The hydrochemistry of water resources in selected mining communities in Tarkwa

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Abstract

Tarkwa is one of the most heavily mined localities in Ghana. Mining activities are associated with the release of toxic chemicals into the environment which pollute water resources in mining communities within the catchment of mines. The study was undertaken in communities within the catchment of three mining companies in Tarkwa to find out the impact of mining on the water quality of these settlements. The research was conducted by taken water samples of both surface and groundwater within these communities for laboratory analysis using Instrumental Neutron Activation Analysis (INAA) and Atomic Absorption Spectrophotometer (AAS) to determine the concentration levels of elements in the water.

The analysis showed that, concentration levels of certain elements namely, iron, cadmium, copper, cyanide, arsenic and zinc were beyond allowable limits of World Health Organization (WHO), Ghana Standards Board (GSB) and Ghana Water Company (GWC) guidelines for drinking water in certain samples confirming the communities' perception that, their water resources are polluted owing to the mining activities. Excess levels of iron and arsenic were found in 65% of samples, cadmium 23%, copper 58%, cyanide 12%, and zinc 42%. Concentration levels of 3.75 mg/l and 1.76 mg/l of iron and arsenic were detected in certain samples. Maximum concentration level for cadmium was 0.37 mg/l, copper 7.45 mg/l, cyanide 8 mg/l and zinc 10.2 mg/l.

Toxicity level of other elements such as mercury, lead, chloride, nitrates and others was low. Except mercury and cyanide whose presence in the environment is introduced by mining activities, the presence of other elements in water resources is mobilized from weathered rocks of the underlying geology.

Highlights

► A study to determine the impact of mining on water quality. ► Used Instrumental Neutron Activation and Atomic Absorption Spectrophotometer analysis. ► Concentration levels of certain elements were high. ► Mining activities influence the levels of elements in water.

Introduction

Ghana is heavily mineralized due to the abundance of geological formations of proterozoic rocks of the Birimian and Tarkwaian in the country especially within the south western part (Kesse, 1985). These rocks are rich in gold deposits which have been mined since the colonial times till today. The Tarkwa-Nseum Municipality in the Western Region, which was formerly part of the Wassa West District now split into Tarkwa-Nsuem Municipality and the Prestea-Huni Valley District has been one of the mining enclaves in this country. Out of 16 multinational companies in Ghana, eight are located in this mining enclave, and three in Tarkwa township. The three companies which are the focus of the study are Gold Fields Ghana Ltd (GGL), Anglogold Ashanti (AGA) – Iduapriem Mine and Ghana Manganese Company (GMC) – Nsuta.

Despite being a major export earner for the nation, gold productivity declined from the 1960s till the mid 1980s when the Government adopted Economic Recovery Programme (ERP) to revamp the economy. New minerals and mining laws such as Minerals and Mining Law (PNDCL 153) were enacted in 1986 in an effort to reverse the decline in the mining industry. The law put in place a number of concessions for mining investors and also provisions were made for generous capital allowances and reduced income taxes (http://www.oxfamamerica.org). As a result of the attractive investment climate, mineral production and contribution to gross foreign earnings of the economy have been quite significant. The ramifications of this historical record of mining have not only been that of economic prosperity but also of environmental pollution, land appropriation, displacement of people from their lands, environmental devastation and marginalization and oppression of people belonging to the lower economic sectors of the society particularly women.

The industry has been associated with serious environmental and health impacts. Mining communities have been victims of air and water pollution as well as other forms of environmental degradation resulting from mining operations. In Tarkwa the principal environmental problems caused by the mining industry both large and small scale include the release of heavy metals and hazardous chemicals into the environment, deforestation which leads to land degradation, and physical hazards which threaten the health and safety of people at mine sites and communities. The release of heavy metals and hazardous chemicals into the environment is generated mainly through ore processing and the discharge of mine waste. In Tarkwa the amalgamation process of gold recovery is heavily used by small scale miners and this introduces mercury into the environment. Cyanide, a toxic chemical is also use in the processing of gold ore by large mining companies. Alkaline cyanide solution is used to dissolve gold from its ore and precipitated from the cyanide solution by using powdered zinc metal. If the waste water is not properly managed it contaminates the environment. This can be hazardous to human health, animal and aquatic life both in toxicity and bioavailability. Hayford et al. (2008), found levels of mercury in soils at Teberebe and the University of Mines and Technology campus to be higher than permitted levels. In addition, the concentration levels of heavy metals (e.g. arsenic, mercury, zinc, copper etc.) in food stuffs such as cassava and plantain were higher than proposed limits by FAO, Expert Committee on Food Additives of WHO and EPA-Ghana (Hayford et al., 2008). Also according to Akabzaa et al. (2009) in a study conducted in Prestea and Tarkwa, the average concentration levels of several metals in the mine-impacted streams are well above the maximum allowable limits in drinking water established by WHO and EPA-Ghana. Metals of particular concern included Ni, Fe, Cu, As, Hg and Mn. Akabzaa, 2000, Asklund and Eldvall, 2005 have also detected higher metal content than WHO guidelines in the water resources of mining communities of the Wassa West District. For instance NO3-, Al, Fe, Mn, and As were higher in 17 wells that serve as drinking water for communities (Asklund and Eldvall, 2005).

