Arab J Geosci (2017) 10:171 DOI 10.1007/s12517-017-2887-2

ORIGINAL PAPER

Precipitation controlled spatial variations in groundwater quality indices-suitability for drinking and irrigation purposes in the basalts of South India Soumya Siva B 1 & Ravindra B. Kamble 1

Received: 29 June 2015 / Accepted: 8 February 2017 # Saudi Society for Geosciences 2017

Abstract Regional study on the impact of variations in input rainfall over groundwater quality and its suitability for utilitarian purposes is essential for its extraction and management. Water chemistry from 456 observations wells for 2007–2011 period in hard rock Basaltic terrain of Upper Godavari basin is supported with 8 field samples (in 2014) in this analysis. Based on mean annual rainfall (MAR), four narrow climatic zones are identified in the basin, defined as Bhumid^ (MAR > 1600 mm), Bsub-humid^ (1600–1000 mm), Bsemiarid^ (1000–600 mm), and Barid^ (MAR < 600 mm). NICB ratio (<±10%), and anionic percentages demarcated the polluted areas from rest Bgood data^, composing of 1818 samples. Hydrochemical facies are studied using Piper diagram, secondary alkalinity exceeded 50% and not one cation–anion pair exceeded 50%, and silicate–carbonate plot, arid zone nearer to silicate pole indicated the dominance of SiO2 in Ca/Na vs Mg/ Na plot. These geochemical variations emphasize a detailed study on role of climatic gradient on groundwater suitability for different purposes, for groundwater extraction, and its management. Suitability of groundwater for drinking based on water quality indices (WQI) indicated 98% of the samples as suitable (WQI < 50%). TDS in humid zone is 150–500 and 500–1000 mg/L in rest of the zones with ∼68% in permissible range, 15% as hard water (TDS > 600 mg/L) and not acceptable for drinking. Suitability of groundwater for irrigation is studied using sodium percentage (Na %), Wilcox diagram, sodium absorption ratio (SAR), US salinity diagram, residual

sodium carbonate (RSC), permeability index (PI), Kelly’s ratio (KR), ancd magnesium absorption ratio (MgAR). Na % in four zones is < 60% and permissible for irrigation. Very few water samples fall in Bdoubtful to unsuitable^ and Bunsuitable^ category of Wilcox diagram. Region is observed to have SAR < 6, indicating that water would not cause any problem to the soil and crop. Humid and sub-humid zones belonged to C1S1 and C2S1 categories (low and medium sodium), while semi-arid extended to C3S1 category (salinity hazard zone) in US salinity plot. RSC for all the three zones ranged from 1 to 1.5 meq/L, with 90–95% of the area safe for irrigation. Out of 1818 samples, 1129 belonged to class 2 of PI classification (PI ranging from 25 to 75%) while rest 689 samples had PI >75% (class 1). KR varied from 0.05 to 12.81, with 70–80% of the area having KR < 1. MgAR ratio ranged from 67% to 96%, with sub-humid, humid zones having higher Mg concentrations (increased salinity). Thus, 90% of the samples indicated non-alkaline water with 1% of normal alkalinity. Hence, the current study systematically analyzed the effect of precipitation and geology on groundwater quality and on its usability for various purposes. This stepwise procedure categorized the regions, and the same can be adopted for any regional hydrogeochemical studies.

* Soumya Siva B [email protected]

Introduction

1

Environmental and Water Resources Division, Department of Civil Engineering, College of Engineering (COEP), Pune, Maharashtra 411005, India

Keywords Hydrogeochemistry . Climatic gradient . Pollution . Weathering . Water quality indices . Sodium-salinity hazard

Hydrogeochemical cycle involves transformation of the rainwater (pure form) into groundwater, which is in chemically mixed state. Most of the chemical transformations occur in this part of the cycle resulting in decrease in concentrations of

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marine elements and subsequent increase in the concentrations of other major elements. Groundwater chemistry is an indicator of both natural mineralogical transformations on regional scale and of external influences (anthropogenic activities) on local scale. Principal factors that have an impact are as follows: (1) dissolution of primary minerals forming secondary minerals, (2) cation exchange, (3) atmospheric input, (4) evaporation, and (5) pollution due to human activities. A scientific and detailed study of geochemical transformations is essential in both practical aspects of developing water resources for utilitarian purposes and as a part of groundwater management. Due to rapid urbanization, extension of irrigation, and domestic needs of the people, the groundwater demand has tremendously been increased in many regions of the world. Chemistry of rainwater naturally gets modified with atmospheric interaction and transformed by water–rock interactions before it reaches the aquifer and further altered by both direct and indirect anthropogenic activities (human interventions). Thus, establishing the balance between geogenic (Huizar-Alvarez 1997; Zhou and Li 2005; Fantong et al. 2009), anthropogenic (Kamra et al. 2002; Karmegam et al. 2010; Gemitzi 2012; Khan et al. 2013), and climatic influences (Kumar et al. 2006; Vijith and Satheesh 2007; Soumya et al. 2013) over a long time period (Broers and Grift 2004; Pavelic et al. 2012; Chen and Feng 2013) in aquifer hydro systems is crucial for developing groundwater resources for utilitarian purposes—domestic and irrigation (Brown et al. 2011; Obiefuna and Sheriff 2011; AlMashagbah et al. 2012; Romanelli et al. 2012; Ewusi et al. 2013; Herojeet et al. 2015). Hard rock aquifers, sometimes known as Bdual permeability aquifers,^ are vertically stratified into loose regolith (saprolite and soils) porous medium, underlying weathered–fissured transmissive zone and deep fractured zone. These aquifers have relatively poor productivity and prone to acute groundwater pumping for both agricultural (rural) and domestic (urban) purposes. Quite a few studies in these hard rock terrains of Southern India had been carried out to correlate mineral weathering and regional scale groundwater chemistry (Anbazhagan and Nair 2004; Naik et al. 2009; Ramkumar et al. 2010; Babar 2012; Latha and Rao 2012; Pavelic et al. 2012; Sonkamble et al. 2012; Soumya et al. 2013). Fewer case studies analyzed the impact of this direct and indirect pumping on groundwater chemistry (Vijith and Satheesh 2007; Marghade et al. 2011; Ahamed et al. 2013). Thus, the main objective of the study is to decipher the relative impacts of geogenic and anthropogenic factors on basin scale groundwater chemistry of hard rock basaltic aquifer along a climatic gradient. Effect of climate, i.e., precipitation impact, is studied thoroughly with the help of experiments conducted in the basin across all the defined zones. These experimental results are compared with the chemical behavior observed in the adjacent zones. The influence of streamflow on groundwater is neglected in this study. Further, groundwater is the only source

of water in some of these peninsular semi-arid and arid regions of the country. Hence, regional analysis should be carried to in these terrains to ascertain the impact of hydrogeological conditions on the suitability of groundwater for drinking and agricultural purposes.

