Instrumentation & control and distribution systems

Chapter 9: Instrumentation & Control

Instrumentation and controls should be provided to allow safe and efficient operation of all parts of the drinking water treatment plant and distribution system. The requirements for instrumentation and control will be highly dependent on the size and complexity of the plant and the extent of remote operability. The municipality/owner and the designer together should determine the degree of automation to be provided to support operation of the drinking-water system.

9.1 General

The objectives of instrumentation and control are to support the continuous production of high quality drinking water in an efficient manner in terms of staff and resources used, and to satisfy the regulatory requirements for monitoring and recording operational data in accord with a control philosophy document prepared by the designer.

For information regarding monitoring and control systems for poisonous gases such as chlorine or ozone, the designer should refer to the supplier or manufacturer recommendations for health and safety.

9.2 Process narrative & basis of control

The designer should prepare a report which provides a process narrative for the drinking-water system that briefly describes each component of the drinking-water system, including the raw water quality, intake structure, treatment and pumping equipment, distribution system components, instrumentation, and monitoring and sampling equipment as applicable. In addition, the report should also identify and explain the basis of control for the system.

Process and instrumentation diagrams (P&ID) should be developed for all drinking-water system facilities and should include all major and minor processes along with all ancillary process equipment.

Control systems should be designed with a user-friendly human-machine interface (HMI) system to facilitate plant operation and on-line monitoring. Equipment status, flow rates, water levels, pressures and chemical feed rates should all be displayed via an HMI. All automated systems should be designed with a manual override or another form of redundancy to allow safe operation in the event of a hardware or communication failure.

9.3 Control systems

The type of control provided for the operation of a drinking-water system can vary from simple manual control without any automatic function (either local or remote), through semi-automatic control which combines manual control with automatic control for a single piece of equipment, to a fully automatic control system which turns equipment on and off or adjusts operating status in response to signals from instruments and sensors.

In selecting a control system, the designer and the municipality/owner should consider the following factors. Manual Control Systems:

• Are simpler to maintain and repair than automatic systems and are lower in initial cost, but require the on-site presence of an operator when producing drinking water; and
• The initial low costs may be outweighed by high labour and operating costs including, chemical and energy costs incurred by poorer process control.

Automatic Control Systems:

• Provide a more consistent product with lower labour costs;
• Require skilled maintenance;
• Should provide a level of reliability appropriate for the control function; and
• Should be designed to have the capability to manage any set of conditions which may occur.

The designer should select a control system based on the risks to public health, the complexity of the processes to be controlled, and should take into consideration the capability and limitations of the knowledge and skill of regular operating staff.

Control systems should be fully alarmed with process deficiencies immediately apparent to the operators. All automatic controls should be provided with manual override and/or back-up systems, depending on the nature of the process being controlled, as well as status and alarm archiving for review as required.

Automatic remote control systems should include means for detecting communication failure (e.g., by using "heartbeat" communication integrity confirmation). In the event of communication failure, the designer should ensure safe mode operation or safe shut down of the remote part of the system. The designer should make provision for the system to resume operation automatically when communication is restored or remain shut down until attended by an operator. Redundant communication pathways should be considered for critical remote controls, with either automatic or manual switching. Primary instruments (sensors or analyzers) which form part of an automatic control loop should have appropriate redundant means of avoiding unsafe operation in case of instrument failure. The design should minimize pressure transients in the water distribution system following shut downs.

9.4 Monitoring

The design must satisfy the minimum requirements for drinking-water systems monitoring as set out in the Safe Drinking Water Act, 2002 (SDWA), regulations under it and the Procedure for Disinfection of Drinking Water in Ontario (Disinfection Procedure).

Table 9-1 shows frequently used surface water treatment process related monitoring systems that the designer could consider (but not be limited by) in designing instrumentation and control systems. Selection of the level of instrumentation and control should be made in conjunction with the municipality/owner, considering factors such as:

• Level of maintenance and calibration required;
• Desired versus required level of automation;
• Data retrieval and storage requirements; and
• Capital costs.

The use of single analyzers or primary devices on a time-share basis for monitoring multiple points is discouraged. However, if adopted, the rate of sample flow to the instrument should be sufficient to give a true indication of the sample value within the time allotted to that sample. Sample line length and transport time to the analyzer should be taken into account for proper loop control. The designer should ensure any specific instrument installation requirements are met (e.g., upstream/downstream minimum pipe lengths for flow meters, turbidity analyzer de-bubblers¹³, and minimum/maximum instrument flow rates).

The designer should ensure that samples taken are fully representative of the true conditions, (e.g., proper mixing and reaction of chemicals has occurred).

Where analysers are part of an automatic control loop, the system lag time should be minimized to avoid hunting or other instabilities.

Table 9-1: Frequently Used Surface Water Treatment Process Related Monitoring System

