California has faced droughts the last three years and there are many possibilities we could continue facing some more in the future. Combined with the potential impacts of climate change and a growing population, it makes sense then to balance our water supply with a source of water that doesn’t rely on rain.
Water desalination is the process of taking salt and other minerals out of seawater to make freshwater. Municipalities, water districts, and private companies in California and other parts of the U.S. are primarily considering using reverse osmosis (RO) technology to develop new seawater desalination.
Reverse osmosis and other membrane technologies force liquid at high pressure through a membrane with pores that block the passage of larger salt and mineral molecules.
The membranes used formed a dense barrier layer designed to allow only water to pass while preventing the passage of salt ions. Reverse osmosis is the final category of membrane filtration “Hyperfiltration” capable of removing particles larger than 0.1 nanometers.
Despite the promise of desalination technology to help rid the world of water scarcity, significant challenges exist including high energy consumption making it an expensive option, impact in marine life at water intakes and outfalls, operational issues, and social and political considerations.
*Water Intake
One of the main environmental concerns associated with seawater desalination is the feedwater intake which may affect the biota of marine life surrounding the system. Impingement and entrainment of fish and other aquatic life may occur when aquatic organisms are trapped against intake screens by the velocity and force of flowing water.
Seawater wells are a viable option to minimize ecological impacts and provide more reliable intake water due to natural filtration suspended solids, organics, reduce turbidity, and lower salt density but intakes depends on the hydrogeology and substrates characteristics associated with the subsurface system and may not be practical for large desalination plants.
Determining the appropriate location and type of intake should include a thorough site assessment and evaluation that will help implementing mitigating measures and reduce environmental impact.
*Energy use
Desalination plants are expensive to construct and operate. The process requires that high pressure be exerted on the high concentration side of the membrane, usually 600-1000 (psi) for seawater, requiring a substantial amount of energy and making the technology more costly than other treatment processes. For example, State Water Project requires an intensive 6.75 kwh per1000gal to transport water more than 3,000 vertical ft from the Delta (Sacramento – San Joaquin River). A typical reverse osmosis plant uses 22kwh per 1000 gal.
Another concern about the high rate of energy which desalination consumes is that plants could lead to increased carbon emissions and contribute to global climate, depending on the energy source used to operate. Renewable energy, such as wind and solar, provides an opportunity for desalination plants to be carbon neutral by reducing fossil fuel use and associated greenhouse gas emissions.
Regardless of the high energy costs, California governments are under pressure to look for new water sources including desalination. The state’s long-standing water supply problems have continued to worsen in recent years due to drought, contamination of groundwater, increasing requirements to maintain water instream for endangered species protection, and population growth.
*Brine (Concentrate) disposal
Among the more challenging issues with respect to desalination processes is disposing of the waste concentrates. Desalination concentrate have higher salinity than seawater, and is denser sinking to the seabed and negatively impacting the environment surrounding the outfall. Several considerations may help facilities develop environmental disposal such as co-discharge with other wastewater effluent that is currently discharging to the ocean; locate concentrate outfalls in a tidal zone; and/or add diffusers to improve mixing.
Regulatory and permitting process
The most significant hurdles to implement desalination technologies come from the complexity of regulations, and local/state/federal agencies limited permitting experience. Agencies involve in the permitting process are the California Regional Water Quality Control Board, the City, the California Department of Health Services, the California Coastal Commission, the State Lands Commission, and EPA.
Multiple agency involvement may contribute to unproductive project time and costs.
California has over a dozen desalination plants and plans for at least four new ones. The Carlsbad Plant is scheduled to begin operating in 2012 with a capacity of 50 MGD ($300M); Huntington Beach Desalination Plant starts this year with a capacity of 50 MGD ($250M); Camp Pendleton with a capacity of 100 MGD ($1.9 Billion); and the Marin Municipal Water District approved construction of what would be the first desalination plant in the San Francisco Bay area, is expected to open in 2014 ($105M).
Friday, March 19, 2010
Saturday, March 13, 2010
Wastewater Lift Station Design Guidelines
Wastewater lift station structures, equipment, piping, controls, and accessories must be engineered according to City requirements, standard guidelines, and in conjunction with the Public Works Design Manual.
General Requirements:
*Lift stations will not be allowed where an acceptable alternative gravity route exists.
*All wastewater lift stations shall have multiple pumps and shall be capable of delivering the design flow rate with the largest pump out of service.
