DETERMINATION OF ARSENIC CONCENTRATION AND OTHER PHYSICOCHEMICAL PARAMETERS IN GROUNDWATER

KWAME NKRUMAH UNIVERSITY OF SCIENCE AND TECHNOLOGY,

KUMASI

COLLEGE OF SCIENCE

DEPARTMENT OF CHEMISTRY

DETERMINATION OF ARSENIC CONCENTRATION AND OTHERPHYSICOCHEMICAL PARAMETERS IN GROUNDWATER AT OBUASI

A PROJECT SUBMITTED TO THE DEPARTMENT OF CHEMISTRY, COLLEGEOF SCIENCE: KNUST-KUMASI IN PARTIAL FULFULMENT OF THEREQUIREMENTS FOR THE AWARD OF BSc. DEGREE IN CHEMISTRY

BY:

OSEI ATTA ISAAC

SUPERVISOR: MR. JOSEPH APAU

MAY, 2014

KWAME NKRUMAH UNIVERSITY OF SCIENCE AND TECHNOLOGY,

KUMASI

COLLEGE OF SCIENCE

DEPARTMENT OF CHEMISTRY

DETERMINATION OF ARSENIC CONCENTRATION AND OTHERPHYSICOCHEMICAL PARAMETERS IN GROUNDWATER AT OBUASI

A PROJECT SUBMITTED TO THE DEPARTMENT OF CHEMISTRY, COLLEGEOF SCIENCE: KNUST-KUMASI IN PARTIAL FULFULMENT OF THEREQUIREMENTS FOR THE AWARD OF BSc. DEGREE IN CHEMISTRY

BY:

DANSO NINA

OSEI ATTA ISAAC

OKLU KOMLA NOVISI

SUPERVISOR: MR. JOSEPH APAU

MAY, 2014

DECLARATIONWe hereby solemnly declare that this work is based on the

study undertaken by us. It represents the genuine records of

the task we set ourselves to accomplish. To the best of our

knowledge, no part of it has been previously presented for

award in any institution of higher learning.

………………………….. ……………………………..

Danso Nina Date

………………………….. ……………………………..

Osei Atta Isaac Date

………………………….. ……………………………..

Oklu Komla Novisi Date

………………………….. ……………………………..

Mr. Joseph Apau Date

i

(Supervisor)

ii

ACKNOWLEDGEMENTWe thank the Almighty God for how far He has brought us and

for the grace and strength to go through this project

successfully.

We say a big ‘Thank you’ to everyone who supported us in one

way or the other to accomplish this project. Our immense

gratitude however goes to Mr. Theophilus Nicholas Bruce

(Environmental Department, AGA-Obuasi), Mr. Charles Amoako

(Director of Testing Division, GSA), John and Malik

(Metallic laboratory, GSA) and finally Steven Bandoh and

Henry Jumpah (Chemistry Department, KNUST).

Our sincere appreciation goes to Mr. Joseph Apau, our

supervisor for his guidance and for spending time off his

busy schedule to attend to our project.

God bless you all.

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DEDICATIONWe dedicate this project to God Almighty and also to our

families especially, Mr. and Mrs. Danso, Mr. Timothy Oklu

and Mrs. Christiana Oklu, and then finally Mr. Anane

Thompson, for their love, support and encouragement

throughout all these years.

iv

SUPERVISOR’S APPROVAL“DETERMINATION OF ARSENIC CONCENTRATION AND OTHER

PHYSICOCHEMICAL PARAMETERS IN GROUNDWATER AT OBUASI”

I do hereby promulgate that, Danso Nina, Osei Atta Isaac and

Oklu Komla Novisi have been the genuine writers of this

project work and have written it all by themselves. I

supervised this research. I duly approve of their work.

Supervisor’s Name Mr. Joseph Apau

Signature ..…………………….

Date ....……………………

v

ABREVIATIONS

OEPA – (Ohio Environmental Protection Agency)

DEQ – (Department of Environmental Quality, Wyoming)

WHO – (World Health Organisation)

RPD – (Relative Percentage Difference)

EPA – (Environmental Protection Agency)

vi

ABSTRACT

Arsenic is widely distributed in nature. Arsenic toxicity is

a global health problem affecting many millions of

people.Obuasi, considering its geology has arsenopyrites

occurring there naturally hence it is important to know the

background Arsenic concentrations especially in groundwater.

Ten borehole samples were selected for the study. Arsenic

concentrations together with some physico-chemical water

parameters were determined. The results obtained are as

follows: pH, 3.80 – 5.67; Total Dissolved Solids (TDS),

21.94 – 320.45mg/l; Temperature, 26.80 – 29.00˚C;

Conductivity, 31.91 – 459.15µS/cm; Turbidity, 0.21 –

2.58NTU; Total Hardness, 2.79 – 132.06mg/l; Alkalinity, 10 –

140mg/l; F-, 1.663 – 5.152mg/l; Cl-, 10.039 – 85.279mg/l;

NO3-, 3.754 – 59.414mg/l; SO42-, 3.692 – 21.709mg/l; Na,

1.243 – 54.176mg/l; K, 0.203 – 12.045mg/l; Ca, 0.858 –

11.701mg/l; Mg, 25.561 – 72.038mg/l, As, 0.12055 –

2.4367µg/l. Two methods were used to determine the

background arsenic concentrations, the DEQ and the OEPA

vii

methods. The estimated arsenic concentrations obtained from

the methods were 0.533875µg/l and 0.550425µg/l respectively.

viii

CHAPTER ONE

1.0 INTRODUCTION

1.1 ArsenicThe semi-metal Arsenic is a naturally occurring element

found in small quantities practically everywhere, in soil,

water, and air. Arsenic appears in three allotropic forms:

yellow, black and grey; the stable form is a silver-gray,

brittle crystalline solid. It tarnishes rapidly in air, and

at high temperatures burns forming a white cloud of arsenic

trioxide. Arsenic is a member of group Va of the periodic

table, which combines readily with many elements. The

metallic form is brittle, tarnishes and when heated it

rapidly oxidizes to arsenic trioxide, which has a garlic

odor. The non metallic form is less reactive but will

dissolve when heated with strong oxidizing acids and alkalis

(Lenntech, 2014).There are series of arsenic compounds and

these have different properties (Smedley & Kinniburgh,

2002). Arsenic occurs in natural watersmainly as arsenite

[As(III)], arsenate [As(V)], monomethylarsonic acid (MMA,

1

oxidation stateV), or dimethylarsinic acid (DMA, oxidation

state V). (Shraimet al., 2002; Hung et al., 2004).

In nature arsenic occurs in air,soil, water, rocks, plants,

and animals. Natural activities suchas volcanic eruption,

rocks erosion and forest fires, can release arsenic to the

environment.Anthropogenic activities such as farming,

mining, uses of fossil fuels, pulp and paper production,

cement manufacturing and others, contribute as additional

sources of arsenic in the environment.

The major sources of arsenic in natural waters include

arsenic minerals, together with aoncewidespread use of

arsenic in pigments, insecticides and herbicides. About 70%

of all arsenicuses are in pesticides.Many studies document

the adverse health effects in humans exposed to inorganic

arsenic compounds (Panagiotaras et al., 2012).

1.2 Applications of ArsenicArsenic and its compounds are in wood preservatives, glass

manufacture, electronics, catalysts, alloys, feed additives

and veterinary chemicals. It also finds its use in the

semiconductor gallium arsenade, which has the ability to2

convert electric current to laser light. Arsine gas AsH3,

has become an important dopant gas in the microchip

industry, although it requires strict guidelines regarding

its use because it is extremely toxic (Lenntech B. V, 1998-

2014).

1.3 Toxicity of ArsenicArsenic toxicity is a global health problem affecting many

millions of people. Contamination is caused by arsenic from

natural geological sources leaching into aquifers,

contaminating drinking water and may also occur from mining

and other industrial processes. Arsenic is present as a

contaminant in many traditional remedies. Arsenic is a well

documented human carcinogen affecting numerous

organs.Absorption occurs predominantly from ingestion from

the small intestine, though minimal absorption occurs from

skin contact and inhalation. Arsenic exerts its toxicity by

inactivating up to 200 enzymes, especially those involved in

cellular energy pathways and DNA synthesis and repair

(Ratnaike R. 2003).

3

Among the arsenic species that are present in natural

waters, inorganicarsenicals [As(III) and As(V)] are

considered as the most toxic species followed by MMA andDMA

(Hughes, 2002; Shraimet al., 2003). Inorganic arsenic

compounds, e.g. arsenic trioxide (As2O3), are reactive and

may have veryharmful effects on the body

(Smedley&Kinniburgh, 2002).Inorganic arsenicals have been

classified as group-Icarcinogens and were included in the

US-EPA “list of priority pollutants” (Shraim et al,2008 ).

Acute or immediate symptoms of a toxic level of exposure to

arsenic may include Vomiting, Abdominal pain, Diarrhea, Dark

urine (termed black water urine), Dehydration, Cardiac

problems, Hemolysis (destruction of red blood cells),

Vertigo, Delirium, Shock, Death. Long-term exposures to

arsenic lower than toxic levels can lead to skin changes

(darkening or discoloration, redness, swelling and

hyperkeratosis (skin bumps that resemble corns or warts).

Whitish lines (Mees' lines) may appear in the fingernails.

Both sensory and motor nerve defects can develop.

Additionally, liver and kidney function may be affected

4

(Davis C.P. 2013) .Due to the toxicity of inorganic

arsenicals, many countries have lowered theirarsenic

drinking water guidelines to less than or equal to 10 μg/L

[e.g. Australia, WHO, andUSEPA] (Shraimet al., 2000). There are

no evidence based treatment regimens to treat chronic

arsenic poisoning but antioxidants have been advocated,

though benefit is not proven. The focus of management is to

reduce arsenic ingestion from drinking water and there is

increasing emphasis on using alternative supplies of water

(Ratnaike R. 2003).In natural conditions there is a much

higher probabilityof elevated arsenic concentrations in

groundwater than in surface water (Smedley&Kinniburgh,

2002).

