AQUIFER SYSTEMS OF NDOKWA LAND DELTA STATE, NIGERIA

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1 SYSTEMS OF NDOKWA LAND DELTA STATE, NIGERIA Oseji Julius Otutu Department Of Physics, Delta State University, Abraka, Delta State. ABSTRACT The execution of water borehole project is expensive; there is therefore the need for surface resistivity measurements before drilling. Vertical Electrical Sounding (VES) using Schlumberger configuration is one of the most reliable geophysical techniques and was carried out in Ndokwa land to obtain and document not only the layers of the near surface aquifer but to determine the thickness and depth to the aquifer and hence recommend the area/s boreholes could be drilled for potable and sustainable water supply. A total of 569 vertical electrical soundings data were obtained from 36 locations evenly spread and spaced km apart using the Schlumberger array method. The apparent resistivity values obtained in the field were plotted against half current electrode spacing in a log-log graph. The resulting curves were interpreted both qualitatively by inspection and quantitatively by matching small segments of the field curves using two-layer model and their corresponding auxiliary curves. The resistivity and thickness obtained from the partial curve matching were improved upon by employing an iterative computer program to obtain the layer parameters. The type of curves, the resistivity of the sediments and the knowledge of the local geology of Ndokwa land were used as guides in the analysis and interpretation of the layer parameter in terms of probable and sustainable water supply. In Ndokwa land, 4 layers of aquifer were identified within the third and the fourth geoelectric layers of the earth. These layers consists of the medium to coarse grained sand formations of resistivity values ranging from 300 Ωm to 1500 Ωm with an average thickness of 35 m, Boreholes for potable and sustainable water supply is therefore recommended at a depth of between 30 m and 45 m in Ndokwa land. Key words: Ndokwa Land, Vertical electrical sounding, groundwater, aquifer, elevation and water table. 1. INTRODUCTION Ndokwa Land consists of three Local Government Areas: (Ndokwa West, Ndokwa East and Ukwuani). It is in the Southeastern region of Delta State situated in the South southern part of Nigeria and lies between latitudes N and N and longitudes E and E. It has common boundaries in the North with Ika South and Aniocha South Local Government Areas. Isoko South and Isoko North bound it in the South while it also has common boundaries with Ughelli North and Ethiope East Local Government Areas and Edo State as well as River Niger in the West and East respectively. The important rivers in the region are Niger, Ethiope, Adofi and Umu while the Ase creek is the major creek. The political map of Ndokwa land (inset map of Nigeria) is shown in Figure 1.. GEOLOGY OF NDOKWA LAND One of the greatest oil producing areas in Nigeria is the Niger Delta basin. The study area Ndokwa land is within this zone. The Niger-Delta in this project applies to the entire 3-Dimensional bodies of continental, transitional and marine deposits formed by sediments from Rivers Niger and Benue. The continental deposits form the land area otherwise called the sub aerial regions. The marine deposits are the water filled region otherwise called the sub aqueous region. While the transitional deposits forms the swampy (mangrove) regions. (Hospers. 1965); (Ejadiavwe, 1981). The structure of the continental geologic framework directed River Niger and Benue towards the present site of the Delta. Hence the geology of Niger-Delta, like other parts of the earth has undergone different changes right from the tectonic setting through the paleogeographic evolution to the present day. This development of the Delta has been dependent on the balance between the rate of sedimentation and subsidence. The balance and the resulting sedimentary patterns appear to have been influenced by the structural configuration of tectonics of the basement. (Evany, et al, 1979). The geology and Geomorphology of the Niger delta have been described in detail by various authors (Allen, 1965; Merki, 1970; Akpokodje, 1979 and 1987; Assez 1970 and 1976; Avbovbo, 1970; Oomkens, 1974; Burke, 197; Rement, 1965 and Short and Stauble, 1967). The formation of the present day Niger delta started during early 315

