The purpose of the maintenance program is to provide scheduled cleaning maintenance and inspection of the sanitary sewer collection system. The system is designed to use gravity by following the drainage contours throughout the City. Missouri Basins I,II, and III, Mud Creek, Copper Creek, and Quail Creek are among some of the sub-drainage basins. The large basins are broken up into smaller sub-basins of which there are 24 total throughout the City. The sanitary sewer mains and manholes within those sub-basins are then scheduled and targeted for maintenance and inspection as a group, broken up into identifiable network systems.
Cleaning of the pipelines is necessary to prevent stoppages from happening. A stoppage occurs when the pipe becomes clogged, and wastewater can no longer flow and starts to backup within the pipe. This backing up of wastewater could lead to a Sanitary Sewer Overflow (SSO). An SSO is defined as any overflow release, discharge, or diversion of untreated or partially treated wastewater from a sanitary sewer system. The two most common SSOs are basement backups and wastewater discharges from manholes.
Stoppages are caused by a variety of factors: debris; fat, oil and grease (FOGs); tree roots; and paper products. These factors intermingle within the pipelines and start sticking together to create a mass that can eventually become the full diameter of the pipe and causes it to clog. The City works very hard to keep this from happening as part of the Collection System Maintenance Program.
Sanitary Sewer Overflow (SSO) and Sewer Inspection (SI) Program
PRIVATE SEWER ISSUES – Information for Homeowners and Residents
Number of Stoppages Per Year are approximately 12-15
Yearly Reliability Goal Rate of 99.9% for approximately 55,000 Wastewater Customers
As you can see, the City does a pretty good job in keeping the number of stoppages low and under our target of 20 or less per year.
High Pressure Sanitary Sewer Cleaning Equipment – Called a Jet truck
To help prevent stoppages the City uses "jet trucks" to provide maintenance cleaning of the sanitary sewer system. Two manholes are opened on either end of the pipe segment to be cleaned. On the downstream end the jet nozzle is lowered into the bottom of the manhole. It is connected to the truck by a long, high pressure hose. The water pressure is turned on and the jet nozzle is propelled up the line, against the flow of water, until it reaches the upstream manhole. Then the nozzle is brought slowly backward while spraying a jet of water onto the interior walls of the pipe. This water knocks down debris, grease, some roots and cleans the inside of the pipe smooth again. The cleaned pipe is now free flowing and at full capacity once again. Most pipes are cleaned once a year. Some pipes are cleaned as often as every three months.
Another maintenance effort involves the removal of tree roots from sanitary sewers. Tree roots can be a real menace, damaging sewers, catching debris and causing sewers to clog. Tree roots seek the moisture and nutrients offered by leaky pipe joints and service connections. Tree roots are most often found in vitrified clay pipes, which are often in parts of town built before 1980.
To control the growth of roots within the collection system a mechanical cutting device or rootsaw is used. Mechanical cutting involves attaching a cutting blade to the jet nozzle, which will spin inside of the pipe to cut the roots off. While this method is effective in removing the roots it does not keep them from growing back.
Internal Pipeline T.V. Inspection (CCTV)
One of the critical components of the preventative maintenance program involves internal inspection of sanitary sewers using a T.V. camera. The camera has a rotating head, lights, and zoom functions which allows 360 degrees of viewing of the pipe interior. The camera is attached to a crawler track which is remotely controlled. There is a video cable attached to the crawler track and camera providing power, control and video feed back to the TV van. The camera head is turned to view service connections and any defects found, which are then recorded and put into an asset management system. This information is then used to determine the conditional rating of that pipe segment and if immediate repairs are required or not. The video information is also used to determine the effectiveness of the pipeline cleaning and root control maintenance activities. New sanitary sewers are also inspected to make sure they were installed per plan and City specifications. The City's goal is to video inspect each pipe on a 12 year or less interval.
Sewer Line Repairs
The Collection section staff self-performs some sanitary sewer line and manhole repairs. City staff usually performs repairs on lines and manholes that are found to be in critical condition with signs of imminent failure. Other repairs are grouped together, bid out, and performed by contractors.
Types of pipeline repairs and rehabilitation
- Point Repairs – When less than a 5' section of pipeline needs to be replaced.
- Pipe Line Replacement – When a greater than 5’ section needs replacement, has is a low spot in the line, or when the line needs to be moved to an alternate location. This type of repair uses an open trench excavation method of construction.
- Pipe Bursting – When the entire line needs replaced, but the location and grade are still good. This method displaces the old pipe with a new pipe and requires only minor excavations.
- Cured in Place Pipe Lining (CIPP) – This method inserts a new pipe lining into the old pipe to increase structural strength and seal up any cracks and holes.
- Spot lining – This method inserts a new lining into an old pipe but only covers a 2-4' section
The City typically repairs and rehabilitates over 2,000 feet of pipeline yearly. The budgeting for the repairs can be seen in Wastewater's Capital Improvement Program (CIP). These CIP projects are reviewed and approved by the Bellevue City Council.
I/I Removal and Reduction
Infiltration/Inflow (I/I) is extraneous water that enters the sanitary sewer system. Inflow is water that is intentionally and illegally put into the collection system by sump pump connections, roof drains or foundation drains. Infiltration is water that enters through cracks or leaky joints. An important ongoing task is to locate and remove these sources of I/I. Excessive I/I can overload the sewer system, cause basement flooding and overload the sewage treatment facilities. The City is working on developing additional programs to mitigate I/I sources.