The coarse–grained sandstones inter-bedded with shales, thin

The Aquifer of the
Awe Formation

The
Awe Formation is underlain by the Asu River Formation, known to be the oldest
group of all the formations in Nigeria. The formation is made up of
flaggy-whitish, medium to coarse–grained sandstones inter-bedded with shales,
thin limestone and clays from which brines spring up. The multi-layered beds of
sandstone usually appear highly porous (confine aquifer) and yield much water
contaminated by the brines from the inter-bedded shales. Offodile (2002)
reported the yields from two boreholes at Awe, one each from New Awe and Old
Awe to be 3.0 l/s and 3.3 l/s respectively. This implies that the formation
yields much brine or water that could not be used readily for drinking mainly
due to high concentration of the brine.

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1.2.2
   Aquifer of the Makurdi / Keana and
Ezeaku Formations

The
Makurdi Formation is made up of highly indurated medium to coarse grained
sandstones which are almost impermeable in some places and act as aquitards
(poorly permeable strata with poor yield). In cases where the sandstones are
well fractured or less indurated, the formation is porous, permeable and acts
as an aquifer. Offodile (2002) reported the hydraulic characteristics of
boreholes from two (2) locations to be as follows:

First
borehole: Depth = 79.3 m, drawdown = 31.9 m, yield (Q) = 3 l/s, SWL = 14.7 m,
Coefficient of Tranmissivity (T) = 19 and Specific Capacity (Q/S) = 94 L/m/d.

Second
borehole: Yield = 3 l/s, T = 29.8, Specific Capacity (Q/S) = 66 L/m/d and
drawdown (s) = 5.14 m.

The formations
of the Makurdi/Keana and Ezeaku are very useful as aquifers. The Sandstones are
used as potential reservoirs of groundwater. This depends on secondary
permeability which results from fracturing and weathering.

1.2.3    Aquifer of the Awgu Formation

The
formation is made up of greybedded shales with occasional sandstone beds and
limestones. The sandstone beds are usually fine to coarse-grained. Where coarse
grained, they are very permeable and bear water. But it is often limited in
thickness and lateral extent, hence reducing the groundwater potential.
Offodile (2002) reported that a borehole drilled in Assakio east of Lafia
coincided with artesian water table having a depth of 150 m and yields 3.0
litre/sec with a head of 1.5m above ground level.

1.2.4    Aquifer of the Lafia Formation:

The
Lafia Formation comprises mainly sandstones of varied facies that overlie the
Awgu Formation. It is fine to coarse grained, highly porous and permeable. At
the point of contact between the Lafia Formation the underlying Awgu Formation
which is less permeable, many springs outcrop which gives rise to a watershed.
Drilling of boreholes enabled the assessment of groundwater potential of the
area. Offodile (2002) reported averages of some borehole characteristics as:

Yield =
4.2 l/s, SWL = 8.13 m, draw down = 15.5 m and depth = 152 m.

Table 2.1:  Characteristics of sedimentary aquifers of the Middle Benue Trough
in Nasarawa State (Source: Nasarawa
State Ministry for Resources, Lafia, (2011) and Offodile, (2002).

S/No

Aquifer/Borehole No.

Yield (1/s)

Depth (m)

SWL (m)

Drawdown (s)

Spec. Cap (1/m/d)

Coeff of Trans. (T)

1

Awe
Formation
Borehole
Nos. 1 & 2

3.0
&
3.3


 





2

Makd/Keana/Ezeaku

 

 

 

 

 

 

Borehole
No. 1

3.0

79.3

14.7

31.9

94

19

Borehole
No. 2

3.0

5.14

66

29.8

3

Awgu
Formation

0.3

150

1.5

4

Lafia
Formation

4.2

152

8.13

15.5

2.3       Groundwater
Quality

The quality of groundwater
resources in Nigeria has been a major concern over the years. This is shown in
studies carried out by researchers who attribute the causes to different
sources ranging widely from natural processes to anthropogenic activities. Ocheri et al, (2014)
opined that these causes include the
geology/geochemistry of the environment, urbanization rate, degree of
industrialization, leachates from landfill/dumpsite,  bacteriological pollution, heavy metals and
effect of seasons. According to Ravikumar et al. (2011), evaporation and
transpiration, wet and dry deposition of atmospheric salts, oxidation and
reduction, cation exchange, dissociation of minerals from soil and rock–water
interactions, precipitation of secondary minerals, mixing of waters, leaching
of fertilizers and manure and biological process are responsible for altered
groundwater composition in any region. Sajad et al
(1998) asserts that groundwater quality is a function of natural processes and
anthropogenic activities, and that the type, extent and duration of
anthropogenic activities on groundwater quality are controlled by the
geochemical and physical processes as well as the hydrological condition
present. Hence different factors influence groundwater chemistry in an
environment.

