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Cross-Connection Case Histories

Back-Siphonage Case - Pesticide

A breakdown in a 24" water distribution main triggered an event which endangered residents of an eastern city who receive water service from the local township municipal utilities authority.

An exterminating contractor created an illegal cross-connection by diluting a quantity of the highly toxic insecticide by means of a submerged garden hose into a drum of this material. The main break, which occurred during this operation, caused a negative pressure in the distribution system resulting in the siphonage of the entire contents of the drum, through the house service connection and into the distribution system.

This incident exemplifies the danger of illegal cross-connections, and indicates the need for the provision of check valves or breakers on all outside hose bibs.




Back-Siphonage Case – Pesticide

Approximately three gallons of chlordane, a highly toxic insecticide, was sucked (back-siphonage) into the water system of a residential area of a good size eastern city. Water Customers complained that the water looked milky, felt greasy, foamed and smelled.

The problem developed while water department personnel were repairing a water line. An exterminator, meanwhile, was treating a nearby home with chlordane for termites. The exterminating company left one end of the home’s garden hose connected to an outside spigot while the other end was left in a barrel of diluted pesticide. During the water service interruption, the solution was siphoned from the barrel into the home’s water pipes and eventually into the main water system.

The water department undertook an extensive program of flushing the mains and the possibility exists that some of the mains, service lines, hot water heaters and appliances, will have to be replaced.

A water department employee stated that the homes in the affected area, because of hilly terrain, are particularly susceptive to siphoning in the water lines and were built 17 to 20 years before the city building code required backflow valves in new construction.

Even though the back-siphonage condition existed in the street water mains, the reverse flow of the pesticide through the garden hose and resultant contamination of an entire neighborhood could have readily been prevented with the use of a Residential Dual Check Backflow Preventer or Hose Bib Vacuum Breaker.


Contaminated Water Supply – Insecticide

A county housing authority replaced the plumbing piping, both inside and outside, of a large housing authority development. The development consists of twenty-three buildings, each consisting of four apartments, owned and operated by the housing authority. The piping was made unserviceable as a result of chemical contamination of the drinking water as a direct result of insecticide getting into the potable water supply. Chemical tests of the water showed that the chemicals, chlordane and heptachlor, which are toxic and which have been banned since 1976 for agricultural use, entered the potable water supply as a result of a cross-connection.

The insecticide entered the water supply system while an exterminating company was mixing the chemicals, chlordane and heptachlor, in a tank truck with water from a garden hose connected to one of the apartment’s water tap. The end of the garden hose was submerged in the chemicals, at the same time the water to the area was being shut-off and the lines were being drained so that a new valve could be installed. As the water main was being drained a back-siphonage condition began. The drainage point was downstream of the tank truck. Consequently, the chemicals were siphoned out of the tank truck and into the new development piping system.

The water services to seventy-five apartments, housing about three hundred people, were contaminated. Repeated efforts to clean and flush the lines were not satisfactory and it was finally decided to replace the water line and all of the plumbing that was affected. There were no reports of illness, however, residents of the development were told not to use any tap water for any purpose and they were given water that was trucked into the area by volunteer fire department personnel. They were without water for 27 days.


Dialysis Machine Contamination – Anti-freeze Solution

In a large Midwest City a coroner’s jury ruled that renal dialysis machines, that were accidentally contaminated by anti-freeze solutions in a large medical center, were found to be a significant condition in the deaths of two patients.

What is known is that anti-freeze entered the dialysis equipment through a series of events triggered by a manually operated valve being left slightly open. The open valve permitted water to flow into a holding tank that was used to replenish a mix of anti-freeze and water to the air conditioning system. The anti-freeze is customarily utilized in air conditioning water to keep the water from freezing in cold weather. With: the valve partially open, water continually flowed slowly into the anti-freeze/water mixture holding tank until it filled to the point where the pressure in the closed tank equaled the pressure in the water supply system. At this point, the stage was set for disaster.

As long as the supply pressure in the line with the valve partially open did not decrease, no backpressure flow would occur. If, however, the supply pressure dropped for any reason, the potable supply lines in the hospital would be contaminated with the anti-freeze/water mix as the direct result of the cross connection at the holding tank combined with backpressure backflow.

It is theorized that someone in the medical center flushed a toilet or turned on a faucet which, in turn, dropped the pressure in the water pipes and allowed the anti-freeze/water mixture to drain out of the holding tank and into the medical center water pipes. In so doing, the contaminated water entered the dialysis filtration system that is used to purify the water for the dialysis machines. This filtration system takes out trace chemicals, such as those used at the city water treatment plant; however, the system couldn't handle the heavy load of chemicals to which it was suddenly subjected. The effect on the dialysis patients was dramatic; patients became drowsy and confused. Some fell unconscious. All were moved promptly to intensive care where blood samples were taken. The blood samples revealed a buildup of acid and the medical director stated that, "Something has happened in dialysis." Dialysis was repeated on the patients a second and third time. In the meantime, detective work was initiated to determine the cause of the problem.

Test of the water supply to the filtration system determined the presence of "an undesirable chemical in the water purification system." The defective valve that had permitted water containing anti-freeze to drain from the air conditioning holding tank into the dialysis filtration system and from there into the dialysis machines was discovered.

If the water supply to the anti-freeze tank had been air-gapped or protected with a Reduced Pressure Principle Backflow Preventer, the incident would not have occurred. This highlights the need for hydraulic containment of other hazardous areas present in all hospitals and medical centers. Mortuary rooms, autopsy rooms, laundry rooms, boiler rooms, air conditioning units, pharmacy rooms should all be isolated and contained with the use of backflow preventers on their potable supply lines.


Backflow Case - Fast Food Chain Restaurant – Boiler Water Chemical

In a moderate size city along the East Coast, a major fast food chain restaurant received complaints of a bitter taste in the soft drinks they were selling. Over 300 people were served soft drinks during the period in question.

The local water department traced the problem to a chemical in the water and determined this particular chemical was used to treat boiler water in a fertilizer plant, located one-half mile away from the restaurant. Investigation at the fertilizer plant revealed that a check valve on the supply line to the boiler was leaking and allowed the chemicals in the boiler to Backflow into the water main supplying the restaurant



Backflow Incident –Car Wash

An automatic car wash, which recycles its soapy water for reuse, had a water pump break down. It was a high-pressure pump, which drew reclaimed wash and rinse water from an underground tank and pumps (recycles) it into the initial (scrubber) cycle of the car wash. This cycle is not normally connected to the city’s potable water supply.

After the pump broke down, the piping in the rinse cycle, which operates with city water pressure, was manually connected to the scrubber cycle piping by means of a two-inch hose. This arrangement allowed the car wash to remain in operation.

The pump was repaired the next day, but the two-inch hose (cross-connection) between the scrubber and rinse cycle was still connected. A volume of the reclaimed wash/rinse water had been forced into the city water main through the cross-connection and the car wash’s metered service connection when the pump was restarted.