Environmental Assessment
Volume E-3.7
Tailings Facility
Hydrogeology
Ambatovy Project
57
January 2006
Table 3.7-4 Reduction in Groundwater Component to Stream Flows – End of
Decommissioning Phase
Subcatchment
Drainage Areas
Groundwater
Component
Reduction
A1
69%
A2
8%
B1
75%
B3
1%
C1
46%
C2
15%
The potential impact to surface water flows is described and evaluated in greater
detail in the subsequent section on hydrology (Volume E, Section 3.8).
3.7.5.6 Results for Key Question HG-2: What Effect Will the Tailings
Facility Have on Groundwater Quality?
Baseline groundwater quality studies identified that groundwater in the area does
not currently meet WHO drinking water guidelines in the natural condition;
aluminium was measured at ranges of <0.01 mg/l to 0.78 mg/l, compared with
the WHO guideline value of 0.02 mg/l, and zinc ranged from 0.22 mg/l to
9.1 mg/l, compared with the WHO guideline value of 3 mg/l.
Testing of tailings slurry water indicated that tailings seepage is likely to have
high concentrations of total dissolved solids, calcium, magnesium, sulphate,
cobalt, manganese and nickel compared to background groundwater
concentrations.
Initial contaminant transport modeling by GCS in April 2005 determined that the
concentrations of salts in groundwater will increase as a result of placement of
the tailings and seepage of tailings pore water into groundwater. Total dissolved
solids (TDS), sulphate and manganese were used as indicator constituents to
show the movement and relative concentrations of the resultant salt plume in
groundwater, and manganese was predicted to exceed WHO guidelines. Without
mitigation, the groundwater salt plume would extend up to 500 m downstream
the tailings facility, and would likely affect surface water quality. To mitigate
these impacts, a groundwater recovery system was designed to abstract impacted
groundwater from immediately downgradient of the embankments of each
tailings basin. The abstracted groundwater would be pumped into the lined water
basins, ultimately reporting to the process plant or for ocean disposal.
