The International Journal Of Engineering And Science (IJES) || Volume || 4 || Issue || 11 || Pages || PP -29-39|| 2015 || ISSN (e): 2319 – 1813 ISSN (p): 2319 – 1805 Geophysical Investigation for Groundwater Potential in Rufus Giwa Polytechnic Owo, Southwestern Nigeria 1 1,2,3 O.O. Falowo, 2A.O. Daramola , 3O.O. Ojo Department of Civil Engineering, Faculty of Engineering Technology, Rufus Giwa Polytechnic, Owo, Ondo State, Nigeria. ------------------------------------------------------------ABSTRACT--------------------------------------------------------------Geophysical investigation was conducted at Rufus Giwa Polytechnic, Owo, Southwestern, Nigeria with the aim of evaluating the groundwater potential in the area. The geophysical survey involved Very Low Frequency Electromagnetic (VLF-EM) and Vertical Electrical Sounding (VES). A total of twenty seven (27) traverses were established along West – East and Southwest – Northeast direction in the studied area; covering a total distance of 8.45 km. The lengths of the traverses vary between 110 m and 920 m. Measurements were taken at 10 m spacing along the traverses for the VLF-EM. The result of the VLF-EM was used to determine the data point for the VES. The VLF-EM result reveals the presence of conductive zones. The geoelectric section revealed 3 to 5 major layers comprising the topsoil, clay, laterite, weathered layer, partly weathered layer/fractured basement, and fresh basement rock. The topsoil has resistivity that varies between 46 Ω-m and 1644 Ω-m, and depth that ranges from 0.3 m to 19.8 m. It is composed of clay/sandy clay, clayey sand, lateritic clay and laterite. The clay substratum has resistivity that ranges from 20 to 95 Ω-m and depth that varies from 1.5 m and 9.3 m. Laterite is characterized by resistivity that varies between 106 Ω-m and 1223 Ω-m with thickness that varies from 0.8 m to 11.4 m. The weathered layer which constitutes the first aquiferous zone and is characterized by resistivity that ranges between 28 Ω-m and 823 Ω-m, while its thickness varies from 0.4 m to 144.2 m. The composition of the weathered layer is predominantly clayey sand indicating an aquitard i.e. a subsurface geological formation that stores but fairly transmit water. The partly weathered layer/Fractured aquifer is the second aquiferous zone; it has resistivity that is between 16 Ω-m and 914 Ω-m with thickness in the range of 0.3 m to 148.6 m. The fresh basement has resistivity values that vary from 327 Ω-m to 17578 Ω-m. The low resistivity values (< 500 Ω-m) are due to screening effect by the overlying conductive material. The weathered layer and fractured basement aquifers correlate the suspected water filled geologic formation observed by the VLF-EM. Therefore the area shows a very good prospect for groundwater development. Keywords – aquiferous zone, conductive material, geological formation, geophysical investigation, groundwater ------------------------------------------------------------------------------------------------------------- ------------------------------Date of Submission: 14 November 2015 Date of Accepted: 30 November 2015 -------------------------------------------------------------------------------------------------------------------------- ------------------ I. INTRODUCTION Access to clean water is a human right and a basic requirement for economic development. The safest kind of water supply is the use of groundwater. Groundwater accounts for about 98 % of the world‟s fresh water and is fairly evenly distributed