Why Are CSOs a Problem in Terre Haute?
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More than 130 years ago, Terre Haute built a sewer system to carry stormwater away from homes, businesses, and streets. They were generally directed to the west in order to discharge into the Wabash River. When indoor plumbing was developed, homes and businesses hooked their sanitary sewage lines to many of the storm sewers, making them combined sewers. In the 1960’s a large interceptor sewer was constructed along the river to the wastewater plant. This new sewer interceptor collected the sewage from the original sewers during dry weather and delivered it to the wastewater plant. However, when it rains or snow melts, combined sewers and this interceptor sewer are occasionally overloaded with incoming stormwater. When this happens, overflows are directed into the river through CSO diversion structures (see image), so the sewers do not back up into homes and basements. This is called a combined sewer overflow, or CSO. At the time they were built, CSOs were an acceptable way of handling excess flows, but their environmental impacts are now controlled under the present regulations of the federal Clean Water Act. Our combined sewers are located primarily within the city limits and older parts of the system, while other parts of the sanitary district are served by separate sanitary and storm sewers. However, due to the routing of the overall sewer system, sewage from many outlying areas eventually flows through the combined sewer system in the center of the city before flowing to the treatment plant.
Are CSOs a problem in other Cities?
Terre Haute is not alone in this problem. There are roughly 772 communities across the U.S. with aging combined sewer systems, according to the U.S. EPA. Over 100 of these communities are in Indiana, including Indianapolis.
Combined sewer systems are remnants of the country's early infrastructure and so are typically found in older communities. Many of these communities are faced with overflow problems similar to those experienced in Terre Haute, and they must develop plans to reduce these overflows under the Clean Water Act and subsequent adopted regulations.