Groundwater Quality Issues and Challenges for Drinking and Irrigation Uses in Central Ganga Basin Dominated with Rice-Wheat Cropping System

water

Article Groundwater Quality Issues and Challenges for Drinking and Irrigation Uses in Central Ganga Basin Dominated with Rice-Wheat Cropping System

Sumant Kumar 1,* , Manish Kumar 2, Veerendra Kumar Chandola 2, Vinod Kumar 1, Ravi K. Saini 1, Neeraj Pant 3, Nikul Kumari 4 , Ankur Srivastava 4,* , Surjeet Singh 1, Rajesh Singh 5 , Gopal Krishan 1 , Shashi Poonam Induwar 6, Sudhir Kumar 3, Brijesh Kumar Yadav 7, Nityanand Singh Maurya 8 and Anju Chaudhary 1

1 Groundwater Hydrology Division, National Institute of Hydrology, Roorkee 247667, India; [email protected] (V.K.); [email protected] (R.K.S.); [email protected] (S.S.); [email protected] (G.K.); [email protected] (A.C.) 2 Department of Farm Engineering, Institute of Agricultural Sciences, Banaras Hindu University, Varanasi 221005, India; [email protected] (M.K.); [email protected] (V.K.C.) 3 Hydrological Investigation Division, National Institute of Hydrology, Roorkee 247667, India; [email protected] (N.P.); [email protected] (S.K.) 4 School of Engineering, The University of Newcastle, Callaghan, NSW 2308, Australia; [email protected] 5 Environmental Hydrology Division, National Institute of Hydrology, Roorkee 247667, India; Citation: Kumar, S.; Kumar, M.; [email protected] 6 Chandola, V.K.; Kumar, V.; Saini, R.K.; Central India Hydrology, National Institute of Hydrology-Regional Centre, Bhopal 462016, India; [email protected] Pant, N.; Kumari, N.; Srivastava, A.; 7 Department of Hydrology, Indian Institute of Technology, Roorkee 247667, India; [email protected] Singh, S.; Singh, R.; et al. 8 Department of Civil Engineering, National Institute of Technology, Patna 800005, India; [email protected] Groundwater Quality Issues and * Correspondence: [email protected] (S.K.); [email protected] (A.S.) Challenges for Drinking and Irrigation Uses in Central Ganga Abstract: Increased population and increasing demands for food in the Indo-Gangetic plain are Basin Dominated with Rice-Wheat likely to exert pressure on fresh water due to rise in demand for drinking and irrigation water. The Cropping System. Water 2021, 13, study focuses on Bhojpur district, Bihar located in the central Ganga basin, to assess the groundwater 2344. https://doi.org/10.3390/ w13172344 quality for drinking and irrigation purpose and discuss the issues and challenges. Groundwater is mostly utilized in the study area for drinking and irrigation purposes (major crops sown in the area

Academic Editors: Claudia Cherubini are rice and wheat). There were around 45 groundwater samples collected across the study region 2+ 2+ and Domenico Cicchella in the pre-monsoon season (year 2019). The chemical analytical results show that Ca , Mg and − HCO3 ions are present in abundance in groundwater and governing the groundwater chemistry. Received: 9 July 2021 Further analysis shows that 66%, 69% and 84% of the samples exceeded the acceptable limit of arsenic Accepted: 23 August 2021 (As), Fe and Mn respectively and other trace metals (Cu, Zn, Pb, Cd) are within the permissible limit Published: 26 August 2021 of drinking water as prescribed by Bureau of Indian Standard for drinking water. Generally, high As concentration has been found in the aquifer (depth ranges from 20 to 40 m below ground surface) Publisher’s Note: MDPI stays neutral located in proximity of river Ganga. For assessing the irrigation water quality, sodium adsorption with regard to jurisdictional claims in ratio (SAR) values, residual sodium carbonate (RSC), Na%, permeability index (PI) and calcium published maps and institutional afﬁl- alteration index (CAI) were calculated and found that almost all the samples are found to be in iations. good to excellent category for irrigation purposes. The groundwater facie has been classiﬁed into

Ca-Mg-HCO3 type.

Keywords: Bhojpur; groundwater; drinking; irrigation; quality; central Ganga Copyright: © 2021 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and 1. Introduction conditions of the Creative Commons Attribution (CC BY) license (https:// Groundwater (GW) act as a vital natural resources for millions of people in India creativecommons.org/licenses/by/ and around the globe for drinking, irrigation and industrial uses. Several studies have 4.0/). highlighted tremendous overexploitation of the groundwater across the world probably

Water 2021, 13, 2344. https://doi.org/10.3390/w13172344 https://www.mdpi.com/journal/water Water 2021, 13, 2344 2 of 19

due to the advancement in industry and urban sectors [1,2]. GW being one of the most important components of the hydrological cycle which contributes to the sub-surface flow, makes it crucial in several hydrological models [3,4]. In order to decide the water suitability for various purposes such as domestic usage and irrigation, the GW quality requires special attention. Deteriorating GW quality on both regional and global scale causes apprehension for policy makers, researchers, engineers etc. [5]. Geogenic contamination of groundwater occurs due to various geo-chemical and biological reactions takes place while interaction of water with aquifer material, and anthropogenic contamination is due to human interferences in the environment [6,7]. Recently, various activities extending from GW extraction, excessive utilization of fertilizers, pesticides and domestic and industrial discharge reflects serious GW contamination [8–11]. It is very difficult to restore GW once it gets contaminated. Groundwater serves about 80% of rural population and 50% of urban population of India [12,13]. Groundwater structures are increasing at an exponential rate to meet the water requirement for different purposes. The Indo-Gangetic plain accounts for 25% of global GW extraction and is one of the most important water systems on the Earth. The middle Gangetic plain (GP) plays an important role in providing livelihood to millions from its dominant rice–wheat cropping system [14]. The people use groundwater due to its fascinating features, such as its large storage volume, it can be extracted based on requirement, its lower risk compared to other surface water sources, etc. The key factor such as demand management, recharge enhancement and alternative water sources needs to be examined for GW sustainability and maximizing the value by proper utilization [15]. Various parts of India have been reported by GW contamination due to the presence of salinity, fluoride, arsenic, iron and nitrate content in the water. The use of natural resources in unplanned way resulting into more production of waste which pose a threat to groundwater. The groundwater pollution in several parts of the India is increasing at an alarming rate and it is high time to identify the sources and abate or remediate before it causes extensive damage to public health. The GW quality assessment is an important tool for examining groundwater utilization for drinking and irrigation purposes [16]. It is also affected by different processes extending from atmospheric condensation to the water discharged from a well. Additionally, GW quality differs from aquifer to aquifer, water table depth, season to season and retention time which affect the composition of dissolved solids present in it. It is necessarily required to perform water quality assessment for drinking water and irrigation purposes [17–19]. The Bhojpur district, Bihar located in the central Ganga basin has been selected for the present study. The economy of the district is dominated mostly by agriculture. The alluvial plain of study area shows dynamic characteristic of rivers (Ganga and Son) and depositional pattern of sediments. The lower and middle GP including Bhojpur district is affected by rampant occurrence of arsenic [11,20]. A numbers of studies have been carried out in lower GP to investigate occurrence and distribution of arsenic including other water quality parameters. However, very few studies have been reported for the present study area. A hydro-chemical study was carried out to identify groundwater chemistry and to assess the suitability for drinking and irrigation uses. A systematic approach was adopted for sampling, analyses and interpretation of primary and secondary data viz. hydrogeological and hydro-chemical. The outcome of this study may help in designing groundwater monitoring networks and remedial measures at regional and national levels.

