Abstract
The aim of the study is to determine if pit lakes are a sustainable coal mine closure option in South African. The water balance, chemistry, limnology, and bacterial population of three selected pit lakes were investigated. The lakes are in the three major coal basins of South Africa and are associated with different lithologies and mining methods. The major factors driving the water balance of the pit lakes are direct rainfall, runoff, inflow from old mine workings, and groundwater infiltration, with the major losses being evaporation or discharge onto surface. The study indicated that pit lakes can be designed as 'terminal sinks' to provide a sustainable mine closure option. The pit lakes sampled have an alkaline pH, and mostly a sodium/calcium sulphate water with total dissolved solids content of less than 3000 mg/l. The phytoplankton and microbiological data indicates that the pit lakes support aquatic life. The study shows that correctly designed pit lakes can be an environmentally sustainable closure option for South Africa's coal mines. A suggested design manual has been developed to assist mine owners and regulators in developing sustainable coal mine pit lakes as a closure option.
Highlights
Coal mining started in South Africa in the early 1800s, initially by conventional underground methods, but since the 1950s the majority of the coal production has been from opencast operations
This study evaluates the environmental sustainability of using pit lakes as a closure option for coal mines in South Africa
A fundamental change in thinking and legislation is required for pit lakes to be accepted as an environmentally sustainable closure option for South African coal mines
Summary
Coal mining started in South Africa in the early 1800s, initially by conventional underground methods, but since the 1950s the majority of the coal production has been from opencast operations. This study evaluates the environmental sustainability of using pit lakes as a closure option for coal mines in South Africa. The major factors that determine the environmental sustainability of a pit lake are the water balance and quality. A fundamental change in thinking and legislation is required for pit lakes to be accepted as an environmentally sustainable closure option for South African coal mines. This will prevent uncontrolled discharge from opencast mining operations and avoid the expense of ongoing water treatment and associated impacts. Designed pit lakes offer an environmentally sustainable closure option for opencast coal mines in South Africa. SWin is the sum of any surface water inputs, which includes runoff and diverted streams
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