Figure 1: The L-L embankment of the Valley impoundment
The Highland Valley Copper Mine is located just outside the town of Kamloops in British Columbia, Canada. The mine produces copper (435,000 tonnes in 2003) and molybdenum (6405 tonnes in 2003) concentrates. The tailings pumped to the Valley Impoundment in 2003 were 48.5 million tonnes.
Valley Impoundment
The Valley Impoundment has two containment embankments, the H-H and L-L. The names relate to trial axes of dam sites starting at A-A, B-B etc. the dams were eventually built on the H-H, J-J ( now buried in the pond), and the L-L axes, that were eventually chosen as the optimum dam axes, for a variety of reasons.
The L-L dam is built using the centreline technique and is a zoned earth fill structure (figure1). The downstream face of the embankment has compacted cycloned sand berms to aid seismic resistance. The H-H dam at the other end of the impoundment is only 57 m high and consists of an earth and rock filled centreline structure (figure 2).
Figure 2: The H-H embankment of the Highland impoundment
The L-L embankment
is raised by the sand fraction of the tailings and is currently 130
m high. By the time operations cease in 2009 the impoundment is expected
to be 170 m high. As the sands are deposited, mechanical equipment is
used to compact the embankment before additional layers of sand are
added. Hydraulic cells are also used to raise the downstream side of
the embankment and aid with consolidation of the sands.
Other impoundments
Previous to the
Valley impoundment the tailings were deposited in the Highmont, Trojan,
and Bethlehem one and two impoundments. These impoundments are now inactive
and have been restorated. These impoundments are perfect examples of
how the decommissioning of tailings dams should be carried out. The
company has made a great effort to restorate the sites to blend in with
the natural surrounding. Eagles flew over as I snapped a shot of the
Trojan Pond which has rainbow trout, fresh water shrimp and insects
which have naturally moved back into the area. A spawning channel was
created to generate a stable fish stock. Bears and wild horses are a
common sight now the ponds have minimal human intrusion.
Many research projects have been carried out at the Highland Valley
Mine to determine the best methods of restoration for the ponds. Agriculture
Canada and the BC Cattlemans Association have been working with the
mine to determine the effects of molybdenum on cattle. The hay grown
on the restorated Bethlehem ponds presented no problem to the cattle
over the four years they were grazed there.
