Geosynthetics February/March 2021 - 18

Bituminous geomembranes for ponds in mining

FIGURE 5 Welding high-density polyethylene (HDPE) geomembrane/BGM

FIGURE 6 BGM installation at Kiitilä
Mine in Finland

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Geosynthetics | February March 2021

water from the gold-processing plant.
Water from the ponds then recirculates
back to the process, which makes the
water circulation a closed system. As part
of the environmental permit for the mine,
a watertight liner was required and BGM
was accepted by the Finnish Ministry
of the Environment (Figure 6) (Huru,
Palolahti and Breul 2008).
The design of the ponds called for an
excavation surrounded by dikes to get
the required volume. The cross section
of the dam consists of a core built with
blasted rock with particle size up to 2 feet
(600 mm) in diameter. The upstream side
of the dike was covered with a layer of
blasted rock but with a maximum diameter of 1 foot (300 mm) and protected by
a layer of gravel not exceeding 2.2 inches
(55 mm) in diameter. This last layer was
compacted using an excavator equipped
with a compacting plate to provide a
smooth surface with no ruts. The dikes

were designed to function like a zoned
dam built with material recovered from
the mining operation. A 3.3-foot (1-m)
thick sealing layer was then placed on
the bottom of the pond, which consists
of the excavated moraine rolled and compacted, exhibiting a saturated hydraulic
conductivity less than 5 × 10-8 m/s. BGM
has a low thermal expansion coefficient,
so there are no wrinkles throughout the
day when temperatures vary. With this
characteristic, the geomembrane lies flat
on the ground and provides, in combination with the low-permeability moraine,
a permanent and durable double layer of
watertightness. The project was initially
designed with a polymeric geomembrane
(HDPE or linear low-density polyethylene [LLDPE]), but the client expressed
interest in switching to a bituminous geomembrane to line the ponds at the Kiitilä
Mine for the mentioned economic reasons and because BGM can be installed
at temperatures as low as 5°F (-15°C),
which was a critical element with respect
to the schedule in the northern region,
since the construction was anticipated
to extend until October, the most moist
and humid period of the year. A local
contractor did the installation with an
output of 86,111 square feet (8,000 m2)
per day after on-site training by a manufacturer monitor. The total surface area
of BGM covered is 30 million square feet
(2.5 million m²).
In Russia, the Kinross Kupol Gold
Mine is in the northwestern part of
the Anadyr foothills in the Chukotka
Autonomous Okrug, which has site access
by helicopter or fixed-wing aircraft. Every
winter a 249-mile (400-km) ice road is
constructed from the northern port of
Pevek to the site; it is used to transport
goods to the site. The Kinross Kupol Gold
Mine requires a tailings dam to store
tailings produced by the milling process.
The Kinross Kupol tailings impoundment
is formed by a rockfill dam that utilizes
Geosynthetics February/March 2021

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