A geohydrological situation analysis for the construction of a groundwater management plan for the Sasolburg industrial and mining area

English: The Department of Water Affairs in South Africa has recently moved towards the management of regions on a catchment and subcatchment scale. The Taaibos and Leeu Spruit catchments were identified as catchments where groundwater research was needed. The final objective of this work would be the implementation of a Catchment Management Plan These catchments house several influences on groundwater quality. These include the urban area of greater Sasolburg, several chemical industries (petrochemical, fertilizers, plastics ete), mining activities, power stations and agriculture. A groundwater situation analysis was therefore undertaken to highlight all relevant groundwater components. To achieve this, the study included a literature study, the creation of a database, fieldwork including sampling of 101 sites in the catchment for inorganic analysis, sampling of 10 sites for toxicity testing to indicate true toxicity of the water, aerial geophysics over a portion of the catchment and resistivity soundings at points surrounding the industries. Based on information gathered by this work it was possible to identify the principal aquifers in the area and classify them according to methods set out by Parsons (1995). The chief controls on groundwater movement and pollution sources on each site were identified. It was found that a dolerite sill of variable depth and thickness was the main control of groundwater movement underlying the industrial areas. The collected data and sampling highlighted the most important pollution sources. Use of toxicity testing showed the potential of these tests in indicating the true toxicity of samples. These results with, simplified numerical modelling in the area gave an indication of pollution migration and areas of concern. The area was subdivided into groundwater management areas based on the activities in each area. Three zones were defined representing the industrial and mining areas, a buffer zone and the areas to be protected respectively. In each zone different quality guidelines were proposed. A Threat Action Guide spreadsheet was developed to identify and prioritize areas of concern. It uses water quality data for different parameters, the aquifer classification, the water quality guideline for the zone and the distance to the nearest area of concern as inputs. A threat index is thereby calculated using various empirical equations and this index then suggests different generalized management options to be followed. The situation analysis has provided an overview of this heterogeneous area and put a basic framework in place on which the eventual Groundwater Management Plan will be based.