INTRODUCTION

The Department of Environmental Protection (DEP) is authorized under the Pennsylvania Safe Drinking Water Act to establish standards for the construction of a water supply to assure compliance with the provisions of the act. Accordingly, Section 109.608 of DEP’s rules and regulations, requires that "a public water system may not be designed or constructed in a manner which creates a cross-connection." In addition, Section 109.709(b) further requires that "At the direction of DEP, the public water supplier shall develop and implement a comprehensive control program for the elimination of existing cross-connections or the effective containment of sources of contaminations, and prevention of future cross-connections."

DEFINITIONS

1. Air Gap Separation - The unobstructed vertical distance through the free atmosphere between the lowest opening from any pipe or faucet supplying potable water to a tank, plumbing fixture, or other device and the flood level rim of the receptacle. The differential distance shall be at least double the diameter (2 x D) of the supply pipe measured vertically above the top of the rim of the vessel. In no case, shall the air gap be less than one inch.

 

2. Approved - A backflow prevention device or method that has been accepted by the public water supplier as suitable for the proposed use.

 

3. Atmospheric Vacuum Breaker (AVB) - A fixture outlet device containing an optional shutoff valve followed by a valve body containing a soft-seated float-check, a check seat and an air inlet port. If the shutoff valve is open, the flow of water causes the float to close the air inlet port. If the shutoff valve is closed, the float falls and forms a check valve against backsiphonage and at the same time opens the air inlet port. If no shutoff valve is provided, the flow of water will determine the opening and closing of the air inlet port.

 

4. Auxiliary Water System - Any water source or system on the premises of, or available to, the customer except connections to other approved community water supply systems.

 

5. Backflow - A flow condition, induced by a differential in pressure, that causes the flow of water or mixtures of water and other substances into the distribution pipes of a potable water supply system from a source other than its intended source. Backflow can result from either backsiphonage or backpressure.

 

6. Backflow Preventer - A device or other means which will prevent the backflow of water or any other substance into the public water supply system.

 

7. Backpressure - The backflow of water or a mixture of water and other substances from a plumbing fixture or other customer source, into a public water supply system due to an increase of pressure in the fixture or customer source to a value that exceeds the system pressure.

 

8. Backsiphonage - The backflow of water or a mixture of water and other substances from a plumbing fixture or other customer source, into a public water supply system due to a temporary negative or sub-atmospheric pressure within the public water supply system.

 

9. Consumer - The owner or person in control of any premises supplied by or in any manner connected to a public water supply system.

 

10. Consumer’s Water System - Any water system, located on the consumer’s premises, supplied by or in any manner connected to a public water supply system. A household plumbing system is considered to be a consumer’s water system.

 

11. Containment - Cross-connection control which isolates the customer’s entire facility from the public water supply system so as to provide the protection necessary to prevent contamination of the public water supply in the event of backflow from the customer’s facility. Though containment control prevents contamination of the public water supply, it offers no protection to the water distribution system within the facility. Reduced pressure zone devices are used for containment control.

 

12. Contamination - The degradation of the quality of the drinking water by wastewaters, processed fluids, or any water of a quality less than accepted drinking water quality to a degree which would create an actual hazard to the public health through poisoning or through the spread of disease.

 

13. Cross-connection - An arrangement allowing either a direct or indirect connection through which backflow, including backsiphonage, can occur between the drinking water in a public water system and a system containing a source or potential source of contamination, or allowing treated water to be removed from any public water system, used for any purpose or routed through any device or pipes outside the public water system, and returned to the public water system. The term does not include connections to devices totally within the control of one or more public water systems and connections between water mains.

 

14. Degree of Hazard - An evaluation of the potential risk to health and the adverse effect upon the public water supply system.

 

15. Double Check Valve Assembly (DCVA) - An assembly composed of two single, independently acting, soft-seated, spring-loaded check valves including tightly closing shutoff valves located at each end of the assembly and suitable connections for testing the water tightness of each check valve.

 

16. Fixture Outlet Protection - Cross-connection control which isolates all free-flowing fixture outlets (i.e., faucets) from the water distribution system within a facility. Fixture outlet protection prevents backflow contamination of both the facility water system and the public water supply. Examples of fixture outlet protection devices include atmospheric vacuum breakers, hose-bibb vacuum breakers, and pressure vacuum breakers.

