OR/17/056 Ibadan case study
| Lapworth, D J, Stuart, M E, Pedley, S, Nkhuwa, D C W, and Tijani, M N. 2017. A review of urban groundwater use and water quality challenges in Sub-Saharan Africa. British Geological Survey Internal Report, OR/17/056. |
Setting
With a total estimated population of 160 million Nigeria is the most populous nation in Africa with a large number of cities and smaller growing urban centres. Notable among these urban centres are Lagos, Kano and Ibadan which are also among the top hundred largest cities in the world. With the reality of poor landus/infrastructural planning, the attendant pressures on land and infrastructure translate into socio- and environmental problems in most urban centres in Nigeria.
This section is an appraisal of the environmental setting of Ibadan metropolis, south-western Nigeria, with particular reference to the impacts of urbanization on water resources. The overall intent is to assess the main anthropogenic drivers/sources of groundwater contamination related to the need for integrated urban planning, water resources and waste management.
A number of published and unpublished hydrochemical data were collated and assessed in respect of data quality protocols, including a database of 40 hydrochemical samples from Tijani and Onodera (2005)[1], a database of 77 hydrochemical samples from NGSA (2010) and a data base of 57 hydrochemical samples from Tijani and Diop (2011)[2]. In addition, a database of 50 microbiological profiles and a number of other published and unpublished literatures were also incorporated.
Location and spatial extent of Ibadan
Ibadan metropolis, located in the south-western part of Nigeria, is the largest pre-colonial city in Nigeria, and Sub-Saharan Africa. It is 128 km northeast of Lagos and 530 km southwest of Abuja, the Federal capital, and is a prominent transit point between the coastal region of the south and the areas to the north in the extreme western portion of the country. The total land area of Ibadan metropolis is 3,123 km2 15% of which represents the urban old city centre while the remaining 85% represents the surrounding peri-urban areas. Administratively, Ibadan metropolis is made up of eleven (11) Local Government Areas (LGA) five (5) of which encompassed the core traditional areas of the city (i.e. Ibadan North, Ibadan North-East, Ibadan North-West, Ibadan South-West, Ibadan South-East) while the remaining six (6) constitute the surrounding peri-urban settlements (i.e. Akinyele, Egbeda, Ido, Lagelu, Ona-Ara and Oluyole) (see Figure 9.1).
Furthermore, the spatial analysis of spectral signatures of Landsat satellite imageries of 1972, 1984 and 2006 by Afolayan (2010)[3] as presented in Table 9.1, revealed that the land-use of Ibadan has changed dramatically, reflecting an expanding (but essentially unplanned) development of urban areas. The rapid expansion of the coverage of urban and sub-urban areas from about 24% in 1972 to 66% of the land-use area in 1984 can be attributed to the transformation of the former rural and vegetated areas in the periphery of the city (such as Lalupon, Alakia, Olodo, Ogbere, Apata, Odo- Ona, Podo, Akanran, Bode-Igbo and Moniya) into the peri-urban entities to form the Ibadan metropolis.
| Category of Land Use (in %) | 1972 | 1984 | 2006 |
| Urban | 5 | 14 | 15 |
| Peri-Urban | 19 | 52 | 53 |
| Water | 13 | 8 | 5 |
| Rural/Vegetation | 63 | 26 | 17 |
The highlighted remarkable urbanization between 1972 and 1984 can be attributed to the oil boom era and the attendant rural to urban migration that prompted drastic utilization of land resources, especially in terms of building houses and erecting facilities for businesses (Ajayi and Abegunrin, 1994[4]). The increase in population density of 586 person/km2 in 1991 to 816 person/km2 in 2006 is a consistent with the observed spatio-temporal changes in the land-use pattern of Ibadan metropolis. The increasing population of the metropolis and its suburbs as well as the outward residential mobility of people from the city to the suburbs are said to be the forces responsible for the merging together of the city with its former peri-urban zones to become the Ibadan metropolis (Udo, 1994[5]).
Demography and socio-economic settings
Ibadan is the capital city of Oyo State, Nigeria. It is the largest metropolitan geographical area and is the third largest in Nigeria in terms of population, after Lagos and Kano, with a population of 2.5 million (Shemang, 1990[6]). Ibadan was founded in 1829 and was initially occupied by immigrants, who moved into the city in search of security from intertribal wars (Wright and Burgess, 1992[7]). Ibadan had since grown to be a big metropolis characterized by rapid remarkable growth with a population of 100 000 in 1851, to 175 000 in 1911 and 745 448 in 1952 during the colonial era. Subsequently, the population rose to 1 141 677 in 1963 at a growth rate of 3.95% per annum. In 1991 the population rose to 1.8, and then to 2.5 million in 2006 (Shemang, 1990[6]). With a projected annual population growth of 4%, the population of Ibadan metropolis can be put at well over 3.3 million inhabitants today.
Udo (1994)[5] reported that the population density of the urban area increased by 9.5% while that of the surrounding rural area increased by 100% within a period of 15 years (1991–2006). A situation that can be attributed to the movement of population towards the peri-urban area, consequent to the rapid urbanization of the core area and industrialization of the peri-urban centre where lands are readily available for industrial development. The economic activities of Ibadan include commerce, handicrafts, small- and medium-scaled manufacturing and service industries as well as agriculture mainly in the surrounding peri-urban areas. A number of the farming activities are on part-time basis aimed at augmenting earnings from other jobs while the predominant crop production in Ibadan is staples such as cassava, maize and vegetables such as spinach, okra, tomatoes and pepper. Due to its strategic location in southwestern Nigeria, Ibadan is an important commercial centre with market square or stalls at virtually every street and corner in the traditional core area and the inner suburbs of the city. Within the city there are many daily neighbourhood markets and a number of periodic (8th-day or 3rd-day) markets.
The challenges of the demographic and social settings are summarised by (Onibokun and Kumuyi, 1996) and attributable to:
- Unplanned growth and inefficiently managed land use planning over the years
- Poorly managed waste disposal system, poorly constructed dumpsites and drainage systems
- Grossly inadequate public utilities and social infrastructural services such as poor and inadequate housing/sanitation, poor/inadequate water supply and attendant environmental contamination problems
Environmental setting
The traditional core neighbourhood, as the oldest part of the city, is a high density area occupied mainly by residents of the city and centred on the famous Mapo Hill with characteristic rusty red roofs and unplanned buildings (Figure 9.2). There are hardly any gaps between the buildings, a situation causing serious ventilation and accessibility problems among others. Where roads are available, these are narrow and usually without drainage gutters and walk ways, thus constituting challenges to household waste and sewage collection, with attendant environmental implications.
Furthermore, like many urban centres in developing countries, poor land-use planning, lack of adequate water supply, lack of proper sewage, and waste disposal systems also characterize the Ibadan metropolis. Consequently, many households, especially within the congested central portion of the city lack toilet and waste disposal facilities while most rely on in-house hand-dug (shallow) wells for their domestic water supplies. As a result, direct discharge of sewage water and dumping of domestic wastes/refuse into the drainage channels are common practices (Tijani and Onodera, 2005[1]). Since late 1970s, many of the municipal facilities have declined to almost zero functionality. Top on the list of those municipal services that have seemed to fail most strikingly is waste collection and disposal followed by the public water supply system, the coverage of which had not been extended beyond the pre-1970 limit. The service is frequently inadequate, resulting in refuse generated remaining uncollected, and with large parts of the drainage systems blocked by refuse dumps (Figure 9.3a and b).
