Page 343 - 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 303
Washington/Baltimore newspapers that evening. The news media contended that lethal
pesticides may have contaminated the water supply and among the contaminants was
paraquat, a powerful agricultural herbicide.
The investigation disclosed that the water pressure in the town water mains was tem-
porarily reduced due to a water pump failure in the town water supply pumping system.
Coincidentally, a gate valve between an herbicide chemical mixing tank and the town
water supply piping had been left open. A lethal cross-connection had been created that
permitted the herbicide to flow into the potable water supply system (see Fig. 9.5). On
restoration of water pressure, the herbicides flowed into the many faucets and outlets
hooked up to the town water distribution system.
This cross-connection, which could have been avoided by the installation of a back-
flow preventer, created a needless and costly event that fortunately did not result in serious
illness or loss of life. Door-to-door public notification, extensive flushing, water sample
analysis, and emergency arrangements to provide temporary potable water from tanker
trucks all incurred expenses on top of the original problem, all of which would have been
unnecessary had the proper precautions been taken.

Mixing sink

Herbicide holding tank

Potable town water

Recommended installation of
backflow preventer
Figure 9.5 Paraquat in the Water System