 

17. Health Hazard - Any condition, device, or practice in a water system or its operation that creates, or may create, a danger to the health and well being of its users. The word "severe", as used to qualify "health hazard", means a hazard to the health of the user that could reasonably be expected to result in significant morbidity or death.

 

18. Hose-Bibb Vacuum Breaker (HBVB) - A fixture outlet device that contains a soft-seated, spring-loaded, air inlet valve and is designed to be attached to an outlet having a hose connection thread.

 

19. Interchangeable Connection - An arrangement or device that will allow alternate, but not simultaneous, use of two sources of water.

 

20. Internal Protection - Cross-connection control which isolates all non-outlet, water-use appliances within a facility (e.g., kitchen appliances, air conditioners, boilers, process tanks, photo developing equipment) from the water distribution system within the facility. Internal protection prevents backflow contamination of both the facility water system and the public water supply. Reduced pressure zone devices and double check valve assemblies are used for internal protection.

21. Non-Health Hazard - Any condition, device or practice in a water system or its operation that creates, or may create, an impairment of the quality of the water to a degree which does not create a hazard to the public health, but which does adversely and unreasonably affect the aesthetic qualities of such water for domestic use.

 

22. Non-Potable Water - Water not safe for drinking, personal, culinary, or any other type of domestic use.

 

23. Person - Any individual, partnership, association, company, corporation, municipality, municipal authority, political subdivision or any agency of federal or state government. The term includes the officers, employees and agents of any partnership, association, company, corporation, municipality, municipal authority, political subdivision or any agency of federal or state government.

 

24. Pollution - The presence in water of any foreign substance that tends to degrade its quality so as to constitute a hazard, or to impair the usefulness or quality of the water to a degree which does not create an actual hazard to the public health, but which does adversely and unreasonably affect such waters for domestic use.

 

25. Potable Water - Water which is satisfactory for drinking, personal, culinary, and domestic purposes and meets the requirements of DEP.

 

26. Pressure Vacuum Breaker (PVB) - A fixture outlet device containing an independently operating, soft-seated, spring-loaded check valve and an independently operating, soft-seated, spring-loaded, air inlet valve on the discharge side of the check valve.

 

27. Process Fluids - Any fluid or solution which may be chemically, biologically or otherwise contaminated or polluted in a form or concentration such as would constitute a health, pollutional, or system hazard if introduced into the public or a consumer’s water system. This includes, but is not limited to:

 

a. Polluted or contaminated waters;

b. Process waters; sanitary quality;

d. Cooling waters;

e. Contaminated natural waters taken from wells, lakes, streams, or irrigation systems;

f. Chemicals in solution or suspension;

g. Oils, gases, acids, alkalis, and other liquid or gaseous fluids used in industrial or other processes, or for fire fighting purposes;

h. Heating system waters from boilers or heat pumps.

28. Public Water Supplier - A person who owns or operates a public water system.

 

29. Public Water Supply System - A system which provides water to the public for human consumption which has at least 15 service connections or regularly serves an average of at least 25 individuals daily at least 60 days out of the year. The term includes any collection, treatment, storage, and distribution facilities under control of the operator of the system and used in connection with the system. The term includes collection or pretreatment storage facilities not under such control which are used in connection with the system. The term also includes a system which provides water for human consumption via bottling, vending machines, retail sale, or bulk hauling methods.

30. Reduced Pressure Zone Device (RPZD) - A device which contains two independently acting, soft-seated, spring-loaded check valves, together with a soft-seated, spring-loaded, diaphragm-activated, pressure differential relief valve located between the two check valves. During normal flow and at the cessation of normal flow, the pressure between these two checks shall be less than the supply pressure. In case of leakage of either check valve, the differential relief valve, shall maintain the pressure between the checks at less than the supply pressure by opening to the atmosphere. The device must include tightly closing shutoff valves located at each end, and each device shall be fitted with properly located test cocks.

 

31. Residential Dual Check Valve (RDCV) - A non-testable backflow prevention device that is used for containment control of residential homes and consists of two independently operating, soft-seated, spring-loaded, consecutive check valves.

 

32. Service Connection - The terminal-end of a service line from the public water supply system. If a meter is installed at the end of the service line, then the service connection means the downstream end of the meter.

 

33. System Hazard - A condition posing an actual or potential threat of damage to the physical properties of the public water system or to the consumer’s potable water system.

