DISTRIBUTION SYSTEMS


8.0 MATERIALS
8.1 WATER MAIN DESIGN
8.2 VALVES
8.3 HYDRANTS
8.4 AIR RELIEF VALVES, VALVE, METER AND BLOW-OFF CHAMBERS
8.5 INSTALLATION OF MAINS
8.6 SEPARATION OF WATER MAINS, SANITARY SEWERS AND STORM SEWERS
8.7 SURFACE WATER CROSSINGS
8.8 CROSS-CONNECTIONS AND INTERCONNECTIONS
8.9 WATER SERVICES AND PLUMBING
8.10 SERVICE METERS
8.11 WATER LOADING STATIONS

8.0 MATERIALS

8.0.1 Standards, materials selection

Pipe, fittings, valves and fire hydrants shall conform to the latest standards issued by the AWWA and/or NSF, if such standards exist, and be acceptable to the reviewing authority. In the absence of such standards, materials meeting applicable Product Standards and acceptable to the reviewing authority may be selected. Special attention shall be given to selecting pipe materials which will protect against both internal and external pipe corrosion. Pipes and pipe fittings containing more than 8% lead shall not be used. All products. shall comply with ANSI/NSF standards.

8.0.2 Permeation of system by organic compounds

Where distribution systems are installed in areas of groundwater contaminated by organic compounds:

a. pipe and joint materials which are not subject to permeation of the organic compounds shall be used.

b. non-permeable materials shall be used for all portions of the system including water main, service connections and hydrant leads.

8.0.3 Used materials

Water mains which have been used previously for conveying potable water may be reused provided they meet the above standards and have been restored practically to their original condition.

8.0.4 Joints

Packing and jointing materials used in the joints of pipe shall meet the standards of the AWWA and the reviewing authority. Pipe having mechanical joints or slip-on joints with rubber gaskets is preferred. Lead-tip gaskets shall not be used. Repairs to lead-joint pipe shall be made using alternative methods.

8.1 WATER MAIN DESIGN

8.1.1 Pressure

All water mains, including those not designed to provide fire protection, shall be sized after a hydraulic analysis based on flow demands and pressure requirements. The system shall be designed to maintain a minimum pressure of 20 psi (140 kPa) at ground level at all points in the distribution system under all conditions of flow. The normal working pressure in the distribution system should be approximately 60 to 80 psi (410 - 550 kPa) and not less than 35 psi (240 kPa).

8.1.2 Diameter

The minimum size of water main for providing fire protection and serving fire hydrants shall be six-inch diameter. Larger size mains will be required if necessary to allow the withdrawal of the required fire flow while maintaining the minimum residual pressure specified in Section 8.1.1.

8.1.3 Fire protection

When fire protection is to be provided, system design should be such that fire flows and facilities are in accordance with the requirements of the state Insurance Services Office.

8.1.4 Small mains for domestic service

the minimum size of water main in the distribution system where fire protection is not to be provided should be a minimum of three (3) inch in diameter. Any departure from minimum requirements shall be justified by hydraulic analysis and future water use, and can be considered only in special circumstances.

8.1.5 Hydrants

Water mains not designed to carry fire-flows shall not have fire hydrants connected to them.

8.1.6 Dead ends

a. In order to provide increased reliability of service and reduce head loss, dead ends shall be minimized by making appropriate tie-ins whenever practical.

b. Where dead-end mains occur, they shall be provided with a fire hydrant if flow and pressure are sufficient, or with an approved flushing hydrant or blow-off for flushing purposes. Flushing devices should be sized to provide flows which will give a velocity of at least 2.5 feet per second in the water main being flushed. No flushing device shall be directly connected to any sewer.

8.2 VALVES

Sufficient valves shall be provided on water mains so that inconvenience and sanitary hazards will be minimized during repairs. Valves should be located at not more than 500 foot intervals in commercial districts and at not more than one block or 800 foot intervals in other districts. Where systems serve widely scattered customers and where future development is not expected, the valve spacing should not exceed one mile.

8.3 HYDRANTS

8.3.1 Location and spacing

Hydrants should be provided at each street intersection and at intermediate points between intersections as recommended by the state Insurance Services Office. Generally, hydrant spacing may range from 350 to 600 feet depending on the area being served.