throughout the world. It provides a reasonable constant supply which is not completely susceptible to drying up under natural condition unlike fresh water. Water from beneath the ground has been for domestic use, irrigation and livestock. Lakes, swamps, reservoirs and rivers account for 3.5 % and soil moisture accounts for only 1.5 % ([4]). The works of ([1], [3]) revealed that it is necessary to monitor water quality on regular basis. Since groundwater normally has a natural protection against pollution by the covering layers, only minor water treatment is required. Detailed knowledge on the extent, hydraulic properties, and vulnerability of groundwater reservoirs is necessary to enable a sustainable use of the resources. The total replenishable water resource in Nigeria is estimated at 319 billion cubic metres, while the groundwater component is estimated at 52 billion cubic metres. Nigeria has adequate surface and groundwater resources to meet its current water demands. However, in spite of the tremendous efforts put by the various Governments to improve access to potable water supply to all Nigerians, estimates shows that only 58% of the inhabitants of the urban and semi-urban areas and 39% of rural areas have access to portable water supply. www.theijes.com The IJES Page 29 Geophysical Investigation for Groundwater Potential… Water shortages are acute in some major centres and in numerous rural communities due to a variety of factors including variations in climatic conditions, drought increasing demands, distribution system losses, and breakdown of works and facilities. Other challenges facing the sector include funding constraints for improving and rehabilitating broken down schemes, competition between water users, pollution from point and non-point sources and lack of competent and skilled human resources. 1.1 Description of the Project Environment Rufus Giwa Polytechnic, Owo, Ondo State, is located in Owo “Fig. 1” which is within the south western part of Nigeria. The institution “Fig. 2” is situated in Owo local Government of Ondo State “Fig. 3”. It lies within longitudes 6 ̊ 00ˡ E and 5 ̊ 30ˡ E and latitudes 7 ̊ 30ˡ N and 7 ̊ 00ˡ N. The study area is easily accessible by roads like Ikare – Owo highway, Benin – Ifon highway and Akure – Owo highway. 1.2 Geomorphology, Climate and Vegetation Owo is relatively flat, as the terrain ranges from 940 ft to 1100 ft “Fig. 4”. The terrain slopes from Rugipo down to Isuada town “Fig. 5”. Elevation is much higher at Ikare Junction and lower around Emure and Isuada towns. In RUGIPO, the topography ranges from 311 m to 342 m above the sea level. The study area has a gently undulating topography. The area lies geographically within the tropical rain forest belt of hot and wet equatorial climatic region characterized by alternating wet and dry climate seasons ([6]), which is strongly controlled by seasonal fluctuation in the rate of evaporation. The available rain data shows that mean annual rainfall ranges from 1000 mm - 1500 mm and mean temperature of 24 ̊ C to 27 ̊ C. There is rapid rainfall during the month of March and cessation during the month of November. June and September are the critical month when rainfall is usually on the high side. The vegetation is of tropical rainforest and is characterized by thick forest of broad-leaved trees that is ever green. The vegetation of the area (especially in undeveloped areas) is dense and made up of palm trees, kolanut trees and cocoa trees. Part of this area is also made the