Sulphide ore mining in Northeast New Brunswick has produced waste piles containing
acid generating pyritic rock. The generation of acidic drainage from these waste rock
piles create immediate environmental control problems in addition to long-term
reclamation challenges.
The Heath Steele property, located approximately 50 km northwest of Newcastle, New
Brunswick and about 60 km southwest of Bathurst, was developed in the late 1950’s.
The highly pyritic waste rock at the site continues to pose a challenge to currently
available reclamation technology.
A proposal was submitted to various federal and provincial agencies to use several of
the waste rock piles at Heath Steele to develop and test strategies for the long-term
management of acid generating waste rock. A four phase program was developed, and
on December 16, 1988, an agreement to fund the first three phases was signed. This
report describes the work comprising the first three phases of the project. Phase IV is
the installation of an engineered cover, designed on the basis of the results of Phase III
work, on one of the piles and the evaluation of the effect.
Phase I of the study involved the selection of four acid generating waste rock piles
most amenable to monitoring and evaluation of remedial measures. Selection criteria
and weighting factors were established and the piles were ranked. Piles identified as
18A, 18B, 17 and 7/12 were selected.
Phase II involved the installation of monitoring equipment to define the detailed
characteristics and background data for the four piles identified in Phase I.
Piles 18A, 18B and 17 were contoured to provide 3:1 slopes and ditched to divert
surface water and runoff as well as isolating them from surrounding topographic
influences. Waste rockpile 7/12 was moved, as part of the ongoing site reclamation
program, onto an impermeable membrane to permit the water balance to be evaluated
before and after placement of the cover. Leachate collection was not possible at the
insitu piles due to the fractured nature of the underlying bedrock. Each pile was
instrumented to permit measurement of oxygen and temperature at various points
throughout the pile.
In Phase III, the performance characteristics of natural soils in the vicinity of the Heath
Steele mine site as potential engineered covers for the waste rock piles were
determined. The study also developed the most appropriate cover design scenario for
the waste rock piles.
The study involved site exploration for natural soil materials (such as tills, clays, and
sand), laboratory geotechnical testing, column fabrication, testing of the soils for their
hydraulic characteristics, and measurements of oxygen diffusion coefficients.
Laboratory geotechnical testing consisted of measurements for grain size distribution,
specific gravity, compaction and consolidation characteristics, and hydraulic
conductivity. The hydraulic characteristics (moisture drainage curves) of these natural
soils were also determined to assess the potential for their inclusion in composite or
layered cover systems. The exploration for the soils was restricted to a 15 km radius of
the mine site, since soils located at greater distances would not be economical.
A composite soil cover was designed using natural soil materials. The proposed cover
system of a 3-layer composite cover, consisting of a fine-grained saturated till,
sandwiched between two coarse-grained layers, will be an effective oxygen barrier. If
the till is compacted and placed at a water content slightly wet of optimum, it can be
expected to have a low hydraulic conductivity and be an effective water barrier as well.
Computer modelling indicated that much lower oxygen fluxes can be expected from
this composite system than from a single till layer.