8.3.2 Valves and nozzles

Fire hydrants should have a bottom valve size of at least five inches, one 4-1/2 inch pumper nozzle and two 2-1/2 inch nozzles.

8.3.3 Hydrant leads

The hydrant lead shall be a minimum of six inches in diameter. Auxiliary valves shall be installed in all hydrant leads.

8.3.4 Drainage

Hydrant drains should be plugged. When the drains are plugged the barrels must be pumped dry after use during freezing weather. Where hydrant drains are not plugged, a gravel pocket or dry well shall be provided unless the natural soils will provide adequate drainage. Hydrant drains shall not be connected to or located within 10 feet of sanitary sewers or storm drains.

8.4 AIR RELIEF VALVES; VALVE, METER AND BLOW-OFF CHAMBERS

8.4.1 Air relief valves

At high points in water mains where air can accumulate provisions shall be made to remove the air by means of hydrants or air relief valves. Automatic air relief valves shall not be used in situations where flooding of the manhole or chamber may occur.

8.4.2 Air relief valve piping

The open end of an air relief pipe from automatic valves shall be extended to at least one foot above grade and provided with a screened, downward-facing elbow. The pipe from a manually operated valve should be extended to the top of the pit. Use of manual air relief valves is recommended wherever possible.

8.4.3 Chamber drainage

Chambers, pits or manholes containing valves, blow-offs, meters, or other such appurtenances to a distribution system, shall not be connected directly to any storm drain or sanitary sewer, nor shall blow-offs or air relief valves be connected directly to any sewer.

Such chambers or pits shall be drained to the surface of the ground where they are not subject to flooding by surface water, or to absorption pits underground.

8.5 INSTALLATION OF MAINS

8.5.1 Standards

Specifications shall incorporate the provisions of the AWWA standards and/or manufacturer's recommended installation procedures.

8.5.2 Bedding

A continuous and uniform bedding shall be provided in the trench for all buried pipe. Backfill material shall be tamped in layers around the pipe and to a sufficient height above the pipe to adequately support and protect the pipe. Stones found in the trench shall be removed for a depth of at least six inches below the bottom of the pipe.

8.5.3 Cover

All water mains shall be covered with sufficient earth or other insulation to prevent freezing.

8.5.4 Blocking

All tees, bends, plugs and hydrants shall be provided with reaction blocking, tie rods or joints designed to prevent movement.

8.5.5 Pressure and leakage testing

All types of installed pipe shall be pressure tested and leakage tested in accordance with the latest edition of AWWA Standard C600.

8.5.6 Disinfection

All new, cleaned or repaired water mains shall be disinfected in accordance with AWWA Standard C651. The specifications shall include detailed procedures for the adequate flushing, disinfection, and microbiological testing of all water mains. In an emergency or unusual situation, disinfection procedure shall be discussed with the reviewing authority.

8.5.7 External corrosion

a. Provide for a system of records by which the nature and frequency of corrosion problems are recorded. On a plat map of the distribution system, show the location of each problem so that follow-up investigations and improvements can be made when a cluster of problems is identified.

b. If needed, perform a survey to determine the existence of facilities or installations that would provide the potential for stray, direct electric currents. Also, determine whether problems are caused by the users* of water pipes as grounds for the electrical system.

c. In previously unexplored areas where aggressive soil conditions are suspect, or in areas where there are known aggressive soil conditions, perform analyses to determine the actual aggressiveness of the soil.

d. If soils are found to be aggressive, take necessary action to protect the water main, such as by encasement of the water main in polyethylene, provision of cathodic protection (in very severe instances), or using corrosion resistant water main material.

8.6 SEPARATION OF WATER MAINS, SANITARY SEWERS AND STORM SEWERS

8.6.1 General

The following factors should be considered in providing adequate separation:

a. materials and type of joints for water and sewer pipes,

b. soil conditions,

c. service and branch connections into the water main and sewer line,

d. compensating variations in the horizontal and vertical separations,

e. space for repair and alterations of water and sewer pipes,

f. off-setting of pipes around manholes.