1.4 Arsenic in ObuasiThe area around the Obuasi mining operation is known for its

naturally high level of arsenic inbedrock and soil, which

originates from minerals such as arsenopyrite (FeAsS).

Arsenic seeps naturally intothe water of the area. Moreover,

long-time mining activity has caused large amounts ofarsenic

to be released, adding to the current pollution. Obuasi ore5

occasionally contains very largeamounts of arsenic

(Ahmad&Carboo, 2000). The crushing and grinding of ore, as

well as the processing and exposure of oreto water result in

sharply increased amounts of arsenic in water. For decades

therehas been information available about very high arsenic

pollution levels at Obuasi (Amase, S.K. 1975; Amonoo-Neizer,

et al, 1996; Smedley, P.L. 1996).The Anglogold Ashanti

company is aware of concerns raised by local residents and

NGO’s in respect to elevated levels of arsenic in and around

Obuasi. One of the main significant areas of concern is the

safe disposal of the tailings. When the host rock is crushed

to release the gold, arsenic together with the base metals

may be released into the tailings or waste residues. As a

short term remediation step, a lined storage dam has been

constructed where tailings are moved, stored and gradually

disposed off, by blending. This controls arsenic

contamination by their mining activities but yet still, high

levels of arsenic are recorded. It is unclear whether all

existing arsenic levels are naturally occurring or due to

mining activities (AGA, 2006).

6

1.5 PROBLEM STATEMENTArsenic is widely distributed in nature (Smedley et al.,

1996). Various surveys have been conducted which have served

to quantify levels of arsenic in different environments and

have provided an understanding of the natural and the

anthropogenic sources of arsenic concentration in drinking

water (Smedley and Kinniburgh, 2002). The main source of

arsenic exposure for the general population is ingestion of

surface and groundwater sources (Smedley et al., 1996).

Concentrations of arsenic in groundwater reach up to 64µgl-

1. The main sources are mine pollution and by natural

deposits like arsenopyrites(FeAsS) (Smedley, et al,

1996).Obuasi, considering its geography has arsenopyrites

occurring there naturally. Therefore, it is unknown as to

how much arsenic occurs in their groundwater naturally and

it is however not clear whether a groundwater source has

been polluted from mining activities or by natural deposits

(AGA, 2006). This can be solved by estimating a background

concentration of the Arsenic in groundwater at Obuasi.7

1.6 JUSTIFICATIONBackground concentration is the amount of naturally

occurring chemical substances derived from natural processes

in the environment as close as possible to natural

conditions, exclusive of specific anthropogenic activities

or sources. The source of these naturally occurring chemical

substances is typically from processes such as erosion and

dissolution of mineral deposits and they are found in

groundwater at varying concentration (EPA, 2008). Therefore,

background analyses are essential for distinguishing between

groundwater that has been impacted by natural processes and

groundwater that has been impacted by anthropogenic

activities. It will also help environmental agencies set up

remediation levels.

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1.7 OBJECTIVESThe main objective of this project is to determine the

background concentration of arsenic in groundwater atObuasi

by taking samplesfrom areas that have not been affected by

mining activities. The specific objectives of this research

are:

To identify areas of Obuasi Township that has not been

affected by mining activities by using the groundwater

flow.

To collect groundwater samples from boreholes of these

areas.

To determine some physico-chemical properties of the

water samples.

To determine the levels of arsenic of the water

samples.

To estimate the background concentration of arsenic

from the results.

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CHAPTER TWO

2.0 LITERATURE REVIEW

2.1 Mining operation in ObuasiLarge-scale commercial extraction of gold at Obuasi started

at the end of the 19th century. Thecompany Ashanti

Goldfields Corporation Limited was a very important economic

player in the Britishcolony of the Gold Coast, and later,

after 1957, in the independent country of Ghana. Today the

goldmining is continued by AGA (GPFG, 2012).

Currently the gold production at Obuasi is based on

underground mines that operate down to 1,500 mbelow ground.

The ore consists of two main types, one which is made up of

quartz veins containingfree gold and another one with

sulphide minerals such as arsenopyrite in which the gold is

bound sothat the ore requires special treatment. In the

early 1990s, an arsenic precipitation plant was installed at

the Pompora Treatment Plant (PTP) in Obuasi for the

commercial recovery of arsenic from the roaster flue gases.

10

The arsenic trioxide was precipitated, recovered, placed in

bags, and initially sold into Europe for commercial

applications (arsenic trioxide is used for preserving wood

and as a pesticide). However, the market for arsenic

declined and this ultimately led to the cessation of sales

in the mid-1990s. With no markets, or alternative disposal

methods, bags of arsenic were accumulated on site at Obuasi,

creating a large stockpile of approximately 10,000 tons of

unusable product. The PTP roaster facility was shut down in

2000 and arsenic generation ceased.

In the interim, the Biox treatment process was introduced at

the SansuSulphide Treatment Plant (STP). During this

process, arsenic trioxide is converted to arsenic pentoxide

(and other more stable compounds) and deposited onto the

tailings dams. It appears, however, that over the years, the

Pompora stream has been polluted by arsenic from Obuasi as a

result of inadequate storage of the stockpiled bags. This

issue was identified as a significant concern during the

AngloGold due diligence study, prior to the business

combination with Ashanti. Subsequently, AngloGold Ashanti

11

has set about addressing the problem.As a short-term

remediation step, a lined storage dam has been constructed

at the old heap leach site, at the south end of the mine

adjacent to the new STP plant. This is a secure area where,

with all the appropriate personnel protective equipment and

handling facilities, it will no longer pose an uncontrolled

hazard. The bagged arsenic is being moved to this new

facility where it will be stored and gradually disposed of

by blending it into the Biox process circuit (at a pre-

determined rate) where it will be chemically stabilised.

From the STP it will be deposited as a component of the

tailings residue onto the Sansu Tailings Storage Facility.

At current production rates, it will take approximately six

years to dispose off in this fashion. One of the

alternatives to disposing off the arsenic trioxide into a

lined hazardous waste land-fill facility, which will require

indefinite management, is to convert the arsenic into a more

stable complex and dispose of it onto the conventional

tailings storage facility. This approach continues to be

evaluated.

12

The Ghanaian Environmental Protection Agency (EPA) has given

its permission for the arsenic to be moved to the new

holding pond where it will be stored until the EPA is

satisfied that the Biox treatment process is a reliable

method of disposal (AGA, 2004).

2.2 Water Sources in ObuasiGroundwater is the major source of water supply for

communities in and around the Obuasi municipality. The

occurrence of groundwater depends on the geology and areas

where the rocks are highly weathered, fractured or inter-

bedded with quartz veins. The groundwater flow is mostly

restricted to joints, fractures or other openings within the

crystalline rock formations and borehole yields are

therefore often limited. In someareas, the regolith provides

potential for increased groundwater storage. The bedrock is

not inherently permeable but secondary permeability or

porosity has developed because of fracturing and weathering.

In general, two types of aquifers are identified: weathered

rock aquifers and fractured rock aquifers that can be

categorized as confined or semi confined.Apart from the13

natural drainage line, the municipality also has rivers and

streams that drain the area: Pompo,Akapori, Kwabrafo, Nyam,

Kwaw, Enewopeanom, NkesuandGyimi. Others include Wheaseamo,

Konka, and Nyankuma streams (Ewusi et al, 2012).

2.3 Arsenic mobility in aquifersThe conditions that favour arsenic dissolution (becoming

dissolved in the water) and mobilization (movement with the

groundwater to boreholes) depend on certain circumstances.

If the arsenic is not soluble, it will precipitate and

remain in the solid phase of the groundwater system as part

of the soil. If there is a binding site on the soil surface

that is available, and the arsenic is in a form that binds

strongly, it will also leave the water phase and attach to

the soil. So for most types of arsenic, they’ll just stay

put. The deciding factor is probably some process that

converts those stable, insoluble or stuck-on-surfaces forms

of arsenic to a form that is soluble in the water (Macrae,

2014).

Two categories of processes largely control arsenic mobility

in aquifers: (1) adsorptionand desorption reactions and (2)14

solid-phaseprecipitation and dissolution reactions.

Arsenicadsorption and desorption reactions are influenced by

changes in pH, occurrence of redox(reduction/oxidation)

reactions, presence ofcompeting anions, and solid-phase

structuralchanges at the atomic level. Solid-phase

precipitation and dissolution reactions are controlled by

solution chemistry, including pH,redox state, and chemical

composition (Hinkle et al., 1999).Most of the arsenic found

in groundwater is either inorganic As(III) mainly as

uncharged arsenious acid, or inorganic As(V) in the form of

arsenic acid minus one or two of its protons (so with a

charge of –1 or –2). That’s the case at neutral pH.The

charge on As(V) allows it to bind to sites on the surface of

soil particles, removing it from the water. As the pH is

raised, the compounds will tend to become more and more

negatively charged as the arsenic and arsenious acid lose

H+groups. So the charge of these arsenic compounds depends

on the pH. You might (rightly) guess that as the pH goes up,

the charge on the arsenic compounds becomes more negative

and they should be better at binding to positively charged

15

sites on the soil surface. The trouble is that the soil

binding sites are also affected by the pH. As the pH goes up

and the water becomes more basic, OH- groups from the water

also associate with the adsorption or ion exchange sites on

the soil, neutralizing them. Once they have been

neutralized, they are not attractive to the arsenic

compounds. The solubility of metals in water is also

affected by pH, so if you get to a pH that dissolves the

mineral phase, that will result in the release of anything

bound to it. So instead of decreasing in concentration, the

arsenic concentration in high pH water can actually go up.

