NKOMATI ANTHRACITE (PTY) LIMITED - Sentula Mining

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Environmental Impact Assessment Report: Nkomati Anthracite (Pty) Limited, Madadeni Opencast Mining Project Page 72 6.4.6 An i m a l L i f e Normally following cessation of mining activities in the area, animals will begin to migrate back into the area within 2 years. No significant residual impacts on animal life will therefore occur. 6.4.7 S u r f ac e W a t e r 6 . 4 . 7 . 1 S u r f a c e W at e r Q u a n t i t y Following re-establishment of natural runoff patterns by rehabilitation and shaping of the disturbed areas, and removing of the pollution control dam, all diversion trenches and berms, surface water runoff will re-establish. No significant residual impacts are therefore predicted. 6 . 4 . 7 . 2 S u r f a c e W at e r Q u a l i t y Following rehabilitation of the disturbed areas, all sources of dirty water from the mining area will be eliminated. In view of this, no dirty water will be emanating from the mining area. No significant residual impacts are therefore predicted. 6.4.8 G r o u n d w a t e r This phase of the mining operation is the period following the completion of mining and rehabilitation of the Madadeni Mining Area. The following possible impacts were identified at this stage: NKOMATI ANTHRACITE (PTY) LIMITED COMPILED BY GEOVICON ENVIRONMENTAL (PTY) LTD
Environmental Impact Assessment Report: Nkomati Anthracite (Pty) Limited, Madadeni Opencast Mining Project Page 73 Activities Opencast mining Nature of impacts Groundwater Quantity: After closure, the water table will rise in the rehabilitated pits to reinstate equilibrium with the surrounding groundwater systems. It is estimated that the groundwater will recover to 50% of pre-mining levels in about eight years. However, the backfilled opencast areas will have a large hydraulic conductive compared to the pre-mining situation. This will result in a relative flattening of the groundwater table over the extent of the rehabilitated opencast, in contrast to the gradient that existed previously. The end result of this will be a permanent lowering of the groundwater level in the higher topographical area and a rise in lower lying areas. Intuitively, it would be expected that this raise in groundwater could result in decanting of the opencast area. Inspection of the predicted groundwater levels indicates that the post mining groundwater levels in the proposed mining area is not predicted to decant. The reason for this is that this opencast is much smaller and the rise (and decline) of post mining groundwater levels are much less pronounced, as depicted in the above-mentioned Figure 19. Groundwater Quality: Once the normal groundwater flow conditions have been re-instated, polluted water can migrate away from the rehabilitated areas. Although the overburden is mostly intermediate acid forming, some coal and discards normally remain in the pits and the outflow could thus be contaminated, as a worst case scenario. The migration of contaminated water from the mining area has been modelled as described, and the results are presented in Figure 20 to Figure 23 in terms of the extent of the pollution plume 10, 20, 40 and 80 years after the pits has been closed. Experience has shown that the plume stagnates after about 80 years, and no further movement after such time is expected. Within the limitations of the abovementioned assumptions, it can be estimated from these figures that: • Movement of the plume will be mostly downstream in the direction of the non perennial tributaries of the Komati River, as can be expected. • However, the movement of the plume is predicted to be very slow due to the low hydraulic conductivity and the low gradients in the area. • After forty years the front of the plume will have moved about 250 metres. The area where the groundwater might exceed domestic drinking water standards is expected to be about 70 metres from the pits where it will impact on the upper reach of the non perennial tributary of the Komati River. • Eighty years after closure of the opencast, the plume is predicted to impact over a wide area on the non perennial tributaries of the Komati River. By this time the plume would have moved about 250 metres. The results must be viewed with caution as a homogeneous aquifer has been assumed. Heterogeneities in the aquifer are unknown and the effect of this cannot be predicted. Furthermore, no chemical interaction of the sulphate with the minerals in the surrounding bedrock has been assumed. As there must be some interaction and retardation of the plume, it is hoped that this prediction will represent a worstcase scenario. Impact assessment Groundwater Quantity Extent Possibility Significance S H L Groundwater Quality Extent Possibility Significance L M M Mitigation measures A relative big change in groundwater level is expected, Furthermore, some unpredictable negative impacts regarding groundwater levels could occur as a result of aquifer heterogeneities. It is thus important to monitor static groundwater levels on at least a quarterly basis in all boreholes within a zone of two kilometres surrounding the mine to ensure that NKOMATI ANTHRACITE (PTY) LIMITED COMPILED BY GEOVICON ENVIRONMENTAL (PTY) LTD
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