Research Journal of Chemical Sciences ______________________________________________ ISSN 2231-606X Vol. 2(6), 21-29, June (2012) Res.J.Chem.Sci. International Science Congress Association 21 Mapping of Groundwater Facies using anion Geochemistry in Angware Area, JOS Northcentral NigeriaIshaku J.M., Nur A. and Bulus J.A.Department of Geology, Federal University of Technology Yola, NIGERIA Department of Geology, University of Jos, NIGERIAAvailable online at: www.isca.in (Received 5th March 2012, revised 10th March 2012, accepted 16th March 2012)Abstract The use of anion geochemistry in mapping groundwater facies in Angware area was discussed. The objective of this work is to specially use only anion species to identify the facies present in the groundwater and the processes responsible for the modification of water chemistry in the area. 20 water samples were collected and analyzed using DR 2000 spectrophotometer and titrimetric method. The results indicated that pH range from 5.8 – 7.6 with an average of 6.5 while HCO, SO2- and Clreveal values ranging from 19.6 mg/l – 318.4 mg/l, 0.1 mg/l – 6.0 mg/l and 1.1 mg/l – 28.4 mg/l with mean values of 74.8 mg/l, 1.4 mg/l and 7.5 mg/l, respectively. CO2- was not detected in all the samples due to acidic to neutral pH condition. Based on the mean values, the anions were in the order of abundance as HCO� Cl� SO2-. The study identified Bicarbonate-Chloride-Sulphate facies as the only facies-type which is an indication of recently recharged groundwater with limited rock-water interaction. The plot of Cl/Cl + HCO against LogTDS revealed precipitation induced chemical weathering along with dissolution of rock forming minerals. Key words: Facies-type, mapping, groundwater, geology, weathering, angware. IntroductionFacies are identifiable parts of different nature belonging to any genetically related body or system1, 2. Hydrogeochemical facies are distinct zones that have cation and anion concentrations describable within defined composition category. The chemical composition of groundwater is influenced by factors such as composition of precipitation, mineralogy of the aquifers, climate, topography and anthropogenic activities3,4. These factors can combine to create diverse water types that change in composition spatially and temporarily5,4. The use of major ions as natural tracers has become a common method to delineate flow paths in aquifers. Generally, the approach is to divide the samples into hydro chemical facies which is groups of samples with similar chemical characteristics that can then be correlated with location. The observed spatial variability can provide insight into aquifer heterogeneity and connectivity, as well as the physical and chemical processes controlling water chemistry. The overall implication of this is that hydro geochemical facies of groundwater changes in response to its flow path. This also implies that mineralogical composition can exert important control on the final water chemistry. So the quality of water is likely to change day by day from different sources. Earlier studies on the characterization of groundwater facies and chemical evolutionary history utilized graphical9,10. These schemes were useful in visually describing differences in major ion chemistry in groundwater and classifying water compositions into identifiable groups11, which are usually of similar genetic history12. Domenico13 specifies that hydrochemical facies can be studied in terms of anions or cations or both, and Back proposed a classification guide for defining different facies. Chebotarev14 used anion species only and concluded that the composition of groundwater varies from bicarbonate at outcrops to sulphate water at intermediate