Study area Upper Godavari basin lies along western coast of South Peninsular India (Fig. 1) and associated with the rifted continental passive margin of the basaltic plateau has strong climatic and geomorphological gradients. Majestic Western Ghats with lofty ridges is the prime glory of the region, which is interspersed with magnificent forests. Basin stretches from 18.3° to 20.8° N and from 73.2° to 76° E, covering three demographic districts, Nasik, Ahmednagar, Aurangabad, with a population of ∼12 million people depending on agriculture and cultivating ∼28,660 km2 of area. Demographic features Nasik district situated in north western part of Maharashtra has a geographical area of 15,530 km2. The district is further subdivided in to 15 taluks viz., Nasik (NNa), Igatpuri (NIg), Dindori (NDi), Peint (NPe), Trimbakeshwar (NTr), Kalwan (NKa), Deola (NDe), Surgana (NSu), Baglan (NBa), Malegaon (NMa), Nandgaon (NNad), Chandwad (NCh), Niphad (NNi), Sinnar (NSi), and Yeola (NYe) covering 1931 villages. Ahmednagar is the largest district (area = 17,114 km2) situated in the central part of the state. Forest covers 1520 km2 of the district area, while gross cultivable area is 12,264 km2 and net area sown is 10,408 km2. It is divided into 14 taluks namely Ahmednagar (AhAh), Shevgaon (AhSh), Pathardi (AhPat), Parner (AhPar), Sangamner (AhSa), Kopargaon (AhKo), Akola (AhAk), Shrirampur (AhShrr), Rahata (AhRat), Rahuri (AhRar), Shrigonda (AhShrg), Jamkhed (AhJa), Karjat (AhKa), and Newasa (AhNe), covering 1581 villages in the district, out of which 2 villages are not habited. Aurangabad district is towards the eastern end of the basin, covering an area of 10,107 km2 (814.15 km2 under forest, 8135.57 km2 as cultivable and 7150.55 km2 as sown area). World famous Ajanta and Ellora caves are situated in this Aurangabad district. The district has been divided in nine taluks viz., Aurangabad (AuAu), Kannad (AuKa), Soegaon (AuSo), Sillod (AuSi), Phulambri (AuPh), Khuldabad (AuKh), Vaijapur (AuVa), Gangapur (AuGa), and Paithan (AuPa). Geological and geomorphological features Upper Godavari basin forms a part of Western Ghats and Deccan Plateau. Physiographically, the region composes of

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Fig. 1 Upper Godavari basin—study area

varied topographies—Hill ranges, Eastern and Southern plains, and Godavari Valley. The main system of hills is Sahayadri and its offshoots. Western Ghats section in Akole taluk (AhAk) is hilly which extends to relatively flat areas in Shevgaon (AhSh) and Jamkhed (AhJa) taluks in the east. Morphologically, the region can be broadly divided in four major characteristic landforms—hill and ghat section (7.6% of area), foothill zone (19.4% of area), plateau (3.71% of area), and plains (occupy 69.30% of area). The region is underlain by basaltic lava flows of upper Cretaceous to lower Eocene age. These lava flows were formed by the intermittent fissure type eruptions during upper Cretaceous to lower Eocene age. Shallow alluvial formation of recent age also occurs as narrow stretch along the banks of Godavari and Girna rivers flowing in the area. Hard Rock Basalt covers the entire region with 10% covered with soft rock alluvium. Fissured and porous formations are the two distinct hydrogeological units of basalts in the area. Soft alluvium occurs in small areas in the form of discontinuous patches along the flood plains of major rivers like Godavari,

Pravara, Mula, Girna, and their tributaries. It consists of reddish and brownish clays with intercalations of sand, gravel, and kanker. Soils of the region, weathering products of basalt, have various shades from gray to black, red, and pink color. These soils are classified in four categories, lateritic black soil (Kali), reddish brown soil (Mal), coarse shallow reddish black soil (Koral), and medium light brownish black soil (Barad). Black soil (Kali) contains high alumina and carbonates of Ca and Mg with variable amounts of K, low N, and P. Red soil is less common and suitable for cultivation under heavy and consistent rainfall. In massive unit of Deccan Trap Basalt, ground water occurs in soil cum weathered mantle, joints, cracks, and other weaker zones. Upper portion of the massive traps retain more groundwater in these rocks in comparison to beneath compact massive unit. Storage of ground water in compact massive unit totally depends upon the presence of joints and their nature, distribution and interconnection. Yield of dug wells tapping upper phreatic aquifer down to the depth of 12–15 m below range between 45 and 90 m3/day, depending upon the local

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hydrogeological conditions. Groundwater in alluvium occurs under both semi-confined and confined conditions. Thickness of alluvium is <30 m and aquifer thickness is limited to 3 m. Yield of dug wells and shallow tube wells ranged from 1 to 53L/s and 0.08 to 7.14 L/s, respectively. Climatic and hydrological features Upper Godavari region is crisscrossed with major Godavari River and its tributaries. Northern part of the basin is drained by easterly flowing Tapi and Girna rivers with their tributaries, whereas central region is crisscrossed by Godavari and Bhima river basins. Other important rivers in the district are Pravara, Purna, Dudhna, Shivna, Mula, Adula, Mahalungi, Damanganga, Vaitarna, Darna, Kadva, Aram, Mosam, Panjan, and Manegad. All the rivers have sub-parallel to semi-dendritic drainage pattern, and the drainage density is quite high. Based on geomorphological setting and drainage pattern, the basin is divided into ∼180 watersheds. Aquifer parameters are available from ground water exploration carried out in alluvial area and from pumping tests (conducted by Groundwater Survey and Development Agency (GSDA)) carried out on dug wells in Basaltic and alluvial terrain. Transmissivity of shallow basaltic aquifers is <80 m2/day and in 369–757 m2/day range in alluvial terrain. In basaltic formation, the specific capacity of dug wells is generally <200 L/min/m of drawdown whereas alluvium formations have specific capacity ranging between 0.7 and 3.2 L/ min/m of drawdown. Climate is characterized by general dryness throughout the year except during the southwest monsoon season. June to September is the southwest monsoon season, whereas October and November constitute the post-monsoon season. Maximum temperature in summer is 42.5 °C, and minimum temperature in winter is less than 5.0 °C. Relative humidity ranges from 43 to 62%. Except during the southwest monsoon season, when the relative humidity is high, the air is generally dry over the district. The summer months are the driest when the relative humidity is generally between 20 and 25% in the afternoon. Study of negative departures of the annual rainfall over normal mean revealed that major part of the region (about 80%) is drought. Falling east of Western Ghats regions composing of NSi, NNi, NSu, NKa, NBa, NCh, NYe taluks of Nasik; AhAh, AhRar, AhNe, AhSh, AhJa, AhKa, AhShrg, AhPat, AhPar taluks of Ahmednagar; and extreme western parts around AuVa and southern parts of AuPa of Aurangabad experienced moderate to severe drought conditions for >20% of years. Major existing groundwater issues Groundwater in Deccan Trap Basalt occurs mostly in the upper weathered and fractured parts down to 20–25 m depth. At

