Section 5 - Planning Criteria Section 5
SECTION 5 PLANNING CRITERIA This section presents the design criteria and methodologies for analysis used to evaluate the existing distribution system and its facilities and to size future improvements. 5.1 Design Criteria Design criteria are established for the evaluation of EVWD s potable water system. Peaking factors for EVWD s system are determined based on a review of daily production data for the years 2009 to 2012. The criteria are developed using the typical planning criteria used in the systems of similar water utilities, local codes, engineering judgment, and commonly accepted industry standards. The industry standards are typically ranges of values that are acceptable for the criteria in question and, therefore, are used more as a check to confirm that the values being developed are reasonable. The design criteria and analytical methodologies used to conduct this evaluation are presented in Table 5-1. Table 5-1 Water System Evaluation Criteria Evaluation Criteria Value Units (1) Demand Evaluation Conditions (2) Peaking Factors /ADD 1.8 - - PHD/ADD 3.6 - - System Pressure Maximum Pressure 125 psi MinDD Minimum Pressure, normal conditions 40 psi PHD Minimum Pressure, with fire flow 20 psi Minimum Pressure, transmission mains with no water services 5 psi PHD Maximum Pipeline Velocity Existing Pipelines (excluding fire hydrant runs) 6 fps New Distributions Pipelines ( 12-inch in diameter) 4 (4) fps New Transmission Mains (>12-inch in diameter) 6 (4) fps Pump Station suction pipelines 4 fps Distribution System Pipeline Life Expectancy 75 years n/a Minimum Diameter for New Pipelines 8 inches n/a Storage Volume Operational 25 % of MG Fire Fighting Highest fire flow requirement per zone MG Emergency 100 % of MG Fire Flow Requirements (3) Single Family Residential 1,500 2 hours Multi-Family Residential 2,500 2 hours Project Number: 10502575 5-1 February 2014
Section 5 Planning Criteria Table 5-1 (cont d) Water System Evaluation Criteria Commercial 3,000 3 hours Public 3,000 3 hours Industrial 4,000 4 hours Agricultural 1,500 2 hours Supply Capacity Entire System Provide with largest single source out of service By Pressure Zone Provide with firm transfer/booster capacity between zones Tank Replenishment Provide sufficient supply and transmission capacity to balance reservoirs in 24 hours System Reliability Pipe Breaks Maintain service with a single transmission pipeline out of service No Wells Maintain service for 7 days with all groundwater wells out of service No Purchased Water Maintain service for 7 days with no Single Largest Source Out of Service per Pressure Zone purchased water Maintain service for 7 days with a single source out of service in each pressure zone (1) psi = pounds per square inch, fps = feet per second, gpm = gallons per minute, MG = million gallons (2) PHD = peak hour demand, = maximum day demand, ADD = average day demand, MinDD = minimum day demand (3) Based on discussions with the San Bernardino County Fire Department and generally accepted planning standards (4) Maximum pipeline velocities up to 15 fps under are acceptable for new pipelines under fire flow scenarios. 5.1.1 System Pressures Minimum system pressures are evaluated under two different scenarios: Peak Hour Demand (PHD) and Maximum Day Demand () plus fire flow. The minimum pressure criterion for normal PHD conditions is 40 pounds per square inch (psi), while the minimum pressure criterion under with fire flow conditions is 20 psi. The pressure analysis is limited to demand nodes, because only locations with service connections need to meet such pressure requirements. Lower pressures are acceptable for junctions at water system facilities and on transmission mains that have no service demands; however, no pressure shall be less than 5 psi except for short lengths near reservoir inlets and outlets where the water main is on premises owned, leased or controlled by the EVWD per State regulations. 5.1.2 Pipeline Velocities Pipeline velocities are evaluated for the future system for three different conditions as listed in Table 5-1. The maximum velocity is 6 feet per second (fps) provided that the system pressures are sufficient. This criterion is intended to decrease the potential for pipeline lining erosion and minimizing head loss. This criterion does not apply to flow in fire hydrant laterals. Under fire flow conditions, maximum pipeline velocities up to 15 fps are acceptable for new pipelines. New distributions system pipelines ( 12-inch in diameter) that are installed within the EVWD s system shall have a maximum design velocity of 4 fps under conditions. The maximum Project Number: 10502575 5-2 February 2014