Due to improper management of wastes (through the use of household pit toilets and bathrooms), contaminants from human excreta and urine seep into shallow weathered basement aquifers and thus contaminate many households’ hand-dug wells that are not well protected (e.g. Figure 9.3c). Poorly managed waste disposal systems, as a result of poorly constructed dumpsites and drainage systems as well as waste and sewage management, remains one of the most pressing and unresolved issues that portends negative impacts in terms of groundwater contamination.
Sanitation and waste management
The overcrowded and unplanned nature of the city centre is characterized by the lack of adequate basic environmental infrastructural services such as water supply, proper sanitation, solid waste disposal sites, good drainage and good roads. Inadequate collection and disposal of household/municipal wastes is a typical problem. It has been reported that most municipal governments spend 20–50% of their available operational budgets for solid waste services and around half of the urban households benefit from collection services (Udo, 1994[5]).
In 1998, the Oyo State government, in its continuous efforts to rid Ibadan of indiscriminate dumping of wastes on the road side and other undesignated areas, commissioned four waste dumping sites (Awotan, Ajakanga, Amuloko and Lapite) which are currently active. Nonetheless, most municipal wastes that are collected, in the Ibadan metropolis, end up in open dumps site or open-air incineration sites. A significant portion of household waste also ends up in the drainage systems through the uncontrolled disposal of both solid and liquid wastes into open drains and along roads sides (Figure 9.4). This poses a threat to both surface water and groundwater quality, and flooding as well as serious health hazards in form of waterborne diseases that are common in the city, particularly in the older traditional indigenous areas. Such situations forces the inhabitants to spend appreciable portions of their low income and time on improving their personal health, with adverse consequences for general economic well-being (Onibokun, 1989).
In addition, Akintola and Agbola (1989) projected the amounts of liquid waste for 1990 and 1995 at 113.7 million and 126.5 million litres, respectively. A number of industries (chemical, paper and poultry among others) make private arrangement for the disposal of their waste, without adequate monitoring to ensure proper environmental safeguards. Also, according to the National Population Commission (Shemang, 1990[6]), only 18.47% of households in Oyo State have a water closet linked to a reticulated system, 32.73% use pit latrines and 37.13% use open defecation. (Awosika, 2008[8]).
Consequently, the lack of the most basic waste management services in overcrowded low income neighbourhoods is said to be a major contributor to the high morbidity and mortality among the urban poor (Udo, 1994[5]). For example, mortality rate of children (under the age of five) through diarrheal disease is high (about 50%), largely as a result of poor sanitation, contaminated drinking water and associated problems of food hygiene (World Bank 1993), as is the case in many other countries in SSA.
Water supply
Water supply still poses a serious problem in both the urban and peri-urban parts of Ibadan metropolis. The Ibadan metropolis accounted for nearly two thirds of the total domestic water supplies in the whole Oyo State since mid-1980s. Consequently, Oyo State in recent years has embarked on a programme of rehabilitation of the major waterworks serving the Ibadan metropolis. These include Asejire and Eleyele waterworks as well as Osegere water scheme through a loan from the African Development Bank (ADB). The impacts of these projects has not been felt by the wider population in Ibadan, due to the fact that the water supply networks are only supplying 7% of the households, mainly in the central area of the city (Ajayi and Abegunrin, 1994[4]).
The total output of 200 Ml/d (i.e. Eleyele with 27 ml/d, Osegere with 13Ml/d and Asejire Phases I&II with 80 Ml/d each) was envisaged following the ADB assisted upgrade. However, this is dwarfed by the projected water demand of >600 Ml/d for Ibadan metropolis by the beginning of the 21st century (Udo, 1994[5]). Therefore, sources of water for a large proportion of the Ibadan metropolis still remain the streams, springs, ponds, dug-well, shallow boreholes and harvested rainwater as highlighted in Table 9.2.
| S/No. | Sources of Water Supply | No. of Households | Percentage |
| 1 | Pipe-borne Inside Dwelling | 34 348 | 2.75% |
| 2 | Pipe-borne Outside Dwelling | 50 912 | 4.41% |
| 3 | Tanker Supply/Water Vendor | 28 833 | 2.31% |
| 4 | Borehole | 85 895 | 6.88% |
| 5 | Hand-dug Well | 695 720 | 55.74% |
| 6 | Rain Water | 103 800 | 8.32% |
| 7 | River/Stream/Spring | 204 891 | 16.41% |
| 8 | Pond/Dugout/Lake | 10 063 | 0.81% |
| 9 | Others | 33 733 | 2.70% |
| TOTAL | 1 248 105 | 100% |
Data source: Udo (1994)[5]
In summary, the problems and challenges posed by the rapid population growth of Ibadan are immense. Prominent among these are the inadequate infrastructure including potable water supplies and waste management. Environmental degradation is widespread, including contamination of drainage channels and shallow groundwater systems, due poor waste disposal and management systems.
Physical geography and drainage
The main physiographic features of the city is characterized by undulating terrain which consist of quartzite ridges and inselbergs of gneiss that run approximately in northwest — southeast direction. These ridges are surrounded by the adjoining plains and valleys while the ridges are characterized by peaks such as Mapo, Mokola and Aremo in the central part of the city with elevation range of 160 to 275 metres above sea level.
In terms of hydrology, the metropolitan area of Ibadan is drained by two main rivers, the Ogunpa River and its tributaries drain the eastern parts of the metropolis, while the Ona River and its tributaries drain the western parts of the metropolis. The drainage systems are dendritic, characterized by unmodified stream channels that run in a southerly direction through much of the Ibadan metropolis (Figure 9.5).
River flows are irregular during the dry season, and the considerable influence of population pressure have resulted in built-up areas encroaching river banks. Consequently, direct discharge of household waste, as well as refuse dumps at various points along stream channels, are common. These constitute obstructions to flow and hence pose a constant danger of flooding during the peak of the rainy season within the metropolis, a situation that resulted in catastrophic flooding event in August 1980 and lately the devastating flood of 25th August 2011.
Climate, vegetation and soils
The Ibadan metropolis and its environs are characterized by tropical humid climates with two distinct seasons: the wet season, which occurs between March and October with an average annual rainfall of about 1250 mm and dry season from November to February (Ileoje, 1987). During the wet season, the area is under the influence of the moist maritime south-west monsoon winds from Gulf of Guinea, while the dry season is characterized by dry dust-laden and northeast–southwest trade winds from the Sahara desert. The distribution of rainfall is bimodal with the two peak regimes i.e. May–June with average monthly rainfall of 190 mm and September-October with average monthly rainfall of 170 mm, separated by a period of lower precipitation in August (Ileoje, 1987).
The mean annual temperature is 26°C with a minimum of 21°C while the average temperature for rainy and dry seasons is 27°C and 30°C respectively. Humidity is relatively high for most parts of the year (except during the peak of the dry season) with annual average greater than 80 percent.
The natural vegetation was moist deciduous tropical rainforest with thick undergrowth (Eduvie, 2006[9]). However, due to population pressure and the attendant human impact, most of the surrounding peri-urban forest vegetation has been replaced by secondary forests and derived savanna for field crops such as maize, yams and cassava. There exists two cropping seasons in the area as a result of the bimodal rainfall pattern observed. The first is from late April to early August while the second and shorter one is between early September and November. The dominant field crop production system is that of rotational bush fallow with a long fallow period of 8–10 years (in the past) which has been reduced to 2–4 years due shortage of farmland and intensification of the farming system due to the rapid population growth.
As expected the soils in and around Ibadan metropolis were formed from the underlying crystalline basement rock units (Awosika, 2008[8]) under moist semi-deciduous forest cover (Hopkins, 1965[10]). The soils were mapped and classified into four soil associations and series by Smyth and Montgomery (1962)[11]. These are (i) Iwo, (ii) Okemesi, (iii) Egbeda and (iv) Mamu soil associations. The classification, according to Awosika (2008)[8] is largely based on soil parent materials and the soil associations represent the weathered soil/mottled soil layer (pedolith) over the main bedrock types in Ibadan metropolis.
