Electrical Resistivity Survey to Investigate Causes of Borehole Failure in Ikwuano/Umuahia Area of Abia State of Nigeria

International Journal of Innovative Scientific & Engineering Technologies Research 3(1):47-61, Jan-Mar 2015 © SEAHI PUBLICATIONS, 2015 www.seahipaj.org ISSN: 2360-896X

ELECTRICAL RESISTIVITY SURVEY TO INVESTIGATE CAUSES OF BOREHOLE FAILURE IN IKWUANO/UMUAHIA AREA OF ABIA STATE OF NIGERIA

1*CHUKWU, G.U., 2OKEREKE, C.S., 3OKWUEZE, E.E. & 4CHIBOKA, V.O. 1 Department of Physics, Michael Okpara University of Agriculture, Umudike -Umuahia, Nigeria 2Department of Geology, University of Calabar, Calabar, Nigeria 3Department of Physics, University of Calabar, Calabar, Nigeria 4 Dept. of Mathematics, Michael Okpara University of Agriculture, Umudike -Umuahia, Nigeria *Corresponding author E-mail: [email protected] Phone: +2348025691478, +2347034394600

ABSTRACT The prevailing shortage of potable water supply in Ikwuano/Umuahia and the efforts made towards ameliorating the ugly situation through groundwater supply system are not meeting the desired results. There have been several cases of rampant borehole failure within the area. Some boreholes give out poor yield at certain periods of the year; many others go dry shortly after well completion while some do not show any indication of water presence after drilling several meters of depth in the subsurface. The wasted resources added more hardship to the prevailing water scarcity and thus make life very unbearable for the people. Vertical electrical sounding (VES) technique using Schlumberger configuration was employed to carry out electrical resistivity surveys to determine the causative geological/geophysical factors that give rise to the problem. Data sets of both productive and non-productive boreholes were acquired together with global positioning system (GPS) measurements to investigate the problem of borehole failure within the study area. The geology of every site location of the boreholes among several other considerations was taken into account during the study. Results from the study depict that the study area traverses three distinct geological formations of Benin, Bende-Ameki and Imo shale. There are many functional water boreholes in Benin Formation, very few in Bende-Ameki whereas there has never been any in the Imo shale Formation enclave. Drilling borehole for water in Imo shale is regarded as a waste of time, energy and resources if we go by mean total drill depth (TDD) of 120 meters. However, as an older formation (about 65 Ma, Paleocene) than the other two formations, it may be possible to accommodate fractured aquifer at much deeper depth. Keywords: electrical resistivity, borehole, aquiferous zone, Imo Shale Formation, Ikwuano/Umuahia, GPS

INTRODUCTION Following many cases of borehole failure occasioned by wild-cat drilling and no pre-drilling investigation coupled with unsuccessful efforts to locate water-bearing aquifers in parts of Ikwuano/Umuahia, concerted and detailed geophysical study becomes very necessary. This is to make it possible to proffer solutions to the problem of rampant borehole failure and water scarcity. Water is essential for life. Out of the four basic needs of man to live, water is next to air. Water is the elixir of life, the climatic thermostat and the global heat exchanger (NRC, 2012). Goni (2006) maintained that fresh water is a finite and valuable resource essential to sustain life, development and environment. Access to safe and sufficient water and sanitation are standard necessities for good health and well-being. Whenever and wherever the availability of this resource is vague or doubtful, something is done quickly to redress the situation (UNESCO, 1992; UNFPA, 2003; WHO, 1987 and Black, 1998).

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Life and water are inseparable and interacting for both fauna and flora species. There are completely new possibilities for learning how water shapes the surface of the Earth (and the other planets) and creates vegetation patterns, how the hydrology of the land surface both dries and is driven by atmospheric processes, and how complex biogeochemical processes are intertwined with hydrological processes and how a host of the research questions posed can be attacked advantageously. In addition to establishing the conceptual, empirical and theoretical foundations of the science, refining and bolstering the fundamental base for hydrologic sciences is essential to support those who grapple with a multitude of water-related problems in a world that needs increasingly more energy, food, and water for humans while protecting ecosystem integrity, biodiversity, and irreplaceable landscapes, all in the face of a changing climate (NRC, 2012). Here lies the significance and relevance of the study. Demand for water compels the inhabitants to trek many kilometers in search of surface water (rivers, streams, ponds, etc) in order to stay alive. The investigated area is within latitudes 4.8o-6.1oN and longitudes 7.2o-8.1oE located at the northern part of the Niger delta region around the eastern flank of the Niger River.

Figure 1: Location map of Abia state showing the study area.

