The purpose of this review and report was to provide a transfer of recent Norwegian
experience and technology on the remediation of acidic rock drainage (ARD) at four
sulphide mines in Norway to Canada, and to provide an opinion as to the immediate
and long term effectiveness of the remediation measures to the Norwegian State
Pollution Control Authority (SPT).
The sites visited and remediation measures reviewed were:
- The consolidation of mine rock at the Kjøli mine and the placement 0f.a geosynthetic
membrane cover to control infiltration, and hence migration of ARD from the mine rock
pile. The composite geosynthetic cover comprised a sequence of a filter fabric, a 2mm
HDPE liner, geonet drainage layer, a filter fabric and a till cover. Rip rap was placed for
erosion control and the till cover was revegetated. The lower drainage adit was
plugged resulting in the flooding of about 70% of the underground mine workings.
- The excavation of mine rock from the original rock pile site at the Skorovas mine and its
placement in a nearby lake under a permanent water cover of 2 m. The mine rock was
excavated with a back hoe and transported in dump trucks to the new site. The original
site was cleaned by hand to minimise the migration of stored ARD products from
residual mine rock .Placement of the old mine rock in the lake required temporary
lowering of the water level by pumping to allow 'placement in the dry', construction of a
retention berm for stability purposes, and placing a till cover over the mine rock.' During
mine rock placement, the water quality in the lake water was controlled by adding lime.
On completion of mine rock placement, a concrete dam was constructed at the lake
outlet to permanently raise the water level in the lake to 2 m above the mine rock level.
- At the Killingdal mine site, the mine rock was consolidated and covered with a till
cover. A seepage collection ditch was constructed to divert ARD into the underground
workings, with the objective of utilizing the evaporative action of the natural convective
air flow through the mineto evaporate the ARD as it trickled down through the
workings, and thus deposit salts in the mine.
- At the Løkken underground mine dewatering has been discontinued and the mine
allowed to flood. Natural improvement of the water quality in the Wallenberg shaft has
been observed. Sulphate reducing bacteria have been isolated from the deep
anaerobic zones of the water filled shaft. The presence of the sulphate reducing
bacteria, and the observed natural improvement in the water quality observed,
presents an in.situ ARD treatment alternative. It is turned to divert ARD from mine
rock in surface piles into the mine and to rely on the natural processes occurring in the
mine to improve water quality.
The report describes the implementation techniques applied at the respective sites,
and where possible provides a performance evaluation based on the site water quality
monitoring data. Summaries of the cost incurred for the implementation of the various
measures are provided.
The geosynthetic membrane cover was found to be effective in reducing the overall
metal load transported from the Kjøli mine rock pile through the prevention of water
infiltration. Large reductions in the measured oxygen concentrations indicate that the
cover also served to reduce, but not eliminate, the entry of oxygen into the rock pile.
The decreasing temperature profiles of the pile after covering shows that the oxidation
process is considerably reduced.
Since relocating the mine rock to a below water location at Skorovas mine it has been
possible to discontinue lime treatment without an increase in downstream contaminant
discharges. This represents a very large decrease in acidity and contaminant release
from the mine rock. Water quality monitoring in the lake appears to indicate that long
tenn pH values of 4.5 will be achieved. The old mine rock was not treated with lime
prior to placement in the lake and this results in a pH of about 2.5 in the water in the
submerged pile. Stored oxidation products were therefore not neutralized and
precipitated prior to submergence. Migration of this low pH water to the lake could
result in lake water qualities that are less than what may have been achieved if such
neutralisation had been completed.
The costs for all mine rock remediation at each of the Kjøli and Skorovas mine sites,
including placement of mine rock under a permanent water cover or providing a
geosynthetic cover, are comparable at approximately 59 NOK per tonne mine rock
(CAD$l0.00). Costs for individual remediation measures are summarized in the report.
The effectiveness of placement of a till cover only, as at the Killingdal mine, could not
be evaluated from available data. Substantial quantities of low pH seepage was
observed to be occurring from below the collection ditch. It- is not known if this
seepage originates from seepage flow in the bedrock below the ditch or from the ditch
itself. Although the concept of collection and treatment in the mine by evaporation . is
unique, its effectiveness is dependant on the effectiveness of the collection system.
The collection ditch was incomplete at the time of the site visit.
