Professional paper Received: January 30, 2015 Accepted: May 2, 2015 Evaluation of groundwater occurrences in the precambrian basement complex of Ilorin metropolis, southwestern Nigeria Ocena virov podtalnice iz predkambrijske podlage območja deželne prestolnice Ilorina v jugozahodni Nigeriji Anthony T. Bolarinwa1- *, Sulyman Ibrahim1 University of Ibadan, Department of Geology, Ibadan, Nigeria Corresponding author. E-mail: atbola@yahoo.com Abstract Surface water from the Asa and Agba dams, which hitherto supply water to Ilorin metropolis is inadequate, hence the need to supplement with water from boreholes. Forty two boreholes drilled into migma-tites, granite gneiss and quartzite in Ilorin area were evaluated. Borehole data showed varied overburden thickness (1.00 m to 36.00 m). The static water level (SWL) contour map showed a radial groundwater flow pattern trending in the NE-SW and NW-SE directions, which is consistent with the structural trends in the area. Estimated yields of the boreholes ranged from 0.30 l/s to 2.75 l/s. Pumping/recovery test of four selected boreholes showed increase in productivity from granite gneiss (transmissivity, T = 11.42 m3/d; permeability, K = 4.94 x 10 1 m/d) through migma-tites (T = 13.4 m3/d; K = 6.93 x 101 m/d) to quartzites (T = 17.56 m3/d; K = 9.54 x 101 m/d). The groundwater occurrence in the area is adjudged to be moderately high. Strong correlation coefficients (+0.99) exist between Vertical Electrical Sounding (VES) and borehole log indicating that the success of borehole in the area depends strongly on production of VES report. Based on this study, minimum borehole depth of 33 m is recommended for the area. Key words: groundwater, basement complex, borehole yield, aquifer, Ilorin Izvleček Površinska voda iz zajezitev Asa in Agba ne zadostuje potrebam deželne prestolnice Ilorina, zato iščejo dodatne vodne vire z vrtanjem. Na območju Ilorina so izvrtali dvainštirideset vrtin v migmatitih, granitnem gnajsu in kvarcitu. Debelina prevrtanega preperinske-ga pokrova je med 1 m in 36 m. Iz razporeda plastnic na karti statične gladine podtalnice je videti, da gre za radialni vzorec tečenja podtalnice v smereh NE-SW in NW-SE, kar tudi ustreza geološki zgradbi območja. Ocenjene izdatnosti vrtin so med 0,30 l/s in 2,75 l/s. Črpalni preizkusi v štirih izbranih vrtinah pričajo o naraščanju izdatnosti od granitnega gnajsa (prevodnost, T = 11,42 m3/d; prepustnost, K = 4,94 x 101 m/d) prek migmatitov (T = 13.4 m3/d; K = 6.93 x 101 m/d) do kvarcitov (T = 17,56 m3/d; K = 9,54 x 101 m/d). Vire podtalnice na preiskovanem območju so ocenili za zmerno izdatne. Visoki korelacijski koeficient (+0,99) med rezultati vertikalne električne karotaže (VES) in karotažnih profilov vrtin priča o močni povezavi uspešnosti vrtin od opravljene vertikalne električne karotaže. Iz raziskave izhaja, da je na tem območju priporočljiva minimalna globina vrtanja 33 m. Ključne besede: podtalnica, kamnine podlage, izdatnost vrtine, vodonosnik, območje Ilorina Introduction Rapid population growth, due to rural-urban migration resulted in increase in the number of commercial and industrial activities in Ilorin area. This population growth in turn is responsible for the rapid increase in water demand and persistent water shortage in the area. Water supply from Asa and Agba dams could no longer meet the water demand of the populace contrary to the report of Oluyide [1], which stated that Ilorin area has excess water and that boreholes are unnecessary. As a result of water inadequacy, the State Government decided to look for additional and sustainable water sources that can supplement water supply from the existing dams through the introduction of various water supply schemes. These water supply schemes include drilling of numerous boreholes. However, as laudable as this policy seems, it was not supported by adequate geological and hydrogeological baseline data, which include information on the degree of weathering and fracturing of the crystalline basement rocks and hence, the high number of low yield and outright unproductive wells reported in the area. Alao [2] investigated the occurrence of lateritic brick-clay within the weathered profiles at Okelele/Dada of Ilorin Local Government area. It is believed in this study that the occurrence of such interstitial clay in large quantity within the weathered basement could result in low yields. Other published works on the groundwater situations of the Ilorin area include those of Oyegun [3] who identified water resources, development and management strategies in Kwara State, including Ilorin, based on a few borehole data, which is grossly inadequate to generalize the groundwater situation of the study area. Olasehinde [4] and Olasehinde and Taiwo [5] compared the geological and geophysical exploration methods for groundwater in the basement complex of the study area. They were able to establish positive