walkerton e. coli outbreak walkerton e. coli outbreak the walkerton e. coli outbreak was the result of a contamination of the drinking water supply of walkerton, ontario, canada, with e. coli and campylobacter jejuni bacteria. the water supply was contaminated as a result of improper water treatment following heavy rainfall in late april and early may 2000, that had drawn bacteria from the manure of nearby cattle used to fertilize crops into the shallow aquifer of a nearby well. the first reported case was on may 17. the contamination caused gastroenteritis and sickened more than 2,000 people and resulted in seven deaths. walkerton e. coli outbreakbacteria strainescherichia coli o157:h7 and campylobacter jejunisourcecontaminated drinking water supplieslocationwalkerton, ontario, canadafirst reportedmay 17, 2000datemay 12–24, 2000confirmed cases2,000+severe cases27deaths7 subsequently, associate chief justice of ontario, dennis o'connor led an inquiry into the outbreak, called the walkerton inquiry. walkerton public utilities commission operators stan and frank koebel, neither of whom had any formal training, were sentenced on december 20, 2004, after pleading guilty to charges of common nuisance stemming from the contamination—stan to one year in jail, and frank to nine months house arrest. as a result, stricter water treatment guidelines were put in place by the government. town background walkerton, ontario is a small township in the municipality of brockton, 180 kilometres (110 mi) northwest of toronto. it serves as the administrative centre of brockton, into which it was merged in 1999, and as the county seat of bruce county. the population of walkerton in 1996 was recorded as 5,036 individuals in an area of 6.4 square kilometres (2.5 sq mi). at the time of the 2000 events, the town's drinking water was drawn from three chlorinated wells to the west and southwest of the town. the wells were owned and operated by the walkerton public utilities commission (puc), which was managed by stan koebel and run by foreman frank koebel. contamination background walkerton public utilities commission system operators in 2000, the walkerton public utilities commission was under the supervision of two men, brothers stan and frank koebel. both men had been working for the walkerton public utilities commission (puc) since the 1970s, when they were teenagers and their father worked at the puc. neither man had formal training in public utility operation or in water management, but by 2000, both had been promoted to management positions on the basis of their experience. both brothers carried certification as class 3 water distribution system operators, licences obtained through a grandfathering program run by the ministry of the environment (moe) and based on their work experience in their positions. though ontario law required that water systems operators receive 40 hours of continuing education per year, stan koebel interpreted this to include activities only marginally related to water systems, such as cpr certification, and as a result neither brother used continuing education time to gain or maintain expertise in water safety. as a result of their lack of formal training and their overseeing themselves, the koebel brothers were relatively uninformed about water safety. both later testified that they were not familiar with sections of the ontario drinking water standards documentation (odws) that dealt with tasks they needed to be aware of to do their jobs adequately: manager stan koebel had not read the section of the odws about identifying contaminated water, while foreman frank koebel had not read the chapter on chemical testing of water for safety purposes. neither man had more than a passing familiarity with e. coli or the danger the bacteria posed to water systems, nor with chlorination standards and best practices. well system and maintenance the wells that drew water for walkerton were known as well 5, well 6, and well 7, with well 5 being both the southernmost and the closest to the residential portion of the township. well 5, drawing water from depths of 5.5 to 5.8 metres (18.0 to 19.0 ft) and 7.0 to 7.3 metres (23.0 to 24.0 ft) through soft limestone, was brought online to the walkerton water system in 1978, following a hydrological evaluation commissioned by the puc. because well 5's aquifer drew partially from spring-fed, gravel-soiled zones that were prone to absorbing surface runoff, the hydrological evaluation recommended that well 5 be monitored regularly to ensure that water was being drawn from lower well depths rather than higher ones. it also recommended that land usage in the immediate area of the well be limited in light of agricultural waste runoff being detectable in the well's water. neither of these recommendations was implemented as conditions of operation when well 5 received a certificate of approval in 1979. multiple subsequent tests on the well between 1979 and 2000 continued to conclude that due to the shallow depth at which well 5 was drilled and the tendency of its water level and makeup to be directly affected by surface runoff, caution toward contamination levels in the well was advisable. wells 6 and 7 were drilled more deeply and drew from areas of land with significantly less fractured bedrock than well 5. in 2000, ontario law indicated that in a community the size of walkerton, at least thirteen water samples per month should be submitted for microbiological testing, with the samples being drawn from "the point at which the treated water enters the distribution system". a longstanding standard at the walkerton puc, however, was to comply with an earlier governmental requirement of nine samples per month. employees were instructed to collect four weekly samples from each of the three wells that served walkerton. this meant that even in an ideal month, the puc typically submitted one fewer sample than required by law; in practice, it was more common for eight or nine samples to be submitted than for thirteen to be. in addition, the samples that were submitted often had their points of origin mislabelled; for the sake of convenience, testing employees might draw two samples from one location but label the bottles as having come from two locations, or draw a water sample from the water supply of their own home rather than from within distribution points of the system. as