EVALUATION OF AQUIFER CHARACTERISTICS OF VOLTAIAN SEDIMENTARY ROCKS IN THE BRONG OF

1Patrick A. Mainoo, 1Anthony Duah, 1William A. Agyekum and 2Aboagye Menyeh 1CSIR Water Research Institute, P. O. Box M.32, -Ghana. 2Department of Physics, Geophysics Section, Kwame Nkrumah University of Science and Technology, -Ghana

ABSTRACT Groundwater potential of the sedimentary formation in the Brong Ahafo Region of Ghana has been evaluated using computed transmissivity and specific capacity values. Data on multiple step and constant-discharge tests on twenty (20) boreholes were analyzed. The Cooper-Jacob’s straight line analytical approach was used to determine the aquifer characteristics. Computed transmissiv- ity coefficients of the underlying aquifer ranged widely from 0.82 – 61.27 m2d-1. The specific ca- pacity values obtained varied between 0.59 and 75.20 m3d-1m-1. Total head loses of the boreholes ranged generally between 5.49 and 99.2%. Hydrogeologically, the aquifer systems can be described as fairly heterogeneous in accordance with Krasny’s transmissivity classification model. Ground- water potential of the sedimentary aquifer system could be classified as high to intermediate to yield substantial groundwater resource for domestic and industrial water supply. To secure sub- stantial quantity of water for sustainable water supply in areas underlain by this sedimentary aqui- fer system in Ghana, integrated geophysical approach including 2D-Continuous Vertical Electrical Resistivity (CVES) survey, and other related tools such as Remote Sensing (RS) and Geographical Information Systems (GIS) should be used to enhance the delineation of deeper aquifer zones of high groundwater potential

Keywords: Ghana, Brong Ahafo, groundwater, sedimentary rocks, transmissivity, aquifer, sustainable, specific capacity

INTRODUCTION live in rural and peri-urban communities, which The Brong Ahafo Region of Ghana has a total are widely distributed within the Region. Ayi- land size of 39,557 km2 and constitutes about botele (1975), indicated that many communities 16.7 % of the total land size of the country and peri-urban towns in the region lack potable (Ghana Statistical Services, 2012). In terms of water and therefore depend on raw water sources size, the region ranks second to such as streams, rivers, lakes, ponds, dug-outs of Ghana (Ghana Statistical Services, 2012). and impoundment reservoirs. However, due to The population of the region is estimated to be anthropogenic activities, these traditional 2,310,983, representing 9.4% of the national sources are heavily polluted resulting in water- population. More than 55% of this population borne and water-related diseases such as diar- rhoea, guinea worm, bilharzia, etc. The Brong urban communities in Ghana, sought to provide Ahafo Region of Ghana lies within the semi-arid some selected communities in the Brong Ahafo region where mean annual evapotranspiration Region with sustainable potable water supply. exceed the mean annual rainfall by 49% (Gyau- Consequently, a network of boreholes were Boakye & Timbulto, 1996). The surface water drilled and their combined yield rallied into over resources dry up during the dry season -head water storage tank for onward distribution (November-February) and they severely affect to consumers via standpipes and a distribution domestic and agricultural water supply. In network to residential and industrial establish- Ghana, the recommendations from the Water ments. This paper assesses the groundwater po- Resources Sector Studies (WRSS), which was tential and characteristics of aquifer regimes commissioned by the Government of Ghana which underlie the study area. The boreholes (GoG), recommended making a policy to supply under this study were drilled to supply sustain- potable water through groundwater development able potable water to 14 Small Towns in 6 se- (Nathan Consortium for Sector Studies, 1970). lected Districts of Brong Ahafo Region of The policy recommended that communities with Ghana. Under this project, the potential thresh- population less than 500 are to be helped to se- old for a successful borehole was 5.0 m3/h. cure water supply through digging and construc- tion of hand-dug wells. Water supply to commu- THE STUDY AREA nities with population ranging between 500 and The study area comprises fourteen (14) small 2000 should be through boreholes fitted with towns in five (5) Administrative Districts that hand-pumps; whilst Small Towns and Peri- are scattered throughout the central and eastern Urban Towns with population higher than 2000 part of the Brong Ahafo Region. The geographic are to benefit from pipe-borne water supply location of the beneficiary communities are pre- through mechanized borehole systems. sented in Fig. 1 and Table 1. Geographically, Groundwater resources have some attributes that the areas lie between the boundaries of latitudes 7o 45’ N and 8o 23’N, and longitudes 0o 7’ W make it suitable for water supply in Ghana (Quist et. al., 1988). Firstly, the aquifer systems 3°0'0"W 2°0'0"W 1°0'0"W 0°0'0" 1°0'0"E underlie a large extent of the geographic area of BURKINA FASO the country and can be tapped at moderately 11°0'0"N ± 11°0'0"N shallow depths to meet the water demands of widely dispersed communities and towns. Sec- 10°0'0"N 10°0'0"N ondly, water stored in aquifer systems have proven to be protected from evaporation and 9°0'0"N 9°0'0"N