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places, potential zones are encountered at deeper levels in the form of fractures and inter-flow zones. Upper weathered and fractured parts form phreatic aquifer and groundwater occurs under unconfined conditions. At deeper levels, the ground water occurs under semi-confined to confined conditions. Bore wells drilled down to 70 m depth, tapping weathered and vesicular basalt are found to yield 18 to 68 m3/day. Generally, the shallower zones down to the depth of 20 m bgl form phreatic aquifer. Water-bearing zones occurring at 20–40 m depth are weathered interflow or shear zones and yield water under semi-confined conditions. Deeper semiconfined to confined aquifers occur below 40 m. Massive portion of basaltic flows are devoid of water, but when it is weathered, fractured, jointed or contain weaker zones, ground water occurs in it. Yield of the dug wells ranges from 2 to 3655 L/min, whereas that of bore wells ranges from 500 L/h to about 20,000 L/h, when favorably located. Average depth range of dug wells is 12–15 m and that of bore wells is 50– 60 m in hard rock areas. Groundwater in isolated alluvial pockets in the Godavari, Shivna, Purna, and their tributaries occur under both water table and semi-confined conditions. The aquifer horizons were encountered as coarse sand mixed with clay and silt between 15 and 26 m bgl, which constitute the potential aquifer in the area with discharge up to 4.50 L/s. Dug wells are generally down to 20 m depth and yields varying between 0.5 and 0.8 L/s. Highest rainfall on western end reduces the dependency on groundwater and hence no pumping in this zone. Slightly away from coast as we move into land, conjunctive usage of surface water and groundwater for agriculture demands pumping of resources. Eastern end of this basin is subject to severe groundwater pumping due to less rainfall. Pre-monsoon water level trend shows fall in water level up to 0.2 m/year in major parts of the region. Thus, the future water conservation and artificial recharge structures needs to be prioritized in these areas. Groundwater quality is also non-potable at many places as observed by regular GSDA monitoring. Groundwater quality is also affected from industrial pollution from sugar and allied industries like distillery and paper. Thus, variations in lithology, climate, land use pattern, and groundwater levels in this basin necessitate the study of impact of these controlling factors on the groundwater chemistry.

Materials and methods Piezometer and rain gauge network A database encompassing rainfall, groundwater levels and groundwater chemistry is gathered from regularly monitored agencies—Indian Meteorological Department (IMD), Hydrological Data Users Group (HDUG), and GSDA. District wise mean annual rainfall (MAR) for a decade period

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(1901–2000) procured from IMD indicated narrow climatic zones. Further, around 56 rain gauges regularly monitored by HDUG for daily rainfall measurement using auto-recorders are identified in the study area. These rain gauges are spread across the three districts as shown in Fig. 1 (blue triangles). Around 10–15 observation wells are monitored by GSDA for groundwater data in each taluk of a district. There are 456 observation points (colored circles in Fig. 1) distributed across 38 taluks of the three districts in Upper Godavari basin. These groundwater sampling sites are marked with a prefix denoting the taluk (BDemographic features^ section and encircled in Fig. 1) to which they belong suffixed by well number. For some sampling points, both rain gauge and observation well are located at the same station, hence overlapping circles and blue triangles in the figure. Groundwater is sampled by GSDA at different levels of the regolith mantle and in fractured hard rock aquifer for its chemistry. Water levels are measured 3–4 times a year and the data is obtained from 1973 to 2011. Water quality data is procured from GSDA for 2007– 2011 period, wherein quality is measured twice a year— pre-monsoon and post-monsoon. This data included the location details—latitude–longitude, district–taluk–village names, date of sampling and date of analysis, physical parameters (pH, electrical conductivity (EC), total dissolved solids (TDS), total hardness (TH), Ca-HR, and turbidity), major anions (Cl, total alkalinity (TA), CO3, HCO3, Cl, SO4, F, and NO3), and major cations (Ca, Mg, Na, K, and Fe). Water quality data from all these 38 taluks, sampled at 456 observation wells, had overall 2143 readings. This huge data is further validated through few field experiments conducted in April 2014. Two sampling stations are chosen from each district, and one sample is collected at each of these six locations. Groundwater samples collected are analyzed for pH, EC, TDS, turbidity, TH, TA, Cl, and SO4. Location details and the quality measurements made in the field are given in Table 1, which are included in the subsequent analysis. Concentrations corresponding to other major cations, i.e., Na, Ca, Mg, and K, could not be measured due to limited available experimental setup. Table 1