relationship between the two exploration techniques. Offodile [6] studied the groundwater occurrence in basement complex of Nigeria with reference to Pam-po, a village in the southern outskirts of the study area. The study was based on pumping test of a single borehole. A single borehole is considered inadequate to study the groundwater potential of such a large area. The objectives of this study were to determine the hydrogeological characteristics of the rock units within Ilorin metropolis, to evaluate the influence of geology on the groundwater flow and development in the area, to assess the groundwater occurrence with a view to determine whether the groundwater of Ilorin metropolis could serve as additional and sustainable water supply sources. The Study Area Ilorin area lies between longitude 4o 30' E-4o 37' E and latitude 8o 26' N-8o 33' N (Figure 1). It covers an approximate area of 200 km2. The sampling areas include Agbo-Oba in the west, Airport in the southwest, Sobi Hill in the northwest, Oyun in the northeast, Tanke and Fate in the east. The study area is underlain by the Precambrian basement rocks, which comprise of migmatite, granite gneiss and quartzite. The area falls between semi arid in the north and sub-humid in the south. It is characterized by two main seasons: Wet season -(March - Mid October) and Dry season - (Mid October - March). Rainfall is moderate with annual average of 1 250 mm. Humidity is relatively low. It is about 50 % between June and August. The annual mean temperature is 27 °C. The area is well drained by various streams and their tributaries. The distributaries show dendritic drainage pattern. The main rivers are Asa and Agba Rivers, while minor rivers include Oyun and Aluko rivers. The terrain is undulating and dissected by rivers and streams. The highest altitude is about 1 200 m above sea level corresponding to the top of Sobi Hill (migmatite), while along major streams the altitude is about 250 m above sea level. The vegetation cover is basically Guinea savannah with ruminant tropical forest. Geology and Hydrogeology of the Area The Ilorin area is part of the Precambrian basement complex of southwestern Nigeria (Figure 1). The main rock types that characterize the geology of the area are migmatite-gneiss, granite gneiss and quartzite (Figure 2). Intrusions of pegmatite, dolerite dykes and quartz veins cut across the major rock units in the area. The migmatite-gneiss 119 complex is presumably the oldest rock in the basement complex of Nigeria [7]. It is the most abundant and the most widespread in the study area. It is foliated and jointed. The migmatite is closely associated with quartzite in the southeastern part. Granite gneiss extends from the eastern to the southeastern part. Mineral components of the migmatite and granite gneiss are mainly microline, quartz, plagioclase, biotite and muscovite. The constituent quartz and few mica grains in the quartzite of the area are recrystallised with interlocking mosaic textures. Other rock types include pegmatite and quartz veins within the migmatite and the granite gneiss. They are of few millimeters to about a metre. They are concordant or discordant unmetamorphosed rock bodies cutting across foliation planes in the gneisses. These crystalline basement rocks are generally older than 500 million years and contain negligible amount of groundwater when not weathered or fractured. However, significant aquifers may develop within those areas with thick weathered overburden and most importantly, fractured bedrock [8]. Annor and Olasehinde [9] noted that the basement complex of Ilorin area has varied weathered horizons as well as fractured rocks. The fractured rocks represent the deeper aquifers, which are overlain by shallow porous lateritic soil cover. Although, these rocks have low groundwater content, places abound where there are thick weathered, gritty overburden and fractures which aid groundwater accumulations. Areas with high clay contents are usually characterised by low permeability and poor aquifer conditions. Pegmatite and quartz vein filled fractures in the migmatite and quartzite of Ilorin metropolis are generally NS and NW-SE while those in the granite gneiss are NS and NE-SW (Figure 2). Methodology Collection of hydrogeological data from 42 boreholes within the three main rock types, namely migmatite, granite gneiss and quartzite in Ilorin metropolis were undertaken. Thirty seven (37) of the boreholes were sited within migmatite, four (4) within granite gneiss and one (1) within quartzite. The hydrogeological data were collected in November 2005 when the boreholes were completed. Location and elevation of each of the borehole above sea level was measured with Geographical Positioning System (GPS) equipment [10]. The static groundwater level in the boreholes was determined using dipper water level indicator. Computation of static water level, above sea level (SWLasl) from static water level, below ground level (SWLb ) and elevation above sea level (£'asl) were carried out. Depths to basement, depth to the overburden and basement aquifers, as well as, aquifer thickness were extracted from borehole log reports. Also, Vertical Electrical Sounding (VES) data on depth-to-basement were taken to facilitate comparison r r^xj / I : 1 Cretaceous to Recent sedments 1 Basement complex I H Study Area s^fn\ V/ M<~ и 200 Km Figure 1: Generalised geological map of Nigeria showing the location of Ilorin area. M \ M • BH34 \ A •BH32 \ I . ' \ л- ( » онв\^- Z^M / \ \*BH28 • BH41 \BH36 ! •BH14 .BH42 \* м •BH40 BH37 I S • / BH23 * / I / / \ / »BH2 »1 / M ILORIN \ •BH27 M \?