Cross Connections & Backflow Prevention Services

What you can do to prevent backflow.

What is a cross connection?

"Cross connection" means any actual or potential physical connection between a public water system or the consumer's water system and any source of non-potable liquid, solid, or gas that could contaminate the potable water supply by backflow.

How does a cross connection occur?

For a drinking water (potable water) supply to become contaminated via a cross connection, three things need to happen simultaneously:

1. The potable water supply piping must be unprotected (or improperly protected) from a cross connection;
2. A physical cross connection must be made between the potable water supply piping and a contaminant source; and
3. Backflow conditions must occur.

What is a backflow?

"Backflow" means the undesirable reversal of flow of water or other substances through a cross connection into the public water system or consumer's potable water system.

Backflow is the flow of water (or other solid, liquid, or gas from any source) back into the potable water supply. Backflow may be due to either: Backsiphonage; or Backpressure.

"Backsiphonage" means backflow due to a reduction in system pressure in the purveyor's distribution system and/or consumer's water system. "Backpressure" means a pressure (caused by a pump, elevated tank or piping, boiler, or other means) on the consumer's side of the service connection that is greater than the pressure provided by the public water system and which may cause backflow.

Causes of Backflow

Causes of Backflow: Backsiphonage

Backsiphonage is backflow caused by a negative pressure (vacuum or partial vacuum) in the supply piping. Backsiphonage occurs when system pressure is reduced below atmospheric pressure. The effect is similar to sipping water through a straw.

The following scenario illustrates how backsiphonage backflow conditions could occur in a public water system:

• A public water system main is shut off to repair a leak. The water main is at the base of a hill.
• The water main is at a lower elevation than the homes on the hill. This creates a situation where water in the plumbing in the homes on the hill can drain into the public water system main.
• When a customer at the bottom of the hill uses water, a siphon is created at households at the top of the hill and water drains out of their plumbing systems.
• At one household at the top of the hill, a garden hose is being used to fill a child's wading pool. The hose is submerged in the pool. See Illustration 1.
• When the backflow conditions occur, the non-potable water from the wading pool is siphoned through the cross connection (submerged hose) into the household plumbing and then into the water main.
• The water from the wading pool contaminates the water main.
• When water service is restored, contaminated water is delivered to customers served by the public water system.

Causes of Backflow: Backpressure

Backpressure is backflow caused by pressure in the customer's plumbing being greater than the pressure in the water supply piping. The higher pressure in the customer's plumbing may be from a booster pump, heating boiler, etc. The following scenario illustrates how backpressure backflow could occur in a water system:

1. The fire department withdraws water from a hydrant. This reduces the pressure in the public water system main from 50 pounds per square inch (psi) to 20 psi.
2. A customer served by the public water system installed a lawn irrigation system. The customer’s irrigation system is supplied with water from a pond. The pump supplying the irrigation system operates at 30 psi. To ensure a supply for the irrigation system when the pond is dry, the customer installed a standby connection to the household plumbing (potable water piping).
3. On the day of the fire flow situation, the normally closed valve between the household plumbing and irrigation piping is accidentally left open.
4. Backflow wouldn’t normally occur at this customer’s connection, because the pressure in the public water system is greater than the pressure supplied by the irrigation pump. However, during the fire flow situation, the pressure from the irrigation pump is greater than the pressure in the water main. Water from the pond is pumped into the household plumbing, and then into the public water system main. See Illustration 2.
5. When the fire flow ends, pressure in the public water system water main increases, and contaminated water is delivered to customers served by the system.

Methods of Backflow Prevention

Backflow can be prevented in two ways, either through installation of:

1. An approved air gap (AG) that provides a physical separation between the contaminant and the drinking water supply; or
2. Mechanical devices or assemblies that prevent backflow from occurring.

Air gaps (AGs) are commonly used to prevent backflow in household plumbing systems. Examples of AGs can be found in typical household kitchens and bathrooms. The physical separation between the kitchen faucet and kitchen sink rim is an approved AG. Similarly, the physical separations between the bathroom faucets and rims of the sinks and bathtubs are approved AGs. Current plumbing codes require all sinks and bathtubs sold in the United States to have "built in" approved AGs (designed for above the rim faucets) to prevent contamination of the household plumbing.

Mechanical devices or assemblies. In addition to AGs, there are several methods of preventing backflow by mechanical means. These range from simple single check valves to elaborate approved backflow prevention assemblies. All mechanical devices and assemblies will prevent backflow to some degree when properly installed and maintained. However, not all mechanical devices and assemblies are created equal. Thus, not all mechanical devices and assemblies provide equivalent backflow protection.

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Regarding backflow application conditions, some devices and assemblies are designed to prevent backsiphonage backflow only. These are not effective in preventing backflow under backpressure conditions. Others are designed to prevent both backsiphonage and backpressure backflow. When selecting a backflow preventer to protect the public water system, the purveyor must make sure that the preventer is suitable for the backflow application conditions likely to occur for a particular connection (or fixture).

Backflow preventers must also be commensurate with the degree of health hazard (high vs. low) posed by the customer’s plumbing system (or fixture) to the public water system. For example, some backflow preventers (i.e., assemblies) are manufactured to a very high standard, and thus, are more reliable in preventing backflow than devices manufactured to a lower standard. The more reliable assemblies must be used to prevent backflow in high hazard cross-connection situations.

