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Walkerton

The hydrogeological investigations at Walkerton provide a vivid example of how carbonate aquifers may be highly vulnerable to contamination, and how expertise in karst hydrogeology is needed to adequately characterize them.

In May 2000 the municipal wells at Walkerton became contaminated with pathogenic bacteria, resulting in seven fatalities and illnesses in more than 2000 people. A public inquiry was ordered, and a major groundwater investigation took place in the summer of 2000. This concluded that the 30-day groundwater time of travel zones extended up to only 300 m from the wells. Steve Worthington (Worthington Groundwater), Chris Smart (University of Western Ontario), and Wilf Ruland (Citizens Environmental Consulting) reviewed the reports on behalf of Concerned Walkerton Citizens and suggested that the wells were contaminated because of far more rapid groundwater velocities through the karstified carbonate bedrock. We carried out a number of field studies in 2001, and presented the results to the Walkerton Inquiry. The most important tests needed were tracer tests. Tests were carried out in October 2001 and in 2002, and showed that groundwater velocities were 240 - 480 m/d. The combination of thin fractured till and carbonate bedrock made the wells at Walkerton susceptible to bacterial contamination.

Further information:

The transcripts of the year-long Walkerton Inquiry are available at www.tscript.com An overview of the hydrogeology was given on October 16 2000, and the hydrogeology at Walkerton was covered on February 28, March 1, and July 19 2001.

The two reports of the Walkerton Inquiry are available online as pdf files

Our July 2001 report to the Walkerton Inquiry is available here as three pdf files - text (235kb), figures (1094kb) and a description of the appendices (83kb). In November 2001 we produced an Addendum Report (524 kb) following the completion of the first two tracer tests. We have also published a paper giving an overview of the hydrogeology and how groundwater velocities were determined (pdf, 190 kb).