REPUBLIC OF TOGO OF REPUBLIC thus, borehole/well yields are sufficient to meet COTEI VOIRE D' requirements, providing water security to areas that experience protracted drought. Thirdly, pre- 8°0'0"N Brong Ahafo 8°0'0"N vailing aquifers in Ghana have relatively excel- lent microbial and intrinsic physico-chemical 7°0'0"N 7°0'0"N quality that requires no or minimal treatment to improve portability. Lastly, groundwater devel- 6°0'0"N 6°0'0"N opment can be phased as the population grows rendering cost of development relatively modest

5°0'0"N 5°0'0"N as compared to the traditional surface water GULF0 OF GUINEA100 200 Km treatment. Community Water and Sanitation 3°0'0"W 2°0'0"W 1°0'0"W 0°0'0" 1°0'0"E Agency (CWSA), the official institution man- dated in Ghana for the provision of potable wa- Fig. 1: Map of Ghana showing the Brong ter and sanitation facilities in rural and peri- Ahafo Region Table 1: Geographic location of project towns and geologic setting

Geographic Location Town District Geological Formation Latitude Longitude Jema Kintampo south N: 7.89235 W:1.77021 Damango sandstone Amoma Kintampo south N:7.78745 W:1.88054 Damango sandstone Anyima Kintampo south N:7.89286 W:1.86781 Damango sandstone Babatokuma Kintampo North N:8.14189 w:1.69736 Anyaboni sandstone Gulumpe Kintampo North N:8.54986 W:1.57845 Obosom undifferentiated Portor Kintampo North N:8.57768 W:1.56085 Obosom undifferentiated Kadelso Kintampo North N:8.65786 W:1.52397 Obosom undifferentiated Manso North N:7.70260 W: 1.83989 Damango sandstone Busunya Nkoranza North N:7.68677 W: 1.65258 Anyaboni sandstone Nkwabeng Nkoranza South N:7.49062 W: 1.74341 Anyaboni sandstone Ayirede Nkoranza South N:7.48341 W: 1.65312 Afram sandstone Kajeji Sene N:7.78371 W: 0.22656 Tease sandstone Bantama Sene N:7.70914 W: 0.75815 Obosom undifferentiated Akokoa Atebubu N:7.59154 W: 1.15338 Sandstone and 1o 56’ W. The area is bordered to the north the adjoining moist-semi deciduous forest into by Northern Region, to the south by Ashanti interior wooded savannah type (Dickson & Ben- Region and to the east by the Volta Lake and neh, 2004). Baobab, dawa-dawa, acacia and shea . butter trees are amongst the most conspicuous adaptable trees of the harsh prevailing climate Physical settings of the project area conditions. The trees are widely scattered and The area falls within the modified Tropical Con- the vegetation is quite open and dominated by tinental or Interior Savannah climate type, which short grasses, which grow in tussocks to an aver- is characterized by double maxima rainy season age height of about 3 m above the ground sur- (Dickson & Benneh, 2004). The major rainy face. Geomorphologically, the study area falls season is experienced within the period of May within the Southern Voltaian plateau, which is to June, whilst the later rains are experienced characterized by layers of sandstone undulating from September to October, followed by a pro- terrain of gently dipping or flat-bedded sand- longed dry season between November and Feb- stone, shales, mudstones (Dickson & Benneh, ruary. The heaviest rainfall occurs in August. 2004). The almost flat and extensive plain has an The mean monthly temperatures vary from about average elevation ranging from 60 - 150 m, 30 0C in March to about 24 0C in August. Rela- whilst the high points rise to elevation of 450 m. tive humidity prevailing in the study area varies The western corridor of the study area is drained from 90 to 95 % in the rainy seasons and it re- by Tankor, Pru, Afram and Sene rivers, which duces to 75 – 80 % in the dry season. The vege- are all tributaries of the main Volta River. The tative cover of the project area is of the Interior Nyemu river principally drains the north-western Wooded Savannah type, which is the largest in part of the study area and empties into the Black Ghana. It is highly envisaged that, the increasing Volta river at a confluence near Bupei in the effect of land use and climate change may turn Northern Region of Ghana. Geological and Hydrogeological Settings Ahafo Region, showing the locations of the pro- Fig. 2 shows the Voltaian sub-provinces in ject towns. A wider portion of the study area is Ghana. Generally, the Voltaian hydrogeological underlain by rocks associated with Upper Vol- province is associated with sandstones, shale, taian sandstone and the