Blasting at a Vedder Mountain rock quarry was the “likely” cause of the Feb. 18 landslide in Chilliwack above Vedder Mountain Road in Yarrow.
That’s the conclusion of a consultant who prepared a geotechnical report for the quarry’s owner, according to the Ministry of Energy and Mines.
A ministry investigation into the incident is ongoing, but provided the conclusion of the geotechnical report to the Progress on Thursday.
The report found that the slope failure was “likely” induced by a blast in the northwest corner of the quarry.
The conclusion differs from what the quarry’s owner, Western Explosives, reported after the landslide, which happened at 10 a.m. on Feb. 18 and was noticed by local residents and nearby trail walkers.
Nobody was injured and no private property was damaged, but three homes were evacuated on Vedder Mountain Road and the ministry said a protective berm was constructed on Feb. 23 above one residence.
Scott Gouldsborough posted on Facebook that he and his wife were among the evacuees, and that he witnessed the landslide.
"At 10 a.m. Saturday morning my house shook from yet another blast from the rock quarry on top of the mountain," he wrote on Feb. 19. "This time it was loud and shook the house."
Shortly after the incident, Western Explosives’ president Bryan Kirkness said in a press release that there were many factors at play including the weather and a four-magnitude earthquake on Vancouver Island.
"This slide was not caused by blasted rock overloading the dirt slope," Kirkness said. "The blasted rock was contained within a small area in and around the blast zone, as evidenced by the pictures taken by media and published. Our seismograph on site recorded minimal vibrations at 200 metres away from the blast. It appears ground conditions were unstable from the freezing/thawing and saturated ground. On the north slope ground conditions for unthawing are significantly slower than elsewhere. These conditions can potentially make soils become unstable and potentially sensitive to vibration. Indeed, perhaps the earthquake this morning had an effect of adding more sensitivity to ground conditions, we just do not know. What we do know is that the soils slid, without loading from blasted rock, right down to bedrock. We note that there have several slides in the Chilliwack area in the last few days due to conditions, regardless of any potential blasting effects."
After the slide, ministry inspectors issued a written order that blasting be ceased until the investigation is complete, and inspectors were on site on March 8 to review current site conditions, the slopes below the quarry and blasting records.
Kirkness pointed out that in 15 years of operation at the site, this was the first slide on the north slope.
"We wish to assure the public that our geotechnical engineer is engaged and will focus on this incident to ensure that the best and current information on geotechnical safety presented to us."
- with files from Jessica Peters
paul.henderson@theprogress.com
@PeeJayAitch