Environmental Assessment
Volume B-3.7
Mine
Hydrogeology
Ambatovy Project
86
January 2006
site investigations were used to develop a model to predict impacts from the
proposed mine development. This included incorporating measured groundwater
levels and transmissivities obtained from the aquifer tests within the model.
Calibration of the model (matching calculated groundwater levels to observed
groundwater levels) proved to be difficult. During the calibration process the
aquifer parameters such as transmissivity and recharge percentage were varied
within realistic values in order to obtain the best possible correlation between the
calculated and observed groundwater levels.
3.7.5.2 Impact Description Criteria
The assessment criteria used for hydrogeology are presented in Table 3.7-2.
Table 3.7-2 Impact Description Criteria and Numerical Scores for Hydrogeology
Resource
Direction
(a)
Magnitude
(b)
Geographic Extent
(c)
Duration
(d)
Reversibility
(e)
Frequency
(f)
mine site
hydrogeology
positive
,
negative
or
neutral
for the
measurement
endpoints
negligible
: <5%
change
low
: 5 to 10%
change
moderate
: 10 to
30% change
high
: >30%
change
local
: effect restricted
to the LSA
regional
: effect
extends beyond the
LSA into the RSA
beyond
regional
:
effect extends beyond
the RSA
short-term
:
<3 years
medium-term
:
3 to 30 years
long-term
:
>30 years
reversible
or
irreversible
low
: occurs
once
medium
: occurs
intermittently (1
to 10 times per
year)
high
: occurs
frequently (>10
times per year)
(a)
Direction: positive or negative effect for measurement endpoints, as defined for the specific component.
(b)
Magnitude: degree of change to analysis endpoint.
(c)
Geographic Extent: area affected by the impact.
(d)
Duration: length of time over which the environmental effect occurs. Considers a three-year construction period and a 27-year
operations period.
(e)
Reversibility: effect on the resource (or resource capability) can or cannot be reversed.
(f)
Frequency: how often.
3.7.5.3 Mitigation
Project design involves the development of the open pits in phases. This
approach requires localized dewatering of active work areas in a phased approach
rather than constant dewatering of a large area. This will reduce the amount or
rate of groundwater withdrawal from storage in the aquifer and facilitate more
expedient recovery of groundwater levels at closure.
At closure, disturbed areas will be restored by providing natural vegetation and
topography, to re-establish natural runoff conditions and ensure that drainage
areas of each sub-watershed are close to pre-development values.
