Intervenor: vol. 26, no. 4 September - December 2001

CELA at the Walkerton Inquiry - CELA's Client Tackles Groundwater

One of the fundamental questions to be addressed in the pending Report of the Walkerton Inquiry may be simply stated - how and why did Walkerton's water system become contaminated in May 2000?

To answer this question, Commission lawyers presented extensive evidence from hydrogeologists, consultants, and members of an expert panel (known as the "physical cause" panel) in Part I of the Inquiry. With the assistance of experts retained by the Concerned Walkerton Citizens (CWC), CELA lawyers undertook detailed cross-examinations of these witnesses, and filed additional exhibits on various hydrogeological issues.

Upon completion of the Commission's evidence regarding hydrogeology, the CWC and its experts concluded that several key hydrogeological issues remained unresolved. For example, there was conflicting and/or incomplete evidence on the specific pathway(s) that allowed pathogens to enter Walkerton's water supply wells in May 2000 (e.g., overland flow or contaminated aquifer?).

In the CWC's view, this important issue required further investigation to determine whether the May 2000 contamination was an unfortunate but isolated "one-time" event, or whether it was reflective of systemic vulnerability to bacteriological contamination. Accordingly, the CWC made arrangements with the Commission to have Dr. Stephen Worthington called as a witness to offer expert opinion evidence on the outstanding hydrogeological questions.

Accordingly, Dr. Worthington and two colleagues (Dr. Chris Smart and Mr. Wilf Ruland) undertook fieldwork, reviewed numerous documents, and prepared a detailed hydrogeological report (Exhibit 416). On July 19, 2001, Dr. Worthington testified as an expert witness before the Commissioner, and he presented the main findings and recommendations of the report.

For example, Dr. Worthington testified that Walkerton's three supply wells (Wells 5, 6 and 7) are located in "karst aquifers". In general terms, karst aquifers contain complex, interconnected networks of solutionally enlarged conduits (e.g., bedrock fractures or openings) that permit high-velocity groundwater flow over large distances in relatively short periods of time. Because of these flow characteristics, the U.S. EPA has recognized that karst aquifers are highly susceptible to bacterial contamination.

Dr. Worthington also made a number of recommendations aimed at ensuring the current and future safety of drinking water in Walkerton and other municipalities that draw water from karst aquifers. In particular, Dr. Worthington and his colleagues recommended that Ontario should identify, map, and assess aquifers on the basis of their vulnerability to contamination. Similarly, the report recommended that Ontario should develop guidelines for assessing and monitoring supply wells located in karst or other fractured bedrock settings.

Subsequent to his testimony before the Inquiry, Dr. Worthington and his colleagues continued to undertake fieldwork, data collection/analysis, and tracer testing in the vicinity of Wells 5, 6 and 7. The results of this additional work were summarized in an Addendum Report, which was filed by CWC and admitted as evidence by the Commissioner in late 2001.

In essence, the Addendum Report confirmed earlier evidence respecting the vulnerability of Wells 5, 6 and 7, and provided new insight on the physical cause(s) of the Walkerton Tragedy. For example, the tracer testing revealed that groundwater flow rates in the vicinity of Wells 5, 6 and 7 were 50 to 100 times faster than the rates predicted by computer modelling undertaken by the Town's consultants. In addition, the Addendum Report concludes that:

  • the most likely pathways for bacterial contaminants to reach the Walkerton wells are rapid downward flow through fractures or other breaches in the overburden, followed by rapid groundwater flow through the bedrock via karst features; and
  • bacteriologically contaminated water from Well 5 is implicated in the majority of human illnesses in Walkerton in May 2000, but there is evidence that Well 6 and/or 7 could have served as secondary sources of bacteriologically contaminated water.

It remains to be seen whether - or to what extent - these conclusions will be accepted and acted upon by the Commissioner in his forthcoming Report. In any event, the hydrogeological investigations of Dr. Worthington and his colleagues clearly underscore the complexity, difficulty, and highly technical nature of trying to determine the cause of well water contamination.
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Rick Lindgren is a lawyer at CELA