school farm. 1.3 Geology of the Studied Area The area of study falls within the Southwestern basement rock “Fig. 6” which is part of Nigerian Basement complex. The area is underlain mainly by rocks of the Migmatite - Gneiss Complex “Fig. 7”. RUGIPO is predominantly underlain by quartzite, granite and granite gneiss “Fig. 8”. Quartzite is the most dominant rock; which mineralogically contains quartz dominating mineral, other minerals such as muscovite, tremolite, microcline and biotite are common as well. Quartzites which are prominent as ridge vary in texture from massive to schistocity due to the presence of flaky minerals like mica. II. METHODS OF STUDY Twenty seven traverses were established in W-E and SW-NE direction with length that varies between 110 m and 920 m “Fig. 9”. The total length of the traverses established is 8450 m (8.45 km). o o o o 5 30 5 00 4 30 6 00 N Oke-Agbe AKOKO NW Ikun Ogbagi Arigidi EKITI STATE o IFEDORE Ijare ILE-OLUJI OSUN STATE Araromi Uso Alade Idanre Ore Omotoso Ofosu IRELE Okitipupa OKITIPUPA Irele ILAJE Igbokoda o 7 00 Okeluse Otu E D O Igbotaku o 6 30 N Okpe OSE Ifon Ute Omifunfun Loda Ayadi Ode-Aye MAKURDI ENUGU A T E Kajola AKURE S T Oniparaga ILORIN IBADAN LAGOS Ipele Sanusi IDANRE ODIGBO ABUJA o 7 30 N Ala-Ajagbusi Jimgbe Ibagba Asewele Ominia Odigbo MAIDUGURI Afo Idoani Sasere OWO Odole ONDO-WEST OGUN STATE Emure KANO NORTH Bolorunduro o Oba-Ile AKURE Akure Ile-Oluji Ondo 7 00 Iju Ita ogbolu SOKOTO KOGI STATE Auga AKOKO NE Akungba Ikare Ise Oka Ibillo Isua AKOKOIkun SW AKOKO SE Oba 7 30 Onikoko Ayere o 6 30 Akotogbo Igbekebo L. Gov't. Headquarters ESE-ODO Towns & Villages Minor Road o 6 00 N Major Road ATLANTIC OCEAN o 6 00 N State Boundary DELTA STATE o 4 30 E o 5 00 25 o 5 30 0 25 Km o 6 00 E Figure 1: Road/Administrative Map of Ondo State www.theijes.com The IJES Page 30 Geophysical Investigation for Groundwater Potential… 345000 344000E 361250N 347000 346000 349000 348000 350000E 361250N 361000 N 361000 SOKOTO Stre am KANO MAIDUGURI GAMES RESERVE ABUJA 360000 360000 Ata m op ere MANAGEMENT STAFF QUARTERS AREA 359000 FOR T AR QU EXPANSION ARTIFICIAL LAKE FUTURE N SE AGRICULTURAL IOR ILORIN O.S.P.O. CONSULT ESTATE AREA RESERVATION IBADAN AKURE MAKURDI ENUGU LAGOS S ER 359000 F AF ST STAFF CLUB DAM DEVELOPMENT AGRIC EXTENSION AREA O.S.P.O. CONSULT 358000 W.T. R ST AF F QU AR TE RS 358000 NEW SPORT COMPLEX RESEARCH/ PRESS CENTRE C.S From Akure NC PART-TIME STUDENTS RESERVATION REC SCHOOL OF BUSINESS STUDIES MAINTENANCE DEPT. STAFF CLUB F O ING Y O.S.P.O. GUEST L O E R OG HOUSE Str HO INE OL SCHOOL OF SC N G H N GENERAL E EC STUDIES C OM T MER CIA L m ea e Op 357000 CENTRAL AUDITORIUM/ ADMINISTRATIVE/ CONFERENCE CENTRE SUB. PLACE OF WORSHIP AREA CENTRAL POOL ALUMNI CENTRE Aa u nk e OSPO. COMM. CEN. 357000 SCHOOL G.H. ETF OF FOOD RESERVATION TECHNOLOGY PLACE OF WORSHIP HOSTEL Quarry HOSTEL AREA NIO Stream ACTIVITY JU Gate 356000N To Oluku 356000N 344000E 345000 348000 347000 346000 560m 560 0 1120 349000 350000E 1680m LEGEND Existing Road Streams Hostel Boundary Pillar Trees and Hedges Management Staff Quarters Lecture Halls/Existing Buildings New Sport Complex Fence Proposed Roads School Boundary Gate Commercial Centre Faculties/Conference Centres Administrative Blocks/ Conference Centres R.C. Artificial Lake/Pond S.U.B. Recreation Ground Student Union Building C.S. Corner Shop O.S.P.O. Ondo State Polytechnic, Owo W.T. Waste Treatment Ceded Land Stadium Figure 2: Land-Use Master Plan of RUGIPO 5 15 E 6 00 E 7 30 N 7 30 N EKITI STATE AKOKO