70 © 2019 by the authors; licensee Asian Online Journal Publishing Group Asian Review of Environmental and Earth Sciences Vol. 6, No. 1, 70-77, 2019 ISSN(E) 2313-8173/ ISSN(P) 2518-0134 DOI: 10.20448/journal.506.2019.61.70.77 © 2019 by the authors; licensee Asian Online Journal Publishing Group Groundwater Quality Determination for Drinking Purpose by Using Water Quality Index Technique: A Case Study of Gadap Town, Karachi, Pakistan Asal Eghbal Bakhtiari1 Adnan Khan2 Zubaid Saeed3 Ayesha Kanwal4 ( Corresponding Author) 1,2,3,4Department of Geology, University of Karachi, Karachi, Pakistan. Abstract Present study is aimed at assessment of groundwater quality of Gadap Town for drinking purpose using water quality index (WQI) technique. Gadap is located in the outskirt of Karachi city and mainly influenced by the agriculture activities. Groundwater samples (n = 22) were collected mainly from boring wells and a few through tube wells from variable depths (100-600 feet). The analytical results of water reveal occurrence of very high TDS (range: 466-3810; mean: 1402) and hardness contents (range: 250-2800 mg/L). On the other hand, pH varies (range: 6.9-8.1; mean: 7.5) within WHO guidelines (6.5-8.5) with a few samples showing turbidity. About one third of total collected samples (n = 8) were analyzed for qualitative determination of microbial contamination which are found positive, except one sample, indicating the sewage mixing. Major chemistry of groundwater is also found disturbed in terms of high content of Na (mean: 219 mg/L), K (mean: 15 mg/L), Ca (mean: 144 mg/L) and Mg (mean: mg/L 137). Similarly, anions varied in the order of Cl > HCO3 > SO4 > NO3. Although some parameters show the bad quality of water but Water quality index (WQI) value (16.18) indicates that the groundwater quality is suitable for drinking purpose. It is inferred from the present study that water quality is partly polluted due to anthropogenic activities mainly by sewage infiltration. Keywords: Groundwater, Geochemistry, Drinking quality, WQI, Gadap Town, Karachi. Citation | Asal Eghbal Bakhtiari; Adnan Khan; Zubaid Saeed; Ayesha Kanwal (2019). Groundwater Quality Determination for Drinking Purpose by Using Water Quality Index Technique: A Case Study of Gadap Town, Karachi, Pakistan. Asian Review of Environmental and Earth Sciences, 6(1): 70-77. History: Received: 3 September 2019 Revised: 7 October 2019 Accepted: 13 November 2019 Published: 30 December 2019 Licensed: This work is licensed under a Creative Commons Attribution 3.0 License Publisher: Asian Online Journal Publishing Group Acknowledgement: Authors are indebted to Department of Geology, University of Karachi for providing the analytical facilities. Dr. Ghulam Murtaza Arain, laboratory Incharge of Pakistan Council for Research in Water Resources (PCRWR) is also thanked for analyzing the samples to determine some parameters. Funding: This study received no specific financial support. Competing Interests: The authors declare that they have no conflict of interests. Transparency: The authors confirm that the manuscript is an honest, accurate, and transparent account of the study was reported; that no vital features of the study have been omitted; and that any discrepancies from the study as planned have been explained. Ethical: This study follows all ethical practices during writing. Contents 1. Introduction ...................................................................................................................................................................................... 71 2. Materials and Methods ................................................................................................................................................................... 71 3. Results and Discussion ................................................................................................................................................................... 73 4. Conclusion ......................................................................................................................................................................................... 