KUB addresses SSO issues through a combination of ongoing preventive maintenance (PM) programs, which monitor and clear lines on a regular schedule, and capital improvement projects, which are designed to provide long-term relief to SSO problems. PM programs use regularly scheduled inspections and cleaning to provide short-term relief for recurring problems. For example:
- Flushing/Vacuuming: Using a combination cleaner truck, high-pressure, high-velocity water is flushed through a main to move debris and grease to the next downstream manhole, where it can be vacuumed into the combination cleaner tank.
- Root trimming: Using a circular blade, roots are cut by remote control from a vehicle attachment. Cuttings are removed at the downstream manhole by the combination cleaner truck.
- Chemical treatments: A foaming chemical is sprayed into the sewer, which kills roots that have infiltrated the sewer. The roots rot over a period of months. Subsequent flushing/vacuuming will remove the remnants. Chemical treatment is effective in slowing the rate of root re-growth and is not harmful to trees or the environment.
There are also several types of capital improvements that can provide long-term relief for different problems in the system.
- Open-Cut Replacement: In traditional replacement projects, the existing sewer is excavated and replaced. It is the preferred method in gravity sewer mains that “sag,” and therefore reduce the capacity of the collection system. This type of system defect cannot be corrected by other means. It is also more applicable in areas with multiple lateral reconnections, or where the sewer must be increased in size more than the constraints of pipe bursting will allow.
- Pipe Bursting: A new main (or pipe) of the same size or larger is attached to a cone-shaped head and inserted into the existing main through a manhole or an excavation pit. As it is pulled through the existing main by pneumatic or hydraulic means, the leading cone shatters the existing pipe in place, leaving a large void where the trailing new main is pulled into place. Laterals are reconnected by excavation, but surface disruption is less than with open-cut construction. The advantage of pipe bursting over other trenchless methods is the ability to enlarge the pipe.
- Lining: A flexible resin-soaked felt liner is inserted into an existing main through a manhole, using water pressure. The liner is “cured” using steam or hot water for several hours. The liner hardens, and laterals can be reinstated using a remote cutter, without excavation. The advantage of this method is that, under ideal conditions, sewers can truly be rehabilitated “trenchlessly.” The disadvantage is that the new main diameter is slightly smaller.
If You See This Sign
If you see a sign like this one, it means that KUB has identified a sanitary sewer overflow (SSO) occuring in this area. In the event that you or your pets come in contact with overflowing water or debris from the SSO, wash the contacted area thoroughly with soap and water. The signs are temporary and will be removed by KUB personnel after the site is properly cleaned and disinfected.
How can I help? Stopping overflows and cleaning up our creeks will take hard work from all of us. You can start by discarding cooking grease in your trash and not down your drain. For more information, see our Can the Grease section.
KUB had an improvement plan in place since it began operating the city's sewer system in 1987, trying to balance system needs with rates customers could afford to pay. In recent years, however, changing emphasis on overflows by regulators and increasing public concern have driven the need to make planned improvements more quickly.
In January 2003, KUB received a Commissioners Order from the Tennessee Department of Environment and Conservation. We worked with TDEC and reached an Agreed Order in May 2003 that gave us a 10-year deadline for addressing SSOs.
With increasing expectations and the need for rate increases to fund improvements more quickly, we saw the need to develop and communicate a detailed program with clear goals and increased public education and involvement. The Corrective Action Plan included in the TDEC Agreed Order formed the backbone of the PACE 10 wastewater system improvement program that we launched in October 2004, with the understanding that it might need to be expanded based on negotiations with the EPA.
In February 2005, KUB finalized a Consent Decree that settled outstanding legal matters between us, the EPA, the City of Knoxville, the Tennessee Department of Environment and Conservation, and the Tennessee Clean Water Network.
Under the February 2005 Federal Consent Decree, KUB is spending $530 million on capital improvements over 10 years to address sewer overflows, meet regulatory mandates, and help improve area waterways to meet Clean Water Act requirements.
The cost of PACE 10, the 10-year, $530 million sewer improvement project is funded through a series of rate increases and bond issues phased in over time. KUB implemented a 50 percent rate increase in April 2005 and another 50 percent increase in January 2007. Other smaller rate increases may be needed in the future.
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