Middle Voltaian Forma- arkose, mudstone, sandy and pebbly-beds and tions (Oti siltstone and Obosum shale beds). limestone. Based on lithological and field rela- Nkwabeng, Busunya, Babatokuma, Manso, tionships earlier geologists such as Junner & Amoma, Jema and Anyima communities are Hirst (1946) and Soviet Geological Survey mainly underlain by the Anyaboni and Damango Team (1964-1966) sub-divided the Voltaian sandstones. The Anyaboni sandstones are char- system into three hydrogeological sub provinces acterized by dune-bedded to cross-bedded, me- namely (i) Upper Voltaian (thin-bedded massive dium-grained, arkosic with mudstone towards sandstone), (ii) Middle Voltaian (Obosom and the base. The Damango sandstone on the other Oti) and (iii) Lower Voltaian (Basal sandstone). hand, is flaggy to laminated, fine to medium- Geologically, the study area is predominantly grained and micaceous in nature (Geological Survey Department, 2009). Kajaji community is underlain by sedimentary rocks associated with underlain by the laminated and sometimes, cross the Voltaian Formation. Fig. 3 is a geological -laminated sandstone with some degree of map of central to the eastern corridor of Brong quartzose of the Tease sandstone (Oti-Pendjari formation). Ayerede community is at a geologic contact between Kwahu-“Morago” formation (Anyaboni sandstone) and the Oti-Pendjari Group (Afram sandstone) of the Voltaian forma- tion. Similarly, Bantama community is located at the geologic boundary between the Obosum formation and Densubon Sandstone formation. Hydrogeologically, Voltaian formation is one of the major hydrogeological provinces underlying about 45% of Ghana’s surface area (Gill, 1966). According to Dapaah-Siakwan & Gyau-Boakye (2000), the average borehole yield of the Vol- taian formation range between 6.2 and 8.50m3/h. The sandstones associated with the Middle Vol- taian located to the west and south of the project area are capable of storing considerable volume of water, which discharge into springs along weak zones such as joints and bedding planes. Borehole yields vary widely from place to place but it averages 8.5 m3/h. However, the yield could be improved when integrated geophysical techniques are used to select the drilling points (Dapaah-Siakwan & Gyau-Boakye, 2000). On the other hand, the Middle Voltaian (Obosom and Oti Beds) are associated with interceded mudstones, sansdtones, arkose, conglomerate Fig. 2: Hydrogeological sub-provinces of the and some sandstones. These rocks are generally of the Voltaain System (Geological Survey of gently-dippping. Because they are well- Ghana, 1965) consolidated, they are inherently impermeable except some isolated areas such as along the belt heads were informed by the drill depths, SWL between and Sang. In the wet sea- and screen placement sections. Short-duration son, large areas underlain by the rocks of the tests were conducted on the boreholes to estab- Middle Voltaiain are covered with shallow lish sustainable pumping rates to be used for the ephemeral lakes or ponds that quickly disappear longer duration constant pumping tests. Results during the dry season. Relatively, the formation obtained from the short-duration tests were used has low success rate of drilling productive bore- to determine the efficiency of each borehole at hole. The success rate of drilling a successful incremental pumping rates. The test was con- borehole in this Sub-Voltaian unit is about 56 % ducted using three (3) to six (6) different pump- and has an average yield 3.6 m3/h. ing rates depending on the response of the bore- hole to the subjected stresses. The boreholes Materials and Methods were allowed to rest for a day to ensure that they In this study, pumping test data generated from had recovered. They were then subjected to con- twenty (20) successful out of twenty five (25) stant-discharge test at varying pumping rates 3 boreholes drilled were used. The depth of the ranging between 45.3 and 460.0 m /d at varying boreholes ranged between 53.0 m and 186.0 m. pumping durations ranging between 420 and For each borehole, the static water levels (SWL) 1440 minutes. During the constant-discharge were recorded before the commencement of the tests, water levels were recorded at regular time pumping test. The placement of pump suction intervals. Immediately the pumping test was

