Ground Water Resources of British Columbia
Chapter 13 — Case Histories
13.4 GROUND WATER DEVELOPMENT FOR MINING IN THE HIGHLAND VALLEY OF BRITISH COLUMBIA
Three open pit copper mines are located in the Highland Valley 200 air km northeast of Vancouver (Figure 13.1). In 1983, these mines produced 124.4 million kg of copper worth 233 million dollars Canadian. This production amounted to 20% of all the copper produced in Canada. Small amounts of silver, gold and molybdenum are also produced as a by-product of the copper production. In 1983, 1600 people were directly employed by the three producing mines. The three mines are dependent upon ground water for their milling process. This water is obtained from wells completed in the unconsolidated sediments of the Highland Valley. The valley has a width of approximately 1.5 km, is fault controlled, glaciated and filled with up to 350 m of unconsolidated glacial, glacio-fluvial and lacustrine deposits. The sediments consist of glacial tills, sand and gravels, silts and clays. The sands and gravels were deposited in a cut and fill environment and form the three main aquifers of the valley.
Figure 13.1 Intermontane valleys in the Southern Interior System showing
locations of Keremeos wells (adapted from Foweraker et al, 1985)
Prior to 1959, several international mining companies had looked at a proven high tonnage low grade copper deposit in the valley. At that time no suitable mill water supply was thought to be within economic reach of the valley. The nearest dependable surface water supply was 22 km distant and 1.2 km below the mill site. In the winter of 1959-60, the Canadian owner of this proven deposit retained a hydrogeologist.
Calculations made on limited precipitation and runoff data indicated that sufficient ground water to satisfy the mill needs should be available beneath the valley floor adjacent to the deposit. Therefore, a test drilling ground water exploration program was undertaken. The first test well discovered a water-bearing sand and gravel aquifer between depths 75 and 90 m. This aquifer had an artesian head of 2.4 m above ground surface and free flowed at 6.3 L/s through perforated casing. Pump testing of the well showed that a properly designed and constructed production well would have a productive capacity of 75 L/s. A well field of two production wells with large diameter casings and wire wound well screens was completed in January, 1962. The mine went into production in 1963 and though the original open pits have been worked out, the mill is still using ground water from this well field to mill ore from a new open pit.
In the late 1960s, the second mine was developed in the valley. An extensive ground water drilling and testing program was undertaken to determine if sufficient ground water was available for the much larger milling operation. This program consisted of a series of mud rotary wells which were electrologged. A 200 mm cable tool test hole was drilled to confirm the electrolog data and to test the water producing potential of the aquifers present.
This testing program proved that sufficient ground water was available in the Highland Valley. However, the financiers of the mine decided to construct a river intake and pipeline in the belief that a surface water supply is more reliable than a ground water supply. A 24 km pipeline was built from the Thompson River to a surface storage reservoirs above the mill. The reservoir is 1.2 km above the river. During this period a highly productive pressure relief well was also constructed behind one of the tailings dams on the valley floor. When the mine and mill had been operated for only a short time the use of river water decreased. With the construction of a second pressure relief well in the valley the demand for river water ceased entirely. A comparison of the pumping costs of ground water from wells in the valley with those of water from the Thompson River shows that the ratio of pumping costs are 27 to 1 in favour of well water. The well water costs are also not affected by a high electrical standby demand cost or the payment of fees for surface water.
When development of the third mine started, a third ground water exploration, testing, and development program was conducted. This program finished with the construction of three production wells using cable tool drilling machines and pull down jacks. The wells are 400 mm and 600 mm in diameter and as deep as 135 m. The total productive capacity of the well system is 250 L/s. After the tailings ponds were filled at mill startup, the water demand decreased to 100 L/s.
By the end of 1983, the total amount of ground water being pumped from the Highland Valley was equivalent to 1 x 107 m3 per year. This amount of water is equivalent to 42 mm of precipitation over the drainage basin of the valley. The average precipitation across the basin is 376 mm per year.
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