*Pumps and related equipment must be designed so that it can be removed from the wet well with a vehicle mounted crane or other lifting device.
*Lift stations may be submersible pumping stations, package wet well / dry well stations or site designed vertical, dry pit, non-clogging, centrifugal pumping stations, depending on station size, head requirements and motor horse power. All pumps must be capable of passing a minimum three (3”) inch diameter sphere and shall be single speed. They must be designed specifically for handling raw, unscreened domestic sanitary wastewater.
*Above grade stations are preferred. They shall have a finished concrete floor with floor drains and be housed in an easily removable, pre fabricated fiberglass enclosure unless otherwise specified by the City. Below grade pump stations shall be reinforced concrete and shall extend at least 6 inches above finish grade.
**Adequate access, lighting, ventilation (minimum 10 air changes per hour), heating, Net Positive Suction Head (NPSHA), and potable water supply shall be provided to all wastewater lift stations.
Wet Well Design
*Wet wells shall be considered a hazardous environment. Whenever practical wastewater lift station wet wells shall be constructed of pre-cast reinforced concrete and shall be circular to a minimum of seventy two (72”) in diameter with 4-hour capacity or as necessary to accommodate the influent sewer, provide for adequate pump suction pipe or pump submergence as recommended by the pump manufacturer and to provide adequate volume to prevent the excessive cycling of pumps.
*Every effort will be made to prevent wastewater in the wet well from becoming septic. The wet well shall contain adequate vertical room for level sensing adjustments above and below the design levels.
*Primary high water alarm shall be set to wet well influent invert.
*Wet well interior walls and ceiling shall be lined with a material that is resistant to hydrogen sulfide and sulfuric acid. (i.e. fiberglass) and shall have a water proof system if anticipated to be below the water table. Regardless of the elevation of the water table, all joints in the concrete and all penetrations through the concrete shall be grouted with non-shrink grout on both sides of the joint or penetration.
*Access to well shall be through a top slab opening with aluminum hatch cover and frame. It shall allow for the removal of all equipment from the wet well, in no case smaller than 36 by 36 inches.
*Each wet well shall contain a sump (2 feet wide and 12 inches deep minimum) immediately underneath the inlet pipe to help assist in trapping large items to prevent them from entering the pumps.
*A sixty (60”) inch diameter approach manhole shall be constructed upstream of all wet wells, serving as a common point of connection for all sanitary sewer pipes tributary to the pump station. A single pipe shall extend from the approach manhole to the wet well. The approach manhole shall be located within the site fencing of the lift station.
*Provide restrained flexible couplings on all outlet piping within two (2’) feet of the station wall and a resilient-seat gate valve on the line into the wet well.
*Provide a bypass and a magnetic flow meter on the discharge of the pump station within a vault.
Pump Selection and Design Criteria (Consult Local Requirements)
Station Type / Influent Flow Range (gpm) / Maximum TDH / Maximum Motor HP
**Packaged wet well/ dry well; Up to 3,000 gpm (influent); Up to 45 feet (TDH); 100HP@1450 rpm
**Vertical centrifugal; no restrictions for influent flow; no restrictions for TDH; No restrictions for Max. HP
**Submersible Pump; Up to 2,000gmp (influent); Up to 160 feet (TDH); 100 HP @ 1800 rpm
TDH = Total Dynamic Head (estatical lift+ minor losses (i.e. valves) + mayor losses (i.e. pipe friction).
HP = Horse Power = {(Flow (Q gpm) x TDH)/ (3956 x Efficiency of the Pump -ηp)}
1. Submersible Pumps
The lift station will consist of a minimum of two submersible centrifugal sewage pumps, guide rails, wet well access, discharge seal and elbow, motor control center (MCC), starters, liquid level control system and all hardware necessary to make a complete working system.
Pump volute, impeller and motor housing shall be of cast iron construction. Submersible wastewater pumps shall be fitted with leakage sensors for detecting the presence of water in the oil and/or stator housing. (Consult pump manufacturers such as ITT Flygt, Gorman Rupp, Goulds pumps, Peerless Pumps).
Each pump will be furnished with a discharge connection system, which will permit removal and installation of pump without the need for the operator to enter the wet well.
2. Self Priming Centrifugal Pump
The lift station will employ vertical, dry pit, single stage non-clogging centrifugal sewage pumps with motors totally enclosed, fan cooled, and premium efficiency.