It covers a landmass of about 1,257 square kilometers in area. Rivers Imo and Kwa Iboe and their various tributaries constitute good dentritic drainage network system in the area with six to seven months (April - October) of rainfall per annum. Annual rainfall is between 2000 mm and 2250 mm. There are many perennial and ephemeral streams which recharge the borehole aquifers where they exist. The number of sunshine hours here is about 3600 hours per year. The maximum daily mean temperature is 29oC (i.e. between 28o and 30oC) during the month of March and minimum daily mean temperature is 23.5oC (i.e. between 23o and 24oC) during the month of July. Topographically, the crustal mass distribution for Ikwuano/Umuahia is not even; thus, the lowest and highest elevations recorded in the study are 29 m and 176 m above mean sea level respectively. The main objective of this study is to investigate the cause/causes of rampant borehole failure that is experienced in parts of the study area.

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Geology: The study area, in terms of geology, falls within three out of eleven geological units in Abia State of Nigeria. These are Imo Shale Formation in the extreme north, Bende-Ameki Formation in the central portion and the Benin Formation in the lower south of the research location.

ABIA STATE NIGERIA Cross River State Ofeme 39 38 Akpahia Umulenso 17 77 Umu - Agu Afugiri Ohafia 19 To Uzuakoli Ubani 75 Ama - ogugu Umukabia Uzuakoli Aro Umuahia Nkwoegwu 65 Imo State 300 Umuawa Umuire 35 26 Ekeoba Okahiauga 31 76 Akwa Ibom Ameke State 23 Ekenobizi 400 Odide Umujieze Isiadu 59 45 Mbom Aba STUDY Isingwu AREA Rivers State 43 Isieke Amafor 66 To Bende 60 Cocoa Research 49 40 15 Ogbodi Amachara Eziama Ossa 46 Nkata Ajala Okwuru 72 Ugba 42 Umuoriehi Umuahia Ohiya 71 33 Umuohu Umuobia Umuarako 30 73 Bende L.G.A Afara 63 Umuezela 21 69 Umu - Isi Court GCU

Nwanwa 500 ABSU Ama - Igbo

Ahia Ukwu 11 500 44 FGGC 09 Nkalu Nta UBAKALA 18 Avodim 34 Umuariaga Itaja 46 MOUAU 68 Itu Amakama Aro - Okporoenyi Umudike 74 10 Nsirimo Apumiri

67 32 Ihim Okwu 100 Mbara - Akuma Amuro 500 11 12

Amaoba 500 Ahi River Ime 500 06 Itu Nta Amawom 13

Iberenta 400

400 Umusoro 08 Elemaga TO ABA Ndoro Umuhu FROM ABA Isiala Ngwa L.G.A Iyila 07 20 Nnono Mbinyang

Anya River

Oronta Okwe Legend Oleri Obuohia Isiala 05 State Boundary State Headquarters Ntalakwu Ogbuebule

Local Government Area Headquarters 79 Akwa Ibom State 02 04 Ekebedi Ekpiri Local Government Area Boundary Alala Oloko Azunchai Local Government Headquarters 51 Awom ukwu Main Road 78 54 Obugwu Usaka Umu ogo Amizi Ukwu Secondary Road Alala 52 Ariam Ndi Okoro 02 VES Point Obeoma 53 Ndi Eke Ariam Bore hole location Ohuhu 57 Ekpiri Settlement 400 Oboni 400 01 300 55 Railway Ndiorie Otoro Nchara 500 Eluelu 56 Obohia Ariam Contour Ariam

River Akam Asano

FigureFig 2: 1.3 Topo/Geological Topo/Geological Mapmap of ofthe studyStudy Area area showing showing VES/Borehole borehole/VES Locations sites.

The Imo Shale consists of thick clayey shale, fine-textured dark gray to bluish-gray with occasional admixture of clay ironstone bands with a thickness of about 500 m (Wilson, 1925; Simpson, 1955; Kogbe, 1976). This formation rests conformably on the Nsukka Formation. The Bende-Ameki Formation constitutes the main bulk of Eocene strata overlying the Imo Shale. It is made up of a series of highly fossiliferous grayish-green sandy-clay with calcareous concretions and white clay sandstones. There are two lithological groups recognized in parts – the lower with fine-to-coarse sandstones and intercalations of calcareous shale and thin shally limestone and upper with coarse, cross-bedded sandstones, bands of fine, gray-green sandstone and sandy clay. Bende-Ameki strata consist of rapidly alternating shale, sandy shale, mudstone, clayey sandstone and fine-grained argillaceous sandstone with limestone bands. In some places the thickness is about 33 m and it is richly fossiliferous all through. The beds dip gently between 5o and 7oS; the strata show steeper dips than the underlying Imo Shale Formation which indicates unconformable relationship. The Bende-Ameki Formation is of Lutetian to Lower Bartonian age and it is richly fossiliferous with mollusks, foraminifera and corals predominating (Kogbe, 1976). The Benin Formation is more than ninety per cent sandstone with shale intercalations. It is coarse- grained, poorly sorted and sub-angular to well-rounded and bears lignite streaks and wood fragments. The formation is a continental deposit of probable upper deltaic depositional environment. In the sub-surface it is of Oligocene age becoming progressively younger southwards. It ranges from Miocene to Recent. The study area is a part of the Tertiary Niger Delta of Nigeria (Table 1). It is believed that the