depths to chloride at greater depths of continuous flow. The objective of this work is to specially use only anion species to identify the facies present in the groundwater and the processes responsible for the modification of water chemistry in Angware area. Geology of the Area: The study area is Angware in Jos north central local government area. It is located between latitudes 58’N to 1000’N and longitudes 905’E to 908’E, and covers an area of about 19.4Km (figure 1). Water supply to the people of the area is from hand-dug wells, boreholes and surface water obtain from streams and ponds. These sources of water supply have questionable quality due to anthropogenic activities such as agricultural activities and indiscriminate waste disposal practice. The population of the area is about 250015. The area falls within the Savannah wood land16 with mean annual rainfall ranging from 1250 mm to 2500 mm17. The area is largely drained by River Saradam. The altitude of the area ranges from 100 m to 1500 m17. The Plateau province is underlain by the younger granite suite, which includes granites, syenites and rhyolites16 and met sediments and volcanic rocks of different petrology17. The study area lies within the Plateau province, and is underlain by the undifferentiated migmatites, hornblende-biotite granite porphyry and rhyolites (figure 2). The areas underlain by the undifferentiated mignatites are relatively flat, low lying and occur in massive forms. They are characterized by leucocratic Research Journal of Chemical Sciences __________________________________________________________ ISSN 2231-606X Vol. 2(6), 20-29, June (2012) Res.J.Chem.SciInternational Science Congress Association 22 and melanocratic banding caused possibly by metamorphism. The mafic minerals are characterized by fine crystals while the felsic minerals have larger crystals. The phenocrysts of the feldspars range from 0.3 cm to 0.5 cm. The undifferentiated migmatites form the dominant rock types and covers extensive areas. Minerologically, the rocks consist of quartz, feldspars and mafic minerals. The hornblende-biotite granite porphyry occurs as elongate ridge with a relatively high topography of about 1234 m in the southern part of the study area. It is exposed in the north-eastern and northern parts of the study area. Minerologically, the rocks consist of hornblende, biotite, quartz and feldspars. The feldspars range in size from 1 cm to 1.6 cm and quartz phenocrysts range from 0.1 cm to 0.6 cm. The biotites are fine grain in texture and form the groundmass. The rhyolites outcrop in the northern part of the study area. It is extrusive in nature, and characterized by fine grain texture. It occurs at an elevation of about 1034 m. Figure 3 indicates that regional groundwater flow takes place from the recharge area at Saradam in the south, and flows towards Dan Kurma and Zangam in the southwest. Another flow zone takes place from Shere Jankasa in the northwest and flows towards the northern part of the study area. A minor recharge zone occurs between Rafin Sanyi and Lenge areas in the north and flows towards the north-eastern part. The major discharge area occurs between Anguwan Saradam and Angware areas. Shoeneich and Aku18identified two groundwater zones into fractured aquifer and soft overburden aquifer with yield exceeding 10 m/hr. The soft overburden aquifer consists of clay lenses, sandy clay and gravels with effective porosity ranging from 2.0 to 2.518. Bulus19carried out geophysical investigation in the area and discovered that most of the fractures vary between the depth ranges of 5 m to 25 m and are isolated fractures with average weathered overburden thickness of 19.4 m. Material and Methods Twenty (20) water samples were collected consisting of 14 samples from the hand-dug wells and 6 samples from boreholes (figure 1). The samples were collected from existing wells use for water supply according to Chilton20 method. All samples were filtered through 0.45 µm membrane filter immediately after sampling. Before the collection of the samples, pH determined in the field using pH meter (Wagtech), the sample containers were rinsed thoroughly with the water to be analyzed according to Matini et al21 method. The chemical parameters consisting of SO2- was analyzed using flame photometer (ELE International), spectrophotometer (Model DR2000, USA). HCO, CO2- and Cl were analyzed using titrimetric method. The water samples were analyzed at the Acts laboratory, Canada. The results in milligram per litre were converted to milli equivalent per litre. The resulting values of HCO + CO2-and Cl +SO2- were then expressed as percentages of all anions. The resulting percentages were correlated with Back standards to define the facies present in the groundwater. The direction of facies was then fitted into the facies types in the anion diamond shape proposed by Domenico13 (figure 4). To determine the processes influencing the groundwater chemistry LogTDS was plotted against Cl/Cl + HCO according to Gibbs22 procedure. Results and DiscussionThe results of anions expressed in milligram per litre are presented in table 1 and table 2 contains the concentrations of anions expressed in milliequivalent per litre. Table 1 indicates that pH values range from 5.8 -7.6 with an average of 6.5 indicating acidic to neutral condition. Most samples indicate acidic condition with 4 samples (Hw5, Hw6, Hw9 and Hw10) reveal neutral conditions. Bicarbonate concentrations range from 19.6 mg/l to 318.4 mg/l with a mean value of 74.8 mg/l. The presence of HCO is influenced by the pH conditions of the groundwater system. Below pH of 8.2, HCO forms CO3 2- by addition of H+1. The maximum pH recorded from all the samples was 7.6 and this favours the formation of HCO. Carbonate ion range from 0.04 mg/l to 0.08 mg/l with mean value of 0.04 mg/l. Carbonate ion was detected at low concentrations in all the samples. The low concentration of carbonate ion could be to the acidic to neutral pH conditions. The pH condition therefore does not favour the formation of CO3 2- at high concentrations by the dissociation of HCO. Davis and Dewiest23 indicates that dissociation of HCO to form CO3 2- occurs largely above pH of 8.2, below this pH, most of CO3 2- add H to form HCO through the following equation; + CO3 2- =H CO3 (1) Chloride concentrations range from 1.1 mg/l to 28.4 mg/l with an average of 7.5 mg/l. The detection of chloride in all the samples is favoured by the conservative nature of chloride. Sulphate reveals values ranging from 0.1 mg/l to 6.0 mg/l with mean value of 1.4 mg/l. Although sulphate occurs in all the samples, the concentrations were low, and this could probably be due to sulphate reduction. According to Domenico13 that sulphate reduction accounts for diminishing concentrations of sulphate in groundwater. Based on mean values of the anions, the anions occur in order of abundance as HCO� Cl� SO2-. Hydrogeochemical facies: Using the Back standards in table 3 indicates the dominance of Bicarbonate-Sulphate-Chloride facies as the only facies-type (table 4) embedded in the groundwater of the study area. Based on Chebotarev14 well-known sequence which states that groundwater composition evolves towards the composition of sea water through the following equation; Travel path HCO HCO + SO SO + HCO SO + Cl Cl + SO Cl- (2) Increasing age Chebotarev14 further states that the composition of groundwater varies from