In groundwater assessment studies, Harter (2003) examined
groundwater quality and groundwater pollution of an area and remarked that
groundwater contains dissolved mineral ions which it slowly dissolved from soil
particles, sediments and rocks as the water travels along mineral surfaces in
the pores or fractures of the unsaturated zone and the aquifer. He then grouped
the dissolved ions into primary (or major), secondary and tertiary constituents
in natural groundwater and further remarked that human activities can alter the
natural chemistry of groundwater through indiscriminate disposal or
dissemination of chemicals at the land surface and into soils.

In Basement Complex, Adegoke et
al, (2009) examine the concentrations of heavy metals in water and soil of
Ikogosi, Warm Spring, in Ondo state of Nigeria. The high concentration of heavy
metals in the area is attributed to anthropogenic sources and opined that such
high concentrations is highly toxic to human health and can result to chronic
human diseases.

Adeyemo and Temowo (2010) in
a hydrogeological investigation of waste dumps in Ibadan noted the
concentration levels of electrical conductivity, total dissolved solids,
sodium, potassium, magnesium, nitrate and chloride were higher in water samples
collected near the dumpsite than those far away. This is traced to leachate
from dumpsite. Bayode et al (2012) assessed the impact of some waste dumpsite
on the groundwater quality in some parts of Akure metropolis and of the
parameters analysed; pH, electrical conductivity, total dissolved solids,
calcium, and nitrate concentrations exceeded WHO prescribed limit for drinking
water. This is especially true of water samples collected within the vicinity
of the dumpsite implying that leachates have contributed to the high
concentration level of the elements in the groundwater assessed. The quality of
groundwater in parts of Kaduna Metropolis were investigated by Jatau et al
(2006), he noted the groundwater of the area is slightly acidic, with high
iron, nitrate and faecal coliform concentrations. He remarked that leachates
from wastes and dumpsites that characterized the area are responsible for the
altered water chemistry.

In sedimentary terrain, Oyeku
and Eludoyin (2010) assessed the level of heavy metal pollution in groundwater
resources of Ojota area in Lagos using Atomic Absorption Spectrometry (AAS) and
remarked that hand dug wells and boreholes near Olusosun landfill were
contaminated with heavy metals. They linked the source of the heavy metals (Pb,
Cu and Fe) to uncontrolled disposal of lead batteries and spent petroleum
products since spatial and seasonal variations in the concentration level
suggest point sources pollution. Ikem et
al (2002) evaluated groundwater quality characteristics near two waste sites
in Ibadan and Lagos, they found the concentrations of nitrate, ammonia,
Chemical Oxygen Demand, aluminium, cadmium, chromium iron lead nickel and total
coliform to exceed WHO prescribed limit for drinking and as such post threat to
the health of humans consuming such water. The elevated concentration of these
elements in groundwater is traced to leachates from the dumpsites. Alexander
(2008) Efe et al (2008), Al-Hassan and Ujo (2011) found groundwater to be
slightly acidic, and calcium, magnesium, chloride and sodium concentrations
were within WHO guide limit in Mubi town; hand dug wells located close to
dumpsites in Onitsha have higher levels of turbidity, total suspended solids,
calcium bicarbonate, electrical conductivity, salinity, acidity, lead. iron and
bacteria loads; and for Masaka, water from all the wells analysed were polluted
with chemical and bacteria, turbidity, dissolved oxygen, nitrates, chromium,
total bacteria count, and concluded that water was not safe for drinking.

In Jemeta area of Yola town,
Ishaku and Ezeigbo (2010) analysed the quality of groundwater and found
concentrations of chloride, nitrate, total dissolved solids and coliform to far
exceed the WHO allowable limit for drinking water and were higher in the wet
season. This is traced to anthropogenic activities as household wastes,
wastewater find their way into water sources. Relationship show positive
correlation for chloride, total dissolved solids, nitrate, sulphate, nitrate
and total dissolved solids and sulphate for dry season, while nitrate and
sulphate total dissolved solids and sulphate, chloride and sulphate and
chloride and nitrate.

Amadi et al (2010) assessed the effect of urbanization on
groundwater quality of Makurdi metropolis. The results of this analyses shows
low pH, higher concentration of iron, manganese, calcium and total dissolved
solids and total coliform in water samples collected within the vicinity of
dumpsite when compared to those far away from the dumpsite which suggests the
leachate resulting from the dumpsite has influenced the groundwater chemistry
of the area. The presence of coliform is traced to sanitary condition of the
well. The Groundwater in the area is of Ca- SO4 type.

Generally, the rate and
characteristics of leachate production depends on a number of factors such as
solid waste composition, particle size, degree of compaction, hydrology of the
sites, age of the landfill, mixture and temperature of the condition and
availability of oxygen (Ogundiran and Afolabi, 2008).

