![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
www.theijes.com The IJES Page 29
Geophysical Investigation for Groundwater Potential in Rufus Giwa
Polytechnic Owo, Southwestern Nigeria
1
O.O. Falowo, 2
A.O. Daramola , 3
O.O. Ojo
1,2,3
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.](https://image.slidesharecdn.com/f041103029039-151205062642-lva1-app6891/85/geophysical-investigation-for-groundwater-potential-in-rufus-giwa-polytechnic-owo-southwestern-nigeria-1-320.jpg)
![Geophysical Investigation for Groundwater Potential…
www.theijes.com The IJES Page 30
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).
Figure 1: Road/Administrative Map of Ondo State
Igbekebo
Igbokoda
Ore
Irele
Okitipupa
Okeluse
Ute
Ifon
Ipele
Sanusi
Okpe
Emure
Sasere
Ayere
Oke-Agbe
Auga
Ise
IbilloIsua
Oka
Ikare
Ikun
Afo
Idoani
Akungba
Ikun
Ogbagi
Arigidi
Oba
Uso
Iju
Ita ogbolu
Ijare
Akotogbo
Otu
OmotosoKajola
Oniparaga
Ode-Aye
Igbotaku
Loda
Ayadi
Ondo
Ibagba
Asewele
Ominia
Odigbo Ofosu
Omifunfun
Jimgbe
Odole Ala-Ajagbusi
Oba-Ile
Akure
Onikoko
Araromi
Ile-Oluji
Alade
Idanre
ESE-ODO
ILAJE
IRELE
OKITIPUPA
ODIGBO
ONDO-WEST
IDANRE
ILE-OLUJI
Bolorunduro
IFEDORE
AKURE
NORTH
OWO
OSE
AKOKO SW
AKOKO NE
AKOKO NW
AKOKO SE
E
D
O
S
T
A
T
E
EKITI STATE
OSUN
STATE
OGUN
STATE
DELTA STATE
KOGI
STATE
ATLANTIC OCEAN
MAIDUGURI
ENUGU
MAKURDI
ILORIN
SOKOTO
KANO
LAGOS
AKURE
IBADAN
ABUJA
N
L. Gov't. Headquarters
Towns & Villages
Minor Road
Major Road
6 00
o
5 30
o
5 00
o
4 30
o
6 00 E
o
4 30 E
o
5 00
o
5 30
o
6 00 N
o
6 30
o
7 00
o
7 30 N
o
6 00 N
o
6 30 N
o
7 00
o
7 30
o
State Boundary
025 25 Km](data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7)
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Geophysical Investigation for Groundwater Potential in Rufus Giwa Polytechnic Owo, Southwestern Nigeria
- 1. 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 www.theijes.com The IJES Page 29 Geophysical Investigation for Groundwater Potential in Rufus Giwa Polytechnic Owo, Southwestern Nigeria 1 O.O. Falowo, 2 A.O. Daramola , 3 O.O. Ojo 1,2,3 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.
