Environmental Assessment
Volume E-3.10
Tailings Facility
Water Quality
Ambatovy Project
120
January 2006
3.10.3 Baseline Summary
3.10.3.1 Water Quality
Water quality in the tailings facility area ranges from mildly acidic to neutral
with pH values of 5.4 to 7.1. Dissolved oxygen concentrations are generally
below saturation. Water temperatures range from 23 to 32°C. Surface waters
near the tailings facility area are generally very soft with hardness values of 6 to
26 mg/L as CaCO
3
. The majority of results for alkalinity indicated that the water
bodies within the tailings facility area are potentially sensitive to acidification.
Nutrient levels are generally low for nitrogen parameters, including nitrate,
nitrite, Total Kjeldahl Nitrogen (TKN) and ammonia, and generally below
detection limits for total phosphate.
Based on the Madagascar classification system (Table 3.10-1), background
surface water quality in the tailings facility area are typically classified as
moderate (Class B), with some watercourses classified as poor quality (Class C).
There were no surface waters that are considered to be excessively contaminated
(Class HC). Manganese is the only water quality substance with observed
concentrations above the World Health Organization (WHO) (2004) drinking
water guideline value in the baseline data.
Table 3.10-1 Madagascar Classification System for Surface Water Quality
Parameters
Class A
Class B
Class C
Unclassifiable
(Class HC)
classification definition
good quality: multiple
uses possible
moderate quality: non-contact
recreation allowed; swimming
may not be allowed
poor quality: swimming not
allowed
excessive contamination:
no use possible except
for boating
Biological Factors
dissolved oxygen (mg/L)
DO
≥
5
3 < DO < 5
2 < DO
≤
3
DO < 2
5-day biological oxygen
demand (BOD
5
)
BOD
5
≤
5
5 < BOD
5
≤
20
20 < BOD
5
≤
70
BOD
5
> 70
chemical oxygen demand
(COD)
COD
≤
20
20 < COD
≤
50
50 < COD
≤
100
COD > 100
presence of pathogenic
bacteria
no
no
no
yes
Physical and Chemical Factors
colour (TCU)
colour < 20
20
≤
colour
≤
30
colour < 30
n/a
water temperature (°C)
temperature < 25
25
≤
temperature < 30
30
≤
temperature < 35
temperature > 35
pH
6.0
≤
pH
≤
8.5
5.5 < pH < 6.0 or
8.5 < pH 9.5
pH
≤
5.5 or pH
≥
9.5
N/A
total suspended solids
(TSS) (mg/L)
TSS < 30
30
≤
TSS < 60
60
≤
TSS < 100
TSS > 100
conductivity (µS/cm)
conductivity
≤
250
250 < conductivity
≤
500
500 < conductivity
≤
3000
conductivity > 3000
TCU = True colour unit.
N/A =
Not applicable.