ВН1в\ • BH38. j /__ <^VSoRI«A ATVA, ! ■/« ,BH2° !» Tanke s'iti l'i )S • . BH4 \ I "мши / / M \ ■Qaladima BH3l\ M QS - Quartzite LEGEND Major Roads G - Granite gneiss Geological boundary Strike and dip of foliation M - Migmatite Roads Fractures Railwa BH 42 - Sample locations Figure 2: Geological and structural map of Ilorin area showing borehole locations (BH1-BH42). with borehole log. Yields from selected boreholes were estimated. Correlation of the borehole parameters with estimated yields and Vertical Electrical Sounding (VES) report with borehole-logs were carried out. Computation of aquifer parameters [Transmissivity (T) and Permeability (K)] from constant pumping/recovery test was carried out, for 8 h, using 1HP submersible pump. The static water levels (above sea level) (SWLasl) for the 42 boreholes were computed and used to produce SWL contour map which was used to determine the groundwater flow direction in the study area. The pumping and recovery test data are presented in supplementary Tables S1-S8 and Figures S1-S10. Results and Discussion The borehole data are presented in Table 1 with the summary in Table 2. The geological and structural map of the area is presented in Figure 2. Summary of the pumping and recovery tests are presented in Table 3. Results of correlations of the borehole parameters are presented in Table 4. Other details are presented as supplementary Tables and Figures. The depth of boreholes in the study area ranged between 19.50 m and 67.60 m with mean value of 33.59 m (Table 1). Borehole productivity in the area is not strictly a function of the total depth drilled as reflected in some deep boreholes (> 30 m) with low yield (BH15, 23, 28 and 30), and some shallow boreholes (< 30 m) with high yield (BH 13, 25, and 36) (Table 1). However, it is recommended that the depth of borehole to be drilled in the area must not be less than 33.00 m so that the borehole can penetrate the fractured basement and to create sufficient space for water accumulation within the hole. The SWL contour map showed a radial groundwater flow direction in the study area (Figure 3). It is multidirectional, trending in the NE-SW and NW-SE directions. This is consistent with the structural trends in the area (Figure 2). Depth to basement varies between 1.00 m and 36.0 m with a mean value of 12.23 m (Tables 1 and 2). Borehole log report shows that twenty four of the forty two boreholes have overburden thickness of less than 10 m (Table 1). The overburden is characterized by lateritic and clayey formations which constitute an aquitard. Aquifer thickness is between 3.00 m and 30.00 m with a mean value of 12.03 m (Table 2). Most of the aquifers occurred in the saprolite of the weathered zone and the fractured basement. However, in the northwestern part of Ilorin metropolis around Okelele and Dada area (BH 35 and BH 38), reasonable amount of groundwater occur within the thick overburden on highly fractured migmatite. Estimated yield (Tables 1 and 2) ranged between 0.30 l/s and 2.75 l/s. This determines how successful a borehole is, and showed the maximum rate a borehole can sustain reasonable drawdown in the study area. The average value of 1.60 l/s; suggested a high groundwater potential for the study area. This is in agreement with the yield of 1.5-20 l/s obtained by Offodile [6] for aquifers in some crystalline basement rocks in Nigeria. Results of the Pumping/Recovery tests (Table 3) showed transmissivity (T) values between 9.11 m3/d and 17.56 m2/d, averaging 13.43 m3/d, and permeability (K) values between 4.52 X 10-1 m/d and 9.54 x 10-1 m/d with mean value of 6.65 x 10 1 m/d. Generally, the pumping/recovery test of the four (4) selected boreholes showed increase in borehole productivity from granite gneiss (T = 11.42 m3/d; K = 4.94 X 10 1 m/d) through migmatites (T = 13.4 m3/d; K = 6.93 x 101 m/d) to quartzite (T = 17.56 m3/d; K = 9.54 x 101 m/d). The highest values of T (17.56 m3/d) and K (9.54 x 10^m/d) occurred in the borehole drilled through quartz-ite reflecting the highly fractured nature of the metasediment, while the lowest values (T = 9.11 m3/d and K = 5.35 x 101 m/d) are obtained in boreholes within the granite gneiss (Table 