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HomeMy WebLinkAbout2017-0215B Resolution approving Preliminary Engineering Report - May 6, 2017 Bond Election2 Trophy Club Municipal Utility District No. 1 Proposed Transmission Line Improvement from TCMUD Pump Station to Eastern Elevated Storage Tank ENGINEERING REPORT January 2017 1 Introduction This Preliminary Engineering Report (PER) is prepared at the request of Trophy Club Municipal Utility District No. 1 (TCMUD) and is intended to provide an overview of a proposed transmission line improvement to TCMUD's existing water system. 1.1 Background TCMUD was formed in 1975. In 1983 the area now known as Solana located in Westlake, was annexed into TCMUD. The original Municipal Utility Districts No. 1 and No. 2 were consolidated in 2009 to form Trophy Club Municipal Utility District No. 1 and is the remaining district providing water and sewer service to its retail customers within Town of Trophy Club and the Solana area in the Town of Westlake, as well as providing wholesale water and sewer service to the Town of Trophy Club. A hydraulic study was completed in February 2016 by CP&Y, Inc. for the TCMUD distribution system. The study included development of a hydraulic model of the distribution system, including piping, pumping units, ground storage tanks (GST) and elevated storage tanks (EST). The purpose of the study was to evaluate the existing distribution system as a whole and apply future water demands to identify required improvements to meet the future build-out conditions of the District’s entire service area. 1.2 Evaluation Methodology The TCMUD distribution system was evaluated in regards to source, capacity and demand. The evaluation of municipal water systems starts with an evaluation of the water system source, followed by an evaluation of the capacity to move water through distribution piping to provide customer consumption demand and fire flows 24 hours a day and 365 days per year. Source: The water supplied from the City of Fort Worth comes from Caylor Tank, a 5 MG ground storage tank on Caylor Road in the Northside Water System pressure plane. The transmission line from Caylor Tank connects to ground storage tanks in Westlake along US 377. From this connection point in Westlake, a 21” line continues to Trophy Club for delivery into TCMUD’s ground storage tanks. This 21” line runs approximately 22,500 linear feet and is the sole source of water supply from Fort Worth. Capacity: A hydraulic model of the TCMUD system was developed using Infowater Suite 11.5 to evaluate the capacity of the system to deliver water to all customers connected to the system currently and for future build-out conditions. Demand: Current demands were determined from water usage data provided by TCMUD. Future demands were estimated based on the projected population of TCMUD’s build-out assuming a similar water demand per capita as experienced over the last few years. 3 2 Distribution System The TCMUD water distribution system consists of a pumping facility, ground storage facilities and elevated storage tanks serving a single pressure plane. The major elements of the model include: • Pipe Diameters from 6” to 24” • Five High Service Pumps • Two Ground Storage Tanks, 3 MG each (6 Million Gallons) • Two Elevated Tanks, 400,000 gal and 500,000 gal (900,000 Gallons) • Supply Pipeline from Fort Worth, 21” diameter In Figure 1 below, the hydraulic model (yellow pipes, green nodes, blue tanks) of the existing distribution system is shown with an aerial photograph background. Figure 1 - Existing Water Distribution System 4 3 Water Demands Water utilities must be able to supply water over a wide range of fluctuating flow rates. Yearly, monthly, daily, and hourly variations in water use occur with typically higher use in dry and hot periods. Additionally, municipal water use follows a diurnal pattern, beginning low at night and peaking in the early morning and late afternoon. Usage rates most important to the hydraulic design and operation of a water distribution system are average day (AD), maximum day (MD), and peak hour (PH). Average day use is the total annual water use divided by the days in the year. This average day rate is used as a basis for estimating maximum day and peak hour demands when no hard data is available. Maximum day demand is the maximum amount of water used on any single day of the year. Peak hour use is the peak rate at which water is required during any one hour of the year. Minimum system pressures are usually experienced during the peak hour; therefore, the sizes and locations of distribution facilities are generally determined based on this condition. Historical water usage records were analyzed for years 2010 through 2014. TCMUD No.1 provided the average day demand and the maximum day demand for this time period as well as the number of connections at the end of each year. The data is shown in Table 1. Table 1 - Demand and Connection Data Provided by TCMUD No. 1 Data 2014 2013 2012 2011 2010 Average Daily Demand (MGD) 2.654 2.543 2.783 2.718 2.209 Maximum Daily Demand (MGD) 5.757 6.447 6.556 6.797 5.165 Peaking Factor 2.17 2.54 2.36 2.50 2.34 Number of Meters (# Connections) 4371 4173 3880 3582 3351 SCADA data also provided a source to verify the peak hour demands experienced in the TCMUD distribution system. The peak hour typically occurs in the early morning in Trophy Club due to lawn watering. Recent SCADA data showed that the morning peak is the largest demand experienced throughout the day and routinely amounts to an 11,000 gpm flow rate (15.8 MGD) or slightly higher during the peak hour. Based on the observed SCADA data a diurnal pattern was developed for the hydraulic model. The pattern has the peak hour at 8:00 am where demand on a maximum day is about 11,000 gpm (15.8 MGD) and a smaller peak in the evening at 9:00 pm. Each bar in the diurnal pattern represents the average flow rate over a one hour period expressed as a ratio, so that when the flow from each hour is added together, it equals the total flow for the 24 hour period. The diurnal pattern can be applied to the average day demand, the max day demand, or any other daily demand of interest. The diurnal pattern used in the hydraulic model is shown in Figure 2 below. 