Environmental Assessment
Volume C-3.7
Slurry Pipeline
Water Quality
Ambatovy Project
65
January 2006
construction activities will not affect the stream channel; therefore, no changes in
water or sediment quality are expected to occur.
Most crossings will be buried and will involve excavating across the channel,
laying the pipe and backfilling the trench. Construction of the crossings will
typically be conducted during low flow conditions to minimize the amount of
suspended sediment generated and transported to downstream reaches. Best
management practices will be used to control erosion and minimize sediment
from entering the water via runoff from disturbed areas. Water quality
substances associated with particulate matter (i.e., nutrients and metals) may
increase temporarily due to their release from disturbed bed material. The
duration of these increases is expected to be short (i.e., hours for small crossing
and a few days for larger crossings); therefore, the overall predicted effects on
water quality during construction are negligible.
No effects on water or sediment quality are expected in the streams during
operation or post-closure due to implementation of best management practices,
and stabilization and restoration of stream banks. Design and construction
specifications, as discussed in the Hydrology Section (Volume C, Section 3.6),
will also minimize the possibility of sediments being introduced as a result of
channel instability or geomorphic change.
Hydrostatic Testing
Hydrostatic testing of the pipeline will require water withdrawal from rivers
and/or streams. The pipeline will be tested in sections and may require multiple
water withdrawals along the pipeline length. Withdrawal volumes and rates will
be specified at later stages of the project. Withdrawal locations will also be
selected with the aim of minimizing potential changes in water and sediment
quality in affected watercourses and water bodies. Water will typically be
disposed of to designated vegetated areas but may also be disposed directly to
watercourses and water bodies. However, before any discharge, the quality of all
disposed water will meet required effluent criteria, which will be dependent on
the following conditions:
•
receiving environment (i.e., vegetated areas, watercourse or water
body);
•
discharge volume (flow rate and duration) and concentrations; and
•
assimilative capacity of receiving environment (i.e., flow and water
quality concentrations if receiving environment is a watercourse).
