Environmental Assessment
Volume E-3.7
Tailings Facility
Hydrogeology
Ambatovy Project
63
January 2006
Monitoring of the effectiveness of erosion control measures, slope stability and
reclamation success are described in Volume B, Section 6.
3.7.7
Conclusions
During operation, the tailings facility will have effects on both groundwater
flows and quality. Groundwater flows and quality will experience high
magnitude changes (i.e., >30% change from baseline) due to the blanketing effect
of the tailings, seepage of tailings pore water, and the operation of the
groundwater recovery system. The result is high environmental consequence
physical changes to groundwater flows and groundwater quality, although these
effects decline rapidly with distance. With mitigation utilizing the groundwater
interceptor system, the potential impacts to water quality in downstream surface
flows will be minimized.
Changes to groundwater flows and quality have consequent social impacts, with
respect to effects of lowered groundwater levels and impaired groundwater
quality on groundwater use for human consumption or agriculture. The extent of
a lowered groundwater table and elevated manganese is relatively localized but
does extend beyond the 300 m buffer assigned around the tailings facility. The
impacts of these changes, evaluated in the social impact assessment (Volume D,
Section 5.1), were determined to be low following mitigation.
In addition, reduced groundwater flow has a subsequent effect on surface water
flows. Since groundwater contributions to stream baseflow is estimated at about
6%, the high magnitude change to groundwater flow translates to a low
magnitude effect on surface water flows, discussed further in the section on
hydrology (Volume E, Section 3.8).
The resultant effect of groundwater impacts (primarily elevated manganese) on
surface water quality is relatively minor, considering the small contribution of
groundwater to stream flows. Mass balance modeling of surface water quality,
considering contributions of constituents in groundwater, is evaluated in detail in
the section on water quality (Volume E, Section 3.10).