2°0'0"W 1°0'0"W 0°0'0"

Legend H! Kadelso H! Project Community H! Potor Lake H! Gulumpe ³ Northern River Road Geology Upper Voltaian Middle Voltaian Upper Birimian Babatokuma H! Lower Birimian Volta Granite

8°0'0"N Volta Lake 8°0'0"N BA Boundary Regional Boundary H! AnyimaH! Jema Geological Map of Brong Ahafo Region Amoma H! H! Kajaji Client: CWSA-Brong Ahafo Region Consulatnt : Water Research Intitute Brong Ahafo Manso Bantama P.O. Box M 32, Accra H! H! Busunya H! Tel : 233-21-779514/5 Date : September 2010 H! Akokoa

Nkwabeng H! H! Ayerede

Ashanti

0 20 40 80 120 Km Eastern Scale : 1:1,200,000 Map of Ghana showing Brong Ahafo Region

2°0'0"W 1°0'0"W 0°0'0"

Fig. 3: Geological map of Eastern part of Brong Ahafo Region showing Project Communities completed, recovery measurements were re- uted to a combination of factors including partial corded for a maximum duration of 6 hours. penetration of aquifer regime as a result of non- Darcian flows in the zone of the gravel pack, losses through screen slots, frictional losses in RESULTS OF THE STUDY casings, as well as losses inside well screens due Step-Test to momentum and friction (Jacob, 1947). By re- For each borehole, a linear graph of drawdown arranging equation (1), equation 2 is obtained as: against time was plotted from the results of the step-drawdown tests. The purpose was to deter- mine the response of the borehole to increasing Sw/Q  B CQ (2) pumping rates than their natural yields, and fur- ther to obtain the optimum pumping rate to be From the step-drawdown test results, values of used for the long-duration pumping test. Rora- Sw/Q were plotted against Q to produce a linear baugh’s (1953) simplified version of Jacob’s graph with slope C and the intercept on the verti- equation between the drawdown Sw, and the cal axis (Sw/Q) equal to B. Sample of the plot of pumping rate Q is given by Sw/Q against Q is presented in Fig. 4 from which the parameters B and C were computed Sw BQ CQ2 (1) and used as inputs to estimate the efficiencies (E%) the production boreholes using the relation below: where BQ is the aquifer loss term due to laminar 2 flow and CQ is the well loss term due to turbu-  BO  lent flow, which is attributed to inefficiency of E (%) *100  2  (3) the well. Well losses in boreholes may be attrib-  BQCQ 

Fig. 4: Estimation of B and C values to establish borehole efficiencies The results of the estimated B and C values from step-test and the computed efficiencies (E %) of the boreholes are presented in Table 2 – 4.

Table 2: Step-drawdown results and efficiency calculations

Esti- Pumping mated Drawdown, Sw/Q BH ID Community Step Rate (m3/ B (d/m2) C (d/m5) E (%) Yield S (m) (d/m2) w d) (m3/d) 1 1.46 41.33 0.0353 97.74 2 2.74 72.94 0.0376 96.07 AFD- 3 5.68 144.00 0.0394 0.0357 2.00E-05 92.53 490 AM-01 Amoma 4 7.61 187.20 0.0407 90.51 5 10.82 267.41 0.0405 86.97 6 13.96 330.34 0.0423 84.38 1 5.43 48.83 0.1112 98.09 2 11.34 79.1 0.1434 96.94 AFD- 3 16.46 118.99 0.1383 95.47 Anyima 403 AN-01 4 24.44 178.85 0.1367 0.1255 5.00E-05 93.35 5 35.54 265.31 0.1340 90.44 6 43.32 305.28 0.1419 89.16 1 7.41 57.18 0.1296 95.69 2 17.23 117 0.1473 91.57 AFD-A 3 28.59 187.2 0.1527 0.1271 1.00E-04 87.16 Anyima 490 N-02 4 38.22 244.22 0.1565 83.88 5 44.58 280.8 0.1588 81.90 6 50.52 303.55 0.1664 80.72 1 0.98 48.83 0.0201 80.57 2 2.92 114.62 0.0255 63.86

