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Contaminated industrial stormwater

Information about authorization for businesses that discharge contaminated stormwater into the King County sewer system.

The King County Industrial Waste Program regulates and gives approval to discharges of contaminated stormwater to the County sanitary sewer system.

Stormwater becomes contaminated by industrial activities when it falls on areas with material handling equipment or activities, raw materials, intermediate products, final products, waste materials, byproducts or industrial machinery. (See King County Code 28.82.360 for a complete list of industrial activities.)

Where applicable, sewer charges will be levied to those discharging contaminated stormwater to the County sanitary sewer system.

The county's sewer capacity may be limited during wet weather months (November to April). Industries should take care not to cause or add to sewage overflows.

Learn more with the Discharging Contaminated Stormwater into the King County Sewer System Fact Sheet (1.75MB)

Discharging contaminated industrial stormwater to King County sewers in separated areas versus combined areas

Discharging to the King County sewer system—separated area

Those wishing to discharge contaminated stormwater to the county sewer system in separated areas must complete the following:

More information is available by contacting us and reviewing the fact sheet.

Discharging to the King County sewer system—combined area

Some areas in the King County sewage system also receive stormwater in addition to sanitary and industrial wastewater. The sewer pipes in those areas are called combined sewers and are found primarily in the City of Seattle.

If facilities are located in a combined sewer area KCIW expects them to follow best management practices. These are contained in the fact sheet.

Facilities in combined sewer areas planning to discharge stormwater contaminated by industrial activities to the county sewer system may need to complete a standard KCIW industrial wastewater discharge permit application and should contact us to evaluate the need for doing so.

Facilities in combined areas will not need to complete a supplemental application for discharge of contaminated stormwater.