Environmental Assessment
Volume E-3.7
Tailings Facility
Hydrogeology
Ambatovy Project
56
January 2006
A groundwater recovery system, described in the next section (Section 3.7.5.6),
will have an additional impact on groundwater levels; groundwater levels will be
reduced by 1 to 5 m within an localized area that extends less than 1 km from the
tailings facility, removing an estimated 640 to 1,040 m
3
/day. GCS (October
2005) Drawing Nos. 11 and 12 in Volume I, Appendix 7.2 show the groundwater
drawdown cone that will result from the groundwater recovery system, at the end
of tailings deposition (Year 27) and at the end of the decommissioning phase
(Year 42). Resettlement plans include relocation of residences located within 300
m of the tailings facility. Any impacts to groundwater users (i.e., shallow dug
wells) will be limited to the approximately 700 m outside the resettlement area.
The mitigation and residual social impacts arising from groundwater impacts is
addressed in the social impact section (Volume D, Section 5.1).
Tables 3.7-3 and 3.7-4 show the estimated reduction in groundwater component
to stream flows as a result of the interceptor borehole abstraction in the
production phase and at the end of the decommissioning phase, respectively.
GCS Drawing No. 3, included in Volume I, Appendix 7.2, shows the
subcatchment drainage areas in relation to the development phases of the tailings
facility.
Table 3.7-3 Reduction in Groundwater Component to Stream Flows – Operations
Phase
Subcatchment Drainage Areas
Groundwater Component Reduction
Phase 1 –
Year 14
Phase 2 –
Year 20.5
Phase 3 –
Year 27
Phase 1 Tailing Facility
-
-
-
Phase 2 Tailing Facility
9%
-
-
Phase 3 Tailing Facility
-
-
-
Phase 1 Water Basin
5%
27%
-
A1
37%
41%
43%
A2
1%
1%
2%
B1
5%
5%
34%
B3
0%
1%
2%
C1
0%
43%
46%
C2
0%
10%
12%
Since the groundwater component of stream baseflow is small (about 6%),
changes in groundwater flow have a relatively low magnitude of impact on
surface water flows. The exception to this may be in the dry season when a
larger portion of flow is expected from groundwater. However, baseline data
collected in 2004-2005 indicates considerably larger dry season flows than
expected from baseline groundwater modeling, which suggests that dry season
flows may also be maintained by basin storage.
