Evaluation of Sources and Options for Possible Clean up of Anthropogenic Mercury Contamination in the Ankobra River Basin in South Western Ghana

doi:10.4236/jep.2011.210149

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Journal of Environmental Protection, 2011, 2, 1295-1302

doi :1 0.4236/ jep.2011. 210149 Published Online December 2011 (http://www.SciRP.org/journal/jep)

1295

Evaluation of Sources and Options for Possible

Clean up of Anthropogenic Mercury

Contamination in the Ankobra River Basin in

South Western Ghana

Thomas Mba Akabzaa, Sandow Mark Yidana*

Department of Earth Science, University of Ghana, Legon, Ghana.

E-mail: *[email protected], *[email protected]

Received October 9th, 20 11; revised November 11th, 2011; accepted December 4th, 2011.

ABSTRACT

The study assesses the spatial distribution and sources of mercury contamination in the Ankobra River Basin in south-

western Ghana and discusses possible remediation options and challenges. Eighty-two (82) samples of water and

streambed sediments from areas of active and historic artisanal mining and historic mine spoil from large-scale mining

were analysed for their total mercury content using cold vapour Atomic Fluorescence Spectrometry (CV-AAS). The

highest Hg concentrations were recorded from historic mine tailings, legacy of large scale mines in the area, which

averaged 795 ppb but ranged from 80 ppb to 2500 ppb. Concentrations in streambed sediments averaged 139 ppb, but

ranged from 63 ppb to 270 ppb. Water, expectedly, gave the lowest Hg concentrations with a mean value of 1.5 ppb, but

ranged from below detection to 8 ppb. Areas worked by artisanal miners and historic tailings dumps at Bondaye and

Prestea recorded the highest mercury values. These high mercury concentration sites constitute potential sources of

major mercury pollution in the area and therefore require major and urgent clean up to mitigate any major health risks.

However, any remediation strategy would require further and detailed study of the contaminated sites and an evalua-

tion of known remediation techniques to achieve maximum results.

Keywords: Ankobra Basin, Mercury Contamination, Clean-Up, Old Tailings, Sediments, Water

1. Introduction

Mercury pollution is a very serious environmental pro-

blem because elevated concentrations are toxic to living

organisms with the degree of toxicity varying with its

chemical form. Organic mercury, particularly methyl mer-

cury is said to be more than 1000 times as toxic as ele-

mental mercury. The effects of mercury on humans are

well documented. It causes damages to the central nerv-

ous system and is especially toxic to the foetus [1,2].

Mercury in the environment comes from both natural

and anthropogenic sources. Naturally, cinnabar (HgS) is

practically the only source of the metal, while the most

important anthropogenic sources of mercury pollution

are from the mining industry [3].

Commercial deposits of cinnabar have not be reported

in Ghana, although stream channel sampling have re-

vealed a promising mercury dispersion zone in the valley

of Tromia in Brong Ahafo region of the country [4]. On

the whole, no significant natural sources of the metal are

known in Ghana as efforts at other areas in the country

have so far not indicated mercury concentrations signifi-

cantly above its crustal abundance of 30 ppb. However,

studies in traditional mining centres in Ghana such as

Obuasi and Tarkwa have reported elevated mercury lev-

els in stream water, sediments, fish, and plants [5,6]. Most

of these studies a ssig ned the activitie s of artisa nal miners,

who use mercury for gold recovery, as the primary sour-

ce of mercury dispersion in Ghana. The present study are a

has over 500 years of artisanal activ ities. Apart from these

artisanal miners, mercury was pervasively used in large-

scale mining in Ghana until the early 1990s when it was

officially prohibited in large-scale mining. During that

period, over 15 large-scale gold mines in the Tarkwa mi-

ning district, many of them abandoned today, used mer-

cury for gold recovery. The area has seen over 100 years

of large-scale gold mining [7]. These mines left on their

Evaluation of Sources and Options for Possible Clean up of Anthropogenic Mercury Contamination 1296 in the Ankobra River Basin in South Western Ghana

trail scattered mercury-laced tailing dumps. For instance,

over hundred years of gold extraction using mercury in

the three underground mines at Prestea, Tuapim and Bon-

daye, about 65 km from Tarkwa, has generated three vast

expanse of tailings dumps, covering a total area of about

30 km2, while similar operations at the Tarkwa under-

ground mine has also ge nerated tailings covering over 16

km2 of land space.

