Using a temporary sewage bypass pumping system and nondisruptive pipe rehabilitation methods, a half-mile section of trunk sewer buried beneath a Tucson roadway was rehabilitated.
The lines location under Grand Road, a major east-west artery through the city, and the large volume of sewage it transports both contributed to the projects complexity, according to Jon Schladweiler, deputy director of engineering for Pima County, Ariz., Wastewater Management, which oversaw the rehabilitation project.
The trunk sewer, which serves 35,000 residents of southern and southwestern Tucson, transports between 10 and 12 million gallons of sanitary sewage each day. Video inspections showed extensive deterioration in a 2,500 foot section of the 42-inch diameter pipe.
"We had to be able to keep everyone in service, with zero tolerance for any leakage of sewage out of the system during the rehabilitation process," said Schladweiler.
Pima County Wastewater Management awarded Insituform Technologies a $1.8 million contract to repair the line using the Insituform process, a nondisruptive technology that restores structural integrity. To maintain service to customers, Pima County also required the company to develop a temporary sewage bypass pumping system capable of conveying the 12 million gallons per day of sewage flow normally transported by this reach of pipe.
The Process
The first challenge was to dry up the damaged sewer and reroute the flow. Workers began by cutting into the interceptor and releasing the raw sewage into a wet well they had created just upstream from where the rehabilitation was to be completed. Using 10 portable diesel-driven pumps, the workers pumped sewage from the wet well into four 18-inch diameter HDPE pressure pipes. Secured against the concrete-lined bank of an existing drainage ditch, these mains carried the sewage downstream approximately 3,000 feet, where it was returned to the interceptor. The 10 pumps were far more than was needed for the sewers daily average or peak flow, according to Mike York, technical representative for Insituform.
The Process
"We needed a certain comfort zone in case any stormwater got in the line. Thats why we sized the pumps for peak wet weather flow," York said. "Plus, we needed the appropriate number of pumps and safeguards so that if for any reason something stopped working, at any time of the day or night, wed have the excess capacity to take over right away."
The Process
After several weeks of preparation, the workers put the bypass pumping system into operation in late August 1998. Despite the heavy rain and the large volume of sanitary sewage it had to accommodate, it operated to expectations.
The Process
Over the next four weeks, on-site technicians worked around the clock overseeing the systems operation, while the installation crew set about the task of rehabilitating the deteriorated line.
The Process
The installation crew divided the rehabilitation project into two parts, rehabilitating 881 linear feet of the nearly one-half-mile long trunk sewer in the first inversion, and the remaining 2,115 linear feet in the second.
The Process
For each installation, a custom-made felt tube was impregnated with a liquid thermosetting resin. The installers then inverted the tube into the structurally deteriorated pipe from an existing manhole access point. Water pressure was used to propel the tube through the sewer.
The Process
Installers then circulated hot water through the tube, curing the resin and forming a jointless and corrosion-resistant pipe. After the pipe had cured, the service connections were restored.
The Process
To cause the least possible disruption to traffic, the workers installed the resin-saturated tubes in the early evening hours. The curing process continued throughout the night, with the laterals restored by morning.
The Process
By late September, the sewer rehabilitation was completed and the pumping system, dismantled, having met all of Pima Countys objectives.