SOUTH WEST L.G.A. Eporo Baga Sasere Ago-Panu Ipeme Ago-Panu Emure AKUR E NOR L.G.A. TH Amurin RUGIPO L.G .A. Uso Alaga OdofinAlaro Oluka Daji Camp Iyere Ilale Ipele Alasa Isijogun Olefa Ipele Ijegunmo Junction Obasoro Igodi Okififioko Isewe Sanusi Araromi OS E Emaajomo IDA NR Alafiatayo EL A. .G. Igbatoro 6 45 N 5 15 E 6 45 N 6 00 E LEGEND SCALE Major Road 0 Minor Road 5 Km Main Paths Towns and Villages RUGIPO Rivers and Streams Figure 3: Map of Owo Local Government Area of Ondo State www.theijes.com The IJES Page 31 Geophysical Investigation for Groundwater Potential… Figure 4: Topographical map of Owo and Environs Figure 5: 3-D Surface Elevation Map around the studied Area www.theijes.com The IJES Page 32 Geophysical Investigation for Groundwater Potential… Owo Study Area Figure 6: Geological sketch map of Nigeria showing the major geological component; Basement, Younger Granites, and Sedimentary Basins ([5]). Figure 7: Geological Map of Owo and Environs, showing the Study Area ([5]). www.theijes.com The IJES Page 33 Geophysical Investigation for Groundwater Potential… 345000 344000E 361250N 347000 346000 349000 348000 350000E 361250N 361000 N Str eam 361000 GAMES RESERVE 360000 360000 OSPO CONSULT ESTATE AREA Ata mo per e RESERVATION Management Quarters QU EXPANSION AREA FOR FUTURE AGRICULTURAL DEVELOPMENT 359000 SE R NIO T AR ER S 359000 F AF ST CEDED AREA AGRIC EXTENSION AREA From 358000 STAFF CLUB Akure Str SCHOOL OF BUSINESS STUDIES m ea Quarry HOSTEL 358000 e Op 357000 357000 HOSTEL 356000N To Oluku 356000N 344000E 345000 348000 347000 346000 560m 0 349000 350000E 560 m LEGEND Quartzite Stream Granite Gneiss / Granite Ceded Area Dam Quarry Figure 8: Geological Map of RUGIPO 357750 Tr.19 MANAGEMENT QUARTERS V46 CEDED AREA V47 Millenium Lecture Theatre V52 POULTRY V48 V54 Tr.21 V49 V51 V59 FACULTY OF GENERAL STUDIES/ MASS COMMUNICATION DEPT V56 357000 V50 Tr.20 V53 Tr.22 V55 ADMINISTRATIVE BUILDING V58 V57 Tr.27 V72 V75 GUEST HOUSE V27 V60 V63 Tr.14 V39 V42 V37 V41 V35 V34 Tr.13 V33 V61 V1 .9 Tr V22 V20 .8 V40 V36 Block-Five V23 ICT V25 V45 V28 V44 Hostel Sc ho ol Fa rm Tr.24 Tr.23 Tr.15V38 Tr.25 V66 rm Fa V62 Sc ho ol To Akure V65 V30 Tr.17 Tr.16 Hostel Tr.18 V43 V67 V64 V31 HEALTH CENTRE V70 B.Tech. Est. Mgt V24 V26 LOW RISE V21 V29 LIBRARY Tr .1 1 Sc ho ol Fa rm V71 Tr.26 V69 Tr .1 2 Tr .1 0 V32 V68 SUB V2 T T r r. 7 .6 ARTISAN Tr V74 V19 STADIUM V73 V16 V12 Tr.5 V15 V13 V14 Tr.4 V11 S.S. V10 V8 Tr.3V9 V6Tr.2 V7 V3 Tr.1 V18 V17 V5 V4 To Ifon 356000N 348000E 347000E SCALE: 0 200 m LEGEND Road Stream VES Point Tr.1 Traverse Number Minor Path Gate Borehole Location V8 VES Number Grid Lines Traverse Line (VLF & Magnetic) Hand Dug Well Location VLF & Magnetic Data Point Figure 9: Data Acquisition Map of the Study Area www.theijes.com The IJES Page 34 Geophysical Investigation for Groundwater Potential… 2.1 VLF-EM Survey The VLF - EM method utilized the inline profiling technique. The measurements were taken at 10 m intervals along each traverse. The ABEM – WADI EM-VLF was used for the measurements. Although both real and quadrature components of the VLF-EM field were measured, the real component data, which are usually more diagnostic of linear features, were processed. The real and filtered real components were plotted against stations position using „KHFFILT‟ software version 1.0 ([7]). The 2-D modeling of the filtered real component was carried out using the same software. The profiles were interpreted qualitatively by visual inspection of anomalies (conductor) that are diagnostic of possible geological structures in the bedrock while the 2-D modeling output was used for quantitative interpretation. 