Stud ies ha ve sho wn t hat the A nkob ra Ri ver Ba sin, whic h

takes drainage from these mining anthropogenic activi-

ties, and is indeed itself being mined by both legal and

illegal artisanal miners, has poor abundance of fish and

invertebrates because of heavy metal pollution. Other stu-

dies have reported widespread augmented mercury levels

in food crops such as cassava, cocoyam and in fish in the

area [6].

There has not been any systematic study to assess the

extent of Hg contamination in the area. In fact, the im-

pacts and extent of mercury pollution in Ghana are not

yet understood. This exploratory data clearly shows that

the need to clean up merc ury in the area is a delaye d pri-

ority. This paper, which explores the problem of mercury

pollution in the Ankobra River Basin and its mosaic of

tributaries, has provided data that justifies the urgent call

for the clean up of the contaminated sites. Various clean

up options have b een discussed.

2. The Study Area

The study area is in the Wassa West District of the West-

ern Region of Ghana (Figure 1), and is a major mining

hub in Ghana, defined by several major mining towns

such as Nsuta, Tarkwa, Damang, Abosso, Bogoso, and

Prestea. The area is one of the few remaining corridors of

Ghana’s tropical rain forest that is fast depleting by hu-

man activity, including mining. Annual rainfall data for

the area indicate minimum and maximum values of 1449

mm and 2608 mm respectively, while annual tempera-

tures range from 25˚C to 29 ˚C [8].

The Ankobra River and its mosaic of tributaries (Fig-

ure 2) receive various mine-impacted water from large-

scale gold mines at Prestea, Bogoso, Tarkwa and Da-

mang, as well as small-scale, often illegal mining opera-

tions, within the area.

The gold occurs in lenses of sulphide-bearing quartz

veins, mainly in carbonaceous phyllite, as disseminated

sulphides in the metavolcanics, or as oxidised derivatives

of the two types in the Birimian rocks and in conglomer-

itic horizons as free milling gold in the Tarkwaian. It is

the oxidised ores and the free milling varieties that are

most amenable to dressing with mercury.

3. Materials and Methods

A total of 70 water samples from streams, boreholes, and

hand dug wells; 6 samples each of stream sediment from

channel-bed alluvium and material from old tailings dum-

ps, respectively, were collected and their locations noted

with a Global Positioning System (GPS) and recorded on

a sample location map (Figure 2). Sample collec tion, pre -

servation, storage, preparation and quality control/quality

assurance (QC/QA) protocols followed those outlined by

Figure 1. A map of Ghana showing the study area.

Evaluation of Sources and Options for Possible Clean up of Anthropogenic Mercury Contamination 1297

in the Ankobra River Basin in South Western Ghana

Figure 2. Mercury conta minated sites identified for po ssi ble clean-up planning.

Eppinger et al. [9], APHA [10], Bloom and Fitzgerald

[11] and Barcelona et al. [12]. Water samples were acidi-

fied with pure nitric acid (HNO3) to pH less than 2 to

prevent possible reaction of the dissolved species [13]

and total merc ury deter mined by cold vapour Ato mic Fl uo-

rescence Spectrometry (CV-AAS) and expressed in parts

per billion (ppb) with detection limit of 1 ppb.

Plastic scoop was used to sample stream sediments

and tailings material into p olyethylene sampling bags and

tightly secured. The samples were oven-dried at 40˚C

and sieved to 80 meshes. Total nitric acid extraction was

then applied to this fraction to obtain a leachate, which

was then analysed for Hg using the same cold vapour

Atomic Fluorescence Spectrometry.

Analyses were performed at the Water Research Insti-

tute (WRI) of the Council for Scientific Research (CSIR),

with duplicat es of select samp les anal ysed at the SGS Com-

mercial laboratory and the Ecological Laboratory (Ecolab)

of the University of Ghana for quality assurance and con-

trol purpos es.

4. Results

The results of mercury concentrations in the various me-

dia are presented as summarised descriptive statistics in

Table 1. T he concentration of total mercury in stream se-

diments and mine tailings are presented in Tables 2 and

3, respective ly. Th e sa mpl es e xhibit var iable total Hg mer -

cury concentrations ranging from 33 ppb - 25,000 ppb in

old mine tailing dumps, 63 ppb to 270 pbb in streambed

sediments and from <1 ppb to 8 ppb for water samples

(Table 1).