The following partial listing gives examples of the types of facilities which would require an acceptable reduced pressure zone device (RPZD) or air gap to be installed in the service connection to the public water distribution system. Additional facilities needing RPZDs or air gaps can be found in Table 1.

Type of Facility	Potential Hazard
Sewage, industrial wastewater treatment plants and pumping stations, sewer flushers, etc.	Sewage, industrial wastewater, contaminated water, toxic chemicals, etc.
Paper manufacturing or processing, dye plants, petroleum processing and storage facilities, printing plants, chemical manufacturing or processing, industrial fluid systems, steam generation, rubber processing, tanneries, etc.	Toxic chemicals, water conditioning compounds Examples:  Toxic dyes, acids, alkalies, solvents, quaternary ammonia compounds, mercury, chromium
Canneries, breweries, food processing, detergents, milk processing, ice manufacturing, meat packers, poultry processing, rendering companies, etc.	Process wastewater, steam, acids, caustics, refrigeration lines
Hospitals, clinics, laboratories, solutions, veterinary hospitals, mortuaries, embalmers, shipyards, marinas, nuclear reactor facilities	Bacteria cultures, laboratory blood and tissue waste, toxic materials, sea water, sewage, contaminated water, etc.
Metal-plating, photo processing, cleaning laundries, commercial car washes, commercial refrigeration systems, dry cleaning establishments	Toxic chemicals, concentrated agents, solvents Examples:  Cyanides, fluorides, copper, chromium, caustic and acid solutions, etc.
Commercial greenhouses, spraying and irrigation systems using weedicides, herbicides, exterminators	Toxic chemicals Examples:  ammonium salts, phosphates, 2,4-D, sodium arsenite, lindane, malathion, etc.
Boiler systems, cooling towers or internal fire-fighting systems using conditioners, inhibitors, etc.	Toxic chemicals Examples:  Hydrazine, anti-freeze solutions, etc.

                                                                    

The following partial listing gives examples of the types of facilities which would require an acceptable double check valve assembly (DCVA) device to be installed in the service connection to the public water distribution system. Additional facilities needing DCVAs can be found in Table 1.

 

RECOMMENDED CROSS-CONNECTION CONTROL
AND BACKFLOW PREVENTION DEVICES

In selecting for use of the devices outlined in this section, it is vital that the degree of protection provided be commensurate with the degree of hazard present. It also is important that the limitations of each device be understood since the degree of protection provided will depend on the type of backflow prevention device and the maintenance program employed.

Acceptable backflow prevention devices used for cross-connection control are as follows:

A. Air Gap

B. Double Check Valve Assembly (DCVA)*

C. Reduced Pressure Zone Devices (RPZD)*

D. Residential Dual Check Valve (RDCV)

E. Atmospheric Vacuum Breaker (AVB)

F. Hose-Bibb Vacuum Breaker (HBVB)

G. Pressure Vacuum Breaker (PVB)

*DCVAs and RPZDs should conform to ANSI/AWWA Standards C510 and C511, respectively.

An air gap separation provides a complete physical separation between the free flowing discharge end of a potable water supply line, faucet, plumbing fixture, or other device and the flood level rim of an open or nonpressure receiving vessel. An acceptable air-gap separation shall be at least double the diameter of the supply line. In no case shall the air gap be less than one inch. See Figure 1.

 

Advantages:

 

By preventing backflow caused by both backsiphonage and backpressure, air gap installations provide the maximum degree of protection against backflow. Air gaps are recommended for health hazard risks.

 

Limitations:

 

Air gap separations can be defeated by the thoughtless addition of a hose that in effect extends the discharge end of the pipe to a point below the highest possible water level of the fixture. Fixture outlet devices should be installed when there is any possibility of hose installation.

 

Under some conditions the cost of an air gap separation may be high when compared to a mechanical backflow prevention device.

 

Air gaps cause a loss of line pressure. Therefore, certain commercial processes will need to re-establish pressure through pumps or elevation.

 

Figure 1. Air Gap

* Side walls, ribs or similar obstructions do not effect air gaps when spaced from inside edge of spout opening a distance greater than three times the diameter of the effective opening for a single wall, or a distance greater than four times the diameter of the effective opening for two intersecting walls.