2.2 Electrical Resistivity Survey The electrical resistivity method utilized Vertical Electrical Sounding (VES) using the Schlumberger array. The same traverses were used in each locality as in VLF method. Sounding stations were determined from conductive zones delineated by the VLF – EM. The location of each sounding stations in both geographic and Universal Traverse Mercator (UTM) coordinates was recorded with the aid of the GARMIN 12 channel personal navigator Geographic Positioning System (GPS) - unit. The instrument used for the resistivity data collection was the Omega. The current electrode spacing (AB/2) was varied from 1 m to 225 m. The apparent resistivity(𝜌𝑎 ) resistivity measurements at each station were plotted against electrode spacing (AB/2) on bilogarithmic graph sheets. The resulting curves were then inspected visually to determine the nature of the subsurface layering. In each way, each curve was characterized depending upon the number and nature of the subsurface layers. Partial curve matching ([9]) was carried out for the quantitative interpretation of the curves. The results of the curve matching (layer resistivities and thicknesses) were fed into the computer as starting model parameter in an iterative forward modeling technique using RESIST version 1.0 ([10]). From the interpretation results, geoelectric sections along the traverses were produced. The interpreted result was considered satisfactory since a good fit of RMS between the field curves and computer generated curves. III. RESULTS AND CONCLUSION 3.1 Field Curves The number of layers varies between 3-layers and 6-layers. Nine curve types have been identified in the study area: KH, HKH, H, KHKH, QH, HK, KQ, AK, and KAH. The most occurring curve types identified are KH and HKH curve types “Fig. 10”. The root mean square (RMS) error of the generated curves ranges between 1.8 and 10.7; this shows models of well smoothened, iterated curves ([2]). 3.2. 2-D VLF – EM Modeling and Geoelectric Section The 2-D structure of the real component of the VLF – EM along Traverse 2 is shown in “Fig. 11a”. The 2-D structure reveals one strongly conductive zone located around 45 and 87 m. This structure has a depth greater than 20 m. This conductive is suspected to be a thick weathered zone or fractured zone. The geoelectric section along this Traverse shows that VES 1, 2 and 3 have thick weathered layer indicating good aquiferous unit for groundwater prospect. The most occurring resistivity range of 400 Ω-m – 700 Ω-m suggests a clayey sand/sand formation which is an aquitard i.e. a subsurface geological formation that can store water but poorly transmits. “Fig. 12” displays the 2-D modeling of the VLF-EM and the geoelectric section along Traverse 8. The 2-D model identifies a highly resistive body suspected to be an outcropping basement at 25 m; and water filled geological formation with a highly weathered/fractured zone between distances 48 and 75 m and 10 and 40 m respectively. The depth of this strongly conductive target ranges between 0 and 35 m. The zone will be good for groundwater development. Figure 10: Bar-Chat of Curve Types obtained from the Study Area www.theijes.com The IJES Page 35 Geophysical Investigation for Groundwater Potential… (a) Distance (m) W 20 40 60 80 VES 6 VES 7 1644 199 Depth (m) 335 575 283 52 330 E 3061 10 136 325 661 320 LEGEND 10 m 0 Weathered Layer