The pumps shall be of standard cast iron construction with ductile iron impeller, oil lubricated mechanical seal, and shall include casing wear rings to maintain sealing efficiency between the wear ring and impeller faces.
Design of lift station enclosure for vertical centrifugal stations will be coordinated with the City and Fire Departments with respect to occupancy class and electrical and HVAC system design.
Emergency Station Operation
To ensure that utility power or equipment failures do not cause sewer system overflows, provisions to maintain wastewater pump station including standby power and emergency storage shall be made.
*A diesel engine emergency electric generator shall be provided for all wastewater lift stations. An automatic transfer switch shall be provided to switch to emergency power on a power failure or a drop in any phase voltage to 70 percent of line voltage.
*Emergency storage capacity shall be provided to hold a minimum of 1 hour of peak hour design flow. The wet well, collection system and emergency storage containment can all serve as the emergency storage provided that the 1 hour requirement is met without a spill occurring. The emergency storage must be available above the high water alarm elevation in the wet well and must be continuously available without the need for an operator to switch valves or diversions.
General Requirements:
*Lift stations will not be allowed where an acceptable alternative gravity route exists.
*All wastewater lift stations shall have multiple pumps and shall be capable of delivering the design flow rate with the largest pump out of service.
*Pumps and related equipment must be designed so that it can be removed from the wet well with a vehicle mounted crane or other lifting device.
*Lift stations may be submersible pumping stations, package wet well / dry well stations or site designed vertical, dry pit, non-clogging, centrifugal pumping stations, depending on station size, head requirements and motor horse power. All pumps must be capable of passing a minimum three (3”) inch diameter sphere and shall be single speed. They must be designed specifically for handling raw, unscreened domestic sanitary wastewater.
*Above grade stations are preferred. They shall have a finished concrete floor with floor drains and be housed in an easily removable, pre fabricated fiberglass enclosure unless otherwise specified by the City. Below grade pump stations shall be reinforced concrete and shall extend at least 6 inches above finish grade.
**Adequate access, lighting, ventilation (minimum 10 air changes per hour), heating, Net Positive Suction Head (NPSHA), and potable water supply shall be provided to all wastewater lift stations.
Wet Well Design
*Wet wells shall be considered a hazardous environment. Whenever practical wastewater lift station wet wells shall be constructed of pre-cast reinforced concrete and shall be circular to a minimum of seventy two (72”) in diameter with 4-hour capacity or as necessary to accommodate the influent sewer, provide for adequate pump suction pipe or pump submergence as recommended by the pump manufacturer and to provide adequate volume to prevent the excessive cycling of pumps.
*Every effort will be made to prevent wastewater in the wet well from becoming septic. The wet well shall contain adequate vertical room for level sensing adjustments above and below the design levels.
*Primary high water alarm shall be set to wet well influent invert.
*Wet well interior walls and ceiling shall be lined with a material that is resistant to hydrogen sulfide and sulfuric acid. (i.e. fiberglass) and shall have a water proof system if anticipated to be below the water table. Regardless of the elevation of the water table, all joints in the concrete and all penetrations through the concrete shall be grouted with non-shrink grout on both sides of the joint or penetration.
*Access to well shall be through a top slab opening with aluminum hatch cover and frame. It shall allow for the removal of all equipment from the wet well, in no case smaller than 36 by 36 inches.
*Each wet well shall contain a sump (2 feet wide and 12 inches deep minimum) immediately underneath the inlet pipe to help assist in trapping large items to prevent them from entering the pumps.
*A sixty (60”) inch diameter approach manhole shall be constructed upstream of all wet wells, serving as a common point of connection for all sanitary sewer pipes tributary to the pump station. A single pipe shall extend from the approach manhole to the wet well. The approach manhole shall be located within the site fencing of the lift station.
*Provide restrained flexible couplings on all outlet piping within two (2’) feet of the station wall and a resilient-seat gate valve on the line into the wet well.
*Provide a bypass and a magnetic flow meter on the discharge of the pump station within a vault.
