Surface water quality often receives significant attention, as the impacts are often visually obvious and the causal chain leading to the reduction in quality is usually clear. However, groundwater quality is equally important, as it often directly feeds surface water bodies and is an important source of drinking water.
One of the primary sources of groundwater pollution in urban areas is infiltration from pit-latrines in areas with on-site sanitation, or from sewers when these are in a state of disrepair. Poorly maintained sanitation infrastructure can allow effluent to contaminate the groundwater. In addition, agriculture (irrigated cultivation and livestock) can degrade groundwater quality, for instance by inorganic nitrates originating from fertilisers containing potassium nitrate and ammonium nitrate. Other groundwater pollutants include herbicides and pesticides.
Groundwater monitoring, Namibia.
Source: Harald Zauter, 2007
( click to enlarge )
The quality of groundwater can also be influenced by the mineralogy of rocks through which it flows (DWAF 2004b). Certain rock formations can increase the Total Dissolved Solids (TDS) levels in groundwater to a point where it is not potable without treatment, which may not be economically viable. This treatment decision is dependent on whether alternative groundwater or surface water sources are close by.
The following key facts summarises the potential sources for groundwater pollution in the Kunene River basin.
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Leakage from pit-latrines in areas with on-site sanitation and dense populations;
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Application of agrochemicals such as fertilisers and pesticides in irrigated and rainfed agriculture;
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Drainage of contaminated water from industrial and mining areas; and
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Intrusion of salt water due to over-exploitation of groundwater in coastal zones.
Although the mining and agricultural sectors do not currently have a significant negative impact on groundwater quality, the enormous development planned for these two sectors raises concern about future groundwater quality.