3 5.17 174.38 0.0296 0.0162 8.00E-05 53.73 AFD- 432 Babatokuma BB-05 4 9.17 267.41 0.0343 43.09 5 12.46 306.86 0.0406 39.76 6 15.5 351 0.0442 36.59 1 2.13 44.21 0.0482 91.04 2 7.17 122.08 0.0587 78.62 AFD- 3 12.2 172.8 0.0706 0.0449 1.00E-04 72.21 Babatokuma 331 BB-07 4 18.88 255.27 0.0740 63.75 5 23.89 288 0.0830 60.92 6 28.99 345.6 0.0839 56.51 1 1.27 110.12 0.0115 44.04 2 2.49 156 0.0160 35.71

3 4.42 234 0.0189 27.03 AFD- Babatokuma 1296 BB-08 4 6.1 276.64 0.0221 0.0052 6.00E-05 23.86 5 8.02 330.35 0.0243 20.78 6 9.93 351 0.0283 19.80 E% = Efficiency coefficient of the borehole Table 3: Step-drawdown results and efficiency calculations (Cont’d)

Estimated Pumping Drawdown, Sw/Q B BH ID Community Yield Step Rate C (d/m5) E (%) S (m) (d/m2) (d/m2) (m3/d) w (m3/d) 1 14.27 97.92 0.1457 97.28 AFD- Bantama 153 2 27.56 195.84 0.1407 BA-03 0.1401 4.00E-05 94.70 3 37.39 244.08 0.1532 93.49 1 4.12 46.66 0.0883 70.83 2 7.48 63.36 0.1181 50.31 AFD- Bantama 147 3 17.45 125.42 0.1391 BA-05 0.0793 7.00E-04 33.84 4 26.97 140.4 0.1921 31.36 5 28.24 151.2 0.1868 29.79 1 5.48 104.77 0.0523 76.86 2 7.05 129.11 0.0546 72.94

AFD- 3 10.49 187.2 0.0560 65.02 Busunya BY-01 245 4 13.62 241.03 0.0565 0.0348 1.00E-04 59.08 5 20.01 295.57 0.0677 54.07 6 29.69 333.49 0.0890 51.06 1 5.48 104.77 0.0523 85.88 2 7.05 129.11 0.0546 83.15 AFD- 3 10.49 187.2 0.0560 0.0446 7.00E-05 77.29 Busunya 490 BY-02 4 13.62 241.03 0.0565 72.55 5 20.01 295.57 0.0677 68.31 6 29.69 333.49 0.0890 65.64 1 20.39 41.76 0.4900 57.84 AFD- Jema 115 2 53.73 64.37 0.8300 JE-03 0.3265 5.70E-03 47.09 3 72.9 92.16 0.7900 38.33 1 1.51 104.98 0.0100 42.10 2 16.41 206.47 0.0800 26.99 AFD- Jema 576 3 21.81 162.86 0.1300 JE-07 0.0229 3.00E-04 31.91 4 28.64 270 0.1100 22.04 5 32.55 312 0.1000 19.66 1 5.00 81.36 0.0610 14.68 2 15.49 122.01 0.1270 10.29 AFD- Jema 576 3 31.95 162.86 0.1960 JE-08 0.014 1.00E-03 7.92 4 43.54 170.18 0.2560 7.60 5 50.25 241.03 0.2080 5.49 1 11.37 81.36 0.1400 59.42 2 23.52 122.01 0.1900 49.40 AFD- Kadelso 294 3 35.62 162.86 0.2200 KL-01 0.0953 8.00E-04 42.24 4 49.78 170.18 0.2900 41.18 5 63.09 241.03 0.2600 33.08 E% = Efficiency coefficient of the borehole Table 4: Step-drawdown results and efficiency calculations (Cont’d)

Estimated Pumping Drawdown, Sw/Q B C BH ID Community Yield (m3/ Step Rate E (%) S (m) (d/m2) (d/m2) (d/m5) d) w (m3/d)

1 11.03 64.56 0.1700 88.94 2 23.57 114.62 0.2100 81.92 AFD- 3 41.65 180 0.2300 0.1558 3.00E-04 74.26 Kadelso 362 KL-02 4 64.72 255.27 0.2500 67.05 5 64.72 288 0.2200 64.33 6 79.25 255.27 0.3100 67.05