Pump Selection and Design Criteria (Consult Local Requirements)
Station Type / Influent Flow Range (gpm) / Maximum TDH / Maximum Motor HP
**Packaged wet well/ dry well; Up to 3,000 gpm (influent); Up to 45 feet (TDH); 100HP@1450 rpm
**Vertical centrifugal; no restrictions for influent flow; no restrictions for TDH; No restrictions for Max. HP
**Submersible Pump; Up to 2,000gmp (influent); Up to 160 feet (TDH); 100 HP @ 1800 rpm
TDH = Total Dynamic Head (estatical lift+ minor losses (i.e. valves) + mayor losses (i.e. pipe friction).
HP = Horse Power = {(Flow (Q gpm) x TDH)/ (3956 x Efficiency of the Pump -ηp)}
1. Submersible Pumps
The lift station will consist of a minimum of two submersible centrifugal sewage pumps, guide rails, wet well access, discharge seal and elbow, motor control center (MCC), starters, liquid level control system and all hardware necessary to make a complete working system.
Pump volute, impeller and motor housing shall be of cast iron construction. Submersible wastewater pumps shall be fitted with leakage sensors for detecting the presence of water in the oil and/or stator housing. (Consult pump manufacturers such as ITT Flygt, Gorman Rupp, Goulds pumps, Peerless Pumps).
Each pump will be furnished with a discharge connection system, which will permit removal and installation of pump without the need for the operator to enter the wet well.
2. Self Priming Centrifugal Pump
The lift station will employ vertical, dry pit, single stage non-clogging centrifugal sewage pumps with motors totally enclosed, fan cooled, and premium efficiency.
The pumps shall be of standard cast iron construction with ductile iron impeller, oil lubricated mechanical seal, and shall include casing wear rings to maintain sealing efficiency between the wear ring and impeller faces.
Design of lift station enclosure for vertical centrifugal stations will be coordinated with the City and Fire Departments with respect to occupancy class and electrical and HVAC system design.
Emergency Station Operation
To ensure that utility power or equipment failures do not cause sewer system overflows, provisions to maintain wastewater pump station including standby power and emergency storage shall be made.
*A diesel engine emergency electric generator shall be provided for all wastewater lift stations. An automatic transfer switch shall be provided to switch to emergency power on a power failure or a drop in any phase voltage to 70 percent of line voltage.
*Emergency storage capacity shall be provided to hold a minimum of 1 hour of peak hour design flow. The wet well, collection system and emergency storage containment can all serve as the emergency storage provided that the 1 hour requirement is met without a spill occurring. The emergency storage must be available above the high water alarm elevation in the wet well and must be continuously available without the need for an operator to switch valves or diversions.
Wednesday, March 3, 2010
Water Distribution System Design
A water system must safely convey the required amount of high quality water throughout a sound distribution system at the least cost. Therefore, the Engineer must consult pertinent and current requirements from federal, State, and regional agencies to ensure the system complies with all standards and regulations.
Drinking Water System Regulators
*Environmental Protection Agency (EPA)
*California Department of Public Health
*California Public Utilities Commission
*County/City Department of Public of Works
*California Administrative Code, regarding cross-connections and backflow prevention.
*Uniform Fire Code
Improvement Plans Requirements
Provide a detailed utility plan showing onsite and offsite public and private water and fire protection systems, including appurtenances and connections. Show location, pipe material, diameters, fire hydrants, valves, backflow protection, horizontal and vertical separations, slopes, cover, inverts, laterals, right-of-way, crossings, and any other necessary facility to demonstrate compliance with engineering principles and agencies regulators.
Materials
Public water mains may be constructed of PVC (http://www.plasticpipe.org/), Ductile Iron (http://www.dipra.org/), ReinforcedConcrete Pipe, RCP (http://www.concrete-pipe.org/), or Wrapped Steel Pipe. Asbestos cement pipe are not allowed under any circumstances.
*Mains eight (8) to twelve (12) inches in diameter will be PVC, pressure class 150, DR 18, AWWA Standard C900 or Ductile Iron, pressure class 350 per AWWA Standard C151. Where the normal mainline static pressure exceeds 100 psi, DI or PVC Pressure Class 200, DR14 must be used.
*Mains sixteen (16) inches in diameter will be PVC, pressure rating 165psi, AWWA C905, DR25 or Ductile Iron (DI) per AWWA Standard C151. Where the normal mainline static pressure exceeds 100 psi, AWWA Standard C905, DR18 with a pressure rating of 235 psi or Ductile Iron (DI) Pipe must be used.
