Environmental Assessment
Volume C-3.7
Slurry Pipeline
Water Quality
Ambatovy Project
64
January 2006
because of the use of appropriate mitigations. The potential changes in water and
sediment quality are addressed in the assessment methods under the following
components of construction, operation and decommissioning of the pipeline:
•
right-of-way;
•
watercourse and water body crossings;
•
hydrostatic testing; and
•
failure or spill.
The potential for additive changes in water and sediment quality due to the slurry
pipeline and other components of the project, including the mine, process plant
and tailings facility, is also assessed.
Right-of-Way
Construction of the pipeline right-of-way will involve land disturbance including
removal of vegetation, excavation and backfilling, and compaction. These
activities will result in higher runoff rates from the disturbed areas which have
the potential to increase loads of sediment and water quality substances in the
runoff compared to baseline conditions. The percentage of disturbed area within
a given basin, however, is typically very small relative to the overall drainage
area. Changes in water and sediment quality in receiving streams are expected to
be negligible provided that best management practices are used and natural
drainage paths are maintained. Any changes in water or sediment quality due to
increases in runoff during construction will return to baseline levels once the
disturbed areas are reclaimed and as vegetation is re-established through the
operations and closure phases.
Watercourse and Water Body Crossings
Construction of the slurry pipeline will involve about 100 watercourse and water
body crossings along the route. As discussed in the Hydrology Section
(Volume C, Section 3.6), a detailed assessment of each crossing prior to
construction will identify highly sensitive areas. Impacts on these sensitive areas
will either be avoided or minimized by fine tuning the route of the pipeline, using
an aerial crossing or applying additional appropriate mitigations.
Based on the initial crossing assessment, aerial crossings are expected to be
required at two rivers as well as several smaller watercourses in deep and narrow
valleys (Volume C, Section 3.6). The pipeline crossing on the Ivondro River
south of the tailings facility and plant will be directionally drilled. In these cases,