2. Study Area Bhojpur district, with a total geographical area of 2395 km2, is situated in Bihar state and was selected as the study area. The study area is located in central Ganga basin and lies within 25◦100 to 25◦400 N and 84◦100 to 84◦500 E. The district is covered by two major rivers viz., Ganga and Son in the north and eastern side (Figure1). The population of the district is 27.20 lakh with population density of 1136 inhabitants per square kilometer. Water 2021, 13, x FOR PEER REVIEW 3 of 19

2. Study Area Bhojpur district, with a total geographical area of 2395 km2, is situated in Bihar state and was selected as the study area. The study area is located in central Ganga basin and Water 2021, 13, 2344 lies within 25°10′ to 25°40′ N and 84°10′ to 84°50′ E. The district is covered by two major3 of 19 rivers viz., Ganga and Son in the north and eastern side (Figure 1). The population of the district is 27.20 lakh with population density of 1136 inhabitants per square kilometer.

Figure 1. Study area located in central Ganga basin, drainage network, geological map with sampling locations. Figure 1. Study area located in central Ganga basin, drainage network, geological map with sampling locations.

2.1.2.1. Hydroclimatology Hydroclimatology TheThe study study area area has has dry dry sub sub humid humid region region with with a warm and humid climate. Figure Figure 22 showsshows the the mean mean monthly monthly precipitation precipitation for for 30 30 years years (1991 (1991–2020)–2020) for the Bhojpur district. It It isis shown shown that JuneJune toto OctoberOctober months months reﬂect reflect the the Kharif Kharif season season while while October October to March to March rep- representsresents the the Rabi Rabi season. season. It canIt can be be seen seen that that the the average average monthly monthly precipitation precipitation is highestis highest in inthe the Kharif Kharif season season accounting accounting 266 mm 266 in July.mm Almost in July. ~87% Almost of average ~87% annual of average precipitation annual precipitationoccurs during occurs Kharif during season Kharif and most season of the and rainfall most of (about the rainfall 85%) occurs (about in 85%) the south occurs west in themonsoon south [ west20]. The monsoon cumulative [20]. precipitation The cumulative increases precipitation from January increases to December from January reaching to Decemberits maximum reaching value its of 950maximum mm. value of 950 mm. AprilApril and and May May are are the the hottest hottest months month suchs such that average that average monthly monthly temperature temperature reaches reacto 35hes◦C, to whereas 35 °C, Januarywhereas experiences January experiences the lowest meanthe lowest minimum mean monthly minimum temperature, monthly temperaturefalling down, falling to ~9 ◦ C.down The to average ~9 °C. monthlyThe average temperature monthlyranges temperature between ranges 25 ◦C between to 35 ◦C 25 in ◦ ◦ °CKharif to 35 season °C in Kharif while ~15seasonC towhile 25 ~15C in °C Rabi to 25 season. °C in Rabi season.

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Figure 2. (a) Average monthly precipitation and cumulative rainfall (b) average, minimum and Figure 2. (a) Average monthly precipitation and cumulative rainfall (b) average, minimum and maximum monthly temperature highlighting the Kharif and Rabi season. maximum monthly temperature highlighting the Kharif and Rabi season.

2.2.2.2. Hydrogeology Hydrogeology TheThe riverriver GangaGanga originatesoriginates from the Himalaya Himalaya and and transports transports sediments sediments through through its itscourse course of of travelling travelling in in the the plain plain area. area. The The deposited deposited sediments sediments determine determine the the water wa- terchemistry chemistry of of the the area area due due to to several several processes such as as rock rock weathering, weathering, rock–water rock–water interactioninteraction etc. etc. AlluvialAlluvial soilssoils areare mainlymainly formedformed duedue toto sediment sediment depositsdeposits byby thethe Indo- Indo- Gangetic-BrahmaputraGangetic-Brahmaputra rivers rivers and Himalayanand Himalayan rocks form rocks the parent form material. the parent Geologically, material. theGeologically, alluvial soils the are alluvial divided soils into are younger divided andinto olderyounger alluvium and older and alluvium they are and best they suited are forbest agriculture. suited for The agriculture. older alluvium The olderrepresents alluvium the upland represents alluvial the tract upland whereas alluvial younger tract alluviumwhereas formsyounger the floodalluvium plains. forms The the district flood Bhojpur plains. is The occupied district by Bhojpur Quaternary is occupied Alluvium, by whichQuaternary forms theAlluvium, potential which aquifers. forms The the Bhojpurpotential district aquifers. is coveredThe Bhojpur by alluvial district formation; is covered northernby alluvial part formation; is enclosed northern by younger part is alluvium enclosed whereas by younger central alluvium and southern whereas part central is cov- and eredsouthern by older part alluvium is covere (Figured by older1). The alluvium older alluvium (Figure 1). of The the studyolder areaalluvium consists of the of darkstudy colouredarea consists clay and of dark silt rich coloured with lime clay nodules and silt locally rich with known lime as nodules Kankars. locally It is generally known as poorlyKankars. sorted It is and generally less permeable. poorly sorted The unconsolidated and less permeable. younger The alluvium unconsolidated occurs along younger the floodalluvium plain occurs of rivers along Ganga the and flood Son plain and itof is rivers characterized Ganga and by sandySon and clay, it loamis characterized and contains by lesssandy calcareous clay, loam matter. and Incontains the study less area, calcareous the top matter. layer of In geological the study stratum area, the (within top layer 30 m of bgl)geological is an aquitard stratum (Figure (within3), 30 which m bgl) supports is an aquitard dug wells (Figure and shallow 3), which hand supports pumps. dug In fact,wells itand works shall asow an hand unconfined pumps. aquifer.In fact, it Fromworks 30 as m an to unconfined approx. 100 aquifer. m bgl, From medium 30 m to approx. coarse sand100 m forms bgl, themedium aquifer to andcoarse after sand that forms a thick the layer aquifer (20–30 and m) after of claythat isa present.thick layer The (20 deeper–30 m)

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aquifers (>130 m bgl) are under either semi-conﬁned or conﬁned conditions which sustain theofof clay deep clay is is wells present. present. in the The The area deeper deeper [20]. aquifers aquifers (> (>130130 m m bgl) bgl) are are under under either either semi semi-confined-confined or or confinedconfined conditions conditions which which sustain sustain the the deep deep wells wells in in the the area area [20]. [20].

(a) (b) (a) (b) Figure 3. (a) Borelogs location in the study area; (b) fence diagram representing geological settings. FigureFigure 3. 3.( a()a) Borelogs Borelogs location location in in the the study study area; area (;b ()b fence) fence diagram diagram representing representing geological geological settings. settings. The groundwater level data analyses (data collected from Central Ground Water TheThe groundwater groundwater level level data data analyses analyses (data (data collected collected from from Central Central Ground Ground Water Water BoardBoard (CGWB))(CGWB)) shows variation of groundwater level level across across the the study study area. area. The The deepest deepest Board (CGWB)) shows variation of groundwater level across the study area. The deepest groundwatergroundwater level was observed in the north and and northeast northeast part part of of the the study study area. area. The The groundwater level was observed in the north and northeast part of the study area. The unconﬁnedunconfined aquiferaquifer has has an an average average groundwater groundwater level level ranging ranging from from 3 m 3 bglm bgl to 9 to m 9 bgl m (databgl unconfined aquifer has an average groundwater level ranging from 3 m bgl to 9 m bgl collected(data collected in pre-monsoon in pre-monsoon season, season, May May 2017); 2017); the hydraulic the hydraulic gradients gradients is about is about 0.0005 0.0005 and (data collected in pre-monsoon season, May 2017); the hydraulic gradients is about 0.0005 groundwaterand groundwater ﬂow flowdirections directions are north are north and northeast and northeast (Figure (Figure4) towards 4) towards the river the Ganga. river and groundwater flow directions are north and northeast (Figure 4) towards the river InGanga. the pre-monsoon In the pre-monsoon season, season, groundwater groundwater feeds into feeds the into Ganga the river.Ganga river. Ganga. In the pre-monsoon season, groundwater feeds into the Ganga river.