Process	Monitoring systems
Raw Water	Raw water turbidity, pH, temperature, conductivity, ammonia Instantaneous flow rate and totalized volume per day Mussel control related sub-systems Particle counters
Coagulation/Flocculation	pH Coagulant and coagulant/filtration aid feed rates Streaming current Mixers speed/power
Sedimentation	Effluent turbidity Sludge level Blow down valve status and flow rate
Solids Contact Clarifiers	Effluent turbidity Sludge level Blow down valve status and flow rate
Proprietary Clarifiers	Instrumentation for proprietary clarifiers including ballasted flocculation and dissolved air floatation should be provided in accordance with manufacturer recommendations Effluent turbidity
Lime Softening	pH following lime addition and recarbonation
Filtration (granular media)	Influent water level Influent turbidity, filter-to-waste turbidity Mandatory individual filter effluent turbidity Filtration rate Effluent control valve position Water level in filters Head loss Filter run time Filter effluent particle counts Filter status (e.g., on-line, backwash required, in backwash, ready, off-line)
Backwash	Backwash flow rate and totalized volume Air scour/ surface wash status When automated, control sequence status
Filtration (membrane)	Instrumentation should be provided in accordance with manufacturer recommendations Turbidity/particle count/integrity test on each individual filter train effluent Filter train flow rate Pressure differential Filter train status (e.g., on-line, backpulse, clean, off-line)
Clearwell	Water level Minimum water level where it is required for confirmation of primary disinfection
Treated water	Turbidity, pH, chlorine residual, fluoride residual (if system fluoridates), colour, temperature, ammonia Instantaneous flow rate and totalized volume per day High lift discharge pressure Minimum water level where it is required for confirmation of primary disinfection
Chemical Systems	See Chapter 6 Chemical Application
UV Systems	Instrumentation needed to monitor and record pass through dose. See Chapter 5 - Treatment
Pumps and Motors	Running time Bearing temperature Power draw Speed, if variable speed See also Chapter 7 Pumping Facilities
Rotating elements (e.g., mixers, flocculators, solids contact clarifier recirculators and rakes)	Torque or torque alarm
Residuals Treatment	As required to ensure proper operation of the process (e.g., flow, turbidity, TSS, pH, temperature, sludge density)

9.4.1 Alarms & Status Indication

The designer should ensure that alarms are included where operator response is necessary to maintain the safety of the water supply and for all control system interlocks that can shut down equipment or systems.

All alarms should be latched (remain active) until an operator has acknowledged them. The automated alarm system should provide clear information on the condition and have a feature that records the identity of the operator and time of acknowledgement/cancelling, allowing proper log book entries that are cross referenced to automated records. If an alarm is indicated on a computer screen, an appropriate colour code or symbol should be used to indicate, for each alarm, whether it has been acknowledged. Alarm prioritization should be considered so that critical alarms on process systems are immediately addressed. The system should archive alarm data for easy retrieval as required.

Valve and equipment status should use a consistent method of symbols and colours, whether the status is indicated through lamps or on a colour computer screen. The colour-coding scheme should be consistent with any existing equipment displays elsewhere in the plant.

In plants that are left unattended for periods of time, an automatic telephone dialer, cellular or other radio communication or pager system for annunciation of alarms should be provided.

9.5 Reliability & Security

Hardware and software should be selected based on reliability, compatibility and vendor support. Equipment should be robust enough for continuous operation in the plant environment. Hardware and software necessary to facilitate back-up of both the system and the collected data should be provided locally.

A system and data recovery procedure should be included in the project documentation which should also be remotely accessible.

The designer should consider methods of improving reliability through transient protection wherever possible (e.g., mains, filters and transient surge protectors). Radio modem and other data transmission equipment should use methods to ensure the integrity of the data transmitted against corruption/interference. Encryption of signals for data/control security may be considered. When long or very long instrument or equipment wiring is present, induced current protection should be installed. Network configurations should be designed with security in mind. Protection of fibre optic or local area network (LAN) cabling in conduits should be considered to protect from physical damage. Harmonics and other electrical related disturbances to signal integrity should be taken into consideration.

Power supply design should include backup power by using true online uninterruptible power supply (UPS) or equivalent power systems. Buffered direct current (DC) power supply should be selected. Critical instrumentation should be connected when possible to the same back up power as the control system to allow monitoring during power outages. Consideration of the impacts of power failures on critical instrumentation and control should be taken into account, especially with respect to the reset conditions of the devices.

The computer human machine interfaces (HMI) should be user-friendly to facilitate operation and on-line monitoring. Where outside access is provided for remote control of the operator interface or other control components, adequate security should be provided.

Reasonable computer security measures should be provided if computer or other control systems are part of a larger system or a wide area control system or network. A vulnerability assessment document should be provided to the municipality/owner. This document should identify all potential access points, the associated risks with each and ways to mitigate those risks. Computer and programmable equipment, including calibration instruments, should use password protection and record accessing identity. Drives (including USB ports) should be locked down under regular operation whenever possible. The HMI should not allow switching to other programs under operator accounts (not even using combination keys). In larger systems which are part of an IT infrastructure, a narrower security policy should be defined that prevents disruption within the process control network (PCN).

9.5.1 Accessibility for Calibration & Maintenance

The design should arrange for easy access to all instrumentation and control systems for calibration and maintenance. Smart instrumentation is an emerging field that may be considered for improving servicing, calibration, failure detection and predictive maintenance of critical devices.

9.6 Automated/ Unattended operation

The designer should consider the consequences and operational response to treatment challenges, equipment failure and loss of communications or power.

Automated monitoring of all critical functions with major and minor alarm features should be provided; dual or secondary alarms may be necessary for critical functions. The designer should consider and document if automatic shutdown and manual restart is necessary or desirable to ensure the safety of the water supply. The control system should have response adjustment capability on all minor alarms. Built-in control system challenge test capability should be provided to verify operational status of major and minor alarms throughout the extreme conditions that can reasonably be expected during facility operation.

Automated shut-downs of high lift pumps due to low concentrations of chlorine residual or other water quality alarms or operational procedure, when sustained, may result in health risks similar to those experienced during power failure (Section 3.12 Standby Power).

Provisions should be made to ensure security of the treatment facilities, pumping stations and storage facilities at all times. Appropriate intrusion alarms should be provided and sound at location(s) which will be monitored 24 hours per day. Video surveillance systems should be considered whenever possible.

