Research Journal of Chemical Sciences ________________________________________ ISSN 2231-606X Vol. 1(6), 30-41, Sept. (2011) Res.J.Chem.Sci. International Science Congress Association 30 The Use of Anion Geochemistry in Mapping Groundwater Facies of Yola Area NE NigeriaGabriel Ike Obiefuna and Donatus Maduka Orazulike2 Department of Geology, Federal University of Technology, Yola, NIGERIA Geology Programme, Abubakar Tafawa Balewa University, Bauchi, NIGERIA Available online at: www.isca.in (Received 18th April 2011, accepted 09th August 2011)Abstract This study was aimed at employing anion geochemistry in mapping groundwater facies in Yola area of Northeastern Nigeria. The concentration levels of sulphate were analysed using the HACH Spectrophotometer model No DR/2400 whereas those of Cl, COand HCO HCO– were done by titrimetric method. The results of the analysed dissolved anions are recorded as HCO (16.2 to 19.2 mg/l), Cl (0.50 to 0.80 mg/l) and SO(1.60 to 3.55 mg/l) for the rainwater and HCO (73.30 to 273 mg/l), Cl (27.90 to 455.20 mg/l) and SO2- (2 to 29.11 mg/l)for the surface water samples. The shallow groundwater and deep groundwater revealed values of HCO (19.90 to 240 mg/l), Cl (0 to 170.17 mg/l) and SO (0 to 35 mg/l) and HCO (50 to 207 mg/l), Cl (0.004 to 159.40 mg/l) and SO2- (0 to 64.50 mg/l) respectively. The absence of SO2- and relatively high concentration of bicarbonate in some of the samples could be attributed to sulphate reduction. The reaction is believed to take place in the presence of sulphate reducing bacteria in the soil zone through which recharge water percolates. The absence of some ions such as COand SO and the varied concentration levels in others such as Cl and HCO also affect the types and numbers of mappable facies in surface water and groundwater systems. Mappable groundwater facies for the different water sources are the bicarbonate-chloride-sulphate facies for the rainwater and the chloride-sulphate-bicarbonate for the surface water and groundwater systems respectively. The results further revealed that the groundwater has a local meteoric origin that evolves towards the composition of sea water. It also suggests that their chemical evolution is associated mainly with progressive dissolution and/or weathering of minerals along the flow paths. Key words:Anion geochemistry, groundwater facies, sulphate reduction, Yola area, NE Nigeria.IntroductionFacies are identifiable parts of different nature belonging to any genetically related body or system. Hydrochemical facies are distinct zones that have cation and anion concentrations describable within defined composition categories. Hydrochemical facies can be studied in terms of anions and cations or both. For instance, Chebotarevused anion species only and developed his well-known sequence which states that all ground waters tend to evolve chemically toward the composition of seawater. Toth used anion facies development in mapping groundwater discharge and recharge areas in Canada. Amadi et al used both anion and cation species in mapping the groundwater facies type housed in a north-south direction of some part of the Niger Delta region. Although each option may differ in scope but all are directed towards the definition and delineation of hydrochemical facies types found in groundwater flow systems. Groundwater flow systems has been mapped and correlated with hydrochemical patterns to varying degrees using hydrochemical facies. As