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Feasibility Study <br />Water Treatment Plant <br />City of Lino Lakes, MN <br />WSB Project No. 015822-000 Page 25 <br />8. WATER DISTRIBUTION SYSTEM MODELING <br />8.1 Existing System Impacts <br />The City’s existing WaterCAD model was expanded to evaluate the impact of a central water <br />treatment plant location with plant capacities that increase over time. Extended period <br />simulations (EPS) were modeled to observe the filling and emptying patterns of the water towers <br />as the system experiences variable water demands and the well pumps turn on and off <br />throughout the day. All scenarios used maximum days demands. A series of additional demands <br />were added at the extents of the system, where expansion will occur, in order for the total <br />maximum day demand to equal the treatment capacity of the water treatment plant for each <br />scenario. This was done in order to simulate the system hydraulics as additional wells are <br />connected to the plant to meet water demand increases over time. <br />The hydraulic conditions in the existing trunk watermains near the potential plant location were <br />analyzed for conformance with AWWA standards. AWWA Manual M32 Computer Modeling of <br />Water Distribution Systems recommends a maximum headloss gradient of 10 feet per 1,000 feet <br />and a maximum flow velocity of 5 feet per second in distribution watermains. The headloss <br />gradients, velocities, and pressure changes in the existing watermains in the vicinity of the <br />potential plant location are shown in Table 8-1 for a various plant flow rates into the distribution <br />system. <br />Table 8-1. WaterCAD Results with Existing Watermain <br />WTP Flow <br />(gpm)* <br />Low <br />Pressure <br />(psi) <br />High <br />Pressure <br />(psi) <br />Pressure <br />Change <br />(psi)** <br />Max. Headloss <br />Gradient <br />(ft/1,000ft)*** <br />Max. Velocity <br />(ft/s)**** <br />4,000 62 - 69 73 - 80 11 3.5 4.0 <br />5,000 62 - 70 76 - 84 14 5.0 4.8 <br />6,000 62 - 70 94 - 101 31 - 32 6.2 5.6 <br />7,000 62 - 70 100 - 106 36 - 38 8.1 6.4 <br />8,000 62 - 70 103 - 110 40 - 41 15.0 8.8 <br />9,000 62 - 70 114 - 121 51 - 52 18.5 10.0 <br />10,000 62 - 71 115 - 122 51 - 53 27.0 12.0 <br />*System max day demands increased to necessitate WTP flow rate. <br />**AWWA does not prescribe a particular maximum pressure change. However, pressure changes <br />greater than 20 psi could be noticeable and objectionable to water users. <br />***AWWA M32 recommends a maximum headloss gradient of 10 ft per 1,000 ft. <br />****AWWA M32 recommends a maximum velocity of 5 ft/s. <br />The existing trunk watermains in the City distribution system can accommodate a water treatment <br />plant capacity of 5,000 gpm without exceeding the maximum recommended flow velocity of 5 ft/s. <br />The four wells located near the potential plant location (Well Nos. 1, 3, 5, and 6) have a combined <br />total pumping rate of 4,175 gpm. Beyond 5,000 gpm, the velocities, pressure changes, and <br />headloss gradients become prohibitive (in that order). Therefore, if additional wells and treatment <br />capacity are added to the plant beyond 5,000 gpm, the trunk watermains will need to be upsized <br />or additional parallel trunk watermains will need to be installed to provide acceptable water <br />pressures for all customers. Based on the layout of the existing trunk watermains, it is <br />recommended that additional parallel trunk watermains be installed in order to provide redundant <br />trunk watermains along Birch Street.