77 References .............................................................................................................................................................................................. 77 http://crossmark.crossref.org/dialog/?doi=10.20448/journal.506.2019.61.70.77&domain=pdf&date_stamp=2017-01-14 http://creativecommons.org/licenses/by/3.0/ http://creativecommons.org/licenses/by/3.0/ https://www.asianonlinejournals.com/index.php/AREES/article/view/1191 https://orcid.org/0000-0001-7889-820X https://orcid.org/0000-0001-6607-4190 https://orcid.org/0000-0002-8741-1392 https://orcid.org/0000-0002-7737-0048 https://www.asianonlinejournals.com/index.php/AREES/article/view/1191 https://orcid.org/0000-0001-7889-820X https://orcid.org/0000-0001-6607-4190 https://orcid.org/0000-0002-8741-1392 https://orcid.org/0000-0002-7737-0048 https://www.asianonlinejournals.com/index.php/AREES/article/view/1191 https://orcid.org/0000-0001-7889-820X https://orcid.org/0000-0001-6607-4190 https://orcid.org/0000-0002-8741-1392 https://orcid.org/0000-0002-7737-0048 https://www.asianonlinejournals.com/index.php/AREES/article/view/1191 https://orcid.org/0000-0001-7889-820X https://orcid.org/0000-0001-6607-4190 https://orcid.org/0000-0002-8741-1392 https://orcid.org/0000-0002-7737-0048 https://www.asianonlinejournals.com/index.php/AREES/article/view/1191 https://orcid.org/0000-0001-7889-820X https://orcid.org/0000-0001-6607-4190 https://orcid.org/0000-0002-8741-1392 https://orcid.org/0000-0002-7737-0048 https://www.asianonlinejournals.com/index.php/AREES/article/view/1191 https://orcid.org/0000-0001-7889-820X https://orcid.org/0000-0001-6607-4190 https://orcid.org/0000-0002-8741-1392 https://orcid.org/0000-0002-7737-0048 Asian Review of Environmental and Earth Sciences, 2019, 6(1): 70-77 71 © 2019 by the authors; licensee Asian Online Journal Publishing Group Contribution of this paper to the literature This paper will augment the worth of WQI technique being used for explaining the water quality objectively. It will also add the information about groundwater behavior occurring in the suburbs of the mega city. 1. Introduction Groundwater is one of the imperative natural resource to drive the life cycle. It is widely used for various purposes including industry, drinking, washing and irrigation. It can only be used if available in sufficient quantity with acceptable quality [1]. Hydrological cycle naturally works as a big pump which continuously transfers the water from oceans to land; mainly underground [2]. Modern agricultural practices, urbanization and industrialization have created the menace of water pollution [3]. These anthropogenic activities not only alter the physicochemical characters of water bodies but also contaminate the environment. Once the groundwater gets polluted it is difficult and costly to be cleaned up. Hence, to identify the potential toxicants and mechanism of release from their sources is important to prevent these water resources. Agricultural practices are common in areas where the fertile soil and water is available in copious amount. However, due to nutrient deficiency in agricultural soils, plenty of fertilizer or manure is used to get required crop yield. On the other hand, eutrophication, a result of high nutrient loads (mainly nitrogen and phosphorus), is considered to be the prevailing water quality problem for surface water [4]. Other pollutants originating in agricultural activities include sediments, oxygen-demanding substances and pesticides. Similarly, salinization is also reported as the most widespread groundwater quality problem and as having the greatest environmental and economic impacts [5]. This in turn leads to release various toxic elements into the water which ultimately contaminate the groundwater resources. This groundwater is also used by the dwellers of the agriculture-based community as main source of cooking, washing and drinking. As a result, the health and life of such community gets threatened. It is therefore