Climatic gradient—Zones Uniqueness of Upper Godavari basin is the narrow range of variations in rainfall, defined as climatic zones. MAR varied from 3000 to <600 mm of rainfall, where western region received highest (3400 mm) and eastern end received the least rainfall (470–680 mm). Another feature characterizing the precipitation in the study area is its irregular annual distribution. Narrow climatic zones, classified based on MAR, are grouped into four major classes defined as Bhumid^ (MAR = 1500–2500 mm), Bsub-humid^ (MAR = 1000– 1500 mm), Bsemi-arid^ (MAR = 600–1000 mm), and Barid^ (MAR < 600 mm). Humid zone composed of Igatpuri (NIg), Trimbakeshwar (NTr), and Surgana (NSu) taluks of Nasik district with MAR varying from 1520 to 2100 mm. Entire rainfall occured in one stretch in this zone during monsoon period from June to November. Sub-humid zone covered the next narrow zone to the eastern side of humid with entire rainfall distributed over 8 months (April–November). Rainfall in this zone reached as low as 1000 mm during drought years and picked up to 1600 mm in high rainfall years. This zone transited between humid and semi-arid zones. Dindori (NDi) and Peint (NPe) taluks of Nasik district are classified under this climatic zone. Thus, most of the taluks of Nasik (Na) district lied in humid and sub-humid zones. Semi-arid zone covered middle portion of Upper Godavari basin receiving an annual rainfall of 750 (±250) mm. Rainfall occurred twice in this zone, once in April–June period and again during September–November period of the same year. This climatic zone covered 50% of Nasik and Aurangabad districts with three taluks from Ahmednagar district. Arid zone (MAR varying from 470 to 680 mm) covered the eastern region of the basin, where rainfall is lower than 300 mm/year in drought year. Much of the Ahmednagar (Ah) district is covered under this climatic zone. Further, eastern end of the basin experienced a semi-arid climate with MAR = 600– 1000 mm. This zone formed a small patch in extended arid zone on eastern end (Fig. 1). Impact of these narrow zones on

Field experimental data, sampled in April 2014

Taluk

Village

Depth of sampling (m bgl)

pH

EC (μS/cm)

TDS (mg/L)

Turb

TH (mg/L)

TA (mg/L)

Cl (mg/L)

SO4 (mg/L)

Igatpuri (NIg) Triambakeswar (NTr) Peint (NPe) Dindori (NDi) Gangapur (AuGa) Nevasa (AhNe) Paithan (AuPa) Shevgaon (AhSh)

Igatpuri Triambakeswar Nirgude (Harsul) Dindori Kinhala Newasa Paithan Ghotan

3 2.2 6.8 9.8 11.3 7.2 8.8 5.3

8 7.5 8 8 8 8 8 7.5

365 820 302 1247 861 1018 900 1489

219.14 437.84 198.00 716.27 534.67 691.20 572.60 930.30

0.1 0.2 0.4 0.2 0.6 0.3 0.5 0.5

121 133 118 450 280 329 351 581

122 47 131 221 173 259 146 285

36.1 74 22 178 82 112 110 200

14.58 19.50 7.30 69.78 120.00 89.40 92.00 120.30

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groundwater chemistry and its usability is explained in next sections after a preliminary check on the consistency of the sampled data.

Hence, influence of anthropogenic activities on groundwater is studied in terms of pollution percentage as defined by Pacheco and Van der Weijden (1996)

Preliminary data check

%Pollution ¼

Samples are analyzed as per the procedures available in BStandards Methods for Water & Waste Water Analysis^ (APHA-WWA-WPCF 1998) for Ca, Mg, Na, K, F, HCO3, CO3, NO3, Cl, and SO4. Cations (Ca, Mg, Na, K) and anions (F, HCO3, CO3, NO3, Cl, SO4) are both identified using ion chromatography (IC) technique by GSDA. Analytical precision for ions is determined by normalized ionic charge balance (NICB) ratio (Kumar et al. 2006), given as percentage of fractional difference between the total cations (TZ+) and total anions (TZ−) as (Σ TZ+ − Σ TZ−) / (Σ TZ+ + Σ TZ−). NICB is computed for all samples collected at 456 locations and observed to have NICB within ±10%. Some of the samples showed positive charge imbalance, but some inversely with a negative charge deficit. Positive excess charge indicate load from external inputs such as rain chemistry or excess pumping effect. Imbalance of negative charges could be related to missing HCO3 and CO3 concentrations. Thus, samples with NICB > ± 10% are eliminated from further analysis, considering that water quality of these samples is inconsistent or erroneous. Reliability of the experimental groundwater data is checked by considering EC and molecular sum of cationic concentration (TZ+). Every water sample is checked if the difference between EC and TZ+ is not more than ±10%. Sum of cationic concentrations (TZ+) are observed to be 10 times of EC in magnitude and varied linearly with strong correlation. As a further check on chemistry data, the correlations between EC and TDS and between EC and TH are computed. Strong linear correlation of 0.94 is observed between EC and TDS along all the four climatic zones. Hence, in groundwater samples having a charge imbalance, i.e., NICB >±10% and/or deviating from EC–TZ+ linearity, EC–TDS linearities are eliminated from further analysis as such data is assumed to be subject to external influences.

Results Pollution percentage as elimination criteria Water chemistry of the area, based on NICB ratio, reflected continental weathering and other anthropogenic impacts (Singh et al. 2008; Soumya et al. 2013). Apart from data consistency criteria (BPreliminary data check^ section), which help in eliminating the erroneous data, some of the sampling stations are subject to local contamination.

½Cl þ ½SO4  þ ½NO3  *100 ½Cl þ ½SO4 þ½NO3  þ Alkalinity

ð1Þ

where, Alkalinity = [CO3] + [HCO3] and all concentrations are in microequivalents per liter. Cl, CO3, and HCO3 occur naturally while SO4 and NO3 come from agricultural areas, altogether influencing the anionic percentage. Stations with mean anion percentage >60% are considered to be polluted and with 40–60% are moderately polluted as per the definition given by Pacheco and Van der Weijden (1996). Percentage of pollution (% pollution) is calculated using Eq. (1) for every sample, averaged over each of the 456 sampling stations and plotted as a contour map using Arc GIS as shown in Fig. 2. Contour map indicated that % pollution is low in northwestern end of the basin, composing mainly of humid and sub-humid zones. As we move eastward, % pollution increased from ∼45 to 65% in semi-arid and arid zones. All the four climatic zones have some zones of moderate pollution (% pollution ∼40%) and some zones of higher pollution (> 70%). At such stations, few sampling points showing zero or low alkalinity resulted in high % pollution. Such individual water samples are eliminated at well scale (377 out of 2195 samples) resulting in reduction of % pollution from 40 to 60% to < 30%. Finally, data pertaining to ideal–natural chemistry is sorted out using this anionic ratio, and contaminated samples are eliminated for further analysis. Descriptive statistics in relation with BIS standards Sites indicating ideal–natural chemistry are sorted out as explained in previous section and are now used to characterize and analyze the hydrochemical facies. At each of the 456 sampling sites, mean and standard deviation of physical (pH, EC, TDS, turbidity, TH) and chemical parameters (Ca, Mg, Na, K, Cl, CO3, HCO3, SO4, NO3) are calculated for 2007–2011 period. Mean and standard deviation of all above physical and chemical parameters for Bgood^ sampling points at 38 taluks are computed. Based on Bureau of Indian Standards (BIS 2003), water quality standards are listed in terms of different quality parameters in Table 2 and compared with water quality observed in Upper Godavari basin. From the table, it is observed that pH in some of the water samples across all the four zones exceeded maximum limit of 8.5 (gray shades in Table 2). TA in the study area ranged from 36 to 338 mg/L in humid and sub-humid zones, while increased to 1200 mg/L in semi-arid and arid zones, causing unpleasant taste to the groundwater. EC is observed to range from 69 to 10,000 μS/cm at 25 °C. TDS in humid, sub-humid, semi-arid, and arid zones varied from 97 to 599 mg/L, 30.3 to 1203 mg/L, 95 to 5168 mg/L, and 0.1