Regarding backflow preventer design, an important difference between various types of backflow preventers is whether the design allows them to be tested and repaired while in-line. The purpose of the testing is to determine whether they are properly functioning to prevent backflow. Preventers that are not testable are called devices, whereas assemblies are preventers designed for in-line testing and repair. Assemblies include isolating valves and test cocks.

Regarding approval status, in Washington, backflow preventers that protect public water systems from contamination via cross connections must appear on the Backflow Prevention Assemblies Approved for Installation in Washington published by DOH. Yet, not all backflow preventers appear on the approved list. The list identifies only those assemblies that have successfully completed rigorous laboratory and field tests conducted by the University of Southern California’s Foundation for Cross-Connection Control and Hydraulic Research available at: http://www.usc.edu/dept/fccchr/list.html.

The last difference between the various types of backflow preventers is whether they can be used to isolate the customer’s plumbing from the public water system distribution system. This concept is called premises isolation. Premises isolation assemblies are usually located at the meter or property line. Some assemblies can be used for premises isolation, whereas others are used to prevent backflow at fixtures only. The concept of installing a backflow preventer at a particular fixture, such as a boiler, is called fixture protection. When selecting a backflow preventer for a specific situation, it is important to consider whether the preventer is to be used for premises isolation or fixture protection. Note: Washington Administrative Code (WAC) 246-290-490(4) mandates premises isolation for high hazard premises.

Peninsula Light Company’s Cross Connection Specialist determines the degree of hazard and specifies the minimum backflow preventer that must be used to protection against a potential cross connection.

Typical Installation Standards

Double Check Valve Assembly; and Reduced Pressure Backflow Assembly.

Double Check Valve Assembly Installation

• DOUBLE CHECK VALVE ASSEMBLY SHALL BE A WASHINGTON STATE DEPT. OF HEALTH APPROVED MODEL.
• DOUBLE CHECK VALVE ASSEMBLY MUST BE INSTALLED IN THE ORIENTATION APPROVED FOR.
• THE WATER LINE SHALL BE THOROUGHLY FLUSHED PRIOR TO INSTALLING THE BACKFLOW ASSEMBLY.
• DO NOT INSTALL DOUBLE CHECK VALVE ASSEMBLY IN AN AREA SUBJECT TO FLOODING.
• THE BACKFLOW ASSEMBLY SHALL BE TESTED AFTER INSTALLATION, PRIOR TO ACCEPTANCE AND ALSO YEARLY THEREAFTER BY A CERTIFIED BACKFLOW ASSEMBLY TESTER.
• TEST RESULTS SHALL BE SENT TO THE PENINSULA LIGHT COMPANY’S CROSS CONNECTION SPECIALIST.

Reduced Pressure Backflow Assembly Installation

• REDUCED PRESSURE BACKFLOW ASSEMBLY SHALL BE A MAKE AND MODEL APPROVED BY WASHINGTON STATE DEPT. OF HEALTH.
• REDUCED PRESSURE BACKFLOW ASSEMBLY MUST BE INSTALLED IN THE ORIENTATION APPROVED FOR.
• THE WATER LINE SHALL BE THOROUGHLY PROTECTED FROM FREEZING AND FLOODING.
• THE WATER LINE SHALL BE THOROUGHLY FLUSHED PRIOR TO INSTALLING THE BACKFLOW ASSEMBLY.
• THE BACKLOW ASSEMBLY SHALL BE INSTALLED A MINIMUM OF 12-INCHES ABOVE FINISHED GRADE.
• THE BACKFLOW ASSEMBLY SHALL BE TESTED AFTER INSTALLATION, PRIOR TO ACCEPTANCE AND ALSO YEARLY THEREAFTER BY A CERTIFIED BACKFLOW ASSEMBLY TESTER.
• TEST RESULTS SHALL BE SENT TO THE PENINSULA LIGHT COMPANY’S CROSS CONNECTION SPECIALIST.

Backflow Prevention Services

Backflow Prevention Services Available from PLC:

• Backflow prevention assembly installation.
• Backflow assembly testing for newly installed devices.
• If we install assembly, initial test is included.
• Annual backflow assembly testing to satisfy State regulations and local requirements.***
• We take care of all necessary paperwork. Copy mailed or faxed to local water purveyor, if not owned or managed by Peninsula Light Company.
• Copy available for customer record upon request.
• Original testing records kept at Peninsula Light Company in the Water Department files.
• Estimate of installation and/or repair cost provided to customer based on time and materials. Repairs done based on actual time and materials, unless a bid is requested.
• Bids for repairs and/or repair cost can be provided, but include contingency factor for unknown conditions and billed based on actual bid amount.
• If repairs are necessary and PLC does the repairs, the second test is included.

***Backflow Assembly Annual Testing Service Agreements available at current rate of $45 per test (for next three years). Scheduling for annual test done automatically by Peninsula Light Company Water Department based on past testing record and to coincide with PLC’s quarterly schedule.***

Call Peninsula Light Company Water Services at (253) 853-1357 for more information or to schedule a backflow prevention assembly test.

Additional Cross Connection Information (LINKS)

Cross Connection Regulation (WAC 246-290-490): http://www.doh.wa.gov/ehp/dw/our_main_pages/regula.htm

WSDOH Fact Sheet: http://www.doh.wa.gov/ehp/dw/Programs/cross_connection.htm

PNWS-AWWA pamphlet on cross connection: http://www.pnws-awwa.org/publications/PDF/Hlth%20Hazards.pdf

University of California list of approved backflow prevention assemblies: http://www.usc.edu/dept/fccchr/list.html

 

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