Figure 4. Water table elevation and groundwater flow direction in the study area. Figure 4. Water table elevation and groundwater flow direction in the study area. Figure 4. Water table elevation and groundwater ﬂow direction in the study area.

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2.3. Land use Use Land Land Cover Cover The land use land cover (LULC) map has beenbeen preparedprepared usingusing Landsat-8Landsat-8 satellitesatellite imagery (year (year 2018, 2018, 30 30 m resolution) m resolution) obtained obtained from from United United States States Geological Geological Survey (USGS)Survey website.(USGS) website. The LULC The classiﬁcationLULC classification (Figure (5Figure) showed 5) showed the major the major land use land types use types such thatsuch vegetationthat vegetation constitutes constitutes ~46.13% ~46.13 of% total of area, total followed area, followed by built-up by built area-up (21.64%), area (21.64 fallow%), (16.52%),fallow (16.52 barren%), barren land (7.37%), land (7.37 sand%), bank sand (6.08%) bank (6.08 and% water) and (2.26%). water (2.26%).

Figure 5. The Land use and Land cover (LULC) classiﬁcationclassification in the study area.

2.4. Agricultural Practices Agriculture is the principal economic activity in thethe BhojpurBhojpur district.district. The district is considered as the rice bowl in the state and Rice-Rice- mill is a traditional industry. The major food crops apart from ricerice areare wheat,wheat, pulses,pulses, oiloil seedsseeds andand maizemaize etc.etc. TheThe geographicalgeographical area is 233,729 Ha out of which 188,134 Ha is net cultivable area with nil forested area as per data of DepartmentDepartment of Agriculture,Agriculture, Govt.Govt. of Bihar. The net irrigation area in KharifKharif season is 100,407 Ha and in Rabi seasonseason itit becomesbecomes 68,78168,781 Ha.Ha. In the KharifKharif season,season, thethe irrigated area covered by canal, private tube well, lift irrigation, statestate tubetube wells andand other sources are are 7 72,952,2,952, 24 24,478,,478, 838, 838, 454, 454, 1685 1685 Ha Ha where where as as in inRabi Rabi season season the the areas areas covered covered by theby theirrigation irrigation sources sources are are 29 29,700,,700, 36 36,717,,717, 153, 153, 526 526 and and 1685 1685 Ha Ha,, respectively. respectively. The major kharif crops in the district are rice, maize and gram etc and major rabi crops are wheat, pulses, gram, mustard, potatoes etc. 3. Methodology 3. Methodology 3.1. Data Collection and Instrumentation 3.1. Data Collection and Instrumentation A systematic sampling campaign was made and 45 groundwater samples were col- lectedA in systematic the pre-monsoon sampling season campaign (May 2019) was as made shown and in Figure45 groundwater1. A clean polypropylene samples were collectedbottles were in used the for pre storing-monsoon the water season and (May the samples 2019) as were shown brought in toFigure laboratory 1. A for clean the polypropyleneions and trace metals bottles analyses. were used The for groundwater storing the sampleswater and were the collected samples fromwere thebrought existing to laboratoryhand pumps for (HPs) the in ions the and study trace area metals (screening analyses. depth The of HPs groundwater varies from samples 15 m to 60 were m collectedbelow ground from surfacethe existing in unconfined hand pumps aquifer) (HPs) and in the the details study of area water (screening sampling depth is presented of HPs variesin Table from A1. 15 The m purgingto 60 m below of hand ground pumps surface for 15–20 in unconfined min was conducted aquifer) and before the taking details the of water samples.sampling The is presented water samples in Table were A1. filtered The purging through of 0.45 handµm pumps membrane for 15 filter–20 andmin thenwas conductedstored in the before sampling taking bottles. the water The physicalsamples. parameters The water suchsamples as pH, were and filtered EC were through measured 0.45

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in-situ using portable instruments (HQ40d portable meter, Hach, CO, USA). The water samples were analyzed for major ions using Ion-Chromatography (Dionex Series ICS-5000, Thermo Fisher Scientiﬁc, CA, USA) and Inductively Coupled Plasma-Optical Emission Spectrometry (VDV 5110, Agilent Technologies, CA, USA) respectively. The inorganic chemical parameters were analyzed following the procedures of standard methods [21,22]. The samples were run in triplicate and relative errors were less than ±6% for the analyzed water quality parameters. Groundwater samples were acidiﬁed onsite with HNO3 to reduce pH < 2 for trace metals (As, Fe, Mn, Pb, Zn, Cu and Cd) analyses.

3.2. Electrical Conductivity (EC) and Sodium Percentage (Na%) The EC and Na% are important water quality indicator for classifying irrigation water [23]. Dissolved substance as salts are always present in water used for irrigation. The Na% was calculated by the equation:

(Na + K) Na% = ∗ 100 (1) (Ca + Mg + Na + K)

where Na, Ca and Mg concentrations is in milli-equivalents per liter.

3.3. Alkali and Salinity Hazard (SAR) The sodium or alkali hazard was determined by sodium adsorption ratio (SAR). SAR is determined by ratio of sodium and divalent cations as mentioned below:

Na SAR = (2) r 2 Ca+Mg 2

where Na, Ca and Mg concentrations is in milli-equivalents per liter.

3.4. Residual Sodium Carbonate (RSC) Residual Sodium Carbonate (RSC) is also used as an index to indicate salinity hazard. When RSC increases, Ca and Mg gets precipitated from the water solution and thus increases the sodium percentage which increases the potential of sodium hazard. This excess is denoted by RSC and is expressed as

2− − 2+ 2+ RSC = (CO3 + HCO3 ) − (Ca + Mg ) (3)

2− − where CO3 and HCO3 are expressed in milli-equivalents per liter. Generally, water with RSC value > 2.5 is not considered ﬁt for irrigation use, whereas RSC less than 1.25 is considered safe for irrigation water. A negative RSC values suggest that Ca2+ and Mg2+ is in surplus, while a positive RSC indicates presence of Na+ in the soil [7,24]. Based on the of RSC value, sodium hazard is classiﬁed as low (RSC < 1.25, medium (RSC 1.25–2.5) and high (RSC > 2.5).

3.5. Chloroalkaline Indices (CAI-I and CAI-II) The Chloroalkaline indices are used to study the ion exchange processes between the groundwater and the aquifer while travelling and interacting with each other. Schoeller [25] proposed the CAI-I and CAI-II and expressed by following equations.

Cl− − (Na+ + K+) CAI − I = (4) Cl−

Cl− − (Na+ + K+) CAI − II = (5) 2− − − − SO4 + CO3 + HCO3 + NO3 Water 2021, 13, 2344 8 of 19

The CAI-I and CAI-II indices indicates the exchange processes between alkali and alkaline earth metals and the values may be positive or negative. If CAI value is positive then it describes the exchange of Na+ and K+ in water with Mg2+ and Ca2+ in rocks. If CAI value is negative then it implies that a reverse exchange process occurs i.e., Mg2+ and Ca2+ in water with Na+ and K+ in rocks.