bicarbonate at outcrops to sulphate at intermediate depths to chloride at greater depths. It can be concluded from the above consideration that the dominance of Bicarbonate-Sulphate-Chloride type facies identified in the groundwater of the study are indicates recently recharge groundwater with short Research Journal of Chemical Sciences __________________________________________________________ ISSN 2231-606X Vol. 2(6), 20-29, June (2012) Res.J.Chem.SciInternational Science Congress Association 23 rock-water interaction and occurs at shallow depth. When the facies is fitted into the anion diamond field of Domenico13(figure 4) indicates no facies change in the groundwater (figure 5) which further buttress that the groundwater occurs at shallow depth and experienced limited mixing with the host rock. Sources of variation in the Hydro geochemistry of groundwater from the study area: The plots of Cl/Cl + HCO against logTDS indicates that the sample points plotted in the region of rock dominance and weathering zone (figure 6) suggesting precipitation induced chemical weathering along with dissolution of rock forming minerals. ConclusionThe following conclusions can be drawn from this study as follows; the presence of HCO in the groundwater is due to acidic to neutral pH condition. Low concentration of SO2-could be attributed to sulphate reduction. The low concentration of CO2- could be attributed to acidic to neutral pH condition. The results of the anions indicated that the anions were in the order of abundance as. HCO- � Cl� SO2- based on their mean values. CO2- was not detected due to acidic to neutral pH condition. The study identified Bicarbonate-Chloride-Sulphate facies-type which is an indication of recently recharged groundwater with short rock-water interaction. The plot of Cl/Cl+HCO against LogTDS revealed precipitation induced chemical weathering along with the dissolution of rock forming minerals. AcknowledgementsThe authors are most grateful to the Acts laboratory Canada for carrying out the water analysis. References1.Amadi P.A. and Egboka B.C.E., The use of Anion Geochemistry I Mapping Groundwater in the Port Harcourt Area of the Niger Delta, Nigeria. Global Journal of Geological Sciences, 8(2), 155-166 (2010)2.Obiefuna G. I. and orazulike D.M., The use of Anion Geochemistry in Mapping Groundwater Facies of Yola Area NE Nigeria, Research Journal of Chemical Sciences .1 (16), 30-41(2011)3.Kumar A.R. and Riyazuddin P., Application of Chemometric techniques in the assessment of groundwater pollution in a suburban area of Chennai city, India, Current Science, 94(8),1012-1022 (2008)4.Chenini I. and Khemiri S., Evaluation of groundwater quality using multiple linear regression and structural equation modeling, Int. J. Environ. Sci. Tech, 6(3), 509-519(2009)5.Thyne G., Guler C. and Poeter E., Sequential Analysis of Hydrchemical Data for Watershed Characterization, Groundwater, 42(5), 711-723 (2004)6.Back W., Hydrochemical facies and groundwater flow patterns in northern part of Atlantic Coastal Plains, US Geol. Surv, Profess. Papers, 498-A (1966)7.Nwankwoala H.O. and Udom G. J., Hydrochemical Facies and Ionic Ratios of Groundwater in Port Harcourt, Southern Nigeria, Res. J. Chem. Sci., 1(3) (2011)8.Murhekar G. H., Assessment of Physico-Chemical Status of Ground Water Samples in Akot city, Res. J. Chem. Sci. 1 (4), 117-124, (2011)9.Schoeller H., Les eaux souterraines, Masson and Cie, Paris 642 (1962)10.Hem J.D., The study and Interpretation of the chemical characteristics of natural water, 3rd edn. USGS Water Supply Paper 2254, US Geological Survey (1989)11.Freeze R.A. and Cherry J.A., Groundwater. New Jersey, Prentice-Hall Inc., 604 (1979)12.Olobaniyi S.B and Owoyemi