Assessment of the Concentration of Inorganic Chemical Elements in the Pollution Status of Water Boreholes in Awka- Anambra Sedimentary Basin, Se, Nigeria

Since Awka town was made the capital of Anambra State, population growth, innumerable industries and other new land uses have been on the increase. There is the fear that inorganic geochemical elements may have contaminated the groundwater making it unfit for consumption. This research is thus intended to estimate the magnitude to which borehole waters and by extension the groundwater system in the area have been contaminated. Six borehole water samples were collected and analysed for inorganic geochemical elements. The parameters analysed were colour, acidity, pH, conductivity, total dissolved and suspended solids (TDS and TSS). Others are nitrate (NO3), chloride (Cl ), sulphate (SO4 2), phosphate (PO4 3 ) copper (Cu 2+ ), lead (Pb 2+ ), cadmium (Cd 2+ ), zinc (Zn 2+ ), iron (Fe 2+ ), total hardness (calcium hardness and magnesium hardness) (total hardness) and alkalinity. The analyses were conducted with appropriate geochemical equipment. It was discovered that other anions Environmental Management and Sustainable Development ISSN 2164-7682 2017, Vol. 6, No. 1 http://emsd.macrothink.org 169 apart from phosphate are within the concentrations recommended for safe drinking water. The concentration of the cations is in the following order: Cl> HCO3> SO4> NO3, and that for anions is Mg> Ca> K> Na, thus making the water in the area potentially magnesium chloride water. Iron and lead are the only heavy metals whose concentrations are high. Lead is toxic but iron only stains and causes intestinal disturbance.


Introduction
The creation of Anambra State with Awka as its capital has engendered high population growth rate, innumerable industries and other new land users have continued to generate wastes that are inappropriately disposed. The fear that groundwater in the area may have been contaminated and unfit for consumption is therefore certain and a cause for concern. The aim of the study is therefore to determine the extent to which inorganic chemical constituents in the study area has polluted the groundwater system as an appropriate measure for pollution control and sustainable development. Environmental Management and Sustainable Development ISSN 2164-7682 2017 Geologically, Awka area is underlain by the Ameki (Eocene) Formation and Imo Shale Group (Paleocene) Figure (2). The Ameki Group consists of Nanka Sandstone, Nsugbe Formation and Ameki Formation (Nwajide, 1979). The Ameki Formation outcrops in the study area and consists predominantly of alternating shale, sandy shale, clay, sandstone and fine grained fossiliferous sandstone with thin bands of limestone (Reyment, 1965;Arua 1986). The age of the formation has been considered to be either early Eocene (Reyment, 1965) or early-mid Eocene (Bergeren, 1960;Adegoke 1969). The depositional environment has been interpreted as estuary and open marine based on faunal content. Nwajide (1979) and Arua (1986) suggested environments that ranged from nearshore to intertidal and subtidal zones of the shelf, whereas Fayose and Ola (1990) suggested that the sediments were deposited in shallow marine waters of 10 and 100 m paleobathymetry.  The Imo Formation consists of blue-grey clays and shales with bands of calcareous sandstone, marl and limestone (Reyment, 1965). Imo Formation is the outcropping lithofacies equivalent of Akata Formation in the subsurface Niger Delta (Short andStauble 1967, Avbovbo, 1978).

AWKA
The stratigraphic sequence of the study area is shown in Table 1. ISSN 2164-7682 2017

Climate and Physiography
The study area lies within the humid tropical rainforest belt of Nigeria. It is bounded by fresh water swamp to the south and the guinea savannah grassland to the north. The major climate variables are Rainy and Dry seasons brought about by the two predominant winds in the area. These winds are the south western monsoon wind from the Atlantic Ocean and the north eastern dry winds from across the Sahara desert, respectively. The rains last between April and October, followed by five months of dryness (November to March), (Illoeje, 1980). A short spell, the Harmattan period, is particularly dry and dusty, and commences in the study area by December. It is characterized by a grey haze that limits visibility and blocks sun rays.
Forest vegetation in the study area have been lost due to farming and other anthropogenic activities. Fringing forest however exit around rivers, streams and other wetlands that dot the area.

Materials and Method
Six water samples were collected from boreholes located at different points in the study area. The water samples were stored in pre-treated 50 cl plastic containers and taken to the laboratory for analyses. The water quality analyses followed recommended standard methods. The parameters analysed were colour, pH, conductivity, total dissolved solids (TDS) and Total suspended solids (TSS total hardness (calcium hardness and magnesium hardness) and alkalinity.
The analyses in the laboratory were carried out using atomic absorption spectroscopy for Ca 2+ , Na + , Mg 2+ and Cl -, while Pb 2+ , Cd, and Cu were analysed with the aid of spectrometer. K + was determined using the flame photometer. pH was measured with standard pH meter, while the concentration of the total iron (Fe 2+ ) was determined calorimetrically using Spekker absorption meter. Total dissolved solids (TDS) were determined using glass fibre. Turbimeter was used to assess turbidity. Physical parameters like pH and dissolved oxygen were measured in situ in the field with the appropriate standard meters. Anions like HCO 3 were estimated by titrimetric method. All details of analytical procedures used, have been reported in Freeze and Cherry (1979).
The concentrations of cations like Ca 2+ , Mg 2+ and Na + in milliequivalent per litre were later used to obtain sodium absorption ratio (SAR). ISSN 2164-7682 2017

