Cross Connection Control

There have been numerous instances of illness caused by cross-connections.178 A discussion of water system design would not be complete without reference to cross-connection control and backflow prevention. The goal is to have no connection between a water of drinking water quality (potable) and an unsafe or questionable (nonpotable) water system or between a potable system and any plumbing, fixture, or device whereby nonpotable water might flow into the potable water system.

A cross-connection is any physical connection between a potable water system and a nonpotable water supply; any waste pipe, soil pipe, sewer, drain; or any direct or indirect connection between a plumbing fixture or device whereby polluted water or contaminated fluids including gases or substances might enter and flow back into the potable water system. Backflow of nonpotable water and other fluids into the potable water system may occur by backpressure or backsiphonage. In backpressure situations, the pressure in the nonpotable water system exceeds that in the potable water system. In backsiphonage, the pressure in the potable water system becomes less than that in the nonpotable water system due to a vacuum or reduced pressure developing in the potable water system.

Negative or reduced pressure in a water distribution or plumbing system may occur when a system is shut off or drained for repairs, when heavy demands are made on certain portions of the system causing water to be drawn from the higher parts of the system, or when the pumping rate of pumps installed on the system (or of fire pumps or fire pumpers at hydrants) exceeds the capacity of the supply line to the pump. Backpressure may occur when the pressure in a nonpotable water system exceeds that in the potable water system, such as when

Spring-loaded ^-Pressure relief valve check valves j^x/

Spring-loaded ^-Pressure relief valve check valves j^x/

Normal direction of flow Reversed direction of flow

FIGURE 2.12 Reduced pressure zone backflow preventer—principle of operation. Malfunctioning of check or pressure-relief valve is indicated by discharge of water from relief port. Preferred for hazardous facility containment. (Source: Cross-Connection Control, EPA-430/9-73-002, U.S. EPA, Water Supply Division (WSD), Washington, DC, 1976, p. 25.)

Normal direction of flow Reversed direction of flow

FIGURE 2.12 Reduced pressure zone backflow preventer—principle of operation. Malfunctioning of check or pressure-relief valve is indicated by discharge of water from relief port. Preferred for hazardous facility containment. (Source: Cross-Connection Control, EPA-430/9-73-002, U.S. EPA, Water Supply Division (WSD), Washington, DC, 1976, p. 25.)

a fire pumper at a dock or marina pumps nonpotable water into a hydrant or when a boiler chemical feed pump is directly connected to the potable water system.

The more common acceptable methods or devices to prevent backflow are air gap separation, backpressure units as shown in Figures 2.12 and 2.13, and vacuum breakers.179 The non-pressure-type vacuum breaker is always installed on the atmospheric side of a valve and is only intermittently under pressure, such as when a flushometer valve is activated. The pressure-type vacuum breaker is installed on a pressurized system and will function only when a vacuum occurs. It is spring loaded to overcome sticking and is used only where authorized. The vacuum breaker is not designed to provide protection against backflow resulting from backpressure and should not be installed where backpressure may occur.

The barometric or atmospheric loop that extends 34 to 35 feet above the highest outlet is not acceptable as a backflow preventer because backpressure due to water, air, steam, hot water, or other fluid can negate its purpose. The swing joint, four-way plug valve, three-way two-port valve, removable pipe section, and similar devices are not reliable because nonpotable water can enter the potable water system at the time they are in use.180

An elevated or ground-level tank providing an air gap, the reduced pressure zone backflow preventer, and the double-check-valve assembly are generally used on public water system service connections to prevent backflow into the

FIGURE 2.13 Double check valve-double gate valve assembly. For aesthetically objectionable facility containment.

distribution system. The vacuum breaker is usually used on plumbing fixtures and equipment.

An approved backflow preventer or air break should be required on the water service line to every building or structure using or handling any hazardous substance that might conceivably enter the potable water system. In addition, building and plumbing codes should prohibit cross-connections within buildings and premises and require approved-type backflow preventers on all plumbing, fixtures, and devices that might cause or permit backflow. It is the responsibility of the designing engineer and architect, the building and plumbing inspector, the waterworks official, and the health department to prevent and prohibit possibilities of pollution of public and private water systems.

There are two major aspects to a cross-connection control program. One is protection of the water distribution system to prevent its pollution. The other is protection of the internal plumbing system used for drinking and culinary purposes to prevent its pollution.

The water purveyor has the responsibility to provide its customers with water meeting drinking water standards. This requires control over unauthorized use of hydrants, blowoffs, and main connections or extensions. It also means requirement of a backflow prevention device at the service connection (containment) of all premises where the operations or functions on the premises involve toxic or objectionable chemical or biological liquid substances or use of a nonpotable water supply, which may endanger the safety of the distribution system water supply through backflow. However, although these precautions may protect the water system, it is also necessary to protect the consumers on the premises using the water for drinking and culinary purposes. This responsibility is usually shared by the water purveyor, the building and plumbing department, the health department, and the owner of the structure, depending on state laws and local ordinances. The AWWA Policy Statement on Cross-Connection states, in part, that the "water purveyor must take reasonable precaution to protect the community distribution system from the hazards originating on the premises of its customers that may degrade the water in the community distribution system."181 The water purveyor has been held legally responsible for the delivery of safe water to the consumer and the Safe Drinking Water Act bases compliance with federal standards on the quality of water coming out of the consumer's tap. Under these circumstances, a cross-connection control program is needed in every community having a public water system to define and establish responsibility and ensure proper installation and adequate inspection, maintenance, testing, and enforcement.

A comprehensive cross-connection control program should include the following six components:182

1. An implementation ordinance that provides the legal basis for the development and complete operation of the program

2. The adoption of a list of devices acceptable for specific types of cross-connection control

3. The training and certification of qualified personnel to test and ensure devices are maintained

4. The establishment of a suitable set of records covering all devices

5. Public education seminars wherein supervisory, administrative, political, and operating personnel, as well as architects, consulting engineers, and building officials, are briefed and brought up-to-date on the reason for the program as well as on new equipment in the field

6. An inspection program with priority given to potentially hazardous connections

In some states, the legal basis for the adoption of a local cross-connection ordinance is a state law or sanitary code; hence, consultation with the state health department or other agency having jurisdiction is advised in the development of a local ordinance and program. Model ordinances and instruction manuals are available.183* Enforcement is best accomplished at the local level.184

Implementation of a control program requires, in addition to the above, that a priority system be established. Grouping structures and facilities served as "Hazardous," "Aesthetically Objectionable," and "Nonhazardous" can make inspection manageable and permit concentration of effort on the more serious conditions. Estimating the cost of installing backflow prevention devices is helpful in understanding what is involved and obtaining corrections. Some devices are quite costly. An inspection program, with first priority to hazardous situations, is followed by review of findings with the local health department public health engineer or sanitarian, official notification of the customer, request for submission and approval of plans, establishment of a correction timetable, inspection and testing of the backflow device when installed, enforcement action if indicated, follow-up inspections, and testing of installed devices. The program progress should be reviewed and adjusted as needed every six months.185

* See also local building and plumbing codes.

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