Environmental Assessment
Volume B-3.9
Mine
Water Quality
Ambatovy Project
116
January 2006
3.9.2
Study Area
The Local Study Area (LSA) for water quality is the same as the hydrology study
area presented in Volume A, Figure 7.2.1. The area covers the likely spatial
extent of mine development and effects on water and sediment quality. The LSA
includes the following areas:
•
six main basins draining the mine (i.e., Antslahalava, Sahaviara,
Torotorofotsy, Sakalava, Sahamarirana and Ankaja rivers);
•
location of the water intake pipe on the Mangoro River; and
•
the Torotorofotsy Wetlands.
3.9.3
Baseline Summary
3.9.3.1 Water Quality
Based on water quality sampling conducted during both the dry and wet seasons
in 2004, water quality near the mine area has pH values of 6.8 to 7.2, and
dissolved oxygen values generally near saturation. Water temperatures typically
range from 18 to 24°C, although higher temperatures have been observed in
some of the watercourses and water bodies.
Hardness values for surface waters near the mine area range from very soft to
moderately soft. Based on observed alkalinity results, some water bodies appear to
be sensitive to acidification. Nutrient levels are generally low for nitrogen
substances, including nitrate, nitrite, total kjeldahl nitrogen (TKN) and ammonia,
and typically below detection limits for total phosphate.
In general, there are no clear seasonal patterns for most of the water quality
substances measured in the mine area. In addition, with few exceptions, there is
no clear spatial variability in water quality. The exceptions include magnesium
and chromium during the dry season, which appear to have higher concentrations
at stations downstream of the Ambatovy and Analamay ore bodies relative to
stations located further away from the ore bodies.
Based on the Madagascar classification system for surface waters (Table 3.9-1),
most watercourses and water bodies near the mine site are assigned to “Class A”
(i.e., water is suitable for multiples uses). No stations were classified as
excessively contaminated (Class HC) in the mine area. Concentrations of lead
and nickel, in the dry season and arsenic in the wet season were higher than the
World Health Organization (WHO 2004) drinking water quality guideline values.
