Allegheny County


In 1981, Allegheny County, Pennsylvania, spent approximately $300,000 to replace plumbing and water mains of a large housing authority development. The piping was permanently contaminated when chlordane and heptachlor, toxic chemicals which have been banned since 1976 for agricultural use, entered the potable water supply system through a cross-connection. A pesticide contractor was mixing the chemicals in a tank truck, using water from a garden hose attached through one of the apartments. The end of the hose was submerged in the chemical solution. At the same time, a gate valve was being installed in the
distribution line. Water to the area was shut off, allowing the chemical to
back-siphon into the potable water system as the distribution lines drained. This type of backflow is more common at commercial connections, like factories, however, it still can occur in a residence if there are pumps, or pressurized air connected to the plumbing system. Unlike back-siphonage, it is not necessary to have a drop in distribution system pressure for backpressure to occur. When-ever the pressure at the point of the cross-connection exceeds the pressure of the distribution system, the direction of the flow will reverse. Without adequate protection non-potable water will be forced into the potable system. Water services to seventy-five apartments housing nearly three hundred
people were contaminated. Attempts to clean and flush the lines were not successful; evidence of contamination remained and water quality standards could not be met. The housing authority was without water for 27 days while the main and all affected plumbing were replaced (both inside and outside). Water was transported to the area for drinking and cooking purposes. Costs to the water company were substantial, but an estimate of the damage incurred by water consumers cannot be reasonably determined. A simple hosebib or hose connection vacuum breaker could have prevented the incident.