Roy L Hales/ CKTZ News - CKTZ news recently asked Dr Diana Allen, head of the Groundwater Resources Research Group in the Department of Earth Sciences at Simon Fraser University, some vital questions about Cortes Island’s aquifer.
Does drilling a well threaten to collapse Cortes Islands aquifer and thus inadvertently threaten the community’s water supply?
The question arose during an interview last week, in which it was also pointed out that what used a to be year round wetland now dries up every summer.
Local well driller Red Williams says that while he sometimes hears the idea of collapsing an aquifer, he has never encountered a case of this happening. The main problem he has seen is shallow wells going dry: you will always have shallow wells that dry up and the aquifer is replenished by rainfall.
“Yes, I agree with him,“ said Allen, who immediately added, “Well, I guess it depends what someone considers to be collapsing an aquifer.”
Allen went on to talk about subsidence, adding that she has heard of it in places like California’s Central Valley and Mexico City, but not British Columbia.
“When you take ground water out of an aquifer that consists of interlayers of sand and clay, there is the potential for the clay to lose whatever water it has in it and squish. That can cause subsidence,” she explained. “You have to take a lot of water out … huge quantities, or also where oil and gas have been taken out of deep sedimentary rocks … but for small aquifers, like what you would find on Cortes Island, I do not think subsidence would be a real problem.”
Taking CKTZ News on a tour of the registered aquifers on the iMapBC website, Allen discovered that all three of the aquifers that cover much of Whaletown (#843, #844 & #845) are in crystalline bedrock rock, where subsidence is not an issue.
Aquifer #841 which feeds most of the land between Mansons Landing and Sutil point, is sand and gravel.
“When the glaciers were all melting, they would have dumped a whole bunch of sand and gravel on this point. This is actually a confined aquifer, so there is some clay over the top of it that is providing natural protection to that aquifer. So this would be a good quality aquifer,” she explained.”
Aquifers #842 and #846, which feed the area between Mansons Landing and Cortes Bay, are in rock.
“So it is really only this southern tip. All the other areas that have been mapped with aquifers show bedrock,” said Allen.
The aquifers feeding more than three quarters of Cortes Island – Tiber Bay, Squirrel Cove and all the lands in the north – are not mapped.
Allen explained that this would have been because this area is so sparsely settled.
The 2002 geological survey of Cortes Island map show that most of Squirrel Cove is sand, mud and gravel, but the rest of northern Cortes is primarily rock.
So, if Cortes Island’s aquifers aren’t collapsing, how do you explain that wetland, that used to be filled with water year round and has dried up the last few summers?
She explained, "That's where Climate Change comes in."
Photo credit: Photo by Roy L Hales