1 0.84 38.97 0.0220 77.47 2 1.33 93.6 0.0140 58.88 3 3.87 137.23 0.0280 0.0134 1.00E-04 49.40 AFD- Kajaji 294 4 6 166.18 0.0360 KA-01 44.64 5 6.83 201.31 0.0340 39.96 6 6.42 201.31 0.0320 39.96 7 6.83 201.31 0.0340 39.96

1 5.67 77.76 0.0730 99.22 2 8.98 138.24 0.0650 98.62 AFD- Kajaji 367 3 11.63 169.92 0.0680 KA-03 0.0693 7.00E-06 98.31 4 13.64 190.08 0.0720 98.12 5 14.79 200.59 0.0740 98.01

1 1.82 32.11 0.0567 71.25 AFD- 2 3.49 53.28 0.0655 0.0398 5.00E-04 59.90 Nkwabeng 115 NK-01 3 10.59 118.08 0.0897 40.27 4 11.98 108 0.1109 42.43

1 0.18 79.78 0.0023 84.04 2 0.36 125.14 0.0029 77.04 AFD- 3 0.59 179.57 0.0033 0.0021 5.00E-06 70.05 Nkwabeng 360 NK-02 4 0.82 246.82 0.0033 62.99 5 0.92 272.16 0.0034 60.68 6 0.97 280.8 0.0035 59.93

1 1.7 115.2 0.0150 85.69 2 2.58 148.95 0.0170 82.25 AFD- 3 3.66 200.58 0.0180 77.48 Nkwabeng 490 NK-03 4 4.43 242.06 0.0180 0.0138 2.00E-05 74.03 5 5.04 280.8 0.0180 71.08 6 5.67 295.57 0.0190 70.01 E% = Efficiency coefficient Constant pumping test results where Q is the pumping rate in m3d-1, ∆S is the The boreholes were each subjected to 24-hour drawdown of water level of pumped borehole continuous pumping and allowed to recover within a log cycle of time and Sw is the maxi- within 13 hours The Copper-Jacob semi-log mum drawdown recorded in the borehole during straight line method was used to estimate the pumping. The computed transmissivity and the transmissivity coefficient (T) and specific capac- specific capacity values are presented in Table 5. ity (Sp. Cap) values of the aquifers. The hydrau- lic parameters were calculated from the output DISCUSSION OF RESULTS of drawdown-time graphs for each borehole as The results obtained from the study indicated typically presented in Fig. 5. Similarly, plots of that boreholes had efficiency values ranging residual drawdown (s’) values verses the time between 5.5% and 99.2% and this is due to the ratios (t/t’) from recovery measurements were effects of total head losses as a result of lami- made. A linear graph obtained from this plot was nar and turbulent flows into them. According to used to estimate the residual transmissivity val- Driscoll (1995) these head losses could be attrib- ues (T’). The average transmissivity values (Tav) uted to poor borehole design and/or insufficient were then computed from both pumping and development. It has been proved that well losses recovery plots to serve as a representative trans- may even occur in well-constructed and exten- missivity value for the aquifer systems underly- sively-developed boreholes when the hydraulic ing each borehole. The fundamental formulae conductivity is primarily from fractures rather used to compute the transmissivity and specific than inter-grannular porosity (Kelly, Anderson, capacity values were: & Burnham, 1980; Mackie, 1982). Two (2) ar- tesian boreholes at Jema (AFD-JE-07 & AFD-JE 0.183 3 Transmissivity(T)  Q -08) and a high yielding borehole (1296 m /d) at S Babatokuma (AFD-BB-08), which were drilled Q through heavily fractured system were amongst SpecificCapacity(Sp.Cap)  the least efficient boreholes with efficiency val- Sw

Fig. 5: Drawdown plot for the computation of aquifer characteristics Fig. 6: Residual drawdown plot for the computation of aquifer characteristics

Table 5: Computed transmissivity and specific capacity values of the project boreholes

Drill Pumping Transmis- Specific Drawdown BH-ID Community Depth Rate sivity (T) Capacity Aquifer material (m) (m) (m3d-1) [m2d-1] (m3/d-1/m-1)

