these programs.

Low-income senior exemption

If you are a low-income senior citizen who lives on property you own, you may be exempt from the surface water fee. The Office of the King County Assessor determines qualifications for exemption, and applications can be made by phoning 206-296-3920. Only residential properties are eligible.

Administrative appeals process

If you believe the impervious surface measurement on your property is incorrect, the calculation of your SWM fee is incorrect, or that a discount has not properly been applied to your surface water management fee, please speak to one of our customer service representatives at 206-477-4800 so that we can review your assessment promptly. In some cases, you may already qualify for a discount; in others, fee reductions may not be granted until the next year.

Visit the Common Questions and Answers page for answers to other surface water management-related questions. For more detailed, technical information about SWM fee measurement, discount requirements, how to apply for a cost-sharing grant or about pervious surface credits, refer to SWM Fee Protocols document.

For more information about SWM fee discounts and cost-sharing, please call King County Water and Land Resources Division at 206-477-4800.