3). It can therefore be said that borehole productivity increases from granite gneiss through migmatite to quartzite in the study area. However, value for storativity could not be obtained due to lack of observation wells to be used for the pumping / recovery tests. Borehole parameters are correlated in order to obtain baseline data and relationships, which can serve as a guide to borehole site and drill depth recommendations that could be applied in related basement areas. Correlation results (Table 4) showed very high positive values for Yield/T (0.96), and moderately high positive value for Yield/Aquifer thickness (0.50). These showed very strong and strong dependence of yield on transmissivity and aquifer thickness respectively. However, for Yield/Total depth and Yield/depth to basement, the correlation values are low (0.26 and 0.28 respectively). This indicated weak dependence of yield on the two parameters. Yield/ SWL gave an extremely low correlation value of +0.004, which suggested borehole yield does not depend on SWL in the area. Correlation of VES data with Borehole-logs also gave a very high positive value of 0.99. This confirmed that the VES results obtained from the area are very reliable and can be used for borehole location. Table 1: Borehole Data of Ilorin metropolis (Source: Field Survey, 2005) BH No. Borehole location SWL(b n (bgl) SWL( l) (asl) BH depth Depth to basement (m) Depth to aquifer Aquifer thickness Estimated yield (m) (m) (m) BH Log VES (m) (m) (l/s) BH 1 Ikokoro street 9.50 290.50 46.60 5.00 6.50 15.00 30.00 2.00 BH 2 Sango Area 8.20 301.80 34.60 19.00 22.50 22.00 9.00 1.50 BH 3 Union Bank 11.50 288.10 53.60 2.00 5.00 39.00 12.00 2.20 BH 4 Tanke 5.00 305.00 46.60 15.00 16.00 15.00 21.00 1.50 BH 5 Ilt Kewu 8.00 312.00 37.60 9.00 10.00 12.00 21.00 1.80 BH 6 Oyun 7.40 307.60 37.60 9.00 10.00 9.00 22.00 1.90 BH 7 Golf Club 16.90 295.10 67.60 3.00 6.00 42.00 5.00 2.40 BH 8 Pakata 6.30 323.70 26.00 9.00 10.00 9.00 6.00 0.30 BH 9 Ile Seriki 7.60 317.40 27.60 8.00 12.00 11.00 16.00 1.50 BH 10 Olorunshogo 5.90 304.00 21.00 15.00 16.00 15.00 8.00 1.30 BH 11 Tanke Iledu 5.90 299.10 36.00 15.00 17.00 15.00 18.00 1.75 BH 12 Gaa Akanbi 4.30 325.70 33.00 3.00 5.00 33.00 12.00 2.70 BH 13 Alore Primary School 5.30 319.70 27.00 18.90 33.00 21.00 9.00 2.00 BH 14 Ile Oloje 7.20 303.80 26.25 24.00 21.00 18.00 10.00 1.50 BH 15 Airport 5.00 357.00 34.00 24.00 28.00 25.00 4.00 1.25 BH 16 Ile Iya Balogun 7.30 316.70 32.00 6.00 9.00 6.00 15.00 1.50 BH 17 Ile Jimba 4.50 313.50 26.00 6.00 8.00 6.00 12.00 1.90 BH 18 Ode Alfa Nda 7.90 315.10 38.20 18.00 22.00 18.00 12.00 2.00 BH 19 Parliament Village 6.00 339.00 21.50 6.00 7.00 6.00 7.00 1.30 BH 20 Kitibi's residence 5.40 326.6 30.00 15.00 17.50 20.00 15.00 2.10 BH 21 C.A.C. Taiwo road 6.25 303.75 33.00 15.00 16.00 15.00 8.00 2.00 BH 22 Ojatuntun 5.00 300.25 30.75 1.00 1.50 3.00 27.00 2.75 BH 23 Railway station 11.30 239.70 38.00 3.00 4.00 3.00 15.00 1.00 BH 24 Akerebiata 5.80 300.20 29.00 12.00 14.00 12.00 12.00 1.95 BH 25 Baboko/Eruda 7.50 297.50 26.00 15.00 16.00 15.00 12.00 1.80 BH 26 Agbo-Oba 7.00 293.00 19.50 6.00 6.50 6.00 15.00 1.80 BH 27 Popo Giwa 4.00 326.00 21.00 6.00 7.50 12.00 9.00 1.50 BH 28 FGC, Ogigi 6.00 343.00 40.00 7.00 9.00 10.00 6.00 1.00 BH 29 Olunlade 3.00 337.00 38.00 10.00 12.50 20.00 17.00 1.35 BH 30 Ita Alamu 8.00 329.00 40.00 8.50 10.00 10.00 3.00 0.40 BH 31 Idera 4.00 303.00 31.00 7.00 9.00 12.00 6.50 1.25 BH 32 Oloje Housing Estate 4.00 316.00 31.00 5.00 6.00 6.00 18.00 2.00 BH 33 G.S.S. Ilorin 6.80 293.20 22.00 6.00 8.50 6.00 3.00 0.35 BH 34 Oko Olowo Garage 8.00 321.00 33.00 7.00 8.00 10.00 8.00 1.40 BH 35 Okelele 5.30 319.70 27.00 18.00 19.00 21.00 9.00 1.50 BH 36 Banni area 5.75 318.25 24.00 9.00 10.00 9.00 9.00 1.90 BH 37 Gaa Osibi 7.00 329.00 33.00 8.50 10.00 15.00 5.00 1.45 BH 38 Dada 6.00 324.00 29.00 27.00 28.00 23.00 12.00 1.60 BH 39 Ita Kudimo 6.00 298.00 32.00 7.00 8.00 22.00 6.00 1.20 BH 40 Ile Ikare Okelele 9.00 324.00 39.00 36.00 38.00 24.00 12.00 1.50 BH 41 Ile Gbongbon Okelele 7.00 328.00 33.00 33.00 34.00 18.00 15.00 1.30 BH 42 Ile Oniponmo 8.00 322.00 39.00 24.00 26.00 24.00 12.00 1.60 Okelele SWL „-Static Water Level ,, .. „ BH - Borehole, (bgl) (below ground level)' ' SWLm - Static Water Level (above sea VES - Vertical Electrical Sounding Table 2: Summary of Borehole data of Ilorin metropolis SWL,. „ (bgl) SWL, n (asl) BH depth Depth to basement (m) Depth to aquifer Aquifer thickness Estimated yield (m) (m) (m) BH Log VES (m) (m) (l/s) Minimum 3.00 288.50 19.50 1.00 1.50 3.00 3.00 0.30 Maximum 16.90 357.00 67.60 36.00 38.00 42.00 30.00 2.75 Mean 6.80 313.84 33.59 12.23 14.15 15.86 12.03 1.60 Standard 2.66 15.63 9.99 8.06 8.30 11.39 6.43 0.52 SWL(bgl)- Static Water Level (below ground level), BH - Borehole, SWL - Static Water Level VES - Vertical Electrical Sounding Table 3: Summary of the results of constant-rate pumping and recovery tests