Chukwu et al…. Int. J. Inno. Scientific & Eng. Tech. Res. 3(1):47-61, 2015 transgressive regime which followed the close of the Cretaceous gave rise to a thick sequence of the Tertiary shale and limestone deposits whose sediments include Imo Shale, Bende-Ameki and Benin Formations (Short and Stuable, 1967; Kogbe, 1976; GSN, 1985).

Table 1: The stratigraphic sequence of the study area. AGE FORMATION TIME STRATIGRAPHY LITHOLOGY Quaternary Benin (CPS) Oligocene/Miocene Sands and Clays Tertiary Bende-Ameki Middle Eocene Clays, Clayey-Sands and Shales Tertiary Imo Shale Lower Eocene (Paleocene) Clays and Shale-with-Sandstones Source: Geological Survey of Nigeria (GSN) (1985).

MATERIALS AND METHODS The three main instruments used in this work to acquire geophysical data are ABEM Terrameter (SAS) 300B, Magellan GPS 310 (a powerful satellite access technology device) and compass-clinometers. From the topographic map of Nigeria the study area was delineated and culled up as well as the same study area map obtained from geological map of Nigeria. In effect, a geological map of the study area was superimposed on the topographical map and reproduced cartographically. This is to make it possible to relate the borehole sites/data succinctly located to the actual geological formation. Thus, the importation of global positioning system (GPS) measurements into the GIS apparatus was hereby actualized (GSN, 1985; Woodfine, 1995).

Figure 3: Schlumberger arrangement of electrodes.

The instruments were used to acquire field data for electrical resistivity measurements (Webb et al., 2011) using Schlumberger electrode arrangement to carry out Vertical Electrical Sounding (VES) at location point VES stations with AB/2=500 meters spread were covered between March and April 2009. All necessary precautions required in geo-electric measurements were duly considered. With a seven-man crew, the survey lasted between 0900 and 1700 GMT daily for two weeks under favorable weather conditions. Usually, every VES point measurement is preceded by GPS data acquisitions such as latitude, longitude and elevation parameters as they are taken and recorded in-situ. Thorough geological observations, rock/outcrop breaking using sledgehammer, sample collection, photographs, etc were made where necessary. The actual VES survey involved the determination of the variation of resistivity of geologic formations with depth. Resistivity of a formation often depends on the contained electrolyte of the sub-surface and is inversely related to the porosity and degree of saturation of the formation (Vingoe, 1972). The normal practice in resistivity survey is to pass electric current into the ground by means of two electrodes and measure the potential difference between a second pair of electrodes placed in line with the first pair. For Schlumberger array, the apparent resistivity, ρa is given as

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ρa = *( ) ( ) + { }

Thus, in terms of electrode spacing, equation (1) can be written as 2 2 ρa = 훑/4R[L – a ]/a . . . 2 where R = V/I (i.e. from Ohm’s law). The following mathematical models are used to obtain total transverse resistance, R and total longitudinal conductance, S – these are the basic measurement parameters necessary in aquifer studies.

R = ∑ . . . 3 and S = ∑ . . . 4

th where hi and ρi are the layer thickness and resistivity of the i layer in the section respectively. From equation (4), Si = σihi . . . 5 here σ is the layer conductivity. R and S are referred to as Dar Zarrouk parameters and they have been proved to be powerful interpretational aids in groundwater surveys (Zohdy et al., 1974). Niwas and Singhal (1981) determined analytically the relationship between aquifer transmissivity, Tr and R on one hand and between Tr and S on the other hand as follows: Tr = KσR = KS/σ = Kh . . . 6 where K is hydraulic conductivity. This relationship was used in this study and K was obtained from pumping test by Abia State Water Board. Niwas and Singhal (1981) maintained that for areas where the geology and water quality do not vary very much, the product of hydraulic conductivity and conductivity (Kσ) values remain fairly the same. Equations 2-6 were used to generate very useful field data from the VES field measurements. Thereafter, the field data were processed; first, manually and then computer-aided using RESIST and autoCAD software. This exercise produced the data sets that are shown in Table 2.