4.1. Hg in Mine Tailings and Streambed

Sediments

Mine tailings and stream sediments have mercury con-

centrations of over 10 - 100 fold the levels in water. The

highest Hg concentrations were recorded from historic

mine tailings with average concentration of 795 pbb.

Table 1. Summary descripti ve statisti cs of Hg c once ntrations in various media i n ppb.

Sampling Media Mean Media n Standard Deviation Minimum Maximum Count

Water 1.5 1 1.25 <1 8 70

Streambed sediments 139 100 87.65 63 270 6

Old Mine Tailing Dumps 795 72 1154.67 33 2500 6

Evaluation of Sources and Options for Possible Clean up of Anthropogenic Mercury Contamination 1298 in the Ankobra River Basin in South Western Ghana

Table 2. Conce ntration of mercury in vari ous mine s poil and stream sediments .

Sample Description Hg (ppb)

Old mine tailing dumps

PGRTD01 Old Tailings at Prestea, now being mined by PSGL 2500

SSPGRB01 Sediments from stream ta kin g seepa ge from tailings at Bondaye 97

SSGFL01 Soil from rehabilitated waste rock site 43

TSGFL01 Tailings from abandoned underground mine 80

PGRTD02 Old tailings being re-mined by Bondaye 2050

TSGFL04 Ancient tailin gs from Tarkwa und erground mine 33

Streambed Sediments

SSA01 Sediments from the Ankobra river at point where drainage from PSGL Operations enter it 230

TSPGRB01Sediments from stream draining old tailings at Bondaye 270

GMCTS01 Stream sediments from the Kawere stream near Nsuta 103

SSPGRB03 Stream draining ancient tailings dump near Bonda ye 63

SS1 Stream sediments from Bonsa Stream 63

SSTGL-6 Stream sediment s from Bedibewuo stream near Tarkwa 70

Material taken from tailings dumps in Bondaye and Pre-

stea underground mines gave the highest mercury values

of 2025 ppb and 2500 ppb respectively (Table 2) and

area A in Figure 2.

Merc ury le vels i n strea m sedi ments a re ge neral ly lo w-

er than those from the tailings dumps. The highest Hg

values of 270 ppb and 230 ppb were obtained from stream

sedi ments samp les ta ken fro m a tr ibutar y of t he Anko bra

draining the old tailing dump at Bondaye and the Anko-

bra River itself respectively. Augmented mercury con-

centrations ranging from 63 ppb to 103 ppb were ob-

tained from sediment samples at the Bonsa River, Be-

dibewuo stream, and the Kawere, where active artisanal

mining activities are brisk (Table 2).

4.2. Water Samples

Water samples showed the lowest mercury concentra-

tions among the three media sampled, and ranged ge-

nerally from below detection to 8 ppb, with high concen-

trations coincident with areas of small-scale mining ac-

tivity, such as streams in the Bogoso area, including the

Ankobra River. All samples from streams with artisanal

mining activities gave Hg concentrations of at least 1 ppb.

High merc ury val ues wer e a lso obs erved from wa ter fro m

streams that drain the old tailings dumps at Prestea and

Tarkwa, with the highest value of 8 ppb recorded in a

stream that takes drainage fro m the Bonda ye old tailings

dump which gave the very high Hg concentration of 2050

ppb.

4.3. Discussion

The data presented can be considered as one of the first

steps to understanding the sources and problem of mer-

cury contamination in the Ankobra River Basin. Water

exhibited much lower Hg concentrations than tailings

and sediments. Hg concentration in water from many

streams far exceeded the World Health Organization

(WHO) maximum guide limit of 1.0 ppb [14]. These ele-

vated mercury concentrations occur in streams in areas

with intense small-scale mining activity and from strea-

ms carrying drainage from the old tailings dumps with

high Hg levels. The most pervasive contamination of Hg

in stre am water s ge ner all y come fr om t he A nkobr a Ri ver

and a mosaic of tributaries around the Bogoso area where

artisanal mining activities are most profound, par- ticu-

larly around the village of Dumasi and its satellite com-

munities (Figure 2). However, the single highest mer-

cury concentration in water came from a stream draining

old tailings dumps at Bondaye with elevated mercury le-

vels.

