Wastewater services

The story of the wastewater treatment utility (King County Wastewater Treatment Division) now serving the Seattle-King County region began in 1956 when a group of local residents became concerned about the effect of rapid urban growth, especially the decline of Lake Washington. Learn more.

Sewage treatment capacity charge information
Information about the charge for building sewage treatment capacity. You can now pay your sewage treatment capacity charge online. Payments can be made through your checking account (e-check) or by credit card (Visa and Master Cards are accepted).

Industrial Waste Program
Designed to prevent businesses from discharging substances that can degrade the wastewater treatment process, harm workers or facilities, or affect surface-water quality.

Septage disposal
King County provides septage disposal for commercial haulers at the South Treatment Plant, Renton.

Infiltration and inflow regional control
A partnership between the county and the 34 local sewer agencies to study & identify sources of inflow and infiltration into local sewer systems.

Combined sewer overflow (CSO) control
Information on what a CSO is, where they are found in the King County system, and ongoing control projects.

Sediment management
The Sediment Management Program was developed in the late 1990s to remediate sediment contamination near county outfalls for combined sewer overflows, or CSOs, in Seattle.

Duwamish Waterway
This portal page describes King County programs to improve water quality and sediments in the Lower Duwamish Waterway.

Conveyance system improvement (CSI)
The King County wastewater conveyance system is an array of more than 250 miles of pipes and 42 pump stations that moves wastewater from local communities to the treatment plants. The CSI program focuses on upgrading and improving the existing regional conveyance system as well as planning for future conveyance extensions.

Water Quality Trouble Call Program
This program supports the Wastewater Treatment Division and other agencies by responding to water quality emergencies in King County.