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Table 2: Resistivity profile for some VES data in the study area

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RESULTS/DISCUSSION Table 2 shows the VES/borehole data obtained from the area of investigation. The interpretations of the variations in the GPS information, lithologic information, static water level/piezometric levels, geologic formation and layers, with their thicknesses are of paramount importance in the study of the aquiferous conditions or otherwise of the subsurface. The interpretational endeavor is enhanced by constructing geoelectric cross-sections AA΄, BB΄, CC΄, DD΄, EE΄ and FF΄ as shown in Figure 4. This exercise was taken to enable us investigate and establish clearly the subsurface characterization so that the hydro geoelectric nature along the profiles traversed could be unveiled and ascertained.

Fig. 4: Map of study area showing profiles.

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Figure 5: Geo-electric cross-section along AA΄

Geo-electric section AA΄: This profile traverses SW-NE of the study area across the three geologic formations. Here, it is observed that Umulenso (VES 17) and Umuezehiri-Umuagu (VES 19) are along this profile at the extreme north of the study area. They are made up of hard modular lateritic top surface with the sub-surface being entirely shale which constitutes a conducting zone. No sane person should expect a productive borehole here. The two locations are within the Imo shale formation. The VES data obtained were very poor and getting this type of geo-electric section was not a surprise. The researchers were told that several boreholes (more than twenty in number) had been tried in these places without success. The next station in the same traverse is Ekeoba (VES 31) probably sitting on a transition zone between Imo Shale and Bende-Ameki/Benin Formations. It is neither in the aquiferous zone nor in the conducting zone. Still along the traverse towards south, Umujieze (VES 05) is sitting right in the aquiferous zone of Benin Formation and the site supports productive borehole (Fig. 5). It has aquiferous thickness of about 200 meters.

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Figure 6: Geo-electric cross-section along BB΄.

Geo-electric section BB΄: From B΄ end of the profile ie north, Odide (VES 23) and Umuire are within Imo Shale Formation also. There is a top soil range of 0.5 to 0.7 meter in thickness and a clay lithology of about 3.8m in thickness. The rest of the subsurface lithology comprises of shale which does not hold water and no borehole thrives here. Ossa (VES 49) along the same profile has almost the same top (soil) layer thickness with Odide but Ossa sits some distance away from the conducting zone of Odide. The BB΄ profile in Fig. 6 shows that as one gets gradually nearer to the aquiferous zone, one moves closer to the coastal plain sands of the Benin Formation whose sub-surface structures support conducive environment for groundwater storage. The aquifer resistivity here is about 3937 Ωm. There is also an intercalation of clay with resistivity of 776 Ωm.

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Fig. 7: Geo-electric cross-section along CC΄

Geo-electric cross-section CC΄: The profile CC΄ (Fig. 7) is an interesting traverse in the study. It depicts the true sub-surface geology with reference to the layering pattern and distribution of crustal materials within this sedimentary environment. This top soil layer ranges from 0.4 to 0.8m in thickness which is made up of unsaturated dry sand while the second layer is between 2.5 and 15.9 m. The aquifer thickness here varies considerably among the VES/borehole points. At Oloko (VES 04) it is about 32.4 m, Amawom (VES 13) 15.1m, MOUAU (VES 46) 81.6 m and at Ajata Okwuru the thickness is 35.6 m. In the same manner the resistivity varies from point to point. It is important to note that the same aquifer is common to these location points but a borehole of 150-200 m (TDD) at Oloko or MOUAU could get water whereas one at same depth at Amawom would not as the borehole would encounter a conducting zone of shale.

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Figure 8: Geo-electric cross-section along DD΄

