The District plays an important role in the water
care cycle. We treat and return over one hundred million gallons of water a day
back into the environment. Our collection system, over 2,000 miles of
underground pipe, provides valuable infrastructure for protecting the public
health. We may have several ongoing projects to rehabilitate pipelines and manholes to ensure the continued reliability of the sewer system.
These projects will also increase the capacity of the valley's sewer system as needed, enabling it to continue to efficiently and effectively serve our communities for many years to come.
Manholes are important components of the wastewater collection system that need to be repaired or rehabilitated over time. Older manholes can deteriorate with corrosion. A newer way to rehabilitate manholes is by using cured in place liners, rather than digging up the entire structure. And unlike relining sewer lines, the wastewater does not need to be diverted during the rehabilitation process.
In order to reline the manholes, the surface of the manholes must be cleaned with a high pressure wash, hydro blasting, abrasive blasting or grinding. Once the surface preparation has taken place, the manhole is inspected for any signs of leaks, cracks or other defects. Once these defects are repaired, a cured-in-place liner is installed.
The cured-in-place liner is saturated with an epoxy resin and is then lowered into place inside the structure. To cure the liner, high pressure and steam is injected. This process causes a removable inflation bladder to expand, forcing the liner to fill gaps and bond to the surface. After curing, the inflation bladder is removed, leaving a new lining in place and sealed.
When replacing the frame and cover of the manhole, a 5'x5' area is excavated. Workers only need to excavate down one foot. If more extensive repairs are warranted, or if the manhole needs to be brought up to newer codes and standards, a 10'x10' excavation is needed. Regardless of the repair that is being conducted, traffic control is required for the entire width of the traffic lane.
Traffic impacts are minor for the manhole rehabilitation projects. While workers must open cut the asphalt to replace the frame and cover and to conduct other repairs, this work can be completed rather quickly. However, if a manhole is too deteriorated to be rehabilitated, it may need to be replaced, causing traffic control to be in place for a longer duration. Traffic control will only be in place near the manhole being repaired.
When we repair or rehabilitates sewer lines, the pipes must be free of wastewater. The wastewater that normally flows through these pipes must be diverted. Bypass pumping is used to temporarily divert the wastewater through above-ground pipes that will feed into a downstream access structure or manhole.
Above-ground pipelines are attached to suction pumps at an upstream manhole. The bypass pumping lines bring the wastewater back into the public system at a downstream manhole. While the wastewater is not flowing through the original pipelines, they may be rehabilitated or even replaced.
Bypass pumping is safe, as the pipes are made of a rigid, sturdy material, that hold up even if a car drives over them. When bypass pumps are in operation, the suction pumps are manned 24 hours a day. The pipes are thoroughly inspected every hour. Odor control technologies are also utilized at both the suction pits and the receiving access structure to reduce the impacts.