F.B., Characterization by factor analysis of the chemical facies of groundwater in the Deltaic plain sands Aquifer of Warri Western Niger Delta. Nigeria, African Journal of Science and Technology,(AJST),7(1), 75-81 (2006)13.Domenico P.A., Concepts and Models in groundwater hydrology. McGraw-Hill Book Company, New York, pp 288-293 (1972)14.Chebotarev I.I., Metamorphism of natural waters in the crust of weathering, Geochem. Cosmochim. Acta., (8), 22-212 (1955)15.National Population Commission, Population Commission of the Federal Republic of Nigeria, Plateau State Statistical Tables, National Population Commission Final Results of population Census of Nigeria (2005)16.Du Preeze J.W. and Barber W., The distribution and chemical Quality of groundwater in Northern Nigeria Bull.,36, 93 (1965)17.Offodile M.I., Groundwater Supply and Development in Nigeria. 2nd Ed., Mecon Geology and Engineering Services, Ltd. 453p (2002)18.Shoeneich I.N and Aku, I.M., The study of degraded mine ponds on Jos-Bukuru, Riyom, Barki-Ladi and Bokkos area of Jos Plateau State for development possibilities, Report for Government of Plateau State (1996)19.Bulus J.A., Geo-electric Investigation for groundwater in Angware area Jos North central, M.Sc Thesis Department of Geology, Federal University of Technology, Yola, Nigeria (2010)20.Chilton J., Groundwater Water quality Assessment-A guide to use of biota: sediment and water in environmental monitoring, 2nd ed. UNESCO/WHO/UNEP (1992) Research Journal of Chemical Sciences __________________________________________________________ ISSN 2231-606X Vol. 2(6), 20-29, June (2012) Res.J.Chem.SciInternational Science Congress Association 24 21.Matini L., Tathy C. and Monutou J.M., Seasonal Groundwater Quality Variation in Brazzville, Congo,Research Journal of Chemical Sciences, 2 (2), 7-14 (2012)22.Gibbs R.J., Mechanisms Controlling World’s Water Chemistry, Science 170,1088-1090 (1970)23.Davis S.N and De Wiest R.J.M., Hydrology, Wiley, New York (1966) Table-1 Anion concentrations and pH values for groundwater samples Sample location Sample No. pH HCO 3 - mg/l CO 3 2 - mg/l SO 4 2 - mg/l Cl - mg/l Rafin Sanyi BH1 6.4 89.6 0.06 1.5 10.6 Angware BH2 5.8 63.3 0.08 1.0 7.2 Angware BH3 6.2 62.2 0.07 1.0 7.2 Angware BH4 5.8 73.2 0.05 1.0 8.1 Shere Jankasa BH5 6.1 312.7 0.06 1.0 28.4 Gurgu BH6 5.9 40.1 0.06 1.0 6.1 Rafin Sanyi Hw1 6.1 68.2 0.07 0.5 7.1 Angware Hw2 6.5 65.4 0.08 3.5 7.2 Angware Hw3 6.9 64.6 0.08 1.0 7.5 Shere Jankasa Hw4 6.1 318.4 0.07 1.0 28.4 Zangam Hw5 7.6 64.1 0.07 1.0 7.6 Zangam Hw6 7.6 67.5 0.08 0.1 6.5 Zangam Hw7 6.1 41.6 0.07 0.5 4.3 Gurgu Hw8 6.1 28.7 0.08 1.5 3.5 Saradam Hw9 7.5 24.1 0.06 6.0 1.6 Saradam Hw10 7.6 19.6 0.07 1.7 1.3 Saradam Hw11 6.7 21.4 0.05 1.5 1.1 Saradam Hw12 6.8 24.4 0.04 1.0 1.3 Dan Kurma Hw13 6.3 24.4 0.06 1.0 2.4 Lenge Lenge Hw14 Nil 21.6 0.06 1.2 2.6 Table- 2 Anions concentrations in meq/l for groundwater samples Location Sample No. SO 4 2 - CO 3 2 - HCO 3 - Cl - Total Rafin Sanyi BH1 0.03123 0.0019998 1.468544 0.29892 1.8006938 Angware BH2 0.02082 0.0026664 1.037487 0.20304 1.2640137 Angware BH3 0.02082 0.0023331 1.019458 0.20304 1.2456511 Angware BH4 0.02082 0.0016665 1.199748 0.22842 1.4506545 Shere Jankasa BH5 0.02082 0.0019998 5.125153 0.80088 5.9488528 Gurgu BH6 0.02082 0.0019998 0.657239 0.17202 0.8520788 Rafin Sanyi Hw1 0.01041 0.0023331 1.117798 0.20022 1.3307611 Angware Hw2 0.07287 0.0026664 1.071906 0.20304 1.3504824 Angware Hw3 0.02082 0.0026664 1.058794 0.2116 1.2938804 Rafin Sanyi Hw4 0.02082 0.0023331 5.218576 0.80088 6.0426091 Zangam Hw5 0.02082 0.0023331 1.050599 0.21432 1.2880721 Zangam Hw6 0.002082 0.0026664 1.106325 0.1833 1.2943734 Zangam Hw7 0.01041 0.0023331 0.681824 0.089526 0.7840931 Gurgu Hw8 0.03123 0.0026664 