Decommissioning of South Bay: phosphate rock/brush application in Boomerang Lake; EM34 background Mud Lake survey; seepage Canyon definiton: 1995 final report / submitted to Mr. David Porter (Talisman Energy Inc.)
Abstract
In 1994, the decommissioning activities for the South Bay mine site focused on two main
areas. For the overall site the measures taken in 1993 were evaluated (trial phosphate rock
application to tailings and Boomerang Lake sediment and ARUM beach installation on Decant
Pond). The biological polishing process used in Boomerang Lake was summarized, focussing
on contaminant fate.The mine/mill site was surveyed using EM to determine changes brought
about by the diversion of the seepage from the Back fill Raise area to Boomerang Lake. A report
was issued in December1994 which concluded that the measures for Decant Pond had been
successfully curtailing the deterioration of the water quality. The seepage from the mine/mill
site have been diverted away from Confederation Lake. However, the contaminant load to
Boomerang lake has increased. It was recommended that application of phosphate rock to the
lake sediments is required to curtail acidification due to iron oxidation. Due to logistics problems encountered in 1993, the phosphate rock application to Boomerang lake was carried
out in 1994. Eighty tonnes of phosphate rock were made into a slurry and applied via barge
to the lake sediment in 1994. The tailings have given rise to a deterioration of the water quality in Mud Lake, which was predicted based on the reevaluation of the hydrological conditions in the tailings basin in
1993. Insufficient quantities of water were reporting to the ground water diversion ditch at the
southern end of the tailings deposits. In early 1994, the deterioration of Mud lake was
documented. Subsequently, activities in 1995 centred around the hydrology of the tailings
and drainage basin. The hydrology of the tailings basin was originally defined in 1987, excluding the area around Mud Lake. During 1994, the sampling efforts in and around Mud Lake were intensive in order
to define the origin and the pathways of the contaminants moving towards Mud Lake. A report
was issued summarizing the historic and current status of the area. Based on a preliminary
hydrological investigation focusing on the area between the tailings and Mud Lake, a deep
bedrock valley was described, which appeared to define the seepage path underneath Mud Lake, leading to the discharge of the seepage at the north end of Mud Lake. Many hydrological
questions were raised by the investigations of 1994, the first year when Mud Lake was
contaminated. Thus, to answer key questions, extensive EM surveys were carried out in 1995
to define the contaminant pathway and bedrock conditions. This information wasconsidered essential to any remedial action plan. After completion of the 1994 investigation, it was possible to estimate, utilizing elemental concentrations of surface water in the drainage basin along with flows and precipitation data, a contaminated ground water discharge volume of 0.6 to 1.0 L/s. This volume of contaminated seepage was
considered significant, leading to potential contamination of lakes further north. The 1995
work therefore concentrated on defining possible pathways of contaminants to lakes further
north of MudLake. The hydrological balance (precipitation/ infiltration/ evaporation) produced
an expected surface waterflow volume for the drainage basin containing the tailings and Mud
lake. These estimates agreed very well with the measured flow volumes leaving Mud Lake,
the ground waterseepage discharge and flows leaving Decant Pond. These results suggested
that it might be possible to contain the contaminants in Mud Lake, if the drainage basin
provides a solid containment structure. Extensive coverage of the site by EM measurements in the areas surrounding Mud Lake was implemented in early 1995, followed by a hydrogeological investigation where piezometers were installed to define the seepage characteristics. The bedrock topography of the tailings
needed to be refined, as containment of the contaminants within the drainage basin could also
be assisted through identification of the location where the ground water seepage was leaving
the tailings deposit. If such a location could be defined, many alternatives would arise in
selecting options to contain contaminants. Therefore, the activities in 1995 focused heavily on collecting hydrological information addressing the spatial distribution of the seepage path and locating the origin of the seepage from within the tailings basin. A summary of the key findings of the hydrology and bedrock definitions is given in Section 2. Although water balance calculations for the Mud Lake/tailings drainage basin agreed with the relatively sporadic flow measurements and the mass balance using conservative elements of
in the surface water, the aerial extent of a plume which would be moving below ground out
of the drainage basin was not known. In Section 3, electromagnetic survey data are presented
which are used to define the extent of the plume in the Mud Lake drainage basin. The EM
survey can also be used as a monitoring tool to determine movement of the plume through
repeat surveys in subsequent years. From the hydrological understanding, based on the data collected in 1987, it was expected that surface and ground water would leave the tailings basin via Decant Pond outflow and
passing through the muskeg between the tailings and Mud Lake. Zinc removal was effective
to date with extensive algal growth. Surface water leaving Decant Pond could only improve
further upon passage through the muskeg. Contaminants leaving the tailings basin via the
ground water was evaluated in 1987 and 1988. Piezometer water quality was used, together
with modelling of natural contaminant attenuation, to determine potential problem areas of
Confederation lake. The assessment indicated that sufficient attenuation will take place and
contaminants would not reach Confederation Lake. At the time this assessment of a reasonable
evaluation had to be reconsidered, given the findings in 1994. The 1994 hydrological investigation found the depth of the seepage path at16 m, discharging directly into the north end of Mud Lake with a water quality which suggested no natural attenuation of contaminants. A reassessment of the status of the ground water chemistry,
collected sporadically since 1987, was carried out along with an evaluation of seasonal
changes in the surface waters, monitored on a more regular basis. The objective of these
evaluations, presented in Section 4, was to determine if the ground waterand surface water
conditions of the entire drainage basin had undergone significant changes which warranted
attention.
Description
Keywords
Boomeran Lake, Mud Lake, ARUM beach installation, Decant Pond, biological polishing process, seepage, phosphate rock application, iron oxidation, Mud Lake deterioration of water quality, hydrology of tailings and drainage basin, pathways of contaminants, hydrological balance (precipitation/infiltration/evaporation), distribution of seepage path