The inadequate management of mining activity waste has historically caused water pollution and threatened the water supply available to communities. Open cast mining not only results in chemical waste from the ore processing but also from the stripping of topsoil, mine effluents,and ore stockpiling. In the water-scarce Ishiagu mining area of southeastern Nigeria, the water supply has been severely compromised by over 40 years of intensive zinc and lead open cast mining. Ezekwe et al. investigated the occurrence of groundwater, flow patterns, and water well and geological data in an attempt to assess the contamination threat as well as to create a basin-wide model in the Ishiagu area. The researchers also identified the recharge areas (the areas where groundwater was replenished by precipitation) and discharge areas (the areas where groundwater flowed to the surface). The researchers found that the basin had a deep and shallow water circulation which was distributing the contaminants, but the effects of mining could be mitigated by the decontamination of polluted water and soil, the treatment of mine effluents, and the implementation of environmental guidelines in Nigeria. The authors proposed that their basin model could be used for groundwater assessment and for pollution and contaminant management in other mining countries.—Monkgogi Otlhogile
Ezekwe I C., Odubo E., Chima G N., Onwuchekwa I S., 2012. Groundwater occurrence and flow patterns in the Ishiagu mining area of southeastern Nigeria. Frontiers of Earth Science published ahead of print January 5, 2012, DOI: 10.1007/s11707-011-0203-0.
Ezekwe et al. collected samples from 26 groundwater sources and established the altitude and location of each source in the Ishiagu area. The locations were obtained using a handheld GPS while a dip meter determined the water level and depth. The water samples from each source were then analyzed for metal content by atomic absorption spectrophotometry. The groundwater data in conjunction with well profiles, which provided geologic data, allowed the authors to create groundwater flow patterns and to locate recharge and discharge areas in the Ishiagu area. Well and geological information was used to constrain and validate the groundwater flow model. The groundwater samples underwent a statistical analysis called cluster analysis that allowed the authors to group the water samples in terms of the similarities and to differentiate those not as similar. The authors used cluster analysis to further confine and validate their flow model. The groundwater flow, contour, and profiles were then displayed using computer programs such as AutoCAD, which gave the authors digital access to the data. Other pertinent information such as historical water levels, land geography and geology, and water use were obtained through visual observation, photography and localized interviews.
Ezekwe et al. found that the groundwater occurrences in the study area ranged between 1.2 m and 9 m and fluctuated for each site between the rainy and wet season by 1 m on average. Most of the sample sites had varying depths of both coarse grained sandstone and slate shale. At most of the sample sites the groundwater was located in-between these layers. The researchers located five groundwater recharge areas and noted that these areas were elevated by 366 m, 130 m, and 110 m and had considerable sandstone which allowed the easy infiltration of surface water from precipitation. They then located five discharge areas including the Ishiagu triangle and the Ivo River. The scientists concluded that the basin had a shallow, localized groundwater circulatory system—which was highly affected by precipitation and infiltration—as well as a more regional, deep water system. The types of groundwater circulation and the location of discharge and recharge areas allowed the authors to create an accurate model of groundwater flow in the basin and therefore accurately follow the transport of contaminants in groundwater.
The groundwater flow pattern and groundwater analysis pointed to high groundwater pollution in the Ivo River, the Ishiagu Triangle, and the Ndi-Ugbugbor areas. In particular, the high concentrations of calcium, magnesium, sulfate, and chloride in the Ndi-Ugbugbor areas prove that the polluted recharge from the Lokpaukwu and Ihetutu mines is finding its way into the groundwater as a result of regional and local flow patterns. This example holds true for the other areas with groundwater pollution, specifically those affected by lead and zinc mines as lead and zinc mineralization extends further up the basin to recharge sites because of flow patterns. The cluster analysis of the groundwater samples produced three groups of groundwater in the Ishiagu mining area; recharge areas which had been unaffected by mine effluents, areas affected by polluted recharge caused by mining activities, and samples taken from the mining sites. These clusters allowed the scientists to validate their groundwater flow model as the clusters gave definite answers regarding the pollution status of various areas which had been predicted by the model.
The authors’ basin-wide model could be used to investigate the groundwater of mining countries to allow proper management of mining waste and water pollution control. However in the Ishiagu area, in order to remedy the situation, the authors suggest that the polluted soil and water sources be decontaminated using chemical and biological remediation methods. The authors also recommend the treatment of any mine effluents prior to discharge into the environment. They suggest that the building of topsoil walls would be effective in stalling the discharge of untreated mine effluents from active and abandoned mines into water sources. Most importantly, the authors believe the formation of new laws and the strict enforcement of environmental guidelines for effluent management will be crucial in mitigating the water pollution in the Ishigua region. — Monkgogi B Otlhogile