- 2. Geophysical Investigation for Groundwater Potential… www.theijes.com The IJES Page 30 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). Figure 1: Road/Administrative Map of Ondo State Igbekebo Igbokoda Ore Irele Okitipupa Okeluse Ute Ifon Ipele Sanusi Okpe Emure Sasere Ayere Oke-Agbe Auga Ise IbilloIsua Oka Ikare Ikun Afo Idoani Akungba Ikun Ogbagi Arigidi Oba Uso Iju Ita ogbolu Ijare Akotogbo Otu OmotosoKajola Oniparaga Ode-Aye Igbotaku Loda Ayadi Ondo Ibagba Asewele Ominia Odigbo Ofosu Omifunfun Jimgbe Odole Ala-Ajagbusi Oba-Ile Akure Onikoko Araromi Ile-Oluji Alade Idanre ESE-ODO ILAJE IRELE OKITIPUPA ODIGBO ONDO-WEST IDANRE ILE-OLUJI Bolorunduro IFEDORE AKURE NORTH OWO OSE AKOKO SW AKOKO NE AKOKO NW AKOKO SE E D O S T A T E EKITI STATE OSUN STATE OGUN STATE DELTA STATE KOGI STATE ATLANTIC OCEAN MAIDUGURI ENUGU MAKURDI ILORIN SOKOTO KANO LAGOS AKURE IBADAN ABUJA N L. Gov't. Headquarters Towns & Villages Minor Road Major Road 6 00 o 5 30 o 5 00 o 4 30 o 6 00 E o 4 30 E o 5 00 o 5 30 o 6 00 N o 6 30 o 7 00 o 7 30 N o 6 00 N o 6 30 N o 7 00 o 7 30 o State Boundary 025 25 Km
- 3. Geophysical Investigation for Groundwater Potential… www.theijes.com The IJES Page 31 Figure 2: Land-Use Master Plan of RUGIPO Figure 3: Map of Owo Local Government Area of Ondo State O.S.P.O. CONSULT ACTIVITY AREA AREA FOR FUTURE AGRICULTURAL DEVELOPMENT GAMES RESERVE RESERVATION O.S.P.O. CONSULT ESTATE AREA MANAGEMENT STAFF QUARTERS NEW SPORT COMPLEX Atamopere Stream AGRIC EXTENSION AREA ARTIFICIAL LAKE STAFF CLUB HOSTEL HOSTEL SCHOOL OF BUSINESS STUDIES SCHOOL OF GENERAL STUDIES SCHO O L O F ENG IN EERIN G TECHNO LO G Y SENIOR STAFF QUARTERS EXPANSION Ope Stream JUNIO R STAFF QUARTERS COMMERCIAL SCHOOL OF FOOD TECHNOLOGY CENTRAL AUDITORIUM/ ADMINISTRATIVE/ CONFERENCE CENTRE PLACE OF WORSHIP CENTRAL POOL OSPO. COMM. CEN. RESEARCH/ PRESS CENTRE PART-TIME STUDENTS RESERVATION DAM ETF RESERVATION AREA From Akure To Oluku C.S REC NC STAFF CLUB G.H. MAINTENANCE DEPT. O.S.P.O. GUEST HOUSE PLACE OF WORSHIP W.T. SUB. ALUMNI CENTRE 344000E 345000 346000 347000 348000 349000 350000E 344000E 345000 346000 347000 348000 349000 350000E 356000N 357000 358000 359000 360000 361000 361250N 356000N 357000 358000 359000 360000 361000 361250N Quarry Aaunke Stream Gate 560m 0 560 1120 1680m Existing Road Boundary Pillar Fence Proposed Roads Streams Trees and Hedges Commercial Centre Faculties/Conference Centres Administrative Blocks/ Conference Centres School Boundary Hostel Management Staff Quarters Lecture Halls/Existing Buildings New Sport Complex Artificial Lake/Pond StadiumGate R.C. Recreation Ground S.U.B. Student Union Building C.S. Corner Shop O.S.P.O. Ondo State Polytechnic, Owo W.T. Waste Treatment Ceded Land LEGEND MAIDUGURI ENUGU MAKURDI ILORIN SOKOTO KANO LAGOS AKURE IBADAN ABUJA N AKURENORTHL.G.A. IDANREL.G.A. AKOKO SOUTH WEST L.G.A. OSE L.G.A. EKITI STATE Igbatoro Alafiatayo Araromi Sanusi Emaajomo Isewe Okififioko Daji Camp Sasere Ago-Panu Ipeme Ipele Iyere Baga Eporo Obasoro Ilale Alasa Ijegunmo Olefa Igodi Oluka Odofin- Alaro Alaga Emure RUGIPO Uso Ago-Panu Amurin Ipele Junction Isijogun 5 15 E 5 15 E 7 30 N 7 30 N 6 00 E 6 00 E 6 45 N6 45 N Major Road Minor Road Main Paths RUGIPO Towns and Villages Rivers and Streams LEGEND 0 5 Km SCALE