5 Figure 2 - Diurnal Curve Based on SCADA Observed Data 3.1 Minimum System Pressure Criteria Normal minimum working pressure in a distribution system should be approximately 50 psi and not less than 35 psi during a peak hour. A normal working pressure in most systems will vary between 50 to 56 psi. Systems must be designed to maintain a minimum pressure of 20 psi at ground level at all points in the water distribution system under fire flow conditions. 4 Existing System Analysis The water distribution system was analyzed for three operating conditions: Average Day, Maximum Day and Peak Hour. A 24 hour extended period simulation (EPS) was performed for the Average Day and the Maximum Day, which included the Peak Hour. Examining the water system under a 24 hour period for both average and maximum day demands allows the determination of issues with pressure and flow and if the storage tanks are filling or draining as desired, and if the pumping facilities are adequate to meet the required demand at acceptable pressures. The TCMUD distribution system consists of a single pressure plane; however, the system has an East and a West side that are only connected through the pump station discharge header and a couple of 8” diameter lines. This results in operating in a practical sense with two pressure planes, because flow or pressure deficiencies on one side are not significantly helped by the opposite side. The pump station provides water to both sides simultaneously. The flow split to the east and to the west sides at the pump station header is determined by the head losses experienced in each direction. Flow will take the least resistive path. The east and west sides have their own elevated storage tanks. While elevated storage 6 tanks serve to maintain system pressures, these two tanks are only effective in maintaining pressures on their own side of the overall system. The west tank cannot effectively provide flow and pressure to the east side and the east tank cannot effectively provide flow and pressure to the west side. Figure 3 shows the two sides of the overall system. While they are technically not isolated by valves to form two pressure planes, they do operate to some degree as separate pressure planes. Figure 3 - East and West Sides of the TCMUD Distribution System As shown in Figure 3 above, the east and west sides are connected only at the pump station header, by an 8” diameter line in the northeast, and by another 8” connection just south of the pump station. The model simulations showed that in the existing pipe network with current water demands, the eastern tank is more difficult to fill and maintain at near full level as compared to the western tank. This is because the piping to the east tank has smaller diameters and creates greater head losses as compared to the pipe transmitting flow to the west tank. This condition was verified with TCMUD Operations as existing in the actual system. Operations does experience difficulty in filling the eastern tank and compensates by regulating a valve at the western tank to restrict flow there and force more flow to the east. The piping network for the east system is shown in Figure 4 below. Flow from the pump station header is delivered to the east in a 14” diameter line that reduces to 10” and 8” diameters before reaching the southeast elevated tank. This creates a significant bottleneck in the system and prevents the elevated tank from operating efficiently. 7 Figure 4 - Existing - Pipe Diameters in Eastern Distribution System The pipe segments that are undersized for today’s water demands are highlighted in red in Figure 5. For future demands, even the 14” existing line that goes about half the distance to the elevated tank will not provide sufficient capacity. The entire line to the elevated tank will need to be upsized or paralleled with another line. Figure 5 - Existing System Bottleneck with Current Demands 8 4.1 Identifying Capacity Issues Simulations were run for future water demands in the existing system to identify the system components that will require capacity improvements. The west system’s existing piping network performed well in the simulations. For the most part, the pipe diameters in the west system are adequate for future water demands. While some head losses seen in the western system piping are greater than desired in terms of ft of head loss per 1000 ft of pipe (ft/1000 ft), the flow velocities and customer pressures are adequate. The east system requires more extensive improvements to provide the future water demands. During a future maximum day demand with the existing pipe network, the east tank will almost empty during the peak hour. It will be below the 33% full level for a three hour period. Figure 6 shows the elevated tank levels as percent full over a 24 hour period during a future maximum day. Figure 6 - Level in Elevated Storage Tanks – Existing System, Future Max Day Demand The east elevated tank comes within 2 feet of emptying near the peak hour demand. The west tank is able to stay above 75% full. Pressures