8.6.2 Parallel installation

Water mains shall be laid at least 10 feet horizontally from any existing or proposed sewer. The distance shall be measured edge to edge. In cases where it is not practical to maintain a ten foot separation, the reviewing authority may allow deviation on a case-by-case basis, if supported by data from the design engineer. Such deviation may allow installation of the water main closer to a sewer, provided that the water main is laid in a separate trench or on an undisturbed earth shelf located on one side of the sewer at such an elevation that the bottom of the water main is at least 18 inches above the top of the sewer.

8.6.3 Crossings

Water mains crossing sewers shall be laid to provide a minimum vertical distance of 18 inches between the outside of the water main and the outside of the sewer. This shall be the case where the water main is either above or below the sewer. At crossings, one full length of water pipe shall be located so both joints will be as far from the sewer as possible. Special structural support for the water and sewer pipes may be required.

8.6.4 Exception

The reviewing authority must specifically approve any variance from the requirements of Sections 8.6.2 and 8.6.3 when it is impossible to obtain the specified separation distances. Where sewers are being installed and Section 8.6.2 and 8.6.3 cannot be met, the sewer materials shall be waterworks grade 150 psi (1.0 MPa) pressure rated pipe or equivalent and shall be pressure tested to ensure water tightness.

8.6.5 Force mains

There shall be at least a 10 foot horizontal separation between water mains and sanitary sewer force mains. There shall be an 18 inch vertical separation at crossings as required in Section 8.6.3.

8.6.6 Sewer manholes

No water pipe shall pass through or come in contact with any part of a sewer manhole.

8.6.7 Separation of water mains from other sources of contamination

Design engineers should exercise caution when locating water mains at or near certain sites such as sewage treatment plants or industrial complexes. Individual septic tanks must be located and avoided. The engineer must contact the reviewing authority to establish specific design requirements for locating water mains near any source of contamination.

8.7 SURFACE WATER CROSSINGS

Surface water crossings, whether over or under water, present special problems. The reviewing authority should be consulted before final plans are prepared.

8.7.1 Above-water crossings

The pipe shall be adequately supported and anchored, protected from damage and freezing, and accessible for repair or replacement.

8.7.2 Underwater crossings

A minimum cover of two feet shall be provided over the pipe. When crossing water courses which are greater than 15 feet in width, the following shall be provided:

a. the pipe shall be of special construction, having flexible, restrained, or welded watertight joints,

b. valves shall be provided at both ends of water crossings so that the section can be isolated for testing or repair; the valves shall be easily accessible, and not subject to flooding; and the valve closest to the supply source shall be in a manhole,

c. permanent taps shall be made on each side of the valve within the manhole to allow insertion of a small meter to determine leakage and for sampling purposes.

8.8 CROSS-CONNECTIONS AND INTERCONNECTIONS

8.8.1 Cross-connections

There shall be no connection between the distribution system and any pipes, pumps, hydrants, or tanks whereby unsafe water or other contaminating materials may be discharged or drawn into the system. Each water utility shall have a program conforming to state requirements to detect and eliminate cross connections.

8.8.2 Cooling water

Neither steam condensate nor cooling water from engine jackets or other heat exchange devices shall be returned to the potable water supply.

8.8.3 Interconnections

The approval of the reviewing authority shall be obtained for interconnections between potable water supplies.

8.9 WATER SERVICES AND PLUMBING

8.9.1 Plumbing

Water services and plumbing shall conform to relevant local and/or state plumbing codes, or to the applicable National Plumbing Code. Solders and flux containing more than 0.2% lead and pipe and pipe fittings containing more than 8% lead shall not be used.

8.9.2 Booster pumps

Individual booster pumps shall not be allowed for any individual service from the public water supply mains.

8.10 SERVICE METERS

Each service connection should be individually metered.

8.11 WATER LOADING STATIONS

Water loading stations present special problems since the fill line may be used for filling both potable water vessels and other tanks or contaminated vessels. To prevent contamination of both the public supply and potable water vessels being filled, the following principles shall be met in the design of water loading stations:

a. there shall be no backflow to the public water supply,

b. the piping arrangement shall prevent contaminant being transferred from a hauling vessel to others subsequently using the station,

c. hoses shall not be contaminated by contact with the ground.

Acceptable Water Loading Station Devices

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