AFD-AM-01 Amoma 91.0 288.0 16.05 30.38 17.94 Sandstone AFD-AN-01 Anyima 114.9 288.0 48.45 9.26 5.93 Sandstone AFD-AN-02 Anyima 103.0 269.4 49.43 5.74 5.45 Sandstone AFD-BB-05 Babatokuma 79.5 288.0 31.82 8.92 10.74 Sandstone AFD-BB-07 Babatokuma 103.0 280.8 33.28 9.20 8.44 Sandstone AFD-BB-08 Babatokuma 53.0 460.8 33.52 10.90 13.75 Sandstone AFD-BA-03 Bantama 99.6 96.5 39.79 1.37 2.42 Mudstone AFD-BA-05 Bantama 103.0 116.1 34.08 4.31 3.41 Mudstone AFD-BY-01 Busunya 103.0 213.2 13.30 45.95 16.03 Sandstone AFD-BY-02 Busunya 168.0 396.0 39.09 19.00 10.13 Sandstone AFD-JE-03 Jema 121.0 45.3 76.15 0.82 0.59 Sandstone AFD-JE-07 Jema 150.0 403.2 52.38 8.34 7.70 Sandstone AFD-JE-08 Jema 156.0 403.2 62.91 8.05 6.41 Sandstone AFD-KL-01 Kadelso 126.0 216.0 67.57 3.47 3.20 Sandstone/Mudstone AFD-KL-02 Kadelso 132.6 259.2 79.28 2.57 3.27 Sandstone/Mudstone AFD-KA-01 Kajaji 100.0 201.6 21.93 9.21 9.19 Sandstone AFD-KA-03 Kajaji 90.0 244.8 30.26 6.13 8.09 Sandstone AFD-NK-01 Nkwabeng 121.0 109.0 13.76 39.30 7.92 Sandstone AFD-NK-02 Nkwabeng 75.0 345.6 4.57 61.27 75.62 Sandstone AFD-NK-03 Nkwabeng 67.0 403.2 14.52 20.31 27.77 Sandstone ues ranging between 5.49 and 42.1% (<50%) can be classified as high to intermediate indicat- and this reasonably confirms the assertion by ing that the deep aquifer systems can be ex- Mackie (1982) and Kelly et. al (1980) that head ploited to yield reliable and sustainable water losses in boreholes could be attributed to frac- supply to major and small towns. This is con- tured aquifer systems. Again some boreholes trary to earlier results obtained from shallow that registered lower efficiency values corre- boreholes in similar geophysical formation in sponded with those that were pumped at slightly Ghana (Dapaah-Siakwan and Gyau-Boakye, higher rates than their natural yields, a situation 2000). However, due to the fairly heterogeneous that could be attributed to higher frictional losses nature of the hydrogeological setting of the Vol- at higher pumping rates (Agyekum and Kankam- taian sedimentary in Brong Ahafo Region, it is Yeboah, 2011). The results of the computed recommended that, an integrated geophysical transmissivity and specific capacities of the Vol- approach together with other related tools such taian sediments are highly variable with trans- as Remote Sensing (RS) and Geographic Infor- missivity values ranging from 0.820 – 61.27 mation System (GIS) should be used to delineate m2d-1. The specific capacity values ranged be- zones of high groundwater potential at greater tween 0.59 and 75.20 m3d-1m-1. Applying depths to guarantee sustainable water supply to Krasny’s (1986) transmissivity classification meet both domestic and industrial use in the system to the aquifers of the study area, it is con- areas underlain by similar rocks in the region. cluded that aquifers underlying the project area fall within high to intermediate classification, ACKNOWLEDGEMENT indicating that the groundwater potential of the The authors express their gratitude to Agence aquifer Region has the capacity to supply sus- Françaises de Développement (AFD) and Brong tainable potable water supply to small towns Ahafo Regional Office of Community Water and and peri-urban communities. The hydrogeologi- Sanitation Agency (CWSA) for making avail- cal environment of the Voltaian aquifer system able borehole and pumping test data for the in the Brong Ahafo Region can be classified as preparation of this paper. fairly heterogeneous in character (Krasny, 1993). REFERENCES Agyekum, W., & Kankam-Yeboah, K. (2011). CONCLUSION AND RECOMMENDATION Characteristics of crystalline granitic aquifer Over 80% of the Brong Ahafo Region of Ghana in North-Western Ghana. Ghana J. Sci., 51, is predominantly underlain by sedimentary rocks pp 3-10. of Voltaian geological setting. Groundwater Ayibotele, B. (1975). A historical sketch of wa- potential varies spatially within the three Vol- ter resources development in Ghana. Accra: taian hydrogeological sub-provinces. 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