Results and Discussion
The results of the analyses Table 2, show the concentrations of the physicochemical constituents of the underground water borehole samples in Awka area with the corresponding WHO, 2006 standard for safe drinking water.  (3) and Table 3. It should be pointed out that phosphate that is high in groundwater in the area is probably introduced from agricultural activities, leachates and seepages from dump sites and animal farms. Even though sulphate and nitrate concentrations are below their respective limits, their future status should be monitored because they together with phosphate are associated with fertiliser applications. ISSN 2164-7682 2017 Excess sulphate in water causes diarrhoea and purgatives in humans while high nitrate is dangerous to pregnant women and poses serious problems to infant less than three to six months of age, because of its ability to cause methemoglobinaemia or blue baby syndrome, in which blood losses its ability to carry sufficient oxygen.

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The concentrations of total solids (TS), total dissolved solids (TDS) and total suspended solids (TSS), are well below the limits recommended for safe drinking water Figure (4) and Table 4. This result is indicative of excellent borehole construction and development.    The pH of the groundwater is neutral to alkaline Figure 5; Table 5. This result shows that mean pH value of 6.90 for the groundwater in Awka area is potable and indicates also that the groundwater will not corrode pipes and other metal fittings (Corrodible materials).   Table 6. The results showed that while zinc and copper were not detected in most of the groundwater in the area, iron and lead are in excess in some of the boreholes according to the scale of WHO, 2006. It also showed that the high iron content for example is localised (in BH1, BH3 and BH4), which may be indicative of point sources, like an auto village or the direct result of the geology of the affected areas. High concentration of iron in water is not generally poisonous but causes brownish precipitates due to oxidation of iron in form of Fe 2 (OH) 3 which does not present an aesthetic appeal to toilets and other household items. Lead is toxic (Short and Stauble 1967) as it forms lead oxide (PbO 2 ) when mixed with blood. This process reduces the permeability of soils resulting to poor internal drainage (Collins and Jenkins, 1960). Richard (1985) classified water standard for irrigation based on sodium absorption ratio Table 7.
SAR of water in the area was obtained using equation 1 to generate SAR values, Table 8 which were compared with the Richard (1985) classified standard for irrigation. On comparism it was shown that the inorganic elements of the groundwater in the study area are excellent for irrigation purposes Where Na + , Mg and Ca 2+ are the respective concentrations of sodium, magnesium and calcium in Mg/l contained in the groundwater. ISSN 2164-7682 2017   The average concentrations of major cations and anions were used in equation 2 to derive values, which are converted values from mg/l to meq/l Table 9. The converted values were plotted into the piper trilinear diagrams (Piper, 1944) in order to decipher the potability, water types and classes of the borehole waters in Awka area Figure (6).

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(2)  The spatial distribution of anions and cations in the study area were also used to compute the water types of the groundwater system at various locations in the study area Table 10 and Figure 7. The spatial distribution shows that the dominant water type is tending toward magnesium chloride.  It is also possible to examine the extent of pollution of the groundwater based on the application of Hortons scales (1995). Hortons scale stipulates the scale of rating of pollution extent Figure 8. If the value of pollution falls at zero, it is of critical value. If it plots to the right of zero value (positive side), the water is polluted in that order. If it plots to the negative side, the water is not polluted in that order.  (Horton, 1995) The computation of Horton Index number is shown in Table 11. ISSN 2164-7682 2017  From the Hortons scale of Figure (8), the water is slightly polluted. The pollution is probably Environmental Management and Sustainable Development ISSN 2164-7682 2017 due to the fact that the groundwater is heavily polluted by phosphate and in some cases, iron. Phosphate is high probably due to the fact that the surrounding villages use excess phosphate fertilizer in agriculture. Animal defecation may also be a factor.

Conclusion
Iron content in the area is high (WHO, 2016). High iron may be due to the effect of industrial activities relating to the release of iron compounds. The composition of some heavy metals like lead is on the increase due probably to effluent from battery industries. High concentrations of Chloride in groundwater in the study area, though not in excess, may be due to wastes from nearby markets and septic tank leakages. High concentration of Phosphate can also be traced to leachates from waste disposals. Again sources of phosphates may be runoff from agricultural sites using phosphate fertilizers, poor management of sewage and /or due to decayed plant tissues, since phosphates are tied up in plant tissues. The area might have been used as cemetery in the past as phosphates are present in fossilized bones or animal droppings, especially, cattle reared by Fulani nomads. It may also be that apatite is somewhere in the subsurface rock. As potassium is found in aluminates KAL 3 (SO 4 ) 2 (OH) 6 , the phosphate may have originated also from the laterite of Ameki Formation. Lead could also be due to sawmills, woodworks, auto repair workshops and can affect red blood cell chemistry in humans (Franson, 1995). Finally, the water tilted to magnesium chloride water which is good for irrigation and other household activities. Periodic monitoring of the groundwater system in the area is recommended as a management strategy.