*Mains twenty (20) inches in diameter and larger water mains will be concrete cylinder pipe, wrapped steel pipe, or Ductile Iron.
*Service laterals will be copper, PVC, or DIP per applicable City Standards.
Alignment
Public water mains shall be designed inside the street right-of-way. In general, public water systems shall be designed only where they serve multiple lots and where appropriate access for maintenance can be provided.
Horizontal Alignment
*Conform to the State of California Department of Health Services “Criteria for the separation water Main and Sanitary sewers”, appendix A. In general, ten (10) feet wall to wall separation.
*Conform to manufacturer requirements for minimum allowable radius curvatures. In situations such as streets with smaller radius curves, the water system will be designed in straight segments parallel to the sewer or storm drain system.
*Minimum separation from storm drains is five (5) feet and from monuments, gas, electrical, phone, cable and other dry utility shall be four (4) feet clear.
*All public water mains must be designed a minimum of five (5) feet from all structures such as manholes or drop inlets. A minimum of three (3) feet from the lip of gutter shall be provided.
* Five (5) feet separation from the edge of easements shall be provided for public water mains.
*Dual water mains shall have a minimum five (5) feet clear horizontal separation.
*Crossings shall be designed close as 90 degrees to that facility. Crossing less than 45 degrees will only be approved when no other design is possible.
*Minimum separation between water and sewer lateral services shall be five (5) feet clearance.
Vertical Alignment
*Provide a minimum of six (6”) inches of vertical separation from storm drains and “dry” utilities.
*Conform to State of California Department of Health Services “Criteria for the Separation of Water Main and Sanitary Sewers”, Appendix “A”. In general, one (1) foot wall to wall separation.
*When the minimum cannot be maintained, concrete encasement or ductile iron pipe may be submitted for approval.
Main Sizing Criteria
*Allowable nominal sizes for public water mains are 8”, 12”, and 16”. The minimum new public main size for residential developments is 8" inches and when serving industrial/commercial and/or multi-family residential developments greater than two units, must be a minimum of 12" inches.
*Public water mains must be sized to meet minimum Fire Code requirement in addition to domestic and irrigation demands.
Cover
*Cover is the distance from the top of the pipe to final finished grade. Typically the minimum standard depths of cover for 4” to 8” inches water mains is 3”-0” feet; for mains 10” to 12” shall be 3’-6”; and for mains 16” or greater minimum cover is 4’-0”.
*Where standard cover cannot be maintained, either an under-crossing or over-crossing shall be provided.
Design Criteria
*Operation Conditions
Pressure (psi) and velocity (fps)
Maximum day: 60 psi(max); 40 psi (min); 5 fps (max)
Maximum day and Fire: 80 psi(max); 20 psi(min); 10 fps (max)
Peak hour: 80 psi(max); 30 psi(min); 7 fps (max)
*If pressure measured at any faucet is less than 35 psi, a pressure booster system is required. If pressure at any faucet exceeds 80 psi, a private pressure regulating device is required.
Rate of Domestic use
*Land Use
Average Day Demand (ADD) - Gallons per Acre Day
Fire Flow (FF) - Gallons per minute (gpm)
Fire Duration (FD) - Hour (hr)
Low Density Residential: 2,500(ADD); 1,500(FF); 2(FD)
Medium Density Residential: 3,200(ADD); 1,500(FF); 2(FD)
High Density Residential: 3,600(ADD); 2,500(FF); 3(FD)
Commercial: 2,200(ADD); 3,000(FF); 3(FD)
Schools: 2,200(ADD); 4,000(FF); 4(FD)
*Potable water demand for planning purposes shall be estimated using the water demand factors outlined in the Master Plan.
**Maximum Day Demand (MDD) = 2.0xAverage Day (ADD)
**Peak Hour Demand = 4.0xAverage Day (ADD)
** The Hazen-William formula shall be used in the hydraulic study of the system, using a “C” value of 130 for cement-lined pipe, PVC C900, and ductile iron pipe.
Looping
For system reliability, to minimize pipe size, and to minimize the number of people affected by a system shutdown, either for domestic or fire protection purposes, no more than 100 residential units may be served by a single-feed water system. Where more than 100 units are to be served, a dual-feed (or looping) public water system must be designed.
Valve Placement
*Intersecting mainlines should be equipped with isolation or shut-off valves (usually gate valves) to minimize disruption during repairs. “T” intersections typically require three valves and cross intersection typical require four valves.