These observations are not surprising as mercury is the

chemical used in gold e xtraction by t hese traditional small

miner s. All sa mpl es take n fro m str ea ms whe re t hes e s ma ll

miner s oper ate gave high mer cury val ues. So me of thes e

miners amalgamate their concentrate right in the streams

leading to the spilling of the Hg into the streams (Figure

3). In fact the low level of mercury in even stream waters

with active artisanal mining activities is not surprising.

Hem [15] has pointed out that mercury in water opened

to the atmosphere is like ly to be much lower owing to its

tendency to escape via vaporization. It may also form

chloride and hydroxide complexes depending on pH and

total chloride concentration.

Sediments from streams and old tailings dumps have

Hg concentrations far in excess of the maximum allow-

ble concentration of 10 ppb of Hg in these media that a

Evaluation of Sources and Options for Possible Clean up of Anthropogenic Mercury Contamination 1299

in the Ankobra River Basin in South Western Ghana

Table 3. Su mmary of remediation meth ods.

METHOD DESCRIPTION ADVANTAGES DISADVAN-TAGES SPECIAL REQUIREMENTS

Removal Dredging and pu mping out

contaminated materials Well-tested and effective

Expensive, lengthy process;

disposal sites can leak and

re-release contaminant; significant

disturbance of the environment

Expensiv e equipment; mu st be

monito r e d perio di cal l y and

followed by either treatment

and/or burial and containment

in other location

Physical treatment (i.e. sorting) Good for large q uantities

of sediment (20 - 40

tons/hour)

Doe s not work wi th high silt, clay

content soils/sediments

Therm al treatment res ulting in

volatilization

Mercury compounds are

highly volatile at low

temperature

Causes more atmospheric mercury

pollution

Treatment

Ch emical treatment on site or

off site

Mercury reacts with

other c om pounds and

can be made biologically

unavailable

Adding foreign chemicals into an

ecosystem can be dan g erous when

you aren’t sure of the out come

These methods often a re best

applied of site in contaminated

medium that has been removed

Immobilization

Physical barriers placed on site

to contain the contaminant so it

can no longer spread through

th e ecosystem

Well-tested and effective

High cost, barriers are of

questionable permanence,

unkn own unintended ecological

effects fr o m the destruction of the

benthic ecosystem

Barriers can be top, bottom or

lateral side barriers; sometimes

barrie r s can be nat ur al and not

man made

Microbial Act ion Using microbes that can

demethylate mercury to clean

contaminated mediums

Effective in sludges,

wastewater and

controlled environments

like the lab oratory

Not proven for on site remediation Forms the basis of

phytoremediation

Phytoremediation

Various techniques using plants

to remove mercury from the

environment or immobilizing it

within th e environment;

methods include degradation,

extraction, containment or a

combo of all three

Cost effective, less

intrusive than other

meth ods, pollution

captured can be recycled

and r eused in stead of

mining more

Plants grow slow and results take a

while, mercury captured in the

plant may be available to wildlife

feeding on the plant, not well

tested, envir onment must be

suitable t o the acc umula ting plant

Best for sites with low to

medium levels of

contamination

Water Quality

Management

Manipulating the water quality

such as oxygen content or pH to

ensure methyl mercury

prod uction will not occ ur

Cost effective, less

intrusive, not highly

technical

Mani p ul a tions ne e d to be

monitored, and may likely need

manipulati on often; ma y disrupt

some ecosy funcstem tioning

Mos t easily implemented by

current water managing

agencies

Source: (Adopted from Fuller [3]).

would require immediate remedial action [16]. Mercury

concentrations in these media are about 5 to more than

500 times the maximum allowable limits. The results de-

monstrate that Hg use by artisanal miners and Hg in old

tailings dumps of large scale mining activities constitute

the two major anthropogenic sources of mercury con-

tamination in the area.

The two extremely high anomalous Hg values in the

Evaluation of Sources and Options for Possible Clean up of Anthropogenic Mercury Contamination 1300 in the Ankobra River Basin in South Western Ghana

Figure 3. Artisanal miners wining gold from the bed of the

Bonsa River using mercury.