There is a general trend between pH and arsenic

concentration in groundwater. As the pH increases, the

arsenic concentration tends to go up (Macrae, 2014).Under

reducing conditions, the most stable soluble form of

inorganic arsenic is arsenious acid (As(III)). Under

oxidizing conditions, most of the arsenic will be in the

As(V) form, arsenic acid, because it is more stable under

oxidizing conditions. Again, the mobility of arsenic may

depend on its charge, so at neutral pH, arsenious acid is

16

more mobile than the dissociated forms of arsenic acid. That

means arsenic will probably be more mobile under reducing

conditions because more of the arsenic will be present as

arseniousacid.Just as the pH of the system affects binding

sites on soil particles, the redox potential also affects

the binding sites. Many of the binding sites for arsenic are

made of oxidized iron, aluminum or manganese species that

form a coating on the soil particles or on the rock surface.

Sometimes, the metals on the soil surface can also be

reduced, releasing them into solution. That means the

binding sites are no longer available on the surface and the

arsenic that used to be bound is released into solution.That

makes two independent factors that are likely to increase

the mobility of arsenic under reducing conditions; reduction

of As(V) to As(III), which is more mobile and reduction of

binding sites, releasing bound arsenic (Macrae, 2014).

2.4 Background ConcentrationsNaturally-occurring background concentrations are the

concentrations of metals in the environmentthat existed

before any human activities (e.g., waste management, mining,17

industrial activities) mayhave affected those

concentrations. Naturally-occurring background

concentrations of metals mayvary regionally and locally

based on the soil and bedrock present (DEQ, 2000).

2.5 Locations for background groundwater samplingChemicals can be transported with groundwater over long

distances down gradientof their sources; groundwater flow

direction is therefore a primaryconsideration when selecting

locations for background groundwater sampling,or evaluating

existing well networks. Areas up gradient of a site

orpotential contaminant source typically are considered the

best locations for

background groundwater monitoring wells. However, side-

gradient or evendown gradient locations also may be suitable

for background wells. Chemicalcharacteristics of groundwater

can vary significantly with depth. Therefore,

samplingdepths, aquifer thickness, and chemical properties

should be considered whenevaluating background conditions

(Naval Facilities Engineering Command, 2004).

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The appropriate locations to sample for site-specific

background are those that match, as closely aspossible, the

same conditions that the onsite data represent but that are

unaffected by humanactivities. This means that the sampling

locations should be as close in distance to your site

aspossible, and not influenced by site or other

anthropogenic sources (DEQ, 2000).

2.6 Arsenic DeterminationTotal arsenic in the environment samples is measured most

often by Atomic Absorption Spectrophotometer (AAS), mainly

coupled to Hydride Generation (HG-AAS) and electro-thermal-

AAS (ET-AAS). Other methods employed include Atomic

Fluorescence Spectrometry (AFS), Atomic Emission

Spectrometry (AES), generally with ICP (ICP-AES) have been

successfully coupled to HPLC for arsenic speciation,

Inductively Coupled Plasma-Mass Spectrometry (ICP-MS), X-ray

Spectrometry, Neutron-Activation Analysis (NAA) and

Capillary Electrophoresis (CE).

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2.7 Determination of Background Concentration

2.7.1 The DEQ MethodThe background concentration is calculated based on the 90th

percentile of thedata set. Note that this is not a tolerance

interval approach, but a direct estimate of the actual

datapercentile. There are two basic approaches to this

calculation. If the background data set containsnine or

fewer samples, then background concentrationlevels are

established usinga non-parametric method. If the background

data set has 10 or moresamples then background concentration

levels are calculated using either aparametric or non-

parametric approach. Typically a parametric approach is used

if the backgrounddata set is lognormally or normally

distributed based on criteria described below. If

thebackground data set is not lognormally or normally

distributed based on these distributional testcriteria, then

a non-parametric method is used (DEQ, 2000).

2.7.1.1 Non-Parametric Estimating TechniquesFor background sample data sets with nine or fewer samples,

for data sets with more than 50

20

percent non-detect values, or for data sets where the

distribution is neither normal nor log-normal,non-parametric

methods should be used to estimate the background level. The

background concentration used for comparison with the

cleanup level is the 90th percentilevalue from the

background data set. Note that if you have 9 or fewer

samples, the 90th percentileshould be set at the maximum

value of the data set. Note that for a data set containing

between 5and 9 samples, the maximum value of the data set

will represent a value that is less than or equalto the 90th

percentile of the data set and therefore is biased low.

The responsible party can eliminate this low bias by

collecting additional samples. For example, the maximum

value of 9 samples is more likely to be higher than the

maximum value of 5 samplessimply due to random chance.To do

the calculation by hand, arrange the background data set in

order of lowest to highestconcentration. Assign the lowest

value a rank of 1, the second lowest value a rank of 2,

andcontinue until all concentrations have been ranked. The

largest concentration will have a rank of“n”, where “n” is

21

the total number of data points in the data set. If two

samples have the sameconcentration, list those

concentrations consecutively and assign each a rank. If the

data setincludes non-detect results (censored data), those

results should be ranked before the lowestdetected

concentrations.

Estimate “z” as indicated:

z= 90100

(n+1)

where “z” is the rank of the 90th percentile value.If “z” is

an integer, then the background concentration is the

concentration from the data setwith a rank of “z.” If “z” is

not an integer, then the background concentration is

linearlyinterpolated from the two concentrations in the data

set that are ranked with the two closestintegers to “z”. Use

the same procedure to calculate the 50th percentile value

bysubstituting 50 for 90 in the equation above.Compare the

90th percentile value to 4 times the 50th percentile value.

If the 90thpercentile value is greater, use 4 times the 50th

22

percentile value as the background level;otherwise, use the

90th percentile value as the background level (DEQ, 2000).

2.7.1.2 Parametric Estimating TechniquesFor background sample data sets with 10 or more samples,

normal or lognormal distribution, and

not greater than 50 percent non-detect results, parametric

(statistical) methods should be used to

estimate the background level. The procedures for

determining if the data set meets the criteria foruse of a

parametric method and a default parametric method for

estimation of site background aredescribedas follows.

Establish the distribution of each data set. Whether a data

set is normally or lognormally

distributed will determine how subsequent statistical tests

and/or calculations are conducted.

The responsible party should assume the data is lognormally

distributed and test this distribution first. Ifa lognormal

distribution is rejected, then a normal distribution should

be tested. This is becausethe lognormal distribution is most

commonly associated with environmental data sets. If the23

points fall on an approximately straight line, the

distribution is judged to be normally distributed. For

lognormal data, the data are transformed first using the

natural logarithm of the data. If the log-transformed points

fall on a relatively straight line, the distribution is

judged to be lognormally distributed and all further

statistical analyses should be done using the log-

transformed data. If the data are neither normally nor

lognormally distributed, use a non-parametric method to

estimate the background concentration.

Identify the site-specific background concentration by

calculating the 50th and 90thpercentile value from the

distribution (not the sample data set). Compare the

90thpercentile value to 4 times the 50th percentile value.

If the 90th percentile value is greater,use 4 times the 50th

percentile value as the background level; otherwise, use the

90thpercentile value as the background level. The 50th and

90th percentile of a normallydistributed data set can be

calculated using the following formula:

X50 = x, and

24

X90= x + 1.28 x S

where:

X50 is the rank of the 50th percentile value

X90 is the 90th percentile value

x is the sample mean

S is the sample standard deviation (DEQ, 2000).

2.7.1.3 Evaluation of distribution of dataPrepare a normal probability plot by following these steps:

1. Calculate the natural logarithm of each data point.

2. Rank the data.

3. Calculate the percentile associated with each rank using

the formula:p = (x-0.375)/(n+0.25)

where:

n = total number of data points

p = percentile

x = rank

4. Calculate the normal score associated with each

percentile using the Excel™ function

NORMINV(x,0,1)

where:25

x = the percentile

0 = the mean of the standard normal distribution

1 = the standard deviation of the standard normal

distribution.

5. Plot Normal Score (x axis) versus Logarithm of Data (y

axis).

6. Inspect the plot visually.

A measure of how the data fit a straight line can be

quantified byperforming a linear regression of Normal Score

versus Data and calculating the linearregression correlation

coefficient. This can be done using the linear regression

routine inExcel™.Generally, a correlation coefficient of

greater than 0.90 is sufficient to assume thedata fits the

tested distribution (DEQ, 2000).

2.7.2 The OEPA MethodAnother method developed by the (Ohio EPA, 2009) can be

used. It states that, the determination of background levels

employs a method commonly associated with a graphical

technique for the detection of outliers from a population26

(i.e., box plot). This methodology also can be used for the

selection of a reasonably-protective estimation of an upper-

bound value of a data set. Specifically, background

concentration levels are to be calculated as the upper

cutoff value of the data set defined as the upper quartile +

1.5 (interquartile range).

The upper cutoff value is to be calculated using the

following equation:

U = Q3 + k(Q3 - Q1)

Where, Q1 is the lower quartile, Q3 is the upper quartile,

(Q3 - Q1) is the interquartile range, and the multiplicative

constant k is one of two factorsfor determining the upper

cutoff value.The common range for k is between 1.5 and 3.0.

For the “standard” boxplot, k equals 1.5 hence for this

purpose (selection of a background concentration), a value

of 1.5 is recommended for k. Many software applications have

functions that can be used to identify the quartile values

of a data set an example is Microsoft Excel’s® QUARTILE. The

upper cutoff value is to be used as the background

27

concentration level and it should be compared to samples

taken on-site on a point by point basis. No reduction of

site data, such as developing an average concentration term,

should be considered. Any site concentration exceeding the

background level (upper cutoff level) should be considered

evidence of contamination.

2.8 Some Physical water parametersPhysical parameters of pollution include but not limited to

pH, temperature, colour, turbidity, electrical conductivity,

light permeability, suspended matter and dissolved matter.

2.8.1 Electrical ConductivityThe electrical conductance of water is a measure of the

ability of the water to conduct electricity. It is also an

indirect measure of the presence of ions, such as nitrate,

sulfate, phosphate, sodium, magnesium, calcium, and iron.

These substances conduct electricity because they are

negatively or positively charged when dissolved in water.