important to monitor and regulate the groundwater of such areas to prevent from any catastrophe. About 60% of urban population in Pakistan is using groundwater for drinking and domestic purpose without regulating the water as per World Health Organization (WHO) standards [1]. Karachi is the largest city of Pakistan which is blessed with several ephemeral streams and channels culminating at two main rivers namely Lyari and Malir which ultimately discharge to Arabian Sea. The land around these natural water courses is being used for agricultural activities since long. Some agricultural sites are still pristine however others are rapidly transforming into the urban centers. Gadap Town is the agricultural periphery of Karachi city which is the hub of vegetable supply to this mega city and adjoining areas. Some reports on the base line data have shown the occurrence of high nitrate in the groundwater of Gadap (e.g. Chughtai, et al. [6]). As a result, the health of people living in Gadap town is questioned. However, no detailed work has been carried out so far to address the groundwater quality and possible sources of contamination in this part of Karachi city. Therefore, present study is aimed at assessing the groundwater quality of Gadap town using a new approach i.e. water quality index (WQI). Other objective is to statistically trace out the factors responsible for influencing the chemistry of groundwater in study area. 2. Materials and Methods 2.1. Study Area Gadap town is subdivision of Malir district which situated in the northwestern part of Karachi city Figure 1. This town is also forming the provincial border between Sindh and Balochistan, while to the north and east are Jamshoro district and the Kirthar Mountains. Gadap town has 8 union councils with over 400 rural villages accommodating the population of about 289,564 (1998). Gadap basin is influenced by the ephemeral channels occurring in the outskirt of Karachi city and mainly influenced by the agriculture activities. Over the last decade the Gadap is transformed into semi-area urban. Figure-1. Location map of Gadap Town, Karachi, (after Mahboob, et al. [7]). Source: This map has been taken from Mahboob, et al. [7] paper which is cited in the figure caption. https://en.wikipedia.org/wiki/Town https://en.wikipedia.org/wiki/Karachi https://en.wikipedia.org/wiki/Sindh https://en.wikipedia.org/wiki/Balochistan_(Pakistan) https://en.wikipedia.org/wiki/Jamshoro_District https://en.wikipedia.org/wiki/Kirthar_Mountains Asian Review of Environmental and Earth Sciences, 2019, 6(1): 70-77 72 © 2019 by the authors; licensee Asian Online Journal Publishing Group 2.2. Sample Collection Twenty-two groundwater samples were collected from boring wells at a depth range of 100-600ft. Groundwater was electrically pumped for 2-3 minutes to get true samples. Location of the wells was marked with the help of Global Positioning System (GPS) on the Google earth image and transformed on the map prepared by using GIS Technique Figure 2. Groundwater samples were collected in plastic bottles of 1.5-liter capacity for physico-chemical analysis. Bottles were properly washed and rinsed thoroughly with distilled water and then with groundwater at sampling site. To determine nitrate concentration groundwater samples were collected in bottles of 100 ml capacity and one ml boric acid solution was injected through sterile syringe in each water sample to cease any further reaction. Figure-2. Sample location map of study area. 2.3. Groundwater Analysis All the physico-chemical tests were carried out in the laboratory of Geology Department, University of Karachi. The pH and TDS/EC of collected groundwater samples (n=22) were measured with the glass electrode pH meter (ADWA AD 111) and EC meter (ADWA AD 330) respectively. Concentration of sodium and potassium was determined by using flame photometer (Model No. JENWAY PFP7). Sulphate content was tested by gravimetric method, while bicarbonate and chloride were estimated by Argenometric titration method. The method used for the analysis of calcium and total hardness was EDTA Titration Standard Method (1992). Magnesium was estimated as the difference between hardness and calcium with the help of formula. Groundwater samples preserved in the boric acid were analyzed to determine the nitrate concentration by Cadmium Reduction method (HACH-8171) on Spectrophotometer. 