9.7 Commissioning/ acceptance testing

A demonstration period to verify the reliability of procedures, equipment and surveillance system should be planned. Challenge testing of each critical component of the overall system should be included as part of the demonstration period. A report following the demonstration period should identify and address any problems and alarms that occurred during the demonstration period as well as a description of tests performed and their evaluation.

The designer should make provision for testing the control system during a period of operation or an appropriate period that reflects the range of operating conditions anticipated, which includes periods of seasonal changes or variations, to compare the actual control sequences with those described in the control narratives. Control narratives should be updated after the testing and as needed to reflect the "as is" status.

9.8 Documentation

The designer should provide a reasonable level of documentation for the control installation. As a minimum, the following items should be included:

• Control philosophy document and control manual, including redundancy philosophy for critical systems;
• Process narrative;
• Instrument specifications;
• Loop diagrams;
• P&ID drawings for the entire control system, including remotely controlled equipment;
• Electrical and Interlock diagrams;
• Equipment manuals;
• Comprehensive maintenance and calibration procedures for instruments and control systems; and
• A disaster recovery procedure (system and data recovery procedures).

Refer to Chapter 2 Project Design Documentation for more detailed information.

Chapter 10: Distribution systems

These guidelines outline parameters to assist in the design of water distribution systems. Other approval authorities such as the local or regional municipality may have standards that are more stringent than these guidelines. The designer should, therefore, ensure that he/she is aware of the requirements of all other approving authorities before commencing design.

Although some aspects of the guidelines relate only to municipal services, these guidelines are meant to apply to other systems such as mobile home parks and condominium developments.

10.1 General

10.1.1 High Quality Distribution Systems

The report of the Walkerton Commission includes the following definition: "A high-quality distribution system is reliable, providing a continuous supply of potable water at adequate pressure. Reservoirs within the system balance pressure and cope with peak demands, fire protection, and other emergencies without causing undue water retention, while looped watermains prevent stagnation and minimize customer inconvenience during repairs. Since water quality declines with the length of time the water remains in the system, and the rate of decline depends partly on the attributes of the distribution system, a high-quality system has as few dead ends as possible and maintains adequate flow and turnover"¹⁴. The designer should strive to achieve these objectives.

10.1.2 Fire Protection

Whether or not fire protection is provided via the communal drinking-water system is the decision of the municipality/owner of the system and can be subject to a cost/risk-benefit analysis, especially for smaller systems. However, once the decision has been made to provide fire protection via the communal drinking-water system, the designer should consult the Fire Code (O.Reg. 388/97) made under the Fire Protection and Prevention Act, 1997 and the latest edition of Fire Underwriters Survey document Water Supply for Public Fire Protection¹⁵ and the municipality/owner decision respecting fire protection. The designer should refer to AWWA Manual of Water Supply Practices M31 Distribution System Requirements for Fire Protection and Section 8.4 Sizing of Storage Facilities for more information regarding required fire flows.

The designer should also consider local fire flow rates when sizing the pipes. In some cases, it may be necessary to evaluate the provision of separate pipes for fire and potable supplies to maintain water quality.

10.1.3 Maintaining Water Quality

Water distribution systems should be designed to provide a balance between hydraulic water supply needs and water quality. Water quality issues are categorized as microbiological (e.g., bacteria, regrowth, nitrification), chemical/physical (e.g., disinfection by-products, lead and copper, maintenance of secondary disinfectant residual) or aesthetic (e.g., colour, taste, odour). Many water quality issues have a direct potential public health impact.

Water quality deteriorates through interactions between the pipe wall and the water, and reactions within the bulk water itself. Depending on the retention time in the system, water flow, treated water quality, pipe materials and condition and deposited materials (i.e., sand, iron, manganese), the water quality will change to a greater or lesser extent¹⁶. Therefore, water age, a function of system design, water demand and system operation, is a major factor in water quality deterioration within the distribution system. Systems should be designed to maximize turnover and to minimize retention times and water age. Careful consideration should be given to distribution main sizing, providing for multidirectional flow, adequate valving for distribution system control and provisions for flushing and occasional "swabbing". In addition, positive pressure must be maintained at all times to prevent intrusion of contaminants. The designer should consult references such as the AwwaRF report Guidance Manual for Maintaining Water Quality in the Distribution System (Project #357), 2000 and the USEPA document Distribution System White Papers.

10.1.4 Interconnections

If interconnections between distribution systems or different water supply sources are planned, consideration should be given to differences in water quality and characteristics, and the implications of mixing different waters, such as water from a distribution system where chloramination is used with water from a system where free chlorination is used for secondary disinfection.

10.1.5 Multiple Pressure Zone Systems

The designer should have regard to the effects of water age and potential water quality deterioration when designing interconnections between pressure zones, as well as pressure impacts upstream and downstream of the interconnections.

10.2 Hydraulic design

10.2.1 Design Period

Although a 20-year design period is most frequently used for water treatment supply systems, it is recommended that longer design periods be used based on long-term population projections, given that water distribution systems have useful life expectancies well in excess of 20 years. Consideration should also be given to water quality deterioration arising from potential oversizing of the initial equipment.

Refer to Section 3.4 Design Flow for more issues relating to water demand.