The concentration of dissolved solids, or the conductivity,

is affected by the bedrock and soil in the watershed. It is

28

also affected by human influences. For example, agricultural

runoff can raise conductivity because of the presence of

phosphate andnitrate. It is important to measure the

conductivity of water because aquatic organisms require a

relatively constant concentration of the major dissolved

ions in the water.

Levels too high or too low may limit survival, growth or

reproduction. Electrical conductivity is affected by

temperature, it is thus important to report temperature data

along with conductivity values. In unpolluted waters,

conductance increases by 2 to 3% per °C. The international

standard temperature to which conductivity measurements are

corrected is 25°C. This measurement is expressed in

microsiemens per centimeter (uS/cm) at 25 degrees Celsius.

Conductivity values can be used to estimate the total

concentration of dissolved solids (commonly referred to as

total dissolved solids, or TDS). The desired level of

conductivity in drinking water according to the WHO (2004a)

is 1,000 uS/cm and that of the Ghana EPA, (1997) is 750

uS/cm (Gyawu-Asante, 2012)

29

2.8.2 Total Dissolved Solids (TDS)Total dissolved solids refers to the residue remaining in a

weighed dish after the sample has been passed through a

standard fiber glass filter and dried to constant mass at

103 to 105 degrees

Celsius. Many dissolved substances are undesirable in

water (Putz J, 2003). Dissolved minerals, gases and

organic constituents may produce aesthetically displeasing

colour, taste and odour.

Some dissolved organic chemicals may deplete the dissolved

oxygen in the receiving waters and some may be inert to

biological oxidation, yet others have been identified as

carcinogens. Water with higher dissolved solids content

often has a laxative and sometimes the reverse effect upon

people whose bodies are not adjusted to them (Akorli,

2012).As far as health aspects are concerned, there is no

evidence of adverse physiological reactions atTDS levels

greater than 1000 mg/L (World Health Organization, 1993).

The guideline value for TDS in drinking water is 1000 mg/L

30

(Ghana Standards Board, 1998; World Health Organisation,

2007).

2.8.3 TurbidityThe turbidity of water is the reduction of transparency due

to the presence of particulate matter such as clay or silt,

finely divided organic matter, plankton or other microscopic

organisms. Turbidity is commonly used as an indicator for

the general condition of the drinking water. Particles in

drinking water (suspended solids) are aesthetically

objectionable, and can serve as shields for pathogenic

microorganisms. Moreover, many toxic chemicals such as

pesticides and heavy metals are selectively adsorbed on

suspended particulate matter.The efficiency of disinfection

may be reduced in the presence of high suspended solids and

the disinfectant is unable to contact the target organism

because of a physical barrier or chemical reactions with

suspended solids, consequently decreasing the available

disinfectant concentration. More chlorine is required to

effectively disinfect turbid water. Turbidity above five

NTU may be noticeable and consequently objectionable to31

consumers (Akorli, 2012). The guideline value for turbidity

is five (5) Nephelometric turbidity units (Ghana Standards

Board, 1998; World Health Organisation, 2007).

2.8.4 pHpH is the term indicating the hydrogen ion (positively

charged hydrogen atom) concentration of a solution, a

measure of the solution’s acidity. It is a measure of the

acidic or alkaline content of water. The pH level of

drinking water reflects how acidic it is. pH is measured on

a scale that runs from 0 to 14. Seven (7) is neutral,

meaning there is a balance between acidity and alkalinity. A

measurement below 7 means acid is present and a measurement

above 7 is basic (or alkaline). It is classified as a

secondary drinking water contaminant whose impact is

considered aesthetic.

However, the WHO, (2004a) and the EPA, (1997) recommend that

public water systems maintain pH levels of between 6.5 and

8.5, a good guide for individual well owners. Water with a

low pH is acidic, naturally soft and corrosive. Acidic water

can leach metals from pipes and fixtures, such as copper,32

lead and zinc. It can also damage metal pipes and cause

aesthetic problems, such as a metallic or sour taste,

laundry staining or blue-green stains in sinks and drains.

Water with a low pH may contain metals in addition to

copper, lead and zinc. Drinking water with a pH level above

8.5 indicates high levels of alkalinity. High alkalinity may

not pose a health risk, but can cause aesthetic problems,

such as an alkaline taste to the water; scale build-up in

plumbing; and lowered efficiency of electric water heaters

(Gyawu-Asante, 2012).

2.8.5 TemperatureTemperature has both direct and indirect effects on aquatic

ecosystems. Variations in water temperature occur both

seasonally and daily. Maximum daily temperatures usually

occur in the afternoon; minimum temperatures are recorded in

the early morning hours. Variations in daily temperature are

attributed to radiation into and out of the water. Short-

term variations are greatest in unshaded, shallow streams

and less in deep-water streams and near the source of

spring-fed streams. In large rivers or streams away from33

their source, the water temperature nearly equals the mean

monthly air temperature. Temperature is a critical water

quality parameter, since it directlyinfluences the amount of

dissolved oxygen that is available to aquatic organisms.

Water temperature is a major factor in determining which

species are present in the stream. Different species have

different temperature requirements and optimal temperatures

may change for fish and invertebrate life stages. As the

temperature of water changes, chemical and physical

properties of the stream are affected. Specific conductivity

and pH are temperature dependent. Increase in temperature of

water also increases the velocity of salt ions and, in turn,

the conductivity of the water. Changes in chemical nature of

the stream can have significant impacts on biological

processes. Temperature of water for drinking and domestic

use should not exceed 30°C (EPA, 1997).

2.9 Some Chemical ParametersChemical parameters of pollution include but not limited to

total hardness, total alkalinity, phosphate content, and

different heavy metal ions present in water.34

2.9.1 AlkalinityAlkalinity is a measure of the presence of bicarbonate,

carbonate or hydroxide constituents. Concentrations less

than 100 ppm are desirable for domestic water supplies. The

recommended range for drinking water is 300 to 400

mg(CaCO3)/L. A minimum level of alkalinity is desirable

because it is considered a “buffer” that prevents large

variations in pH. Alkalinity is not detrimental to humans.

Moderately alkaline water (less than 350 mg(CaCO3)/L), in

combination with hardness, forms a layer of calcium or

magnesium carbonate that tends to inhibit corrosion of metal

piping. Many public water utilities employ this practice to

reduce pipe corrosion and to increase the useful life of the

water distribution.High alkalinity (above 500 mg(CaCO3)/L)

is usually associated with high pH values, hardness and high

dissolved solids and has adverse effects on plumbing

systems,especially on hot water systems (water heaters,

boilers, heat exchangers, etc.) where excessive, scale

reduces the transfer of heat to the water, thereby resulting

in greater power consumption and increased costs. Water with

35

low alkalinity (less than 75 mg(CaCO3)/L), especially some

surface waters and rainfall, is subject to changes in pH due

to dissolved gasses that may be corrosive to metallic

fittings due to the presence of bicarbonate (HCO3-),

carbonate (CO32-) or hydroxide (OH-). Most of the natural

alkalinity in water is due to HCO3-produced by the action of

groundwater on limestone or chalk.

CaCO3 + H2O + CO2 → Ca(HCO3)2.

Alkalinity is usually divided into caustic alkalinity above

pH 8.2 and total alkalinity above pH 4.5. Alkalinity can

exist down to pH of 4.5 because of the fact that HCO3-is not

completely neutralised until this pH is reached. The amount

of alkalinity present is expressed in terms of CaCO3 (Gyawu-

Asante, 2012).

2.9.2 Total HardnessThe hardness of water is caused by dissolved polyvalent

metallic ions principally calcium and to a lesser extent

magnesium. Public acceptability of the degree of hardness

of water may vary considerably from one community to another

depending on local conditions and in someinstances; hardness36

in excess of 500 mg/L is tolerable. Hard water may assist

in strengthening bones and teeth because of its high calcium

concentration. It may also decrease the risk of heart

diseases. Drinking water hardness must be above 8.4 mg/L.

Depending on the interaction with other factors such as pH

and alkalinity, water with hardness above approximately 200

mg/L may cause scale deposition in the distribution system

and may result in excessive soap consumption and subsequent

“scum” formation (Akorli, 2012). The guideline value for

total hardness is 500 mg/L (Ghana Standards Board, 1998;

World Health Organisation, 2007).

2.9.3 ChlorideChloride is one of the major inorganic anions in drinking

water. In potable water, the salty taste is produced by the

chloride concentrations and it is variable and dependent on

the chemical composition. There is no known evidence that

chlorides constitute any humanhealth hazards. For this

reason, chlorides are generally limited to 250 mg/L in

supplies intended for public use. In many areas of the

world where water supplies are scarce, sources containing as37

much as 2000 mg/L are used for domestic purposes without the

development of adverse effects, once the human system

becomes adapted to the water. However, high chloride

contentmay harm metallic pipes and structures (Akorli,

2012). The guideline value of chloride in drinking water

is 250 mg/L, based on taste considerations (Ghana Standards

Board, 1998; World Health Organisation, 2007).

2.9.4 SulphateThe ingestion of water containing high concentrations of

sulphate can have a laxative effect, which is enhanced when

the sulphate is consumed in combination with magnesium

(World Health Organisation, 1984). The major physiological

effects resulting from the ingestion of large quantities of

sulphate are catharsis, dehydration, and gastrointestinal

irritation. Water containing magnesium sulphate at levels

above 600 mg/L acts as a purgative in adult humans.

The presence of sulphate in drinking water can also result

in a noticeable taste. The human body only absorbs small

amounts of sulphates, but these amounts are sufficient to

stimulate peristalsis by binding magnesium and sodium to38

water in the intestine. Sulphate may also contribute to

the corrosion of distribution systems (Akorli, 2012).The

World Health Organisation(2007) guideline value for sulphate

in drinking water is 400 mg/L but the Ghana standards set it

at 250 mg/L (Ghana Standards Board, 1998).