*Valves within 250' feet of an intersection may be considered as part of the intersection.
*All hydrants must be on separately valved sections of the public main.
*Valves shall be designed to maximum interval of 1,000 feet.
Air release and Vacuum relief valves (ARV)
*Air release and vacuum relief valves are required at substantial high points in the system that are one pipe diameter or higher than the remainder system, such as over a hilltop or at the upper end of a dead end main.
Pressure reducing valves (PRV)
*Design pressure reducing valves to maintain overall system balance and to maintain service pressure levels within the parameters established within the system design standards.
Backflow Prevention Devices
These devices are a reasonable and effective mean of protecting water system from backflow.
Backflow prevention devices or air-gaps of a type shall be located as close as possible to the service connection and shall be installed as follow:
*Premises within which any substance is handled under pressure that could potentially permit backflow or back-siphonage into the potable water system.
*Premises which have more than one service connection and which may contain cross-connections that may result in the pollution of the potable water system.
*Premises having gray and/or recycled water use systems.
*Examples of premises which require the installation of a backflow prevention device are: Auto repair/painting, car wash, chemical or processing facilities, fire systems, gas stations, hospital and medical facilities, irrigation systems, restaurants, schools, laundry facility, swimming pool.
**All backflow devices must be listed on the latest revision of the approved USC Foundation for Cross-Connection Connection and Hydraulic Research list. List includes (manufacturer’s name, model, size, etc).
**In General City standards provide a list of premises requiring backflow prevention devices along with the type needing to be installed (Air gap, double check, reduced pressure, double check with detector).
Fire Hydrants
*Design of hydrant locations must meet the Fire Code requirements and be approved by the Fire Department for logistics and by the Utilities Department for maintainability. In general, hydrants shall have 500’ feet maximum spacing or 300’ feet in high fire severity zones.
*Locate hydrants at intersections. If not possible locate them near a property line, and/or five (5’) feet from residential driveways.
Joint Restraint
Thrust blocking or restraints should be provided where changes in water direction occur and where reductions in pipe diameter are made and dead ends. A concrete mass or a mechanical joint restraint device may provide thrust restraints. Water mains installed at a slope of fifteen (15) percent or greater will be designed with restrained joints.
*Typical standard bend angles (degrees) are: 11 ¼ , 22 ½, 45, 90.
Hot Tap
Hot taps are not allowed within two (2’) feet of a joint, otherwise, a “cut-in-tee” shall be used.
Easements
An easement must be provided over any public water system when it is outside the public right-of-way. The easement must be a minimum of fifteen (15’) feet wide if it only contains a water main or twenty (20’) feet if it contains another facility. Separate access easements may be required depending on site conditions.
No structures may encroach on, above or below the surface of the ground in any public water easement.
Abandonment of water mains and services
*remove the valve and saddle for all water services two (2) inches or less and install a full circle clamp on the main.
*For flanged or mechanical joint tees remove the valve and install a blind flange or mechanical joint plug.
*For push-on tees, the tee, valve and thrust restraint must be removed and the main repaired with approved pipe and suitable couplings.
*Valve boxes for abandoned valves must be removed.
*Pipes twelve (12”) inches and larger to be abandoned need to be removed or broken every fifty (50’) feet and filled with sand slurry. (Check City Standards)
*Where a fire hydrant is to be abandoned, the hydrant barrel, break off riser, and check valve are to be removed. Abandonment of fire hydrants must be approved by the Fire Department.
Connections
*A permit shall be obtained for each connection to the water system.
Drinking Water System Regulators
*Environmental Protection Agency (EPA)
*California Department of Public Health
*California Public Utilities Commission
*County/City Department of Public of Works
*California Administrative Code, regarding cross-connections and backflow prevention.
*Uniform Fire Code
Improvement Plans Requirements
Provide a detailed utility plan showing onsite and offsite public and private water and fire protection systems, including appurtenances and connections. Show location, pipe material, diameters, fire hydrants, valves, backflow protection, horizontal and vertical separations, slopes, cover, inverts, laterals, right-of-way, crossings, and any other necessary facility to demonstrate compliance with engineering principles and agencies regulators.
Materials
Public water mains may be constructed of PVC (http://www.plasticpipe.org/), Ductile Iron (http://www.dipra.org/), ReinforcedConcrete Pipe, RCP (http://www.concrete-pipe.org/), or Wrapped Steel Pipe. Asbestos cement pipe are not allowed under any circumstances.