The soils of the Iwo association were formed from the granite gneisses, those of Okemesi and Egbeda from quartzite and schist while those of Mamu were formed from the pegmatites. Due to the relative resistance to weathering of the schist quartzites, the associated Okemesi soil group is usually shallower; it contains a high proportion of coarse sands, and particularly those that occur in the upper and middle slope portions of the catena. The soils belonging to the Iwo and Mamu association derived from granite gneiss and pegmatite are fairly clayey with a characteristics humus layer, especially over the granite gneiss. The Iwo and Egbeda soil association are the most extensive in the eastern part of the region while those of the Mamu association occur mainly in the south of Ibadan city.
Generally, the soils have low nutrient-holding capacities as reflected in their general low cation exchange capacities that usually vary between 5.0 and 12.0 mili-equivalent per 100 grams of dry soil in the top 20 cm of the profile, due to prominently kaolinitic nature of the associated clay minerals (Moorman and Van De Wetering, 1985[12])
Geology and hydrogeology
Geologically, Ibadan metropolis and environs are underlain by Precambrian basement rocks, which comprise of crystalline igneous and metamorphic rocks mostly quartzite and quartz-schist of meta-sedimentary series and the migmatites complex comprising of banded gneiss, augen gneisses, granite-gneiss, and variably migmatized biotite-hornblende gneiss with intruded pegmatites, quartz veins, aplites and dolerite dykes (Burke et al., 1976[13]) (Figure 9.6).
In general, the minerals in the rock types are quartz, biotite, muscovite, iron oxide and plagioclase feldspar in various percentages. The rocks have undergone various episodes of tectonism depicted by foliation with characteristic alternating light and dark coloured bands (Jones and Hockney, 1964[14]) while major lineament trends are commonly in NNE-SSW or N-S directions. In fact, most rock types stated above are covered in most places by weathered regoliths, but outcrop in few places.
Weathering provides avenues for water percolation and forms weathered regolith aquifers. These are generally discontinuous with groundwater occurring in localised disconnected (Tijani and Diop, 2011[2]) regolith aquifers under unconfined to semi-confined conditions while trough geophysical measurements. Olayinka et al. (1999)[15]showed that the regolith can be up to 60 m thick.
Hydrogeologic setting and hydraulic characteristics
The hydrogeology of an area depends on the bedrock geology, structure and climate of the area while the underlying geological formation structures determine the types of aquifer as well as the nature of recharge (Jones and Thornton, 2003[16]; Lewis, 1987[17]). However, the climatic and hydrologic situations do determine the amount and rate of recharge of the aquifer (Olayinka and Yaramanci, 1999[15]). From a hydrogeologic point of view, availability of groundwater in crystalline basement rock settings, like Ibadan metropolis, depends on the mineralogy of the rocks, which in turn dictates the degree of fracturing and weathering. Hence, significant aquifer units can develop within the weathered overburden and deeper fractured bedrock zones. In these zones, the groundwater resources depend on the depth of the water level and the relative thickness of the weathered horizon. Usually, deeper (thicker) weathering profiles are an indirect indication of good groundwater potentials. Nonetheless, due to the complex interactions of the various factors affecting weathering, water-bearing horizons may not be present at all at some locations.
In Ibadan the tropical humid setting does enhance active weathering with resulting thick and generally well developed weathered profiles. Consequently, the weathered zone can be as much as 60 m thick, but more commonly in the range of 20–30 m. Below this zone the rock becomes progressively less weathered and more consolidated until fresh fractured bedrock is reached (Figure 9.7). In such profiles, it has been observed that porosity generally decreases with depth while permeability, however, has a more complicated relationship, depending on the extent of fracturing and the clay content of the weathered overburden (Chilton and Foster, 1995[18]). Usually beneath the soil zone, the rock is often highly weathered and clay rich, therefore permeability is low. The saprock zone representing the base of the weathered zone, near the fresh rock interface consists of fractured rock, and is often permeable allowing free movement of water (Chilton and Foster, 1995[18]). Wells or boreholes that penetrate this horizon can usually provide sufficient water to sustain a hand pump. Deeper fractures within the basement rocks are also an important source of groundwater, particularly where the weathered zone is thin or absent. These deep fractures are tectonically controlled and can sometimes provide appreciable water supplies (Laniyan et al., 2013[19]).
Weathered basement aquifers of Ibadan
As mentioned earlier, Ibadan is underlain by Precambrian basement rocks, which comprise of crystalline igneous and metamorphic rocks mostly granite-gneiss, quartz-schist, augen-gniess, pegmatite intrusions and variably migmatized biotite-hornblende gneiss. Assessment of previous studies revealed varied weathered profiles over the different bedrock units within Ibadan, suggesting influence of rock types and mineralogy on the extent of weathering and in essence the occurrence of groundwater. A schematic presentation of such profiles for granite-gneiss, pegmatite and quartz-schist settings (Piper, 1944[20]) indicate thickness variability of weathered basement rocks (Figure 9.8).
For Ibadan, studies have revealed relatively poor aquifers with low groundwater potential, high groundwater yield are said to be found areas where thick overburden overlies fracture zones (Moormann and Greenland, 1980[21]). Recent studies indicated that yields from wells in areas underlain by quartzite and quartz-schist are much higher than areas with rock types such as: granites, migmatites and gneisses. This is due to the higher occurrences of fissures in the former rock types with enhanced transmissivities and permeabilities in contrast to the areas underlain by the latter rock types (Aweto, 1994[22]; Tijani et al., 2010[23]).
Two aquifer units have been identified, the weathered overburden unit which usually sustain shallow hand-dug wells (5–15 mbgl) and fractured saprock units that sustain shallow boreholes (30–60 mbgl) (Aweto, 1994[22]). More detailed evaluation of hydraulic data from pumping tests of a number of boreholes within Ibadan metropolis were undertaken by Aweto (1994)[22] and Tijani, et al., 2010[23]. As presented in Table 9.3, the depth of wells within the different geologic settings range from 12.12–68 m (mean 47.7 m) for augen gneiss, 21.6–60 m (mean 36.2 m) for banded gneiss and 60–87 m (mean 66.4 m) for schistose quartzite setting (Table 9.3). This variability in well depths signifies the geologic control and differences in the extent of weathering. Nonetheless, the thicknesses are within the range that can be anticipated for shallow boreholes in a basement terrain aquifer (Tijani, 1994; Uma and Kehinde, 1994; Edet and Okereke, 2005).
Depths to water level in the boreholes vary widely from <1 m to more than 10 m but generally less than 15 m below ground surface in the different geologic settings with quartz-schist bedrock exhibiting relatively deeper water level. This facilitates the development of hand-dug wells and shallow boreholes for domestic water supply. Saturated thickness in the boreholes shows a wide variation of 8.02 m (in gneiss) to 81.58 m (in the quartz schist setting).