Geo-electric section DD΄: A very close look at DD΄ profile (Fig. 8) shows that the top soil which is mainly gravel/laterite at Itunta (VES 06) of thickness 0.1m with very dry unsaturated sand at Iyila (VES 08), Isiala (VES 05) and Oloko (VES 04); their thicknesses are 0.7, 0.6, and 0.5 meter respectively. At these sites for the second layer which is lateritic zone, the thickness is as follows: Itunta 3.1m, Iyila 5.3m, Isiala 5.7 m and Oloko 15.9 m. The third layer which constitutes the aquiferous zone is broad just after Itunta coming from D΄ axis. With a closer look at Figures 2 and 11, it is easy to see that Itunta belongs to Bende-Ameki Formation. The vertical electrical sounding data are really revealing the sub-surface for us to make reasonable inferences. The resistivity range of the aquifer is 1011-4084 Ωm. The perennial Akwu River between Itu-nta and Elemaga recharges the aquifer zone during the rainy season. It is also easy to observe that the zone appears to constitute a geological pinch out as the aquifer fails to get to Itunta (VES 06) there has never been any functional borehole in or around Itunta. Several efforts made to drill one failed (Personal communication, 2009). In the same manner, the geo-electric cross-sections along EE΄ and FF΄ give their descriptions as shown in Figures 9 and 10 respectively.

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Figure 9: Geo-electric cross-section along EE΄.

Figure 10: Geo-electric cross-section along FF΄.

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Figure 10: Geoelectric cross-section along FF΄.

Figure 11: Map of study area showing possible borehole zones.

The major findings from this work include the following: i. At the present level of depth drilling (100-130 m TDD), the Imo Shale Formation cannot support groundwater supply system. Deeper drilling may succeed if we target fractured aquifer since it is an older formation. ii. Part of the reasons for drilling unproductive boreholes in the area is that the hydro-geological and hydro-geophysical knowledge of the area is very poor. Not putting geology into account while considering borehole site could constitute a very serious negligence. iii. Total absence of pre-drilling geophysical investigations can lead to borehole failure. Wild-cat drilling has been in constant practice within the study area. iv. The activities of quacks and inexperienced geoscientists could result into unproductive boreholes. Time without number they would encounter a perched aquifer while drilling with exhilarating jubilation for a seeming success. This borehole water is very limited and it is an unreliable long-term supply. v. Application of global/regional geophysics to solve local problem could equally give rise to failed boreholes. Each location should be treated on its own merits based on pre-drilling findings. vi. Non-adherence to professional/expert advice can be responsible in getting un-successful boreholes for groundwater harvest (see Figure 9). Bad handling of casing materials, screening, pumping, etc can also create serious problems.

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vii. Many boreholes were sited based on political reasons and such boreholes become wasted resources, time, hope and aspirations of the people as the projects now become poverty sustainability ventures to the people instead of poverty alleviation as initially visualized.

RECOMMENDATION/SUGGESTIONS Whenever any water scheme is to be embarked upon, a qualified geoscientist (preferably a COMEG registered member) should be involved from the onset. This will reduce a lot of unnecessary expenditure and also give some assurance on the on-going enterprise. COMEG stands for Council of Nigerian Mining Engineers and Geoscientists. This is a body established by the Federal Republic of Nigeria Decree No. 40 of 1990 that regulates mining and geo-scientific activities in the country. For the areas where boreholes are surely not viable, intensified research could be carried out towards rainwater harvesting since we have considerable amount of rainfall in this geographical zone. This is actually the research thrust of the researchers for the problem areas in the near future.

CONCLUSION Concerted efforts have been made to investigate problems of borehole failure in Ikwuano/Umuahia whose lateral area falls into three major geological units. Some parts of the area do not have good prospects for groundwater abstraction. The Imo Shale Formation which is characterized by thick clayey-shale lithology constitutes an excellent aquitard and has never supported any borehole program. Embarking on drilling program in defiance of its geology may be a risky venture. It is in fact classified as a borehole-failure zone. The best option in those communities within the area is surface water development using river/water pumping station or rainwater harvesting scheme. For the boreholes that run momentarily and stop, (they are scattered within Bende/Ameki and Benin Formations, but more pronounced and rampant in the former than the latter). The wells are located within one of the two formations or their transition zones. Some viable boreholes are in Bende-Ameki while many more are in the coastal plain sands. Causes of failed boreholes have been verified. For the benefit of prospective drillers or borehole owners within Ikwuano/Umuahia, Fig. 11 could serve as a guide. Benin Formation labeled 3 supports borehole development. The portion labeled 1 is within the Imo Shale enclave which is mainly impermeable and impervious clay-shale strata. There is no reported or observed functional borehole here. It is a ‘no-go- area’ for borehole development within the study area. Electrical resistivity method has been used applying VES technique of geophysical investigation which is environmental friendly. It is also reliable, economical, prone to high quality data and result-oriented. Its measurements are safe, fast, non-destructive and non-inclusive as tangible results were obtained.

ACKNOWLEDGEMENT The authors are grateful to Michael Okpara University of Agriculture, Umudike (MOUAU) for granting the first author financial assistance through ETF Staff Development Scheme that made it possible for the completion of the research project.

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