Environmental Assessment
Volume E-3.7
Tailings Facility
Hydrogeology
Ambatovy Project
53
January 2006
3.7.5
Impact Assessment
3.7.5.1 Impact Pathway Evaluation
Project activities during construction, operations and closure will result in the
following: i) reduced groundwater recharge; and ii) changes in groundwater
quality.
During construction there will be little impact on groundwater resource, as
disturbance to the landscape primarily involves site clearing and the development
of embankments for the tailings and water basins.
During operations as deposition of low permeability tailings progresses,
groundwater recharge within the tailings basin(s) will decrease due to decreased
infiltration rates. Reduced groundwater contribution to downstream surface water
reaches may occur. In addition, the seepage from the tailings basins will contain
elevated salts (primarily manganese and sulphate).
Seepage of tailings water into groundwater will decrease at closure when tailings
deposition ceases. The only seepage through the tailings will be from
precipitation and infiltration will further decrease with revegetation and
consolidation of the tailings.
Changes in groundwater flows may have an impact on socio-economics and land
use, with decreased availability of groundwater and possibly surface waters for
human consumption and agricultural use. Changes in the quality of groundwater
may also impair groundwater for human consumption or other uses and may
impair surface water quality.
3.7.5.2 Assessment Methods
Groundwater Consulting Services (GCS) (Pty) Ltd. carried out numerical
modeling to predict impacts on groundwater conditions during planned tailings
deposition activities, as well as the recovery of groundwater levels following
closure (GCS, April 2005).
Two dimensional, steady state and transient state seepage analyses were
conducted utilising finite element software SEEP/W
©
. The method is based on
grid patterns, which divides the flow region into discrete elements. Material
properties, such as permeability and volumetric water content, are specified for
each element and boundary conditions (heads and flow rates) are set. The
operational conditions were simulated by a steady state analyses and the output