The measured yields of the tested boreholes revealed relatively low values between 30 m3/d–138 m3/d, and mean 80 m3/d (Table 9.3) with higher yields in the augen gneiss (range 30-138.2 m3/d; mean 82.87 m3/d). Banded gneiss sustained yields between 31–88.6 m3/d; mean 55.9 m3/d) while quartz-schist aquifer have yield of 62–86.4 m3/d. High yields typify boreholes that intersect fractured bedrock with shallow weathered overburden, while low yield boreholes are associated with thick weathered regolith and no prominent fractured intersection (Tijani et al., 2010[23]).
| Parameters | Banded gneiss (N = 6) |
Augen gneiss (N = 13) |
Quartzite (N = 5) | ||||||
| Min. | Max. | Mean | Min. | Max. | Mean | Min. | Max. | Mean | |
| Well depth (m) | 21.6 | 60.0 | 36.2 | 12.1 | 68.0 | 47.7 | 60.0 | 87.0 | 66.4 |
| Depth to WL (m) | 0.94 | 5.9 | 3.4 | 0.75 | 11.2 | 4.67 | 3.07 | 11.3 | 6.1 |
| Drawdown (m) | 2.2 | 26.4 | 13.7 | 3.3 | 29.4 | 11.3 | 15.1 | 34.7 | 28.9 |
| Sat. thickness(m) | 16.4 | 54.9 | 30.7 | 8.02 | 62.8 | 42.2 | 48.7 | 81.6 | 62.7 |
| Yield (m3/d) | 31.0 | 88.6 | 55.9 | 30.0 | 138.2 | 88.7 | 62.8 | 86.4 | 75.4 |
| Sp. Capacity (m2/d) | 2.92 | 7.9 | 5.6 | 1.25 | 37.8 | 13.0 | 1.86 | 17.5 | 5.23 |
| Trans. (m2/d) | 1.10 | 4.16 | 2.8 | 0.76 | 27.2 | 7.25 | 0.41 | 10.6 | 2.71 |
| Sensitivity, Cc | 0.24 | 2.0 | 0.7 | 0.25 | 0.7 | 0.43 | 0.17 | 0.42 | 0.28 |
| Hydr. Cond.(m/d) | 0.07 | 0.15 | 0.1 | 0.02 | 0.5 | 0.2 | 0.01 | 0.18 | 0.05 |
Source: Alichi (2006)[24]
In addition, the evaluated transmissivity T values for the three rock types ranged from 1.1–4.16 m2/d (mean 2.79 m2/d) for banded gneiss, 0.76–27.16 m2/d (mean 7.25 m2/d) for augen gneiss, and 0.41–10.55 m2/d (mean 2.71 m2/d) for the quartzitic rock. These imply that quartz-schist and banded gneiss settings show lower potential when compared to the augen gneiss. Nonetheless, the majority of the boreholes (47%) revealed values ranging between 1.0 and 5 m2/d which are said to be typical of the weathered basement aquifers (Offodile, 1983) while 29% exhibit transmissivity in excess 5 m2/d which is indicative transmissive fractured zones. This variation is a clear indication of variability and localized nature of the basement aquifer as also dictated by bedrock and the degree of weathering.
The hydraulic conductivity was estimated from evaluated transmissivity and saturated thickness of the aquifer with values of 0.01–0.18 m/d for banded gneiss and quartz-schist compared to 0.2–0.5 m/d for augen gneiss (Table 9.3). These values cut across the various ranges of likely hydraulic conductivity for weathered granite and metamorphic rocks (Halford and Kuniansky, 2002) and are indicative of regolith aquifers with generally low permeability. Specific capacity generally, gives a better indication of aquifer performance than yield since it also reflects aquifer transmissivity and saturated thickness (Mace, 2000; Uma and Kehinde, 1994). Specific capacity of the tested boreholes range from 1.3–37.8 m2/d; mean 13.8 m2/d (Table 9.3) for augen gneiss. Banded gneiss and quartz-schist have specific capacity of 2.9–7.9 m2/d (mean 5.6 m2/d) and 1.86–17 m2/d (mean 5.2 m2/d) respectively.
Assessment of groundwater quality degradation
In the following sections, selected hydrochemical and water quality studies are reviewed and summarized for the purpose of highlighting the groundwater quality scenarios in Ibadan.
Microbiological contamination and hydrochemistry
Adetunji and Odetokun (2011)[25] assessed the impact of septic tanks on the bacterial quality of dug wells. All the wells sampled had high total coliform counts (2.29 ± 0.67 log cfu/mL). There were no significant differences in the bacterial counts between covered and uncovered wells. The mean distance (8.93 ± 3.61 m) of wells from the septic tanks was below the limit (15.24 m or 50 ft) set by the United State Environmental Protection Agency (USEPA). Ifabiyi (2008)[26] investigated relationships between water quality and well depth, and Amidu and Olayinka (2006)[27] looked at impact of a septic tank plume.
Oloruntoba and Sridhar (2007)[28] assessed the bacteriological quality of drinking water from wells, spring, borehole, and tap sources together with that stored in containers by urban households in Ibadan during the wet and dry seasons. Results showed that majority of households relied on wells, which were found to be the most contaminated of all the sources. At the household level, water quality significantly deteriorated after collection and storage as a result of poor handling. Furthermore, there was significant seasonal variation in E. coli count at source (P=0.013) and household (P=0.001). A summary of inorganic water quality studies carried out across Ibadan are presented in Table 9.5.
| Supply | SEC/TDS | Total Coli (counts/100 mL) | Faecal coli (counts/100 mL) | Reference |
| Dug wells SE LGA | TDS 174 | Max = 5,120 | Ochieng et al. (2011) | |
| Boreholes residential areas | 73% | E coli 18% | Abiola (2010) | |
| Dug wells across city | SEC 561 | Total heterotrophs 600 (20–3500) | 26 (1–200) | Tijani and Diop (2011) |
| Dug wells | TC 2.29 ± 0.67 log cfu/mL | Adetunji and Odetokun (2011) |
| Supply | NO3 (mg/L) Mean (Range) |
NH4 (mg/L) |
Cl (mg/L) | SEC (µS/cm) | Alkalinity and other mg/L and (µg/L) |
Reference |
| Dug wells across city | 30.1 (3–178) |
39.5 (3–128) |
561 (85–1572) |
HCO3 134 (15–532) mg/L |
Tijani and Diop (2011)[2] | |
| Boreholes residential areas | Pb 4.9 µg/L | Abiola (2010)[29] | ||||
| Dug wells SE LGA | 5 | TDS 174 | Alkalinity 48.2 mg/L | Ochieng et al. (2011)[30] | ||
| Dug wells SE LGA | 8.01 | 136 | Alkalinity 108 mg/L Fe 0.56 mg/L |
Ifabiyi (2008)[26] | ||
| Orita-Aperin waste site | 16.3 | 1.67 | 68.9 | TDS 349 | Fe 4.6 mg/L Cr 0.07 |
Ikem et al. (2002)[31] |
| Waste disposal sites | Cd 1 | Adelekan and Alawode (2011)[32] | ||||
| Auto-mechanic villages | Cu 4.55–9.02 | Adelekan and Abegunde (2011)[32] | ||||
| Lead battery factory, Wofun | 4.31 | 0.32 | 0.7 | Fe 0.57 Cu 1.22 Ni 0.52 Pb 1.05 Cd 0.003 all mg/L |
Dawodu and Ipeaiyeda (2007)[33] |
Sangodoyin and Agbawhe (1992)[34] monitored slaughter house pollution in adjacent wells. Slaughter house waste generally has a high COD and TDS. Groundwater approximately 250 m from the abattoir site was found to be unsatisfactory as a raw water source for drinking purposes. Results from a study characterising the hydrochemistry of shallow groundwater compared to surface water from Ibadan metropolis by Tijani and Onodera (2005)[1] are summarized in Table 9.6. The major ion chemistry in groundwater samples are within the WHO limits with the exception of NO3, the main critical quality index, and associated slight elevated Na and Cl concentrations. Nitrate concentrations range from 17.2 to 412 mg/L (average 112.3 mg/L) indicate contamination of the shallow groundwater system. Nonetheless, a closer look at the nitrate concentrations reveal that all the sampled dug-wells have NO3 concentrations of >15 mg/L, while about 50% of them have NO3 concentrations of >50 mg/L above the WHO recommended limits.
