Environmental Assessment
Volume E-3.10
Tailings Facility
Water Quality
Ambatovy Project
128
January 2006
The concentration of the surface runoff was back-calculated based on the
concentrations and flows observed during baseline conditions in the watercourses
within the tailings facility area. The following mass balance equation was used:
C
sur
= ([Q
sur
+ Q
gw
] *C
mixb
– Q
gwb
*C
gwb
)/Q
surb
Equation 3
Where: C
mixb
= average baseline substance concentrations in surface
watercourses within tailings facility area
Q
gwb
= baseline groundwater flow
C
gwb
= average baseline substance concentration in
groundwater
Q
surb
= baseline surface runoff contribution to total
streamflow.
Concentrations of the surface runoff were estimated for both dry and wet
seasons. Dry season concentrations were based on baseline water quality and
flows observed during dry conditions. Wet season concentrations were
calculated using baseline water quality observed during the wet season and
average flow conditions. Average water quality conditions were based on
average baseline water quality observed during the wet and dry seasons and
average flow conditions.
All water quality constituents for which sufficient data were available were
predicted at the assessment nodes within the tailings facility area (Table 3.10-2).
Values for pH were not predicted with the mass balance model. However, the
potential range of instream pH value was characterized for all scenarios using
observed and predicted pH values for baseline flows and tailings seepage,
respectively.
Table 3.10-2 Water Quality Constituents Assessed in the Tailings Facility Area
Group
Water Quality Variables
conventional
total alkalinity and conductivity
major ions
calcium, chloride, magnesium, sodium and sulphate
nutrients
nitrate and nitrite
total metals
aluminum, arsenic, barium, chromium, cobalt, copper, iron, lead,
manganese, mercury, nickel, silicon, vanadium and zinc