- 4. Geophysical Investigation for Groundwater Potential… www.theijes.com The IJES Page 32 Figure 4: Topographical map of Owo and Environs Figure 5: 3-D Surface Elevation Map around the studied Area
- 5. Geophysical Investigation for Groundwater Potential… www.theijes.com The IJES Page 33 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]). Owo Study Area
- 6. Geophysical Investigation for Groundwater Potential… www.theijes.com The IJES Page 34 Figure 8: Geological Map of RUGIPO Figure 9: Data Acquisition Map of the Study Area N OSPO CONSULT ESTATE AREA CEDED AREA Management Quarters AREA FOR FUTURE AGRICULTURAL DEVELOPMENT AGRIC EXTENSION AREA HOSTEL GAMES RESERVE RESERVATION Atamopere Stream STAFF CLUB HOSTEL SCHOOL OF BUSINESS STUDIES SENIOR STAFF QUARTERS EXPANSION Ope Stream From Akure To Oluku 344000E 345000 346000 347000 348000 349000 350000E 344000E 345000 346000 347000 348000 349000 350000E 356000N 357000 358000 359000 360000 361000 361250N 356000N 357000 358000 359000 360000 361000 361250N Quarry 560m 0 560 m Quartzite Granite Gneiss / Granite Dam Quarry Ceded Area Stream LEGEND SUB S.S. STADIUM ADMINISTRATIVE BUILDING HEALTH CENTRE FACULTY OF GENERAL STUDIES/ MASS COMMUNICATION DEPT SchoolFarm LOW RISE MANAGEMENT QUARTERS 356000N 347000E 357000 357750 348000E 0 To Akure To Ifon Road Grid Lines Gate Traverse Line (VLF & Magnetic) 200 m GUEST HOUSEARTISAN LIBRARY ICT Hostel Hostel Block-Five POULTRY Millenium Lecture Theatre CEDEDAREA Minor Path VES Point SCALE: LEGEND Stream Tr.1 Tr.19 Tr.2 Tr.3 Tr.4 Tr.5 Tr.6 Tr.7 Tr.8 Tr.9 Tr.10 Tr.11 Tr.12 Tr.13 Tr.14 Tr.15 Tr.16 Tr.17 Tr.18 Tr.20 Tr.21 Tr.22 Tr.23 Tr.24 Tr.25 SchoolFarm SchoolFarm Tr.26 Tr.27 Borehole Location Hand Dug Well Location B.Tech. Est. Mgt V1 V2 V3 V4 V5 V6 V7 V8 V9 V10 V11 V12 V13 V14 V15 V16 V17 V18 V19 V20 V21 V22 V23 V24 V25 V26 V27 V28 V29 V30V31 V32 V33 V34 V35 V36 V37 V38 V39 V40 V41 V42 V43 V44 V45 V46 V47 V48 V49 V50 V51 V52 V53 V54 V55 V56 V57 V58 V59 V60 V61 V62 V63 V64 V65 V66 V67 V68 V69 V70 V71 V72 V73 V74 V75 Tr.1 Traverse Number V8 VES Number VLF & Magnetic Data Point
- 7. Geophysical Investigation for Groundwater Potential… www.theijes.com The IJES Page 35 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(𝜌 𝑎) 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
- 8. Geophysical Investigation for Groundwater Potential… www.theijes.com The IJES Page 36 (a) (b) Figure 11: (a) 2-D modeling; (b) Geoelectric section along Traverse 2 (a) (b) Figure 12: (a) 2-D modeling; (b) Geoelectric section along Traverse 8 20 40 60 80 320 325 330 335 Depth(m) Distance (m) VES 6 VES 7 W E 199 575 52 3061 10 0 5 m 10 m LEGEND Partly Weathered Layer/ Fracture Basement Top soil Fresh Basement Resistivity785 Laterite Weathered Layer ( -m ) 1644 283 136 661 20 40 60 80 100 120 140 160 180 310 315 320 325 330 335 340 345 Depth(m) 171 VES 22 VES 23 VES 24 SW NE 141 719 1406 40 376 60 219 1474 562 84 327 270 64 522 5 m LEGEND Weathered Layer 64Top soil Partly Weathered Layer/ Fractured Basement Fresh Basement Resistivity ( -m ) 20 m Existing Borehole Location 4 0
