Letter of the Day
Editor: When a well is drilled a record called a drill log is kept: basically depth drilled, rock type encountered, static water level, sudden flows of water are recorded. The aquifer on P.E.I. is a multi-aquifer system as groundwater occurs in layers.
On pages 23 to 25 in 'Groundwater Hydrology and Water Supply of P.E.I.', by L. V. Brandon, Geological Survey of Canada, there is a discussion and drill log of a Montague fish plant well. When drilling begins the water level is at 22 feet from the surface. When drilling ends at 602 feet the water level is at the surface. In drilling the well, seven distinct water levels are identified. The Montague well is said to be 'typical of low ground' on P.E.I. and on page 19 is called a 'flowing well.'
The seven distinct aquifers above are a reflection of how P.E.I. was geologically formed: wave after wave of sediments deposited in layers 30, 60, even over 100 feet thick. Each layer has basically the same substructure of fine grained sandstone on top, followed by medium grained sandstone, followed by course grained sandstone, all consolidated into a sandstone aquitard. The bottom layer is the unconsolidated alluvial deposits which the driller sees as a relatively thin water aquifer in this multi-aquifer system.
Before the Montague well was drilled, the seven thin aquifers formed an interdependent system, the 'deeper circulation', which self regulated their separate aquifer pressures by means of exfiltration and infiltration through the thick aquitards. Some of the aquifer layers, the strong ones, would have submarine groundwater discharges, a flux of energy rich waters full of chemical nutrients, at their offshore boundaries; a true wonder of nature.
After the Montague well was drilled and the seven thin aquifers have been hydraulically short circuited by a non-porous well hole, the water mounds up near the surface and drains away. The balance of nature has been altered, destroyed. The seven aquifers no longer self regulate as water takes the path of least resistance. The offshore submarine groundwater discharge is now largely silent, static, dead.