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Fig. 2 Contour map of pollution percentage in Upper Godavari basin

Table 2

Drinking water quality BIS standards and ranges in Upper Godavari basin

Parameter

BIS (2003)

Concentrations in study area

Health hazards

Desirable Permissible Humid

Sub-humid

Semi-arid

Arid

pH TA (mg/L) EC (μS/cm) TDS (mg/L) TH (mg/L)

6.5 – 8.5 200 NM 500 300

– 600 NM 2000 600

7 – 10 44 – 280 149 – 1050 97 – 599 56 – 340

6.95 – 10.6. 36 – 338 60 – 1850 303 – 1203 60 – 524

6.74 – 10.87 8 - 1043 149 – 7950 95 – 5168 44 – 1800

5.5 – 10.41 8 - 1200 143 – 10000 0.1 – 7046 60 – 2500

Ca (mg/L) Mg (mg/L) Na (mg/L) K (mg/L) HCO3 (mg/L) Cl (mg/L) SO4 (mg/L)

75 30 NM NM NM 250 200

200 100 NM NM NM 1000 400

9.6 – 104 6.81 – 55 5 – 102 0.1 – 62 20 – 420.9 11 – 206 1 – 169

6 – 129.6 1.2 – 78.7 2.3 – 218 0.1 – 18.8 10.2 – 464 7 – 390 1 – 112

NO3 (mg/L) F (mg/L)

45 1.0

100 1.5

0.1 – 53.05 0.2 – 45 0.03 – 0.92 0.05 – 7

Taste Unpleasent taste – Taste, gastro-intestinal irritation Encrustation in water supply pipes, adverse effect on domestic use 4.8 – 356.8 4.8 – 800 Gastro-intestinal irritation, kidney stones 2.9 – 352.8 82.6 – 401 Adverse effects on domestic use 2 – 917 2.1 – 1268 – – 0.1 - 120.1 0.1 – 703 10.4 – 1272.46 18.29 – 1708 – 7 – 1224 4 – 2440 Salty taste 2 – 782 1 – 1120 Cause gastro-intestinal irritation with MgSO4 and NaSO4 0.05 – 155 0.05 – 183 Methaemoglobinemia - blue baby disease 0.01 – 4.4 0.05 – 2.4 Cripping skeletal flurosis, dental mottling, bone disease and cancer

*Bold & Italics are Ionic concentrations exceeding Permissible BIS standards, an alert to groundwater quality. NM indicates “Not Mentioned”.

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to 7046 mg/L, respectively. Among all these four zones, humid and sub-humid zones on the western end of the basin had TDS < 500 mg/L while rest of the basin had TDS in the range of 500–1000 mg/L. Among all these four zones, humid and sub-humid zones on the western end of the basin had TDS < 500 mg/L, while rest of the basin had TDS in the range of 500–1000 mg/L, as indicated by gray shades in Table 2. BIS defined groundwater to be Bsoft^ with TH (as CaCO3, in mg/L) < 75 mg/L, as Bmoderately hard^ with TH ranging from 75 to 150 mg/L. Water is considered to be Bhard^ and Bvery hard^ when TH varies from 150 to 300 and >300 mg/L, respectively. BIS standards recommend maximum permissible limit for TH to be 600 mg/L in case of absence of alternative source for drinking. Climatic zones of Upper Godavari basin indicated 56–340 mg/L of TH in humid zone, i.e., varying from soft to very hard in the zone. TH in the sub-humid zone varied from 60 to 524 mg/L, indicating water hardness of all ranges. TH in semi-arid and arid zones varied from 44 to 1800 and 60–2500 mg/L, respectively, with small percentages of very hard and Bimpotable^ (TH > 600 mg/L) water. These instances might be due to natural accumulation of salts from contact with soil or due to anthropogenic activities. Water softening techniques should be used in these regions to reduce hardness and its adverse effects. Ca and Mg in the region varied from 4.8 to 800 mg/L and from 1.2 to 401.44 mg/L, respectively. Ca in groundwater exceeded Mg, in general, due to its multiple sources from carbonate nodules, weathering reactions, agricultural inputs, etc. Humid, sub-humid, semi-arid, and arid zones had Na ranging from 5 to 102 mg/L, 2.3 to 218 mg/L, 2 to 917 mg/ L, and 2 to 1268 mg/L, respectively, attributed to cation exchange, human activities, and repeated use of water in irrigated lands. Very high values of K (120–703 mg/L; Table 2) are observed in semi-arid and arid zones, mainly due to potash fertilizers applied in agricultural areas of the region. These concentrations can be reduced by limiting the usage of NPK fertilizers and enhancing organic ways of irrigation. Standard deviations in K and Ca are observed to be as high as their mean values, which might be due to the variations in vegetation patterns (agricultural effect) across the study area. HCO3 in the study area varied from 10 to 1708 mg/L with higher values observed in semi-arid and arid zones. Cl, directly related to mineral content of water, indicating dissolution of chloride salts, is in the range of 7–390 mg/L in humid and sub-humid zones indicating groundwater to be within desirable and permissible limits. On the other hand, semiarid and arid zones indicated higher Cl, ∼ 1224 and ∼2440 mg/L, respectively. This might be due to the presence of NaCl from rocks. SO4, NO3, and F are observed to be very low in the humid and sub-humid zones and higher in semi-arid and arid zones (Table 2), which are due to the fertilizer inputs in the agricultural areas. These high concentrations could cause health issues such as methemoglobinemia (blue baby

