From Transition Sooke News July 2023

Aquifers

Chris Moss

WHAT ARE AQUIFERS?

Watersheds receive and guide precipitation across the land, slowing and filtering the water that soaks into the ground through soil and porous rock until it meets an impervious layer of rock or clay.  At that point the ground above starts to fill and saturate with water. This is an aquifer layer from which many of our wells draw water.  Aquifers can straddle many watersheds; for example, our house is in the Tugwell Creek watershed but on the Muir creek aquifer underground.  

There are many aquifers on the South Island.  The largest is the 606 aquifer which underlies Colwood, Metchosin, East Sooke, Sooke, up to and including the Sooke hills and across in a large arc to north of Jordan River.  You can find it in places beside the road where the dark basalt rock leaks trickles of water through small fissures.

HOW WERE THEY MADE?

Water is contained in fissures that crack through the rock.  If you drill a well into this rock, you must drill through a fissure of water to find your supply.  If you miss them your well is dry no matter how deep you drill.  Water supply is usually poor and the supply is vulnerable to contamination which can spread though connected fissures. 
  
On top of the 606 aquifer are other layers of aquifers. These occurred when the gravel till from the last ice age was pushed over the bedrock. These usually shallow aquifers accept water readily and can provide productive wells if not overused. 

As the glaciers advanced and retreated, sometimes a second layer of gravel and a less permeable layer of glacial silt was deposited over the first layer, creating two shallow aquifers above 606 bedrock aquifer.  This happened in the Otter Point area north of Kemp Lake where aquifer 604 lies on top of the Sooke River Aquifer 599 while both cover 606. You might find water less than twenty feet under the surface in this area; if you kept drilling another thirty feet you might punch through to the second aquifer and if you drill more than two hundred feet you would likely be into the bedrock of aquifer 606.  

MONITORING WATER LEVELS

Groundwater is monitored by the provincial government. Sooke has two provincial observation wells on Phillips Road; a shallow well into aquifer 599 (Sooke River) and a deep well into aquifer 606. It takes ten years’ monitoring of observation wells before data shows long-term trends such as declining water levels. The problem for homeowners with this data is that in the 606 aquifer (solid rock with tiny water fissures) you can drill two deep wells a hundred meters apart and one will hit a fissure and have water and the other will not hit any fissures and turn out as a dry well. So even if the data says water is there, it can be challenging to find it. 

A better use of money would be to require new wells to include a “drop pipe” in the well.  The drop pipe is used to send down a well water ”tape” which measures the depth of the water in the well. One tape can be used throughout the neighbourhood area to measure every well with a drop pipe installed. Tapes cost about $1500 and a drop pipe about the same plus installation by a professional well technician. This would certainly be less expensive than drilling even one observation well. This way we can see the seasonal variations immediately in our own wells and in the neighbourhood area wells. By sharing this information, we can better ration the use of water and forward the data to the government for longer term use. 

To find out more information about aquifers and wells in your area, click here