Pumping recovery test No. BH No. Rock type T-value from PT (m3/d) T-value from RT (m3/d) Average T (m3/d) K-value from PT (x 10-1 m/d) K-value from RT (x 10-1 m/d) Average K (x 10-1 m/d) 1 BH 29 Granite gneiss 8.99 9.24 9.11 5.28 5.43 5.35 2 BH 4 Granite gneiss 13.07 14.38 13.72 4.35 4.7 4.5 3 BH 10 Migmatite 11.48 16.21 13.84 6.37 9.00 7.68 4 BH 24 Migmatite 11.39 14.54 12.96 5.42 6.92 6.17 5 BH 12 Quartzite 16.37 18.75 17.56 9.09 10.00 9.54 Minimum 8.99 9.24 9.11 4.35 4.70 4.52 Maximum 16.37 18.75 17.56 9.09 10.00 9.50 Mean 12.26 14.62 13.43 6.10 7.21 6.65 BH = Borehole, PT = Pumping test, RT = Recovery test, T=Transmissivity, K = Permeability Table 4: Table of correlation of borehole data from Ilorin metropolis S/ No Parameter Correlated Coefficient of correlation Implications 1 Yield/Total depth 0.26 Yield weakly depends on the total depth. 2 Yield/Aquifer Thickness 0.50 Yield moderately depends on aquifer thickness. 3 Yield/Depth to basement (Overburden thickness) 0.28 Yield weakly depends on overburden thickness. 4 Yield/SWL 0.004 Yield is almost independent of static water level. 5 Yield/Transmissivity 0.96 Yield depends strongly on transmissivity of aquifer. 6 Borehole log/VES 0.99 Detection of subsurface structures strongly depends on VES. Figure 3: Static Water Level (SWL) above sea level Contour map of the Study Area showing the groundwater flow direction. Conclusions Groundwater occurred in the weathered and fractured zones of the basement rocks underlying Ilorin metropolis. The groundwater flow direction is generally radial and multidimentional, trending mainly in the NE-SW and NW-SE directions, which is consistent with the fracture pattern in the area. Borehole productivity increases from granite gneiss through migmatite to quartzite. It can be concluded that the groundwater potential of Ilorin metropolis is moderately high, judging from the values of the aquifer parameters, transmissivity (T), permeability (K) and yield, which are consistent with data of good aquifers in the crystalline basement complex of Nigeria. Observation wells should be used during pumping test in order to determine average storativity of the aquifers. Further studies should involve pumping of borehole water for several days to reach equilibrium. This would permit assessment of the groundwater using specific capacity rather than aquifer parameters. The groundwater of Ilorin area can be harnessed through boreholes to support the existing dams however, computation of safe yield is necessary for proper groundwater planning, development and management. Acknowledgements The authors acknowledged the support of the Director, Kwara State UNICEF (WES) Project for the permission granted to undertake the study. Mr. M. A. Oyeyipo (H. O. D, Water Supply Department), Mr. S. O. Aina (UNICEF, WES Project, Ilorin) and Professor P. I. Olasehinde (Department of Geology, Federal University of Technology, Minna, are also appreciated for making some of the reference materials used in this work available. Comments and suggestions of the anonymous reviewers are appreciated. References [1] Oluyide, P. O., Nwajide, C. S., Oni, A. O. (1998): The Geology of Ilorin Area. Nigerian Geological Survey Agency (N. G. S. A.), Bulletin 42, Explanation of the 1:250,000 sheet 50 (Ilorin), 84 p. [2] Alao, W. A., Hussein, A. Y., Olatunde, S. O. (1982): Geological investigations on brick-clay deposits at Okelele/Dada, Ilorin Local Government Area, Kwara State. Unpublished report. Geological Survey of Nigeria (GSN), 10 p. [3] Oyegun, R. O. (1983): Water Resources in Kwara State, Nigeria. Occasional paper, Kwara State Water Corporation. Matanmi Printing and Publishing Company Ltd, 73 p. [4] Olasehinde, P. I. (1999): An Integrated geological and Geophysical exploration techniques for groundwater in the basement complex of West Central Nigeria. Water Resources, Journal of Nigerian Association of Hydrogeologists, 11, pp. 46-49. [5] Olasehinde, P. I., Taiwo, K. A. (2000): A correlation of Schlumberger Array Geoelectrical Log with borehole Lithologic Log in the southwestern part of the Nigeria basement complex terrain. Water Resources, Journal of Nigerian Association of Hydrogeologists, 11, pp. 55-61. [6] Offodile, M. E. (2002): Groundwater study and Development in Nigeria, 2nd Edition. Mencon Geology and Engineering Services Ltd, 453 p. [7] Oyawoye, M. O. (1972): The basement Complex of Nigeria. In T. F. J. Dessauvagie and A. J. Whiteman, Eds., African Geology, University of Ibadan Press, pp. 67-97. [8] Wright, E. P., Burgess, W. G. (1992): The hydrogeology of crystalline basement aquifers in Africa. Special Publication No. 66, Geographical Society, London, pp. 1-20. [9] Annor, A. E., Olasehinde, P. I. (1996): Vegetational Niche as a Remote sensor for subsurface aquifer: A geological-geophysical study in Jere Area, Central Nigeria. Water Resources, Journal of Nigerian Association of Hydrogeologists, 