Backflow Incidents
Redmond High School Backflow Incident
On the morning of June 9, 1989, the City of Redmond, Oregon called the Oregon Health Division to report a backflow incident that happened at a high school. The central air conditioning system had built up pressure and pushed coolant back into the school's drinking water supply. Once the problem was discovered, the air conditioning system was shut down and drained and the school was isolated from the rest of the water system. The city was instructed to collect water samples and then begin flushing the school's water lines.
The water samples were analyzed that evening. The water sample taken in the teacher's lounge, the closest point to the cross connection, contained 9,600 ppm of ethylene glycol. Ethylene glycol is highly toxic antifreeze. The school was instructed to continue flushing lines, turn off all drinking fountains, post "DO NOT DRINK" notices, and supply bottled water until further notice from the Oregon Health Division.
Fortunately, school was out on summer break. Eight employees who drank water from the teacher's lounge reported feeling ill and were sent to the hospital. The backflow occurred at the connection between the plumbing system and the air conditioning system, which were only separated by a pressure-reducing valve. About 18 inches upstream from the pressure reducing valve was the connection to the teacher's lounge. Ethylene glycol was detected in the school's water system and also out in the city's water distribution system. An employee of the school mentioned that this problem started about three years prior when people first noticed water quality problems in the teacher's lounge.
Ethylene glycol is easily removed from a water distribution system through vigorous flushing, and the school officials were instructed to locate every water line and flush it. Once the entire system was flushed, they could remove notices and turn on the water fountains. The school was required to install a reduced pressure backflow prevention assembly on the water connection to the air conditioning system.
Source: Summary of Backflow Incidents, Cross Connection Control Committee, Pacific
Northwest Section, AWWA R-89-003
Autumn Lane Backflow Incident
On October 12, 1979 the residents along the 4900 block of Autumn Lane in Roanoke, Virginia complained that their water looked milky, felt greasy, foamed, and smelled like "a combination of kerosene and Black Flag pesticide". Approximately three gallons of Chlordane, a highly toxic insecticide, had backsiphoned into the city water system.
The contamination occurred while water department personnel were repairing a water main. At the same time, an exterminator was treating a nearby home with Chlordane for termite control. The workmen for the exterminating company left one end of a hose connected to an outside hose tap and left the other end in a barrel of diluted insecticide. During the water service interruption, the solution was backsiphoned into the house plumbing, and then the city water main.
The homes in the affected area, because of hilly terrain, were particularly susceptible to backsiphonage. The water department undertook an extensive program of flushing water mains. The insecticide however, adhered to the inside of the pipes. Tests of water samples taken six days after the contamination showed Chlordane levels five times great than considered safe.
The water department tapped into the water main at two points along the street to continue flushing operations. For several days, residents either carried water to their houses from two 400 gallon water tanks the city put up on a vacant lot in the area, or traveled to the homes of friends or relatives to shower and eat meals.
Source: Summary of Backflow Incidents, Cross Connection Control Committee, Pacific
Northwest Section, AWWA, R-79-006.
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