Page 291 - Water Engineering Hydraulics, Distribution and Treatment

Normal operation
positive supply pressure potable water
Cold
Open
Negative supply
Hot
pressure
Closed
“Hydro”
Cold Closed aspirator Open 9.2 Public Health Significance of Cross-Connections 269
Hot
Reverse flow through
aspirator due to Body fluids
back siphonage

Figure 9.1 Reverse flow through
aspirator due to backsiphonage.

and the antifreeze, placed in the heating system to prevent With the potable priming line left open and the pumps
freeze-up of an unused hot water heating system, drained maintaining pressure in the fire lines, raw salt water was
out of the heating system into house water lines and flowed pumped through the priming lines, through the spool piece
out to the street (see Fig. 9.3). If it had not been noticed, it sleeve, to the ship repair facility and the restaurant.
would have entered the homeowner’s drinking water when
the water pressure was restored. 9.2.5 Paraquat in the Water System

“Yellow gushy stuff” poured from some of the faucets in a
9.2.4 Salt Water Pumped into Freshwater Line small town in Maryland, and the state of Maryland placed a
ban on drinking the water supply. Residents were warned not
A nationally known fast-food restaurant located in the south-
to use the water for cooking, bathing, drinking, or any other
eastern United States complained to the water department
purpose except for flushing toilets.
that all of their soft drinks were being rejected by their cus-
The incident drew widespread attention and made
tomers as tasting “salty.” This included soda fountain bev-
the local newspapers. In addition, it was the lead story on
erages, coffee, and orange juice. An investigation revealed
the ABC news affiliate in Washington, DC, and virtually
that an adjacent water customer complained of salty water
all the Washington/Baltimore newspapers that evening. The
occurring simultaneously with the restaurant incident. This
news media contended that lethal pesticides may have con-
second complaint came from a waterfront ship repair facility
taminated the water supply and among the contaminants was
that was also being served by the same water main lateral.
paraquat, a powerful agricultural herbicide.
The investigation centered on the ship repair facility and
The investigation disclosed that the water pressure in the
revealed the following (see Fig. 9.4):
town water mains was temporarily reduced due to a water
A backflow preventer that had been installed on the
pump failure in the town water supply pumping system.
service line to the shipyard had frozen and had been Coincidentally, a gate valve between an herbicide chemi-
replaced with a spool piece sleeve. cal mixing tank and the town water supply piping had been
left open. A lethal cross-connection had been created that
The shipyard fire protection system utilized seawater permitted the herbicide to flow into the potable water supply

that was pumped by both electric and diesel-driven system (see Fig. 9.5). On restoration of water pressure, the
pumps. herbicides flowed into the many faucets and outlets hooked
The pumps were primed by potable city water. up to the town water distribution system.