Environmental Assessment
Volume B-3.9
Mine
Water Quality
Ambatovy Project
131
January 2006
Predicted changes in substance concentrations in the Torotorofotsy River were
used as a guide for determining project-related effects on the Torotorofotsy
Wetlands. The Torotorofotsy River is the main upstream tributary of the
wetlands that would potentially be affected by the project. Water quality changes
in the Torotorofotsy River for the six key representative substances are
summarized in Table 3.9-5.
Table 3.9-5 Concentrations of Key Water Quality Variables in the Torotorofotsy
River and Torotorofotsy Wetlands (Observed and Predicted)
Model Baseline
(Torotorofotsy
River)
Predicted
Operations
(Torotorofotsy
River)
Predicted Post-
closure
(Torotorofotsy
River)
Baseline
Torotorofotsy
Wetlands
Parameters
Units
WHO
Drinking
Water
Guidelines
1
South African
Ecosystems
Guidelines
2
Min.
Max.
Min.
Max.
Min.
Max.
Min.
Max.
cadmium (Cd)
mg/L
0.003
0.00015
3,4
0.0005 0.0050 0.0005 0.0050 0.0005 0.0050 <0.001 <0.01
chromium (Cr)
mg/L
0.05
5
0.014/0.024
6,7
0.006
0.008
0.018
0.019
0.006
0.008 <0.003 0.010
cobalt (Co)
mg/L
-
-
0.002
0.005
0.002
0.005
0.002
0.005
0.002
0.010
lead (Pb)
mg/L
0.01
0.000475
3,7,8
0.005
0.050
0.005
0.050
0.005
0.050
<0.01
<0.1
nickel (Ni)
mg/L
0.4
5
-
0.01
0.01
0.01
0.01
0.01
0.01
<0.003 0.010
zinc (Zn)
mg/L
0.02
4
0.0036
7
0.003
0.014
0.003
0.014
0.002
0.014 <0.001 <0.01
Notes: 1 World Health Organization (WHO) 2004 Guidelines for drinking water quality, 2nd edition. Geneva, World Health Organization.
Results in
bold
are above baseline concentrations by 10% and above South African guidelines.
2 South African Water Quality Guidelines Volume 7 Aquatic Ecosystems (1996) Second Edition. Department of Water Affairs and
Forestry.
3 Based on an alkalinity value of less than 60 mg/L.
4 Based on the lower of two guideline values: 0.0003 mg/L (general) and 0.00015 mg/L (cold-water adapted fish species).
5 Provisional guideline value, as there is evidence of a hazard, but the available information on health effects is limited.
6 South African guidelines presented for chromium are based on hexavalent chromium (0.014mg/L) and trivalent chromium
(0.024 mg/L); see text.
7 South African guidelines are based on the dissolved portion of this metal.
8 Based on a dissolved saturation of at least 80%.
- no guideline.
During operations, the predicted maximum concentration of chromium is higher
than baseline concentrations for the Torotorofotsy River and Torotorofotsy
Wetlands. Therefore, mine-related activities may contribute chromium to the
wetlands. However, the resulting concentrations in the wetlands would be lower
than the WHO drinking water guideline value since predicted maximum
concentrations of chromium in the Torotorofotsy River are lower than the
guideline value. The South African Ecosystems Guideline value for hexavalent
chromium, but not trivalent chromium, is predicted to be exceeded in the
Torotorofotsy River. Potential exceedances in the Torotorofotsy Wetlands would
be lower in magnitude due to dilution from other source waters into the wetlands.
The biological receptor effects of a potential increase in chromium concentration
