Dear Editor:
RE: Quarry opponents proclaim ‘future fly rock danger zone’ on Highway 7, March 21.
A number of statements by James Dick Construction’s (JDCL)Greg Sweetnam in this article are false or misleading. We want to set the record straight.
In spite of the best efforts of blasting contractors, unpredictable flyrock occurs as a result of irregularities in the rock geology such as seams, fissures and voids. The karst geology at the hidden quarry site is characterized by such features.
Testimony to the MOE regarding two flyrock incidents at the Pakenham Quarry near Arnprior, Ontario on July 20 and 23, 2009 demonstrated that even competent, experienced contractors are unable to avoid the possibility of flyrock due to geological irregularities:
– “Any experienced blaster would have had the same fly rock incident take place”;
– “There is no technology available to identify anomalies in rock such as mud seams or voids”;
– “90% of fly rock incidents are unexplainable.”
Mr. Morin, of JDCL’s blasting consultant Explotech, advised “. . . that the hazard zone be increased to 500m when firing any future blasts in this quarry.”
Numerous jurisdictions such as Nova Scotia, Texas, Australia and the UN Food and Agriculture Organization, set minimum requirements of 400 to 800m or more for setbacks for surface blasting. Ontario has no minimum requirement.
Sweetnam implies that the risk of a flyrock incident is effectively zero by stating, “This is a real long shot.” But data from the international blasting contractor, Dyno Nobel, indicates the probability of flyrock is about 0.5% – low but not zero. But risk is probability times consequences and the consequences are often catastrophic. Responsible quarry operators acknowledge that the only protection from flyrock is to provide safe setback from the blasting site to ensure that no flyrock damage or injury occurs, and there are at least two methods used internationally to calculate a safe setback.
Sweetnam also stated the risk of flyrock will be even lower since JDCL intends to blast underwater, at the bottom of a gravel pit.
JDCL is not planning to do underwater blasting “at the bottom of a gravel pit”, rather would blast into a water-filled pit from the excavation face. This doesn’t prevent flyrock due to “cratering” or “rifling” from the explosive-filled boreholes drilled on dry land.
Our attention to this risk to safety and property is not a fundraising ploy, but part of our effort to protect our community.
Doug Tripp,
Cambridge