a result certain broad relationship between chemical composition and the flow distribution of groundwater have been established in the process. Consequently, the mapping of groundwater flow systems using hydrochemical facies has aided the separation of potable and non-potable water. Hence, water quality has been related to the hydraulic regime (inflow, through flow, outflow) and the type (local, intermediate, regional) of the flow system. Finally Egboka and Amadi8 demonstrated the use of anion geochemistry in mapping groundwater facies in the Portharcourt area of the Niger Delta, Nigeria. In this study similar technique was applied in Yola area of Northeastern Nigeria in using anion geochemistry in mapping groundwater and surface water facies. Study Area: The study area occur at an elevation varying from 152m to 455m above mean sea level and falls within the Upper Benue Basin which has a catchment area of about 203,000km. It is located within longitudes 1224'E and 1234'E and Latitudes 911'N and 924’N and lies about 50km south of the Hawal Massifs. It is bounded to the east by the Republic of Cameroun and to the west by Ngurore town. The northern boundary is demarcated by Gokra town and the southern boundary by the Mandarara town (figures 1). The study area falls within the semi-arid climatic zone of Nigeria in Sub-Saharan Africa is characterized by two distinct seasons; a hot dry season lasting from November to April and a cool rainy season lasting from April to October. The study area receives summer rainfall from the south-western monsoon derived from the Gulf of Guinea. Rainfall during 1963/64-2006/2007 water years averaged Research Journal of Chemical Sciences _______________________________________________________ ISSN 2231-606X Vol. 1(6), 30-41, Sept. (2011) Res.J.Chem.Sci. International Science Congress Association 31 827.7mm per annum while the mean annual evapotranspiration is about 2384.6 mm. Material and MethodsA total of forty-three (43) water samples were collected from forty-three (43) locations between the months of November and December 2007. Of this forty-three locations (consisting of 27 groundwater, 11 surface water and 5 rainwater samples) were sampled. These samples were designated as SW1 to SW11 for surface water, RW1 to RW5 for rainwater and HW1 to HW45 and BH21 to BH137 for groundwater samples) respectively (figure 1). A global positioning system (GPS), Garment 12, was used for well location and elevation readings. This was supported by topographic sheets made available from the Ministry of Lands and Survey, Adamawa State of Nigeria. The samples were collected in polyethylene bottles after pumping the sampled wells for about 30 minutes and kept cool until analyses. This was done to remove groundwater stored in the well itself and to obtain representative samples. Various physical parameters were measured in the field using standard equipments. These include Temperature and conductivity (DR 2400), dissolved oxygen (Hach 2400 electronic meter) and pH/Eh (DR 2400 pH meter) measurements were made in the field. The samples were filtered through a thin polycarbonate membrane with 0.45µm pore size and subsequently analyzed in the Laboratory of the Adamawa State Water Board Yola for HCO CO2-, Cl, SO2- and TDS. The chemical analyses were based on the standard methods presented in APHA/AWWA/WPCF. Results of chemical analyses in milligrams per litre were converted to values in milliequivalent per litre