Environmental Assessment
Volume E-3.2
Tailings Facility
Geology and Geochemistry
Ambatovy Project
28
January 2006
Geochemistry
There is one valid impact pathway for geochemistry: the metal leaching from the
tailings may result in effects on water quality. The linkage diagram for
geochemistry is provided in Volume H, Appendix 9.
Derivation of Input Water Qualities for Water Quality Model
A Water Quality Model is used to predict potential water quality impacts to the
receiving environment (Volume E, Section 3.10). The model consists of several
catchments in which the tailings facility contributes runoff. This section
describes the derivation of the water quality from the tailings facility used as an
input to the Water Quality Model.
In collaboration with technical staff from Dynatec, analytical results from six
entrained tailings water samples were reviewed and results selected that best
represented the proposed operational conditions. A dilution factor of 50% was
applied to account for dilution by rain water.
Use of the entrained water results requires the important assumption that they are
representative of tailings porewater under ambient conditions.
Single-stage tests are not capable of simulating transient behavior such as
sulphide oxidation. Although the latter is not of concern for the Ambatovy
tailings due to a general absence of reactive sulphides, sequential leach testing of
tailings identified concentration trends over time that were not captured by the
entrained water quality which formed the basis for the derivation of input water
qualities.
For the tailings, only six entrained water samples were analyzed. Due to this
small sample set, compositional heterogeneity due to variability in slurry
composition and processing methodology was not accounted for. However, the
samples represented a large composite of material from testing programs.
3.2.4
Conclusions
Geochemistry impacts are predicted to occur due to the project. These effects are
not classified as residual impacts in themselves, but have a direct effect on water
quality and are therefore used in the water quality impact analysis (Volume E,
Section 3.10).