Arab J Geosci (2017) 10:171

disease), crippling skeletal fluorosis, dental mottling, bone disease, cancer, and so on. Thus, agricultural practices, tourism, human intervention, and rock interactions to some extent caused higher concentrations in the eastern dry zones. Geochemical evolution along climatic gradient Hydrogeochemical facies Geochemical evolution of groundwater can be understood by plotting the concentrations of major cations and anions in Piper (1944) trillinear diagram. Filtered non-polluted database composing of Ca, Mg, Na, K, CO3, HCO3, Cl, SO4, and TDS concentrations is used to plot Piper’s diagram as shown in Fig. 3a. From the Piper’s diagram with the defined six chemical zones, it is evident that groundwater in the region had Ca(Mg)HCO3 composition (zone 1), which evolved into mixed Ca(Mg)Cl(SO4) type (zone 5a). Some of the samples of arid and semi-arid zone showed Ca(Mg)HCO3 composition (zone 1), which evolved into Na(K)ClSO4 type. Alkaline earths (Ca + Mg) exceeded alkalis (Na + K), and carbonates (CO3 + HCO3) exceeded other anions (Cl + SO4) in the region. In particular, humid and sub-humid zones had alkaline earth water with increased portions of alkalis with prevailing HCO3. Semi-arid zone indicated alkaline waters with some samples having higher portions of HCO3 and other samples with increased portions of prevailing Cl. Most of the samples in arid zone indicated increased portions of alkalis with prevailing Cl (zone 5a) and few samples in zone 4. Hence, it can be concluded that strong acids exceeded weak acids in the region, as most of the samples occurred in zone 1 (Fig. 3a). Transit from humid to arid zone ➔ Silicate–carbonate end poles Variations in concentrations along the climatic gradient are studied in terms of major cations, Ca, Mg, and Na, which indicated the differences in local mineralogy (Soumya et al. 2013). Major cationic concentrations are plotted with Ca/Na as x-axis and Mg/Na as y-axis, as shown in Fig. 3b. Humid zone tended to be slightly aligned towards carbonate pole, while arid zone tended towards silicate pole. This is mainly due to the presence of high Ca and low Na in humid zone as observed in Piper’s diagram (Fig. 3a). On the other hand, lower Ca and higher Na in arid zone caused the samples to cluster at silicate pole, i.e., arid zone is silicaceous, while humid zone is carbonaceous in nature. No samples are observed to be at evaporating end member indicating that evaporation is very low in the region. Sub-humid and semi-arid zones bridged between these two poles, with sub-humid zone spreading towards carbonate pole and semi-arid zone tilting towards silicate pole. Scatter in terms of Mg/Na ratio is due to water–rock interactions resulting from frequent small showers.

Arab J Geosci (2017) 10:171

Page 9 of 20 171

a 100

EXPLANATION Arid Semi-arid Sub-humid Humid

+C

2-

2+ 2+

g

SO

4

+M

1: Secondary alkalinity exceeds 50% 2: Secondary salinity exceeds 50% 3: Primary alkalinity exceeds 50% 4: Primary salinity exceeds 50% 5: No one cation-anion pair exceeds 50%

Ca

l

-

2

5a

0

0

4

100 0

0 100

1

+H CO

2-

3

CO

Mg

2-

+

+K

SO 4

3

+

Na

2+

3

-

5b

100

0 100

100

100

0

0 0

100 -

2+

Cl ANIONS

Ca CATIONS

b

100

Mg/Na

Arid Semi-arid Sub-Humid Humid Carbonate pole

10

1 0.01

0.1

1

Ca/Na

10

100

Silicate pole 100

100

0.1

10

0.1

Semi - arid Humid

10

1 0.01

Arid

Mg/Na

Mg/Na

Arid Semi - arid Sub - Humid Humid

1 1

10

Ca/Na

100

0.01

0.1

0.01

0.1

Non - Monsoon 0.01

Fig. 3 Evolution of groundwater using a Piper diagram and b silicate–carbonate plot

1

0.1

Monsoon 0.01

10

Ca/Na

100

171

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Most of the samples were measured in January–May period of every year, while ∼10% of the groundwater samples were collected in June–September of every year. Classification of the groundwater samples into traditional monsoon–non-monsoon periods and then plotting them on silicate–carbonate plot is also performed so as to study the seasonal effect on groundwater quality. It is observed from the Ca/Na vs Mg/Na plots for monsoon–non-monsoon, as shown in Fig. 3b, that variability in ionic ratios are more in dry non-monsoon period than in wet monsoon period. Scarcity in seasonal data is one of the issues in obtaining the possible dilution–anti-dilution trends in water quality. More dense and well-planned groundwater sampling would help to further study this temporal seasonal impact, while the impact of rainfall spatially is core crux of this article. Concentration depth profiles Depth to groundwater in relation with major ionic concentrations is analyzed by plotting concentration depth profiles (Soumya et al. 2013). Concentration–depth profiles are plotted for individual ions in some of the wells to identify the prominent ions and their conservative behavior (Broers and Grift 2004). Variations in major cations and anions with depth to groundwater are shown in Fig. 4. It is observed that humid and sub-humid zones have low Ca, Mg, and K concentrations, while semi-arid and arid zones have wide variations in concentrations of respective ions. Deeper groundwater is observed in semi-arid and arid zones. Most of the groundwater in humid zone is shallow, 0–8 m, while that in sub-humid zone reaches up to 10 m bgl. Shift in higher concentrations in semiarid and arid zones is clear in terms of Mg. Figure 4 indicates that very few samples in arid zone have K higher than 25 mg/ L, which is mainly at shallow depths. Na does not vary much with depth, but clear distinction in concentrations among the four climatic zones is observed in the figure. This clear increase in concentrations from humid to arid zones is observed in the other marine salt, Cl. Variations in SO4 with depth are similar to that of Cl across the four climatic zones. This could be possibly due to mineralogical reactions of Cl and SO4 with CO3 and HCO3. Control of geology, hydrological, and other natural features on groundwater chemistry is observed along the depth profiles. Suitability of this water chemistry for drinking and irrigation purposes is explained in next sections.