and anions balanced against cations as a control check on the reliability of the analyses results. All the samples were assessed for charge balance and were all within the acceptable range of ± 5 The resulting values of (HCOCO) and those of (Cl– + SO2-) were then expressed as percentages of all anions. The facies of the resulting percentages were then matched with the guidelines proposed by Back10 whereas the direction of facies change was determined by fitting the facies types into the anion diamond field of Domenico11Results and DiscussionAnalytical data of the anion values of the sampled rainwater, surface water and groundwater in milligram per litre are provided in tables 1 to 3 whereas their equivalent values in milliequivalent per liter are presented in tables 4 to 6. The values of the sum of HCOCO and those of Cl– + SO2- expressed as percentages of all anions are displayed in Tables 7 to 9. The results obtained from these tables were interpreted based on the classification guide given by Domenico11, Back12 and UNESCO/WHO13 as given in Tables 10 and 11 respectively. Tables 12, 13 and 14 revealed the hydrochemical facies of the sampled rainwater, surfacewater and groundwater obtained in the study area.Environmental controls on the Anion Concentration Levels: Tables 1 to 3 indicate that sulphate anions varies from 1.60 mg/l to 3.55 mg/l in rainwater and 2 mg/l to 29 mg/l in surface water whereas those obtained for the shallow groundwater and deep groundwater varies from 0 mg/l to 35 mg/l and 0 mg/l to 64.50 mg/l respectively. These results indicate completely absent sulphate values in some sampled water to relatively low values in most samples. The absence of SO2- and relatively high concentration of bicarbonates in some of the samples could be attributed to sulphate reduction resulting from the activities of sulphate reducing bacteria whereas relatively low values obtained in others are due to on-going sulphate reduction. Chemical reduction of oxidized sulphur ions to sulphate ions or to the sulphide state occurs frequently in groundwater. The reaction is believed to take place in the presence of sulphate-reducing bacteria in the soil zone through which recharge water percolates. The process controls the level of occurrence of SO2- in groundwater. The absence of CO in all the sampled water is due to the relatively high acidity of the groundwater system. Tables 1 to 3 revealed pH values ranging from to which are considered unfavourable for the formation of COthrough the dissolution of bicarbonate. This process according to Davis and DeWiest14 is only affective above a pH value of 8.2 as indicated in the following reaction which justified the dependence of individual CO forms on pH (table 11). +CO2- = HCO– (1) Thus the pH range of 4.30 to 8.00 recorded for the sampled rainwater, surface water and groundwater favoured the occurrence of bicarbonate ions as opposed to carbonate ions. This is because a pH of 8.2 and less favours the formation of bicarbonate ion by the addition of H to the CO2- as indicated in equation 1 (table 11). The mean chloride for the surface water bodies and precipitation are 145.87 mg/l and 0.65 mg/l with ranges of 39.93 mg/l and 455.20 mg/l (surface water) and 0.50 and 0.80 mg/l (precipitation). The mean chloride concentration for the shallow groundwater and deep groundwater are 83.46 mg/l and 75.58 mg/l with ranges of 0 mg/l and 170.17 mg/l (Shallow groundwater) and 0.004 mg/l and 159.40 