Dug-wells with depths of <5 m have variable EC ranging from 100 to 2000 µS cm-1, while those with depth of >5 m (are characterized by EC less than 1,000 µS cm-1 and revealed a general tendency of decreasing EC with increasing depth. This is consistent with the fact that the deeper wells (>5 m) have NO3 concentrations of less than 50 mg/L, compared with shallow wells (<5 m) with variable NO3 concentrations of 20 to 410 mg/L. Field observations revealed that NO3 contamination is related to inputs from domestic wastewaters and leachates from household septic tanks and pit latrines. Hence it can be concluded that shallow wells (<5 m deep) are characterized by high TDS and high NO3 concentrations suggesting the impacts of the infiltrating contaminants through the loose weathered regolith materials. However, the relatively deeper wells (>5–14 m deep) are characterized by low TDS and low NO3, indicating fresh groundwater from fractured saprock units, relatively free from infiltrating pollutants from the upper loose weathered regolith unit.
In addition, hydrochemical assessment of 50 shallow groundwater samples from Ibadan metropolis as presented by Tijani and Diop (2011)[2] and summarized in Table 9.7. This study revealed that most of the major ionic parameters are within the acceptable limits of WHO (1994) and the Nigeria’s regulatory standards (NAFDAC) for drinking water quality. Ca and Na dominate major cations with average concentrations of 31.2 mg/L and 20.2 mg/L respectively while the major anions are HCO3 and Cl with average concentrations of 133.8 mg/l and 39.5 mg/L respectively.
| Parameter | Groundwater (N=40) |
* WHO Standard | Surface water (N=40) |
MWR+ | ||||
| Range | Mean | SD§ | Range | Mean | SD | |||
| DWD (m) | 3.2–14.1 | 6.2 | 2.8 | - | - | - | - | - |
| Temp.°C | 27.0–30.5 | 28.7 | 0.80 | Variable | 25.7–37.4 | 30.5 | 2.5 | Variable |
| pH | 5.9–8.3 | 7.4 | 0.62 | 6.5–9.5 | 5.9–8.9 | 7.4 | 0.9 | Variable |
| EC (µS cm-1) | 105–1679 | 586.7 | 405.6 | 400–1480 | 164–1878 | 821.0 | 433.9 | Variable |
| TDS | 66–1063 | 373.5 | 265.4 | 500–1000 | 103–1188 | 516.7 | 277.9 | 90.0 |
| Ca | 0.8–132.0 | 23.9 | 30.2 | 75–200 | 2.0–72.6 | 30.9 | 18.7 | 15.0 |
| Mg | 0.8–41.1 | 15.0 | 12.3 | 50–150 | 2.0–31.1 | 14.7 | 7.0 | 4.1 |
| Na | 6.2–204.4 | 41.2 | 44.3 | 20–200 | 17.8–383.4 | 92.1 | 89.4 | 6.3 |
| K | 0.5–86.4 | 16.4 | 18.8 | 10–12 | 7.3–178.5 | 41.9 | 42.0 | 2.3 |
| Fe | 0.01–4.4 | 0.37 | 0.84 | 0.3–1.0 | 0.03–23.9 | 1.8 | 3.8 | 0.5 |
| HCO3 | 34.0–100.0 | 65.3 | 13.5 | Variable | 38.0–118.0 | 67.1 | 17.7 | 58.0 |
| Cl | 21.0–84.0 | 49.2 | 18.0 | 250–600 | 25.0–150.0 | 74.8 | 33.2 | 7.8 |
| SO4 | 13.0–45.0 | 29.9 | 8.53 | 250–400 | 10.0–49.0 | 29.3 | 12.0 | 11.0 |
| NO3 | 17.2–412.0 | 112.3 | 112.0 | 25–50 | 22.8–366.0 | 104.3 | 95.1 | 1.0 |
§ SD = Standard deviation. * WHO Standard, 1993. DWD = Shallow dug-well depth in metres.
MWR+ = Mean world river (from Hem, 1985: Martin & Maybeck, 1979), values in mg/L, unless otherwise stated
The measured depth range of 2.1–15.5m (av. 8.1 m) for the sampled dug-wells alongside the measured TDS of 54–1,055 mg/L (av. 373 mg/L) are clear indication of low mineralized shallow groundwater system with limited circulatory history typical of a weathered crystalline basement setting. This is consistent with the finding of Tijani and Onodera (2005)[1] as well as other similar studies elsewhere (Tijani, 1994, Tijani and Abimbola, 2003).
Nonetheless, a confirmation of the anthropogenic impact on the shallow groundwater system as highlighted earlier is reflected by the microbial contamination of most of the water samples with total heterotrophic bacteria count (TBC) in the range of 20–3,500 (CFU/100 ml). Also the presence of coliform bacteria (E. Coli) in some of the water samples (1–200 MPN/ml), most of which are also incidentally characterised by high NO3 concentrations and point to impacts of human waste inputs from in-house septic/soak-away pits.
Further indication of water contamination is also revealed by the evaluation of chemical analyses results of both water and stream sediment samples at 40 locations undertaken along the stream channels of Ona-Ogunpa-Ogbere drainage system that drains major parts of Ibadan metropolis. From the summary of results (see Table 9.6), the TDS for the surface water system in Ibadan metropolis is generally low with average value of 516.7 mg/L. This is in line with results from catchments underlain by similar, low solubility Precambrian Basement Complex rocks.
However, isolated locations within the stretches of the sampled drainage network with TDS >700 mg/L also found to have higher NO3 concentration ranging between 80 and 366 mg/L. This can be clearly attributed to the discharge of untreated domestic/municipal sewage water as well as refuse dumps into the drainage channels.
| Parameter | Min. | Max. | Mean | Median | WHO* Standard | NAFDAC Standard |
(N=50) | ||||||
| Temp °C | 25.5 | 29.8 | 27.8 | 27.7 | Variable | |
| pH | 5.8 | 7.9 | 6.8 | 6.7 | 6.5–9.5 | 6.5–8.5 |
| EC (µS/cm) | 85.3 | 1,572 | 561.6 | 465.2 | 480–1480 | 1000 |
| TDS mg/l | 54.4 | 1,055 | 372.8 | 302.1 | 1000 | 500 |
| TH | 13.8 | 437.7 | 153. 9 | 129.2 | 100–500 | |
| Ca | 4.4 | 80.6 | 31.2 | 28.0 | 75–200 | 75 |
| Mg | 0.88 | 65.2 | 18.3 | 13.5 | 50–150 | 200 |
| Na | 0.23 | 107.3 | 20.3 | 12.1 | 20–200 | 200 |
| K | 0.3 | 19.0 | 7.1 | 6.7 | ||
| Fe | bdl | 0.28 | 0.05 | 0.02 | 0.3–1.0 | 3.0 |
| HCO3 | 15.3 | 532.0 | 133.8 | 109.0 | Variable | 100 |
| Cl- | 3.2 | 128.2 | 39.5 | 20.1 | 200–600 | 100 |
| SO4 | bdl | 69.1 | 21.4 | 16.1 | 200–400 | 100 |
| NO3 | 3.3 | 177.5 | 30.2 | 20.9 | 25–50 | 10.0 |
| TBC | 20 | 3500 | 600.2 | 300 | ||
| CC | 10 | 200 | 25.7 | 5.0 | ||
* TH= Total Hardness (mg/CaCO3); CC= Total coliform counts (MPN/mL) and TBC= Total bacterial counts (CFU/100 mL), values in mg/L, unless otherwise stated
A plot of the NO3 and EC along the stretches of the drainage (Figure 9.10) also confirmed the urban anthropogenic influence on the surface water quality as the NO3 peaks coincide with those of EC within the stretches of the urban centres. In addition, the NO3 concentrations are considerably above 100 mg/L in the populated urban section of the metropolis compared to the suburb or peri-urban areas located at the upstream and downstream sections (see Figure 9.9). The field observation revealed that the spatial disposition of the NO3 and EC peaks coincided with sections of the stream channels that receive direct discharge of domestic wastewaters and/or refuse dumps. This also further confirmation of the influence of untreated household/municipal effluents on the urban drainage networks within the populated old city centre and a reflection of poor land-use and waste management services in the Ibadan metropolis.