a result, not all water sources were being tested adequately, and there was little regularity to which ones were tested when. multiple ministry of the environment (moe) documents dating to throughout the 1990s note that walkerton's sampling practices were lacking. walkerton was placed on a list of non-compliant municipalities in 1997, but removed shortly thereafter after assurances from stan koebel that compliance would improve. nevertheless, a 1998 inspection verified that eight or nine samples were still the standard of collection in walkerton. the puc was again warned about noncompliance, and again stan koebel agreed to improve testing practices. moe reports throughout the 1990s also noted that the puc was inadequately chlorinating water that ran through the walkerton system. best practices dictated that chlorine residual levels after fifteen minutes of contact between the chlorine and the water be maintained at 0.5 mg/l, with that level verified through daily testing; this would indicate that the water was being adequately purified of potentially harmful microorganisms. inspections of the walkerton system in 1991, 1995, and 1998 showed chlorine residual levels in the walkerton system of between 0.12 mg/l and 0.4 mg/l, with a mean level of 0.27 mg/l. according to the later walkerton inquiry, "stan koebel testified that he generally set the chlorinator to slightly less than 0.5 mg/l and that frank koebel would lower it to approximately 0.3 mg/l several times a month." both men felt that walkerton water was adequately pure and safe without a 0.5 mg/l chlorine residual—they were known to willingly drink raw water from the wells—and they had received complaints from community members about system water tasting overly chlorinated. the puc's evaluation of chlorine residual levels was typically performed weekly, rather than daily, and actual testing was often eschewed in favour of visually inspecting the "bubble" on the chlorinator for a "guesstimate" of the residual. these "guesstimates" would be noted in the puc's daily operating sheets as if they were actual tested levels. when actual testing was performed, the 15-minute timeframe of the test was often cut short, resulting in higher-than-reality chlorine residual readings. fecal coliform and e. coli testing on well 5 between 1990 and 2000 showed ongoing deterioration in the quality of water from the well. in the mid-1990s, a provision for more intensive monitoring of wells susceptible to groundwater contamination was added to the ontario drinking water objectives (odwo); however, the ministry of the environment (moe) failed to apply this provision to reclassifying existing wells. as a result, despite tests repeatedly showing that well 5 was prone to contamination, it did not have any contamination alarms or emergency shut-off mechanisms. april 2000 sampling done on water from wells 5 and 6 showed fecal coliform present in well 5's water, both raw and treated, but not in well 6's. well 7 was not running during this time period and was not tested. may 1, 2000 tests showed similar results, with well 5 being the sole apparent contaminated water source. may 15 water testing on the highway 9 water main construction project in walkerton returned positive results for fecal coliform and e. coli. due to inaccurate labelling of the samples' sources by puc personnel, it was unclear to the testing laboratory which water samples had come from walkerton's raw water versus its treated water, or which water had come from which well source; however, the laboratory notified stan koebel on may 17 that submitted samples had tested positive for e. coli and fecal coliform. personnel from the testing laboratory, unaware that ontario drinking water objectives mandated the notification of the ministry of the environment in such a case, did not notify any agency besides the puc of the failed testing results. contamination period using knowledge about typical incubation periods of e. coli o157:h7 (average 3–4 days) and campylobacter (average 2–5 days) bacteria and working backwards from the first emergence of symptoms in the community, investigators determined that the majority of infected community members had been exposed to the bacteria between may 13 and may 16 and the contamination had thus likely entered the infective well on or about may 12. in the spring of 2000, walkerton's system typically drew most of its water from one well at a time, alternating unevenly between wells 5, 6, and 7. well 7 was turned off between march 10 and may 2, ran alone from may 2 through may 9 before turning off again, and was then used again between may 15 and may 19. from may 9 to may 13, well 5 provided the bulk of walkerton's water, supplemented from may 10–13 by well 6. though well 7 ran without chlorination between may 3 and may 9, expert evaluation of well 7's pumping schedule and lack of physical vulnerabilities to contamination concluded that it was highly unlikely to have been involved in the outbreak. well 6, which records indicate was out of service beginning may 13, was similarly determined to have been unlikely to have been the source of contamination based on its location and characteristics. source of contamination to the immediate south and west of well 5 lay farmland used as a cattle-breeding operation, occupying four lots (18–21, west to east). on april 22, 2000, following heavy rainfall on april 20–21, manure from the cattle was used to fertilize crops growing on lot 20 of the property, the nearest edge of which lay approximately 81 metres (266 ft) from well 5. the manure was subsequently incorporated into the soil of lot 20 using a disc harrow. the april incorporation of e. coli-contaminated manure into cool, wet soil near well 5 meant that the bacteria were in an ideally suited environment for longevity. subsequent heavy rains totalling 134 millimetres (5.3 in) fell between may 8 and may 12, drawing the bacteria deeper into the soil near well 5. during later investigations of the outbreak, experts on the walkerton commission expert review panel determined that the manure-contaminated water had likely seeped into the aquifer that underlay well 5, though it may have been possible that surface runoff, rather than contaminated groundwater, was the source of the bacteria. cattle manure, even under best practices, typically contains fecal coliform bacteria, including