Laterite Top soil Partly Weathered Layer/ Fracture Basement 5m Resistivity ( 785 Fresh Basement -m ) (b) Figure 11: (a) 2-D modeling; (b) Geoelectric section along Traverse 2 (a) SW 20 40 60 80 100 120 140 NE 160 180 Existing Borehole Location 4 Depth (m) VES 24 345 340 335 330 325 320 315 310 VES 23 VES 22 719 171 219 1474 141 1406 270 60 562 40 64 84 376 327 522 LEGEND 0 5m 20 m Top soil Weathered Layer Partly Weathered Layer/ Fractured Basement 64 Resistivity ( -m ) Fresh Basement (b) Figure 12: (a) 2-D modeling; (b) Geoelectric section along Traverse 8 www.theijes.com The IJES Page 36 Geophysical Investigation for Groundwater Potential… The geoelectric section “Fig. 12b” along this Traverse revealed that weathered layer and the fractured basement (unconfined) constitute the major aquifers as evidenced by the existing boreholes under VES 24 with resistivity that ranges between 64 Ω-m and 562 Ω-m; and 40 Ω-m and 522 Ω-m respectively. The composition of the weathered layer is predominantly clayey sand. The thickness of the weathered layer varies from 5 m to 50 m. The 2-D structure of the real component of the VLF – EM along Traverse 10 is shown in “Fig.13a”. The 2D structure reveals a strongly conductive zone suspected to be water filled geological formation with a highly weathered /fracture zone at distances between 70 and 115 m. The 2-D also identified a very poor conductive zone typical of lateritic hard pan between distances 10 and 60 m. Both have a depth extent greater than 20 m. The 2-D model corroborates the thickly weathered layer (with thickness greater than 20 m) under VES 29 but thin under VES 28. The resistivity of this weathered layer which constitutes the major aquifer unit along this Traverse varies from 28 Ω-m to 229 Ω-m “Fig. 14” displays the 2-D structure of the real component of the VLF-EM and the geoelectric section along Traverse 12. The top of the main conductive target (at distance 80 m) as indicated by the 2-D model correlates with the geoelectric section “Fig. 14b” which identifies this target as a low resistivity (< 50 Ω-m) suspected to be a clayey material. The 2-D structure of the real component of the VLF – EM along Traverse 21 is shown in “Fig. 15a”. It identifies a strongly conductive feature suspected to be water filled geological formation/weathered zone or fractured zone at distances between 15 m and 45 m. This conductive target has a depth extent of 25 m. The geoelectric section delineates this feature as a low resistivity geomaterial composed of clay weathered layer and clayey sand as the topsoil. Therefore, the aquifer unit along this Traverse is clay with resistivity that is generally less than 100 Ω-m. “Fig. 16” displays the 2-D structure of the real component of the VLF-EM and the geoelectric section along Traverse 25. The 2-D “Fig. 16a” model identifies a strongly conductive cross cutting linear feature at distance 400 m. This conductive target has a depth extent greater than 60 m. The presence of this cross cutting linear structure is indicative of weak/incompetent geologic formation. However, on the geoelectric section beneath VES 66 where this cross cutting feature occurred, it‟s revealed as fractured basement at a shallow depth (less than 10 m). IV. CONCLUSIONS Geophysical investigation of Rufus Giwa of Rufus Giwa Polytechnic has been carried out, with the aim of evaluating the groundwater potential of the institution. The 2-D modeling real component of the VLF-EM revealed the presence of conductive zones which were used as data