2015 Issue

44 release vaults, are only accessible by foot through the backyards of homes. CONDITION ASSESSMENT OF THE EXISTING PIPELINE In the mid 2000’s the East Layton Pipeline started experiencing increased leaks and required more frequent repairs. In 2012 the District conducted a leakage test of the existing pipeline and hired a consultant to complete a condition assessment and alignment evaluation study to identify appropriate actions for repairing or replacing this critical facility. Description of the Existing Pipeline The majority of the existing pipeline is 27-inch nonstandard rein- forced concrete pipe (RCP). The pipe is nonstandard in that it does not comply with American Water Works Association (AWWA) or American Society for Testing and Materials (ASTM) standards. The RCP was manufactured by centrifugally casting the pipe in a mold spun at high velocity and is often referred to as “Cenviro” pipe. The steel reinforcing in the pipe wall includes a thin wire mesh designed for internal pressures of 33 to 54 pound per square inch (psi). The pipe was manufactured with standard flared concrete bell and spigot joints utilizing a single rubber-gasket. There is a section of pipe across Hobbs Ravine that includes approximately 1000 feet of 30-inch bar wrapped concrete cylinder pipe (CCP) (in accordance with AWWA C303). The CCP was selected for this reach to handle the higher pressures (90 psi). The District has not experienced any leakage in the CCP and it appears to be in much better condition than the RCP. Leaks In 2012 the District performed a leak detection inspection of the ex- isting line with a Sahara Leak Detection systemwhich uses acoustics and video data to identify leaks and obstructions or abnormalities in the pipeline. A total of 15 leaks were identified as part of this survey. Two leaks were estimated to be between 75 and 128 gpm and the other 13 leaks were estimated at 2 to 75 gpm. All identi- fied leaks were located at joints in the 27-inch RCP pipeline and approximately half were located near the Oak Lane Pump Station Turnout. The video system also captured locations of obstructions that included rocks and unknown debris in the pipeline. Some of the leaks identified were visible at the surface and were being monitored daily by District staff. Figure 2 shows two of the visible surface leaks located near the Oak Ridge Pump Station turnout. Surge Analysis A surge analysis of the existing pipeline was performed to deter- mine the impacts of starting and stopping the Oak Ridge Pump Station that is connected to the East Layton Pipeline. The East Layton Pipeline operates at very low pressures (10 to 15 psi) and is located on the suction side of the Oak Ridge Pump Station. The results of the surge analysis showed that the pipeline was experi- encing significant down surges when the pump station is shut off and it is expected that many of the leaks at the pipe joints are a result of cyclical negative surge pressures wearing out the rubber gaskets. Figure 3 shows a hydraulic profile of the pipeline during a surge event. The red dots shown on Figure 3 show the location of the discovered leaks. Notice the location of known pipeline leaks relative to the down surges. Figure 3. Hydraulic profile showing surge HGL and location of known pipe leaks Figure 2. Pipeline leaks that surfaced near the Oak Lane Pump Station Figure 4. Repair of concrete joint with packed grout CULINARY PIPELINE | continued from page 43