| Parameter | Min. | Max. | Mean | Median | WHO* Standard | NAFDAC Standard |
(N=77) | ||||||
| Temp °C | 24.8 | 29.6 | 26.3 | 25.8 | Variable | |
| pH | 4.8 | 8.0 | 6.8 | 7.0 | 6.5–9.5 | 6.5–8.5 |
| EC(µS/cm) | 102.3 | 3321.0 | 490.9 | 343.0 | 900–1200 | 1000 |
| TDS | 53.2 | 676.0 | 228.6 | 170.7 | 500–1500 | 500 |
| Ca2+ | 6.85 | 89.04 | 32.56 | 27.40 | 75 | 75 |
| Mg2+ | 2.08 | 104.00 | 22.21 | 16.64 | 50–150 | 200 |
| Na+ | 0.90 | 40.40 | 23.97 | 26.20 | 200–250 | 200 |
| K+ | 0.30 | 93.60 | 30.58 | 29.10 | 200 | |
| HCO3- | 1.15 | 590.03 | 162.42 | 157.41 | 100–500 | 100 |
| Cl- | 2.00 | 262.00 | 66.15 | 50.00 | 200–250 | 100 |
| SO4 | 3.00 | 210.00 | 56.88 | 43.00 | 250–500 | 100 |
| NO3 | 0.00 | 4.40 | 0.47 | 0.03 | 10–50 | 10.0 |
| TC | 2.00 | 98.00 | 28.6 | 20.00 | ||
| TTC | 1.00 | 82.00 | 7.85 | 4.00 | ||
TTC= Thermo-tolerant coliform counts (MPN/mL) and TC= Total coliforms counts (CFU/100 mL). Values in mg/L unless otherwise stated.
Further assessments of major ion chemistry and groundwater quality of Ibadan metropolis were undertaken late 2006 by Nigerian Geological Survey Agency (NGSA) including a hydrochemical database of 70 observations, these are summarised in Table 9.6. Like other studies, the major cations revealed similar concentration trends with average of 32.6 mg/L and 22.2 mg/L for Ca2+ and Mg2+ respectively, while Na+ and K+ ions revealed average concentrations of 24 mg/L and 30.6 mg/L respectively. Bicarbonate dominated the anions with an average concentration of 162.4 mg/L followed by Cl- with an average value of 66.2 mg/L while SO42- and NO3 have average values of 56.9 mg/L and 0.50 mg/L respectively.
While the concentrations of Cl ions can be attributed to the occasional disinfection of the some of the dug-wells with chlorinated products, the generally low NO3 concentrations (0.01–4.4 mg/L), compared to the other studies, is perhaps due to the timing of the sampling during the peak of the dry season. The implication is that the low NO3 concentration can be attributed to natural attenuation by de-nitrification process within the weathered regolith, as well as lack of recent rain-induced recharge and vertical leaching of the household waste from latrines and soak-away pits into the underlying groundwater system during the dry season. Nonetheless, the total bacterial count of 2–98 CFU/100 ml and coliform count of 1–82 MPN/mL (See Table 9.8) is also a clear indication that the impacts of poor household waste disposal and management on the groundwater systems in Ibadan metropolis.
Trace metal contamination
To assess the trace metals contamination within Ibadan metropolis, the studies of Tijani et. al., (2004) and Tijani and Onodera (2005) with respect to contamination of selected trace metals in the groundwater and drainage systems within Ibadan were also evaluated and summarized in Table 9.7 and 9.8. As presented in Table 9.7, for the groundwater system, trace metals such as Cu, Pb, Zn and Cd are either below the detection limits and/or occur at low concentrations below the recommended WHO limits for drinking water standards. However, As and Hg are reported in detectable concentration with average values of 1.89 and 0.38 mg/L, respectively, compared to the recommended WHO limits of 0.01 mg/L and 0.001 mg/L, respectively, an indication of impacts of untreated cosmetics-loaded household waste waters.
| Parameters | Groundwater (N=40) |
WHO* Standard | Surface water (N=40) |
MWR+ | ||||
| Range | Mean | SD§ | Range | Mean | SD | |||
| As | 0.1–3.8 | 1.89 | 0.87 | 0.01 | 0.20–3.30 | 1.70 | 0.79 | 0.001 |
| Cu | 0.001–0.02 | 0.008 | 0.005 | 2.0 | 0.001–0.03 | 0.010 | 0.006 | 0.003 |
| Pb | 0.01–0.23 | 0.01 | 0.06 | 0.01 | 0.010–0.58 | 0.089 | 0.110 | 0.003 |
| Hg | 0.1–0.8 | 0.32 | 0.23 | 0.001 | 0.20–0.40 | 0.300 | 0.100 | 0.001 |
# Zn and Cd are below the detection limits; hence are not reported here. § SD = Standard deviation.
* WHO Standard, 1993. MWR+ = Mean world river (from Hem, 1985: Martin & Maybeck, 1979). Values in mg/L unless otherwise stated.
Like the groundwater system, only As and Hg are in elevated concentrations, with average values of 1.7 mg/L and 0.35 mg/L, respectively, in the surface waters of the urban drainage systems in Ibadan metropolis (see Table 9.7). The apparently low concentrations of most of the analysed trace trace/heavy metals in the surface water were attributed to possible preferential partitioning into the sediment phase of the drainage system. This assertion was supported by the relatively higher concentrations of trace metals in the stream sediments (see Table 9.8) compared to the stream and surface waters.
| Metals | Stream sediments (N=40) |
AFgw | AFsw | ||||
| Min. | Max. | Mean | EF | Rtot/ads | |||
| As | 0.30 | 6.80 | 3.22 | 2.22 | - | 188.9 | 1695 |
| Cd | 0.06 | 0.27 | 0.12 | 0.44 | - | - | - |
| Cu | 3.10 | 44.60 | 9.20 | -0.36 | 10.0 | 0.01 | 3.2 |
| Pb | 2.50 | 702. | 36.46 | 0.35 | 27.9 | 9.8 | 29.7 |
| Zn | 55.7 | 115.6 | 31.64 | 0.53 | 5.7 | - | - |
| Hg | 2.0 | 11.20 | 5.75 | 70.9 | - | 316.7 | 300 |
| Fe | 56.6 | 7598 | 35667 | 0.49 | 1519 | 1.23 | 6.0 |
EF, Enrichment factor; Rtot/ads, Ratio of total to adsorbed metal concentration;
AFgw, Anthropogenic factor for groundwater system;
AFsw, Anthropogenic factor for surface water system. Values in mg/L unless otherwise stated.