Heavy metals heavily contribute
to groundwater contamination and can impact human health. Common heavy metals
of toxic effects are arsenic, barium, cadmium, chromium, lead, mercury, iron,
lithium, manganese, zinc, selenium, and silver. They are naturally occurring
substances which are often present in the environment at low level but
augmented by anthropogenic activities. Humans are normally exposed to these
metals by ingestation (drinking and eating) or inhalation (breathing) (Martin
and Griswold, 2009). These metals may come from natural sources, leached from
rocks and soils according to their geochemical mobility or come from
anthropogenic sources, as a result of human land occupation and industrial
operation.

2.3.1    Water
Quality Standards/Guidelines

Water quality is defined based on a set of physical
and chemical variables that are closely related to the water’s intended use.
Solsona (2002) defined a standard as a rule or principle considered by an
authority and by general consent as model in comparative evaluation. He further
remarked that a proper standard for drinking water quality should therefore be
a reference that will ensure that the water will not be harmful to human
health. For each variable, acceptable and unacceptable values must then be
clearly defined so that if water meets the pre-defined standards for a given
use, it is considered suitable for that use. If the water fails to meet these
standards, it must be treated before use (Cordoba et al., 2010).

2.4       Groundwater
Evaluation for Drinking Purposes

2.4.1
   World Health Organization (WHO)
Guidelines

The primary purpose of the guidelines for drinking
water quality is the protection of public health and to improve access to safe
drinking water (WHO, 2004). The WHO water guidelines are divided into four
aspects. These aspects are microbial aspect, chemical aspect, radiological
aspects and the acceptability aspect (aesthetic aspect).

According to WHO (2008) the biological properties
refer to the presence of organisms that cannot be seen by the naked eye and
these include microorganisms such as protozoa, bacteria and viruses. The
physical properties define the water quality properties that may be determined
by physical methods such as conductivity, pH and turbidity measurement. The
physical quality mainly affects the aesthetic quality (taste, odour and
appearance) of water. The chemical aspects describe the nature and
concentration of dissolved substances such as salts, metals and organic
chemicals. Generally, many chemical substances at the appropriate concentrations
in water are essential nutrients that are required for daily intake but at high
concentrations, they make water unpalatable and cause illnesses.

The guideline values selected represent the
concentration of a constituent that does not result in a significant risk to
the health of the consumer after long term consumption. Guideline values have
been set based on the practical level of treatment achievability or analytical
achievability (WHO, 2004).

2.4.2    Nigerian
Standard of Drinking Water Quality (NSDWQ)

The Nigerian water quality guidelines were developed
by Federal Ministry of Health in collaboration with the Standards
Organisation of Nigeria (SON) to provide primary source of
information and a guide to relevant law enforcement agencies in decision making
while judging the fitness of water for use and for other water quality
management purposes .They are used to inform water users about the physical,
chemical, biological and aesthetic properties of water. The quality criteria,
consists of a Target Water Quality Range (TWQR). The TWQR for a particular
water constituent describes the range of the concentrations at which the
constituent would have no known adverse effects on the suitability of the water
when used continually.

2.4.3    United
States Environmental Protection Agency (USEPA)

The United States Environmental Protection
Agency (EPA or sometimes USEPA) is an agency of
the federal
government of the United States which was created for
the purpose of protecting human health and the environment by
writing and enforcing regulations based on laws passed by Congress. It has
the responsibility of maintaining and enforcing national standards under a
variety of environmental laws, in consultation with state, tribal, and local
governments. EPA enforcement powers include fines, sanctions, and other measures (EPA,
2017). USEPA ensures safe drinking water for the public.

2.5        Groundwater
Evaluation for Irrigation Purposes

Irrigation
refers to the application of controlled amounts of
water to plants at regular or needed intervals.The quality of water for irrigation is determined by
both its effects on the soil and plant health (Ramesh and Elango, 2012).
According to Fipps (1996), the main problem in irrigation comes from salt level
in the water. He stated two types of salt problems in water; those that are
associated with salinity (salinity hazard) and those associated with sodium
(sodium hazard) all of which affect both soil and plant health.  Fipps (1996) also opines that these problems
can be evaluated using the analysed total concentration of soluble salts,
relative proportion of sodium to the other cations and the bicarbonate
concentration as related to the concentration of calcium and magnesium in the
water. The individual levels and association of these constituents describe the
suitability of water for irrigation. The
groundwater quality for irrigation purposes in the study area were evaluated
based on the following quality indices:

2.5.1       
            Electrical Conductivity (EC):          

Electrical
Conductivity is directly related to salinity problems; it is an important
parameter to be considered when evaluating quality of water for irrigation
purposes. It is a good measure of salinity hazard to crops as it reflects the
Total Dissolved Solids in groundwater (Sundariah et al. 2014).

