{"id":55090,"date":"2021-08-03T11:02:10","date_gmt":"2021-08-03T15:02:10","guid":{"rendered":"https:\/\/canada-info.ca\/?p=55090"},"modified":"2021-08-04T16:48:57","modified_gmt":"2021-08-04T20:48:57","slug":"cortes-island-aquifers-rainwater-wells-and-climate-change","status":"publish","type":"post","link":"https:\/\/canada-info.ca\/en\/cortes-island-aquifers-rainwater-wells-and-climate-change\/","title":{"rendered":"Cortes Island aquifers: rainwater, wells and climate change"},"content":{"rendered":"

As the Level 4 \u2018drought\u2019 continues, and some shallow well owners are concerned about their water supply, CKTZ News asked an expert about Cortes Island aquifers.<\/p>\n

Dr\u00a0Diana Allen<\/a>\u00a0is the head of the\u00a0Groundwater Resources Research Group<\/a>\u00a0at\u00a0Simon Fraser University<\/a>. While she has not been to\u00a0Cortes Island<\/a>, Allen has been working on islands like\u00a0Hornby<\/a>,\u00a0Mayne<\/a>,\u00a0Saturna<\/a>\u00a0and\u00a0Salt Spring<\/a> since 1996.<\/p>\n

Will the Cortes Island aquifer collapse?<\/h2>\n

The most alarming concern is that people drilling wells could punch holes in the island\u2019s aquifer and cause it collapse.<\/p>\n

This idea was expressed during an\u00a0interview last week<\/a>, during which John Preston also pointed out that what used to a be year round wetland, in Whaletown, has been drying up every summer for the past five years.<\/p>\n

CKTZ news contacted Red Williams, a\u00a0well driller from Parksville<\/a>\u00a0who serves the surrounding area on Vancouver Island, the Sunshine Coast, Quadra and Cortes Islands. While he sometimes hears this fear expressed, Williams said he has never encountered a case of an aquifer collapsing. The main problem he has seen is some shallow wells run out of water during dry spells. He said this is an ongoing problem, but there are ways that homeowners can extend their supply and the aquifer is replenished when the rains come.<\/p>\n

\u201cYes, I agree with him,\u201c said\u00a0 Allen, adding, \u201cWell, I guess it depends what someone considers to be collapsing an aquifer.\u201d<\/p>\n

Allen went on to talk about subsidence, adding that she has heard of it in places like California\u2019s Central Valley and Mexico City, but not British Columbia.<\/p>\n

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Aquifers 843, 844 & 845 in Whaletown are in bedrock. Screenshot from iMapBC.<\/p><\/div>\n<\/figcaption><\/figure>\n<\/div>\n

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Registered wells (since 2007) in Whaletown. Photo courtesy of iMapBC.<\/p><\/div>

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The registered aquifers<\/h2>\n

Allen spoke further about subsidence and aquifers.<\/p>\n

\u201cWhen 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,\u201d Allen explained. \u201cYou have to take a lot of water out \u2026 huge quantities, or also where oil and gas have been taken out of deep sedimentary rocks \u2026 but for small aquifers, like what you would find on Cortes Island, I do not think subsidence would be a real problem.\u201d<\/p>\n

Taking CKTZ News on a virtual tour of the Cortes Island aquifers on the\u00a0iMapBC website<\/a>, Allen discovered that all three of the aquifers that cover much of Whaletown (#843, #844 & #845) are in bedrock, where subsidence is not an issue.<\/p>\n

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Aquifers 841, 842 and 846 in Mansons Landing. Photo courtesy of iMapBC.<\/p><\/div>\n<\/figcaption><\/figure>\n<\/div>\n

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Registered wells (since 2007) in Mansons Landing. Photo courtesy of iMapBC.<\/p><\/div>

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Aquifer #841 which feeds most of the land between Mansons Landing and Sutil point, is sand and gravel.<\/p>\n

\u201cWhen 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,\u201d she explained.\u201d<\/p>\n

Aquifers #842 and #846, which feed the area between Mansons Landing and Cortes Bay, are in rock.<\/p>\n

\u201cSo it is really only this southern tip. All the other areas that have been mapped with aquifers show bedrock,\u201d said Allen.<\/p>\n

Where aquifers are not mapped<\/h2>\n

The aquifers feeding more than three quarters of Cortes Island \u2013 Tiber Bay, Squirrel Cove and all the lands in the north \u2013 are not mapped.<\/p>\n

Allen explained that this would have been because this area is so sparsely settled.<\/p>\n

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Registered wells in Squirrel Cove (since 2007). Photo courtesy of iMapBC.<\/p><\/div>\n<\/figcaption><\/figure>\n<\/div>\n

The 2002 geological survey of Cortes Island<\/a>\u00a0map show that most of Squirrel Cove is sand, mud and gravel, but the rest of northern Cortes is primarily rock.<\/p>\n

If Cortes Island\u2019s aquifers aren\u2019t collapsing, what explains the wetland, that used to be filled with water year round and has dried up the last few summers?<\/p>\n

\u201cThat\u2019s where climate change comes in,\" said Allen.<\/p>\n

She had a great deal to say about the salt water that is sometimes found in wells.<\/p>\n

Some of it dates to the last\u00a0Ice Age<\/a>, when glaciers pushed the islands under the ocean. They remained submerged for 400-500 years, during which time the aquifers were filled with saline water. Rainwater has pushed most of it out, but Allen has found pockets on Salt Spring. She does not know if there is any on Cortes Island, but said it is sometimes found in aquifers that are in rock.<\/p>\n

\u201cIt is fairly deep down, so most people have their drinking water wells relatively shallow, maybe a hundred metres or so \u2026 So they are tapping into water that is replenished on an annual basis, but there is some very deep older water down there that is of Pleistocene\/post Pleisticene Age.\"<\/p>\n

Allen did not know if there is still salt water at the bottom of Cortes Island\u2019s aquifers but, especially in more permeable soils, wells sometimes encounter salt water.<\/p>\n

\u201cYou put a pumping well in and the water from the ocean just says, 'oh, I\u2019ll just go right towards that well.' So any wells that might be nearer to the coast or, if they are in the middle of the island, maybe they are drilled a little bit deeper, there is a natural salt water wedge that underlies all islands,\u201d she explained. \u201cIf you drill down deep enough, you will hit salt water. The higher the topography, like Salt Spring, the deeper that sea water is, and the less topography, the shallower. That\u2019s why having a whole bunch of shallow wells is a good thing.\u201d<\/p>\n

Allen said that parts of Saturna and Hornby Islands have ongoing problems with salinity. People in the Caribbean do not even drill vertically. They excavate long trenches, skim the fresh water off the top of the aquifer and collect it in cisterns.<\/p>\n

One of Cortes Island resident is using rainwater for most of their needs.<\/p>\n

\u201cMore people should be doing a combination of rainwater collection and groundwater \u2026 might as well take advantage of that roof that you have and, if for nothing else, then watering a vegetable garden, flushing toilets, or washing laundry. There are a whole bunch of uses of water that don\u2019t require good quality groundwater,\u201d said Allen.<\/p>\n

Links of Interest<\/h2>\n