mg/l (deep groundwater). The chloride values in precipitation are low in comparison with those obtained for the surface water and the groundwater indicating that pollution is derived from anthropogenic reactions and/or dissolved mineral constituents in the underlying rock formations. It also suggests that chloride behaves as a conservative natural tracer indicating presence of NaCl-type water15. Chloride does not react easily with aquifer materials and tends to be closely associated with water molecules (Mercado 1985). These qualities prevent chloride from being easily removed from solution and enhance its solution in groundwater. Research Journal of Chemical Sciences _______________________________________________________ ISSN 2231-606X Vol. 1(6), 30-41, Sept. (2011) Res.J.Chem.Sci. International Science Congress Association 32 Table-1 Anion Concentration and pH levels in rainwater and Surface Water Samples of the Study AreaS/N Location Date of collection Date of analysis Water table (m) Parameter pH SO2-        Cl 1 Rainwater Yola RW1 15/08/09 15/08/09 Nil 7.40 1.60 Nil 18 0..70 2 Rainwater Yola RW2 15/08/09 15/08/09 Nil 4.30 1.80 Nil 19.20 0.60 3 Rainwater Yola RW3 15/08/09 15/08/09 Nil 7.70 4.50 Nil 16.20 0.65 4 Rainwater Yola RW4 15/08/09 15/08/09 Nil 6.40 2.70 Nil 17.50 0.80 5 Rainwater Yola RW5 15/08/09 15/08/09 Nil 6.20 3.55 Nil 18.73 0.50 6 River Benue SW1 22/11/09 22/11/09 1 7.34 17.00 Nil 148 39.93 7. River Benue SW2 22/11/09 22/11/09 1 7.55 10.00 Nil 183 27.90 8 Lake Geriyo SW3 22/11/09 22/11/09 1 7.70 11.50 Nil 273 227 9 River Benue TPY SW4 22/11/09 22/11/09 1 7.60 22.10 Nil 133 227.6 10 River Benue TPY SW5 22/11/09 22/11/09 1 7.61 2.00 Nil 73.30 284.50 11 River Benue SW6 22/11/09 22/11/09 1 8.00 24.86 Nil 130 40 12 River Benue SW7 22/11/09 22/11/09 1 7.20 20.06 Nil 145 51.31 13 River Benue SW8 22/11/09 22/11/09 1 7.50 29.11 Nil 162 60.00 14 Lake Njuwa SW9 22/11/09 22/11/09 1 7.70 20.50 Nil 57 455.20 15 River Benue SW10 22/11/09 22/11/09 1 7.80 20.21 Nil 153 147.05 16 River Benue SW11 22/11/09 22/11/09 1 7.30 18.34 Nil 48.50 147.05 Table-2 Anion Concentration and pH levels in Shallow Groundwater Samples of the Study Area S/N Location Date of collection Date of analysis Water table (m) Parameter pH SO2-        Cl 1 Lainde HW 1 19-11-09 19-11-09 24.2 6.90 10.10 Nil 61.90 57.90 2 Modire HW 4 19-11-09 19-11-09 23.33 6.60 5.20 Nil 99.50 113.80 3 Girei HW 12 19-11-09 19-11-09 7.27 7.30 12.80 Nil 76 115.0 4 Wuro Chekke 19-11-09 19-11-09 8.00 7.40 0.00 Nil 89.13 85.30 5 Jimeta HW 24 19-11-09 19-11-09 1.40 7.30 0.00 Nil 77.00 110.90 6 Bachure HW25 19-11-09 19-11-09 5.20 6.70 0.00 Nil 51.50 63.30 7. Tofare Buhu HW 36 19-11-09 19-11-09 2.12 6.50 29.80 Nil 92.00 170.17 8 Kabawa 19-11-09 19-11-09 6.70 6.90 17.50 Nil 85.40 112.80 9 Sebore HW 42 19-11-09 19-11-09 12.00 7.10 2.10 Nil 125.00 110.70 10 Yolde Patch II HW45 19-11-09 19-11-09 7.88 7.20 35.00 Nil 41.00 64.90 11 Bajabure Phase II BH21 19-11-09 19-11-09 6.065 7.20 32.50 Nil 93.00 0.00 12 Jambutu BH 37 19-11-09 19-11-09 4.70 7.10 0.90 Nil 240.00 56.89 13 Njobboli BH 117 19-11-09 19-11-09 11.00 7.40 1.50 Nil 103.50 66.90 14 Lainde BH 123 19-11-09 19-11-09 35,00 6.50 16.70 Nil 102.00 132.90 15 Kofare BH 136 19-11-09 19-11-09 16.00 6.90 10.01 Nil 10.90 0.00 16 Yolde Patch II BH137 19-11-09 19-11-09 18.00 6.80 0.00 Nil 82.00 73.90 Research Journal of Chemical Sciences _______________________________________________________ ISSN 2231-606X Vol. 1(6), 