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The Challenge Nationwide, the Federal government has identified at least 772 communities, including Omaha that must address their combined sewer system overflows. This unfunded Federal mandate means we must reduce the number of raw sewage overflows per year to the Missouri River and the Papillion Creek from about 58 to four. The combined sewer area encompasses 51 square miles of eastern
Omaha which has been divided into 10 study basins. The area stretches
from 72nd Street east to the Missouri River and from I-680 on the
north to Harrison Street on the south. However, the entire sewer
system, east and west of 72nd Street function as one sewer system.
Omaha’s total wastewater service area is 275 square miles
in Douglas and Sarpy County and provides sewage treatment for a
population of about.550,000. What is a Combined Sewer System?
In Omaha’s combined sewer system, gates or weirs divert the sanitary sewage during dry weather into an interceptor sewer, which takes it to a wastewater treatment plant. In dry weather, the amount of sewage flow is comparatively small, and can be handled without an overflow. In wet weather, stormwater mixes with the sanitary sewage, significantly increasing the flow rate. If the amount of the mixed flow is large enough, it will flow over the top of the weir or through the gate, and out into the river or stream. When this happens, it’s called a CSO. In Omaha, CSOs are discharged into tributaries of Papillion Creek or directly to the Missouri River. Rainfall greater than about one tenth of an inch is typically enough to cause a CSO event in parts of our Omaha system. In newer areas of Omaha, separate sewer systems conveys sanitary sewage to the treatment plants and stormwater to waterways through separate pipes.
Omaha is one of at least 772 CSO communities nationwide, and one of 22 CSO communities in the four-state region of Nebraska, Iowa, Missouri, and Kansas, whose older areas have infrastructure was designed to overflow in wet weather. Omaha’s combined sewer collection system dates back to the 1800s, and was originally designed to simply move wastewater and stormwater out of the increasingly urbanized areas, and allow the Missouri River to disperse and carry pollution away. By the 1960s, it became apparent that dilution was not the total solution to pollution, and a system of diversion structures, pumping stations, and interceptor sewers was constructed to direct dry weather flow (sanitary sewage) to treatment plants before discharge to the Missouri River.
Since the 1960s, Omaha’s newly constructed sewer systems include separate pipes for wastewater and stormwater and many projects have been initiated to separate parts of the existing combined sewers to prevent backups of sewage into basements. However, we still have most of the old combined sewer system in use. The combined sewer system is generally located between the Missouri River and 72nd Street, ranging from Harrison Street on the south to the I-680 area to the north. It includes over 51 square miles (33,000 acres and 7,300 blocks) and 32 CSO outfalls. Eleven of the CSOs discharge to tributaries of Papillion Creek, and 21 CSOs discharge to the Missouri River. (Add link to Omaha map with CSOs).
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