Apart from these water geochemical studies, there have been direct pollutions of water resources from spillages of the mines. For instance in 1996 a cyanide spillage into the Angonaben stream which is a tributary of the Bonsa River occurred within the concession of the Teberebe Goldfields now Anglogold Ashanti – Iduapriem. An enormous amount of gold pregnant cyanide (36000 m3) solution with cyanide concentration of 8–100 ppm was discharged into the river and nine villages along the banks of the river were affected (Akabzaa, 2000, Botchie et al., 2008). These contaminations weaken the ability of streams, rivers and other water bodies to support aquatic life and aquatic biodiversity. Besides, the people are exposed to health risks since they depend on these foods and resources for livelihood. The national environmental policies have not been able to adequately address the challenges of environmental management in the mines in Ghana. In view of these environmental problems confronting mining communities in Ghana, this study was conducted to find out the impact of mining on the water quality in selected communities of mining companies in Tarkwa and its surrounding settlements to ascertain the veracity of the problem.

Section snippets

Geographical location and physical characteristics of the study area

The study is undertaken in communities around three mining companies namely; Gold Fields Ghana Ltd (GGL) - Tarkwa, Anglogold Ashanti – Iduapriem (AGA) and Ghana Manganese Company Ltd – Nsuta (GMC) located in Tarkwa and its surrounding towns (Fig. 1). Tarkwa is the capital of the newly created district; Tarkwa-Nsuaem Municipal Assembly. This administrative area was part of the Wassa West District Assembly which has now been split into the Tarkwa-Nsuaem Municipal Assembly and Prestea-Huni Valley

Results

Results of samples of water from boreholes in Abekoase, Huniso and Rivers Essumang and Huni which fall within Gold Fields Ghana Ltd concession are presented in Table 3, Table 4 below. All the boreholes that were in good condition at Abekoase had water and they were thus sampled, however at Huniso only two boreholes out of five had water and the yield was very low. As a result the community was forced to use water from Huni River.

As shown in Table 3, Table 4, the pH of both ground and surface

Discussion

Naturally, both ground water and surface water resources contain mineral ions which are dissolved from rocks as the water travels along mineral surfaces in the soil. Thus depending on the extent of exposure of these minerals, they could be in higher concentrations or vice versa. Some of these mineral elements are needed for human growth (Harter, 2003), however beyond certain limits, they become toxic to humans. Consequently, the levels of these elements in water resources are of great concern.

Conclusions

Results of water chemistry show differentials in concentration of elements in both ground and surface water. Water quality analysis affirms the perception of residents that, their water resources are polluted. Concentration levels of trace elements such as iron, cadmium, copper, cyanide, arsenic and zinc were found to exceed WHO and GSB/GWC guidelines for drinking water in certain water resources in all the communities particularly in the surface water bodies. Geology is the primary reason

John Manyimadin Kusimi is a Lecturer in the Department of Geography and Resource Development in the University of Ghana and currently pursuing a PhD Programme in the Department. He holds a BA and MPhil Degrees in Geography and Resource Development from the University of Ghana and an MSc in Environmental Engineering from the Royal Institute of Technology, Stockholm. His research areas include coastal geomorphology (coastal erosion, coastal pollution and management, adaption and mitigation

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John Manyimadin Kusimi is a Lecturer in the Department of Geography and Resource Development in the University of Ghana and currently pursuing a PhD Programme in the Department. He holds a BA and MPhil Degrees in Geography and Resource Development from the University of Ghana and an MSc in Environmental Engineering from the Royal Institute of Technology, Stockholm. His research areas include coastal geomorphology (coastal erosion, coastal pollution and management, adaption and mitigation strategies of coastal communities to climate change), Fluvial geomorphology (river basin management, river sedimentation), surface and groundwater contamination.

Bertha Ansaah Kusimi is a geologist by profession and a graduate of the Environmental Science Programme in the University of Ghana. She holds a BSc Degree in Geology and an MPhil degree in Environmental Science from the University of Ghana. As a Geologist, she is very much interested in researching into environmental issues arising from mining. These include socio-economic impacts of mining, air and water pollution and environmental regulations governing the mining industry.

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