Page 297 - Water Engineering Hydraulics, Distribution and Treatment
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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.
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