Environmental Engineering Reference
In-Depth Information
using the titration method and sulphate using the gravimetric method. All analyses were
done at the University of Zimbabwe.
3 RESULTS AND DISCUSSION
3.1
Golden Quarry Landfill
Levels of coliforms, cadmium, iron, lead, nitrate and pH were above water quality
guidelines, hence the water is generally unsafe for domestic use (Table 7.2). Levels of
metals decreased westwards-with groundwater flow (Fig. 7.9-7.12). Metal levels drop
going westwards from 0.53 mg Cd/l, 11.05 mg Fe/l, 0.21 mg Pb/l and 0.06 mg Zn/l near
the south side of the landfill to 0.22 mg Cd/l, 1.38 mg Fe/l, 0.12 mg Pb/l and 0.02 mg
Zn/l to the southwest end of Westlea. Levels of Pb, Fe and Cd showed high
concentrations in all boreholes, above water quality guidelines, making the groundwater
unsuitable for drinking throughout Westlea. The high metal levels do, however, attenuate
fairly rapidly downflow (within 1 km), as is expected from numerous studies elsewhere
(Christensen et al
.
2001).
Coliform levels also decrease westwards with groundwater flow, from 10,000
coliform units (cfu) near the north side of the landfill to 0 cfu at the southwest end of
Westlea, making the water unsafe for drinking in northern Westlea. Nitrate levels were
highest at 16.55 mg/l near the north side of the suburb and decrease with groundwater
flow to 0.40 mg/l with a spot at BH6 (10.20 mg/l) probably being due to urban
agriculture, sewage leakages and/or pit latrines (Fig. 7.13).
A comparison with the control borehole suggests that the landfill is a source of
groundwater pollution, with metals, nitrates and coliform bacteria all showing elevated
levels in the study boreholes. The metal levels could be explained by the disposal of
industrial waste on the landfill - except for iron, which is most
Table 7.2. Groundwater quality data, 2004, Golden
Quarry Landfill, Harare.
pH
(pH
units)
Cd
(mg/l)
Fe
(mg/l)
Pb
(mg/l)
Zn
(mg/l)
NO
3
(mg/l)
SO
4
(mg/l)
Cl
(mg/l)
CO
3
(mg/l)
Total
coli-
forms/100
ml
Faecal
coli-
forms/100
ml)
BH1
5.79
0.53
11.05
0.21
0.06
16.55
47.73
7.90 273.00
23000
0
BH2
6.35
0.39
1.88
0.14
0.04
10.13
45.30
3.50 129.00
14000
6000
BH3
6.82
0.32
3.79
0.16
0.05
10.89
28.43
2.11
34.05
0
0
BH4
5.97
0.46
1.48
0.12
0.03
3.92
26.53
2.64
32.00
4000
1000
BH5
6.24
0.37
2.26
0.19
0.02
1.49
19.00
2.35
71.00
0
0
BH6
7.03
0.22
2.52
0.19
0.04
10.20
21.83
4.40
46.00
3000
0
BH7
6.15
0.46
4.72
0.15
0.03
0.40
13.63
3.70
31.00
0
0