7(1&2), pp. 26-30. [10] Burrough, P. A. (1986): Principles of Geographical Information Systems for Land Resource Assessment. Clarendon Press, Oxford, U. K. Supplementary Material Tables S1-S8 and Figures S1-S10. Table S1: Pumping Test of Borehole (BH 29) and (BH 4) in granite gneiss of Ilorin metropolis Borehole (BH 29) in granite gneiss Borehole (BH 4) in granite gneiss Time (min) Water level (Draw- down, S) (m) Time (min) Water level (Draw- down, S) (m) Time (min) Water level (Draw- down, S) (m) Time (min) Water level (Draw- down, S) (m) 1 3.105 85 6.040 1 5.205 85 8.099 2 3.230 90 6.115 2 5.352 90 8.199 3 3.271 100 6.175 3 5.484 100 8.225 4 3.271 110 6.263 4 5.610 110 8.360 5 3.472 120 6.324 5 5.785 120 8.451 6 3.575 130 6.410 6 5.812 130 8.525 7 3.652 140 6.505 7 5.903 140 8.580 8 3.794 150 6.613 8 5.981 150 8.642 9 3.839 160 6.721 9 6.091 160 8.795 10 4.030 170 6.800 10 6.180 170 8.805 12 4.030 180 6.901 12 6.297 180 8.875 14 4.176 190 6.984 14 6.365 190 8.993 16 4.275 200 7.072 16 6.444 200 9.192 18 4.340 210 7.183 18 6.540 210 9.275 20 4.455 230 7.254 20 6.641 230 9.388 22 4.596 250 7.331 22 6.721 250 9.465 24 4.663 270 7.430 24 6.782 270 9.530 26 4.701 290 7.531 26 6.884 290 9.622 28 4.877 310 7.610 28 6.992 310 9.720 30 4.945 330 7.699 30 7.100 330 9.801 35 5.076 350 7.792 35 7.203 350 9.890 40 5.170 370 7.881 40 7.298 370 9.967 45 5.293 390 7.979 45 7.406 390 10.065 50 5.384 410 8.067 50 7.492 410 10.184 55 5.455 430 8.157 55 7.585 430 10.275 60 5.531 450 8.247 60 7.665 450 10.351 65 5.620 470 8.325 65 7.763 470 10.415 70 5.735 490 8.413 70 7.822 490 10.487 75 5.845 75 7.901 80 5.957 80 7.985 Location: Borehole (BH 29) Olunlade SWL: = 3.00 m Average pumping rate (Q) = 1.28 l/s Type of Pump: 1 HP Borehole (BH 4) location: Tanke SWL (Static Water Level) = 5.00 m Average Pumping Rare (Q) = 1.82 l/s Pumping Duration = 490 mins Type of Pump = 1 HP Submersible Figure S1: Pumping Test curve of borehole (BH 29) in granite Figure S2: Pumping Test Curve of Borehole (BH 4) in granite gneiss of Ilorin metropolis. gneiss of Ilorin metropolis. Table S2: Recovery Tests of Borehole (BH 29) in granite gneiss of Ilorin metropolis. t' (min) R.W.L (m) S' (RWL-SWL) (m) t (490 +1') (min) t't' t' (min) RWL (m) S' (RWL-SWL) (m) t (490 + t') (min) t/t' 1 8.263 5.263 491 491.00 85 4.677 1.635 575 6.76 2 8.111 5.111 492 246.00 90 4.635 1.635 580 6.44 3 7.966 4.966 493 164.33 100 4.594 1.594 590 5.90 4 7.810 4.810 494 123.50 110 4.559 1.559 600 5.45 5 7.656 4.656 495 99.00 120 4.519 1.519 610 5.08 6 7.506 4.506 496 82.66 130 4.439 1.439 620 4.76 7 7.357 4.357 497 71.00 140 4.404 1.404 630 4.50 8 7.207 4.207 498 62.25 150 4.372 1.372 640 4.26 9 7.058 4.058 499 55.44 160 4.379 1.379 650 4.06 10 6.907 3.907 500 50.00 170 4.307 1.307 660 3.88 12 6.761 3.761 502 41.83 180 4.277 1.277 670 3.72 14 6.746 3.746 504 36.00 190 4.245 1.245 680 3.57 16 6.601 3.601 506 31.62 200 4.214 1.214 690 3.45 18 6.455 3.455 508 28.22 210 4.181 1.281 700 3.33 20 6.303 4.303 510 25.50 230 4.146 1.246 720 3.13 22 6.163 3.163 512 23.27 250 4.114 1.114 740 2.96 24 6.017 3.017 514 21.41 270 4.083 1.083 760 2.81 26 5.872 2.872 516 19.84 290 4.053 1.053 780 2.68 28 5.352 2.742 518 18.50 310 4.018 1.018 800 2.58 30 5.607 2.607 520 17.33 330 3.984 0.984 820 2.48 35 5.472 2.472 525 15.00 350 3.950 0.950 840 2.40 40 5.352 2.352 530 13.25 370 3.911 0.911 860 2.32 45 5.242 2.242 535 11.88 390 3.871 0.871 880 2.25 50 5.143 2.143 540 10.80 410 3.876 0.876 900 2.19 55 5.053 2.053 545 9.90 430 3.875 0.874 920 2.13 60 4.968 1.968 550 9.16 450 3.874 0.874 940 2.08 65 4.898 1.898 555 8.53 470 3.874 0.874 960 2.04 70 4.836 1.836 560 8.00 490 3.874 0.874 980 2.00 75 4.773 1.773 565 7.53 80 4.7231 1.723 570 7.13 SWL = 3.00 m Time of pumping = 490 min Borehole location: Olunlade Average pumping rate (Q) = 1.28 l/s t/ = time since start of recovery t = time since start of pumping R.W.L. = Recovery water level S = Residual drawdown SWL = Static Water Level Table S3: Recovery Tests of Borehole (BH 4) in granite gneiss of Ilorin metropolis t' (min) R.W.L (m) S' (RWL-SWL) (m) t (490 +1') (min) t/t' t' (min) RWL (m) S' (RWL-SWL) (m) t (490 + t') (min) t't' 1 10.265 5.265 491 491.00 85 7.865 2.865 575 6.76 2 10.124 5.124 492 246.00 90 7.767 2.767 580 6.44 3 9.989 4.989 493 164.33 100 7.713 2.713 590 5.90 4 9.864 4.864 494 123.50 110 7.664 2.664 600 5.45 5 9.741 4.741 495 99.00 120 7.608 2.608 610 5.08 6 9.627 4.627 496 82.66 130 7.552 2.552 620 4.76 7 9.524 4.524 497 71.00 140 7.499 2.499 630 4.50 8 9.423 4.423 498 62.25 150 7.445 2.445 640 4.26 9 9.324 4.324 499 55.44 160 7.387 2.387 650 4.06 10 9.225 4.225 500 50.00 170 7.331 2.331 660 3.88 12 9.138 4.138 502 41.83 180 7.272 2.272 670 3.72 14 9.053 4.053 504 36.00 190 7.218 2.218 680 3.57 16 8.971 3.971 506 31.62 200 7.160 2.160 690 3.45 18 8.895 3.895 508 28.22 210 7.101 2.101 700 3.33 20 8.819 3.819 510 25.50 230 6.501 1.501 720 3.13 22 8.749 3.749 512 25.27 250 