Groundwater Contamination with Toxic Metals through Small Scale Mining within the Lower Pra Basin
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Date
2013-06
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Publisher
University of Ghana
Abstract
Small-scale gold mining in Ghana is mainly an informal industry employing
thousands of people. The generally undeveloped nature of the industry has resulted
in lack of proper monitoring and supervision by relevant authorities. As a result,
there is wanton destruction of farm lands and indiscriminate pollution of water
bodies. These water bodies serve us recharge zones for groundwater, thereby
polluting them.
This study assessed the effects of small-scale gold mining on
quality of groundwater in the Lower Pra Basin in terms of heavy metal and other
physico-chemical pollution. The analysis shows that pH values are generally low in
the Basin. More than 95 % of dry season and almost all the wet season values are
acidic or slightly acidic. Approximately 35 % of boreholes in the wet season
recorded values for Cadmium above W.H.O guideline value of 3.0 μg/l. Only two
boreholes recorded values above W.H.O guideline value for the dry season. The
higher wet season pollution suggests anthropogenic origin for Cd. Generally, high
values
were
recorded for Iron,
Manganese,
Lead,
Aluminium
and
Hg.
Approximately 15% and 18 % of dry and wet season values respectively for Fe
were above W.H.O recommended limit of 300 μg/l for drinking water with a mean of
218 μg/l and a median of 166 μg/l. Manganese concentration was in the range 2.5 -
1544 μg/l with a mean of 142 μg/l. Roughly 5 % and 11 % of the dry and wet
season values respectively, were above the W.H.O recommended value of 500
μg/l. The concentration of Lead was higher than 10 μg/l (W.H.O guideline value) in
43% and 41% of the dry and wet season values respectively with a mean of 15.8
μg/l and 20.1 μg/l for dry and wet seasons respectively. About, 88% and 42% of the
dry and wet season values, respectively, were above the W.H.O limit of 1.0μg/l for
mercury. Dry season values ranged between 0.005 and 10.1μg/l with the wet
season recording values between 0.005 to 16.4 μg/l. Approximately 17 % and 11 %
of dry and wet seasons respectively recorded values above the W.H.O
recommended limit of 200 μg/l for Aluminium. Other heavy metals present but were
generally below W.H.O guideline values or were in insignificant concentrations
include Copper, Arsenic, selenium and Zinc. Values recorded for Phosphate,
Sulphate and Nitrate are within acceptable limits. In general, Lead, Copper,
Cadmium, and Manganese showed higher wet season values than dry season
suggesting anthropogenic influence .
Description
Thesis (MPHIL)-University of Ghana, 2013