Bondaye and Preseta mine ancient tailings (Area A in

Figure 2) are related to historic Hg use in gold process-

ing. From the inception of large-scale mining in the area

from 1897 to the early 1990s, Hg was the chemical of

choice for gold extraction b y all co mmercial gold miners

in the area. Small-scale miners are presently reworking

the tailings dumps illegally, sending uncontrolled sedi-

ments and leachate containing Hg into the Ankobra and

its tributaries.

4.4. Containing Widespread Contamination in

the Bas in

The relatively low level of Hg concentration in water-

compared to concentration in sediments and mine tail-

ings is not surprising. The results are indeed consistent

with observation from studies elsewhere, where it has

long been recognised that Hg is more efficiently trans-

ferred from water to bottom sediments [17-19]. Such

rapid transfer is possibly through mechanisms such as

sorption on suspended or bed load material, clay and

organic material [20]. This is supported by the study of

Hg speciation in bottom sediments of water reservoirs,

which has shown that physicall y sorbed admixture is the

predominant form of Hg occurrence in bottom sediments

[17]. Such forms of Hg exhibit weak bonds and can eas-

ily be extracted from the sediments under conditions of

rainstorms resulting in seasonal flushing of doses of Hg

into water [20]. The high Hg co ncentrations in strea mbed

alluvium and old mine tailings in the area constitute ma-

jor sources of Hg contamination in surface waters.

Varekam et al. [18] have pointed out that such high Hg

contaminant sources present serious environmental prob-

lems as erosion of soils with high mercur y loading bring s

these mercury bearing particles into the aquatic system.

Earlier studies have indicated augmented mercury con-

centrations in fish and plant species from the study area

[6]. One possible pathway for fish and plant uptake of Hg

would be transfer fro m sediments through methyla- tion,

which ensures a more bioavailable form of Hg [21]. It is

also known that invertebrates that ingest large quan- ti-

ties of sediments may accumulate higher concentrations

of Hg toxin than species that ingest leaf material [21].

The dangers posed by high mercury concentrations in

sediments have equally been echoed by Hem [15] who

pointed out that mercury ingested from sediments gets

concentrated in the successive biological species along

aquatic food chains so that fish that live in mildly con-

tami nated envir on ment ma y conta in too muc h merc ury to

be used safely for food.

These mercury-laced dumps and sediments pose real

threat to the general environment in the area, as these

sources are capable of re-supplying mobile mercury to

streams in the area during rainstorms. Currently the old

tailings dumps have been evaluated to contain consider-

able gold resources, and ever since this disclosure, thou-

sands of illegal small-scale miners have besieged these

dumps. Their activities are sending considerable tailings

into the drainage system.

There is the urgent need to put intervention measures

in place to clean up the area to prevent widespread mer-

cury contamination in the wider Ankobra basin that ser-

ves numerous communities. Any efforts to contain the

contamination and possibly carry out remediation of

mercury endemic sites would require careful planning. In

the first place, it would require either curtailing the work

of small-scale miners using mercury or providing the

miners with technical support and education to use mer-

cury retorts. However these efforts at ensuring that these

miners use retorts in the past has been quite fruitless.

4.5. Options for Remediation and Challenges

Mercury pollution is an acclaimed human health hazard

and the degree of its toxicity is dependant on its speci-

ation. When converted to methyl mercury by bacteria in

stream water and sediments, its toxicity could be aug-

mented up to a thousand fold that of elemental mercury

due to its facilitated ability to cross cell membranes and

interact in biological systems [1]. Consequently, reme-

diation of mercury contaminated sites, where they are

located close or have the potential to impact watersheds,

is gaining urgent priority in water quality management

globally.

The impacts and extent of mercur y pollution in Gha na

are not fully understood. Remediation strategy for these

contaminated sites would be challenging, as remediation

can only be effective if there is a thorough understanding

of the spatial scale of the pollution and the chemical

forms of the mercury. This exploratory work has pro-

Evaluation of Sources and Options for Possible Clean up of Anthropogenic Mercury Contamination 1301

in the Ankobra River Basin in South Western Ghana

vided useful information on the sources and scale of mer-

cury contamination in the study area. The contaminated

sites are sho wn in Figure 3 as A, B, C, D, and E. Sites A

and C are ancient tailings dumps at Prestea and Tarkwa,

respectively. Site B is the Ankobra River near Dumasi

while sites D and E are streams being worked by small

scale miners.