6.438 1.438 740 2.96 24 8.680 3.680 514 21.41 270 6.376 1.376 760 2.81 26 8.612 3.612 516 19.84 290 6.317 1.317 780 2.68 28 8.545 3.545 518 18.50 310 6.259 1.259 800 2.58 30 8.450 3.450 520 17.33 330 6.201 1.201 820 2.48 35 8.416 3.416 525 15.00 350 6.144 1.144 840 2.40 40 8.451 3.451 530 13.25 370 6.088 1.088 860 2.32 45 8.288 3.288 535 11.88 390 6.032 1.032 880 2.25 50 8.228 3.228 540 10.80 410 5.906 0.906 900 2.19 55 8.170 3.170 545 9.90 430 5.905 0.905 920 2.13 60 8.113 3.113 550 9.16 450 5.904 0.904 940 2.08 65 8.057 3.057 555 8.53 470 5.904 0.904 960 2.04 70 8.022 3.022 560 8.00 490 5.904 0.904 980 2.00 75 7.969 2.969 565 7.53 80 7.919 2.919 570 7.13 SWL = 5.00 m Time of pumping = 490 min Borehole location:Tanke Average pumping rate (Q) = 2.23 l/s SWL = Static Water Level t/ = time since start of recovery t = time since start of pumping R.W.L = Recovery water level S = Residual drawdown Figure S3: Recovery Test curve of Borehole (BH 29) in granite gneiss of Ilorin metropolis. Figure S4: Recovery Test Curve of Borehole (BH 4) in granite gneiss of Ilorin metropolis. Table S4: Pumping Test of Borehole (BH 10) and (BH 24) in migmatite of Ilorin metropolis Time (min) Water level (Draw- down, S) (m) Time (min) Water level (Draw- down, S) (m) Time (min) Water level (Draw- down, S) (m) Time (min) Water level (Draw- down, S) (m) 1 5.105 85 7.621 1 5.095 85 7.950 2 5.165 90 7.690 2 5.145 90 8.020 3 5.210 100 7.790 3 5.185 100 8.167 4 5.273 110 7.910 4 5.295 110 8.284 5 5.381 120 8001 5 5.390 120 8.385 6 5.422 130 8.118 6 5.484 130 8.740 7 5.480 140 8.201 7 5.567 140 8.594 8 5.595 150 8.299 8 5.561 150 8.692 9 5.677 160 8.430 9 5.725 160 8.790 10 5.725 170 8.510 10 5.789 170 8.881 12 5.790 180 8.624 12 5.894 180 8.950 14 5.881 190 8.711 14 5.993 190 9.015 16 5.964 200 8.815 16 6.110 200 9.115 18 6.125 210 8.920 18 6.215 210 9.192 20 6.190 230 9.014 20 6.321 230 9.324 22 6.273 250 9.105 22 6.435 250 9.444 24 6.344 270 9.210 24 6.522 270 9.524 26 6.405 290 9.333 26 6.616 290 9.651 28 6.499 310 9.416 28 6.701 310 9.765 30 6.536 330 9.504 30 6.775 330 9.850 35 6.666 350 9.619 35 6.872 350 9.949 40 6.774 370 9.705 40 6.984 370 10.023 45 6.872 390 9.800 45 7.101 390 10.101 50 6.980 410 9.910 50 7.233 410 10.210 55 7.025 430 10.002 55 7.334 430 10.314 60 7.192 450 10.092 60 7.448 450 10.420 65 7.283 470 10.172 65 7.535 470 10.500 70 7.394 490 10.255 70 7.621 490 10.587 75 7.430 75 7.704 80 7.515 80 7.892 Location: Borehole (BH 10) Olohunsogo SWL (Static Water Level) = 5 900 m Average Pumping rate (Q) = 1.62 1/s Time of pumping = 490 min Type of Pump: 1 HP Submersible Location: Borehole (BH 24) Akerebiata SWL (Static Water Level) = 5 800 m Average Pumping rate (Q) = 1.731/s Time of pumping = 490 min Type of Pump: 1 HP Submersible Time (mini) у - 1.042aLn(s) + Э.53Э5 1 10 1Ш 1DOO Figure S5: Pumping Test Curve of Borehole (BH 10) in Figure S6: Pumping Test Curve of Borehole (BH 24) in migmatite of Ilorin metropolis. migmatite with overburden aquifer in Ilorin metropolis. Table S5: Recovery Tests of Borehole (BH 10) in migmatite of Ilorin metropolis t/ (min) R.W.L (m) S/ (RWL-SWL) (m) t (490 +1) (min) t/t/ t/ (min) RWL (m) S/ (RWL-SWL) (m) t (490 + 10 (min) t/t/ 1 10.102 4.202 491 491.00 85 7.555 1.655 575 6.76 2 9.949 4.049 492 246.00 90 7.513 1.613 580 6.44 3 9.799 3.899 493 164.33 100 7.468 1.568 590 5.90 4 9.648 3.748 494 123.50 110 7.422 1.522 600 5.45 5 9.496 3.596 495 99.00 120 7.378 1.478 610 5.08 6 9.346 3.446 496 82.66 130 7.333 1.433 620 4.76 7 9.196 3.296 497 71.00 140 7.291 1.391 630 4.50 8 9.047 3.147 498 62.25 150 7.246 1.346 640 4.26 9 8.898 2.998 499 55.44 160 7.200 1.300 650 4.06 10 8.750 2.850 500 50.00 170 7.155 1.255 660 3.88 12 8.644 2.744 502 41.83 180 7.109 1.209 670 3.72 14 8.540 2.640 504 36.00 190 7.066 1.166 680 3.57 16 8.450 2.550 506 31.62 200 7.002 1.122 690 3.45 18 8.370 2.470 508 28.22 210 6.917 1.077 700 3.33 20 8.300 2.400 510 25.50 230 6.927 1.027 720 3.13 22 8.250 2.350 512 25.27 250 6.874 0.974 740 2.96 24 8.199 2.299 514 21.41 270 6.770 0.870 760 2.81 26 8.150 2.250 516 19.84 290 6.720 0.820 780 2.68 28 8.102 2.202 518 18.50 310 6.663 0.763 800 2.58 30 8.053 2.153 520 17.33 330 6.662 0.762 820 2.48 35 8.010 2.110 525 15.00 350 6.662 0.762 840 2.40 40 7.964 2.064 530 13.25 370 6.661 0.761 860 2.32 45 7.918 2.018 535 11.88 390 6.661 0.761 880 2.25 50 7.814 1.914 540 10.80 410 6.660 0.760 900 2.19 55 7.829 1.929 545 9.90 430 6.660 0.760 920 2.13 60 7.779 1.879 550 9.16 450 6.660 0.760 940 2.08 65 7.734 1.834 555 8.53 470 6.660 0.760 960 2.04 70 7.686 1.786 560 8.00 490 6.660 0.760 980 2.00 75 7.642 1.742 565 7.53 80 7.598 1.698 570 7.13 SWL = 5.00 m Time of pumping = 490 min Borehole location: Olohunsogo Average pumping rate (Q) = 1.62 l/s t/=time since start of recovery r = time since start of pumping R.W.L. Recovery water level SWL= Static Water Level S' = Residual drawdown Figure S7: Recovery Test curve of Borehole (BH 