Distribution Evaluation
Chapter 5 Distribution Evaluation
5.1 Existing Distribution System
Much of the distribution system is nearing 50 years old and has exceeded its design life. During the 2012 meter pit installation project, City staff added water meters for all service connections.
There is a large number of dead-end lines within the distribution system. Maintaining a regular flushing schedule of these lines is important in maintaining water quality in the lines, and adding looping where possible is recommended.
Fire hydrants in the system are connected to 4-inch-diameter steel main lines in many locations.
The regulatory minimum size water main allowed to supply fire flow to hydrants has been increased to 6-inch-diameter in recent IDAPA revisions. Main waterlines should be replaced with at least 6-inch-diameter pipe to assure adequate fire flow and improve overall system flow. Fire hydrants should be replaced at the same time as the waterline. There are also a number of segments of 2-inch mains within the system. Regulations required a minimum of 3-inch-diameter (typically 4-inch or 6-inch) mains for any future construction.
5.1.1 Pressure Criteria
The distribution system is a single pressure zone system. The entire system is supplied by gravity from the 100,000-gallon storage tank at the treatment plant. The tank provides a minimum
pressure of 30 psi to the highest connection on the hillside and maximum pressures over 100 psi for connections near the lake. These high pressure connections are regulated by individual pressure-reducing valves at each service.
5.2 Distribution System Alternatives
A thorough water model was not completed as part of this analysis. Spot checks for pressures and estimated fire flows were made at end points of the distribution system to evaluate losses. A summary of the calculations made is included in Appendix 5-A. Hydraulic losses become significant at high flows because of small line size and lack of looping within the system. Because of the difficulties with meeting fire flows through the small size lines, the water system was evaluated based on two different scenarios, including 1) replacement of steel lines and 2) replacement of steel lines and improving looping.
The significant elevation difference within the service area allows for the high head losses in the piping in low elevation areas. Table 5-1 shows the estimated fire flows available throughout the system.
Table 5-1 – Estimated Available Fire Flow
Location Estimated
Fire Flow
West end of School Road Loop 700 gpm
School Road and Wellington Place 1,400 gpm
Aspen Lane and Wellington Place 900 gpm
East end of Spring Street 1,250 gpm
East end of Pringle Avenue 1,200 gpm
South end of Sneil's Hill 800 gpm
5.2.1 Distribution System Improvements – Steel Line Replacement
The bulk of the distribution system is comprised of aging steel lines, and replacement of the steel lines 3-inch and larger is the City’s first priority. An increase in waterline size is recommended in some areas and will accomplish reduced friction loss, which may provide improved pressures in some areas within the system. The increased line size will add minimal additional cost (trenching and backfill being 75 percent of the cost) and provide adequately-sized water mains should the City decide to increase system looping to improve fire protection. The recommended priority areas and estimated cost for the project are shown in Table 5-2.
Table 5-2 – Priority Areas and Estimated Cost Project Location Length of Pipe
(ft) Size of New Pipe
Detailed cost estimates are included in Appendix 4-A.
Chapter 5 –Distribution Evaluation
City of East Hope 5-3
2013 Water Facilities Plan
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5.2.2 Distribution System for Improving Looping
System improvements to improve looping and fire protection were also evaluated. Extensive line replacement will be required to provide the improved looping necessary. Two bores crossing Highway 200 would also be included. The City currently has a fire protection rating of 7.
A summary of the improvements is provided in Table 5-3.
Table 5-3 – Improved Looping Estimated Costs Project Location Length of Pipe
(ft)
Detailed cost estimates are included in Appendix 4-A.
5.2.3 Pressure-Reducing Stations
The areas of the City near the lake have very high system pressures (greater than 100 psi) and are currently controlled by individual pressure-reducing valves at the service. The installation of two pressure-reducing stations could reduce the overall system pressures in these lower elevation areas, decreasing the wear and improving the life of the system components (pipe, valves, fittings, meters, etc.) in these areas. Construction plans for these two stations were developed for these stations by Sewell and Associates in 2007, but the stations were not constructed due to budget constraints and the limited number of connections impacted by the work. One station was planned to be located next to Strong Creek, between the Old highway and the railroad tracks, and the other at the bottom of Sneil’s Hill. The plans prepared for these stations are included in Appendix 5-B.
The cost opinion for the construction of two stations is $63,000.
5.3 Discussion and Recommendations
There are three sets of distribution system improvements for the City’s distribution system. The first is to replace the aging steel waterlines that are 3-inch or greater in size with appropriately sized PVC pipe. This replacement work will reduced non-revenue water for the system by replacing leaky lines, and it will improve fire flows within the system by increasing some line sizes and reducing friction losses in the piping. The second set of improvements would reduce dead-end lines and potentially improve water quality in the distribution system. The third is construction of two pressure-reducing stations to lower the pressure in the lower elevation areas near the lake.
The recommended minimum improvement for the distribution system is to replace the aging steel lines. This work will provide significant benefit to the system by improving lost-revenue water, which will reduce daily demands on the treatment system and also improve the system's fire flows and overall infrastructure. Looping projects and the addition of the PRV stations could be
implemented at a later date as budget allows but are a lower priority.
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