2 Palaeocene and it resulted mainly from the build-up of fine-grained sediments eroded and transported by River Niger and its tributaries (Efeotor and Akpokodje 1990). The sub-surface geology of the Niger Delta consists of three Lithostratigraphic units (Akata, Agbada and Benin formations), which are in turn overlain by various types of Quaternary deposits. The Quaternary deposit of Ndokwa land consists mainly of Coastal Plain Sands, Sombreiro Warri deltaic Plain deposits invaded by mangrove, wooded back Swamps Fresh water Swamp and Meander belts. The important rivers in the region are Rivers Niger, Ethiope, Adofi and Umu while the Ase creek is the major creek. However many ponds and streams are found within the area. The Map of Ndokwa land showing the geologic formation, important towns and Assess roads are shown in figure. 3. METHODOLOGY AND DATA ACQUISITION Electrical resistivity method using Vertical Electrical Sounding (Schlumberger array) is adopted in this investigation. Zohdy, 1974; Zohdy et al 1974 and 1993; Ekine and Osobonye 1996; Overneeren 1989; Etu-Efeotor and Akpokodje 1990; Etu-Efeotor et al 1989; Okolie et al 005; Oseji et al 005 and Osemeikhian and Asokhia 1994 gave detailed account of the use of this method. The basic method employed in this work, is the surface resistivity sounding. In this method, current is introduced artificially into the earth through a pair of electrode pinned to the ground (current electrode) and the resulting potential difference due to the current is measured through another pair of electrode (potential electrode) that is also pinned to the ground, any subsurface variation in conductivity alters the current flow; which in turn affects the distribution of electric potential at the surface (Chukwurah, 199; Efeotor, 1981; Dobrin, 1960; 1976; 1988 and Parasins, 1966; 197 and 1986). A total of 36 stations spaced.00 km apart were established and surveyed for 569 vertical electrical soundings using a method whereby readings were taken automatically and the results were averaged continuously with an ABEM SAS 300 terrameter and a maximum half current electrode spacing of 316 m since it is a near surface investigation. The depths to water level in the hand-dug wells close to the VES stations were measured directly with a meter tape and recorded. 316

3 The apparent resistivity values were plotted against half the current electrode spacing on a log-log graph. The curves obtained were interpreted both qualitatively by inspection and quantitatively by matching small segments of the field curves using two-layer model and their corresponding auxiliary curves. The resistivity s and thickness obtained from the partial curve matching were improved upon by employing an iterative computer program to obtain the layers parameter (resistivity, thickness and depth). The numerous layers that were generated by the computer shall be grouped into relevant geologic depth intervals called geoelectric sections. The type of curves (Selemo et al, 1995), the resistivity of the sediments (Oyedele, 001) and the knowledge of the local geology were used as guides in the interpretation and analysis of the geoelectric parameters in terms of probable, potable and sustainable water supply. FIGURE : MAP OF NDOKWA LAND SHOWING THE GEOLOGIC FORMATION, IMPORTANT TOWNS AND ASSESS ROADS. 317

4 4. QUALITATIVE INTERPRETATION The interpretation of the field data began with qualitative process of plotting of the data on a log-log graph and inspection of the resistivity field curves to ensure data reliability. Manual interpretations employing the use of master curves were adopted in the field to gain first hand idea of existing layering configuration and the type of curves as shown in table 1. TABLE 1: QUALITATIVE ANALYSIS OF THE CURVE TYPES IN NDOKWA LAND. VES LOCATION CURVE TYPE RMS % ERROR 1 MAJOR ROAD IN ABOH HAA.10 MAJOR ROAD IN OKPAI-OLUCHI AAK.60 3 IGBUKU HAA ASHAKA AK BENEKU HA.39 6 UMUSEDELI KA UMUSETI HK OBIOGWA UMUSAM KA ND OWESSEI ST.UMUSADEGE KH OSEJI ESTATE UMUSADEGE AK UGILIAMAI HA ONUGA KHQ AMOJI QH EWESHI ONICHA-UKWUANI HA OKPALA-UKU ONICHA UKWUANI HA OSEJI COMPD, IKE-ONICHA KHA OGUME ROAD IKE-ONICHA KHA OBIOGWA OGBE-OGUME KHA UTUE-OGUME AA OBODOUGWA OGUME HA EBENDO HA 1.96 OBODOETI HA OBIOGO HA ETEVIE, EMU-UNO HA IKOSA, EMU-UNO HA. 6 WIRE ROAD OBIARUKU KA GHANA QUARTERS, HA OBINOMBA AA.41 9 UMUKWATA K ADONISHAKA, EBEDEI HKQ UMUTU MIXED SEC. SCHOOL A MICHELIN ROAD UMUTU HA OGBEOLE OGUME AKH AMAI/OGUME ROAD, OGUME AKHK OGBE-ODOLU, OGBE OGUME AK OGUME GRAM. SCHOOL HAK QUANTITATIVE INTERPRETATIONS. Quantitative interpretation of the vertical electrical sounding field curves were interpreted using partial curve matching (Zohdy et al 1974). The resistivity and thickness obtained from the partial curve matching were improved upon by employing an automatic iterative computer program. The number of layers were modified based on the inflation points and were modeled in a step function. Samples of type curves HAA, AAK, AK, HA, HK, KA, KH, KHQ, QH, KHA, AA, K, HKQ, A, AKA, AKHK and HAK are shown in figures