However, the information cannot be said to be ade-

quate for full-scale remediation of the problem as this

would require thorough understanding of the scale of po-

llution, the chemical forms of the mercury in the conta-

minated media, the range of mercury-relevant sites pa-

rameters, that usually vary from location to location due

to changes in temperature, pH, flow rate, solvent types,

etc. [3].

The current levels of data is therefore limited for any

full scale clean up measure, but provide the basis for fur-

ther work to provide the needed information for cleaning

the contaminated sites. According to the USEPA [19] six

main categories of remediation techniques have been wi-

dely used-removal of the contaminated media; treatment

of the medium, immobilisation of the contaminant, mi-

crobial remediation, phytoremediaiton and water quality

management. The merits and demerits of each of these

techniques have been summ arised by Ful l er [3] (Table 3).

Any strategy to deco nta minate the ide nti fied site s would

require an evaluation of these techniques on the basis of

their potential to succeed. Since the Ankobra Basin is ex-

tensive, it will probably require multiple re mediation me-

thods at the different sites. This will probably require de-

tailed individualised response plans that require more

detailed information for the different sites in the basin.

Such a remediation strategy is necessary and urgently

needed to clean the Ankobra River and its tributaries and

the scattered mercury-laced old tailings dumps identified

in this study to prevent a pluming ecological disaster in

the area.

4.6. Securing Pr oc essing A lt er nati ve s t o Me rcury

in the Artisanal Mining Sector

The remediation must address mercury sinks and pro-

duction pathways as the most critical targets for cleaning.

In this particular study area, the challenges presented by

contaminated old tailings site could be overcome once

barriers are erected to prevent dispersal of material from

the contaminated tailings while remediation takes place.

However, it might be more challenging to address this

problem with respect to areas of small scale miners, par-

ticularly, illegal miners. These migratory miners serve as

constant supply of fresh mercury to streams in the area

and unless their activities are curtailed, any remediation

measure would be a wasteful exercise.

It is clear that efforts to stop the operations of these ar-

tisanal miners will be a fruitless venture, under current

constrained opportunities for alternative sources of live-

lihood in the country. The other option is to examine and

possibly implement alternative processing technologies

other than mercury. Alternatives to mercury amalgama-

tion such as, gravity concentration, cyanidation and froth

flotation have successfully replaced mercury in the large-

scale mining sector. However the adoption of such tech-

nologies to the artisanal mining sector would equally be

as problematic as mercury for several reasons including

cost considerations and capacity constraints. Gravity con-

centration presents a better opportunity for success.

However the nature of occurrence of the gold in typical

artisanal work sites in Ghana makes the application of

gravity concentration unattractive. Most of the gold is too

fine and gr avi t y co nc e ntr a tio n would not b e a n effe c - tive

technology.

These problems not withstanding, it is an important

challenge for efforts to be geared towards the develop-

ment of alternative processing technology for the arti-

sanal mining sector. Until an alternative to mercury is

found, any efforts any to clean up contaminated sites might

only constitut e a tempor a ry solut ion.

5. Conclusions and Recommendations

The application of mercury in gold ore dressing in small-

scale mining and historic application of mercury in gold

extraction by large-scale miners have resulted in con-

tamination of portions of the Ankobra Basin, including

scattered mercury-laced old tailings dumps at Bondaye,

Prestea and Tarkwa. These mercury contaminated tai-

lings dumps and streambed alluvium present serious en-

vironmental challenges as these serve as reservoirs for

the supply of Hg into water bodies through erosion. The

regulatory authorities would have to disco urage the direct

discharge of untreated mine drainage into streams, par-

ticularly the Bonsa and Ankobra Rivers, which serve as

sources of domestic water supplies for the area. Urgent

measures are needed to clean up delineated mercury con-

tamination in the area. However, this would require a

more detailed study of the sites and a thorough evalua-

tion of available remediation options and their effective-

ness.

Since small-scale mining is an unavoidable livelihood

activity, efforts should be made to explore the use of

mercury free extraction technology in the sector.

Efforts must be made to develop alternative processing

technologies to replace mercury in the artisanal mining

sector.

6. Acknowledgements

The authors wish to express our sincere gratitude to the

Evaluation of Sources and Options for Possible Clean up of Anthropogenic Mercury Contamination

in the Ankobra River Basin in South Western Ghana

1302

DANIDA-ENRECA Hydrogeological Project for provi-

ding the financial support for this study.

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