10.2.2 System Pressures

10.2.2.1 Maximum & Minimum Operating Pressures

All water mains, including those not designed to provide fire protection, should be sized after a hydraulic analysis based on flow demands and pressure requirements. The system should be designed to maintain a minimum pressure of 140 kPa (20 psi) at ground level at all points in the distribution system under maximum day demand plus fire flow conditions. The normal operating pressure in the distribution system should be approximately 350 to 480 kPa (50 to 70 psi) and not less than 275 kPa (40 psi). Pressures outside of this range may be dictated by distribution system size and/or topography. The designer should also consider pressure losses within serviced buildings due to the installation of equipment or appurtenances (water meters, backflow preventers, etc.) relative to the minimum operating pressure in the system.

The maximum pressures in the distribution system should not exceed 700 kPa (100 psi) to avoid damage to household plumbing and unnecessary water and energy consumption. When static pressures exceed 700 kPa (100 psi), pressure reducing devices should be provided on mains or service connections in the distribution system.

Refer to Section 7.4.3 Booster Pumping Stations for more information regarding distribution system pressures.

10.2.2.2 Transient Pressures

The distribution piping system should be designed to withstand the maximum operating pressure plus the transient pressures to which it may be subjected. A thorough transient pressure analysis should be completed. Transient pressures are caused by rapid valve operation, pump start-up and shutdown or power failure. Pumping systems and stations should be designed to minimize surges and transient pressure conditions including negative pressures which may allow inflow of contaminants.

As a minimum allowance in the distribution system, it is recommended that pipes and joints be able withstand the maximum operating pressure plus the pressure surge that would be created by stopping of a water column moving at 0.6 m/s (2 ft/s). The pressure created by such an event will vary depending upon the diameter, wall thickness and pipe material used in the distribution system. Transient analysis should be undertaken for long transmission lines.

10.2.3 Friction Factors

For new pipe conditions, the designer should refer to the most recent versions of the following AWWA manuals:

• Manual of Water Supply Practices M9 Concrete Pressure Pipe;
• Manual of Water Supply Practices M11 Steel Water Pipe: A Guide for Design and Installation;
• Manual of Water Supply Practices M23 PVC Pipe: Design and Installation;
• Manual of Water Supply Practices M41 Ductile-Iron Pipe Fittings;
• Manual of Water Supply Practices M45 Fibreglass Pipe Design; and
• Manual of Water Supply Practices M55 PE Pipe - Design and Installation.

In evaluating existing systems for expansion, the C-factors should be determined by actual field tests wherever possible. Where these data are not available, common practice in Ontario has been to use the Hazen-Williams C-factors shown in Table 10-1 for the design of water distribution systems with pipes made of traditional materials, or when estimating pressure losses in the existing systems. The designer may choose to use other methods of calculating friction factors such as the Darcy-Weisbach equation or Manning equation.

10.2.4 Pipe Diameters

All watermains, including those not designed to provide fire protection, should be sized according to a hydraulic analysis based on flow demands and pressure requirements (Section 10.2.2 System Pressures), as well as the depositional nature of the water with respect to long term watermain carrying capacity. Any departure from the minimum requirements listed below should be justified by hydraulic analysis. The actual inside pipe diameter should be used in the hydraulic calculations.

Table 10-1: C-Factors

Diameter - Nominal	C-Factor
150 mm (6 in)	100
200 mm 250 mm (8 to 10 in)	110
300 mm 600 mm (12 to 24 in)	120
Over 600 mm (over 24 in)	130

For systems designed to provide fire protection, the minimum size of watermains should be 150 mm (6 in) except beyond the last hydrant on culs-de-sac; in this case, pipes as small as 25 mm (1 in) may be used. Larger size mains may be necessary to allow the withdrawal of the required fire flow while maintaining the minimum pressure specified in Section 10.2.2.1 Maximum and Minimum Operating Pressures.

Where fire protection is not to be provided, the minimum diameter of watermain in the distribution system should be 75 mm (3 in). The minimum size of watermains may also be dictated by the types of available equipment for cleaning watermains (e.g., swabs or pigs). In all cases, pipe diameters should be such that a flushing velocity of 0.8 m/s (2.6 ft/s) can be achieved for cleaning and disinfection procedures.

Refer to Section 10.8 Water Services for more information on water service connections.

10.3 Pipe system design

10.3.1 System Layout

Distribution system layouts are usually designed in one of three configurations, including arterial-loop systems, grid systems and tree systems.

Tree systems often have more dead-ends and the selection of this type of layout is generally not recommended.

Wherever possible, water distribution systems should be designed to eliminate dead-ends by making appropriate tie-ins or looping whenever practical in order to provide increased reliability of service and reduce stagnation and loss of disinfectant residual. Where dead-end mains can not be avoided, they should be designed with a means to provide adequate flushing and prevent stagnation such as a fire/flushing hydrant or blow-off.

10.3.2 Depth of Cover

With the exception of those watermains which will be taken out of service and drained in winter, the minimum depth of cover over watermains and service connections, including that portion on private property, should be greater than the depth of frost penetration. On services, this depth should be measured to the goose neck when it is vertical. If, for economic or practical reasons, it is not possible to install watermains below the frost line, the design should ensure that the watermain will be unlikely to freeze or be damaged by heaving or increased trench loads caused by frost penetration. Applicable temperature loss calculations should be performed to ensure the water will not freeze (Section 12.2 Climatic Factors).

Large diameter watermains [over 300 mm (12 in)] without service connections and that are not dead-ends may be installed so that the frost-free depth corresponds with the springline of the pipe rather than the crown.

The increased external loads caused by frost may cause beam breaks in the pipe when bedding is non-uniform. For this reason, care should be taken in the selection of pipe materials, pipe classes, bedding types and the proper installation and compaction of the bedding to the springline.