3.6. Permeability Index (PI) The PI is an indicator to assess the appropriateness of water for irrigation uses. The permeability of soil may get affected when long term irrigation water containing high salt is applied in the ﬁeld. Doneen [26] formulated PI as given below:

+ q − Na + HCO3 PI = × 100 (6) Ca2+ + Mg2+ + Na+

The ions concentrations of the above equation are in meq/L Doneen [26] classiﬁed water into three classes: suitable (class I, PI > 75%), good (class II, PI is in the range of 25–75%) and unsuitable (class III, PI < 25%). class I and class II is considered suitable for irrigation.

4. Results and Discussion The analytical result of major ions, trace metals etc. is presented in Table1 and the results were compared with prescribed limit for drinking water by Bureau of Indian Standard (BIS) [27]. The chemical results were correlated with hydro geomorphological characteristic of the area. The Na%, SAR, RSC, CAI and PI values were calculated to check suitability for irrigation purpose.

Table 1. Statistical summary of groundwater quality in the study area.

BIS (2012) BIS (2012) Parameters Minimum Maximum Average Std. Dev. Acceptable Limit Permissible Limit pH 6.9 8.5 7.6 0.4 6.5–8.5 - EC 277 1415 683 213 - - TDS (mg/L) 237 1034 538 161 500 2000 TH (mg/L) 122 616 292 105 200 600 Ca (mg/L) 32 140 74 25.1 75 200 Mg (mg/L) 10 65 26 12.2 30 100 Na (mg/L) 10 73 28 13.0 - - K (mg/L) 0.42 70.37 3.93 10.1 - - F (mg/L) BDL 0.58 0.22 0.13 1 1.5 Cl (mg/L) 1 91 18 19.0 250 1000 HCO3 (mg/L) 166 639 373 373 - - SO4 (mg/L) 4 43 11 11 200 400 NO3 (mg/L) BDL 29.4 2.3 6.7 45 NR As (ppb) BDL 336 73 99.7 10 50 Fe (ppm) 0.06 14.39 2.8 3.69 0.3 NR Mn (ppb) 2.1 1303 390 291 100 300 Pb (ppb) BDL 24 7.1 4.97 10 NR Zn (ppb) 110 2190 310 432 5000 15,000 Cd (ppb) BDL 2.7 0.7 0.58 3 NR Cu (ppb) BDL 10 4 1.86 50 1500 BDL: Below detection limit; NR: No relaxation.

4.1. Hydrochemistry and Groundwater Quality Assessment for Drinking Water The pH value shows that GW is slightly alkaline in nature and all the samples were found to be in the acceptable limit of Indian drinking water standards. The EC value Water 2021, 13, 2344 9 of 19

indicated the occurrence of fresh water. The results show that 48% of the samples exceeded acceptable limit for TDS though they were within the permissible limit of BIS [27]. The total hardness (TH) is classified in soft, moderately hard and very hard category. About 64% samples were found under hard category and 36% under very hard category with concentration above 300 mg/L. In general, hardness of groundwater was not found within the acceptable limit of 200 mg/L but was within the permissible limit (600 mg/L). It is observed that the GW in this study area is dominated by alkaline earth metals. For instance, Ca alone constitute 55.9% of the total cations in the groundwater of the study area. The majority of the water samples follow the majority of ions in order of Ca2+ > Na+ > Mg2+ > K+. About 58% of samples were found within the acceptable limit for Ca; while 42% of samples exceeded the acceptable limit. Magnesium (Mg) is abundant in earth crust and is a common constituent of natural water [28]. Results suggested that 77.8% of samples were within acceptable limit for drinking water, while remaining 22.2% of sample crossed the prescribed acceptable limit. The sodium is actually derived from different sources ranging from atmospheric deposition, evaporate dissolution and silicate weathering [29,30]. The sodium and potassium concentration was low and were found within the acceptable limit. Generally, potassium reported to be one-tenth or even one-hundredth that of sodium in groundwater. In anions, bicarbonates is the dominant anion and follows the abundance − − 2− − − in the order of HCO3 > Cl > SO4 > NO3 > F in the groundwater samples. HCO3 contribute to alkalinity (acid neutralizing capacity) and 91% of the samples were found within the permissible limit. HCO3 shows a strong positive correlation with Ca, Mg and Na (Table2). The chloride concentrations were within the acceptable limit. High concentrations of chloride lead to a salty taste in water. High sulphate level produces salty taste which makes it unpleasant for drinking and very high concentration might cause laxative effect in human. For the present case, sulphate concentration were within the acceptable limit. The excess application of fertilizers, leakages from sewage system etc. may cause GW contamination by nitrate, and fluoride occurrence in the groundwater is reported to be geogenic [31]. The nitrate and fluoride concentration were within the prescribed drinking water limit but nitrate concentration was observed high at few locations.

Table 2. Inter-elemental correlation matrix of major ions.

pH EC TDS F Cl HCO3 SO4 NO3 Ca Mg Na K pH 1.0 EC −0.3 1.0 TDS −0.6 0.5 1.0 F 0.2 0.1 −0.3 1.0 Cl 0.0 0.6 0.3 0.0 1.0 HCO3 −0.3 0.8 0.3 0.1 0.3 1.0 SO4 0.1 0.5 0.2 0.1 0.8 0.2 1.0 NO3 0.1 0.3 0.2 0.1 0.5 0.2 0.5 1.0 Ca −0.4 0.7 0.4 0.0 0.6 0.7 0.4 0.3 1.0 Mg −0.1 0.8 0.3 0.1 0.6 0.8 0.5 0.4 0.7 1.0 Na −0.1 0.7 0.4 0.1 0.7 0.6 0.6 0.4 0.6 0.7 1.0 K 0.1 −0.1 0.0 0.0 0.0 −0.1 0.2 0.0 −0.1 −0.1 0.0 1.0

The hydrochemistry of groundwater depends on various factors such as water–aquifer matrix interaction, residence time, weathering processes and various chemical processes takes place while surface water moves through the sediment and reaches to groundwater. There are three major processes control the geochemistry of the area: carbonate dissolution, evaporite dissolution and silicate weathering [11,14]. The Gibb’s plots and bivariate plots indicate the source of solutes and for the present case rock–water interaction is the dominant process controlling the geochemistry of the area (Figure6). Water 2021, 13, x FOR PEER REVIEW 10 of 19 Water 2021, 13, x FOR PEER REVIEW 10 of 19

groundwater.groundwater. There There are are three three major major processes processes contr controlol the the geochemistry geochemistry of of the the area: area: carbonate dissolution, evaporite dissolution and silicate weathering [11,14]. The Gibb’s Water 2021, 13, 2344 carbonate dissolution, evaporite dissolution and silicate weathering [11,14]. The Gibb’s10 of 19 plotsplots and and bivariate bivariate plots plots indicate indicate the the source source of of solutes solutes and and for for the the present present case case rock rock–water–water interactioninteraction is is the the dominant dominant process process contr controllingolling the the geochemistry geochemistry of of the the area area (Figure (Figure 6). 6).

Figure 6. Gibb’s plot of logarithmic value of TDS vs. Cl−/Cl− + HCO3− and Na+/Na+ + Ca++ Figure 6. Gibb’s plot of logarithmic value of TDS vs.− Cl−/Cl− − + HCO3−− and Na+/Na+ + Ca++ ++ Figure 6. Gibb’s plot of logarithmic value of TDS vs. Cl /Cl + HCO3 and Na /Na + Ca .