5 The type of curves (Selemo et al, 1995), the resistivity of the sediments (Oyedele, 001) and the knowledge of the local geology were used as guides in the interpretation and analysis of the geoelectric parameters in terms of probable, potable and sustainable water supply (Tables and 3). These depths were correlated with that obtained from direct measurements of the water level in the hand-dug wells using Pearson correlation coefficient (Table 4). The result was confirmed using the SPSS computer program (Table 5). The obtained reveal that there is significant difference between the depths to water level measured in the hand-dug wells and that obtained from the VES interpretation. Hence the interpretation is valid and reliable. Consequently, 4 layers of aquifer were identified in Ndokwa land (Table 6 and 7), These layers consists of the medium to coarse grained sand formations of resistivity values ranging from 300 Ωm to 1500 Ωm with an average thickness of 35 m, Boreholes for potable and sustainable water supply is therefore recommended at a depth of between 30m and 45m in Ndokwa land. TABLE : RESISTIVITIES AND DEPTHS OF THE FIRST WATER BEARING FORMATION FROM THE VES INTERPRETATION VES LOCATION S/N RESISTIVITY OF THE FIRST WATER DEPTH TO THE FIRST WATER BEARING BEARING FORMATION IN THE VES FORMATION FROM THE VES INTERPRETATION INTERPRETATION M Ωm 1 MAJOR ROAD IN ABOH MAJOR ROAD IN OKPAI-OLUCHI 3 IGBUKU ASHAKA BENEKU UMUSEDELI BY AGIP PETROL STATION 7 OPPOSITE ONEFELI S COMPD, UMUSETI 8 OBIOGWA UMUSAM ND OWESSEI ST.UMUSADEGE 10 OSEJI ESTATE UMUSADEGE 11 UGILIAMAI ONUGA AMOJI ADOH PRI. SCH EWESHI/IKE-ONICHA 15 OKPALA-UKU ONICHA UKWUANI 16 OSEJI COMPD, IKE ONICHA 319

6 TABLE 3: RESISTIVITIES AND DEPTHS OF THE FIRST WATER BEARING FORMATION FROM THE VES INTERPRETATION S/N VES LOCATION RESISTIVITY OF THE FIRST WATER DEPTH TO THE FIRST WATER BEARING FORMATION IN THE VES BEARING FORMATION FROM THE INTERPRETATION Ωm VES INTERPRETATION M 17 OGUME ROAD IKE-ONICHA OBIOGWA OGBE-OGUME UTUE-OGUME OBODOUGWA OGUME EBENDO OBODOETI OBIOGO ETEVIE, EMU-UNO IKOSA, EMU-UNO WIRE ROAD OBIARUKU GHANA QUARTERS, OBINOMBA UMUKWATA ADONISHAKA, EBEDEI UMUTU MIXED SEC. SCHOOL MICHELIN ROAD UMUTU OGBEOLE OGUME AMAI/OGUME ROAD, OGUME CONSTRUCTION OF ROAD ( ) OGBE-ODOLU, OGBE OGUME OGUME GRAM. SCHOOL TABLE 4: DATA FOR PEARSON S CORRELATION COEFFICIENT S/N VAR001 X VAR00 Y X Y XY

7 n XY X Y n X X n Y Y Where n =36 X = Y = X = Therefore Y = XY = ( ) = ( ) = ( ) = SPSS CORRELATION USING COMPUTER PROGRAM TABLE 5: CORRELATION OF THE DEPTHS OBTAINED AT THE FIRST WATER BEARING FORMATION FROM THE VES INTERPRETATION WITH THAT MEASURED IN THE HAND-DUG WELLS VAR00001 VAR0000 Cor relati ons Pearson Correlation Sig. (-tailed) N Pearson Correlation Sig. (-tailed) N VAR00001 VAR ** ** **. Correlation is signif icant at the 0.01 lev el (-tailed). 31