10.3.3 Materials

10.3.3.1 Standards & Material Selection

All water contacting materials used in the construction and operation of drinking-water systems including pipe, fittings, valves, fire hydrants and materials used for the rehabilitation of watermains should meet all applicable quality standards described in Section 3.26 Chemicals and Other Water Contacting Materials.

The designer should refer to the Ontario Ministry of Transportation Ontario Provincial Standards for Roads and Public Works (OPS) for the minimum recommended specifications for pipe, joints and fittings, bedding and cover materials.

Special attention should be given to selecting pipe materials which will protect against both internal and external corrosion.

In selecting a pipe material, the designer should consider the following factors:

• Trench foundation conditions;
• Location and other site specific factors;
• Soil conditions:
  • Corrosivity (need for cathodic protection);
  • Chemical composition and its effects on pipe material; and
  • Ability to provide thrust restraint.
• Drinking water corrosivity;
• Water temperature variations;
• Behaviour of the pipe material in the event of transient pressures and catastrophic failure;
• Costs (capital, operating, maintenance and other costs);
• Available labour skills; and
• Availability of suitable fittings and appurtenances acceptable to/or recommended by the pipe manufacturer, as well as spare parts and/or repair pieces.

When non-metallic pipes are selected, the designer should consider the use of pipe tracers for locating purposes.

10.3.3.2 Permeation by Organic Compounds

Where distribution systems are installed in areas of groundwater contaminated by organic compounds, materials which do not allow permeation of the organic compounds should be used for all portions of the system, including pipe, joint materials, O-rings, gaskets, hydrant leads and service connections (e.g., avoid HDPE where gasoline contamination may exist and PVC where dry cleaning solvent may be present).

10.3.3.3 Pipe Strength

Section 10.2.2 System Pressures discussed distribution system operating and transient pressures. Buried watermains are also subjected to external loads imposed by the trench backfill, frost loading and superimposed loads (static and/or dynamic). The watermain pipe selected for a particular application should be able to withstand, with an acceptable margin of safety, all the combinations of loading conditions to which it is likely to be exposed.

Pipe strength designations and the methods for selecting the required pipe strength vary with the types of materials used. The designer should evaluate pipe supplier information and consult such references as CSA, ANSI/AWWA standards, OPS and design manuals.

10.4 Fire hydrants

10.4.1 Introduction

Fire hydrants should only be installed on watermains capable of supplying fire flow. For non-design requirements respecting fire hydrants (e.g., colour coding and maintenance) refer to the Fire Code (O.Reg. 388/97) made under the Fire Protection and Prevention Act, 1997 and system municipality/owner or municipal requirements.

10.4.2 Location & Spacing

Fire hydrants should be provided at each street intersection, in the middle of long blocks and at the end of long dead-end streets. The required hydrant spacing decreases as the fire flow requirement increases. Hydrants should, therefore, be placed much closer together in high risk, high density areas, than in low density residential areas. Fire hydrant spacing ranges from 90 m to 180 m (300 to 600 ft) depending on the area being served. For more detailed information on hydrant spacing, refer to the latest edition of the Fire Underwriters Survey document Water Supply for Public Fire Protection and system municipality/owner or municipal requirements.

10.4.3 Hydrant Specifications

To minimize freezing problems, all fire hydrants used in Ontario should be the dry-barrel type and should conform to the latest edition of AWWA Standard C502: Dry-Barrel Fire Hydrants. All fire hydrants should be provided with adequate thrust blocking to prevent movement caused by thrust forces.

10.4.3.1 Hydrant Leads

The hydrant lead should be a minimum of 150 mm (6 in) in diameter. Auxiliary valves should be installed on all hydrant leads to allow for hydrant maintenance and repair with a minimum of disruption.

10.4.4 Hydrant Drainage

In areas where the water table will rise above the hydrant drain ports, the drain ports should be plugged. The barrels should be kept dry to prevent freezing damage to the barrel and water contamination.

Where hydrant drains are not plugged, they should drain to the ground if soil conditions permit, or to a dry well/drainage pit provided for that purpose.

10.5 Flushing & Swabbing

Flushing hydrants or devices are recommended for systems which are not capable of providing fire flow and for dead-ended watermains and areas where the degradation of water quality may be possible due to low consumption/flow conditions. Flushing devices should be sized to provide flows which will give a velocity of at least 0.8 m/s (2.6 ft/s) in the watermain being flushed. No flushing device should be directly connected to any sewer.

The designer should take into account operational procedures such as unidirectional flushing and watermain swabbing when designing looped watermain systems. In watermain loops, unidirectional flushing (strategic valve closing to direct flow to promote flushing velocity) may be required to produce the required flushing velocity. Valve placement to promote unidirectional flushing velocities should be considered in the design stage. This may require more valves than recommended in Section 10.6 Valves.

Swabbing is another effective method used to clean watermains. For small diameter mains without hydrants, swab launching and retrieval ports need to be included in the design if swabbing is contemplated in the operations. Valve specifications also need to be considered. Butterfly valves cannot be used as they will trap the swab.

10.6 Valves

The municipality/owner of the system should be consulted with respect to valve locations at intersections, line valve spacing, types of valves permitted, direction of rotation to open and the maximum size of valve permitted in a valve box.

10.6.1 Valve Placement

A sufficient number of valves should be provided on watermains to minimize inconvenience and contamination during repairs. Valves should be located at not more than 150 m (500 ft) intervals in commercial and industrial districts and at not more than one block or 240 m (800 ft) intervals in other districts. Where systems serve rural areas and where future development is not expected, the valve spacing should not exceed 2 km (1.25 mi).

In distribution system grid patterns, to minimize disruption during repairs, intersecting watermains should be equipped with shut-off valves as indicated in Table 10-2.

