A 130 cm thick composite soil cover was constructed on an experimental waste-rock
pile at the Heath Steele Mines site near Newcastle, New Brunswick. The cover
consists of a 30 cm thick sand base, a 60 cm thick compacted glacial tilt a 30 cm thick
granular layer, and a final 10 cm thick gravel layer for erosion protection. The till was
compacted on the sand base in three finished lifts each of 20 cm thickness. Results of
a preconstructed pad test indicated six passes of a 5 tonne vibratory compactor were
required to attain the design specifications of 95 percent of the Modified Proctor
maximum dry density at a moulding water content of 2-3 percent wet of the optimum.
These compaction specifications also ensure that the till has a degree of water
saturation of at least 95 percent, which is required to reduce oxygen and acid fluxes in
the underlying pile. Quality control measures were taken during the construction to
ensure the specifications were followed. Monitoring instrumentation was installed
during the construction of the cover.

Results indicate a reduction in gaseous oxygen concentrations in the pile from 20
percent before cover to about 1 percent after cover placement The decreased oxygen
penetration implies reduced oxygen flux and acid production. Volumetric
water-contents averaged about 32 percent in the till immediately following cover
installation and 7 months later. The water-content data are corroborated by soil suction
measurements. Temperatures in the pile have decreased following cover installation
but appear to be more influenced by climatic variability than by a decrease in heat
production and hence sulphide mineral oxidation. Observed discharge from two
lysimeters, installed below the cover indicate infiltration of 2 percent of precipitation
during a 55 Day period when rainfall was heavy. The volume of the seepage has been
reduced but the quality from the pile has not changed since cover installation. Further
monitoring will be required to confirm the reduction in acid production.