Published in The BANAR June 2003
On May 5th, 2003 the BCA hosted an information evening with experts from Lafarge, independent consultants, and the City of Ottawa Forrester. The purpose of the meeting was to present technical and non-technical information concerning the effect of the intensity of quarry blasting, soils, water table, and trees on foundation and house damages reported in the community. There were 72 residents in attendance and virtually all agreed that the session went well. This public meeting was organized in response to inquiries received by the BCA.
Rick Chevrier, Lafarge Resource Manager, opened the meeting with a presentation on the operation of the quarry and the intensity of blasts allowed by Provincial regulation. He explained that seismographs placed around the Hamlet indicate the intensity is always less than half the allowable limit.
Rob Cyr and René of Explotech presented charts and answered questions concerning the extent of damage caused by varying degrees of blast intensity. Their data indicated that the levels legislated by the province have a safety factor of approximately 10 before damage will occur. Blasts at the quarry are set off in a series of small sequential charges 25 milli-seconds apart, which is normal practice for this type of operation.
Craig Huff, the City Forrester, explained that foundation problems were not unique to Blackburn. He mentioned that due to considerably less rain over the past three summers, trees in some areas of the city have sucked water from the clay causing its structure to collapse, resulting in differential settling and foundation damage. He mentioned ways of mitigating this problem by pruning and/or watering your trees. There were pamphlets distributed on this subject, and more information may be found on the CMHC website.
An interesting aspect of the meeting were the comments made by some attendees with experience in blasting that confirmed data presented by Lafarge and Explotech on the intensity of a blast that would result in damage to houses. There were also attendees with experiences on the effect of trees on their foundations, which confirmed information provided by Craig Huff.
The presentations lasted about an hour and there was a one-hour question period after which refreshments were served and the presenters discussed specific concerns with individual residents.