Suitability of groundwater for different purposes Rapid urbanization, increase in tourism, development of industrial, agricultural, and domestic activities increased the demand for Bgood water.^ On the other hand, disposal of industrial effluents, agricultural residues, and domestic sewage in unlined drains, etc., caused deterioration of groundwater

quality in the basin. Hence, different ionic indices are computed as discussed below, to check the suitability of groundwater in the basin for both drinking and irrigation purposes. Suitability for drinking—WQI Evaluation of quality of groundwater in a scientific manner is done using an integrated water quality index (WQI) developed for multiple parameters at all sampling sites. WQI provides a simple, comprehensible, mathematical tool to transform long list of water quality parameters into a single number. Several authors had proposed the use of WQI as a means to derive a numerical expression for the general quality of surface and/or groundwater (Tiwari and Mishra 1985; Debels et al. 2005; Fulazzaky 2009; Rosemond et al. 2009; Banerjee and Srivastava 2010; Herojeet et al. 2015). Major ten chemical parameters are considered for WQI calculation, computed using the formula
 n WQI ¼ Antilog ∑ wi log10 qi ð2Þ i¼1

where i is each of the chemical parameters, pH, TA, TDS, TH, Ca, Mg, Cl, SO4, NO3, F, and qi is quality rating of ith param  −vi eter = vvas −v * 100; va is actual value obtained from laboratory i analysis of ith parameter; vs is standard value of ith parameter; vi is the ideal value (pH = 7 and 0 for all other parameters); wi is the weightage factor of ith parameter = k / Sn and k = 1 þ 1 þ11 …… 1 ; vs1

vs2

vs3

vsn

and Sn is standard value of ith parameter. Water quality standard values, corresponding weightage factor and ideal values, are presented in the Table 3. Standard vs values for 10 parameters given in Table 3 are used to compute k as 1.146. Thus, k/Sn with Sn is used to compute weightage factor wi as given in the last column of Table 3. Standard values, vs and vi, are further used to compute qi for each parameter for every sample. Weightage factor, wi, is multiplied with log10 (qi) for every ith parameter and summed together for every sample. Antilog of this sum of i values of {wi * log10 (qi)} for every sample is computed and given as WQI. Based on WQI indices, water samples can be classified into three categories for drinking—Bsuitable^ (WQI < 50), Bmoderately polluted^ (50 < WQI < 80), and Bseverely polluted^ (WQI > 80), as described in Latha and Rao (2012). WQI computed for every sample, as explained above, indicated that 1739 samples had WQI < 50, 5 samples had WQI in 50–80 range, and 29 samples had WQI > 80. Thus, 98% of water samples are observed to be suitable for drinking purpose based on WQI, and rest 2% of the samples are indicated as severely polluted and unfit for drinking. These 2% sampling sites are classified into moderately polluted and severely polluted based on WQI and are listed in Table 4. The table indicated that sites in NIg (NIg05), NSu (NSu02, NSu04, NSu06),

Arab J Geosci (2017) 10:171 10

Ca (mg/L) 100

1000

K (mg/L) 1000

1 0

4

4

4

8

8

8

12

16

Depth to Groundwater (m)

0

20

12

16

24

10

Na (mg/L) 100

1000

16

Arid Semi-arid Sub-humid Humid

28

1

10

Cl (mg/L) 100

1000

1 0

4

4

4

8

8

8

16

20

Depth to Groundwater (m)

0

Depth to Groundwater (m)

0

12

12

16

20

24

28

SO 4 (mg/L) 10 100

1000

12

16

20

24

24 Arid Semi-arid Sub-humid Humid Field Data

Arid Semi-arid Sub-humid Humid

1000

24

28

1

100

12

Arid Semi-arid Sub-humid Humid

Arid Semi-arid Sub-humid Humid

28

10

20

20

24

Depth to Groundwater (m)

Mg (mg/L) 10 100

1

0

Depth to Groundwater (m)

Depth to Groundwater (m)

1

Page 11 of 20 171

28

Arid Semi-arid Sub-humid Humid Field Data

28

Fig. 4 Concentration depth profiles for all major ions

NTr (NTr02, NSu09) of humid zone and some sites in NPe (NPe02, NPe03) of sub-humid zone had WQI > 80 and are

severely polluted. Similarly, NIg06, NIg09, and NIg12 of NIg and NTr01of NTr in humid zone and NPe04 of NPe in sub-

171

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Table 3 Water quality standards, ideal value, and weightages for WQI computation Parameter

Standard value Sn and vs

Ideal value vi

Weightage factor wi

pH TA TDS TH Ca Mg Cl SO4 NO3

8.5 200 500 300 75 30 250 200 45

7 0 0 0 0 0 0 0 0

0.135 0.006 0.002 0.004 0.015 0.038 0.005 0.006 0.026

F

1.5

0

0.764

humid zone had WQI in 50 to 80 (moderately polluted) range. High WQI index in these individual sites could be due to urbanization; domestic sewage from open drains; increase in tourism in Nasik (NNa) and Triambakeswar (NTr) taluks, which is the starting point of River Godavari; and possible contamination from external sources along Kalwan river in Surgana (NSu) and Peint (NPe) taluks, etc. But for these sampling sites, rest of the humid and sub-humid zones had WQI < 50 and suitable for drinking. All the sampling sites of semi-arid and arid zones have WQI < 50, and hence, entire eastern region of the study can be considered as suitable for drinking based on WQI index. Suitability for irrigation—Sodium salinity hazards Agriculture is the main occupation in the study area and thus, essential to understand groundwater quality with regards to usability for irrigation. Standard indices used in identifying the suitability of groundwater for irrigation purpose are sodium absorption ratio (SAR), soluble sodium percentage (SSP), salinity hazard, residual sodium carbonates and bicarbonates (RSC/RSCB), permeability index (PI), and Kelly’s ratio (KR). These parameters are computed one by one and zones with water for irrigation suitability are demarked from unfit zones in this section. Soluble sodium percentage - SSP Na replaces Ca in the soil by the process of base exchanges and reduces permeability of soil with little or no support for plant growth. Hence, sodium content is essential for irrigation water classification and is expressed in terms of soluble sodium percentage (SSP) as % Na as Na þ K SSP ¼ %Na ¼ *100 Ca þ Mg þ Na þ L