2.4. Water Quality Index (WQI) Groundwater quality index of Gadap town was determined by using weighted arithmetic index method as proposed by Brown, et al. [8] to evaluate the water quality status of study area. Physicochemical parameters including pH, TDS, major cations (Na, K, Ca, Mg) and anions (HCO3, Cl, SO4, NO3) were used to calculate WQI of groundwater in Gadap town. WQI is calculated by using following formula. WQI=∑QnWn/ ∑Wn Where, Qn is the quality rating of nth water quality parameter. Wn is the unit weight of nth water quality parameter. The quality rating Qn is calculated using the equation . Qn=100*[(Vn – Vi) / (Vs- Vi)] Where, Vn is the actual amount of nth parameter present. Vi is the ideal value of the parameter, Vi = 0, except for pH (Vi = 7). Vs is the standard permissible value for the nth water quality parameter. Unit weight (Wn) is calculated using the formula. Wn= k / Vn, Where, k is the constant of proportionality and it is calculated using the equation K= 1 / ∑Vs= 1, 2, …, n Asian Review of Environmental and Earth Sciences, 2019, 6(1): 70-77 73 © 2019 by the authors; licensee Asian Online Journal Publishing Group 3. Results and Discussion 3.1. Physical Parameters The characteristics of collected groundwater samples (n = 22) have been summarized in Table 1. Although a few samples are slightly saline and some show yellow color but others are safe in terms of color, taste and odor Table 1. The groundwater pH is slightly alkaline (mean: 7.5) with subtle variation in range (6.9-8.1) which is within the permissible range of WHO (6.5-8.5) for drinking. The groundwater temperature is low (mean: 28 °C) which fluctuates between 25 to 32˚C suggesting that it’s meteoric origin which has been hosted in the aquifers through surface water infiltration [9-17]. Only 5 samples (10, 13, 18, 21 and 22) are found turbid Table 1 which are also sewage impacted as indicated by occurrence of pathogenic bacteria Table 1. Turbidity in water is function of suspended load including organic particles, bacterio-plankton units, colloids, air bubbles and other non-uniformities in the water samples [18, 19]. In study area, people use to drain sewage into open pits or channels because they live in semi urban set up where lined sanitation is not yet available. As a result, organic matter and solutes are likely to infiltrate through sediments up to aquifers depths, causing high turbidity [20, 21]. Sewage contamination is reported even at the depth of 500 feet in groundwater of study area. Generally, the sewage contamination occurs at very shallow depth but the presence of sewage at such depths seems to be the function of sediments having good transmissivity and infiltration which is characteristic of alluvial sediments comprising silty-clay to silty-sand. It is consistent with the fact that subsurface rocks in the study area are dominated by silty sand belonging to Nari Formation. These fine clastics have least tendency to hold/adsorb the organic matter on their surface as compared to clays therefore the occurrence of such organic material is plausible in the study area. Total dissolved solids (TDS) and total hardness (TH) of collected samples are found to be highly variable (466-3810 mg/L and 250 to 2800 mg/L respectively) in the groundwater of Gadap town. TDS content occur three times higher than the permissible limit of WHO (500 mg/L) for drinking water in most of the groundwater samples of study area Table 1. This wide variation in TDS content may attribute to geochemical process and anthropogenic activities [22] in the study area. As discussed earlier, the Gadap basin is an agricultural land where organic matter in the surface soil is ubiquitous. This organic matter is prime driver of generating the organic acids which is significantly leaching the ions from soil and sediments resulting in increased specific conductance or salinity of water [23]. On the other hand, semi-arid climate has also concentrated the salts in the groundwater due to intense evaporation [24, 25]. Likewise, sewage infiltration to the aquifer depth is also augmenting the salt contribution in the groundwater of Gadap basin. 