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Wax injectors
Hose connection
made here
Rinse
Rinse
Scrubbers
Recirculating
Recommended To reclaim tanks Soap injectors 9.2 Public Health Significance of Cross-Connections 275
installation of pump
backflow preventer Reclaim tanks
To restrooms
Potable
water supply Figure 9.9 Car wash water enters the
street water main.
On Monday, February 12, the owner repaired the high- coffee from the coffee machines, they noticed that the water
pressure pump and resumed normal car wash oper- smelled rubbery and had a strong bitter taste. On notifying the
ations. The 2 in. (50 mm) hose connection (cross- Manchester Water Company, water samples were taken and
connection) was not removed! preliminary analysis disclosed that the contaminants found
Because of the cross-connection, the newly repaired
were not the typical contaminants associated with fire line
high-pressure pump promptly pumped a large quan- disturbances. Investigating teams suspected that either the
tity of the reclaimed wash/rinse water out of the car nearby fire could have siphoned contaminants from adjacent
wash and into a 12 in. (300 mm) water main in the buildings into the water mains or the contamination could
street. This in turn was delivered to the many resi- have been caused by a plumbing deficiency occurring within
dences and commercial establishments connected to the seven-story building itself.
the water main (see Fig. 9.9). The pH levels of the building water indicated that an
injection of chemicals had probably taken place within the
Within 24 hours of the incident, the owner of the car seven-story building. Tracing of the water lines within the
washhad installeda2in. (50mm) reduced pressure principle building pinpointed a 10,000 gal (37,850 L) hot water storage
backflow preventer on his water service and all car wash tank that was used for heat storage in the solar heating system.
establishments in Seattle that used a wash water reclaim It did not have any backflow protection on the makeup supply
system were notified of the state requirement for backflow line. As the storage tank pressure increased above the supply
prevention. pressure, as a result of thermal expansion, the potential for
backpressure backflow was present. Normally, this would not
occur because a boost pump in the supply line would maintain
the supply pressure to the storage tank at a greater pressure
9.2.10 Health Problems Due to Cross-Connection
than the highest tank pressure. The addition of rust-inhibiting
in an Office Building
chemicals to this tank greatly increased the degree of hazard
A cross-connection incident that occurred in a modern seven- of the liquid. Unfortunately, at the same time that the fire
story office building located in a large city in New Hampshire took place, the pressure in the water mains was reduced
resulted in numerous cases of nausea, diarrhea, loss of work to a dangerously low pressure and the low-pressure cutoff
time, and employee complaints as to the poor quality of the switches simultaneously shut off the storage tank booster
water. pumps. This combination allowed the boiler water, together
On a Saturday, a large fire occurred two blocks away with its chemical contaminants, the opportunity to enter the
from a seven-story office building in a large New Hampshire potable water supply within the building (see Fig. 9.10).
city. On Sunday, the maintenance crew of the office build- When normal pressure was reestablished in the water mains,
ing arrived to perform the weekly cleaning, and after drink- the booster pumps kicked in, and the contaminated water was
ing the water from the drinking fountains, and sampling the delivered throughout the building.