8 TABLE 6: LAYERS OF NEAR SURFACE IN NDOKWA LAND VES FIRST LAYER OF T 1 D 1 1 SECOND LAYER OF THIRD LAYER OF FOURTH LAYER OF T D 3 T 3 D 3 4 T 4 D TABLE 7: LAYERS OF NEAR SURFACE S IN NDOKWA LAND VES FIRST LAYER OF T 1 D 1 1 SECOND LAYER OF THIRD LAYER OF FOURTH LAYER OF T D 3 T 3 D 3 4 T 4 D

9 6. CONCLUSION AND RECOMMENDATIONS In Ndokwa land, 4 layers of near surface aquifer were identified within the third and the fourth geoelectric layers. Apart from Adonishaka in Ebedei and Okpai-Oluchi in Ndokwa East Local Government Area of Ndokwa land that seems to have local clay deposits in the second and fourth geoelectric layers, which though are very thin and appear to create local confined conditions, the aquifer characteristics of Ndokwa land shows that they are not confined. In the event of pollution, groundwater in Ndokwa land is easily contaminated. Borehole for potable and sustainable water supply is therefore recommended at a depth of between m m in Ndokwa land. This depth has an average thickness of m and it coincides with the second relevant geologic layers in Aboh and Utagba-Ogbe environs while in Ogume, Onicha-Ukwuani and Obiaruku environs, the depth is within the fourth relevant geologic layers and in Emu and environs, it is in the fifth layer. These layers consist of the medium-grained sand to the coarse-grained sand formations, which is the best environment to obtain an appreciable quantity of water for sustainable groundwater development. The research did not only pave way for a clear picture of the hydro geological knowledge of Ndokwa land in other to create awareness on the productive and prolific aquifer for sustainable groundwater supply but act as guides to both the Government and individuals especially those involved in groundwater development on the type of near surface aquifers, the formation of the aquifer as well as the thickness of the aquifer and the depths boreholes could be drilled for sustainable water supply. 7. REFERENCES: AKPOKODJE, E. G. (1979): The importance of engineering geological mapping in the development of the Niger Delta Basin. Bull. 1 in Assoc. Eng. Geol. No 19 Pp (10-108). - (1987): The engineering geological characteristics and classification of the major superficial soils of the Niger Delta. Engineering Geology 3 Pp (193-11). ALLEN, J.R.L. (1965): Late Quaternary Niger Delta and adjacent areas: Sedimentary Environments and Lithofacies. Bulleting American of Petroleum Geology. Vol. 49 (5) Pp ( ). ASSEEZ. L. O. (1976): Review of the stratigraphy, Sedimentation and structure of the Niger- Delta in geology of Nigeria Elizabethan Publishing Co., Lagos, Nigeria. - (1970): Groundwater resources of Southwestern Nigeria. Nig. Engr. 7; Pp (-45). AVBOVBO, A. A. (1970): Tertiary Lithostratigraphy of the Niger Delta Bull. American Association of Petroleum Geology 63 Pp (95-306). BURKE, K. K. (197): Long stone drift, Submarine Canyons and submarine fans in the development of the Niger- Delta A.A.P.G. Bull, Vol. 56Pp CHEMICOFF, F AND VENKATAKRISHNAN, R (1999): Introduction to Physical Geology. CHUKWURAH, S. (199): Basic technology of borehole Mavmillan Nigeria Pp (1-1) DOBRIN, M.B (1960): Introduction to Geophysical. 3 rd Edition McGraw Hill Book Company Pp (-7 and ) - (1976): Introduction to geophysical prospecting New York. Hill Book Company. UK. Pp (1-6 and ). DOBRIN, M.B. AND CARL, H.S (1988): Introduction to Geophysical Prospecting 4th Edition. New York McGraw Hill Book Company Pp (1-3 and ). EJADIAVWE, J. E. (1981): The geology of Niger Delta EKINE, A. S AND OSOBONYE, G. T (1996): Surface Geoelectric Sounding for the determination of Aquifer Characteristics in parts of Bonny Local Government Area of River State. Nigerian Journal of Physics Vol. 85, Pp (93 97). EMENIKE, E. A. (000): Geophysical Exploration for Groundwater in a Sedimentary Environment : A case study from Nanka over Nanka formation in Anambra Basin, Southeastern Nigeria. Global Journal of Pure and Applied Sciences Vol.7 No. 1 January Pp (97 110). ETU-EFEOTOR, J. O. (1981): Preliminary Hydro geochemical Investigation os sub-surface waters in Parts of the Niger Delta. Journal of Mining and Geology 18 (1) Pp ( ). ETU-EFEOTOR, J. O AND AKPOKODJE, E. G. (1990): Aquifer systems of the Niger Delta. Nigerian Journal of mining Geology. Vol. 6 () Pp (79 84). ETU-EFEOTOR, J. O; MICHAISKI, A AND ALABO, E. H. (1989): Geophysical investigation for groundwater in part of Eastern Niger Delta. Journal of mining and geology. Vol. 5 No. 1 & Pp (51 54). EVANY et al (1979): The Geology of Niger Delta. HOSPERS, J. (1965): Gravity field and Structure of the Niger-Delta Nigeria Geological Society American Bulletin. Vol.76. Pp (407 4). KOEFOED, O. (1979): Geosounding Principles Elsevier Pub, Co. Amsterdam. 33

