Electrical conductivity (EC) is a useful surrogate for total dissolved solids (TDS). EC is more rapidly and easily measurable with reasonably-priced equipment. However, as an indirect measure EC is subject to uncertainties that are not always apparent to the user. We set out to investigate the relationship between TDS and EC in 144 643 sample results available on the Department of Water Affairs water quality database. TDS is calculated as the sum of the major solutes determined by laboratory analysis and EC is a measurement in a flow cell. The median TDS:EC ratio for 332 high priority sites was 7 mg/ℓ: 1 mS/m. Regional differences ranged from 4.8 to 8.6. Investigation of 38 of these sites using Maucha diagrams suggested that the differences are related to the dominant major ions, with sodium chloride waters having a lower TDS:EC conversion factor than calcium bicarbonate waters. The practical application of these findings is that users of EC meters should not simply apply a blanket conversion factor, but need to select an applicable factor for the river system in which they are measuring.
Determination of data adequacy for detection of long-term salinity changes was an important task in the revision of the South African National Chemical Monitoring Programme (NCMP). The NCMP has been running for more than 30 years with several hundred active monitoring sites. Twenty-five sites on major rivers had sufficient continuous data for the estimation of salinity changes over a 25-year period and statistically significant upward or downward trends occurred at 17 of the 25 sites. Most sites were too far apart for detailed analysis of whole river systems, though an upward trend is apparent in the Lower Orange River and a downward trend in the Great Fish River. Salinity in the Tugela River remained stable, well below the 70 mS m( - 1) guideline for drinking water. The results underline the importance of long-term data sets for assessing and managing aquatic systems and provide the impetus to continue building and maintaining long-term sampling programmes.
The Department of Water Affairs and Forestry (DWAF) has carried out a number of case studies on the radiological quality for the water resources near gold mining activities in South Africa. Elevated levels of radioactivity were found in some areas. It thus became important to establish a national monitoring programme that will report on the radiological quality of South Africa's water resources in order to comply with the water resource quality monitoring requirements of the National Water Act (Act 36 of 1998). The purpose of the National Radioactivity Monitoring Programme (NRMP) is to establish the status of, and trends in, radioactivity levels in South African water resources and to report on their radiological quality on a regular basis. This paper discusses issues and decisions taken with regard to the design of the NRMP. A screening method, using alpha/beta activity is proposed to estimate total radioactivity in surface water resources. Where elevated levels of radioactivity have been identified, an element specific analysis will follow. A biweekly sampling frequency has been recommended. Sampling site selection is catchment based and includes sites in high-risk areas. Where possible, use will be made of existing water quality and flow monitoring sites.
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