2.9.5 CalciumCalcium is a major constituent of various types of rock. It

is one of the most common constituents present in natural

waters ranging from zero to several hundred milligrams per

liter depending on the source and treatment of the water.

Calcium is largely responsible for water hardness, and may

negatively influence toxicity of other compounds. Elements

such as copper, lead and zinc are much more toxic in soft

water. Calcium carbonate has a positive effect on lead

water pipes, because it forms a protective lead (II)

carbonate coating. This prevents lead from dissolving in

drinking water, and thereby prevents it from entering the

human body. Calcium phosphate is a supporting substance and

it causes bone and tooth growth, together with vitamin D.

Bones decalcifies (osteoporosis) and fractures become more39

likely if a body is not getting enough calcium. Since a

guideline value is proposed for total hardness, no guideline

value is proposed for calcium concentration in drinking

water (Akorli, 2012).

2.9.6 MagnesiumMagnesium is a common constituent in natural water.

Magnesium salts are important contributors to the hardness

of water which break down when heated, forming scale in

boilers. Chemical softening, reverse osmosis,

electrodialysis, or ion exchange reduces the magnesiumand

associated hardness to acceptable levels. Magnesium ion is

important for the regulation of muscle contractions and the

transmission of nerve impulses, and it activates energy-

producing enzymes. Nervousness, lack of concentration,

dizziness, and headaches or migraines may result from

magnesium deficiency. Since a guideline value is proposed

for total hardness, no guideline value is proposed for

magnesium concentration in drinking water (Akorli, 2012).

40

2.9.7 NitrateNitrate may be naturally occurring, although its presence in

drinking water is more often associated with contamination

by excessive use of fertilizers (both inorganic and

organic), in addition to inappropriate farming practices and

sewage. The high nitrate level in drinking water is also

associated with the simultaneous presence of bacterial

contamination (World Health Organisation, 1996).The primary

health hazard from drinking water with nitrate-nitrogen

occurs when nitrate is transformed to nitrite in the

digestive system. The nitrite oxidizes iron in the

haemoglobin of the red blood cells to form methaemoglobin,

which lacks the oxygen-carrying capacity of haemoglobin.

This creates the condition known as methaemoglobinaemia

(sometimes referred to as "blue baby syndrome"), in which

blood lacks the ability to carry sufficient oxygen to the

individual body cells causing the veins and skin to appear

blue (World Health Organisation, 1996). Most humans over

one year of age have the ability to rapidly convert

methaemoglobinback to oxyhaemoglobin. However, in infants

41

under six months of age, the enzyme systems for reducing

methaemoglobin to oxyhaemoglobin are incompletely developed

and methaemoglobinaemiacan occur. This also may happen in

older individuals who have genetically impaired enzyme

systems for metabolizing methaemoglobin (Akorli, 2012). The

guideline valueof nitrate-nitrogen is 50 mg/L and that of

nitrite-nitrogen is 1.0 mg/L (World Health Organisation,

2007).

2.9.8 FlourideFluoride is not a generic term for fluorine. Fluorine is an

element and a highly reactivepale yellow gas, but fluoride

is a negative ion [technically called ionic fluoride]

andcombines with a positive ion called a cation, by sharing

a electron, that generallyproduces a very stable molecule

(Thomas G. Reeves). Traces of fluorides are present in many

waters; higher concentrations are oftenassociated with

underground sources. In seawater, a total fluoride

concentration of 1.3mg/litre has been reported (Slooff et

al., 1988). In areas rich in fluoride-containingminerals,

well water may contain up to about 10 mg of fluoride per42

litre. The highestnatural level reported is 2800 mg/litre.

Fluorides may also enter a river as a result ofindustrial

discharges (Slooff et al., 1988). In groundwater, fluoride

concentrationsvary with the type of rock the water flows

through but do not usually exceed 10mg/litre (US EPA,

1985a).

2.9.9 SodiumThe sodium ion is ubiquitous in water. It is washed out from

rocks and soils, ending up in oceans, where it may remain

for about 50×106 years. Drinking water usually contains

about 50 mg/L sodium. This value is clearly higher for

mineral water. In soluble form sodium always occurs as Na+

ions (World Health Organisation, 1997).

Sodium compounds naturally end up in water. Seas, rivers and

lakes contain significant amounts of sodium. Concentrations

however are much lower, depending on geological conditions

and wastewater contamination. Sodium compounds serve many

different industrial purposes, and may also end up in water43

from industries. They are applied in metallurgy, and as a

cooling agent in nuclear reactors. About 60% of sodium is

utilized in chemical industries, where it is converted to

chlorine gas, sodium hydroxide or sodium carbonate, and

about 20% of sodium is utilized in food industries as a

preservative or a flavouring agent. Sodium hydroxide may be

applied to prevent clogging of sewer pipes, and sodium

carbonate is applied in water purification to neutralize

acids. Sodium hydrogen carbonate is a constituent of backing

powder, and is applied in textile and leather industries and

in soap and cleanser production. In sanitary cleanser the

element is present as sodium hypo chlorite (Lenntech B.V,

1998- 2014).

2.9.10 PotassiumPotassium occurs in various minerals, from which it may be

dissolved through weathering processes. Examples are

feldspars (orthoclase and microcline), which are however not

very significant for potassium compounds production, and

chlorine minerals carnalite and sylvite, which are most

favourable for production purposes. Some clay minerals44

contain potassium. It ends up in seawater through natural

processes, where it mainly settles in sediments. Elementary

potassium is extracted from potassium chloride, but does not

serve many purposes because of its extensive reactive power.

It is applied in alloys and in organic synthesis. A number

of potassium compounds, mainly potassium nitrate, are

popular synthetic fertilizers.95% of commercially applied

potassium is added to synthetic fertilizers. Potassium salts

and mixtures of magnesium and calcium compounds are also

applied regularly. Potassium is an dietary requirement for

nearly any organism but a number of bacteria, because it

plays an important role in nerve functions (Lenntech B.V,

1998- 2014).

45

46

CHAPTER THREE

3.0 METHODOLOGY

3.1 Physiography of ObuasiObuasi is located in the Ashanti region of Ghana and is

about 64 km south of Kumasi, the regional capital and 300 km

north-west of Accra, the capital of Ghana. It is situated at

latitude 6° 12’ 00’’ North and longitude 1° 40’ 00’’ West.

It is located in the tropical evergreen rain forest belt. It

covers an area of about 162.4 km2and is bounded on the south

by Upper Denkyira District of the Central Region, east by

Adansi South District, west by Amansie Central District and

north by Adansi North District (Mensah, 2012).

Figure 1. Map of Obuasi Municipality Showing the location ofcommunities

47

3.2 Geology and Topography of ObuasiThe geology of Obuasi consists of Proterozoic rocks of the

Birimian (metasedimentary and metavolcanic) rocks and

Takwaian systems. The metavolcanicBirimian rocks consists of

black slates, sericite schist and phyllites, with

subordinate grey, sandy phyllites and greywackes, whereas

the metasedimentaryBirimian rocks consist of black

phyllites, metasiltstones, metagreywackes, tuffaceous

sediments, tuffs and hornstones (Fig. 2). The Tarkwaian

system is mainly a thick series of white and grey quartzites

48

with a few intercalated bands of bluish and pink mudstone

and phyllite containing chlorite, magnetite, etc., (Ewusi et

al, 2012).

The topography of Obuasi and its environs varies from gently

undulating to hilly. Thereare moderately high-elevated lands

with lowlands and valleys between them. The highlands trend

in differentdirections; they have flat and plateau tops and

are generally amorphous in their shapes (Bempah et al,

2013).

3.3 Sampling locationsSampling locations were carefully chosen in order to acquire

values that represent background levels. This was done by

choosing areas that were not directly affected by the mining

sites and tailing dams. Also groundwater flow was an

important consideration in the selection of the sample

locations. A terrain map of Obuasi, showing its contours

gave us foresight on the direction of the flow of

groundwater. Groundwater flows downhill, and thus the sample

locations were selected side-gradient and up-gradient to the

direction of groundwater flow, also proximity to the49

tailings dams were taken into consideration. Locations

directly in the path of groundwater from the tailing dams

were avoided. The source of water samples taken were

boreholes. The state and conditions of the boreholes were

also taken into consideration before accepted as a sampling

point. Only boreholes which were being used by the locals in

the area were considered for sampling.

Figure 2. A terrain map of Obuasi, showing its contours andestimated groundwater flow

50

3.4 SamplingTwo rounds of sampling were performed. One in December, 2013

and the other inFebruary, 2014. 10 samples were taken for

each round of sampling as well as a duplicate sample and a

field blank making 12 samples per round. A total of 24

samples were taken during the study. To obtain reliable

results, sampling procedures which eliminate or minimize

potential contaminants were adopted. This was done by

washing the sample containers with a detergent and rinsing

thoroughly with distilled water. The containers were then

soaked in 10% Nitric acid and then rinsed again with

distilled water. The samples to be tested for Arsenic were

preserved with 3ml of 6M Nitric acid per 1 litre of sample.

The samples to be tested for ions, alkalinity and hardness

were stored by keeping them around 4°C. Temperature, pH,

conductivity, Total dissolved solids and turbidity were

measured on site. The borehole samples together with the

duplicates (a different borehole was duplicated each round)

and the field blank were given a code which was clearly51

labeled on the containers. The table below shows each

sampling point and their respective code.

Table 1.Sample locations and designated codesSAMPLE LOCATION DESIGNATED CODE

Mampamhwe MAM

Diewuoso DIW

Gyimiso GYM

Akrofuom AKF

Asikafroanmmantem

(Tutuka)

ASI

Nhyiaeso NHY

Bidiem BID

Nyameso NMS

Binsere BSE

Konka KOK

3.5 APPARATUS- SOLAAR AA Series Spectrometer

- HANNA Turbidimeter HI98713

- EUTECH Instrument PCD650

52

- Beaker

- Conical flasks

- Burette

- Pipette

- Measuring cylinder

- Volumetric flasks

- Ion chromatograph

3.6 CHEMICALS- Nitric acid

- Arsenic standard

- Sodium hydroxide

- Hydrochloric acid

- Sodium borohydride

- Methyl orange

- Sulphuric acid

- EDTA

- Calcium carbonate

- Ammonium chloride

- Erichrome Black T

53

3.7 Determination of Physical ParameterspH, Conductivity, Total Dissolved Solids (TDS), Turbidity

and Temperature were measured on field using a multi-

parameter handheld meter, EUTECH Instrument PCD650.

