| October 21, 2003
News Release During the heaviest recorded rainfall in local history Oct. 20, three of King County's 42 wastewater pump stations overflowed into Puget Sound, Lake Washington and the Sammamish River. To protect public health and water quality, crews immediately went to work to correct problems at pump stations in Bellevue, West Seattle and Kenmore. Nearly all the system's pump stations, treatment plants and pipelines were running near capacity. The Sweyolocken Pump Station in Bellevue discharged a mixture of stormwater and sewage into Lake Washington for about 25 minutes. To prevent additional overflows, a crew stayed at the station through the night to monitor and operate equipment. Up to three of the station's four pumps run under normal rainy conditions. The heavy flows Monday, however, started a fourth backup pump, overloading the station's electrical system. The 39-year-old station is undergoing a major renovation to handle flows from increased population growth. Stormwater mixed with sewage flowed intermittently throughout the day from the Murray Avenue Pump Station south of Alki Point. That pump station discharges 108 feet deep into Puget Sound about 800 feet from the shore. The heavy rains overwhelmed the pump station at times, causing intermittent discharges. Normally, stormwater flows from the station to the Alki stormwater control plant for treatment before being discharged to Puget Sound. The Kenmore Pump Station overflowed for about three hours into the Sammamish River. The overflow occurred after the wastewater utility used all available storage options to prevent storm-related problems in the Matthews Park area of Seattle and Sheridan Beach area of Lake Forest Park. Excessive flows to the county's Matthews Park Pump Station in Seattle also caused the mix of rain and diluted sewage to back up in the interceptor sewer that carries wastewater from the Kenmore Pump Station to Matthews Park. Safety flap-gates in that 48-inch-diameter sewer line beneath Lake Washington discharged diluted wastewater for about 2½ hours. County staff notified regulatory agencies of the overflows and took water samples at the three pump stations. Analysis of the results will be available Wednesday, but King County does not expected elevated concentrations of pathogens because of the high volume of stormwater. In other news, the utility diverted wastewater from its regional West Point Treatment Plant in Seattle to its regional South Treatment Plant in Seattle, an operating change that normally takes place in the fall. Both large treatment plants were able to handle wastewater flows, although the West Point plant was at or slightly above capacity because of the enormous volume of stormwater. The total wastewater flow Monday at West Point was 392 million gallons with a peak flow rate of almost 473 million gallons a day. The plant is designed for a peak flow of 440 mgd. The total flow Monday at South Plant was 122 mgd with a peak of 240 mgd. The plant is designed for a peak flow of 324 mgd. In older parts of Seattle, decades-old pipelines carry both rainwater and sewage, causing significant high flows during rainy weather. King County's combined sewer overflow system worked as designed, discharging a diluted mixture of stormwater and sewage through outfalls into lakes Union and Washington, the Duwamish River, Elliott Bay and Lake Washington Ship Canal. During normal weather, sewers in Seattle carry combined stormwater and sewage to the county's West Point Treatment Plant. Overflows occur when the miles of sewer pipe reach their capacity during heavy storms. Signs at overflow locations tell people about the possibility of overflows during storms. To limit possible health risks, King County and Seattle are engaged in a multimillion-dollar program to substantially reduce the number of combined sewer overflows. Two major new projects in the Elliott Bay/Lake Union area and Rainier Beach will store millions of gallons of wastewater until storms subside. King County is also upgrading, building and planning other wastewater treatment facilities to add flexibility and capacity to its 40-year-old system. Those improvements include pump station upgrades, the Brightwater Treatment Plant to serve north King County and south Snohomish County, and local projects to keep clean rainwater out of the region's sewer system. For more information on wastewater treatment improvements, check out these Web sites:
King County's Wastewater Treatment Division protects public health and water quality by serving 18 cities, 15 sewer districts and more than 1.4 million residents in King, Snohomish and Pierce counties. The regional utility now operated by King County has been preventing water pollution for nearly 40 years. Related Information
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