10) in migmatite of Ilorin metropolis. Table S6: Recovery Tests of Borehole (BH 24) in migmatite of Ilorin metropolis t' (min) R.W.L (m) S' (RWL-SWL) (m) t (490 +1/) (min) t't' t' (min) RWL (m) S' (RWL-SWL) (m) t (490 + t') (min) t't' 1 10.442 4.642 491 491.00 85 7.401 1.601 575 6.76 2 10.297 4.498 492 246.00 90 7.361 1.651 580 6.44 3 10.154 4.354 493 164.33 100 7.316 1.516 590 5.90 4 10.009 4.209 494 123.50 110 7.269 1.469 600 5.45 5 9.866 4.966 495 99.00 120 7.224 1.424 610 5.08 6 9.726 3.926 496 82.66 130 7.180 1.380 620 4.76 7 9.583 3.783 497 71.00 140 7.140 1.340 630 4.50 8 9.439 3.639 498 62.25 150 7.100 1.300 640 4.26 9 9.299 3.499 499 55.44 160 7.060 1.260 650 4.06 10 9.158 3.358 500 50.00 170 7.019 1.219 660 3.88 12 9.123 3.323 502 41.83 180 6.978 1.178 670 3.72 14 8.987 3.187 504 36.00 190 6.938 1.138 680 3.57 16 8.855 3.055 506 31.62 200 6.893 1.093 690 3.45 18 8.725 2.925 508 28.22 210 6.858 1.058 700 3.33 20 8.594 2.794 510 25.50 230 6.822 1.022 720 3.13 22 8.461 2.661 512 25.27 250 6.790 0.990 740 2.96 24 8.338 2.538 514 21.41 270 6.757 0.957 760 2.81 26 8.228 2.428 516 19.84 290 6.718 0.918 780 2.68 28 8.128 2.328 518 18.50 310 6.683 0.883 800 2.58 30 8.038 2.238 520 17.33 330 6.651 0.851 820 2.48 35 7.958 2.158 525 15.00 350 6.615 0.815 840 2.40 40 7.881 2.081 530 13.25 370 6.580 0.780 860 2.32 45 7.826 2.026 535 11.88 390 6.550 0.750 880 2.25 50 7.766 1.966 540 10.80 410 6.549 0.749 900 2.19 55 7.711 1.911 545 9.90 430 6.548 0.749 920 2.13 60 7.668 1.868 550 9.16 450 6.548 0.748 940 2.08 65 7.601 1.801 555 8.53 470 6.548 0.748 960 2.04 70 7.560 1.760 560 8.00 490 6.548 0.748 980 2.00 75 7.507 1.707 565 7.53 80 7.453 1.653 570 7.13 SWL = 5 800 m Time of pumping = 490 min Borehole location: Akerebiata Average pumping rate (Q) = 1.73 l/s SWL= Static Water Level l/=time since start of recovery f = time since start of pumping R.W.L = Recovery water level 5= Residual drawdown Figure S8: Recovery Test Curve of Borehole (BH 24) in migmatite of Ilorin metropolis. Table S7: Pumping Test of Borehole (BH 12) in quartzite of Ilorin metropolis Time (min) Water level (Draw- down, S) (m) Time (min) Water level (Draw- down, S) (m) 1 4.396 85 7.105 2 4.455 90 7.185 3 4.536 100 7.295 4 4.625 110 7.395 5 4.741 120 7.523 6 4.850 130 7.595 7 5.018 140 7.747 8 5.057 150 7.762 9 5.125 160 7.815 10 5.295 170 7.892 12 5.360 180 7.978 14 5.450 190 8.058 16 5.550 200 8.128 18 5.601 210 8.237 20 5.715 230 8.304 22 5.830 250 8.423 24 5.924 270 8.507 26 5.997 290 8.589 28 6.095 310 8.684 30 6.185 330 8.790 35 6.290 350 8.890 40 6.375 370 8.995 45 6.447 390 9.081 50 6.455 410 9.163 55 6.570 430 9.230 60 6.690 450 9.302 65 6.763 470 9.385 70 6.814 490 9.471 75 6.950 80 7.015 Location: Borehole (BH 12) Gaa-Akanbi SWL (Static Water Level) = 4.30 m Average Pumping Rate (Q) = 2.23 1/s Pumping Duration: 490 min Type of Pump = 1 HP Submersible (Grundfos) Figure S9: Pumping Test Curve of Borehole (BH 12) in quartzites of Ilorin metropolis Table S8: Recovery Tests of Borehole (BH 12) in quartzites of florin metropol t/ (min) R.W.L (m) S/ (RWL-SWL) (m) t (490 + t/) (min) t/t/ t/ (min) RWL (m) S/ (RWL-SWL) (m) t (490 + 10 (min) t/t/ 1 9.321 5.021 491 491.00 85 6.353 2.053 575 6.76 2 9.170 4.870 492 246.00 90 6.294 1.994 580 6.44 3 9.022 4.722 493 164.33 100 6.241 1.941 590 5.90 4 8.873 4.573 494 123.50 110 6.157 1.857 600 5.45 5 8.728 4.428 495 99.00 120 6.137 1.837 610 5.08 6 8.582 4.282 496 82.66 130 6.092 1.792 620 4.76 7 8.297 4.137 497 71.00 140 6.048 1.748 630 4.50 8 8.162 3.997 498 62.25 150 6.003 1.703 640 4.26 9 8.027 3.862 499 55.44 160 5.961 1.661 650 4.06 10 7.897 3.727 500 50.00 170 5.918 1.618 660 3.88 12 7.897 3.597 502 41.83 180 5.873 1.573 670 3.72 14 7.768 3.468 504 36.00 190 5.829 1.529 680 3.57 16 7.648 3.348 506 31.62 200 5.786 1.486 690 3.45 18 7.527 3.227 508 28.22 210 5.745 1.445 700 3.33 20 7.427 3.127 510 25.50 230 5.705 1.405 720 3.13 22 7.332 3.032 512 25.27 250 5.664 1.364 740 2.96 24 7.239 2.939 514 21.41 270 5.621 1.321 760 2.81 26 7.149 2.849 516 19.84 290 5.577 1.277 780 2.68 28 7.064 2.764 518 18.50 310 5.532 1.232 800 2.58 30 6.981 2.681 520 17.33 330 5.482 1.182 820 2.48 35 6.911 2.611 525 15.00 350 5.432 1.132 840 2.40 40 6.851 2.551 530 13.25 370 5.376 1.076 860 2.32 45 6.786 2.486 535 11.88 390 5.326 1.026 880 2.25 50 6.724 2.424 540 10.80 410 5.277 0.977 900 2.19 55 6.673 2.373 545 9.90 430 5.246 0.946 920 2.13 60 6.623 2.323 550 9.16 450 5.245 0.945 940 2.08 65 6.571 2.271 555 8.53 470 5.245 0.945 960 2.04 70 6.517 2.217 560 8.00 490 5.245 0.945 980 2.00 75 6.465 2.165 565 7.53 80 6.405 2.109 570 7.13 SWL = 4 300 m Time of pumping = 490 min Borehole location: Akerebiata Average pumping rate (Q) = 2.23 l/s SWL = Static Water Level t/= time since start of recovery f = time since start of pumping R.W.L = Recovery water level S/= Residual drawdown Figure S10: Recovery Test Curve of Borehole (BH 12) in quartzites of florin metropolis.