Ground Water Resources of British Columbia
Chapter 13 — Case Histories
13.2 PULP MILLS USING GROUND WATER SUPPLIES
In British Columbia, ground water has been used to supply pulp mills only since the Second World War. Ground water was first used to supply a pulp mill at Harmac on Vancouver Island in 1950. Three other mills in the province presently use ground water for a major part of their requirements.
On Vancouver Island between the cities of Nanaimo and Ladysmith is the large, highly productive Cassidy Aquifer (named after the settlement of Cassidy). The aquifer furnishes an important part of the water supply for the large pulp mill-sawmill complex at Harmac situated on the Strait of Georgia a short distance north of the Cassidy Aquifer (Figures 13.2 and 13.3). The Harmac Mill also takes water from the Nanaimo River, but this contains sediment during high river stages so the ground water is used for clean water supply.
Figure 13.2 Southern Coastal Trough area, locations of selected
high capacity wells (adapted from Foweraker et al, 1985)
Figure 13.3 Cassidy Aquifer and location of Harmac Pulp Mill
and wells (adapted from Foweraker et al, 1985)
The main Cassidy Aquifer consists of post-glacial deltaic sediments deposited by the Nanaimo River and Haslam Creek at the end of the last glacial event about 10,000 years ago. It is underlain by till, which is shown by several water well logs to overlie another gravel aquifer. The upper aquifer, which supplies the Harmac Mill and a number of domestic wells, is about 26 m thick in the thickest part. It consists of gravel and sandy gravel.
Before the Harmac Mill was built, a drilling and pump testing program explored the aquifer which was virtually unknown at that time. Three Ranney type collectors and three screened tube wells all about 20 m deep were constructed to supply the Mill. Each concrete caisson of the collectors has as many as 23 radial, slotted steel collector pipes approximately 30 m in length. Two of the collectors have capacities in the range 380 to 400 L/s; the third, because of its location close to the edge of the aquifer, has a lower capacity — about 190 L/s. In initial attempts to increase the capacities of the collectors and during subsequent maintenance, surface excavations above the lateral pipes caused the collectors to behave partially as intake structures for surface water.
The transmissivity of the shallow aquifer is high - about 7 x 10-2 m2/ s. The present demand at Harmac, of about 1.26 m3/ s is pumped through a long wood stave pipe about 8.6 km to the mill. There is an observation well with a continuous water level recorder in the aquifer. The hydrographs from this well indicate that much more water can be taken from the aquifer. A limiting factor in the use of this aquifer may be the necessity to maintain a minimum flow in the Nanaimo River to permit upstream migration of salmon.
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