30-41, Sept. (2011) Res.J.Chem.Sci. International Science Congress Association 33 Table-3 Anion Concentration and pH levels in deep groundwater sample of the study areaS/N Location Date of collection Date of analysis Water table (m) Parameter pH SO2-        Cl 1 Sabare HW14 18/11/09 18/11/09 36.40 6.8 21.10 Nil 77.80 113.90 2 Karewa HW 26 18/11/09 18/11/09 60 7.10 0.09 Nil 84.00 57 3 Karewa HW 46 18/11/09 18/11/09 62 7.55 27.5 Nil 104.90 133.60 4 Karewa HW 47 18/11/09 18/11/09 58 6.80 0.35 Nil 53.50 171.50 5 Girei BH7 18/11/09 18/11/09 50 6.60 11.88 Nil 153.30 77.00 6 FUT Yola BH 7 18/11/09 18/11/09 56 6.80 64.50 Nil 207 42.00 7. Jimeta BH 10 18/11/09 18/11/09 46 7.40 25.50 Nil 101 11.02 8 Jimeta BH 75 18/11/09 18/11/09 46 7.50 11.20 Nil 94.90 159.40 9 Jimeta BH 81 18/11/09 18/11/09 48 7.80 0.00 Nil 99.60 65.90 10 Demsawo BH 87 18/11/09 18/11/09 37 7.50 0.83 Nil 109 0.004 11 Yola BH 91 18/11/09 18/11/09 52 7.60 0.02 Nil 50 0.03 Table-4 Anions in meq/l for rainfall and surface water samplesS/N Location/Parameters  \n   \n  \r   Cl total 1. Rainwater Yola RW1 0.03331 Nil 0.29502 0.01975 0.34808 2 Rainwater Jimeta RW 2 0.03748 Nil 0.31469 0.01834 0.3691 3 Rainwater Vinikilang RW 3 0.09369 Nil 0.26552 0.01834 0.37755 4 Rainwater FUT Yola RW 4 0.05621 Nil 0.28683 0.02257 0.36561 5 Rainwater Girei RW 5 0.07391 Nil 0.30698 0.01411 0.395 6 River benue SW 1 0.35394 Nil 2.42572 1.12643 3.90609 7 River Benue SW 2 0.2082 Nil 2.99937 0.78706 3.00463 8 Lake Geriyo SW3 0.23943 Nil 4.47447 6.40367 11.11757 9 River Benue TPy SW4 0.46012 Nil 2.17987 6.42060 9.06059 10 River Benue TPY SW5 0.04164 Nil 1.20139 8.02575 9.26878 11 River Benue SW6 0.51759 Nil 2.1307 1.1284 3.77669 12 River Benue SW7 0.41765 Nil 2.37655 1.44746 4.24166 13 River Benue SW8 0.60507 Nil 2.65518 1.6926 4.95385 14 Lake Njuwa SW9 0.42681 Nil 0.93423 12.84119 14.20223 15 River Benue SW10 0.42077 Nil 2.50767 1.24209 4.17053 16 River Benue SW11 0.38184 Nil 0.79492 4.14828 5.32504 Research Journal of Chemical Sciences _______________________________________________________ ISSN 2231-606X Vol. 1(6), 30-41, Sept. (2011) Res.J.Chem.Sci. International Science Congress Association 34 Table-5 Anions in meq/l for shallow groundwater samplesS/N Location/Parameters  \n   \n  \r   Cl total 1. Lainde HW1 0.21028 Nil 1.01454 1.63336 2.85818 2. Modire HW4 0.10826 Nil 1.63081 3.21030 4.94947 3. Girei HW 12 0.26650 Nil 1.24564 3.24415 4.75629 4. Wurochekke HW 22 0.00000 Nil 1.46084 2.40631 3.86715 5. Jimeta HW24 0.00000 Nil 1.26203 3.12849 4.39052 6. Bachure HW25 0.00000 Nil 0.84409 1.78569 2.62978 7. Tafare Buhu HW36 0.62044 Nil 1.50788 4.80050 6.92882 8. Kabawa HW 38 0.36435 Nil 1.39971 3.18209 4.9465 9. Sebore HW42 0.04372 Nil 2.04875 3.12285 5.21532 10. Yolde Patch II HW45 0.7287 Nil 0.67199 1.83083 3.23152 11. Bajabure Phase II BH21 0.67665 Nil 1.52427 0.00000 2.20092 12. Jambutu BH37 0.01874 Nil 3.9336 1.60487 5.55721 13. Njobboli BH117 0.03123 Nil 1.67637 1.88725 3.61485 14. Lainde BH123 0.34769 Nil 1.67178 3.74911 5.76858 15. Kofare BH136 0.21028 Nil 0.32616 0.00000 0.53644 16. Yolde Patch II BH137 0.00000 Nil 1.34398 2.08472 3.4287 Table-6 Anions in meq/l deep groundwater samples S/N Location/parameter  \n   \n  \r   Cl total 1. Sabore HW14 0.43930 Nil 1.27514 3.21312 4.92756 2. Karewa HW26 0.00187 Nil 1.37676 1.60797 2.9866 3. Karewa HW46 0.57255 Nil 1.71931 3.76886 6.06072 4. Karewa HW47 0.00729 Nil 0.87359 4.83802 5.7189 5. Girei BH7 0.24734 Nil 2.51259 2.17217 4.9321 6. FUT Yola