Environmental Assessment
Volume B-3.9
Mine
Water Quality
Ambatovy Project
125
January 2006
Table 3.9-3 Water Quality Variables Assessed
Group
Water Quality Variables
conventional
total alkalinity
major ions
calcium, chloride, fluoride, magnesium, potassium, sodium, sulphate
nutrients
ammonia, nitrate and nitrite
total metals
aluminum, antimony, arsenic, barium, boron, cadmium, chromium,
cobalt, copper, iron, lead, manganese, mercury, molybdenum, nickel,
selenium, silicon, thallium, tin, uranium, vanadium and zinc
Sediment Quality
Changes in sediment quality were predicted based on US EPA (1999) guidelines
for calculating benthic sediment concentrations. The equations provided by
USEPA (1999) estimate the proportion of a substance within a water body that
exists in the sediments, using chemical partition coefficients, sediment porosity,
total suspended solids concentration, water depth and depth of benthic sediments.
Changes in sediment quality during operations and post-closure were calculated
based on water quality predictions.
The sediment quality calculations assumed that sediment load to receiving
downstream watercourses and water bodies will be negligible due to
implementation of appropriate mitigation. Where available, baseline sediment
concentrations were used to calibrate the sediment quality model. The equations
and inputs to the model are provided in Volume I, Appendix 9.2.
Changes in sediment concentrations were assessed for aluminum, antimony,
arsenic, cadmium, cobalt, copper, iron, lead, manganese, mercury, nickel
selenium, thallium, vanadium and zinc. These metals were assessed in the water
quality model and had baseline sediment quality data for calibrating the sediment
quality equations. Baseline sediment quality data was not available for
chromium; however, changes in chromium concentration in benthic sediments
due to the project were assessed because of appreciable increase in water column
concentration of this metal above background levels.
3.9.5.2 Assessment Criteria
Comparison to Baseline Values and Guidelines
Maximum concentrations predicted for the wet and dry seasons during operations
and at post-closure were compared to corresponding baseline values. During
operations or post-closure, maximum predicted concentrations exceeding the
corresponding baseline concentrations by 10% or greater were considered an
