Consideration of site-specific conditions in the assessment of groundwater pollution potential : an ash disposal case study

Abstract

Groundwater resources, which form an important source of readily available potable water supply, are vulnerable to contamination from land-based activities. One of the potential sources of contamination is waste disposal facilities (WDFs). In South Africa, groundwater pollution potential from WDFs is regulated in terms of the National Water Act (36 of 1998) (NWA) and the National Environmental Management: Waste Act (59 of 2008) (NEM: WA). These two laws make use of different approaches to determine the groundwater pollution potential, namely, the (1) the Waste Classification Management System (WCMS), currently prescribed for the assessment of waste for landfill disposal under the NEM: WA; and (2) the source-pathway-receptor (SPR) approach recommended in the guidelines giving effect to Water Quality Management Policy developed under the NWA. It was argued that the current application of the WCMS may not consider site-specific conditions associated with groundwater pollution potential from WDFs. The aim of this study was to understand the extent to which the SPR approach differs from WCMS in terms of consideration of site-specific conditions when assessing potential pollution of groundwater from wet and dry ash disposal facilities (ADFs). SPR is one of the approaches, other than the WCMS, which is believed to make a more suitable provision for site-specific conditions. A case study method for ash disposal from the power generation processes of Eskom Holdings SOC Ltd was considered. One wet ADF and one dry ADF, located at two different Power Stations, with different site-specific conditions were included. Groundwater quality data, measured quarterly from June 1989 to February 2018 (at Site A) and October 1990 to June 2017 (at Site B) of twenty-two (22) different (source-, pathway- and receptor) boreholes were included for consideration during this study. Considering the above, it is clear that the WCMS and SPR approaches differ in how they assess groundwater pollution potential of ADFs, as it relates to the source (indicator: leachable concentration), pathway (indicator: NAP and geological structures) and receptor (indicator: thresholds). The fact that the WCMS approach does not provide for site-specific conditions and apply thresholds that do not adequately protect the most sensitive user identified for that catchment, could result in either over- or under-protection of the surrounding environment. It is, therefore, argued that the SPR approach may be a more suitable method for assessing groundwater pollution potential while taking site-specific conditions into consideration. Keywords: groundwater pollution potential, site-specific conditions, ash disposal facility, waste classification management system, source-pathway-receptor approach.