coli infection, and any patient infected with E. coli O157 was at risk for potentially fatal hemolytic-uremic syndrome. David Patterson, the Assistant Director of Health Protection at Bruce-Grey-Owen-Sound Health Unit (BGOSHU), immediately contacted Beverly Middleton, a public health inspector in the Owen Sound office of the Health Unit, and the two officials began passing along information to local medical facilities about how to properly treat E. coli-based gastroenteritis. Later the same day, Patterson asked James Schmidt, Middleton's counterpart in the Walkerton Health Unit, to contact the Walkerton Public Utilities Commission (PUC) and obtain information on chlorination levels in the water system. Stan Koebel (PUC manager) informed Schmidt that chlorine residuals in the distribution system were 0.1 to 0.4 parts per million; based on lack of familiarity with water chlorination, Patterson concluded that the presence of chlorine residuals at any level indicated that the water system was free of contamination. He proceeded with investigating other possible sources for the E. coli. Throughout May 20, Patterson expressed his understanding to community members and other investigators that Walkerton's water could not be the source of the outbreak; BGOSHU personnel also urged the PUC to issue a press release assuring the public of the safety of the water. Initial Public Utilities Commission response By May 18, rumours were already circulating that Walkerton Public Utilities Commission (PUC) water was the cause of the illness increasing numbers of residents were suffering. Staff at the PUC had also begun receiving calls enquiring as to the safety of town water. On May 19, public health officials contacted the Walkerton PUC about the possibility of the water system being involved in transmission of the gastroenteritis; they were told that the town's drinking water was "okay". After speaking to public health officials that day, Stan Koebel (PUC manager) began the process of flushing the system and increasing chlorination levels, procedures he described to David Patterson as "precautionary". This flushing continued into May 20; Koebel's testing records from that day note sharply increased chlorine residual levels, though evidence later indicated that Koebel's testing had likely been done improperly and thus returned higher-than-reality chlorination results. The same day, Koebel returned Well 5, which had not been feeding Walkerton's water supply since May 15, to service. The well was then turned off at 1:15 a.m. on May 21. Chief Justice of Ontario Dennis O'Connor's later report on the event concluded that by May