Pollution Studies on Ground Water Contamination: Water Quality of Abeokuta, Ogun State, South West Nigeria

Changes in water levels in wells reflect changes in recharge to, and discharge from an aquifer. Generally groundwater is rain water or water from surface water bodies, like rivers, lakes or streams that permeate into the soil and bedrock and is stored underground in the pores spaces between soil particles. Groundwater pollution occurs when hazardous substances come into contact and dissolve in the water in the soil or on the surface. Groundwater is generally less susceptible to contamination and pollution when compared to surface water, naturally impurities in rainwater or surface water which replenishes groundwater systems, get removed while infiltrating through soil strata. In Nigeria, groundwater is used intensively for irrigation and domestic purposes, a variety of land and water-based human activities are causing pollution of this precious resource. Its over-exploitation is causing aquifer contamination in certain instances, while in certain others its unscientific development with insufficient knowledge of groundwater flow dynamic and geo-hydro-chemical processes has led to its mineralization. Adequate supply of safe and portable fresh water is an inevitable factor for socio economic development.  Although the recent global attention focuses on how the current and foreseeable water crisis and associated consequences would be addressed, quite a lot of factors such as  low level of education, insufficient budgetary funding, inefficient government policies,  drought are increasingly contributing to the pollution of domestic water in Nigeria. Keywords: Nigeria, Groundwater, Pollution, soil strata, Qualit

Pollution Studies on Ground Water Contamination: Water Quality of Abeokuta, Ogun State, South West Nigeria

Abstract Changes in water levels in wells reflect changes in recharge to, and discharge from an aquifer. Generally groundwater is rain water or water from surface water bodies, like rivers, lakes or streams that permeate into the soil and bedrock and is stored underground in the pores spaces between soil particles. Groundwater pollution occurs when hazardous substances come into contact and dissolve in the water in the soil or on the surface. Groundwater is generally less susceptible to contamination and pollution when compared to surface water, naturally impurities in rainwater or surface water which replenishes groundwater systems, get removed while infiltrating through soil strata. In Nigeria, groundwater is used intensively for irrigation and domestic purposes, a variety of land and water-based human activities are causing pollution of this precious resource. Its over-exploitation is causing aquifer contamination in certain instances, while in certain others its unscientific development with insufficient knowledge of groundwater flow dynamic and geo-hydro-chemical processes has led to its mineralization. Adequate supply of safe and portable fresh water is an inevitable factor for socio economic development. Although the recent global attention focuses on how the current and foreseeable water crisis and associated consequences would be addressed, quite a lot of factors such as low level of education, insufficient budgetary funding, inefficient government policies, drought are increasingly contributing to the pollution of domestic water in Nigeria. Keywords: Nigeria, Groundwater, Pollution, soil strata, Quality 1.0 Introduction Groundwater is widely distributed under the ground and it is replenish able resource unlike other resources of the earth. Groundwater includes all water found beneath the earth's surface. It is part of the earth's natural hydrological cycle. It is the body of water derived primarily from percolation and contained in pore spaces of a permeable rock. Groundwater is an economic resource and more than 85% of the public water for consumption Journal of Environment and Earth Science www.iiste.org ISSN 2224-3216 (Paper) ISSN 2225-0948 (Online) Vol. 3, No.5, 2013 162 is obtained from groundwater. It is often used for industry, commerce, agriculture and most importantly for drinking. Ayoade The quality of water is of vital importance whether for industrial or domestic purposes. For water to be of consumable quality, it must attain a certain degree of purity. Often, the raw water used for domestic purposes is vulnerable to contamination due to the human influence resulting in pollution. According to Water can also be a source of serious environmental and health problems if the design and development of such water supply system is not coupled and tied with appropriate sanitation measures. According to Houston (1995) reported that the bedrock over much of Africa is of Precambrian formations, which are dominated by relatively impermeable crystalline rocks such as granites, schist, gneiss and quartzite. It was often necessary to drill 60 -80 m deep, with wells often yielding less than 2 m 3 /day A large number of people are dependent on the groundwater resource in the weathered regolith for basic water requirements and abstraction is largely through large diameter wells using a bucket tied to the end of a rope for withdrawing water. The rope-and-bucket arrangement is now being replaced in several households with centrifugal pumps resulting in larger quantities of groundwater withdrawal. Hydrogeology of Abeokuta Ogun State In Abeokuta, as in many areas underlain by the basement complex rocks, the populace depend largely on the surface water, which is supplied by the water corporations from the River Ogun. This source of water supply is 163 not sufficient and therefore does not meet the demand of the populace. This surface water, which is the major source of water consumption in Abeokuta, has a very low output especially during the dry season when the evaporation rate is high (and precipitation is lower than annual average). Normally, most sachet water industries depend on the water from the state water corporations this has increased the problem of water scarcity because the demand for the water becomes greater than the supply especially during dry season. Again, people use hand dug wells, but this poses problem during dry season because the required depth would not be reached due to the terrain and the cost of drilling borehole is very high. For these reasons, groundwater should have been an alternative source of water but there is a great problem about locating high productive aquifers in different parts of Abeokuta. Abeokuta lies within the Basement Complex rocks. These rocks are of Precambrian age to early Palaeozoic age and they extend from the north-eastern part of the Ogun state (which Abeokuta belongs) running southwest ward and dipping towards the coast The individual rock has various hydro-geologic characteristics. Abeokuta belongs to the stable plate which was not subjected to intense tectonics in the past.Therefore, the underground faulting system is minimal and this has contributed to the problem of underground water occurrence in this area. The northern side of Abeokuta like Lafenwa side is characterised by pegmatite underlain by granite and therefore has good hydro-geological history. The southern part (made up of granitic gneiss) enters into the transition zone with the sedimentary basin and is characterised by fairly satisfactory hydro-geological history. The western part is characterised by granitic gneiss which is less porous and various quartzite intrusions (Key, 1992).This area is highly problematic and it is prone to low yield groundwater supply. The terrain of Abeokuta is characterized by two types of landforms; sparsely distributed low hills and knolls of granite, other rocks of the basement complex and nearly flat topography. The rugged rock-strewn relief is prominent towards the north, in the central and south-eastern parts of the city. The city is drained by two major rivers, Ogun and Oyan and many small streams. Some of these streams take their source from local rocky hills while some are distributaries to the two major rivers. Two main climatic conditions exist, the rainy season lasting for between seven and eight months between April and October with an interruption in August, and the dry season; running through November till February. Annual rainfall of about 963mm and the temperature is usually between 26 0 C and 28 0 C. The town has become increasingly cosmopolitan as a result of its elevation in status to state capital in 1976 (Olabisi, Awonusi & Adebayo, 2007). This has continued to place increasing stress on the existing infrastructural facilities in the town. 1.2Water quality monitoring in Nigeria The basis of water quality monitoring is to obtain information which will be useful in management of water resources in the country. It would prove useful in management, control and investigation of pollution cases, Classification of water resources, Collection of baseline data, Water quality surveillance and Forecasting water quality. In Nigeria most of the portable water used for both domestic and industrial purposes is channelled from rivers and groundwater. There is no integrated river/ground water quality monitoring scheme in Nigeria. Vol. 3, No.5, 2013 164 range from 657 to 812 us/cm. These values are below WHO highest desirable level of 900 us/cm, the chloride content in the water samples ranged from 61 -79 mg/l. The result of chloride contents were below the WHO Resul