 

** Vertical walls, ribs, or similar obstructions extending from the water surface to or above the horizontal plane of the spout opening require a greater air gap when spaced closer to the nearest inside edge of spout opening than specified in (*) above. The effect of three or more such vertical walls or ribs has not been determined. In such cases, the air gap shall be measured from the top of the wall.

2. Double Check Valve Assembly (DCVA)

The DCVA consists of two independently acting, soft-seated, spring-loaded, check valves mounted in series with two tightly closing shutoff valves and four test cocks (see Figure 2.).

 

Advantages:

 

The primary advantage of a DCVA is that when its two check valves are in the wide open position, there is relatively little resistance to flow. The head loss through the device ranges between 3 and 11 psi, depending on the rate of flow and diameter of pipe.

 

Double check valve assemblies prevent backflow caused by both backsiphonage and backpressure.

 

Limitations:

 

Because DCVAs lack the differential pressure relief valve that RPZDs have, they are recommended only for non-health hazard risks.

 

DCVAs have the inherent weakness of possible failure without giving exterior indication that a failure has occurred.

 

DCVAs are mechanical devices that require periodic inspection and maintenance.

This device consists of two soft-seated, spring-loaded check valves operating in series, and a soft-seated, spring-loaded, diaphragm-activated, pressure differential relief valve, located in the zone between the check valves (see Figure 3.). Two tightly closing shutoff valves and four test cocks complete the assembly. These devices will indicate leakage through one or both check valves or the relief valve by the discharge of water from the relief valve port. This factor is an important advantage over the double check valve assembly.

 

Advantages:

 

The RPZD, when periodically tested and properly maintained, may be used for backflow protection in situations where it would be extremely difficult, or impractical, to provide an air gap separation.

 

Malfunctioning of the RPZD is indicated by discharge of water from the relief port. The RPZD provides protection from backflow caused by both backsiphonage and backpressure, and is recommended for health hazard risks.

 

Limitations:

 

RPZDs are mechanical devices that require periodic testing and maintenance.

 

Pressure loss through RPZDs may be expected to average between 10 and 30 psi, depending upon the size and flow rate of the device.

 

RPZDs should not be installed below ground level, must be protected from freezing, and must be provided with adequate space to facilitate maintenance and testing.

Figure 3. Reduced Pressure Zone Device

Only the air gap, DCVA and RPZD are testable devices that prevent backflow caused by both backsiphonage and backpressure.* The RDCV prevents backflow caused by both backsiphonage and backpressure, but is non-testable.

 

* The air gap can be considered "testable" in the sense that it can be visually inspected.

 

Residential Dual Check Valve:

 

The RDCV is a practical, non-testable device that can be installed for containment protection at residential homes. The RDCV is installed in-line and downstream of the service meter, and contains no shutoff valves. The RDCV prevents backflow caused by both backsiphonage and backpressure, but is recommended only for residential homes which are considered to be a non-health hazard (see Figure 4.).

 

Figure 4. Residential Dual Check Valve

Note: Check valves are in the backflow position.

 

Atmospheric Vacuum Breaker:

 

The AVB is a non-testable device that is installed at fixture outlets. The AVB prevents backflow caused by backsiphonage, but not backpressure. The AVB must not be kept under continuous pressure for more than 12 hours in any 24-hour period. Because of this requirement, no shut-off valve should ever be installed downstream of the AVB. A shutoff valve upstream of the AVB is recommended. The AVB should be installed at least six inches above the fixture outlet (see Figure 5.).

 

Figure 5. Atmospheric Vacuum Breaker

 

Hose-Bibb Vacuum Breaker:

 

The HBVB is a non-testable device that is installed at fixture outlets. The HBVB prevents backflow caused by backsiphonage, but not backpressure (see Figure 6.).

 

Figure 6. Hose-Bibb Vacuum Breaker

 

Pressure Vacuum Breaker:

 

The PVB is a testable device that is equipped with test cocks and shutoff valves, and is installed at fixture outlets. The PVB prevents backflow caused by backsiphonage, but not backpressure (see Figure 7.).

Figure 7. Pressure Vacuum Breaker

                Table 1. Recommended Backflow Prevention Devices

                    The following table outlines the applicability of the air gap, RPZD, and DCVA for the protection of a community water supply. This is a partial list and is not intended to supplant any ordinances or standards developed by a water company. 

219 Speelman Lane
Monroeville, PA  15146
Phone - 412-372-2677
Fax - 412-372-2523
General Manager - John A. Capor 

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