INNOVATION Mar-Apr 2020

F E A T U R E

I n June 1965, a team led by the Geological Survey of Canada was drilling a six-inch diameter investigative borehole at the Coldstream Ranch, southwest of Vernon, BC, to learn about sediments deposited in the region during the last ice age. The team encountered alternating layers of coarse-grained (sand and gravel) and fine-grained (silt, clay and glacial till) material, when something unexpected happened. When the drill bit reached 61 metres depth, it encountered a high-pressure artesian aquifer, causing water and sediment to forcefully blast out of the drillhole. The driller, with good reason, jumped off the drill rig and moved his truck off the site; a crater quickly formed and swallowed some of the drilling equipment. Groundwater spouted from the open hole in the ground and the drillers had no means to control it. The initial flow rate couldn’t be measured but was later estimated to be 54 litres per second—almost enough to fill two Olympic- sized swimming pools each day. AQUIFERS AND ARTESIAN WELLS: A PRIMER An aquifer—which is a body of sediment or rock that can supply useful quantities of water—can become artesian when precipitation at high elevations infiltrates into the soil and flows below ground surface into low lying areas, like valley bottoms. The hydraulic head (pressure) can build up in the aquifer if an aquitard (i.e., fine-grained materials such as clay or glacial till that act as a barrier to flow) overlies the low- lying portion of the aquifer. Pressures in artesian aquifers can be high when there is a significant elevation difference between the recharge area and the lower portion of the aquifer. At the Coldstream Ranch, for instance, the ground elevation is nearly 1,000 metres lower than the mountains, which are the source of recharge for the deep aquifers beneath the site. When a borehole is drilled into an artesian aquifer, it creates a pathway for upward flow of groundwater. If the pressure in the aquifer is high enough, groundwater will flow up past the top of the well, resulting in a flowing artesian well. When a well is not properly designed for these conditions, water can flow up outside the casing of the well and surface at the wellhead. If this occurs, it can be very difficult to control flow from the aquifer and a sinkhole can develop around the well. A “breakout” like this can cause erosion, impact water quality in surrounding surface water bodies and aquatic habitat, and waste groundwater. Today, drillers and geoscientists have better tools available to identify where to expect flowing artesian aquifers—like the BC Provincial Groundwater Wells and Aquifers (GWELLS) online database. If there is potential to encounter flowing artesian conditions, wells can be designed and constructed to control

This 1965 photo shows drilling of the original exploratory borehole before artesian conditions were encountered.

The 1966 plugging attempt caused a crater to form around the well during the installation of 30-inch casing ( left ) .

This 1966 photo shows sacks of cement powder that were used to seal 50 dump trucks worth of gravel that was backfilled into the crater around the well. The cement plug stabilized but groundwater soon flowed up around the plug.

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