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end of Robinson Tailing Pond. This 2,900-foot length of the pipeline would be founded <br /> entirely on native materials. The top of the knoll would be the location of a utility vault <br /> containing a pipeline vent and an access port for pipeline cleaning using a high pressure jet <br /> wash system. <br /> There are primarily two factors that were considered that justify routing the pipeline <br /> to the top of the knoll, which is 20 to 30 feet higher than the crest of No. 1 Dam. The <br /> most critical of these factors is that the preliminary pipeline surge analysis indicates that <br /> there is a high potential for the occurrence of water column separation at the crest of <br /> No. 1 Dam. Column separation occurs when the hydraulic gradient of a negative pressure <br /> wave causes vacuum conditions in the pipeline. In the extreme case the pressure drop <br /> could be below the vapor pressure of the water and a condition similar to cavitation would <br /> occur. Along with the potential for pipeline collapse that could occur as a result of the <br /> vacuum pressure conditions, the more damaging problem is the extremely high pressures <br /> that occur as the two separated columns of water come crashing back together. Such <br /> negative pressure surges could occur whenever the flow rate in the pipeline changes <br /> dramatically, such as when a pump is started or stopped, or as a result of a power failure <br /> at the pump station. <br /> The occurrence of negative pressure surges commonly occurs in pipelines. <br /> However, uncontrolled water column separation should not be allowed to take place under <br /> any conditions. There are several methods that can be used to minimize the occurrence <br /> and damaging effects of water column separation. Most of these methods involve the use <br /> of mechanical valves and/or pressure tanks that require maintenance and are sensitive to <br /> malfunction or freezing. Both conditions are probable at a remote location such as this. <br /> The proposed design addresses these potential problems by creating the artificial high point <br /> in the pipeline on top of the knoll and eliminating mechanical devices. This high point in <br /> the line will allow a controlled water column separation to occur at the vault where the <br /> pipeline is vented, so the vacuum developed in the pipeline will be nearly atmospheric <br /> pressure and not enough to collapse the pipe. If designed properly, there will be very little <br /> maintenance required, and a very remote chance of malfunction. This high point in the <br /> 17 <br />