3.2. Chemical Parameters Sodium (Na) and potassium (K) are found to be highly variable in the study area ranging between 52.43-620 mg/L and 3.73-105 mg/L respectively. Na with a mean of 219.9 mg/L is found to be the dominant cation among the solutes but only in few samples exceed the permissible limit of WHO (200 mg/L) set for drinking water Table 2. Likewise, distribution pattern of calcium (Ca) is highly variable (range: 12 - 520 mg/L) in the collected samples Table 3. Similarly, the mean concentration of Mg (137.83 mg/L) in the groundwater of Gadap town is double the WHO permissible limit (50 mg/L) which spans between 12.5 to 388 mg/L Table 3. This suggests the role of multiple sources for contributing this element into the aquifer of study area. On the other hand, K content is marginally high (mean: 15.9 mg/L) in some of the samples (n=6) violating the desired limit (12 mg/L) of WHO Table 2. Chloride (Cl) and Bicarbonate (HCO3) are dominant anions followed by sulphate (SO4) and nitrate (NO3). Chloride shows elevated concentration (Mean: 597.31 mg/L) in almost all of the collected groundwater samples which is almost double the permissible limit of WHO (250 mg/L) for dirking water. However, SO4 concentration is found to be within the permissible limit set for drinking water by WHO (250 mg/L) in all of the samples except 5 Table 2. 3.3. Ionic Interrelationship Statistical analysis of the collected groundwater samples shows the strong positive correlation of hardness with all physical and chemical parameters except HCO3, NO3 and F and the same pattern is expressed by TDS Table 4. Strong positive correlation of TDS with Mg (0.6) and SO4 (0.8) indicates the influence of Clay minerals through water rock interaction. Elevated concentration of salts (Na, K, Mg, Cl, SO4) coupled with bacterial occurrence also suggests mixing of sewage with groundwater [26]. On the other hand, very high hardness (mean = 776.7 mg/L) of these collected samples indicate dissolution of limestone and Mg release from clays. 3.4. Hydrofacies Analysis Hydrofacies reflect the effect of chemical processes occurring between minerals within the lithological framework and the groundwater [27]. For this purpose, the Piper diagram is used to show the relative concentration of the major cations and anions [27, 28]. The results of groundwater analysis indicate that dominant hydrofacies occurring in the aquifers of Gadap town is Mg-Cl (50%). Asian Review of Environmental and Earth Sciences, 2019, 6(1): 70-77 74 © 2019 by the authors; licensee Asian Online Journal Publishing Group Table-1. Physical parameter of collected samples from GADAP town. S. No Locality Depth (ft.) Color Taste Odor Turbidity pH TDS mg/L EC µs/cm Temp. ˚C Hardness mg/L Mico. (-ve/+ve) 1 Chanesar Goth 360 Color less Normal Odorless #NT 7.3 1170 150.4 28 500 +ve 2 Khameso Goth 350 Color less Normal Odorless NT 7.8 533 682.9 26.7 250 +ve 3 SorafaqirSorab Goth 300 Color less Normal Odorless NT 7.4 920 1176 31.6 270 +ve 4 BadamBagh 500 Color less Normal Odorless NT 7.6 1240 1562 27.1 780 +ve 5 Gabol Stop 400 Color less Saline Odorless NT 7.6 1050 1382 28.5 560 -ve 6 Manzor Baloch Hotel 600 Color less Saline Odorless NT 7.8 836 1073 25.1 450 TNP 7 Lucky Farm House 350 Color less Normal Odorless NT 8 1370 1709 28.9 700 TNP 8 Bhitai Farm House 330 Yellow Saline Odorless NT 7.1 2110 2707 27.9 1300 TNP 9 Bhitai Farm House 100 Color less Normal Odorless NT 7.3 690 880.6 27.5 480 TNP 10 Bhitai Farm House 320 Color less Saline Odorless Turbid 7.2 1630 2093 27.9 1030 TNP 11 Haji KhudaBaksh F.H. 220 Color less Normal Odorless NT 7.4 466 595 26.4 350 TNP 12 Haji KhudaBaksh F. H. 400 Color less Normal Odorless NT 7.6 532 681 30.2 500 TNP 13 Dattari Farm