The concentration of trace/heavy metals in the stream sediments are about 5–10 orders of magnitude higher than those measured in the water phase of the drainage system within Ibadan metropolis. Fe, Cu, Pb and Zn are found to be the most abundant in the analysed stream sediments with concentrations of 3.1–44.6 mg/L Cu (average 9.7 mg/L), 2.5–702.5 mg/L Pb (average 36.5 mg/L) and 5.7–115.6 mg/L Zn (average 31.6 mg/L), respectively. However, Hg, As and Cd are in relatively lower concentration, with average values of 5.8 mg/L, 3.2 mg/L and 0.12 mg/L, respectively. Nonetheless, it should be noted that the above concentration trends do not reflect the respective degree of contamination; rather the metal contamination index will depend on the reference threshold (background) values (Tijani et al., 2004). By and large, the variability of concentrations of these metals within the stretches of drainage channels (like NO3 in the water column) suggests local anthropogenic input sources through domestic and municipal sewage effluents at various points along the drainage channel.
Therefore, further assessments using contamination indices with respect to environmental bioavailability of the trace metals revealed that the ratio of the total to the adsorbed concentration (Rtot/ads) are 0.24 (Zn), 0.17 (Cu) and 0.09 (Pb) (see Table 9.8). These was interpreted to mean that about 30% of Zn, 20% of Cu and 12% of Pb are in adsorbed form as bio-environmental available portion which can be released back into the water phase in response to changes in the physico-chemical conditions. Hence, it can be concluded that the relatively low concentrations of the trace metals (Cu, Pb, Zn, Cd, As and Hg) in the water column compared to the stream sediments are indications of partition between the water and sediment phase, while the proportions of adsorbed concentration in the stream sediments are potential contamination sources for the water column (Tijani, et al., 2004; Tijani and Onodera, 2005[1]).
Further assessment of the quality status and level of trace metal contaminations in water and sediment samples of the urban drainages in Ibadan metropolis was also undertaken by Tijani and Onodera (2005)[1] using enrichment factor (EF) and anthropogenic factors (AF) (see Table 9.8). Based on the assessment and for the groundwater system, the estimated AF values with respect to the WHO standards, are generally <1.0 for Cd, Cu and Zn, implying no contamination or anthropogenic inputs, while for As, Hg, Pb and Fe the estimated AF are considerably >1.0, suggesting enrichment or contamination above the recommended WHO limits. However, for the surface water system, with the exception of Cd and Zn which are below detection limits, other trace/heavy metals (Cu, Pb, As and Hg) have AF values of >1.0 suggesting contamination or enrichment above the level of mean world river (MWR) and WHO limits. Hence it can be concluded that despite the absolute low concentrations of the analysed trace metals in both surface and groundwater system, there is evidence of slight enrichments of As, Hg, Pb, Cu and Fe relative to the WHO and MWR reference standards.
For the stream sediments, most of the analysed trace metals have enrichment factor (EF) of <1.0, except for As and Hg with values of 2.3 and 70.9, respectively, with respect to the corresponding background values of the granitic crystalline bed rock units in Ibadan metropolis. This is also a reflection of the contamination of As and Hg associated with the stream waters, as mentioned earlier. While the source of As was attributed to anthropogenic activities and dumping of wastes/refuse into the stream channels, the sources of Hg (as a constituent of medicated soaps and cosmetics materials) was attributed to inputs from discharge of untreated domestic/household waste waters into the stream channels.
Hydrochemical characterisation of the groundwater system
Natural water chemistry is said to be dependent on a number of processes including precipitation, mineral weathering and evaporation-crystallization (Didymus, 2012[35]). However, effects of these controlling processes on different chemical species vary as other processes such as cation exchange, anthropogenic contamination and mixing process may also exert some considerable influence on the groundwater chemistry. Hence, the prevailing chemical character of any groundwater system is usually not only a function of the character of recharging water but also a function of the interaction with the aquifer system during subsurface flow (Tijani and Abimbola, 2003). As part of the review of the groundwater contamination in Ibadan metropolis, hydrochemical characterization of the chemical data base using Piper trilinear diagrams were employed as presented in Figure 9.10a and b. In general, there are three main water types namely;
- Ca-Mg-HCO3, at times with significant component of alkali metals as Ca-Mg-(Na)-HCO3
- Ca-Mg-(Na)-SO4, with occasional significant chloride component as Ca-Mg-(Na)-Cl and
- Na-(K)-HCO3 water types.
This is an indication of the fact that the natural chemical composition of the groundwater is influenced by rock–water interaction mostly controlled by CO2-charged mediated weathering and dissolution of silicate minerals as represented by Ca-(Mg)-HCO3 waters, while ion exchange processes in represented by Na-(K)-HCO3 waters.
The overall assessment highlights the geogenic and anthropogenic controls on shallow groundwater system in the study area. The evolution of such water types can be related to the weathering and alteration of calcium- and magnesium-rich minerals within the bedrock units mediated by CO2-charged infiltrated rain waters. This observation is also supported by Gibbs diagram (Figure 9.11) indicating the dominance of weathering — dissolution process in respect of the hydrochemical evolution of groundwater shallow basement crystalline aquifer of Ibadan metropolis.
Factor analysis has been commonly used in a number of hydrogeochemical studies (Briz-Kishore and Murali, 1992[36]; Gupta and Subramanian, 1998[37]; Lambrakis et al., 2004[38]; Subbarao et al., 1996[39]). The R-mode factor analysis was employed to investigate the factors controlling the hydrochemical characteristics of the groundwater systems in Ibadan metropolis. Such analysis provides features that allow interpretation of large data sets (Jayakumar and Siraz, 1997[40]) and allows the identification of variables that are characterized by a similar process using the factor loadings and eigenvalues. As part of further evaluation of the hydrochemistry, the database (n=70) was subject to analysis using principal component analysis (PCA). PCA was performed on the groundwater data in order to better understand their interrelationships, probable source of the major ions and to explore the reduction of the experimental variables. From the results of the factor analysis, three (3) main factors with eigenvalue >1 and all accounting for about 76% of the data matrix were extracted and presented in Table 9.9.
| PCA (Eigenvalue) | pH | EC | Ca | Mg | Na | K | Fe | HCO3 | SO4 | Cl | NO3 | TDI |
| F-1 (5.56) | 0.41 | 0.30 | 0.78 | 0.78 | 0.28 | 0.40 | 0.16 | 0.92 | 0.66 | 0.19 | -0.01 | 0.86 |
| F-2 (2.35) | 0.53 | 0.83 | 0.35 | 0.06 | 0.31 | 0.33 | 0.80 | 0.16 | 0.17 | 0.32 | 0.77 | 0.43 |
| F-3 (1.82) | -0.55 | 0.23 | 0.20 | 0.41 | 0.79 | 0.60 | 0.25 | -0.10 | 0.37 | 0.72 | 0.26 | 0.18 |
The first factor with eigenvalue of >5 which represented about 46% of the data matrix was interpreted as the dominant factor controlling the groundwater chemistry. Furthermore, within each of the factor groups, only chemical variables with loading of at least 0.4 were considered significant members of the respective factor group (see Table 9.9). Further interpretations in respect of each factor are summarized below:
- Factor 1: dissolution-weathering factor which is loaded in respect of pH, Ca, Mg, HCO3, SO4 and TDI. This association strongly represents geogenic influence of the bedrock geology on groundwater which is a reflection of the observed Ca-(Mg)-HCO3 type.
- Factor 2: anthropogenic leaching factor (loaded in respect of NO3, EC and TDS) which is a reflection contamination through household waste pits and
- Factor 3: Alkali-exchange factor (loaded in favour of Na, K, Mg and Cl) as a reflection of the observed Na-(K)-HCO3 exchange water type.