Table 10-2: Shut-Off Valves in Distribution System Grid Patterns

Type of intersection	Number of valves
"T" Intersection	At least 2
Cross Intersection)	At least 3

10.6.2 Valve Standards

There are many different types of valves available and the designer should consider its application when selecting a valve. As a minimum, the recommendations of the manufacturer regarding appropriate valves for an application should be taken into account, with confirmation from the manufacturer that the valves conform to relevant AWWA standards. The designer should also ensure that open/close directions are consistent throughout the drinking-water system, and meets the requirements of municipality/owner.

For large diameter water supply or pressure zone isolation valves, consideration should be given to valved reduced-size bypass piping that can be used to avoid local stagnation and assist with open/close operations.

Valves 300 mm (12 in) in diameter or less may have access provided to the operating nut via a valve box and stem assembly, but it is recommended that all valves larger than 300 mm (12 in) in diameter be placed in valve chambers. All air release valves and drain valves should also be located in chambers. To minimize the number of chambers required, combinations of valves can be located within a single chamber.

10.6.3 Air Release & Vacuum Relief Valves

Air release/vacuum relief valves should be provided at high points in distribution and transmission lines (relative to the hydraulic gradient) where air can accumulate. The valves should conform to AWWA Standard C512: Air Release, Air/Vacuum, and Combination Air Valves for Waterworks Service. The open end of an air release pipe from a manually operated valve should be extended to the top of the chamber and provided with a screened, downward-facing elbow if drainage is provided for the chamber.

The open end of an air release pipe from automatic valves should be extended to at least 300 mm (1 ft) above grade and provided with a screened, downward-facing elbow to ensure it can not be flooded or blocked. Discharge piping from air relief valves should not connect directly to any storm drain, storm sewer or sanitary sewer.

Automatic air release valves should not be used in situations where flooding of the access hole or chamber may occur.

Where the need for an automatic air release valve is uncertain, a manual air release valve or hydrant can be installed initially and later replaced with an automatic valve if significant air accumulations are found.

10.6.4 Drain Valves

With large diameter mains, drain valves positioned at low points may be required to permit main repairs. Small diameter watermains can generally be drained through hydrants by using compressed air and/or pumping.

10.7 Sampling stations

The designer should consider the provision of dedicated sampling stations within the distribution system to facilitate water quality monitoring. In the selection of locations for sampling sites, the designer should consider challenging conditions within the system such as increased hydraulic retention times, temperature variations, materials of construction, etc.

10.8 Water services

In selecting the diameter of a service connection, the designer should consider such factors as the following:

• Peak water consumption in the building serviced;
• Total length of service line from the watermain to the building connection;
• Watermain pressure under peak demand conditions (Section 10.2.2.1 Maximum and Minimum Operating Pressures);
• Loss of head resulting from length and condition of pipe, fittings, and backflows preventers and meters; and
• Required pressure at point of use.

The recommended minimum size of service line for single-family residences is 19 mm (¾ in). Larger residences and buildings located far from the watermain connection should have a 25 mm (1 in) or larger service. For details on proper water sizing of service lines, refer to a publication such as AWWA Manual of Water Supply Practices M22 Sizing Water Service Lines and Meters.

The designer should consider the provision of two services with an isolation valve between the connections to help ensure redundancy to sensitive users (such as hospitals, day cares, long-term care facilities, etc.) in the event of a service line failure.

Water service lines should be constructed of materials acceptable under the Part 7 of Division B of the Building Code (O.Reg. 350/06) made under the Building Code Act, 1992 and should conform to AWWA Standard C800: Underground Service Line Valves and Fittings. Municipalities should be consulted regarding local preferences and requirements. All water services should be equipped with a corporation stop and a curb stop. The curb stop should be provided with a curb box.

Where booster pumps are installed on residential service from the public water supply main, an air gap backflow preventer should be provided.

10.9 Restraint

Adequate restraint must be provided in water distribution systems to prevent pipe movement and subsequent joint failure. In the case of non-restraining mechanical and/or slip-on joints, this restraint should be provided by adequately sized thrust blocks positioned at all plugs, caps, tees, line valves, reducers, wyes, hydrants and bends deflecting 22½° or more. Depending upon internal pressures, pipe sizes, pipe material and soil conditions, bends of lesser deflection may also require thrust blocking. Thrust block material should resist deterioration from moisture or corrosive soil.

An alternative approach that can be used to prevent joint failure is either to use pipe and jointing methods capable of resisting the forces involved (such as welded steel pipe, or polyethylene pipe with thermal butt-fusion joints) or use joint restraining methods, such as metal tie rods, clamps or harnesses.

In designing thrust blocks and other restraint systems, the designer should remember that transient pressures should be added to the normal operating pressures when calculating the thrust forces (if velocity of flow is very high, dynamic thrust should also be calculated); adequate corrosion protection should be provided for external clamps and tie rods; the safe bearing values of soils should be reduced substantially from textbook figures if shallow trenches are used or if bearing against disturbed soils. For further discussion of thrust blocking and joint restraint design, refer to the pipe manufacturer catalogue and other sources such as AWWA standards, OPS, textbooks and watermain design manuals.

10.10 Installation & Rehabilitation of watermains

10.10.1 Installation Standards & Technologies

Installation specifications should incorporate the provisions of appropriate AWWA standards, the OPS and/or manufacturer recommended installation procedures. Pressure and leak testing should be included. The pipe installation should also allow for thermal expansion. The designer should consider site specific conditions when selecting an installation technology. In certain instances, it may be more appropriate to use trenchless technologies, such as directional drilling, tunnelling or micro-tunnelling.