2.5.2       
            Sodium
Adsorption Ratio (SAR):

Sodium
Adsorption Ratio measures the relative portions of Na+ to Ca2+
and Mg2+. It indicates the degree to which irrigation water tends to
enter into cation-exchange reactions in soil. When sodium replaces adsorbed
calcium and magnesium it creates a problem as it may cause the soil to become
compact and impervious (Joshi et al. 2009).

2.5.3       
            Sodium Percentage
(Na %):

Sodium has direct effects on
soil permeability hence it is an important parameter to consider when
evaluating groundwater quality for irrigation purposes. Sodium percentage (Na
%) expresses the percentage of sodium out of the total cations (Nasher and
El-Sagheer, 2012).

2.5.4       
            Permeability Index
(PI):

Permeability Index measures
the effects irrigation water might have on soil permeability in an area. PI
values also depicts suitability of groundwater for irrigation purposes by
evaluating the Na+, Ca2+, Mg2+ and HCO3-contents
in water, it as well measures long term use of the water on soil permeability
(Sundariah et al. 2014).

2.5.5       
            Kelly’s
Ratio (KR)

Kelly’s ratio is a measure
of Na+, against Ca2+ and Mg2+ in water. It is
used to measure Na excess in irrigation water (Ramesh and Elango, 2012).

2.5.6       
            Magnesium Ratio
(MR)

Ramesh and Elango (2012)
asserts that Ca2+ and Mg2+ maintain a state of
equilibrium in groundwater generally, hence more Mg2+   present in waters affects the soil quality
by converting it to alkaline and as a result crop yield is decreased.

2.5.7    Residual Sodium Carbonate (RSC):

Residual Sodium Carbonate is
an important parameter in determining the suitability of water for irrigation;
it indirectly indicates the sodium hazard potential of irrigation water. High
concentration HCO3- and CO3- in
water tend to precipitate Ca2+and Mg2+ which results in
an increase in the relative levels Na+ ions in the water as sodium
bicarbonate (Sadashivaiah, et al., 2008).

2.6       Geochemical
Assessment of groundwater

2.6.1   Analytical Techniques

2.6.1.1             Atomic
Absorption Spectrometry (AAS) Technique

Atomic Absorption Spectrometry (AAS) is a technique widely used for
measuring the concentration of chemical elements present in environmental
samples by measuring the absorbed radiation of the chemical element of
interest. This is usually done by reading the spectra produced when the sample
is excited by radiation. The atoms absorb ultraviolet or visible light and make
transitions to higher energy levels. According to García and Báez (2012), the
atomic absorption methods measure the amount of energy in the form of photons
of light that are absorbed by the sample. A detector measures the wavelengths
of light transmitted by the sample, and compares them to the wavelengths which
originally passed through the sample. A signal processor then integrates the
changes in wavelength absorbed, which appear in the readout as peaks of energy
absorption at discrete wavelengths. Atoms of an element emit a characteristic
spectral line. Every atom has its own distinct pattern of wavelengths at which
it will absorb energy, due to the unique configuration of electrons in its
outer shell. This enabled the qualitative analysis of sample from the study
area. The concentration is calculated based on the Beer-Lambert law. Absorbance
is directly proportional to the concentration of the analyte absorbed for the
existing set of conditions. The concentration is usually determined from a
calibration curve, obtained using standards of known concentration (García
et’al, 2012).

2.6.1.2             Inductively Coupled Plasma Mass Spectroscopy (ICP-MS)

ICP-MS
is an analytical technique used for determination of trace elements and
isotopic analysis as a result of the very low detection limits, good accuracy
and precision. It can also been used for the analysis of a wide range of trace
elements in a single solution, using a small sample (Jenner et al, 1990).
Inductively coupled plasma mass spectroscopy (ICP-MS) was developed in the late
1980’s to combine the easy sample introduction and quick analysis of ICP
technology with the accurate and low detection limits of a mass spectrometer.
The resulting instrument is capable of trace multi-element analysis, often at
the part per trillion levels (B’Hymer et al, 2000).  ICP-MS has been used widely over the years,
finding applications in a number of different fields including drinking water,
wastewater, natural water systems/hydrogeology, geology and soil science,
mining/metallurgy, food sciences, and medicine.

ICP-MS flame technique is capable of determining low-concentrations
(range: ppb = parts per billion = µg/l) and ultra-low-concentrations of
elements (range: ppt = parts per trillion = ng/l) (Newman, 1996). In principle,
atomic elements are lead through a plasma source where they become ionized.
Then, these ions are sorted on account of their masses and samples are
decomposed to neutral elements in high temperature argon plasma then analyzed
based on their mass to charge ratios. 

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