Environmental Assessment
Volume E-3.7
Tailings Facility
Hydrogeology
Ambatovy Project
58
January 2006
The pumping wells will be complemented by a series of monitoring wells that
will facilitate regular monitoring, positioned between each pumping well, to
ensure the groundwater recovery system is meeting design objectives and
groundwater downgradient will not adversely affect people and the environment.
The monitoring wells could also be used as pumping wells if the interceptor
system did not function as predicted.
Table 3.7-5 shows the schedule for implementation of the groundwater
interceptor system at the various time intervals throughout the mine life. GCS
October 2005 Drawing Nos. 13a through 13e in Volume I, Appendix 7.2 show
the arrangement of pumping and monitoring wells from during Years 1, 14, 20,
27 and 42. GCS estimated that the groundwater recovery system will be required
to operate for 15 years following closure at Year 27, to ensure groundwater and
surface water downgradient of the facility is not substantially impacted.
Following closure at Year 27, progressive reclamation will be substantially
underway and tailings deposition will cease, and seepage of tailings seepage
water into groundwater will decrease.
Table 3.7-5 Groundwater Recovery System Schedule of Interceptor Boreholes
Tailings
Phase
Time Interval
(year)
Active Intercepting
Boreholes
Monitoring Boreholes Total
Abstraction
Volumes (m
3
/day)
Phase 1
1 – 14
16
10
26
640
Phase 2
14 – 20.5
20
23
43
800
Phase 3
20.5 – 27
26
28
54
1040
Post-closure
27 - 42
32
22
54
1500-2000
As the groundwater model was used to determine the configuration of the
groundwater interceptor system, the extent of the salt plume will be minimized.
The expected TDS, sulphate and manganese concentrations in groundwater, as a
result of the tailings facility and with mitigation using the groundwater recovery
system, is described in the paragraphs that follow.
The modeled concentrations of TDS at the end of tailings deposition (Year 27),
the end of operation of the groundwater recovery system (Year 42) as well as
long-term (Year 100) are presented on GCS October 2005 Drawing Nos. 1a H4,
1b H4, and 1c H4 in Volume I, Appendix 7.2. The baseline TDS concentration
ranges from 128 mg/l to 282 mg/l, compared to the WHO guideline value of
1,000 mg/l. According to the model, at Year 27 the TDS concentrations will be
less than 600 mg/l only a short distance beyond the footprint of the tailings
facility. This does not change appreciably by Year 42 when the groundwater
recovery system is decommissioned. By Year 100, there has been some
movement of increased TDS downgradient the tailings facility, with the
