The assessment of groundwater quality in rural communities : two case studies from KwaZulu-Natal.

Abstract

The health and life expectancy of populations in developing countries is

largely determined by the availability of good quality drinking water.

Boreholes and springs generally provide water of better microbiological and

physical quality than surface water sources, however, they may cause health

and aesthetic problems due to chemical constituents dissolved out of the host

rock.

As part of a pilot study to assess the health-related quality of community

water supplies, samples were taken from two Quaternary catchment areas in

KwaZulu-Natal. The Umkomazi catchment area is located inland from

Amanzimtoti, while the Umfolozi catchment area is located north-east of

Ulundi. The geology in these areas is significantly different. The Umkomazi

area is predominantly underlain by basement rocks of the Natal Structural

and Metamorphic Province, while the Umfolozi area is underlain by

sedimentary rocks of the Karoo Supergroup.

Geographical information systems (GIS) were used to examine the influence

of lithology, rainfall and landuse activities on groundwater quality. Major ion

analysis of groundwater samples from the Umkomazi area revealed a linear

relationship between borehole and spring concentrations. Dwyka Tillite was

found to produce water with the highest concentrations of major ions, while

Karoo dolerite produced water with the lowest concentrations of major ions.

Samples from basement rocks and Natal Group contained intermediate

concentrations of major ions. In the Umfolozi area Karoo dolerite samples

showed the lowest concentrations of major ions, while the Vryheid Formation

and Dwyka Tillite produced the highest borehole and spring concentrations,

respectively. High salinity levels in sedimentary rocks may be due to marine

influence during deposition. Piper diagrams show relative enrichment of

major cations and anions and Stiff diagrams showed characteristic patterns.

Fluoride is associated with siliceous basement rocks and related to calcium

concentrations through the solubility of calcium fluoride. The trace metals,

manganese, iron and zinc were found to cause significant aesthetic problems

and possibly health problems in sensitive individuals. These constituents are

derived from weathering of bedrock and possibly from the corrosion of metal

pipes.

There is an inverse relationship between mean annual rainfall (MAR) and

electrical conductivity (EC), except near the coast where windblown salinity

increases with rainfall. Nitrate, ammonium and E. Coli contamination are

linked to landuse activities such as occurrence of human and animal excreta

near the water source and the proximity of pit latrines. It is recommended

that rural communities be educated about the nature and importance of

groundwater quality.