The bivariate plots between Ca + Mg and HCO3 + SO4 indicate both carbonate and The bivariate plots between CaCa ++ MgMg andand HCOHCO33 + SO4 indicate both carbonate andand silicate weathering with dominancy of silicate weathering processes as majority of data silicate weathering with dominancy of silicate weathering processes as majority of data pointspoints are are falling falling below below the the equalequal equal line line line (Figure( Figure(Figure7 a).7a). 7a). The The The data data data points points points on on on thethe the equalequal equal line line line representrepresent the the calcite calcite and and gypsum gypsum weathering weathering processes processes and and if if they they are are plotted plotted below below the the equal line, it implies that the excess of HCO3 + SO4 shall be balanced by alkalines (Na + K) equal line, it it implies implies that that the the excess excess of of HCO HCO3 3+ +SO SO4 shall4 shall be bebalanced balanced by byalkali alkalinesnes (Na (Na + K) + provided through silicate weathering. The Ca + Mg should be equal to HCO3 if they providedK) provided through through silicate silicate weathering. weathering. The The Ca Ca + +Mg Mg should should be be equal equal to to HCO33 ifif they derivedderived fromfrom from carbonatecarbonate carbonate source source source as as peras per per stoichiometric stoichiometric stoichiometric of of reaction. of reaction. reaction. The The plotThe plot betweenplot between between Ca +Ca MgCa + + Mg and HCO3 (Figure 7b) shows that maximum groundwater data are near the HCO3 axis Mgand and HCO HCO3 (Figure3 (Figure7b) 7b) shows shows that that maximum maximum groundwater groundwater data data are are near near the the HCO HCO33 axis whichwhich again again justify justify the the prevalence prevalence of of silicate silicate weathering. weathering. It It may may be be observed observed that that arsenic arsenic concentrationconcentration is is high high when when silicate silicate weathering weathering prevails. prevails. The The plot plot between between Ca Ca + +Mg, Mg, Na Na + + KK and and total total cations cations (Figure(Figure (Figure7 7cc,d) 7c,d),d) revealsreveals reveals thatthat that NaNa Na+ + K+K K increasesincreases increases withwith with increasingincreasing increasing dissolveddissolved dissolved saltssalts and and Ca Ca + +Mg Mg Mg are are are contributing contributing contributing more more as as cations. cations.

1414 1414 AsAs conc. conc. <10 <10 ppb ppb 1212 1212 AsAs conc. conc. 10-50 10-50 ppb ppb 1010 1010 AsAs conc. conc. >50 >50 ppb ppb 88 88 66 66 Ca+Mg(meq/L) Ca+Mg(meq/L)

Ca+Mg(meq/L) 4 Ca+Mg(meq/L) 4 bb 44 aa 22 22 00 0 0 00 22 44 66 88 1010 1212 1414 0 2 4 6 8 10 12 14 0 2 4 6 8 10 12 14 HCO3 (meq/L) HCO3 (meq/L) HCO3 + SO4 (meq/L) HCO3 + SO4 (meq/L)

Figure 7. Cont.

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WaterWater2021 2021, 13, 13, 2344, x FOR PEER REVIEW 1111 of of 19 19

18 18 1816 1816 1614 1614 1412 1412 1210 1210 108 108 86 86 c Total Cation(meq/L) 4 d 6 Total Cation(meq/L) 64 2 c Total Cation(meq/L) 4 d

Total Cation(meq/L) 42 0 2 0 0 1 2 3 4 2 0 0 2 4 6 8 10 12 14 0 0 1 2 3 4 Na + K (meq/L) 0 2 4Ca + 6Mg (meq/L)8 10 12 14 Ca + Mg (meq/L) Na + K (meq/L)

FigureFigure 7. 7.Bivariate Bivariate plots plots of of (a ()a Ca) Ca + Mg+ Mg vs. vs. HCO HCO3 +3 + SO SO4,(4,b (b) Ca) Ca + + Mg Mg vs.vs. HCO HCO3,(3, c()c) Na Na + + K K vs.vs. total total cation cation and and ( d(d) Ca) Ca + + Mg Mg vs.vs. total total cation cation concentration concentration in in the the groundwater groundwater samples. samples. Figure 7. Bivariate plots of (a) Ca + Mg vs. HCO3 + SO4, (b) Ca + Mg vs. HCO3, (c) Na + K vs. total cation and (d) Ca + Mg vs. total cation concentration in the groundwater samples. 4.2.4.2. Groundwater Groundwater Facies Facies Classiﬁcation Classification 4.2. TheGroundwaterThe major major ions ions Facies were were Classification plotted plotted on on the the Piper Piper trilinear trilinear diagram diagram to to classify classify and and designate designate ionicionic nature nature of of water water [32 ]. [32]. The The trilinear trilinear diagram diagram clearly clearly distinguishes distinguish thees samples the samples of differ- of The major ions were plotted on the Piper trilinear diagram to classify and designate entdifferent source source and samples and samples of similar of similar qualities qualities are shown are shown as a group. as a group. The ionic The signature ionic signature helps ionic nature of water [32]. The trilinear diagram clearly distinguishes the samples of inhelps understanding in understanding the principal the ionsprincipal controlling ions controlling the chemistry. the Piper chemistry. diagram Piper classiﬁed diagram all waterdifferent samples source into and ‘Ca-Mg-HCO samples of similartype’ qualities (Figure8 ).are shown as a group. The ionic signature classified all water samples into3 ‘Ca-Mg-HCO3 type’ (Figure 8). helps in understanding the principal ions controlling the chemistry. Piper diagram classified all water samples into ‘Ca-Mg-HCO3 type’ (Figure 8).

FigureFigure 8. 8.Piper Piper diagram diagram showing showing the the ionic ionic nature nature of of groundwater. groundwater. Figure 8. Piper diagram showing the ionic nature of groundwater. 4.3.4.3. Trace Trace Metals Metals 4.3. TheTraceThe trace traceMetals metals metals (As, (As, Cr, Cr, Cd, Cd, Mn, Mn, Cu, Cu, Fe Fe and and Zn) Zn) are are naturally naturally present present in in small small and and measurablemeasurable amounts amount ins thein environment. the environment. These These metals metals in small in amounts small amount may bes a necessarymay be a The trace metals (As, Cr, Cd, Mn, Cu, Fe and Zn) are naturally present in small and partnecessary of nutrition part ofbut nutrition a high concentration but a high concentration of these metals of become these metals toxic and become causes toxic health and measurable amounts in the environment. These metals in small amounts may be a hazards. The sources of trace metals contamination in groundwater or surface water may necessary part of nutrition but a high concentration of these metals become toxic and

Water 2021, 13, 2344 12 of 19

be due to industrial waste effluents, weathering of rocks and atmospheric deposition, etc. The statistical summary of trace metal results obtained in the study are given in the Table1. About 66% of samples exceeded the acceptable limit (10 ppb) of arsenic and 44% of samples crossed the permissible limit (50 ppb). The distribution of arsenic concentration present in groundwater in the study area is shown in Figure A1. The highest concentration of arsenic (>50 ppb) were found in recent alluvial deposits, in the north-eastern areas, along a band wide about 20 km and parallel to the river Ganga. It is observed that arsenic concentrations were below 50 ppb at depth greater than 50 m as probably confined aquifer encounters at that depth. In the central and southern part which is covered by older alluvium, the arsenic concentration was found to be less than 10 ppb even if at shallower depth (up to 50 m). The arsenic occurrence may be due to reductive dissolution of iron-hydroxide which is present in sediment [11]. However, the exact nature and mechanism involved in the movement process are still unknown. Various researchers [33–40] reported that river Ganga and its tributaries have carried Himalayan sediment laden with arsenic and deposited in its flood plain. In the present study area, it is observed that high arsenic concentration was present in depth range of 20–40 m in the aquifer in the flood plain of river Ganga. Other investigators [34–36] have also reported that arsenic is present in the unconfined aquifer of shallow depth (15–47 m) and arsenic concentration varied from traces to 1461 ppb. It is witnessed that 69% of the samples surpassed the acceptable limit of Fe. High iron in the study area may be due to the dissolution of iron bearing minerals present in the aquifer material. The result revealed that about 15.6% of the analyzed samples fell within the acceptable limit (100 ppb) of Mn, and 65% of sample crossed the permissible limit. All other trace metals were found to be in permissible limit for drinking water. Arsenic is showing Water 2021, 13, x FOR PEER REVIEWvery good correlation with Fe, moderate relation with Mn and weak or no correlation13 wasof 19 found with other trace metals (Figure9). The correlation between As and Fe also justify our findings that arsenic may be releasing form iron-hydroxide.