Synthesis of groundwater contamination sources
Like many urban centres in developing countries, the environmental setting of Ibadan metropolis is characterized by poor land-use planning, lack of adequate water supply, lack of proper sewage, and waste disposal systems. Consequently, many households, especially within the congested central portion of the city lack toilet and waste disposal facilities while most rely on in-house hand-dug (shallow) wells for their domestic water supplies. As a result, direct discharge of sewage water and dumping of domestic wastes/refuse into the drainage channels are common practices. In summary, the likely causative factors responsible for deterioration of groundwater quality in the study area are improper disposal of waste, increased anthropogenic activities arising from population explosion in the city and limited planning and inadequate infrastructure. Based on the foregoing hydrochemical assessments and evaluations, a conceptual framework of contamination sources and mechanisms with respect to groundwater quality degradation or contamination in Ibadan metropolis are graphically summarised in Figure 9.12.
The main drivers of the groundwater quality degradation come from the urban land use dominated by residential commercial and industrial activities (Figure 9.13). These activities lead to generation of solid and liquid wastes, and poor waste management leads directly to high environmental inputs of chemical and microbiological contaminants. The environmental consequence in terms of quality degradation of groundwater quality through direct infiltration of wastes and leachates on one hand and direct discharge into the riparian aquatic systems are presented. This has obvious heath implications for users of shallow wells for drinking water and domestic purposes, and also has implications for groundwater dependant ecosystems and surface water bodies.
Summary
Major and trace element hydrochemistry of shallow groundwater, surface water and stream sediments from an urbanised drainage catchment, with respect to anthropogenic activities, were evaluated and discussed as a case study of surface and groundwater contamination in a typical growing African urban setting with basement geology. From this study, it is evident that urbanisation coupled with lack of proper waste disposal system has considerable influence on the water quality of urban surface and groundwater bodies with obvious health and environmental implications.
Groundwater samples are within the permissible limits of WHO and NAFDAC standards, with the exception of NO3, the chemical characterisation reveal a geogenic control on the occurrence of most of the major cations through weathering-induced water-rock interactions characterized by Ca-Mg-(Na)-HCO3 water type with subordinate Na-(Ca)-HCO3 exchange water type. Overall the hydrochemical evaluation indicated weathering, dissolution and dilution as the principal mechanism responsible for the hydrochemical evolution of groundwater in the study area. PCA analysis identified an additional anthropogenic factor with high loadings (>0.7) for NO3, Fe and SEC.
Urban surface and shallow groundwaters were typically contaminated with high NO3. The NO3 contamination in the shallow groundwater can be attributed to leaching from household septic tanks/soak-aways and rubbish pits. The observed total coliform count (TC) and presence of TTC counts above WHO standards, alongside elevated NO3 concentrations, is a clear indication of anthropogenic controls on the groundwater quality. This is a consequence of poor and indiscriminate disposal of household waste waters and unsanitary conditions of latrines and soak-away pits within the populated areas of Ibadan metropolis.
The study shows that the concentrations of all the analysed heavy metals Pb, Hg and As in the surface water are slightly higher and suggest contamination compared to the mean composition of world rivers, while the respective concentrations of Pb, Cu, Hg and As in sediment phase revealed an overall enrichment and contamination relative to the background value in the granitic bedrock units.
Evaluation of bioavailability and partitioning of the trace metals revealed that, about 30% of Zn, 20% of Cu, 12% of Pb and <1% of Fe were in adsorbed form compared to the respective total metal concentrations. The implication is that those adsorbed portions are potential contamination sources for the surface water due to possible remobilization and release into the water phase in response to possible changes in the physico-chemical condition of the drainage system.
Finally, there is the need to recognise that the urban development issues facing Ibadan metropolis, and other cities in Nigeria, have and important social and health implications (Udo, 1994[5]) as well as long term implications for surface water and groundwater dependant ecosystems. There is the need for adequate financing of urban infrastructures and the institutional arrangement for delivery of urban services, especially drinking water supplies, solid waste and waste water managements. To date the majority of studies have focussed on major ion chemistry and microbiological parameters. There is a knowledge gap regarding the extent of contamination and potential human and environmental exposure to specific pathogens, trace elements and organic contaminants in urban settings.
References
- ↑ 1.0 1.1 1.2 1.3 1.4 1.5 1.6 1.7 TIJANI, M N, and ONODERA, S I. 2005. Surface and groundwater qualities in an urbanized catchment: Scenario from a developing country. International conference of groundwater quality: bringing groundwater quality research to the watershed scale, Waterloo, Ontario, Canada, 19–22 July 2004, IAHS-AIHS, Vol. 297, 506–516.
- ↑ 2.0 2.1 2.2 2.3 2.4 2.5 TIJANI, M N, and DIOP, S. 2011. Hydrochemical and microbiological assessment of groundwater from the weathered basement aquifer in Ibadan Metropolis, SW-Nigeria. Proceedings of the Seventh International Groundwater Quality Conference: Groundwater quality management in a rapidly changing world, GQ10, Zurich, Switzerland, 13–18 June 2010, IAHS-AISH, Vol. 342, 75–78. Cite error: Invalid
<ref>tag; name "Tijani 2011" defined multiple times with different content Cite error: Invalid<ref>tag; name "Tijani 2011" defined multiple times with different content Cite error: Invalid<ref>tag; name "Tijani 2011" defined multiple times with different content Cite error: Invalid<ref>tag; name "Tijani 2011" defined multiple times with different content - ↑ AFOLAYAN, D T. 2010. The evolution of a mega city: The case of Ibadan, Nigeria. https://www.sensorsandsystems.com/article/features/16973-the-evolution-of-a-mega-city-the-case-of-ibadan-nigeria.html
- ↑ 4.0 4.1 AJAYI, O, and ABEGUNRIN, O O. 1994. Borehole failures in crystalline rocks of South-Western Nigeria. GeoJournal, Vol. 34, 397–405.
- ↑ 5.0 5.1 5.2 5.3 5.4 5.5 5.6 UDO, R K. 1994. Ibadan in its regional setting. 8–17 in Ibadan Region. FILANI, M O, AKINTOLA, F O, and IKPORUKPO, C O (editors). (Ibadan: Rex Charles.) Cite error: Invalid
<ref>tag; name "Udo 1994" defined multiple times with different content Cite error: Invalid<ref>tag; name "Udo 1994" defined multiple times with different content Cite error: Invalid<ref>tag; name "Udo 1994" defined multiple times with different content - ↑ 6.0 6.1 6.2 SHEMANG, E M. 1990. Electrical depth soundings at selected well sites within the Kubani river basin, Zaria, Nigeria. Unpublished MSc thesis, Ahmadu Bello University, Zaria.
- ↑ WRIGHT, E P, and BURGESS, W. 1992. The hydrogeology of crystalline basement aquifers in Africa — Introductory paper. 1–27 in Hydrogeology of Crystalline Basement Aquifers in Africa. WRIGHT, E P, and BURGESS, W (editors). Special Publication 66. (London: Geological Society).
- ↑ 8.0 8.1 8.2 AWOSIKA, O. 2008. Management of environmental problems in the Nigera’s Niger Delta area: The challenge of sustainable human development. Annual meeting of the MPSA Annual National Conference Palmer House Hotel, Hilton, Chicago, IL. Cite error: Invalid
<ref>tag; name "Awosika 2008" defined multiple times with different content Cite error: Invalid<ref>tag; name "Awosika 2008" defined multiple times with different content - ↑ EDUVIE, M O. 2006. Borehole failures and groundwater development in Nigeria. Water Africa Exhibition. Victoria Island, Lagos.
- ↑ HOPKINS, B. 1965. Observations on savanna burning in the Olokemeji Forest Reserve, Nigeria. Journal of Applied Ecology, 367–381.
- ↑ SMYTH, A J, and MONTGOMERY, R F. 1962. Soils and land use in Central Western Nigeria. Govt. Printer, (Ibadan).
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