Future Perspectives on Acid Mine Drainage
The current chapter highlighted how several mining activities along the mine project cycle alter hydrology and promote the generation and dissemination of AMD. However, several constraints and knowledge gaps warrant further public and research attention.
1.4.1 Effectiveness of Environmental and Social Impact Assessments
The hydrogeochemistry of AMD is quite complex, hence AMD often has a long latent or lag period. Therefore, the occurrence and impacts of AMD often manifest long after the mine closure, when no resources are available for implementing mitigation and control measures. Moreover, most ESIAs lack details to address potential long-term AMD risks, yet such ESIAs and their associated environmental management plans (EMPs) are used as a basis for project approval and post-closure mining. Therefore, in most countries, current ESIAs and EMPs have limited potential to address AMD risks.
1.4.2 Rapid Acid Mine Drainage Prediction
Most methods for assessing AMD potential such as pH measurements and short-term leaching tests may underestimate the AMD generating potential of sulphidic geological materials (Kanda et al., 2017). Yet, alternative methods for evaluating AMD are often expensive, time-consuming, and require well-equipped geochemical laboratories. Therefore, such expensive and robust methods are rarely used in feasibility studies such as ESIAs and routine environmental surveillance systems. Hence, the development and validation of rapid and universal methods for assessing AMD potential warrant further research. However, some of the advanced methods for predicting AMD formation are covered in Chapter 2.
1.4.3 Acid Mine Prainage Prevention during the Mine Project Cycle
The bulk of AMD prevention and control methods seem to adopt an 'end- of-pipe' approach (Gwenzi et al., 2017; Mungazi and Gwenzi, 2019; Skousen et al., 2019). Specifically, particular attention is paid to: (1) treatment of AMD using active and passive methods, and (2) use of wet and dry covers to prevent AMD generation from waste rock and mine tailings. By comparison, AMD prevention receives limited attention during the various phases in the mining project cycle highlighted in the current chapter. Given the high cost of AMD control and its health risks, AMD control and prevention may need to be integrated in the whole mine project cycle as part of safety, health and environment (SHE) programme. Some of the techniques for preventing AMD are covered in Chapter 6.
1.4.4 Translating Existing Research into Appropriate Solutions
A significant body of literature exists on the formation, hydrochemistry and control of AMD (Skousen et al., 2019). However, the bulk of literature applies to laboratory and pilot studies, while data on large-scale field applications are still limited, partly due to high costs associated with current technologies. Given the global scale of AMD, and the existence of several legacies associated with it, the next decade should focus on developing appropriate and scalable solutions for AMD prevention and control.
1.4.5 Acid Mine Drainage Control in Underground Workings
Compared to waste dumps and mine tailings, the prevention and control of AMD in current and old mine workings appear to pose serious challenges to both researchers and regulators. First, the spatial extent of AMD in underground mine workings is not known with certainty in most countries. Second, even in most countries, particularly developing nations, where underground AMD and its impacts on human and ecological heath have been detected, feasible control measures appear to be lacking. Hence, further research is required to address AMD in current and old mine workings.
1.4.6 Mapping of Acid Mine Drainage at Country and Regional Levels
Limited data exist on the spatial distribution of AMD hotspots at country and regional levels. Yet such information is critical for devising control measures to safeguard human and ecological health. For example, in sub- Saharan Africa, several surface water and aquifer systems are shared among several countries, hence water pollution risks posed by AMD constitute a shared trans-boundary problem. Thus, there is a need for coordinated efforts to map AMD problems close to major national and regional surface water and aquifer systems. The availability of remote sensing tools, coupled with GIS spatial tools can enable such mapping at various spatial and temporal scales (Masocha et al., 2020).
1.4.7 Hydrological Impacts of Mining
The hydrological impacts of mining activities such as land clearing, excavation, drilling and blasting on water flows and balances are largely based on inferential evidence. Hence, systematic studies are required to understand the hydrological impacts of mining activities on surface and groundwater hydrological processes and water balances at mine, local and catchment levels. Such studies should also investigate impacts on hydrochemistry, including the occurrence of residual chemicals used for drilling, blasting and hydraulic fracturing/fracking.