Figure 9. Cont.

Figure 9. Scatter plot (a) As vs. Fe (b) As vs. pb (c) As vs. Zn (d) As vs. Cd (e) As vs. Mn (f) As vs. depth.

4.4. Groundwater Quality Assessment for Irrigation GW suitability for irrigation purpose was assessed using EC, SAR, Na%, RSC, CAI and PI water quality indicators and the obtained results were compared with the Indian standard prescribed for irrigation uses. The Na% ranged between 12% and 62% (avg. 24%) (Table 3) which is falling under recommended values. The high percentage of Na causes deflocculating and impairment of the tilth and permeability of soils. The CAI-I and CAI- II values are negative for all the samples indicating that ion exchange may have happened between Ca2+ or Mg2+ in the groundwater with Na+ and K+ in the aquifer sediment. The permeability index (PI) ranged between 37.7% and 75.9%, with average value 54.1%. PI index result reveals that ~98% of samples were fallings under good class and while 2% under suitable category (PI > 75%). There is a significant association between SAR and sodium absorbed on the soil. If irrigation water containing high percentage of sodium and low calcium, then sodium may be absorbed on soil and it may disturb soil structure and causes clay particles dispersion. The calculated SAR value ranged from 0 to 2 meq/L and all the samples fell in excellent category. The residual sodium carbonate (RSC) ranged between 2.46 to 2.74 meq/L. The results indicated that about 75.5% samples fell in excellent category (RSC < 1.25 meq/L) while remaining under good category (RSC 1.25–2.5 meq/L). Good rainfall in the area might be one of the reasons which govern low RSC values (suitable range for irrigation).

Water 2021, 13, x FOR PEER REVIEW 13 of 19

Water 2021, 13, 2344 13 of 19

FigureFigure 9. 9.Scatter Scatter plotplot (a(a)) As As vs. vs. FeFe ((bb)) As As vs. vs. pbpb ((cc)) AsAs vs.vs. ZnZn ((dd)) AsAs vs.vs. CdCd ((ee)) AsAs vs.vs. MnMn ((ff)) AsAs vs.vs. depth.depth.

4.4.4.4. Groundwater QualityQuality AssessmentAssessment forfor IrrigationIrrigation GWGW suitabilitysuitability forfor irrigationirrigation purposepurpose waswas assessedassessed usingusing EC,EC, SAR,SAR, Na%,Na%, RSC,RSC, CAICAI andand PIPI waterwater qualityquality indicatorsindicators andand thethe obtainedobtained resultsresults werewere comparedcompared withwith thethe IndianIndian standardstandard prescribedprescribed forfor irrigationirrigation uses.uses. TheThe Na%Na% rangedranged betweenbetween 12%12% andand 62%62% (avg.(avg. 24%) (Table(Table3 )3) which which is is falling falling under under recommended recommended values. values. The The high high percentage percentage of of Na Na causes causes deflocculating and impairment of the tilth and permeability of soils. The CAI-I and CAI-II deflocculating and impairment of the tilth and permeability of soils. The CAI-I and CAI- values are negative for all the samples indicating that ion exchange may have happened II values are negative for all the samples indicating that ion exchange may have happened between Ca2+ or Mg2+ in the groundwater with Na+ and K+ in the aquifer sediment. The between Ca2+ or Mg2+ in the groundwater with Na+ and K+ in the aquifer sediment. The permeability index (PI) ranged between 37.7% and 75.9%, with average value 54.1%. PI permeability index (PI) ranged between 37.7% and 75.9%, with average value 54.1%. PI index result reveals that ~98% of samples were fallings under good class and while 2% index result reveals that ~98% of samples were fallings under good class and while 2% under suitable category (PI > 75%). under suitable category (PI > 75%). TableThere 3. Parameters’ is a significant value for association classification between of irrigation SAR water.and sodium absorbed on the soil. If irrigation water containing high percentage of sodium and low calcium, then sodium may Parameters Minimumbe absorbed Maximum on soil and it may Average disturb soil IS structure 11,624 (1986): and Classification causes clay particles of Irrigation dispersion. Water The calculated SAR value ranged from 0Class: to 2 Lowmeq/L (Below and 1500),all the Medium samples (1500–3000), fell in excellent High EC (µS/cm) 277 1415 683 category. The residual sodium carbonate (RSC)(3000–6000) ranged between Very high 2.46 (Above to 2.74 6000) meq/L. The Na (%) 12results indicated 62 that about 75.5% 24 samples fell in excellent category - (RSC < 1.25 meq/L) Class: Low (Below 10), Medium (10–18), High SAR 0.3while remaining 1.7 under good 0.7 category (RSC 1.25–2.5 meq/L). Good rainfall in the area might be one of the reasons which govern low RSC(18–26), values Very (suitable high (Above range 26)for irrigation). Class-I RSC < 1.25 (low-Safe), Class-II RSC 1.25–2.5 RSC −2.7 2.5 0.3 (med. marginal) Class III > 2.5 (high-unsafe) Suitable (Class I, >75%), Good (Class II, 25–75%), PI 72.4 41.3 52.1 Unsuitable (Class III, <25%). CAI-I −11.7 −0.93 −1.6 Class I Positive (+) CAI, Class II Negative (−) CAI-II −0.14 −0.20 −0.13

There is a signiﬁcant association between SAR and sodium absorbed on the soil. If irrigation water containing high percentage of sodium and low calcium, then sodium may be absorbed on soil and it may disturb soil structure and causes clay particles dispersion. The calculated SAR value ranged from 0 to 2 meq/L and all the samples fell in excellent category. The residual sodium carbonate (RSC) ranged between 2.46 to 2.74 meq/L. The results indicated that about 75.5% samples fell in excellent category (RSC < 1.25 meq/L) while remaining under good category (RSC 1.25–2.5 meq/L). Good rainfall in the area might be one of the reasons which govern low RSC values (suitable range for irrigation). Plot of analytical data on Wilcox diagram [41] relating EC to Na% showed that 97.8% of groundwater samples of the study fell in excellent to good quality region, which can be used for irrigation purposes (Figure 10). Water 2021, 13, x FOR PEER REVIEW 14 of 19

Table 3. Parameters’ value for classification of irrigation water.

