DOCUMENTED BACKFLOW INCIDENTS

Throughout the United States there have been numerous documented cases of potable water systems being contaminated as the result of unprotected cross connections. In many instances these cross connections and backflow situations  resulted in illnesses and in some cases death. Cross connection control and backflow prevention measures are established in national, state and local regulations and must be continuously enforced. 

A cross connection is a connection between the potable water system and a non-potable substance, which can be a gas, liquid, vapor or any other substance that is not part of the potable water supply. This inter-connection is like a “time bomb” and becomes a potable water system hazard when a backflow condition is introduced by any number of causes, e.g., water main break, fire, pumps, elevations, high demand, etc. In many instances, contamination from cross connections goes undetected due to dilution.

An example of a cross connection and backflow situation occurred at a large facility having an  irrigation system on-site that was supplied by a pond  and  the city water supply. The cross connection was discovered after the Water Company received a call from an employee of the facility one Monday morning and complained that people were getting sick after drinking the water. Upon investigating the problem, the Water Company discovered a zero chlorine residual at the office building on-site. The office workers explained the problem and made the comment that “the 5 acre pond on-site had gone dry over the weekend.”

The investigation team found the potable water system inter-connected with the irrigation system being supplied by pond water. The potable water system had a double check valve assembly backflow preventer installed at the connection point to the irrigation system. The backflow preventer was the wrong type and  had not been tested since it had been installed (approximately five years). Both check valves in the backflow preventer were found to be fouled/leaking. The water in the pond was pumped into the irrigation system at 90 psi, while the city water pressure was 70 psi. City water meter readings revealed the meter had ran backwards close to 1,000,000 gallons. The water from the  pond  was pumped into the city’s potable water distribution system.

There are many types of water using equipment and processes that can create  cross connection   hazards as described above. Cross connection control and backflow prevention is a continuous effort and must be diligently pursued. To protect the potable water supply, enforcement agencies are required by national, state and local regulations, to assure approved cross connection control and backflow prevention methods are established and enforced. Private facilities must also protect the water by ensuring cross connections are protected as established by these regulations.