Off-site Facilities

An overview of pump and regulator stations in the King County Wastewater Treatment Service Area
(last revised, June 1999)

The King County wastewater system serves 1.3 million residents within a 420-square-mile service area. A daily average of 200 million gallons of wastewater from homes, industries and streets reach the County's two regional treatment plants through 47 pump stations, 19 regulator stations and more than 335 miles of sewer pipes beneath the streets. These sewers, which are 12-inches to 12-feet in diameter, connect to large trunk lines, which then connect to interceptors. Interceptors are major gravity flow lines that carry wastewater to the two major treatment plants.

The north/south topography, carved out by glaciers over the past ages, requires a significant number of pump stations and tunnels to transport the wastewater west and south so it can be treated and discharged into salt water.

Wherever possible, the County uses gravity to carry wastewater from local drainage basins to the treatment plants. Pump stations are used when necessary to lift sewage over hills and around lakes, to the main interceptors. These stations automatically regulate their pump rates depending on factors such as increased flows caused by heavy rains. The area feeding into the South Treatment Plant in Renton uses pump stations and gravity to transport flows into the plant. The system feeding the West Point Treatment Plant uses pump stations and regulator stations to regulate flows between pump stations and the plant. The regulation is necessary at West Point due to the combined storm drains and sanitary sewage collection system in the older parts of Seattle.

The pump stations range in size from small "package" stations handling about 250,000 gallons of wastewater a day to the largest pump station at Interbay which moves up to 133 million gallons of wastewater per day to the West Point plant. The size and number of pump stations is related to topography, population density and service area. Stations are designed to handle the peak flow from what is known as a "20-year storm" with all pumps operating. Each treatment plant also has a very large pump station to bring wastewater into the plant for treatment and another to discharge effluent, or treated wastewater, out to Puget Sound.

Treatment plant staff continuously monitor operations at each pump station 24-hours-a-day via computerized data and telemetry systems, thereby providing quick response to power outages and equipment failures. Crews check each station several times a week to ensure that equipment is functioning normally. They regularly lubricate and perform preventive maintenance on equipment and each week they clean the wet well where sewage enters the station.

Most of the pump stations were built in the 1960s when the regional treatment system was first constructed. The West Seattle station came on-line in summer 1998; the new North Creek station in fall 1999. Designed with an eye to future expansion, pump stations are improved as needed to increase pump capacity, upgrade control technology, replace old equipment and update odor control units. Architects designing improvements to a pump station consider the station's surroundings to help it blend better with its neighborhood. Many of the new stations incorporate art into the station design.

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Contents

• East Section Pump Stations
• West Section Pump Stations
• How odor is controlled
• How a typical pump station works
• Off-site Facilities Map (May 1999)
• Pump Station Highlights
• West Section Regulator Stations
• Summary
• Definitions