Parameters Minimum Maximum Average IS 11,624 (1986): Classification of Irrigation Water Class: Low (Below 1500), Medium (1500–3000), High (3000–6000) Very EC (µS/cm) 277 1415 683 high (Above 6000) Na (%) 12 62 24 - Class: Low (Below 10), Medium (10–18), High (18–26), Very high (Above SAR 0.3 1.7 0.7 26) Class-I RSC < 1.25 (low-Safe), Class-II RSC 1.25–2.5 (med. marginal) Class RSC −2.7 2.5 0.3 III > 2.5 (high-unsafe) Suitable (Class I, >75%), Good (Class II, 25–75%), Unsuitable (Class III, PI 72.4 41.3 52.1 <25%). CAI-I −11.7 −0.93 −1.6 Class I Positive (+) CAI, Class II Negative (−) CAI-II −0.14 −0.20 −0.13

Water 2021, 13, 2344 Plot of analytical data on Wilcox diagram [41] relating EC to Na%14 ofshowed 19 that 97.8% of groundwater samples of the study fell in excellent to good quality region, which can be used for irrigation purposes (Figure 10).

100

30 good to Excllent

Sodium Sodium (%) Percentage 20

10 Unsuitable Doubtful to to Doubtfulunsuitable 0 permissible to Good 0 1000 2000 3000 4000 5000 Electrical Conductivity (μS/cm)

Figure 10. PlotFigure of sodium 10. Plot percent of sodium (Na%) percent vs. electrical (Na%) conductivityvs. electrical (EC).conductivity (EC).

The total solubleThe salts total in irrigation soluble watersalts in determines irrigation salinity water zone determines as low (EC salinity = <250 zoneµS/cm), as low (EC = <250 medium (EC 250–750µS/cm),µS/cm), medium high (EC (EC 250 750–2250–750 µS/cm),µS/cm) high and (EC very 750 high–2250 (EC 2250–5000µS/cm) andµS/cm) very high. (EC 2250– High value of EC5000 in µS/cm). water leads High to value salinity of andEC in high water sodium leads concentration to salinity and leads high to sodium alkalin- concentration ity in soil. It isleads reported to alkalinitythat generally in soil. high It concentration is reported that of solutes generally is present high concentration in irrigation of solutes is water in areaspresent where evaporation in irrigation is water maximum in areas [42]. where Normally, evaporation salinity isproblem maximum arises [42]. Normally, where drainagesalinity is poor problem in irrigated arises agriculture. where drainage Due tois poor the poor in irr drainage,igated agriculture. water table Due to the poor rises and due todrainage, capillary water action, table sodium rises and salts due accumulate to capillary in action the soil, sodium near the salts root accumulate zone in the soil of the plants. Innear the the present root zone study, of no the samples plants. fellIn the in thepresent low salinitystudy, no category; samples however, fell in the low salinity 69% and 31% samplescategory; fell however, in medium 69% and and 31% high samp salinityles fell category in medium which and may high be salinity due to category which shallow watermay table be in due the to area. shallow Conjunctive water table use in of the water area. by Conjunctive mixing ground use of water water with by mixing ground normal surfacewater water with in proper normal proportion surface water should in beproper practiced proportion to avoid should soil salinity. be practiced The to avoid soil US salinity diagram,salinity. showing The US SARsalinity and di ECagram, that representsshowing SAR alkalinity and EC hazard that represents and salinity alkalinity hazard hazard, respectively,and salinity reﬂects hazard that no, respectively sample fell, reflects in the category that no sample C1S1, while fell in most the category of the C1S1, while Water 2021, 13, x FOR PEER REVIEW 15 of 19 water sample weremost in of C2S1 the water(68.8%), sample C3S1 (31.11%) were in category C2S1 (68.8%), indicating C3S1 medium (31.11%) to category high indicating salinity (Figuremedium 11) but suitableto high salinity for irrigation (Figure use. 11) but suitable for irrigation use.

FigureFigure 11.11. SalinitySalinity diagramdiagram showingshowing thethe distributiondistribution ofof irrigationirrigation waters.waters.

5. Conclusions The hydro-chemical characteristics and groundwater quality have been assessed to check the suitability of GW for drinking and irrigation purpose for Bhojpur district, located in the central Ganga basin. The northern part of the district is covered by younger alluvium generated by the river Ganga, while the central and southern parts contain the older alluvial formation. The GW level analyses revealed that hydraulic gradient is towards river Ganga and GW is contributing to the river in pre-monsoon season. The carbonate and silicate weathering processes are taking place in the area with dominancy of silicate weathering. Overall, the rock–water interaction is controlling the geochemistry of the study region. The groundwater of the study area is classified into ‘Ca-Mg-HCO3 Type’. It is witnessed that 66%, 69% and 84% of the samples exceeding the acceptable limit of As, Fe and Mn respectively for drinking water purpose as prescribed by BIS, 2012 and all other analyzed major ions and trace metals are well within the permissible limit of drinking water. The higher concentration of arsenic was observed in the younger alluvium, flood plain of river Ganga. Generally arsenic is enriched in the depth range of 20–40 m below ground surface and hence this depth zone should be avoided for tapping GW. Arsenic concentrations are in acceptable range at depth greater than 50 m in the Ganga River floodplain. This is probably because a confined aquifer may be encountered at that depth. The samples were also checked for suitability of irrigation purposes based on Na%, SAR, RSC CAI and PI indices values and it is found that all the samples fell in excellent to good quality for irrigation except few samples. The GW in proximity to river Ganga is highly enriched with arsenic and irrigation is being applied by tapping aquifer at shallow depth (contaminated zone). As per the authors’ knowledge, there is no Indian standard guidelines for irrigation which considers the role of toxic metals as it may be absorbed by the plants and harmful to human health. Our research findings may help policy makers or planners to design the monitoring network in heavily cultivated area and investigate the impact of contaminated irrigation water on human health. The future research may be carried out on detailed hydrogeological structure with evolution of arsenic in the study area.

Water 2021, 13, 2344 15 of 19

5. Conclusions The hydro-chemical characteristics and groundwater quality have been assessed to check the suitability of GW for drinking and irrigation purpose for Bhojpur district, located in the central Ganga basin. The northern part of the district is covered by younger alluvium generated by the river Ganga, while the central and southern parts contain the older alluvial formation. The GW level analyses revealed that hydraulic gradient is towards river Ganga and GW is contributing to the river in pre-monsoon season. The carbonate and silicate weathering processes are taking place in the area with dominancy of silicate weathering. Overall, the rock–water interaction is controlling the geochemistry of the study region. The groundwater of the study area is classified into ‘Ca-Mg-HCO3 Type’. It is witnessed that 66%, 69% and 84% of the samples exceeding the acceptable limit of As, Fe and Mn respectively for drinking water purpose as prescribed by BIS, 2012 and all other analyzed major ions and trace metals are well within the permissible limit of drinking water. The higher concentration of arsenic was observed in the younger alluvium, flood plain of river Ganga. Generally arsenic is enriched in the depth range of 20–40 m below ground surface and hence this depth zone should be avoided for tapping GW. Arsenic concentrations are in acceptable range at depth greater than 50 m in the Ganga River floodplain. This is probably because a confined aquifer may be encountered at that depth. The samples were also checked for suitability of irrigation purposes based on Na%, SAR, RSC CAI and PI indices values and it is found that all the samples fell in excellent to good quality for irrigation except few samples. The GW in proximity to river Ganga is highly enriched with arsenic and irrigation is being applied by tapping aquifer at shallow depth (contaminated zone). As per the authors’ knowledge, there is no Indian standard guidelines for irrigation which considers the role of toxic metals as it may be absorbed by the plants and harmful to human health. Our research findings may help policy makers or planners to design the monitoring network in heavily cultivated area and investigate the impact of contaminated irrigation water on human health. The future research may be carried out on detailed hydrogeological structure with evolution of arsenic in the study area.