BH75 1.34289 Nil 3.39273 1.18482 5.92044 7. Jimeta BH10 0.53091 Nil 1.65539 0.31087 2.19717 8. Jimeta BH75 0.22944 Nil 1.55541 4.49667 6.28152 9. Jimeta BH81 0.00000 Nil 1.63244 1.85904 3.49148 10. Demsawo BH87 0.01728 Nil 1.78651 0.00011 1.8039 11. Yola BH91 0.00042 Nil 0.8195 0.00085 0.82077 Research Journal of Chemical Sciences _______________________________________________________ ISSN 2231-606X Vol. 1(6), 30-41, Sept. (2011) Res.J.Chem.Sci. International Science Congress Association 35 Table-7 Values of (HCO+ CO) and of (Cl+ SO2-) as Percentages of all Anions for Rainwater and Surface Water SamplesS/N Location/parameter HCOCOCl- + SO2-) 1. Rainwater Yola RW1 84.756 15.244 2 Rainwater Jimeta RW2 85.259 14.741 3 Rainwater Vinikilang RW3 70.327 29.673 4 Rainwater FUTY Rw4 78.452 21.548 5 Rainwater Girei RW5 77.716 22.284 6 River Benue SW1 62.101 37.899 7 River Benue SW2 75.085 24.915 8 Lake Geriyo SW3 40.247 59.753 9 Rover Benue TPY SW5 24.059 75.941 10 River Benuw TPJ SW5 12.962 87.038 11 River benue Sw6 56.417 43.583 12 River Benue SW7 56.029 43.971 13 River Benue SW8 53.598 46.402 14 Lake Njuwa SW9 6.578 93.422 15 River benue SW10 60.128 39.872 16 River benuw SW11 14.928 85.072 Table-8 Values of (HCO+ CO) and of (Cl- + SO2-) as Percentages of all Anions for Shallow groundwater SamplesS/N Location/parameter HCO+ CO) Cl- + SO2- ) 1. Lainde HW1 35.496 64.504 2 Modire HW4 32.950 67.050 3 Girei HW12 26.189 73.811 4 Wurochekke Hw22 37.776 62.224 5 Jimeta HW24 28.744 71.256 6 Bachure HW25 32.097 67.903 7 Tafare Buhu HW36 21.762 78,238 8 Kabawa HW38 28.299 71.701 9 Sebore HW42 39.283 60.717 10 Yolde Patch II Hw45 20.795 79.205 11 Bajabure Phase II BH21 69.256 30.744 12 Jambutu BH37 70.784 29.216 13 Njobboli BH117 46.928 53.072 14 Lainde BH123 28.981 71.019 15 Kofare BH136 60.801 39.199 16 Yolde Patch II BH137 39.198 60.802 Research Journal of Chemical Sciences _______________________________________________________ ISSN 2231-606X Vol. 1(6), 30-41, Sept. (2011) Res.J.Chem.Sci. International Science Congress Association 36 Table-9 Values of (HCO+ CO) and of (Cl- + SO2-) as Percentages of all Anions for deep groundwater C Samples S/N Location/parameter HCO+ CO) Cl- + SO2-) 1. Sabore HW14 25.878 74.122 2 Karewa HW26 46.097 53.902 3 Karewa HW46 28.368 71.632 4 Karewa HW47 15.275 84.725 5 Girei BH7 50.944 49.056 6 FUT Yola BH75 57.305 42.695 7 Jimeta BH10 66.291 33.709 8 Jimeta BH75 24.762 75.238 9 Jimeta BH81 46.755 53.245 10 Demsawo BH87 99.036 0.964 11 Yola Bh91 99.845 0.155 Table-10 Classification of Hydrochemical Facies12Percentage of constituents, epm Ca + Mg Na + K HCOCOCl + SO2- Cation Facies Calcium – Magnesium 90-100 010 Calcium – Sodium 50-90 1050 Sodium – Calcium 10 – 50 5090 Sodium – Potassium 0 – 10 90 -100 Anion Facies Bicarbonate 90 – 100 010 Bicarbonate – Chloride – Sulphate 50 – 90 1050 Chloride – Sulphate – Bicarbonate 10 – 50 5090 Chloride – Sulphate 0 – 10 90 – 100 Table-11 Dependence of Individual CO forms on pH13% CO at pH CO2 Forms 4 5 6 7 8 8.3 9 10 11 Free 99.5 95.4 67.7 17.3 2.0 1.0 0.2 - - Bicarbonate 0.5 4.6 32.2 82.7 97.4 97.8 94.1 62.5 14.3 Carbonate - - - - 0.6 1.2 5.7 37.5 85.7 . Research Journal of Chemical Sciences _______________________________________________________ ISSN 2231-606X Vol. 1(6), 30-41, Sept. (2011) Res.J.Chem.Sci. International Science Congress Association 37 Table-12 Hydrochemical Facies in Rainwater and Surface Water SamplesS/N Location Hydrochemical facies 1. Rainwater