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                    306  Chapter 9  Cross-Connection Control
                    9.2.8  Boiler Water Entered High School Drinking Water

                                         A high school in New Mexico was closed for several days when a home economics teacher
                                         noticed the water in the potable system was yellow. City chemists determined that samples
                                         taken contained levels of chromium as high as 700 mg/L, “astronomically higher than the
                                         accepted levels of 0.05 mg/L.” The head chemist said that it was miraculous that no one
                                         was seriously injured or killed by the high levels of chromium. The chemical was identi-
                                         fied as sodium dichromate, a toxic form of chromium used in heating system boilers to in-
                                         hibit corrosion of the metal parts.
                                             No students or faculty were known to have consumed any of the water; however, area,
                                         physicians and hospitals advised that if anyone had consumed those high levels of chromium,
                                         the symptoms would be nausea, diarrhea, and burning of the mouth and throat. Fortunately,
                                         the home economics teacher, who first saw the discolored water before school started, imme-
                                         diately covered all water fountains with towels so that no one would drink the water.
                                             Investigation disclosed that chromium used in the heating system boilers to inhibit
                                         corrosion of metal parts entered the potable water supply system as a result of backflow
                                         through leaking check valves on the boiler feed lines (see Fig. 9.8).


                    9.2.9  Car Wash Water in the Street Water Main
                                         This car wash cross-connection and backpressure incident, which occurred in the state of
                                         Washington, resulted in backflow chemical contamination of approximately 100 square
                                         blocks of water mains. Prompt response by the water department prevented a potentially
                                         hazardous water quality degradation problem without a recorded case of illness.







                                                                                         Water cooler
                                                                   High school


                                                                                             Bubbler


                                                                                  Bubbler
                                                            Recommended installation
                                                             of backflow preventer
                                                   Street                         Leaky check valves



                                                            Toxic rust inhibitor and
                                                            defoamant containing
                                                             sodium dichromate



                                                                 Pump

                                                                                High school boilers
                                                   Figure 9.8 Boiler Water Enters High School Drinking Water
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