0.470393 0.0987 0.6029894 Saradam Hw9 0.12492 0.0019998 0.394999 0.04512 0.5670388 Saradam Hw10 0.035394 0.0023331 0.321244 0.03666 0.3956311 Saradam Hw11 0.03123 0.0016665 0.350746 0.03102 0.4146625 Saradam Hw12 0.02082 0.0013332 0.399916 0.03666 0.4587292 Dan Kurma Hw13 0.02082 0.0019998 0.399916 0.06768 0.4904158 Lenge lenge Hw14 0.024982 0.0019998 0.354024 0.07332 0.4543278 BH=Borehole, Hw=Hand-dug we ll Research Journal of Chemical Sciences __________________________________________________________ ISSN 2231-606X Vol. 2(6), 20-29, June (2012) Res.J.Chem.SciInternational Science Congress Association 25 Table- 3 Classification of hydro geochemical facies Cation facies: Percentage of Constituents, epm Ca + Mg Na + K HCO - + CO 2 - Cl + SO 2 - Calcium-Magnesium 90-100 0 10 Calcium-Sodium 50-90 10 50 Sodium-Calcium 10-50 50 90 Sodium-Potassium 0-10 90-100 Anion facies: Bicarbonate 90-100 0 10 Bicarbonate-Chloride-Sulphate 50-90 10 50 Chloride-Sulphate-Bicarbonate 10-50 5090 Chloride-Sulphate 0-10 90-100 (Back, 1966) Table- 4 Values of HCO + CO2- and Cl + SO2- as percentages of all Anions for groundwater samples Location Sample No. HCO - + CO 2 - Cl + SO 2 - Facies type Rafin Sanyi BH1 81.665 18.335 Bicarbonate-chloride-sulphate Angware BH2 82.290 17.710 Bicarbonate-chloride-sulphate Angware BH3 82.029 17.971 Bicarbonate-chloride-sulphate Angware BH4 82.819 17.181 Bicarbonate-chloride-sulphate Shere Jankasa BH5 86.187 13.813 Bicarbonate-chloride-sulphate Gurgu BH6 77.368 22.632 Bicarbonate-chloride-sulphate Rafin Sanyi Hw1 84.172 15.828 Bicarbonate-chloride-sulphate Angware Hw2 79.570 20.430 Bicarbonate-chloride-sulphate Angware Hw3 82.037 17.963 Bicarbonate-chloride-sulphate Rafin Sanyi Hw4 86.402 13.598 Bicarbonate-chloride-sulphate Zangam Hw5 81.745 18.255 Bicarbonate-chloride-sulphate Zangam Hw6 85.678 14.322 Bicarbonate-chloride-sulphate Zangam Hw7 87.255 12.745 Bicarbonate-chloride-sulphate Gurgu Hw8 78.452 21.548 Bicarbonate-chloride-sulphate Saradam Hw9 70.031 29.987 Bicarbonate-chloride-sulphate Saradam Hw10 81.788 18.212 Bicarbonate-chloride-sulphate Saradam Hw11 84.988 15.012 Bicarbonate-chloride-sulphate Saradam Hw12 87.470 12.530 Bicarbonate-chloride-sulphate Dan Kurma Hw13 81.954 18.046 Bicarbonate-chloride-sulphate Lenge lenge Hw14 78.363 21.637 Bicarbonate-chloride-sulphate BH= Borehole, Hw= Hand-dug well Research Journal of Chemical Sciences __________________________________________________________ ISSN 2231-606X Vol. 2(6), 20-29, June (2012) Res.J.Chem.SciInternational Science Congress Association 26 Figure-1 Location map of the study area Research Journal of Chemical Sciences __________________________________________________________ ISSN 2231-606X Vol. 2(6), 20-29, June (2012) Res.J.Chem.SciInternational Science Congress Association 27 Figure-2 Geologic map of the study area Research Journal of Chemical Sciences __________________________________________________________ ISSN 2231-606X Vol. 2(6), 20-29, June (2012) Res.J.Chem.SciInternational Science Congress Association 28 Figure-3 Hydraulic head distribution in unconfined aquifer Research Journal of Chemical Sciences ______ Vol. 2(6), 20-29, June (2012) International Science Congress Association Figure-4 Nomenclature for hydrogeochemical Anion facies in groundwater of Facies Plot of log TDS versus Cl ______ _________________________________ ______________ International Science Congress Association Figure-5 Nomenclature for hydrogeochemical Anion facies in groundwater of the study area Figure-6 TDS versus Cl /Cl + HCO of groundwater in the study area ______________ _____ ISSN 2231-606X Res.J.Chem.Sci 29 Nomenclature for hydrogeochemical Anion facies in groundwater of of groundwater in the study area