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A combined sewer overflow (CSO) is a discharge of raw sewage mixed with stormwater into local waterways during a wet weather event, such as a rainstorm. Overflows occur when there is too much of this mixture for the sewer system or treatment plants to handle. To relieve pressure in the system and minimize backups into homes and businesses, excess sewage overflows into local waterways.
A combined sewer is a one-pipe sewer that is designed to convey both stormwater and sanitary sewage. During dry weather, sanitary sewage alone is conveyed to a treatment facility. During wet weather, a mixture of stormwater and sanitary sewage is conveyed. With as little as 0.1” of rainfall, combined sewers can reach full capacity and begin to overflow to the Papillion Creek or Missouri River.
CSOs contain raw sewage, which can be the source of disease-causing organisms. In addition, the pollutants in CSOs can adversely affect fish and other aquatic life and can create aesthetic problems – such as odors and sewage waste and debris.
Omaha’s combined sewer collection system dates back to the 1800s and was designed to 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, lift stations, and interceptor sewers was constructed to direct dry weather flow (sanitary sewage) to treatment plants before discharge of treated wastewater 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 older combined sewer system in use.
A Combined Sewer Overflow (CSO) contains raw sewage and pollutants that include human bacteria and viruses, chemicals, oils, animal wastes and other contaminants that all have the potential to cause health concerns and illness. A CSO allows millions of gallons of untreated sewage and stormwater to enter the waterways in a typical year. Concerns associated with these discharges include:
The extent of the health concerns from a CSO discharge depend on the amount of water dilution from the size of the receiving stream, the amount of precipitation that causes the overflow, and if the overflow occurs during peak sewage periods such as the morning or evening.
A separate sanitary sewer system is a collection of pipes located under streets and easements that are designed solely to transport sewage away from the sanitary fixtures inside homes, businesses, and industry and convey it to the treatment plant. This system protects public health by treating human and industrial wastes to reduce pollutant concentrations so they can be safely discharged to the Missouri River or Papillion Creek. Cities that have these systems must also have a separate sewer system to handle stormwater.
A storm sewer system is a collection of inlets and pipes – located under streets and easements – designed to transport rainwater and snowmelt away from streets, homes, and businesses and convey it to various receiving waters (such as streams and rivers). Storm sewers are usually much larger than sanitary sewer system pipes because peak stormwater flows from typical rain events greatly exceed sanitary flows. Water discharged through separate storm sewers generally receives no treatment and may contain pollutants.
There are currently over 772 U.S. communities subject to CSO regulations. Most of these communities are located in the Pacific Northwest, Great Lakes, and Northeast portions of the country. This map shows those areas that have combined sewer systems and are on the EPA's list of regulated communities.
Even when CSO solutions are implemented, stormwater from our City will flow to streams and rivers during wet weather events. This stormwater picks up pollutants as it flows across the land, whether it comes from streets, open areas, or rooftops. You can help to reduce this pollution by:
To learn about more ways to reduce pollution, you can invite the City to make a presentation to your civic association or neighborhood group. Just indicate your interest in an educational opportunity on the Contact Form.
In the combined sewer service areas, one pipe exists to convey both sewage and stormwater. When the runoff from rain adds to the sewage component of the flow in the sewer, the system relieves itself to a creek or river at a CSO outfall. If there were no designed overflow points, the excess sewage mixture would overflow at other low-lying locations, like basement floor drains.
The rates for sewer user fees are based on the costs of service by customer classification. All customers of a given class (residential, commercial, industrial) pay at the same rate, based on their contribution. All customers (inside and outside Omaha*) will help the CSO improvements necessary to meet the federal mandates that will improve water quality for the greater Omaha region.
*Included in the service area are the cities of Omaha, Bellevue, Papillion, La Vista, Ralston, Gretna, Bennington, Boys Town and Carter Lake.
Wastewater service is a utility, like water and gas service, with charges based on contribution. However, since 2011 customers that qualify for energy assistance also receive a utility bill credit to help with rising sewer fees. The City also continues to work with local utilities and state agencies to review the existing utility assistance programs and look for ways to improve or enhance assistance to low and fixed income customers.
Nebraska water quality standards and definitions can be found in the Nebraska Department of Environmental Quality's Title 117. The main type of impairment in the metropolitan area is bacteria, and controlling CSOs will allow attainment of the standards in many Omaha streams.
Wastewater service is generally considered a utility, like water and gas service. Federal law requires that costs for wastewater service meet certain “equity” requirements, in terms of cost recovery.
In developing the Long Term Control Plan, Omaha considered how the CSO solutions were integrated into a comprehensive watershed management plan for stormwater. In most cases Green Solutions will serve as an enhancement to the structural controls that form the backbone of the CSO control plan.
Sewer separation work will be funded through fees collected from all users of Omaha’s regional treatment system. The impact of recently approved rates will mean the typical residential, who currently pays about $15/mo in sewer fees will see those bills increase to over $37/mo by 2014. Subsequent rate increases could force rates to rise to over $50 per month by 2017.
Generally, there should be no direct costs assessed to individuals’ homes or businesses where new sewers are constructed.
The rates for sewer user fees are based on the costs of service by customer classification. Customer classifications are defined in Section 31-143 of the Omaha Municipal Code and include residential, commercial and industrial. In 2009, the Omaha City Council voted and approved a rate structure for the years 2010-2014.
The newly proposed alternative rate structure would change the 2013 and 2014 rates for the commercial and industrial customers. The rate for residential customers will remain unchanged from those approved in 2009.
The proposed rate structure for commercial and industrial customers would be based, in part, on the size of the water meter used by any business.
No. Only the portion of the sewer use fee associated with the CSO Program will be determined by meter size for commercial and industrial customers. The other wastewater service fees will continue to be collected based on traditional charges such as flow, customer charges and strength charges.
After the existing rates were approved in 2009, a number of Omaha’s industrial companies told City officials that the proposed rate change would be so substantial that it could cause them to move their business out of Omaha resulting in the loss of thousands of jobs and corporate investment. The City directed the consulting firm that assists with developing sewer rates to try to find an alternate way to gather revenues needed to address the unfunded, federal CSO mandate. Over a period of more than a year, alternatives were evaluated. The City, the Greater Omaha Chamber of Commerce and a coalition of industrial customers believe that proposed alternative will provide the relief needed by our largest customers and improve the fairness of the existing rates.