*Mains eight (8) to twelve (12) inches in diameter will be PVC, pressure class 150, DR 18, AWWA Standard C900 or Ductile Iron, pressure class 350 per AWWA Standard C151. Where the normal mainline static pressure exceeds 100 psi, DI or PVC Pressure Class 200, DR14 must be used.
*Mains sixteen (16) inches in diameter will be PVC, pressure rating 165psi, AWWA C905, DR25 or Ductile Iron (DI) per AWWA Standard C151. Where the normal mainline static pressure exceeds 100 psi, AWWA Standard C905, DR18 with a pressure rating of 235 psi or Ductile Iron (DI) Pipe must be used.
*Mains twenty (20) inches in diameter and larger water mains will be concrete cylinder pipe, wrapped steel pipe, or Ductile Iron.
*Service laterals will be copper, PVC, or DIP per applicable City Standards.
Alignment
Public water mains shall be designed inside the street right-of-way. In general, public water systems shall be designed only where they serve multiple lots and where appropriate access for maintenance can be provided.
Horizontal Alignment
*Conform to the State of California Department of Health Services “Criteria for the separation water Main and Sanitary sewers”, appendix A. In general, ten (10) feet wall to wall separation.
*Conform to manufacturer requirements for minimum allowable radius curvatures. In situations such as streets with smaller radius curves, the water system will be designed in straight segments parallel to the sewer or storm drain system.
*Minimum separation from storm drains is five (5) feet and from monuments, gas, electrical, phone, cable and other dry utility shall be four (4) feet clear.
*All public water mains must be designed a minimum of five (5) feet from all structures such as manholes or drop inlets. A minimum of three (3) feet from the lip of gutter shall be provided.
* Five (5) feet separation from the edge of easements shall be provided for public water mains.
*Dual water mains shall have a minimum five (5) feet clear horizontal separation.
*Crossings shall be designed close as 90 degrees to that facility. Crossing less than 45 degrees will only be approved when no other design is possible.
*Minimum separation between water and sewer lateral services shall be five (5) feet clearance.
Vertical Alignment
*Provide a minimum of six (6”) inches of vertical separation from storm drains and “dry” utilities.
*Conform to State of California Department of Health Services “Criteria for the Separation of Water Main and Sanitary Sewers”, Appendix “A”. In general, one (1) foot wall to wall separation.
*When the minimum cannot be maintained, concrete encasement or ductile iron pipe may be submitted for approval.
Main Sizing Criteria
*Allowable nominal sizes for public water mains are 8”, 12”, and 16”. The minimum new public main size for residential developments is 8" inches and when serving industrial/commercial and/or multi-family residential developments greater than two units, must be a minimum of 12" inches.
*Public water mains must be sized to meet minimum Fire Code requirement in addition to domestic and irrigation demands.
Cover
*Cover is the distance from the top of the pipe to final finished grade. Typically the minimum standard depths of cover for 4” to 8” inches water mains is 3”-0” feet; for mains 10” to 12” shall be 3’-6”; and for mains 16” or greater minimum cover is 4’-0”.
*Where standard cover cannot be maintained, either an under-crossing or over-crossing shall be provided.
Design Criteria
*Operation Conditions
Pressure (psi) and velocity (fps)
Maximum day: 60 psi(max); 40 psi (min); 5 fps (max)
Maximum day and Fire: 80 psi(max); 20 psi(min); 10 fps (max)
Peak hour: 80 psi(max); 30 psi(min); 7 fps (max)
*If pressure measured at any faucet is less than 35 psi, a pressure booster system is required. If pressure at any faucet exceeds 80 psi, a private pressure regulating device is required.
Rate of Domestic use
*Land Use
Average Day Demand (ADD) - Gallons per Acre Day
Fire Flow (FF) - Gallons per minute (gpm)
Fire Duration (FD) - Hour (hr)
Low Density Residential: 2,500(ADD); 1,500(FF); 2(FD)
Medium Density Residential: 3,200(ADD); 1,500(FF); 2(FD)
High Density Residential: 3,600(ADD); 2,500(FF); 3(FD)
Commercial: 2,200(ADD); 3,000(FF); 3(FD)
Schools: 2,200(ADD); 4,000(FF); 4(FD)
*Potable water demand for planning purposes shall be estimated using the water demand factors outlined in the Master Plan.