Section 5 Planning Criteria velocity for transmission mains (> 12-inch in diameter), or suction pipelines at booster stations, should be 4-6 fps under conditions based on trade-offs between pipeline cost and energy usage. The design velocity for transmission mains should consider energy requirements and pipeline length to determine the optimal diameter rather than use a fixed velocity criterion. 5.1.3 Storage The total storage required for a water system is evaluated in three parts: 1) storage for operational use 2) storage for firefighting and 3) storage for emergencies. These three components are determined by pressure zone in order to evaluate the ability of the water system to meet the storage criteria on both an inter-zone basis as well as a system-wide basis. These three storage components are discussed in more detail below. 5.1.3.1 Operational Storage Operational storage is defined as the quantity of water that is required to balance daily fluctuations in demand and water production. It is necessary to coordinate the water source production rates and the available storage capacity in a water system to provide a continuous treated water supply to the system. Water systems are usually designed to supply the average demand on the maximum day and use reservoir storage to supply water for peak hour flows that typically occur in the mornings and late afternoons. This operational storage is replenished during off-peak hours that typically occur during nighttime, when the demand is less. The American Water Works Association (AWWA) recommends that an operational supply volume ranging from one-quarter to one-third of the demand experienced during one maximum day. It is recommended that each pressure zone in the EVWD (Lower, Intermediate, Upper, Foothill, Canal(s), and Mountain zones) have an operational storage of at least 25 percent of. 5.1.3.2 Fire Flow Storage and Criteria The fire flow requirements for the various land use types are listed in Table 5-1. Fire flow storage is determined based on the highest fire flow requirement of each pressure zone multiplied by the corresponding duration. The fire flow duration is dependent on the fire flow criteria and is based on the Uniform Fire Code requirements. For flows less than or equal to 2,500 gpm, the fire flow storage volume is based on a duration of 2 hours. Similarly, for flows between of 4,000 gpm and greater, a duration of 4 hours is used. For example, if the highest fire flow of a zone is 4,000 gpm for duration of 4 hours, the required fire flow storage for that zone is 0.96 million gallons (MG). For analysis purposes, it is assumed that there will only be one fire per pressure zone at any one time. 5.1.3.3 Emergency Storage The volume of water that is needed during an emergency is usually based on the estimated amount of time expected to lapse before the emergency is corrected. Possible emergencies include earthquakes, water contamination, several simultaneous fires, unplanned electrical outages or pipeline ruptures or other unplanned events. The occurrence and magnitude of emergencies are difficult to predict; therefore, the emergency storage criterion is based on past experience and engineering judgment. Typically, emergency storage is set as a percentage of. However, this percentage needs to be based on the water system layout and facilities. Project Number: 10502575 5-3 February 2014
Section 5 Planning Criteria Water systems that have only once source of supply are more vulnerable in emergencies such as an earthquake or supply outage than water systems with a large number of groundwater wells that are located throughout the distribution system. For the purposes of the Water System Master Plan (WSMP), MWH has assumed that the emergency storage criterion for EVWD s system is 1.0 times. 5.1.4 Supply Capacity The water supply reliability is evaluated for the entire system and on a pressure zone basis using a spreadsheet model that calculates the water supply balance by pressure zone including zone transfers. The firm well capacity, all wells with the exception of the largest well, is used as the available groundwater supply for most scenarios. The system demands should be met under conditions with the largest well out of service. The hydraulic model is used to verify that 1) the system can move water between zones according to the transfers calculated using the spreadsheet model, 2) system pressure criteria are met, and 3) that all storage tanks replenish in a 24-hour period. 5.1.5 System Reliability Four evaluation criteria are established for the system reliability evaluation. EVWD should have adequate source water to: Maintain service with a single transmission pipeline out of service during conditions Maintain service for 7 days with all groundwater wells out of service during conditions Maintain service for 7 days with no purchased water during conditions Maintain service for 7 days with a single source out of service in each pressure zone during conditions The intent of these reliability criteria is to identify storage needs during these emergencies to provide reliable service to the customers EVWD s system is evaluated against these criteria and results are presented in Section 6 of this report. Project Number: 10502575 5-4 February 2014
INTENTIONALLY LEFT BLANK