Turbidity was also measured on field using a HANNA

Turbidimeter HI98713.

3.7.1 pH

3.7.1.1 CalibrationThe instrument was calibrated for pH using the NIST buffer

group (4.01, 6.86, 9.18 and 12.45 standard buffer

solutions). A four-point calibration was used. The first

point of calibration was 6.86 followed by 4.01, 9.18 and

finally 12.45. The meter automatically recognizes and

calibrates these standard pH buffer values when the

electrode is dipped into the solution. Distilled water was

used to rinse the electrode before and after each buffer

solution.

54

3.7.1.2 MeasurementA portion of the water sample was placed in a beaker on

site. The electrode was placed in the beaker and the value

of pH was recorded after it stabilized. The electrode was

rinsed with distilled water before and after each

measurement.

3.7.2 Conductivity

3.7.2.1 Calibration84.0 uS, 1.413 mS, 12.88 mS and 111.8 mSstandard buffer

solutions were used in calibrating the instrument. On the

instrument, the 1.413 mSstandard solution was selected.The

probe was dipped into the calibration standard and stirred

gently to create a homogeneous solution. Time was allowed

for the reading to stabilize. The cell constant value was

adjusted to the correct cell constant value of the standard.

The instrument was then set to calibration mode where the

55

calibration was done automatically by the instrument. The

electrode was rinsed with deionised water and placed in the

other standard buffer solutions for automatic calibration by

the instrument.

3.7.2.2 MeasurementA portion of the water sample was placed in a beaker on

site. The electrode was placed in the beaker and the value

of conductivity was recorded after it stabilized. The

electrode was rinsed with distilled water before and after

each measurement.

3.7.3 TDS

3.7.3.1 Calibration and DeterminationThe probe was dipped into the calibration standard and

stirred gently to create a homogeneous solution. Time was

allowed for the reading to stabilize. The TDS cell constant

value was adjusted to the correct cell constant value of the

standard. The instrument was then set to calibration mode

where the calibration was done automatically by the

instrument. The electrode was rinsed with distilled water

56

and placed in the other standard buffer solutions for

automatic calibration by the instrument.

3.7.3.2 MeasurementA portion of the water sample was placed in a beaker on

site. The electrode was placed in the beaker and the value

of TDS was recorded after it stabilized. The electrode was

rinsed with distilled water before and after each

measurement.

3.7.4 Temperature DeterminationA portion of the water sample was placed in a beaker on

site. The temperature probe of the instrument was placed in

the beaker and the temperature value in °C was recorded

after it stabilized. The probe was rinsed with distilled

water before and after each measurement.

3.7.5 Turbidity

3.7.5.1 CalibrationThe instrument was calibrated using 0.1, 15, 100 and 750 FNU

standards. About 10ml of the first standard was placed in

the sample cell and the compartment was covered. The57

instrument auto-calibrated itself after the readings

stabilized. The sample cell content was discarded and rinsed

with distilled water and the process repeated for the

remaining standard solutions.

3.7.5.2 MeasurementA portion of the water sample was placed in the cell and

well covered. The cell was placed in the cell compartment

and covered. The value of turbidity in FNU was then recorded

after it stabilized. The cell content was discarded and

rinsed with distilled water before and after each

measurement.

3.8Determination of Chemical ParametersThe chemical parameters were done in the lab. Total

alkalinity was done by acid-base titration whiles Total

hardness was done by titration with EDTA.

3.8.1 Total Alkalinity50ml of the water sample was pipetted into a clean 250ml

Erlenmeyer flask and about five drops of methyl orange

58

indicator was added. This was titrated with 0.10N H2SO4

until the colour changed from yellow to orange. The titre

value was recorded. The procedure was repeated about two

more times for all water samples. The total alkalinity was

determined based on the following formula:

Total alkalinity (mg CaCO3/L) =

mlofacidaddedxnormalityofacidx50,000mlofsample

3.8.2 Total HardnessA 0.01M EDTA solution was prepared by dissolving 3.725g of

EDTA disodium salt in deionized water, transferring into a

1L volumetric flask and topping up to the mark with

deionized water.

A standard calcium solution was prepared by weighing 1g of

dried calcium carbonate and transferring into a 500ml

conical flask. 21mL of 1M HCL was added slowly and the

content of the flask was then swirled until all the

carbonate dissolved. 200ml of distilled water was added and

boiled to expel the carbon dioxide. The whole solution was

59

left to cool.A 2M sodium hydroxide solution was prepared by

dissolving 8g of NaOH in 100ml of distilled water.

3.8.2.1 Standardization of EDTA solution20ml of the calcium standard was pipetted into a 250ml

conical flask and then diluted to 100ml with deionized

water. 4ml of an NH4Cl buffer solution of pH 10 was added

together with 6 drops of Erichrome Black T (EBT) indicator.

The resulting solution was titrated with the EDTA solution

until the colour of the solution changed from violet to

blue.1ml of the EDTA solution equivalent to calcium

carbonate in mg

E (CaCO3) = volumeofcalciumstandardx1mg(CaCO3)

titrevalue

3.8.2.2 Determination of Total Hardness50ml of the water sample was pipetted into a 250ml conical

flask. 4ml of the buffer solution and 6 drops of the EBT

indicator were added to the sample. The solution was the

titrated against the EDTA solution to a distinct blue

60

endpoint. The total hardness was then determined using the

following formula:

Total Hardness as CaCO3 content (mg/l) =

titrevaluexE (CaCO3 )x1000samplevolume

In order to correct for any error attributable to the

deionized water and the indicator colour transition, a blank

titration was done and the volume of EDTA required for the

titration of the blank was subtracted from all other

titration volumes.

3.8.3 Determination of IonsThe determination of ions was done with an ion

chromatograph. The samples were filtered into beakers and

injected into the loop of the instrument. A chromatogram was

plotted by the instrument and compared with the calibration

curves of the ions to determine the concentrations of ions

in the samples.

61

3.8.4 Determination of ArsenicThe Arsenic content of the samples were determined with an

Atomic Absorption Spectrometer with the Hydride Generation

system (HG-AAS). The AAS used was the SOLAAR AA Series

Spectrometer coupled with the VP100 Hydride generation

system from Thermo Scientific Corporation.

3.8.4.1 Digestion of samplesThe digestion was done with 100ml volumetric flasks

prewashed with 10% Nitric acid. It was done by preparing 10%

Nitric acid solutions of the samples. About 30ml of the

samples were filtered into the volumetric flasks with the

help of funnels and filter papers which were all prewashed

with 10% Nitric acid. 10ml of concentrated Nitric acid was

added and topped up to the 100ml mark with the samples.

3.8.4.2 Preparation of Standard Arsenic solutionsThe standards were prepared from a 1,000ppm stock by serial

dilution. The serial dilutions were done by preparing a

100,000ppb solution of Arsenic and from this a 10,000ppb

solution then to a 1,000ppb and then finally a 100ppb

solution. 5ppb, 10ppb and 15ppb standard Arsenic solutions

62

were prepared from the resulting solution. The solutions

were prepared in 10% Nitric acid.

3.8.4.3 Preparing Spiked Samples for recoveryIn order to check for accuracy of the measurement, two

samples were spiked with 2ppb standard arsenic solution. The

recovery of the instrument was calculated by the following

formula:

Recovery =Spikedvalue−Samplevaluestandardvalue

x100

3.8.4.4 Calibration and MeasurementThe instrument was calibrated with the 5ppb, 10ppb and 15ppb

standard arsenic solutions. The field blank sample was run

with the instrument and used to correct the actual arsenic

concentrations in the samples by subtracting the blank value

from the values of the samples. This was done automatically

by the instrument. The rest of the samples were run with the

instrument and the results printed out.

63

3.9 Precision of the Methods UsedThe precision of the method was checked by finding the

relative percent difference. The relative percent difference

was found by using the following formula.

RPD=(X¿¿1−X2)X100

(X1+X2 )÷2¿

64

CHAPTER FOUR

4.0 RESULTS AND DISCUSSION

4.1 RESULTS

Table2. Physical Parameters of water samples collectedSource Ph TDS(ppm) Temperature(˚C

)

Conductivity(µs/

cm)

Turbidity(NT

U)

MAM 4.25 21.94 27.25 31.91 0.59

DIW 5.67 320.45 27.50 459.15 0.54

GYM 4.08 90.01 28.10 128.6 0.27

AKF 3.80 310.35 27.95 446.05 0.32

ASI 3.95 119.5 29.00 171.2 0.58

NHY 5.35 120.52 27.15 168.7 0.78

BID 5.27 51.53 26.95 73.56 2.58

NMS 5.13 54.39 27.35 77.68 1.65

BSE 4.42 36.03 26.80 34.01 2.01

KOK 4.65 72.14 28.05 102.88 0.21

NIN 6.01 3.940 29.10 5.69 0.19

65

Table 3. Total Hardness of water samples collected

SOURCE

TOTAL HARDNESS( mg/l)

MONTH 1 MONTH 2 AVERAGE

NMS 2.70 2.88 2.79

NHY 70.48 70.88 70.68

MAM 29.55 29.97 29.76

GYM 18.1 18.7 18.6

KOK 33.40 33.56 33.48

BID 7.42 7.46 7.44

ASI 14.90 14.86 14.88

AKF 16.54 16.94 16.74

BSE 5.55 5.61 5.58

DIW 132.0 132.12 132.06

66

Table 4. Alkalinity of water samples collected

SOURCE

ALKALINITY( mg/l)