House 500 Color less Normal Odorless Turbid 7.6 970 1240 28.3 480 TNP 14 Sarim Farm House 340 Color less Saline Odorless NT 7.5 740 947.8 28.1 450 TNP 15 Radho Goth 400 Color less Normal Odorless NT 7.2 3390 4780 29.4 2800 TNP 16 RadhoJokhio Goth 220 Color less Saline Odorless NT 7.3 3810 5280 28.4 2350 TNP 17 Goth Rado 200 Color less Normal Odorless NT 7.3 771 1083 30.1 700 TNP 18 M.Ishaq Baloch Bohlari 150 Yellow Normal Odorless Turbid 7 2870 4040 30 2250 TNP 19 M.Ishaq Baloch Bohlari 120 Color less Saline Odorless NT 7.3 950 1484 30.1 890 TNP 20 Gajan Village 250 Color less Normal Odorless NT 8.1 790 1090 28 *TNP +ve 21 Radho Goth 170 Yellow Saline Odorless Turbid 7.6 3210 4429 29 TNP +ve 22 Haji Arzi Village 200 Color less Saline Odorless Turbid 8 800 1104 28 TNP +ve Note: #NT = Non turbid. *TNP = Test not performed. Asian Review of Environmental and Earth Sciences, 2019, 6(1): 70-77 75 © 2019 by the authors; licensee Asian Online Journal Publishing Group Table-2. Chemical characteristics of collected groundwater samples. Note: *BDL=Below Deduction Level. Table-3. The statistical descriptive of the collected samples in the groundwater of the Gadap town. Parameters Min. Max. Mean SD Depth ( ft) 100 600 308.2 130.4 pH 6.95 8.1 7.47 0.31 TDS (mg/L) 466 3810 1402 1008 EC (µm/L) 150.4 5280 1826 1466 Temp (◦C) 31.6 31.6 28.42 1.46 Ca (mg/L) 520 520 144.63 150.48 Mg (mg/L) 388 388 137.83 102.25 Na (mg/L) 52.43 620 219.19 128.08 K (mg/L) 3.73 105 15.96 21.39 Cl (mg/L) 141.84 1524.78 597.31 488.45 HCO3 (mg/L) 230 1000 390.6 206.1 SO4 (mg/L) 25 490 138.22 108.51 NO3 (mg/L) 0.67 2.71 1.15 0.55 Table-4. Correlation matrix of the collected samples in the study area. Parameters pH Hardness TDS Ca Mg Na K Cl HCO3 SO4 NO3 Fe pH 1 Hardness -0.57 1 TDS -0.42 0.95 1 Ca -0.40 0.93 0.86 1 Mg -0.45 0.95 0.96 0.81 1 Na -0.28 0.80 0.89 0.69 0.80 1 K 0.16 0.92 0.53 0.50 0.48 0.39 1 Cl -0.40 0.91 0.96 0.80 0.94 0.84 0.52 1 HCO3 0.34 -0.12 -0.09 -0.10 -0.14 0.13 0.25 -0.07 1 SO4 -0.14 0.79 0.83 0.66 0.78 0.74 0.81 0.84 0.08 1 NO3 -0.03 -0.53 -0.41 -0.10 -0.36 -0.40 -0.45 -0.31 -0.19 -0.35 1 Fe -0.15 -0.53 -0.04 -0.30 0.04 -0.10 -0.20 0.11 -0.08 0.16 0.27 1 Na-Cl (22.7%), with lesser abundance (9.10% each) of Ca-HCO3, Ca-Cl and Na-HCO3 Figure 3. The occurrence of Mg-Cl facies in the groundwater of study area is due to their high solubility in natural water. The dominance of these two ions clearly indicates the influence of ion exchange and clay mineral alteration or dissolution of dolomite [29-31]. Since the study area is an agricultural land where large amount of clay is present in the soil, the dominance of Mg-Cl is legitimate. On the other hand, subsurface rocks are dominated by silty clay with subordinate limestone. These rocks are also assumed to release their sorbed and structural Mg content into the aquifer system within circum-neutral pH conditions. Generally, bicarbonate species dominates in the meteoric groundwater but the occurrence of excessive chloride ion, the bicarbonate is replaced with latter one. This chloride may originate from various sources including halite and related minerals in evaporate deposits, concentration by evaporation and solution of dry fallout from atmosphere in arid regions. The excessive amount of this ion in the groundwater is due to its conservative nature which makes it free from ion exchange, adsorption and biological activities. On the other hand, anions of strong acids (SO4 + Cl) dominate over weak acids (HCO3 + CO3) which indicate anthropogenic influence in the groundwater system [32]. It is evident by the fact that intense S. No. Ca mg/L Mg mg/L Na mg/L K mg/L Cl mg/L HCO3 mg/L SO4 mg/L NO3 mg/L Fe mg/L 1 40 97.2 319.9 6.89 514 1000 106 1.17 0.05 2 120 12.15 106.8 7.1 163.12 350 42 0.95 0.04 3 12 41.31 182.4 7.69 297.86 400 54 0.76 BDL 4 84 138.51 182.4 7.69 670.19 250 84 0.81 0.02 5 56 102.06 201.1 7.14 370.56 240 112 0.82 BDL 6 80 60.75 163.1 8.67 372.33 250 82 0.91 0.11 7 72 126.36 244.7 8.19 659.56 340 152 1.64 BDL 8 168 213.84 276.6 10.32 1219.82 340 260 1.45 0.34 9 60 80.19 108.7 5.61 241.12 300 77 2.71 