Author Contributions: S.K. (Sumant Kumar): Supervision, Conceptualization, Methodology, Investi- gation, Data Interpretation, Writing—review & editing, M.K.: Sample analysis, Investigation, Writing & editing, V.K.C.: Methodology, Writing—review & editing, V.K.: Sample analysis, Investigation, Software, Data Interpretation, Writing & editing, R.K.S.: Investigation, Data Interpretation, Writing & editing, N.P.: Methodology, Statistical analyses, Data Interpretation, Writing—review & editing, N.K.: Software, Statistical analyses, Writing—review & editing, A.S.: Methodology, Software, Data Interpretation, Writing—review & editing, S.S.: Writing—review & editing, R.S.: Data Interpretation, Writing—review & editing, G.K.: Writing—review & editing, S.P.I.: Writing—review & editing, S.K. (Sudhir Kumar): Writing—review & editing, B.K.Y.: Methodology, Writing—review & editing, N.S.M.: Writing—review & editing; A.C.: Map preparation. All authors have read and agreed to the published version of the manuscript. Funding: Department of Water Resources, RD & GR, Ministry of Jal Shakti, Govt. of India under purpose driven study, National Hydrology Project. Institutional Review Board Statement: Not applicable. Informed Consent Statement: Not applicable. Data Availability Statement: The data presented in this study are available on request from the corresponding author. Acknowledgments: Authors kindly acknowledge Minor Water Resources Department, Government of Bihar and Central Ground Water Board, Faridabad for providing the agricultural and hydrological data. Conﬂicts of Interest: The authors declare no conﬂict of interest. Water 2021, 13, 2344 16 of 19

Appendix A

Table A1. Sampling details with arsenic concentration in the study area.

Screening Sample Aquifer Arsenic S.No. Location Latitude Longitude Depth of Hand Code Type (ppb) Pumps (Meter) 1 S-1 Paiga 25.6387 84.6699 Unconﬁned 24.4 68 2 S-2 Paiga 25.6384 84.6696 ” 21.3 78 3 S-3 Semaria ojhapati 25.6158 84.4311 ” 36.6 11 4 S-4 Semaria ojhapati 25.6158 84.4320 ” 61.0 4 5 S-5 Semaria ojhapati 25.6162 84.4310 ” 15.2 65 6 S-6 Semaria ojhapati 25.6160 84.4300 ” 36.6 308 7 S-7 Semaria ojhapati 25.6160 84.4300 ” 48.8 23 8 S-8 Semaria ojhapati 25.6162 84.4291 ” 20.1 320 9 S-9 Semaria ojhapati 25.6180 84.4296 ” 121.9 14 10 S-10 Semaria ojhapati 25.6152 84.4303 ” 54.9 3 11 S-11 Sahana/mangla 25.6142 84.4303 ” 25.9 80 12 S-12 Sudarpur barja 25.6801 84.5121 ” 33.5 4 13 S-13 Balaharpur 25.6707 84.6940 ” 36.6 BDL 14 S-14 Balaharpur 25.6707 84.6940 ” 41.1 BDL 15 S-15 Barahara 25.6842 84.7269 ” 30.5 35 16 S-16 Barahara 25.6834 84.7265 ” 45.7 37 17 S-17 Sirsiyan 25.6820 84.7628 ” 21.3 337 18 S-18 Sirsiyan 25.6819 84.7623 ” 51.8 60 19 S-19 Hazipur 25.6592 84.6761 ” 42.7 23 20 S-20 Chamarpur 25.6550 84.4532 ” 36.6 141 21 S-21 chamarpur 25.6569 84.4550 ” 30.5 56 22 S-22 Sirhiya 25.6821 84.7627 ” 21.3 4 23 S-23 Sirhiya 25.6819 84.7622 ” 33.5 17 24 S-24 Sirsiya 25.6819 84.7622 ” 18.3 3 25 S-25 Ishwarpura 25.6784 84.3622 ” 18.3 148 26 S-26 Ishwarpura 25.6784 84.3622 ” 54.9 56 27 S-27 Ishwarpura 25.6784 84.3622 ” 21.3 165 28 S-28 Ishwarpura 25.6781 84.3626 ” 16.8 286 29 S-29 Ishwarpura 25.6779 84.3624 ” 19.8 205 30 S-30 Ishwarpura 25.6715 84.3632 ” 27.4 328 31 S-31 Baligaon 25.4149 84.4975 ” 16.8 8 32 S-32 Naika tola 25.4821 84.4311 ” 39.6 3 33 S-33 Jaithwar 25.2791 84.3818 ” 18.3 19 34 S-34 Bahnuwa 25.2083 84.4293 ” 15.2 BDL 35 S-35 Anhari 25.2198 84.5176 ” 42.7 BDL Anhari Surya 36 S-36 25.2198 84.5176 ” 45.7 11 temple Water 2021, 13, x FOR PEER REVIEW 17 of 19

23 S-23 Sirhiya 25.6819 84.7622 ” 33.5 17 24 S-24 Sirsiya 25.6819 84.7622 ” 18.3 3 25 S-25 Ishwarpura 25.6784 84.3622 ” 18.3 148 26 S-26 Ishwarpura 25.6784 84.3622 ” 54.9 56 27 S-27 Ishwarpura 25.6784 84.3622 ” 21.3 165 28 S-28 Ishwarpura 25.6781 84.3626 ” 16.8 286 Water 2021, 13, 2344 17 of 19 29 S-29 Ishwarpura 25.6779 84.3624 ” 19.8 205 30 S-30 Ishwarpura 25.6715 84.3632 ” 27.4 328 31 S-31 Baligaon 25.4149 84.4975 ” 16.8 8 Table A1. Cont. 32 S-32 Naika tola 25.4821 84.4311 ” 39.6 3 33 S-33 Jaithwar 25.2791 84.3818 ” Screening18.3 19 Sample Aquifer Arsenic S.No. Location Latitude Longitude Depth of Hand 34 CodeS-34 Bahnuwa 25.2083 84.4293 Type” 15.2 (ppb)BDL 35 S-35 Anhari 25.2198 84.5176 ” Pumps (Meter)42.7 BDL 37 S-37Anhari Sahar Surya 25.2520 84.6297 ” 18.3 BDL 36 S-36 25.2198 84.5176 ” 45.7 11 38 S-38 Bhagawanpurtemple 25.4281 84.6334 ” 18.3 BDL 3937 S-39S-37 BibiganjSahar 25.575225.2520 84.6297 84.5786 ”” 25.918.3 72BDL 4038 S-40S-38 Bhagawanpur maulighat 25.693725.4281 84.6334 84.5948 ”” 38.118.3 16BDL 39 S-39 Bibiganj 25.5752 84.5786 ” 25.9 72 41 S-41 maulighat 25.6925 84.5951 ” 39.6 5 40 S-40 maulighat 25.6937 84.5948 ” 38.1 16 42 S-42 mauzampur 25.6882 84.5886 ” 45.7 71 41 S-41 maulighat 25.6925 84.5951 ” 39.6 5 43 S-43 Bindgaon 25.6809 84.8289 ” 27.4 6 42 S-42 mauzampur 25.6882 84.5886 ” 45.7 71 4443 S-44S-43 Bindgaon Bindgaon 25.680325.6809 84.8289 84.8281 ”” 30.527.4 113 6 4544 S-45S-44 Bindgaon Manikpur 25.649025.6803 84.8281 84.7849 ”” 21.330.5 89113 45 S-45 Manikpur 25.6490 84.7849 ” 21.3 89

FigureFigure A1. A1.Arsenic Arsenic distribution distribution map map in in the the study study area. area.

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