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From July to September 1998, Sydney, Australia, experienceda drinking water crisis after high concentrations of Cryptosporidiumand Giardia were detected in the city's watersupply and distribution systems. Three boil-water advisories wereissued, the Sydney Water Inquiry was formed to investigate theincident's origin, and outside laboratories, experts, and auditorswere called in to assess the original analytical procedures andresults. This study reviewed the information submitted to theinquiry and found evidence to confirm that the contamination didoccur and explain its causes.The results of the Cryptosporidium and Giardia microbiologicalanalyses are in agreement with the body of limnological evidencecollected from across the supply system. This finding suggeststhat the potable supply was contaminated when flood-waterborneCryptosporidium and Giardia short-circuited the storage reservoirand entered the treatment plant in a series of pulses that alsoproduced rapid fluctuations in water chemistry. Limnological datafrom the reservoir showed how the barrier was circumvented. Asimple mass balance model demonstrated that cysts and oocystsalso crossed the filtration barrier periodically.Prior to the 1998 water crisis, the Sydney Water Corporationhad assumed that the barriers provided by a storage reservoir withthree years' average retention time and a modern filtration plantwould eliminate the risk of microbial contamination to its supply.The water crisis highlighted some of the unforeseen contaminationrisks to surface water supplies and emphasized the benefitsof maintaining multiple barriers against contaminant transportthrough the system. Includes 28 references, tables, figures.

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Edition: Vol. 95 - No. 5 Published: 05/01/2003 Number of Pages: 15 File Size: 1 file , 680 KB