10 MERKI, P. J. (1970): Structural Geology of the Cenozoic Niger-Delta African Geology, Ibadan University Press, Ibadan, Nigeria. Pp (51 68). OKOLIE, E. C; OSEMEIKHIAN, J. E. A; OSEJI, J. O. AND ATAKPO, E. (005): Geophysical Investigation of the source of River Ethiope in Ukwuani Local Government area of Delta State. Nigeria Institute of Physics. Vol. 17. OOMKENS, E. (1974): Lithofacies Relation in Late Quaternary Niger-Delta Complex sedimentology" 1; (115 ). OSEJI, J.O; ATAKPO, E. AND OKOLIE, E. C. (005): Geoelectric Investigation of the Aquifer Characteristics and Groundwater Potential in Kwale, Delta State, Nigeria Journal of Applied Sciences and Environmental Management Vol. 9 (1) Pp ( ) ISSN www. Bioline. Org.br.ja. OSEMEIKHIAN, J. E. AND ASOKHIA, M. B (1994): Applied Geophysics for Engineers and Geologists. Samtos Services Ltd Lagos, Nigeria. OVERNEEREN, R. A. (1989): Aquifer boundaries explored by geoelectric measurements in coastal plains of Yemen A case of equivalence Geophysics Vol. 54 Pp (38 48). OYEDELE, K. F. (001): Geoelectric investigation of Groundwater resources at Onibode is, near Abeokuta Southwest, Nigeria. Pp ( ). PARASINS. D. S. (1966): Principles of Applied Geophysics Third Edition. - (197): Principles of Applied Geophysics ( nd Ed), Chapman and Hall, London - (1986): Principles of Applied Geophysics. Chapman and Hall, REINHARD, K. FROHLICH (1974): Combined Geoelectric and Drill hole Investigation for detecting freshwater aquifers in Northwestern Missouri. Geophysics Vol. 39 No. Pp (340 35). REMENT, R. A. (1965): Aspects of Geology of Nigeria Ibadan press Pp 133. SELEMO, A. O. I; OKEKE, P. O AND NWANKWOR, G. I (1995): An Appraisal of the usefulness of VES in Groundwater Exploration in Nigeria Water Resources Vol. 6 No. 1 & Pp (61 67). SHORT, K. C. AND STAUBLE, A. J. (1967): Outline Geology of Niger-Delta American association of Petroleum Geologists. Bulletin.Vol. 54 and Vol. 51 Pp ( ). ZOHDY, A. A; EATON, C. P. AND MABEY, D. R. (1974): Application of Surface Geophysics to Groundwater Investigation. Tech. water resources investigation, Washington, U.S Geological Survey No ZOHDY, A. A. R; MARTIN, R. J. (1993): A study of sea water intrusion using Direct Current Sounding in the Southern part of the Ox ward Plain California. Open-file reports U. S. Geological Survey Pp ABOUT THE AUTHOR OSEJI, JULIUS OTUTU, Ph.D. is a Senior Lecturer in the Department of Physics, Delta State University, Abraka, Nigeria. His research focus is on groundwater and environmental geophysics, with special interest in aquifer delineation and vulnerability in sedimentary and crystalline basement terrains. 34