Agenda - Council Work Session - 10/20/2020 - Special

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2.1 2.2 addling an additional pipe the model calibrates closely with the field data. The pipe along 147th Ln. NW is a new 8" pipe, so it is believed that the pipe roughness coefficient used for the pipe is accurate. Additionally, Test 10 was conducted on hydrants in a new development_ Previously, this area was at a lower elevation than it is currently. This caused the model to not correlate well with the field testing data. The elevations of the hydrants in the rnodel were adjusted to more closely correlate with the field data, and as the pipe in the development is new, it is believed that the pipe roughness coefficient used for the pip is accurate. Once the computer water model was constructed and calibrated, the model was used to calculate the operating conditions in the water distribution system. Existing System Static Pressures Water system pressure is primarily a function of elevation with sorne degree of pressure Foss as water flows across the system. Static pressures throughout the distribution system as determined by the water model are shown in Figures 1-3 in Appendix B for average day demand (ADD), maximum day demand (MDD), and Peak Hour Demand. Low pressures generally occur in areas where the elevations are relatively high compared to the overflow elevation or hydraulic grade line (HGL) of the system. As you can see in Figures 1-3 in Appendix B, the pressures across the system are generally consistent, and are approximately the same between the three demand scenarios. All areas of the system are within the range of 50 to 80 psi as you can see in Table 3. Table 3 — Water System Static Pressures C Average Day 111111.1 I Demand Minimum Pressure (psi) 56 Maximum Day Demand 56 Average Pressure (psi) 68.5 68.1 Maximum Pressure (psi) Demand (gprin) 77 1,221 77 3,330 Peak Hour Demand 56 67.5 76 5,498 All three demand scenarios were done with the towers at an HGL of 1.031 feet. No wells were running during the model simulation. Existing System 24-Hour Simulation A 24-hour extended period simulation was run for average day demand (ADD) and maximum day demand MDD to model how the existing system performs in terms of pressure, velocity, and tank levels. System pressures are recommended to be in the range of 35 psi to 80 psi, and pipe velocities are recommended to not exceed 5 feet per second. For an average day demand, 1.72 MGD was assumed, and for maximum day demand, a maximum day peaking factor of 2.73 was assumed to get a maximum day demand of 4.7 MGD. For both demand scenarios, diurnal demand curves were used, and were developed by analyzing SCADA operation data documenting system water tower levels, as well as using industry standards and previous experience. These diurnal demand curves are shown in Figures 1 and 2, and were used for all modeling simulations. The operating range of Tower 1 was assumed to be 6 feet where wells would initially turn on when the HGL of Tower 1 went below 1,025 feet, and the wells would turn FEASIBILITY STUDY -DRAFT Page 4 RAMSY 154354