10.10.2 Bedding

Continuous and uniform bedding should be provided in the trench for all buried pipe. Backfill material should be tamped in layers not exceeding 150 to 250 mm (6 to 10 in) around the pipe and to a sufficient height above the pipe to adequately support and protect the pipe. Large stones [75 mm (3 in) or greater] found in the trench should be removed for a depth of a least 150 mm (6 in) below the bottom of the pipe.

Bedding materials and methodology should conform to the appropriate AWWA and OPS specifications, and should be no less than as recommended by the pipe manufacturer.

10.10.3 Disinfection

New, cleaned and repaired watermains should be disinfected in accordance with AWWA Standard C651-05: Disinfecting Water Mains or an equivalent procedure [as required by the Procedure for Disinfection of Drinking Water in Ontario (Disinfection Procedure)]. The specifications should include detailed procedures for the flushing, disinfection and microbiological testing of all watermains before being put into service.

10.10.4 Corrosion

In areas where aggressive soil conditions are suspected, analyses should be performed to determine the actual aggressiveness of the soil. If soils are found to be aggressive, metallic watermains should be protected, such as by encasement of the watermain in polyethylene or concrete, application of corrosion protection tape, provision of cathodic protection or by using corrosion resistant watermain materials. Consideration should be given to protection against galvanic corrosion when appurtenances and metal pipe of differing materials are connected.

Refer to Section 5.18 Internal Corrosion Control for information on the prevention of internal corrosion by water quality adjustment or amendment.

10.10.5 Pipe Rehabilitation

There are a number of methods to rehabilitate water distribution pipes with new or improved technologies and materials being developed every year. The designer should ensure the use of the most up-to-date information when making decisions about pipe rehabilitation. Two leading sources of information are the AWWA and the North American Society for Trenchless Technologies (NASTT). The InfraGuide¹⁷: National Guide to Sustainable Infrastructure report Selection of Technologies for the Rehabilitation or Replacement of Sections of a Distribution System (2003) provides an overview of best practices.

Rehabilitation methods include slip-lining, close fit slip-lining, cured-in-place lining, pipe bursting, horizontal drilling, micro-tunneling, internal joint seals and spray lining (cement or epoxy). Only materials with NSF/ANSI Standard 61: Drinking Water System Components - Health Effects certification should be used (Section 10.3.3.1 Standards and Material Selection). Where iron pipe has been cleaned by pigging, the cleaned surfaces should be protected with a coating or lining so as to prevent severe red water problems and further corrosion. When selecting a rehabilitation or replacement technology the designer should consider the following factors:

• Construction issues such as safety, operability, cost and efficiency;
• Cost of mobilizing specialized equipment and personnel;
• Risk of undertaking (or not undertaking) the project, focusing on the safety of the water supply, environmental and construction issues;
• Depth of the watermains and presence of permafrost which may limit applicability of technologies;
• Density of water services if excavations are required to reconnect each service; and
• Existing customer service needs during the rehabilitation project.

10.11 Separation distances from contamination sources

10.11.1 General

This section describes good engineering and construction practice and will reduce the potential for any health hazard from water-borne disease or chemical poisoning in the event of the occurrence of conditions conducive to possible contaminated groundwater flow into the water distribution system.

Contaminated ground and surface water may enter the water distribution system at leaks or breaks in components such as piping, vacuum air release valves, blow-offs, fire hydrants, meter sets, and outlets with the occurrence of a negative internal or positive external pressure condition. Water pressure in a part of the system may be reduced to a potentially hazardous level due to shutdowns in the system, main breaks, heavy fire demand, high water usage, pumping, storage or transmission deficiency and negative surge pressures.

The relative location of sewers and watermains (including appurtenances) and types of material used for each system are important considerations in designing a system to minimize the possibility of contaminants entering the water distribution system. The use of and adherence to good engineering practice will reduce the potential for health hazards.

10.11.2 Sewer & Watermain Parallel Installations

Sewers/sewage works¹⁸ and watermains located parallel to each other should be constructed in separate trenches. When it is impossible or not practical to maintain a separate trench and a minimum separation distance, the crown of the sewer should be at least 0.5 m (20 in) below the invert of the watermain, and separated by in-situ material or compacted backfill. Also, joints should be offset as much as possible between sewers and watermains.

Where this vertical separation cannot be obtained, the sewers should be constructed of watermain quality pipe, pressure tested in place at a pressure of 350 kPa (50 psi) without leakage using the testing methodology in Ontario Provincial Standard Specification 701 (OPSS 701) of the OPS.

In rock trenches, drainage should be provided to minimize the effects of impounding of surface water and/or the leakage from sewers in the trench.

10.11.3 Crossings

Watermains should cross above sewers wherever possible. Whether the watermain is above or below the sewer, a minimum vertical distance of 0.5 m (20 in) between the outside of the watermain and the outside of the sewer should be provided to allow for proper bedding and structural support of the watermain and sewer pipe. Sufficient structural support for the sewer pipes should be provided to prevent excessive deflection of the joints and settling. The length of water pipe should be centred at the point of crossing so that joints in the watermain will be equidistant and as far as possible from the sewer, crossing perpendicular if possible.

10.11.4 Service Connections

Wherever possible, the construction practices outlined in Part 7 of Division B of the Building Code (O.Reg. 350/06) made under the Building Code Act, 1992 should be applied to sewer and water services.