Yola RW1        2 Rainwater Jimeta RW2         3 Rainwater Vinikilang RW3         4 Rainwater FUTY Rw4         5 Rainwater Girei RW5         6 River Benue SW1        7 River Benue SW2         8 Lake Geriyo SW3        9 Rover Benue TPY SW5         10 River Benuw TPJ SW5         11 River benue Sw6         12 River Benue SW7        13 River Benue SW8        14 Lake Njuwa SW9        15 River Benue SW10         16 River Benue SW11         Table-13 Hydrochemical Facies in Shallow groundwaterS/N Location/parameter Hydrochemical Facies 1. Lainde HW1        2 Modire HW4        3 Girei HW12        4 Wurochekke Hw22        5 Jimeta HW24        6 Bachure HW25        7 Tafare Buhu HW36        8 Kabawa HW38        9 Sebore HW42        10 Yolde Patch II Hw45        11 Bajabure Phase II BH21         12 Jambutu BH37         13 Njobboli BH117        14 Lainde BH123        15 Kofare BH136         16 Yolde Patch II BH137        Research Journal of Chemical Sciences _______________________________________________________ ISSN 2231-606X Vol. 1(6), 30-41, Sept. (2011) Res.J.Chem.Sci. International Science Congress Association 38 Thus the absence of some ions such as COand SO2- and the varied concentration levels of others such as Cl and HCO affect the types and number of mappable facies in groundwater systems. Table-14 Hydrochemical Facies in Deep groundwater CS/N Location Hydrochemical Facies 1. Sabore HW14        2 Karewa HW26         3 Karewa HW46        4 Karewa HW47        5 Girei BH7         6 FUT Yola BH75         7 Jimeta BH10         8 Jimeta BH75         9 Jimeta BH81        10 Demsawo BH87         11 Yola Bh91         Anion Facies in the Groundwater: The percentage of anion concentration in rainwater and surface water samples (table 7) and in shallow groundwater and deep groundwater samples (tables 8 and 9) were matched and compared with the guidelines given in table 10. These resulted in groundwater anion facies for the study area as displayed in tables 12, 13 and 14. These tables indicate that while there is a clear dominance of bicarbonate-sulphate-chloride facies in the rainwater, the surface water revealed an almost equal percentage of both bicarbonate-sulphate-chloride facies and sulphate-chloride-bicarbonate facies respectively. The study also indicated that the shallow groundwater revealed sulphate-chloride-bicarbonate facies whereas the deep groundwater indicated both the sulphate-chloride-bicarbonate facies and the bicarbonate-sulphate-chloride facies. LEGEND: Settlement, Torred Road, - - - - Untorred Road, ------ Footpath, Contour (Ft), River/Stream, Sample Points: Hand-dug wells, Borecholes, Surface water. Figure-1 Map of the study area showing some well location and sampling points Research Journal of Chemical Sciences _______________________________________________________ ISSN 2231-606X Vol. 1(6), 30-41, Sept. (2011) Res.J.Chem.Sci. International Science Congress Association 39 Figure-2 Geological map of the study area Figure-3 Nomenclature for hydrochemical facies: (AFTER: Domenico, 1972) Figure-4 Anion facies in rainwater environment Research Journal of Chemical Sciences _______________________________________________________ ISSN 2231-606X Vol. 1(6), 30-41, Sept. (2011) Res.J.Chem.Sci. International Science Congress Association 40 Thus when the facies types are fitted into the anion diamond field of Domenico (1972) as indicated in figure 3 there is an indication of the following facies change Rainwater Facies