Environmental Assessment
Volume E-3.7
Tailings Facility
Hydrogeology
Ambatovy Project
55
January 2006
Table 3.7-2 Impact Description Criteria and Numerical Scores for the Ambatovy
Project – 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.
3.7.5.4 Mitigation
To mitigate the effects of the tailings facility on groundwater flows and quality,
the Ambatovy Project will implement the following measures:
•
staged development to limit the amount of disturbed and exposed areas;
•
develop tailings basins within former water basins;
•
reduce seepage rates to groundwater by lining the water basins;
•
install and operate a groundwater recovery system downstream of
tailings basins throughout operations and 15-years post-closure to
capture salt elevated groundwater; and
•
return areas to natural runoff conditions through progressive and closure
revegetation.
3.7.5.5 Results for Key Question HG-1: What Effect Will the Tailings
Facility Have on Groundwater Flows and Consequently
Downstream Surface Flows?
The blanketing effect of low permeability tailings deposited within the tailings
basins will reduce recharge to groundwater as the tailings consolidate over time.
This could reduce baseflow contribution to streams by up to 25%, a moderate
magnitude of change to groundwater flow.
