Ground Water Resources of British Columbia
Chapter 13 - Case Histories
13.6 EXPLORATION AND DEVELOPMENT OF A GROUND WATER SOURCE FOR THE TOWN OF SMITHERS, BRITISH COLUMBIA
The Town of Smithers, with a population of about 5,000, is located in the broad valley of the Bulkley River in Central British Columbia between Prince George and the pacific port of Prince Rupert. Until the completion of several wells in 1974, the town obtained raw water from the Bulkley River. In the 1960s, increasing pollution in the Bulkley River, especially during the spring break-up, had motivated the search for another water source. The alternatives considered were ground water or a new intake and treatment plant on the Bulkley River.
The first search for a source of ground water for the Town of Smithers was carried out in 1967. It consisted of drilling two deep test holes near the river intake; the test holes were drilled by the cable tool method. This drilling was followed in 1968 by the drilling of three test holes using the mud rotary method. One of the 1968 holes was drilled near the river intake and two were drilled in the centre of the town. All were considered unsuccessful.
In 1973, a review of the water supply situation showed that the work required to modify the intake at the Bulkley River to obtain additional water for the town, and to correct problems caused by low water and flooding, would be quite expensive. Because of the high cost to upgrade the surface water intake, ground water was again considered as an alternative.
Up to this time, the surficial geology of the Bulkley Valley had not been studied and no assessment had been made of how the geology of the surficial deposits might affect the nature and distribution of aquifers. Information gathered in the 1973 study included the logs and other information from a line of foundation test holes drilled by British Columbia Ministry of Transportation and Highways in preparation for a new highway bridge. This information, along with the logs of the previous test holes, indicated that the valley fill is made up mostly of ice contact deposits that contain occasional patches of permeable sand and gravel. After an examination of air photos and a brief reconnaissance examination of surficial geology, a test drilling program of 200 mm diameter test production wells was proposed. The suggested sequence of drilling was based on the estimated cost of completing a successful well at each site along with the cost of coupling a successful well to the existing distribution system and the cost of operation, particularly pumping cost.
In the Fall of 1973, drilling, using cable tool equipment, started on the gravel fans of two creeks which flow out of Hudson Bay Mountain. Four test wells showed that the fans were rather thin and fine-grained and did not contain aquifers of sufficient capacity to be of interest to the town. The fifth test well in the 1973 exploration program was then drilled at the Smithers Public Works yard in an effort to locate an aquifer in the thick ice contact deposits filling the Valley; it encountered a silty gravel aquifer between 48.5 and 64.6 m. The well was developed with some difficulty and was pump tested at 33 L/sec. The sixth hole in the program, located about 150 m from Well No. 1, was completed as Well No. 2 in the same non-flow artesian aquifer as Well No. 1. In Well No. 2, the aquifer extended from 57.9 to 71.6 m. Well No. 2 was tested at a rate of 22.7 L/sec. The seventh test hole, which was also drilled in the ice contact deposits, was a dry hole.
By this time, it was clear that the aquifers in the ice contact deposits in the Smithers area consist of rather silty sand and gravel which do not appear to be very productive. For this reason, it seemed possible that the previous drilling near the Bulkley River had not been correctly evaluated and that an aquifer might have been missed. To test this theory, a test well was drilled to 72.6 m at a location near the river intake. This test well encountered an aquifer between 18.6 and 26.5 m. The 250 mm diameter well was completed with a screen and pump tested at a rate of 44.4 L/s and had a specific capacity of 6.21 L/s/m.
The Smithers situation is an example in which a correct evaluation of the geology was an important first step in a program of systematic ground water exploration. Other important elements in the success of the program were the selection of an appropriate drilling method and the ability of the driller to correctly evaluate aquifers which at first appeared to have little potential. There is little doubt that highly productive aquifers have been missed in drilling programs where the drilling method has been inappropriate and also where the driller's evaluation of an aquifer has been incorrect.
The total cost of the exploration and ground water development program at Smithers was about 15% of the estimated cost of a treatment plant required to treat Bulkley River water. The warm ground water has been important in minimizing freezing problems in the Smithers water system.
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