This report describes the studies which occurred during a three year program to
assess acid generation and groundwater flow at the Westmin Myra Falls waste rock
dump and to evaluate novel approaches for the prevention of acid mine drainage from
the waste rock dump at the Westmin Myra Falls site.

The waste dump characterization indicated that the most active areas of oxidation
occur within a 10 meter depth of exposed surfaces of the waste rock dump and in
deeper zones where relatively high contents of sulfide minerals are encountered.
During periods of significant rainfall, the shallow acid-generating zones are flushed with
water and acidic water appears beneath the water table. Calculations suggest that a
significant portion of the annual production of acidity is retained in the dump and
therefore remains-available for flushing; As a result, remediation and decommissioning
planning must address the neutralization of this acidity or the control of infiltration and
water-table variation.

Two acid mine drainage control approaches were evaluated; the use of alternative
bactericides to reduce the activity of Thiobacillus ferrooxidans, and the use of solidified
mine waste materials for the purpose of sealing waste rock to minimize moisture and
air transfer and, hence hinder acid generation. The laboratoty studies, and the results
of the dump characterization study, suggested that a bactericidal approach would not
be effective for control of acid mine drainage from the Westmin waste dump.
Limitations include application techniques and the need to control acid formation at
depth.

The study program then focused on the possible formation of a durable solidified
material using mine waste materials such as wastewater sludges and mine tailings as
principal components. The intent is to use the material as a surface sealant and/or
grouting material to minimize water and air transfer in the waste rock dump. More
than 105 test solidification mixtures were prepared and tested for properties such as
strength, setting times, leaching and permeability. Five mixtures were selected for field
application and testing on field waste rock piles. The leachates from the field test piles
were monitored constantly for pH, and tested at intervals for water quality. The
integrity of the solidified materials is observed at intervals and the results suggest that
mixtures which cari stand the “test of time” with respect to physical and chemical
integrity cari be prepared for use as surface sealants. However, it must be recognized
that the time-frame for this study was relatively limited. Mixtures for use as grouting
materials have been prepared and tested on a field scale. Preliminary results suggest
that the mixtures cari be successfully used for grouting.

On the basis of laboratory and limited field scale studies, the approach of using
solidified mine waste materials as a caver and grouting medium appears promising and
further investigation of field application techniques should be pursued. Shotcreting
appears to be the most promising means of covering the waste rock dump with the
cementitious materials, and field trials are anticipated during 1990.