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July Newsline: EPA Rules to Reduce Effects of SSOs, DC Solving CSOs and More--Plus Web Exclusives
A tunnel boring machine may be the answer to the District’s combined sewer overflows (CSOs). Drilling below the city and the Anacostia River could begin as soon as 2011 to create the first of three massive tunnels designed to move urban sewage safely toward the treatment plant and away from D.C.'s rivers.
The tunnels are designed to catch the extra water and release it to the treatment plant. This is one way D.C. can counter the water quality problems from polluted stormwater and meet its requirements under the Clean Water Act.
The District is also upgrading stormwater management in the two-thirds of the city that is not drained by a combined sewer system. In these areas, stormwater and sewage move through completely separate pipes, governed by a federal Municipal Separate Storm Sewer Systems (MS4) permit.
The District has already spent $140 million to add dams, tide gates and pumping stations that have cut the annual volume of overflow by 40 percent, according to the article. But nearly 2 billion gallons still empty into its rivers each year. The Anacostia receives almost 1.3 billion gallons in an average year, followed by the Potomac with 639 million and Rock Creek with 49 million.
New tunnels will serve about one third of the District's land area, which is drained by the combined sewer system. The first tunnel will run along the Anacostia, which suffers the greatest amount of overflows and where people still seek edible fish. Each of the tunnels will be approximately 24 feet in diameter, but the Anacostia tunnel-at 13 miles in length-will be the longest.
The Anacostia tunnel is planned to start catching water in 2017, with those for Rock Creek and the Potomac scheduled for 2025.
The estimated cost is at least $2 billion. According to the Water and Sewer Authority, the annual average of 1.3 billion gallons of overflow in the Anacostia will fall to roughly 54 million. The total annual overflow in the District should drop from nearly 2 billion gallons to 138 million.
The District is seeking federal funds to help pay for its stormwater program. But without a significant influx of federal money, ratepayers could see their bill double or triple over the next 15 years.