**Maximum Day Demand (MDD) = 2.0xAverage Day (ADD)
**Peak Hour Demand = 4.0xAverage Day (ADD)
** The Hazen-William formula shall be used in the hydraulic study of the system, using a “C” value of 130 for cement-lined pipe, PVC C900, and ductile iron pipe.
Looping
For system reliability, to minimize pipe size, and to minimize the number of people affected by a system shutdown, either for domestic or fire protection purposes, no more than 100 residential units may be served by a single-feed water system. Where more than 100 units are to be served, a dual-feed (or looping) public water system must be designed.
Valve Placement
*Intersecting mainlines should be equipped with isolation or shut-off valves (usually gate valves) to minimize disruption during repairs. “T” intersections typically require three valves and cross intersection typical require four valves.
*Valves within 250' feet of an intersection may be considered as part of the intersection.
*All hydrants must be on separately valved sections of the public main.
*Valves shall be designed to maximum interval of 1,000 feet.
Air release and Vacuum relief valves (ARV)
*Air release and vacuum relief valves are required at substantial high points in the system that are one pipe diameter or higher than the remainder system, such as over a hilltop or at the upper end of a dead end main.
Pressure reducing valves (PRV)
*Design pressure reducing valves to maintain overall system balance and to maintain service pressure levels within the parameters established within the system design standards.
Backflow Prevention Devices
These devices are a reasonable and effective mean of protecting water system from backflow.
Backflow prevention devices or air-gaps of a type shall be located as close as possible to the service connection and shall be installed as follow:
*Premises within which any substance is handled under pressure that could potentially permit backflow or back-siphonage into the potable water system.
*Premises which have more than one service connection and which may contain cross-connections that may result in the pollution of the potable water system.
*Premises having gray and/or recycled water use systems.
*Examples of premises which require the installation of a backflow prevention device are: Auto repair/painting, car wash, chemical or processing facilities, fire systems, gas stations, hospital and medical facilities, irrigation systems, restaurants, schools, laundry facility, swimming pool.
**All backflow devices must be listed on the latest revision of the approved USC Foundation for Cross-Connection Connection and Hydraulic Research list. List includes (manufacturer’s name, model, size, etc).
**In General City standards provide a list of premises requiring backflow prevention devices along with the type needing to be installed (Air gap, double check, reduced pressure, double check with detector).
Fire Hydrants
*Design of hydrant locations must meet the Fire Code requirements and be approved by the Fire Department for logistics and by the Utilities Department for maintainability. In general, hydrants shall have 500’ feet maximum spacing or 300’ feet in high fire severity zones.
*Locate hydrants at intersections. If not possible locate them near a property line, and/or five (5’) feet from residential driveways.
Joint Restraint
Thrust blocking or restraints should be provided where changes in water direction occur and where reductions in pipe diameter are made and dead ends. A concrete mass or a mechanical joint restraint device may provide thrust restraints. Water mains installed at a slope of fifteen (15) percent or greater will be designed with restrained joints.
*Typical standard bend angles (degrees) are: 11 ¼ , 22 ½, 45, 90.
Hot Tap
Hot taps are not allowed within two (2’) feet of a joint, otherwise, a “cut-in-tee” shall be used.
Easements
An easement must be provided over any public water system when it is outside the public right-of-way. The easement must be a minimum of fifteen (15’) feet wide if it only contains a water main or twenty (20’) feet if it contains another facility. Separate access easements may be required depending on site conditions.
No structures may encroach on, above or below the surface of the ground in any public water easement.
Abandonment of water mains and services
*remove the valve and saddle for all water services two (2) inches or less and install a full circle clamp on the main.
*For flanged or mechanical joint tees remove the valve and install a blind flange or mechanical joint plug.
*For push-on tees, the tee, valve and thrust restraint must be removed and the main repaired with approved pipe and suitable couplings.
*Valve boxes for abandoned valves must be removed.
*Pipes twelve (12”) inches and larger to be abandoned need to be removed or broken every fifty (50’) feet and filled with sand slurry. (Check City Standards)
*Where a fire hydrant is to be abandoned, the hydrant barrel, break off riser, and check valve are to be removed. Abandonment of fire hydrants must be approved by the Fire Department.
Connections
*A permit shall be obtained for each connection to the water system.
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