Sequence HCO– - SO2- - Cl SO2- - Cl- HCO (2) Surface water Facies Sequence HCO– - SO2- - Cl SO- Cl- HCO (3) Shallow groundwater Facies Sequence HCO– - SO2-- Cl SO- Cl (4) Deep groundwater Facies Sequence HCO– - SO2-- Cl SO2-- Cl- HCO (5) These facies indicate a strong evolution from fresh water to sea water (figures 4, 5, 6 and 7). The order in which groundwater encounter strata of different mineralogical composition influences the final chemistry of the groundwater (Freeze and Cherry 1979). Thus the chemistry of groundwater not only depends on the processes in the vadose zone but also on the reactions operating along the saturated flow system. Most of the same processes affecting ion concentrations in the unsaturated zone are also operative in the saturated zone including the dissolution and precipitation of various minerals and cation exchange (Schwartz and Zhang 2003). This conforms with Chebotarev (1955) study that states that all groundwaters tend to evolve chemically towards the composition of seawater which according to him is normally accompanied by the following regional changes in dominant anion species; Travel along flow pathHCO– HCO + SO2- SO2- + HCOSO2- + Cl Cl + SO2- Cl (6) Increasing Age These findings are therefore in conformity with the theory and observations (Chebotarev 1955; Toth 1984), that the flow of water from inflow to outflow areas may be attended in general by increases in the total dissolved solids contents (TDS) and Mg2+: Ca2+ ratio, and decreases in the SO2-, Cl and Ca2+, Na ratios. Furthermore, local systems may be associated with low TDS and a high percentage of Ca2+, Mg2+ and HCO; intermediate systems Figure-5 Anion facies in surface water environment Figure-6 Anion facies in shallow groundwater environment Figure-7 Anion facies in deep groundwater environment Research Journal of Chemical Sciences _______________________________________________________ ISSN 2231-606X Vol. 1(6), 30-41, Sept. (2011) Res.J.Chem.Sci. International Science Congress Association 41 with intermediate TDS and a high percentage of Na, SO2-and Cl and regional systems with high TDS and a high percentage of Na and Cl, relative to the local and intermediate systems. However, complications are brought about by factors such as mobility of the element, temperature, pressure, contact area between rock and water, contact time, length of flow path, amounts and distribution of soluble salts in rocks and antecedent water quality. Conclusion An anion geochemistry was employed in mapping the groundwater facies found in semiarid Yola area NE Nigeria. Groundwater from different water sources such as rainwater (5) surface water (11), shallow groundwater (16) and deep groundwater (11) were analyzed for the relevant anions (Cl, SO2-, HCO and CO) employing standard methods. The concentration levels of each anions were interpreted and related to the environmental factors that control their availability. The results indicate that all the other water sources have a local meteoric origin that evolves toward the composition of sea water. They also suggest that their chemical evolution is associated mainly with progressive dissolution and/or weathering of minerals along the flow path. AcknowledgementThe work described in this report is based on data generated for a doctorate degree dissertation by the first author Gabriel Obiefuna under the supervision of Prof. D. M. Orazulike. 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