Proactive maintenance, restoration and replacement of sewer system infrastructure is a high priority for the District. It helps ensure we continue to provide reliable, cost-effective service to our customers while at the same time protecting the environment. Sometimes, this requires creative problem solving to manage the system in the least impactful and most cost-effective way. This is especially true when working in sensitive areas like creek and wetland corridors or in busy urban areas.
Pipe "pigging" refers to a method of cleaning pipes by pushing pipe-sized devices, known as pigs, through the pipe to remove build-up. Traditional methods use various devices as pigs; however, sometimes those devices can get stuck and need to be dug out.
For some places in the District, such as the pipeline under Salmon Creek Greenway, digging up a stuck pig would not be an option because of the environmentally sensitive nature of the location. Instead, the District used a new technology called “ice pigging.” This is a very effective and low-risk method for cleaning pipes. A slurry of slushy ice is pushed through to scour the pipe, carrying with it any sediment and built up material on the walls of the pipe. After days of careful planning, this maintenance task is completed in just a few hours without disturbing surrounding natural areas or impacting service to residences. There is also no risk of the pig getting stuck – the ice will simply melt away.
There is only one contractor in the U.S. that does ice pigging for sewer pipes. It is cutting-edge technology in the wastewater industry and perfect for protecting high-value habitat areas like Salmon Creek.
Photos of different types and sizes of traditional pigs used to clean pipes
Photos left to right: Diagram of how ice pigging works; Water retrieved during ice pigging operation that is progressively clearer; Example of the special ice used for ice pigging
Cured-in-place pipe (CIPP) technology was recently used to rehabilitate the trunk lines under Cougar Creek and in St. Johns along I-205.
CIPP involves inserting a flexible, resin-saturated sock through existing pipes and then “inflating” and curing it with boiling water to create a solid, permanent pipe within the original line. The flexible CIPP is inserted through inversion - basically, pushing it inside-out using water pressure (see video). The CIPP is then cured in place by circulating boiling water for 24 hours or using steam and Ultraviolet light. To make sure the curing process happens as necessary, crews work around the clock during this process.
The result is a jointless, fully structural pipe that is tightly fit against the existing pipe and will last for decades.
CIPP installation typically requires four major pieces of equipment:
Each piece of equipment is needed at separate times in the process; for example, once the pre-installation television inspection is completed, the CCTV truck is moved away and the box truck brings the liner over the manhole.
Bypass pumping is used to continue to provide constant sanitary sewer service during construction. Bypass pumping occurs 24 hours a day for the duration of the CIPP installation and post-installation video inspection.
CIPP tube - Left: Flexible tube prior to resin-impregnation; Center: Liner as it is inverted in the pipe;
Right: Finished CIPP product that will last many decades
CIPP process illustrations - Left: Water inverts the flexible lining into existing pipe and manhole; Right: Hot water circulation and curing
CIPP installation at Cougar Canyon (left to right) - Staging area and bypass piping that shows the natural setting crews were working within; Rolling out the uncured lining; Restored manhole following CIPP installation and manhole lining
The District recently used a variety of trenchless techniques on the Discovery Corridor Wastewater Transmission System (DCWTS) project.
One method used was horizontal directional drilling (HDD), which is a steerable method of installing pipes that takes place underground, from one staging area to another, without disturbing the areas above ground. In the case of the Discovery Corridor pipeline, the technology was used to install a 16” diameter pipeline across the Interstate 5 off ramp without any traffic impacts.
Other trenchless techniques used on the DCWTS project included horizontal auger boring, commonly referred to as "jack and bore," and pipe bursting.
Pipe bursting involves laying pipe by pulling a device that is slightly larger than the existing pipe through, breaking the existing pipe and expanding the opening. Along the way, a new larger diameter pipe is pulled through the opening. For the DCWTS project, pipe bursting was used in a arterial road along a busy retail corridor, which limited the impacts of construction on local businesses.
Photos of pipe bursting during the DCWTS project (left to right) - Receiving pit where the new HDPE pipe is being pulled into the existing pipe; Photo showing how an 8" diameter concrete pipe was "burst" and expanded for a new 12" diameter HDPE pipe; Pipe bursting was used in a arterial road along a busy retail corridor, which limited the impacts of construction on local businesses
By specifying the right type of technology for each particular job, the District is able to limit disruption to surrounding areas, keep the system operating efficiently and save rate payers money.