- 9. Geophysical Investigation for Groundwater Potential… www.theijes.com The IJES Page 37 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 2- D 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] 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. [2] 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. [3] 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. [4] R.A. Freeze, and J.A. Cherry, Groundwater (Prentice-Hall, Englewood Cliffs, New Jersey, 1979), 604. [5] Geological Survey of Nigeria, Geological map of Akure Area, Sheet 61. Geological Survey Department, Ministry of Mines, Power and Steel, Nigeria. 1966. [6] N.P. Iloeje, A new geography of Nigeria (New Revised Edition) Longman Nig. Ltd., Lagos, 1981, 201pp. [7] KHFFILT, Karous-Hjelt and Frazer filtering of VLF measurements, Version 1.1a, Markku Pirttijarvi, 2004. [8] Ondo State Surveys Akure, Nigeria. Administrative map of Ondo State, Ministry of works and Housing, Akure Ondo State, Nigeria, 1998. [9] E. Orellana, and H.M. Mooney, Master Tables and Curves for Vertical Electrical Sounding over Layered Structure, Geophy. Prospect 29, 1966: 932-955. [10] B.P.A Vander Velper, Resist Version 1.0, M.Sc. research Project ITC Delf. Netherlands, 1988.
- 10. Geophysical Investigation for Groundwater Potential… www.theijes.com The IJES Page 38 (a) (b) Figure 13: (a) 2-D modeling; (b) Geoelectric section along Traverse 10 (a) (b) Figure 14: (a) 2-D modeling; (b) Geoelectric section along Traverse 12 40 60 80 100 310 315 320 325 330 335 Depth(m) Distance (m) VES 28 VES 29 SW NE 331 50 229 16 2498 82 726 46 284 0 5 m Partly Weathered Layer/ Fracture Basement Fresh Basement 20 m Top soil Weathered Layer 58 Resistivity ( -m ) LEGEND 30 35 40 45 50 55 60 65 70 75 80 85 90 300 310 320 Depth(m) Distance (m) VES 31 VES 32 516 83 14979 19 3941 651258 20 14478 LEGEND Resistivity Partly Weathered Layer/ Fracture Basement ClayTop soil Fresh Basement 5 m 10 m 0 ( -m)19
- 11. Geophysical Investigation for Groundwater Potential… www.theijes.com The IJES Page 39 (a) (b) Figure 15: (a) 2-D modeling; (b) Geoelectric section along Traverse 21 (a) (b) Figure 16: (a) 2-D modeling; (b) Geoelectric section along Traverse 25 20 40 60 80 100 120 140 160 180 200 220 240 260 290 300 310 320 330 Depth(m) VES 52 VES 53 VES 54 369 251 93 17578 538 305 38 105 278240 Distance (m)W E Weathered Layer Fresh Basement 20 m 10 m 0 105 Resistivity ( -m ) Top Soil Partly Weathered Layer/ Fracture Basement 50 100 150 200 250 300 350 400 450 500 550 280 300 320 340 Depth(m) VES 64 VES 65 VES 66 VES 67 Distance (m) 229 247 302 627 936618501 901 207 163 252 355 907 752 914 7581 Fresh Basement 50 m LEGEND Weathered Layer Resistivity Partly Weathered Layer/ Fracture Basement 20 m Top soil Laterite 252 ( -m ) W E 0