Feature ArticleFebruary 13, 2002
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Water up north and down south - Part 2by Gray MerriamOur bedrock changes south on Road 38 between Verona and Hartington into limestone. Up north we live on the granite bedrock of the Canadian Shield. Underground water (or groundwater) is very different in these two types of bedrock.
The old limestone to the south was made as layers of ocean sediments, and these layers easily crack into big rectangular blocks. Rain that percolates down to the rock is slightly acid (acid rain is more so) and that lets the rain dissolve the limestone where it is cracked. The cracks become arm-sized channels for the water to flow downward, and also to flow across the countryside between the layers of blocks. If rain dissolves enough limestone, it makes caves like the Hell Holes near Roblin.
Getting water when you drill wells in the limestone is easy. And you can be sure that the water you get from those channels in the limestone will be hard. It will coat the inside of your kettle with calcium carbonate freshly made limestone.
Up on the very ancient (Precambrian) granite of the Canadian Shield from Verona and Piccadilly to north of 7 and beyond, getting well water is chancy. To get into granite, rain water has to find some crack or fault. Rain does not dissolve granite as it does limestone, and granite is well-known for not having too many cracks. (There has been discussion about burying nuclear wastes in granite because it is so leakproof.) Rain is likely to run off granite bedrock into local ponds and lakes before it finds a way to get into the rock. Eventually it does find ways and so there is water deep inside the rock.
Successful wells drilled into granite usually hit a fault line or the intersection of two faults. These are the edges of giant blocks that have been shifted by earthquake forces. When two giant blocks are rubbed together by such tremendous forces, the edges of the blocks get viciously chipped and that makes a pathway of broken rock where the water can flow. If you are lucky, as we were, you will hit one of these and get a well able to pump 20 gallons per minute. If you are unlucky, like our neighbour, who shares the same ridge with us, you may get very little, even after three tries. Sometimes you can be unlucky right along a lakeshore, because any connection between the lake and the water in the rock is likely to be very indirect, through faults deep in the rock. Another neighbour drilled within 50 feet of a lake that averages only 27 feet deep and didnt get water until 150 feet.If you get water from the Canadian Shield, it will be soft not hard. That is, it will have very little calcium in it. Some of the water from deep in the granite may be from very old fossil water reservoirs that do not get recharged from the rain. Some is from channels that do get recharged, but the rain is likely to spend some time on the surface in creeks, marshes, bogs, and lakes before it finds its way into faults in the rock. There is no guarantee that it will pass through a good sand filter before it gets to your well, so it would be good to keep it clean while it is in our surface waters.
This is the second article in a four-part series. Gray Merriam is a member of the Frontenac News Editorial Advisory Committee, and is a retired professional ecologist.