points for the vertical electrical soundings. The geoelectric section revealed 3 to 5 major layers comprising the topsoil, clay, laterite, weathered layer, partly weathered layer/fractured basement, and fresh basement rock. The weathered layer and fractured basement aquifers correlate with the suspected water filled geologic formation as lineated by the VLF-EM. Therefore the area has a good prospect for groundwater development. REFERENCES [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] A.F. Abimbola, O.M Ajibade, A.A. Odewande, W.O. Okunola, T.A. Laniyan, and T.T. Kolawole, Hydrochemical Characterization of Water Resources around the Semi-Urban Area of Ijebu-Igbo Southwestern, Nigeria. Journal of Water Resources Vol.20, 2008, 10-15. R. Barker, L. Blunt, and I. Smith, Geophysical consideration in the design of U.K. National Sounding Database. First Break, Vol. 14, 1996, No. 2, pp. 45-53. A.E. Edet, and O.E. Offiong, Surface Water Quality Evaluation in Odukpani, Calabar Flank, Southwestern, Nigeria. Journal of Environmental Geology, 36 (3/4), 1998b: 343–348. R.A. Freeze, and J.A. Cherry, Groundwater (Prentice-Hall, Englewood Cliffs, New Jersey, 1979), 604. Geological Survey of Nigeria, Geological map of Akure Area, Sheet 61. Geological Survey Department, Ministry of Mines, Power and Steel, Nigeria. 1966. N.P. Iloeje, A new geography of Nigeria (New Revised Edition) Longman Nig. Ltd., Lagos, 1981, 201pp. KHFFILT, Karous-Hjelt and Frazer filtering of VLF measurements, Version 1.1a, Markku Pirttijarvi, 2004. Ondo State Surveys Akure, Nigeria. Administrative map of Ondo State, Ministry of works and Housing, Akure Ondo State, Nigeria, 1998. E. Orellana, and H.M. Mooney, Master Tables and Curves for Vertical Electrical Sounding over Layered Structure, Geophy. Prospect 29, 1966: 932-955. B.P.A Vander Velper, Resist Version 1.0, M.Sc. research Project ITC Delf. Netherlands, 1988. www.theijes.com The IJES Page 37 Geophysical Investigation for Groundwater Potential… (a) Distance (m) SW 40 60 NE 80 100 VES 28 VES 29 50 335 726 331 82 229 Depth (m) 330 16 325 46 320 315 2498 310 284 LEGEND 0 20 m Top soil Weathered Layer Partly Weathered Layer/ Fracture Basement 5m 58 Resistivity ( Fresh Basement -m ) (b) Figure 13: (a) 2-D modeling; (b) Geoelectric section along Traverse 10 (a) Distance (m) 30 35 40 45 50 55 60 65 70 75 VES 31 80 Depth (m) 65 20 14979 310 90 VES 32 1258 516 83 320 85 19 14478 300 3941 LEGEND 0 5m Top soil Clay Fresh Basement Partly Weathered Layer/ Fracture Basement 19 Resistivity ( -m) 10 m (b) Figure 14: (a) 2-D modeling; (b) Geoelectric section along Traverse 12 www.theijes.com The IJES Page 38 Geophysical Investigation for Groundwater Potential… (a) W 20 40 60 80 100 Distance (m) 140 160 E 120 180 200 220 240 260 VES 52 VES 54 VES 53 369 330 251 305 538 Depth (m) 320 38 310 105 93 300 0 278 240 17578 290 20 m Weathered Layer Top Soil 10 m Partly Weathered Layer/ Fracture Basement Fresh Basement ( Resistivity 105 -m ) (b) Figure 15: (a) 2-D modeling; (b) Geoelectric section along Traverse 21 (a) Distance (m) W 50 100 150 200 250 300 350 340 VES 64 229 Depth (m) 450 500 550 E VES 67 302 247 501 618 901 320 400 VES 66 VES 65 627 936 252 163 207 355 300 914 907 752 7581 280 0 LEGEND 50 m Top soil Laterite Partly Weathered Layer/ Fracture Basement 20 m 252 Resistivity ( Weathered Layer Fresh Basement -m ) (b) Figure 16: (a) 2-D modeling; (b) Geoelectric section along Traverse 25 www.theijes.com The IJES Page 39
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