Page 345 - Fair, Geyer, and Okun's Water and wastewater engineering : water supply and wastewater removal

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9.2 Public Health Significance of Cross-Connections 305
9.2.7 Chlordane and Heptachlor at a Housing Authority

The services to 75 apartments housing approximately 300 people were contaminated with
chlordane and heptachlor in a city in Pennsylvania. The insecticides entered the water
supply system while an exterminating company was applying them as a preventive meas-
ure against termites. While the pesticide contractor was mixing the chemicals in a tank
truck with water from a garden hose coming from one of the apartments, a workman was
cutting into a 6-in. (150-mm) main line to install a gate valve. The end of the garden hose
was submerged in the tank containing the pesticides, and at the same time, the water to
the area was shut off and the lines were being drained prior to the installation of the
gate valve. When the workman cut the 6-in.(150-mm) line, water started to drain out of
the cut, thereby setting up a backsiphonage condition. As a result, the chemicals were
siphoned out of the truck, through the garden hose, and into the system, contaminating
the 75 apartments (see Fig. 9.7).
Repeated efforts to clean and flush the lines were not satisfactory, and a decision
was eventually made to replace the water line and all the plumbing that was affected.
There were no reports of illness, but residents of the housing authority 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 their normal water sup-
ply for 27 days.

Recommended installation
of hose bibb vacuum breaker
backflow preventer

Gate valve
closed

Figure 9.7 Chlordane and Heptachlor in a City in Pennsylvania