MONTH 1 MONTH 2 AVERAGE

BSE 24 26 25

NHY 121 119 120

NMS 29 31 30

KOK 30 30 30

MAM 21 19 20

BID 50 50 50

AKF 8 12 10

ASI 21 19 20

DIW 139 141 140

GYM 10 10 10

67

68

Table 5. Concentration of cations in water samples collected

SOURCE

Na ( K Ca Mg

Month

1

Month

2

Averag

e

Month

1

Month

2

Averag

e

Month

1

Month

2

Averag

e

Month

1

Month

2

Averag

e

ASI 26.914 26.900 26.907 0.701 0.835 0.768 1.815 1.855 1.835 32.961 32.973 32.967

BID 4.871 4.907 4.889 0.255 0.247 0.251 3.498 3.590 3.544 36.254 36.330 36.292

BSE 2.675 2.681 2.678 0.450 0.448 0.449 0.830 0.886 0.858 25.548 25.574 25.561

KOK 14.600 14.658 14.629 0.359 0.379 0.369 3.245 3.265 3.255 47.700 47.744 47.722

NMS 8.222 8.234 8.228 0.500 0.606 0.553 3.870 3.888 3.879 42.745 42.699 42.722

MAM 1.199 1.287 1.243 0.199 0.207 0.203 1.156 1.154 1.155 31.594 31.618 31.606

GYM 14.559 14.647 14.603 3.977 3.981 3.979 2.480 2.504 2.492 41.850 41.836 41.843

DIW 35.200 35.090 35.145 6.000 5.998 5.999 11.703 11.699 11.701 64.410 64.428 64.419

NHY 24.190 24.196 24.193 0.899 0.915 0.907 6.810 6.802 6.806 51.100 51.106 51.103

AKF 53.998 54.354 54.176 12.091 11.999 12.045 5.557 5.591 5.574 71.999 72.077 72.038

69

Table 6. Concentration of anions in water samples collected

SOURCE

F- Cl- NO3- SO4

2-

Month

1

Month

2

Averag

e

Month

1

Month

2

Averag

e

Month

1

Month

2

Averag

e

Month

1

Month

2

Averag

e

ASI 2.311 2.329 2.320 36.000 36.018 36.009 25.040 25.036 25.038 4.988 5.004 4.996

BID 2.346 2.346 2.346 11.001 11.051 11.026 4.439 4.447 4.443 3.687 3.697 3.692

BSE 1.655 1.671 1.663 10.276 10.266 10.256 3.750 3.758 3.754 4.170 4.186 4.178

KOK 3.050 3.024 3.037 26.714 26.704 26.709 14.165 14.193 14.179 4.176 4.180 4.178

NMS 3.509 3.515 3.512 15.359 15.363 15.361 5.600 5.616 5.608 5.298 5.302 5.300

MAM 2.000 2.028 2.014 10.033 10.045 10.039 5.303 5.305 5.304 4.524 4.548 4.536

GYM 3.663 3.707 3.685 21.620 21.628 21.624 33.111 33.145 33.128 4.268 2.274 4.271

DIW 3.266 3.284 3.275 46.660 46.678 46.669 47.000 47.030 47.015 5.847 5.857 5.852

NHY 4.299 4.259 4.279 20.340 20.340 20.340 4.112 4.100 4.106 7.249 7.255 7.252

AKF 5.185 5.119 5.152 85.272 85.286 85.279 59.430 59.398 59.414 21.700 21.718 21.70970

71

Table 7. Concentration of Arsenic in water samples collectedSAMPLES MONTH 1 /ppb MONTH 2 /ppb AVERAGE /ppb

NHY _ 1.06775 0.533875

KOK 0.28535 0.0513 0.168325

BID 3.3883 1.4851 2.4367

BSE 0.3211 0.3091 0.3151

ASI 0.34705 0.33715 0.3421

AKF 0.12445 0.190225 0.1573375

NMS 0.48365 0.1576 0.320625

GYM 0.1878 0.0533 0.12055

MAM 0.2268 0.10805 0.167425

DIW 0.2508 0.12035 0.185575

72

Table 8. Plotted values in distribution determinationRank Cumulative

Probabilit

y

Normal Score Log Value Sorted

Value

1 0.05555555

6

-1.593218818 -2.11569067 0.12055

2 0.14444444

4

-1.060562244 -1.8493621 0.1573375

3 0.23333333

3

-0.727913291 -1.78721979 0.167425

4 0.32222222

2

-0.461493694 -1.78185864 0.168325

5 0.41111111

1

-0.224687715 -1.68429617 0.185575

6 0.5 0 -1.15486523 0.3151

7 0.58888888

9

0.224687715 -1.13748306 0.320625

73

8 0.67777777

8

0.461493694 -1.07265219 0.3421

9 0.76666666

7

0.727913291 -0.62759355 0.533875

74

Figure 3. Graph showing lognormal distribution

-2 -1.5 -1 -0.5 0 0.5 1

-2.5

-2

-1.5

-1

-0.5

0

f(x) = 0.611318235732961 x − 1.28763518299543R² = 0.887063842576325

Normal Score

ln Concentration

75

Figure 4. Graph showing normal distribution

-2 -1.5 -1 -0.5 0 0.5 10

0.1

0.2

0.3

0.4

0.5

0.6

f(x) = 0.15664184853661 x + 0.302956185677038R² = 0.778136071727384

Normal Score

Concentration

76

Table 9. RPD for Duplicate of month 1 BID=IEM

Parameter BID IEM RPD %

Total Hardness

(mg/l)

7.42 7.23 2.59

Alkalinity

(mg/l)

50 51 1.98

Na 4.871 5.167 5.90

K 0.255 0.306 18.18

Ca 3.498 3.262 6.98

Mg 36.252 34.825 4.02

F- 2.346 2.842 19.12

Cl- 11.001 10.222 7.34

NO3- 4.439 5.043 12.74

SO4- 3.687 3.900 5.61

As (ppb) 3.3883 2.80555 18.82

77

Table 10. RPD for Duplicate of month 2NMS=IEM

Parameter NMS IEM RPD %

Total Hardness

(mg/l)

2.88 3.23 11.46

Alkalinity

(mg/l)

31 33 6.25

Na 8.234 8.909 7.87

K 0.606 0.650 7.01

Ca 3.888 4.284 9.69

Mg 42.699 43.833 2.62

78

F- 3.515 4.168 17.00

Cl- 15.363 16.220 5.43

NO3- 5.616 5.730 2.01

SO4- 5.302 6.138 14.62

As (ppb) 0.1576 0.1840 15.46

4.2 DISCUSSIONThe average concentrations of Arsenic in the selected

boreholes are given in Table 7. The values of Arsenic

obtained ranged from 0.12055 – 2.43670µg/l which were all

below the World Health Organization (WHO) guideline value of

79

10µg/l. The low concentrations obtained indicate that the

borehole locations are good representations of background

conditions. Arsenic is usually present in natural waters at

a concentration of less than 1 - 2µg/l, however, in waters,

particularly groundwaters, where there are sulphide mineral

deposits and sedimentrary deposits derived from volcanic

rocks, like in Obuasi, the concentrations can be

significantly higher. From the samples collected, the

relatively higher concentration was from sample BID.This

value was however, rejected from the data set because when

subjected to the Dixon’s Q test for outliers, the Q value

exceeded the critical value for P=0.05. The calculated Q

value was 0.82155 and the critical value for P=0.05 for a

sample size of 10 was 0.464.The method used in the

determination of the Arsenic concentration was also accurate

since it gave a recovery of94.6% for the spiked sample, DIW

and 90.2% for the spiked sample KOK.

The values of the physical parameters are given in Table 2.

The temperature ranged from 26.8 – 29 °C. According to the

(EPA, 1997), temperature of water for drinking and domestic80

use should not exceed 30°C. From the samples the highest

temperature value of 29°C was recorded from ASI. The high

temperature even though within a safe range might enhance

the growth of microorganisms and may increase problems

related to taste, odour, colour and corrosion. The pH values

ranged from 3.80 – 5.67. The WHO, (2004a) and the EPA,

(1997) recommend that public water systems maintain pH

levels of between 6.5 and 8.5. It can be seen that all the

selected boreholes have very acidic water as none of them

were within the safe range. The TDS values ranged from 36.03

– 320.45mg/l, which are far below the WHO guideline value of

1000 mg/l. However, high values of TDS can affect the taste,

colour and odour of the water. The results show that the

water from the boreholes is considered to be palatable. The

values for conductivity ranged from 31.91 – 459.15µS/cm

which are below the guideline values for conductivity of the

WHO, 1,000µS/cm and that of the Ghana EPA, 750 µS/cm. Pure

water doesn’t conduct electricity, any impurities like

salts, in the water enables it to conduct electricity. When

salts are dissolved in water, they separate into ions.

81

Therefore, the higher the conductivity, the more likely the

water has high concentrations of ions. The turbidity values

also ranged from 0.21 – 2.58NTU which are below the WHO

guideline value of 5NTU. This reflects the clear nature of

the water samples collected. According to the WHO, to ensure

effectiveness of disinfection, turbidity should be no more

than 1NTU and preferably much lower. From the results,

samples BID,NMS and BSE had values of 2.58, 1.65 and 2.01

respectively which show that effectiveness of disinfection

will be reduced.

The total hardness values are given in table 3. The values

ranged from 2.79 – 132.06mg/l which are safe below the WHO

guideline of 500mg/l. The results indicate that the water

from the boreholes are soft and hence have low buffering

capacity. The values for alkalinity are also given in Table

4. They ranged from 10 – 140mg/l which are safe below the

WHO permissible level of 200mg/l.

The values for the cations are given in Table 5. Sodium ion

concentrations ranged from 1.243 – 54.176mg/l. According to

82

(Copenhagen, 1979), drinking water usually contains about 50

mg/L sodium.The WHO also states that at room temperature the

average taste threshold for sodium is about 200mg/l.

