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Name: Todd A. Blomstrom <br />Date: October 8, 2020 <br />Page: 2 <br /> <br /> <br />Option 1 - Rehabilitation of the Existing Lift Station <br />The first option considered for rehab of Lift Station 10 includes replacing the existing pumps <br />and piping in the wet well and valve vault. Major components associated with this option <br />include the following: <br />- Install two new submersible pumps with purposely shallow operating conditions <br />- Obtain and install new lift station controls and SCADA equipment <br />- Install new piping in the existing Wet Well and Valve Vault <br />Based on new pump technology and the right pump selection, the maxi mum number of <br />possible pump starts per hour could be increased from the standard ten (pump runs every six <br />minutes) to 30 (pump runs every two minutes). Table 1 below demonstrates that if the starts <br />per hour are allowed to increase, the standard operating depth (vertical distance between the <br />All Off and Lead Pump On levels) can decrease. The decrease in the operating depth would <br />reduce the maximum water level elevation that the station reaches during normal operation <br />and reduce or possibly eliminate the occurrence of wastewater backing up into upstream <br />manholes. <br /> <br />Table 1 - Operating Depths* <br />Starts Per Hour Pump Runtime [min] Volume [ft^3] Design Value [ft] <br />10 6 20.05 0.71 <br />15 4 13.37 0.47 <br />20 3 10.03 0.35 <br />25 2.4 8.02 0.28 <br />30 2 6.68 0.24 <br />*Based on an assumed 6-foot diameter manhole <br /> <br />The margin between the All Off and the Low Water Level (LWL) can also be adjusted to provide <br />more available volume in the wet well, which will help even more to decrease the flooding of <br />manholes upstream. Table 2 below shows the new Lead Pump On elevation based on number <br />of pump starts per hour and the distance between the All Off and LWL set points. <br /> <br /> <br /> <br /> <br /> <br /> <br /> <br /> <br /> <br /> <br />Through conversation between the City and Bolton & Menk, it was determined that the optimal <br />acceptable solution is a 3-inch margin between the All Off and LWL set points, and 20 pump <br />starts allowed per hour. This provides a Lead On elevation of 872.35’, as underlined in Table 2. <br />Table 2 - Lead Pump On Elevations <br />Starts Per Hour <br />Depth from All Off to LWL <br />0" 3" 6" <br />10 872.46 872.71 872.96 <br />15 872.22 872.47 872.72 <br />20 872.10 872.35 872.60 <br />25 872.03 872.28 872.53 <br />30 871.98 872.23 872.48