Frequently Asked Questions

King County Phase I National Pollution Discharge Elimination System (NPDES) Municipal Stormwater Permit

What is stormwater?
Stormwater is rain or melting snow that flows across the ground instead of seeping into it. If the ground is cleared, compacted, or covered with an impervious surface, more stormwater flows occur. This water typically picks up various pollutants, including pesticides and fertilizers, pet waste, oil from vehicles, and trash containing metals and other chemicals. Stormwater can also contain pollutants from sources, such as vehicle emissions, that "wash" out of the air.

What happens to stormwater in King County?
Stormwater flows downhill through various constructed collection and conveyance structures, such as ditches and pipes, and through natural pathways such as streams and rivers. No matter which route it takes, stormwater eventually reaches Puget Sound. In addition to ditches and pipes, other stormwater structures include stormwater ponds, vaults, swales, and culverts. Together, the structures belonging to one municipality such as a city or county make up what is known as that municipality's municipal separate storm sewer system. The storm sewer system is usually separate from the wastewater system, but the storm and wastewater systems are combined in some older areas, such as much of downtown Seattle.

Is stormwater treated?
Unlike wastewater, stormwater isn't sent to high-tech treatment plants before discharge. In King County, stormwater originating from sites developed after 1990 is treated onsite in low-tech facilities such as vegetated swales and "wet" ponds, which remove some of the pollutants. Stormwater generated from sites that were built prior to 1990 is not treated. Approximately 70 percent of the development within unincorporated King County was completed before 1990 and therefore receives no formal treatment.

Is stormwater a threat to the environment?
Stormwater runoff has been identified as the number-one cause of pollution in Puget Sound. Stormwater runoff has increased as land is developed and converted from forests and fields into properties with impervious surfaces. Rather than absorbing into the soil, runoff picks up more pollutants and flows at faster rates into streams and Puget Sound. Increased pollutant levels threaten both human safety and the safety of the fish and wildlife that live in streams and in the Sound. Increased rates of flow destroy the habitat functions of streams and disrupt the Puget Sound ecosystem's food web. For more information on the regional effort to restore and protect Puget Sound, please visit the Puget Sound Partnership (external link) Web site .

What is an NPDES Municipal Stormwater permit?
Congress established the National Pollution Discharge Elimination System (NPDES) as part of the Clean Water Act. The NPDES Stormwater Program is a two-phased national program for addressing non-agricultural sources of stormwater discharges. The municipal NPDES program issues permits to municipalities (cities, counties, ports, and other governmental entities) and requires stormwater best management practices to control pollutants to the maximum extent practicable. For more information on the U.S. Environmental Protection Agency's (EPA) NPDES Permit Program, please visit the NPDES Permit Program Basics (external link) Web page.

Why did the Washington State Department of Ecology issue this permit?
The Clean Water Act allows the EPA to delegate NPDES permitting to individual states that meet specified requirements. The State of Washington has met those requirements and is authorized to implement the NPDES permit program in the state through the Department of Ecology.

Is this King County's first permit?
King County was covered under Washington's first municipal stormwater permit, which was issued in 1995. The current permit became effective on Feb. 16, 2007. However, King County is covered under many other NPDES permits, including individual permits for its wastewater discharges and the Cedar Hills Regional Landfill, the industrial Sand and Gravel permit for road maintenance shops in old gravel pits, and the construction stormwater permit for construction sites of one acre and larger in size.

What other municipalities are regulated under NPDES municipal permits?
The NPDES permits were issued in two phases. Under Phase I, only municipalities of 100,000 or larger based on the 1990 census were covered under the municipal stormwater permit. In Washington, this included Clark, King, Pierce, and Snohomish counties, the cities of Seattle and Tacoma, and the Washington State Department of Transportation. Phase II extends municipal stormwater permit coverage to most municipalities in the Puget Sound Basin, in addition to many others. To see the extent of Phase II coverage in King County, view the King County Stormwater Permit Areas Map (external link, Acrobat pdf) provided by Washington State Department of Ecology.

How will my bills change? How much will I have to pay?
The Surface Water Management fee is a significant source of funds for King County's compliance with its municipal stormwater permit. There are currently no plans to raise the fee to fund the compliance program. However, permit compliance will require substantial increases in funding in some program areas. A business plan is currently being developed to ensure appropriate funding for permit compliance.

What are the repercussions of non-compliance?
The Department of Ecology and third parties (including citizens and environmental groups) can sue municipalities for not complying with permits. Penalties include fines of up to $32,500 per violation, per day.

Is the Surface Water Design Manual part of the permit?
The permit requires the use of Ecology's Stormwater Management Manual for Western Washington or an equivalent. King County is in the process of obtaining a certification of equivalency for its Surface Water Design Manual and related codes.

Will the permit affect development proposals?
Permit requirements will result in minor modifications to the existing thresholds for drainage review of development projects, and could also result in drainage or erosion and sedimentation control inspections for projects that might not otherwise receive them.

Will the permit prevent flooding?
The permit is not intended to address flooding, nor will it prevent future flooding. Visit King County's Flooding Topics Web site for more information.

What will the permit do to clean up Puget Sound?
The municipal stormwater permits are intended to reduce the volume of pollutants entering natural waterbodies, including Puget Sound, through stormwater. If they achieve their goal, the reduction of pollutants flowing into Puget Sound from stormwater could reduce overall pollution in the Sound, particularly for pollutants such as metals and bacteria that are commonly associated with stormwater.