Storing overflows underground

Known for its incredible beauty and diversity of wildlife, the Puget Sound region of Washington provides abundant opportunities for such outdoor activities as kayaking and sailing. However, local water bodies historically have been the recipients of discharges of untreated storm water and, during large storm events, combined sewer overflows (CSOs). King County and the city of Seattle have collaborated on various improvements to regional waste water and storm-water collection systems to reduce and eliminate CSOs. Using state-of-the-art tunneling technology, the Denny Way/Lake Union CSO Control Project will improve water quality in Puget Sound's Elliott Bay and in Lake Union by reducing the volume of CSOs entering these water bodies by 500 million gal a year. The project is expected to reduce the number of CSO discharge events to Elliott Bay and Lake Union from approximately 50 to 20 per year. Planning for the $140-million Denny Way/Lake Union CSO Control Project began in 1993, and operations are scheduled to begin late this year.