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A fourth smaller pump with a variable frequency drive was initially considered. This <br /> pump would allow the station to operate continuously throughout the winter and early <br /> spring which would minimize power consumption and eliminate potential freezing problems. <br /> However, due to the very large capacity of the sump (seepwater pond) of about 60 acre- <br /> feet, and the lack of actual winter inflow data, we believe that the additional expense of <br /> the new pump and VFD would not be warranted at this time. With adequate burial of the <br /> pipeline for freeze protection, it is likely that one pump could be operated during off-peak <br /> periods without significant electrical demand penalties. After a year or two of winter flow <br /> data is collected using pump hour records of the 629 pumps, it may be warranted to <br /> evaluate the feasibility of adding a fourth lower capacity pump and VFD. <br /> The existing 629 pumps would have to be modified to operate efficiently under the <br /> new dynamic head conditions of the new pumping system. These modifications will <br /> include the removal of three of the seven stages and trimming of the remaining impellers. <br /> Due to the much lower dynamic head conditions of the new system, the existing 600 <br /> horsepower motors would be replaced with new 300 horsepower motors. The 629 pumps <br /> are already fitted with stainless steel components designed to withstand the corrosive <br /> nature of the seepage and subdrain water. Use of the 629 pumps will result in a cost <br /> savings for this project. <br /> 8 <br />