10.11.5 Tunnel Construction

If a tunnel is of sufficient size to permit a person to enter it, a sewer and watermain may be placed through the tunnel providing the watermain is hung above the sewer. If the tunnel is sized only for the pipes or is subject to flooding, the sewers should be constructed of watermain quality pipe, pressure tested in place according to OPSS 701 of the OPS at a pressure of 350 kPa (50 psi) without leakage.

10.11.6 Design Factors

When local conditions do not permit the spacing outlined above or other conditions indicate that detailed investigations are warranted, the following non-inclusive list of factors should be considered as a guide:

• Materials, types of joints and identification for water and sewer pipes;
• Soil conditions (e.g., in-situ soil and backfilling materials and compaction techniques);
• Service and branch connections into the watermain and sewer lines;
• Compensating variations in the horizontal and vertical separations;
• Space for repair and alterations of water and sewer pipes;
• Off-setting of pipes around access/maintenance holes;
• Location of groundwater table and trench drainage techniques;
• Other sanitary facilities such as septic tanks and tile fields; and
• Any other factor that may be relevant to the design.

10.11.7 Valve, Meter & Blow-Off Chambers

Chambers, pits or access holes containing valves, blow-offs, meters or other such appurtenances to a distribution system, should not be located in areas subject to flooding or in areas of high groundwater. Where such locations are unavoidable, measures should be taken to prevent infiltration of surface water or groundwater. Chambers or pits should drain to the ground surface, to absorption pits underground, or to a sump within the chamber where the groundwater level is above the chamber floor. Chambers should be lockable to avoid safety and vandalism concerns. Protection against freezing (frost strapping or other means) and frost heave of the chamber should be provided.

The designer should consider venting and drain appurtenances between line valves so as to eliminate air locks during watermain disinfection procedures and watermain restoration procedures.

The chambers, pits and access holes should not connect directly to any sanitary sewer, but may be connected to storm sewers provided backflow prevention is included. Blow-offs and air release valves should not be connected directly to any sewer.

10.11.8 Unacceptable Installations

No water pipe should pass through or come in contact with any part of a sewer access/maintenance hole, septic tank, tile field, subsoil treatment system or other source of contamination.

10.12 Surface water crossings

10.12.1 Above-water Crossings

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

10.12.2 Underwater Crossings

A minimum cover of 0.6 m (2 ft) should be provided over the pipe. Consideration should be given to the potential for the stream bottom to change as a result of scour or dredging. When crossing water courses which are greater than 5 m (16 ft) in width, the following should be provided:

• The pipe should have flexible, restrained or welded watertight joints;
• Valves should be provided at both ends of water crossings so that the section can be isolated for testing or repair; the valves should be easily accessible and not subject to flooding; and
• Permanent taps or other provisions to allow insertion of a small meter to determine leakage and obtain water samples should be made on each side of the valve closest to the supply source.

Where there is any likelihood of marine travel, the designer should refer to the Navigable Waters Protection Act.

10.13 Backflow & Cross-connections control

10.13.1 Cross-Connections

Precautions should be taken in the design of water distribution and plumbing systems to prevent the entrance of contaminating materials into the drinking-water system.

Contaminants can enter water supply systems from various sources including cooling water systems, pump seal water systems, industrial process piping and groundwater. No steam condensate, cooling water from engine jackets or water used in conjunction with heat exchange devices should be returned to the drinking-water supply.

Deterioration can also occur from entry into the system of untreated water due to watermain de-pressurization conditions allowing contamination through vents or other appurtenances.

To control contamination from non-drinking water piped systems, cross-connection control/backflow prevention measures and/or equipment are necessary.

For information on cross-connection control, the designer should refer to the AWWA Manual of Water Supply Practices M14 Recommended Practice for Backflow Prevention and Cross-Connection Control and USEPA Cross-Connection Control Manual, 2003

10.13.2 Backflow Prevention Equipment

There are several types of backflow prevention devices available including air gaps, double check valve assemblies, reduced pressure principle devices, dual check valves, atmospheric vacuum breakers and pressure vacuum breakers. For applications involving health hazards, only air gaps or reduced pressure principle devices should be used. For information on backflow prevention equipment, the designer should refer to:

• Applicable municipal by-laws;
• Building Code (O.Reg. 350/06) made under the Building Code Act, 1992;
• Canadian Standards Association (CSA) standards CAN/CSA-B64 SERIES-01 Backflow Preventers and Vacuum Breakers, CAN/CSA-B64.10-01/B64.10.1-01 Manual for the Selection and Installation of Backflow Prevention Devices/Manual for the Maintenance and Field Testing of Backflow Prevention Devices, and B64.10S1-04/B64.10.1S1-Supplement #1 to CAN/CSA-B64.10-01/CAN/CSA-B64.10.1-01;
• AWWA Standard C510: Double Check Valve Backflow Prevention Assembly and AWWA Standard C511: Reduced-Pressure Principle Backflow Prevention Assembly; and
• AWWA Manual of Water Supply Practices M14 Recommended Practice for Backflow Prevention and Cross-Connection Control.

10.14 Water loading stations & Temporary water services

Water loading stations and temporary water services should be protected against potential backflow, which may allow contamination to enter the distribution system, in accordance with the requirements of CAN/CSA-B64.10-01/B64.10.1-01 Manual for the Selection and Installation of Backflow Prevention Devices/Manual for the Maintenance and Field Testing of Backflow Prevention Devices.

Vessels and water hauling equipment should be equipped with an air gap or reduced pressure type backflow preventer in accordance with CAN/CSA-B64.10-01/B64.10.1-01 Manual for the Selection and Installation of Backflow Prevention Devices/Manual for the Maintenance and Field Testing of Backflow Prevention Devices.