Potassium ion concentration ranged from 0.203 – 12.045mg/l.

Calcium ion concentrations ranged from 0.858 – 11.701mg/l.

The WHO states that the calcium ion range is 100 – 300mg/l

depending on the associated anion. Magnesium ion

concentrations ranged from 25.561 – 72.038mg/l. The

magnesium ion and calcium ion concentrations contribute to

the values of the total hardness.

The values for the anions are given in Table 6. Fluoride

concentrations ranged from 1.663 – 5.855mg/l. According to

the WHO, fluorides in groundwater concentrations vary with

the type of rock through which the water flows but do not

usually exceed 10mg/l. The values obtained are therefore

within the safe range. Chloride concentrations ranged from

10.039 –85.279mg/l. The WHO range is 200 – 300mg/l for

sodium, potassium and calcium chlorides. Concentrations in

excess of 250mg/l are increasingly likely to be detected by

taste. The values obtained are therefore, in the safe range.83

Nitrate concentrations ranged from 3.754 – 59.414mg/l.The

WHO guideline value for nitrate is 50mg/l. All the samples

were below this value except AKF which exceeded it with a

value of 59.414mg/l. Sulphate concentrations ranged from

3.692 – 21.709mg/l. According to the WHO, Taste impairment

varies with the nature of the associated cation; taste

thresholds have been found to range from 250 mg/l for sodium

sulphate to 1000 mg/l for calcium sulphate. It is generally

considered that taste impairment is minimal at levels below

250 mg/l. It indicates that the values obtained are far

below the taste impairment value.

In determination of the background concentration from the

data set using the DEQ method, a test of distribution of the

data was performed by plotting probability graphs by

plotting values or the natural logs of the values against

the normal score from table 8. The data neither showed a

normal or a lognormal distribution as can be seen from

figures 3 and 4 respectively. According to the DEQ method,

if the data does not show distribution, and also if the data

has nine or fewer samples, then the non-parametric method84

should be used. With the non-parametric method, the

background concentration used for comparison is the 90th

percentile value. The rank of the 90thpercentile value was

found to be 9; this corresponds to a value of 0.533875µg/l

which is also the highest value. The rank of the 50th

percentile value was also found to be 5; this corresponds to

a value of 0.185575µg/l. The 50th percentile value

multiplied by 4 gives a value of 0.7423µg/l; since the 90th

percentile value of 0.533875µg/l is not greater than this

value, background concentration of arsenic is set at the

90th percentile value, 0.533875µg/l.

In determination of the background concentration from the

data set using the OEPA method, the upper cutoff value of

the data is to be used as the background concentration

level. To calculate this, the lower (Q1) and upper (Q3)

quartiles of the data have to be determined. From the values

obtained, Q1 was found to be 0.167425µg/l and Q3 was found

to be 0.320625µg/l. These values were obtained by using

Microsoft Excel’s® QUARTILE function. The lower and upper

85

quartiles were then used to calculate the upper cutoff value

which was 0.550425µg/l.

Therefore, it can be estimated that the background

concentration of arsenic in groundwater from boreholes in

Obuasi is 0.533875µg/l for the DEQ method and 0.550425µg/l

for the OEPA method. This means that when the concentration

of arsenic from a borehole from Obuasi is found to be

greater than these values, then that borehole has been

contaminated. But when the concentration is found below

these values, then that borehole, even though it records a

level of arsenic, has not been contaminated but contains the

normal background level of arsenic. This will be very useful

to the stakeholders who are concerned about the levels of

arsenic in groundwater in the sense that it will serve as a

remediation levels. This means that when there is a

contamination, whoever is responsible for the remediation

now has an idea of what level of arsenic concentration at

which he can cease the cleanup. This goes to save cost of

remediation to the environmental protection agencies and the

other stakeholders responsible for remediation of86

contaminations. It will also give a fair idea of locations

of new boreholes. For example when preliminary tests of the

water source show arsenic levels below the background

concentration, that location is fit for use but when the

arsenic level is above the background concentration, then

further tests can be done to find the cause of the

contamination and whether the location can be used.

In terms of quality control, the accuracy of the

determination of the concentration of arsenic was checked by

finding the recovery of spiked samples. The method for the

arsenic determination was accurate since they were all

greater than 90%. The precision of the method was also

checked by finding the relative percent difference of the

duplicate samples (IEM) taken for both months and their

respective samples. From tables9 and 10, it can be seen that

since the relative percent differences were very low for

both months, the methods used were very precise. The methods

for the determination of the background arsenic

concentrations were also precise since the relative percent

87

difference between the two values was 3.05% which is very

low.

CHAPTER 5

5.0 CONCLUSION AND RECOMMENDATION

5.1 CONCLUSIONIn this study, the concentrations of the investigated

physicochemical parameters in the borehole samples were

within WHO guide line values except for pH, even though it

does not have a direct impact on consumers. The estimated

background arsenic concentrations from the DEQ and OEPA

methods are 0.533875µg/l and 0.550425µg/l respectively.

88

5.2 RECOMMENDATIONThere should be periodic monitoring and assessment of the

quality of the borehole water from the studied communities

by the authorities in charge of it. It is also recommended

that the background concentration of soil samples in Obuasi

should also be determined.

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93

TABLE OF CONTENTDECLARATION.....................................................iACKNOWLEDGEMENT................................................ii

DEDICATION....................................................iiiSUPERVISOR’S APPROVAL..........................................iv

ABREVIATIONS....................................................vABSTRACT.......................................................vi

CHAPTER ONE.....................................................11.0 INTRODUCTION................................................1

1.1 Arsenic........................................................11.2 Applications of Arsenic.............................................2

1.3 Toxicity of Arsenic................................................21.4 Arsenic in Obuasi................................................3

1.5 PROBLEM STATEMENT...........................................41.6 JUSTIFICATION...............................................5

1.7 OBJECTIVES..................................................5CHAPTER TWO.....................................................6

2.0 LITERATURE REVIEW...........................................62.1 Mining operation in Obuasi.........................................6

2.2 Water Sources in Obuasi...........................................82.3 Arsenic mobility in aquifers.........................................9

2.4 Background Concentrations........................................112.5 Locations for background groundwater sampling........................11

2.6 Arsenic Determination............................................122.7 Determination of Background Concentration...........................12

2.7.1 The DEQ Method...............................................122.7.1.1 Non-Parametric Estimating Techniques.............................13

2.7.1.2 Parametric Estimating Techniques................................14

2.7.1.3 Evaluation of distribution of data.................................152.7.2 The OEPA Method..............................................17

2.8 Some Physical water parameters....................................182.8.1 Electrical Conductivity...........................................18

2.8.2 Total Dissolved Solids (TDS).......................................192.8.3 Turbidity....................................................19

2.8.4 pH.........................................................202.8.5 Temperature.................................................21

2.9 Some Chemical Parameters........................................212.9.1 Alkalinity....................................................22

2.9.2 Total Hardness................................................232.9.3 Chloride.....................................................23

2.9.4 Sulphate....................................................242.9.5 Calcium.....................................................24

2.9.6 Magnesium..................................................252.9.7 Nitrate......................................................25

2.9.8 Flouride.....................................................262.9.9 Sodium.....................................................27

2.9.10 Potassium..................................................27CHAPTER THREE..................................................30

3.0 METHODOLOGY................................................303.1 Physiography of Obuasi...........................................30

3.2 Geology and Topography of Obuasi..................................313.3 Sampling locations..............................................31

3.4 Sampling.....................................................323.5 APPARATUS....................................................34

3.6 CHEMICALS....................................................343.7 Determination of Physical Parameters................................35

3.7.1 pH.........................................................35

3.7.1.1 Calibration.................................................353.7.1.2 Measurement...............................................35

3.7.2 Conductivity..................................................363.7.2.1 Calibration.................................................36

3.7.2.2 Measurement...............................................363.7.3 TDS........................................................36

3.7.3.1 Calibration and Determination...................................363.7.3.2 Measurement...............................................37

3.7.4 Temperature Determination......................................373.7.5 Turbidity....................................................37

3.7.5.1 Calibration.................................................373.7.5.2 Measurement...............................................37

3.8 Determination of Chemical Parameters...............................383.8.1 Total Alkalinity................................................38

3.8.2 Total Hardness................................................383.8.2.1 Standardization of EDTA solution.................................39

3.8.2.2 Determination of Total Hardness.................................393.8.3 Determination of Ions...........................................39

3.8.4 Determination of Arsenic.........................................403.8.4.1 Digestion of samples..........................................40

3.8.4.2 Preparation of Standard Arsenic solutions...........................403.8.4.3 Preparing Spiked Samples for recovery.............................40

3.8.4.4 Calibration and Measurement...................................413.9 Precision of the Methods Used..............................41

CHAPTER FOUR....................................................424.0 RESULTS AND DISCUSSION.........................................42

4.1 RESULTS......................................................424.2 DISCUSSION.................................................53

CHAPTER 5......................................................58

5.0 CONCLUSION AND RECOMMENDATION..............................585.1 CONCLUSION.................................................58

5.2 RECOMMENDATION.............................................58REFERENCES.....................................................59

TABLES

Table 1.Sample locations and designated codes...........................33

Table2. Physical Parameters of water samples collected......................42Table 3. Total Hardness of water samples collected..........................43

Table 4. Alkalinity of water samples collected..............................44Table 5. Concentration of cations in water samples collected...................45

Table 6. Concentration of anions in water samples collected...................46Table 7. Concentration of Arsenic in water samples collected...................47

Table 8. Plotted values in distribution determination.........................48Table 9. RPD for Duplicate of month 1...................................51

Table 10. RPD for Duplicate of month 2..................................52FIGURES

Figure 1. Map of Obuasi Municipality Showing the location of communities........30Figure 2. A terrain map of Obuasi, showing its contours and estimated groundwater flow............................................................32Figure 3. Graph showing lognormal distribution............................49

Figure 4. Graph showing normal distribution..............................50