Silt Pumping Plant Rehabilitation Preliminary Design

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Preliminary Design Memorandum Silt Pumping Plant Rehabilitation hydraulic transient similar to the one experienced previously from backflow priming would most likely cause the same failure in the discharge pipe segment downstream of the discharge valve. With the current design,backflow priming should not be attempted. The 2,400 VAC motor control center is "non-standard"by today's designs and is also 50 years old. Due to the 2,400 VAC design and age,parts are extremely difficult to find. One of the largest safety concerns is that there is no way to disconnect the motors when they are under load. There is not a main building disconnect. The features on the control panels are very limited by today's standards. For example, if a motor fails to start, a red light is turned on, but the cause of the failure is not indicated. Inside the pump house there was evidence of drainage or water table problems. Many of the electrical conduits beneath the pumping plant floor were full of water,which had caused corrosion failure of the wiring by year 2002. Repairs were made with new wire and conduit. New bearing and temperature sensors were also installed. In the spring of 2012 repairs were made to the underground electrical feed from the transformer to the control panel within the pump house as a problem with electrical shorts had been detected. Currently the discharge from the pumping plant is not measured accurately, as the existing 30- inch propeller-type line meter, intake water level indicator,and pump canal Parshall flume do not work properly. The propeller meter in the discharge pipeline adjacent to the pumping plant has worn out and has been removed. The District would like to install a new flow meter. FUTURE OPERATIONAL CHANGES The original design flow of the pumping plant was 36 cfs but the design flow of the intake canal, the discharge pipeline and the pump canal is only 32 cfs. Based upon data collected during the 2013 irrigation season,the SWCD Board believes a system flow of 30 cfs would meet current and anticipated needs. The pumps would be upsized 3%to account for wear since raw water is being pumped. No other significant operational changes are expected. If Variable Frequency Drives's(VFD's)are used to vary the pump output of the pumping plant, the District would be more able to match water deliveries with water orders but there would be significant losses in pumping efficiency when the pumps are operated at less than 90%speed. CONSTRUCTION SEQUENCING The anticipated schedule for actual implementation of this modernization work will be dictated by the irrigation season. Generally,the construction related to this proposal will begin after water goes out of the collection and distribution systems at the end of October. Depending upon seasonal weather conditions,all construction should be completed by mid-March to allow the irrigation system to be restarted. However,the contract should be initiated well before the end of 9 FOR OFFICIAL USE ONLY