BDL 10 80 201.7 197.9 9.91 886.5 310 162 0.70 0.58 11 20 72.9 52.43 3.73 156.02 230 25 1.59 0.03 12 36 99.63 70.5 4.45 187.93 260 67 1.03 BDL 13 24 102.06 193.6 7.38 429.06 320 90 0.89 0.43 14 40 85.05 158.1 5.53 219.85 380 86 0.64 BDL 15 480 388 386 20 1524.78 340 178.86 0.04 0.024 16 360 352.35 620 25 1489.32 260 341.46 0.03 0.022 17 172 65.61 120 11 141.84 300 80.13 0.03 0.01 18 520 230.85 362 19 1276.84 305 211.38 0.02 0.08 19 180 106.92 130 11 177.3 330 65.04 0.02 0.07 20 84 72 165 28 369 850 143 0.01 BDL 21 378 312 340 105 1504 490 490 0.02 BDL 22 116 71 241 32 270 750 132 0.01 BDL Asian Review of Environmental and Earth Sciences, 2019, 6(1): 70-77 76 © 2019 by the authors; licensee Asian Online Journal Publishing Group agricultural activity is common in Gadap town since long and the unlined sanitation is also adding up the ions in the groundwater system of study area. Figure-3. Piper diagram of groundwater samples from GADAP town. 3.5. WQI for Drinking Water in GADAP The WQI considers eleven weighted parameters including pH, TDS, Hardness, Na, K, Ca, Mg, HCO3, Cl, SO4 and NO3 to characterize water quality which has been summarized in Table 6. Weighted arithmetic index method of WQI has been used to assess the quality of groundwater in Gadap town. It is a simple method that aims at giving a single value to water quality by translating the list of parameters and their relative concentrations present in a sample into a single value. This single value in turn provides an extensive interpretation of the quality of water and its suitability for various purposes like drinking, irrigation, industrial etc. [33]. First step for calculating WQI of groundwater is to estimate the quality rating of each parameter using the formula: Qn=100*[(Vn – Vi) / (Vs‐ Vi)]. If quality rating Qn = 0 means complete absence of pollutants, while Qn ranging between 0 - 100 indicates that the pollutants are within the prescribed standard and in case of Qn >100 implies that, the pollutants are above the standards [34]. Table-5. Water quality index (WQI) of all collected water samples. Parameters Observed value (Vn) WHO Limits (Vs) Ideal value (Vi) Vn-Vi Vs-Vi Qn Wn=k/Vn Qn*Wn pH 7.5 8.5 7 0.5 1.5 33.33 0.38 12.88 TDS 1402.1 500 0 1402.1 500 280.42 0.00 0.58 Hardness 927.5 500 0 927.5 500 185.5 0.00 0.58 Na 219.1 200 0 219.1 200 109.55 0.01 1.45 K 15.9 12 0 15.9 12 132.5 0.18 24.16 Ca 144.6 75 0 144.6 75 192.8 0.02 3.86 Mg 137.8 150 0 137.8 150 91.86 0.02 1.93 Cl 597.3 250 0 597.3 250 238.92 0.00 1.16 HCO3 390.6 300 0 390.6 300 130.2 0.00 0.96 SO4 138.2 250 0 138.2 250 55.28 0.02 1.16 NO3 0.7 10 0 0.7 10 7.0 4.14 29 WQI = 16.18 In collected samples, Qn of TDS (280.42), hardness (185.5), Ca (192.8), Na (109.55), K (132.5), HCO3 (130.2) and Cl (238.92) are above 100 which indicates that these are the main components responsible for deteriorating the water quality Table 5. Moreover, chloride and bicarbonate of Ca, Na and K are mainly responsible for elevated hardness and very high TDS content in the groundwater of study area. However, the overall result determined by operation on concerned quality parameters the WQI value of 16.18 which according to Brown, et al. [8] is still of pristine in nature Table 6. Table-6. WQI range, status and possible usage of the water sample (Brown et al. 1972). WQI Water quality status (WQS) Possible usage 0–25 Excellent Drinking, irrigation and industrial 26–50 Good Drinking, irrigation and industrial 51–75 Poor Irrigation and industrial 76–100 Very poor Irrigation Above 100 Unsuitable for drinking and fish culture Proper treatment required before use Source: Brown, et al. [8]. Asian Review of Environmental and Earth Sciences, 2019, 6(1): 70-77 77 © 2019 by the authors; licensee Asian Online Journal Publishing Group 4. Conclusion Present study revealed that generally the groundwater quality of Gadap town is good for drinking purpose as indicated by water quality index of study area (16.18). However, some parameters are exceeding the permissible limit of WHO in a few wells. 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