in the west system stay above 40 psi indicating the network has the capacity to provide future peak flows. Pressures in some areas of the east system fall below 35 psi indicating capacity issues. The red and yellow nodes in Figure 7 shows areas of concern. % FULL Red is 400,000 gal elevated tank Green is 500,000 gal elevated tank 9 Figure 7 – Pressures in the East System during Future Peak Demand The east elevated tank comes very close to emptying in the future peak hour simulation. If the tank were to empty, the vast majority of the east system would realize pressures below 30 psi and even below 20 psi. Another simulation was run that used the last 2 feet of water in the east tank during a peak hour demand. A situation that could cause this would be a fire event during the peak hour demand. Figure 8 shows the pressures across the system when the east tank is emptied. The red nodes show pressures below 30 psi. Most of the east system is below 30 psi while all of the west system remains at 40 psi and above. Figure 8 - Minimum Pressures in Existing System during Future Max Day Demand 10 4.2 Recommended Improvements Discussions with TCMUD operations identified the fact that the existing 14” water main along Indian Creek Drive has a great number of connections tapped directly to it. This line does not have many isolation valves along its length. Upgrading this line to a larger diameter while maintaining water service to the residents in that area would be very difficult and due to the complexity, could be more expensive than a typical line replacement of this size. To provide an alternative improvement and reduce costs, other improvement options were tested and simulated in the hydraulic model. An alternative option utilizing a parallel line from the pump station to the elevated tank was found to provide the same system capacity improvements while leaving the piping along Indian Creek Drive untouched. An alternative parallel transmission line is shown in Figure 9. Figure 9 - Alternative Proposed Improvements for flow to the Southeast Elevated Tank This improvement option utilizes a new 16” diameter line from the pump station along a back path to Trophy Club Drive, then along the Highway 114 access road to the Solana connection point. From there an 18” diameter pipe continues to the elevated tower. The 16” parallel line is cross connected to the existing main along Indian Creek Road in two locations; a new 12” line and a line improved to 14”, as illustrated. This parallel line provides the same or slightly better results than direct replacement of the 11 existing line along Indian Creek Drive with an 18” diameter upgrade. This option would be a much less complex installation and should save significant cost compared to the original option. The model simulations show the ability to fill and maintain the level in the east elevated tank is greatly improved given existing or future water demands. As shown in Figure 10, the model simulation shows the lowest level in the east tank to be about 65% full during a future maximum day demand. Figure 10 - Level in Elevated Tanks with Alternative Improvements during Future Max Day Demand Upgraded capacity from the high service pump station to the east elevated tank is the most important improvement identified in the hydraulic study and recommended for the piping network. This improvement is needed not only for future demands, but will significantly improve present system performance on the east side of the TCMUD system. Installing a new 16” diameter main operating parallel to the existing 14” main that provides flow to the elevated tank, is recommended. This recommendation includes the new 16” main but also includes the replacement of some smaller diameters to 12”, 14” and 18” pipe as shown in Figure 9 previously. A detailed alignment study will be required to finalize the route of the proposed transmission main and to obtain right of way and easement data. The TXDOT right of way that exists along HWY 114 will be investigated, as this area encompasses the majority of the proposed route. 4.3 Opinion of Probable Construction Cost The estimated cost for this improvement is $2.18 Million. The cost estimate detail is shown in Table 2. Red is 400,000 gal elevated tank Green is 500,000 gal elevated tank 12 Table 2 - Cost Detail for Transmission Main Improvement Description Unit Quantity Unit Cost Extension 1 Mobilization LS 1 95,000 95,000 2 Saw cut, Removal and disposal of Existing Concrete Pavement SY 125 20 2,500 3 Furnishing Concrete Sidewalk SY 25 15 375 4 Furnish & Install 8" Street Concrete SY 125 80 10,000 5 12" PVC Water Line LF 350 70 24,500 6 14" PVC Water Line LF 900 85 76,500 7 16" PVC Water Line LF 8100 100 810,000 8 18" PVC Water Line LF 3500 115 402,500 9 12"GV&B EA 5 2,800 14,000 10 14" GV&B EA 4 3,500 14,000 11 16" GV&B EA 6 4,000 24,000 12 18" GV&B EA 3 3,500 10,500 13 DI Fittings LBS 20000 5 100,000 14 Sod SY 1000 10 10,000 15 Trench Safety Plan EA 1 1,000 1,000 16 Trench Safety LF 12500 3 37,500 17 Erosion Control and SWPPP LS 1 1,500 1,500 18 Furnish & Install Barrier Free Ramp EA 4 1,000 4,000 19 Furnish & Install 6" Compacted Sub base SY 125 15 1,875 20 Traffic Control EA 1 7,000 7,000 Sub-Total $ 1,646,750 Cont. (15%) $ 247,012 Subtotal $ 1,893,762 Engr, & Surveying (15%) $ 284,064 Base Bid Total $ 2,177,827 5 Conclusion For efficient utilization of the eastern elevated storage tank in the TCMUD distribution system, and to maintain acceptable pressures on the east side of the system, both with today’s water demands and with the future projected demands, a new 16” main and some 14” and 18” upgrades as shown in Figure 9, are recommended.