Crop and environmental response to irrigation with mine-affected waters : the development of technical management guidelines

Abstract

Decanting and illegal mine-affected water disposal are problems which have plagued South Africa’s mining industry and have exacerbated the deterioration of the quality of water resources. Expensive and energy intensive mine water treatment has thus become normal practice for mine water management in most South African mines. The reuse of mine-affected waters in other industries allows for alternative mine water utilisation options and may partially alleviate mine water treatment costs.

Another of South Africa’s largest water users is the agricultural industry. The mining industry in South Africa produces large volumes of mine-affected waters and the agricultural industry requires large water inputs to improve and maximize yields of crops. A noteworthy opportunity, therefore, arises for the use of mine-affected water for irrigation. If monitored and correctly managed, mine-affected water irrigation is a sustainable, consumptive, and alternative water utilization option. Due to the lack of concise guidance to facilitate regulatory approval of irrigation with mine-affected waters, it is not practiced on any meaningful commercial scale in South Africa.

Firstly, this study aimed at gaining a fundamental understanding of available literature on irrigation with mine-affected waters. Secondly, an established field trial at Mafube Colliery, (Middelburg, Mpumalanga, South Africa), provides a platform for the long-term quantification, monitoring and modelling of salt and water balances when irrigating with gypsiferous mine-affected waters. Finally, a technical management guideline is proposed as a standardised framework for site selection, constituents of concern identification, applicable environmental risk assessment, monitoring plans and action levels, when using mine-affected water for irrigation.

At the established field trial, white maize was irrigated for three seasons, 2017 to 2020, on unmined land. The quality of the grain produced was well above food and fodder safety standards, with the white maize producing reasonable to good yields with demonstrated profitability, under these irrigation conditions. Irrigation with gypsiferous mine water at this field site, has an acceptable and limited environmental impact, and with appropriate risk-based management, is a feasible and responsible practice. The routinely measured atmospheric, crop, soil, and water data obtained throughout this study were used as inputs for an irrigation water quality Decision Support System (DSS).

The technical management guideline developed here amalgamated the appropriate tools, practices, and guidelines specific to mine-affected water irrigation. The proposed comprehensive and site-specific risk assessment characterises a site’s applicability, susceptibility, and capacity to receive, conduct and function when irrigated with mine-affected water.