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The following information has been provided by the Squamish-Lillooet Regional District:

The Background

Observed rockfall from Mt Currie has increased in the past few years, and was confirmed by an initial report from the Ministry of Forests Lands and Natural Resource Operations (FLNRO). FLNRO also recommended that a detailed assessment be completed to fully understand the risks posed by this increased movement and the potential for future landslides. This assessment work is now underway, thanks to a funding commitment from Emergency Management BC (EMBC).

The SLRD, Líl̓wat Nation and the Village of Pemberton are overseeing the project, which is being conducted by BGC Engineering to assess the landslide hazard from Mt Currie and subsequent potential risk to public safety. The project includes kinematic rock analysis, landslide runout modelling and both quantitative and qualitative risk assessment parameters to the standards set out by the Association of Professional Engineers and Geoscientists of BC.

Once complete, the study will be shared publicly, and presentations will be scheduled with stakeholders and Valley residents. In the meantime, MFLNFRO will continue to monitor Mount Currie.

Residents can direct any questions to Ryan Wainwright, SLRD Emergency Program Manager, at rwainwright@slrd.bc.ca or by telephone at (604) 698-6442.

Blasting Begins July 26

As part of the Mt. Currie Safety Risk Assessment, licensed blasters will be conducting Seismic Refraction Surveys commencing on July 26. The work is expected to continue for a maximum of a week.

These surveys are conducted by laying a survey line and cable, then a corresponding line of small holes are hand dug with small explosive charges laid in each hole. When these are detonated, it creates seismic energy that is then measured by the sensors. The process is repeated across the prescribed survey area, building up detailed information that is used to calculate the density of earth and bedrock.

These charges are small and set away from where rock falls on Mt. Currie have originated. All work will be conducted in compliance with the BC Wildfire Act and corresponding Wildfire Regulation, which regulates high risk activities including the use of spark-producing tools and the preparation or use of explosives. The fire danger rating for the Pemberton Area is currently Level 4 and the survey team is liaising with the Pemberton Fire Service to ensure all precautions are taken. Should the fire danger rating increase to Level 5 and remain there for three days, all work must cease until the fire danger rating has been downgraded.

FAQ  about Seismic Refraction Surveys

Ground survey work near the base of Mt Currie is part of the Mt Currie Landslide Hazard Assessment and Risk Analysis study. To learn more about the study: https://www.slrd.bc.ca/inside-slrd/notices/emergency-notices/local-officials-advised-updated-hazard-potential-mount-currie-rockfall

One aspect of this work is studying the density and volume of previous landslides from Mt Currie as part of assessing the potential for future landslides of a similar or greater volume. Seismic Refraction Surveys  are the method used to gather this data.

Q: What is the process for Seismic Refraction Surveys?
A: A survey line of cable and sensors is laid, then a corresponding line of small holes are hand dug with small explosive charges laid in each hole. When these are detonated, it creates seismic energy that is then measured by the sensors. The process is repeated across the prescribed survey area, building up detailed information that is used to calculate the density of earth and bedrock.

Q: Are these people qualified to be handling explosives?
A: A licensed holder of a WCB Blasters certificate will supervise the handling and detonation of the explosives.

Q: What is this doing to the environment?
A: The smallest feasible charge size is used to record the required information, and there is strict observance of setback distances from waterways, as laid out in the Guidelines for the Use of Explosives in or Near Canadian Fisheries Waters.

Q: So, rockfall from Mt Currie may be increasing, and you are proposing to set off explosives near the base of it. Won’t that potentially make the problem worse!?
A: The short answer is that the charges are small and set well away from where the rockfalls have originated. The longer answer: the smallest feasible charge size is used to record the required information, and the seismic energy created by each set of charges is equivalent to an excavator working on a construction site. The survey area is where historical landslides have settled, not on the mountain itself and not anywhere near where rockfalls are originating.

Q: How long will the work continue?
A: It is anticipated that the process would take a maximum of one week.

Q: What company will be carrying out the work?
A:
Frontier Geosciences. To learn more: https://lilwat.ca/wp-content/uploads/2017/07/Seismic_Refraction_Surveys_using_explosives.pdf