Environmental Assessment
Volume E-3.7
Tailings Facility
Hydrogeology
Ambatovy Project
60
January 2006
There is no expected change in aluminum or zinc concentrations, which already
exceed the WHO drinking water guideline, as a result of operation of the tailings
facility.
The potential to impact groundwater users within the affected area of elevated
manganese is addressed in the social impact assessment (Volume D, Section 5.1).
The groundwater that discharges into watercourses and water bodies downstream
of the tailings facility will be a combination of tailings seepage and unaffected
background groundwater. The consequent impact to surface water quality from
the groundwater salt plume is expected to be minimal, as groundwater
contributions represent on average 6% of baseflow.
A mass balance model was used to conservatively assess changes in water quality
due to seepage from the tailings facility and reductions in flows downstream of
the tailings facility. Volume E, Section 3.10 describes the assessment methods
and impact assessment of the resultant changes in surface water quality that are
predicted to result, in part, from changes to groundwater quality.
3.7.6
Impact Analysis
3.7.6.1 Residual Impacts
Results of the impact analysis indicate that during construction, with the
construction of the tailings facility embankments and lining of the water basin,
impacts to groundwater flows and quality will be negligible (less than 5%
change) and reversible.
Starting with operation and into the long-term, groundwater levels at the tailings
facility will be lowered and groundwater contributions to downstream
streamflows will be reduced. This is due to both the placement of low
permeability tailings and lined water basins, as well as operation of a
groundwater recovery system. The effect on groundwater flows are of a high
magnitude (>30%) according to the rating system for hydrogeology. The impact
of this change on potential groundwater use is addressed in Volume D,
Section 5.1. Groundwater provides an estimated 6% of baseflow in downstream
surface waters, and thus the overall magnitude of groundwater flow reductions to
surface waters is low.
Groundwater quality will be influenced by the tailings facility. Even with
mitigation through operation of a groundwater interceptor system, manganese
concentrations in groundwater above the WHO guideline of 0.4 mg/L (up to