ð3Þ

where concentrations of cations (Na, K, Ca, Mg) are in milliequivalents per liter. SSP ≤ 60% in groundwater is allowed for agricultural zones as indicated in literature (Oladeji et al. 2012). SSP or % Na is computed for every water sample and averaged over each sampling site. Sampling site average of SSP is then classified into Bfit^ (SSP < 60%) and Bunfit for agriculture^ (SSP > 60%). Based on this, sampling sites classified as unfit for agriculture are listed in Table 4. The table showed that humid and sub-humid zones have SSP < 60% and, hence, suitable for irrigation. NDe10 of Deola (NDe), NSi17, NSi27 of Sinnar (NSi), AuGa01 of Gangapur (AuGa), AuPh14 of Phulambari (AuPh), AuPat08 of Pathardi (AuPat), and AhNe16 of Newasa (AhNe) taluks in semi-arid zone indicated SSP > 60%. Similarly, NNad24, AhKo17, AhKo14, AhShrr06, and AhKa19 sites in arid zone had SSP > 60% and, hence, unsuitable for irrigation purpose. Salinity hazard Excess amount of salts present in the water affects plants and agricultural soil physically and chemically, thus reducing the productivity. Total salt content in water is measured in terms of salinity hazard (EC)–high salt content (high EC) in irrigation water leading to the formation of saline soil. Concentrations of soluble salts in irrigation water can be expressed as Blow^ (EC < 250 μS/cm), Bmedium^ (250–750 μS/cm), Bhigh^ (750–2250 μS/cm), and Bvery high^ (EC > 2250 μS/cm) salinity zones. High EC lowers the osmotic pressure in the plant structural cells, thus preventing water from reaching the branches and leaves (Saleh et al. 1999). High salinity waters cannot be used on soil with restricted drainage. Among the water samples collected, 56 samples are classified as low saline (EC < 250 μS/cm), 583 as medium saline (250 < EC < 750 μS/cm), 926 as high saline (750 < EC < 2250 μS/cm), and 207 samples as very high saline (EC > 2250 μS/cm). EC concentrations averaged over each sampling site are mapped in the contour plot of Fig. 5. Around 20% of the sites had EC in 250–750 μS/cm range while 60% of the sites are categorized as Bhigh saline^ (750 < EC < 2250 μS/cm). Rest 20% of the sites indicated very high salinity (EC > 2250 μS/cm). Most of the regions in the basin had 1250–1850 μS/cm of EC with western region having EC < 1250 μS/cm and eastern region, in contrast, having EC > 1250 μS/cm. The contours clearly indicated the increase in EC with transit from humid to arid climatic zones. Sodium hazard—SAR Relative activity of Na in the action exchange reaction with soil is expressed in terms of SAR, an expression pertaining to cation make up of water and soil solution. SAR is used for

Ahmednagar

Aurangabad

Arid Nasik

Ahmednagar

AuGa01

AhAk AhShrr AhKa

AhRat AhRar

AhSa AhKo

AuAu AuPa AuVa AhAh AhSh AhPar

AhShrr AhKa19

AhKo07, AhKo14

AhRar05, AhRar12

AhKo14

AuPa01

NNad03

NNad24

AuGa01 AuPh14 AhPat08 AhNe16

NSi17, NSi27

NDe10

NYe NNad

NPe02, NPe03

NIg05 NTr02, NTr09 NSu02, NSu04, NSu06

Medium polluted (6–9)

Sodium hazard (SAR)

NMa03 NNi02

NP04

NIg06, NIg09, NIg12 NTr01

Unfit for agriculture (> 60%)

Moderately polluted (50–80)

Severely polluted (> 80)

SSP (% Na)

Water quality index (WQI)

NMa NNi

NSi AuKa AuGa AuPh AhPat AhNe

NNa

NKa NDe

NPe

NIg NTr NSu

Taluk ID

Sampling sites indicating unsuitable groundwater for drinking and irrigation

Aurangabad

Sub-humid Nasik Semi-arid Nasik

Humid Nasik

District

Table 4

AhShrr06 AhKa16, AhKa19

AhSa18 AhKo18, AhKo14, AhKo15 AhRat07 AhRar04, AhRar05, AhRar13

AhAh01 AhSh15

NNad03, NNad17, NNad20

NMa03, NMa20 NNi02, NNi18, NNi20

NSi17, NSi27 AuKa18 AuGa01 AuPh14 AhPat08 AhNe16

Unsuitable (>1)

Kelley’s ratio (KR)

AhAk02 AhShrr06 AhKa07, AhKa18

AhSa09, AhKo10, AhKo14 AhRat06, AhRat07 AhRar05, AhRar12

AhPar04, AhPar06, AhPar15

NMa16 NNi05, NNi16, NNi19 NYe11 NNad03, NNad10, NNad13 AuAu04, AuAu08 AuPa18, AuPa19 AuVa04, AuVa16 AhAh14, AhAh19

AuPh06 AhPat02 AhNe13

NKa06, NKa10 NDe07, NDe10 NNa03, NNa11, NNa12, NNa13, NNa14 NSi04, NSi05 AuKa18

Unsuitable (> 67%)

MgAR

Arab J Geosci (2017) 10:171 Page 13 of 20 171

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Page 14 of 20

Fig. 5 Spatial distribution of Salinity hazard (EC) in Upper Godavari basin

characterizing the sodium or alkali hazard of irrigation water ffiffiffiffiffiffiffiffi , where the concentration of ions is in and defined as pNa CaþMg 2

milliequivalents per liter. SAR value is used to calculate the degree to which irrigation water tends to enter into cation exchange section in the soil. Irrigation water with high Na and low Ca will result in ion exchange of Na with Ca and Mg. This ion exchange in the soil destroys the soil structure due to the dispersion of clay particles. Na also contributes directly to the total salinity of the water and may be toxic to sensitive crops. Water with SAR < 6 would not cause any salinity problem while there will be increase in problems for SAR in 6–9 range. Salinity issues will be very high for SAR > 9 and is unsuitable for irrigation purpose. SAR is observed to give accurate results for regions with EC < 2000 μS/cm. Regions with EC > 2000 are checked for sodium hazard by using adjusted SAR (Oladeji et al. 2012). Further, for regions with EC > 3000 μS/cm, sodium carbonate absorption ratio (SCAR) is used in place of SAR to check for soil salinity. SAR is computed for each of the water sample in the study area. SAR in the study area varied from 0.07 to

18.67 meq/L. For few samples in arid zone with EC > 3000 μS/cm, sodium hazard is computed using SCAR (Fig. 5). Around 95.65% of the samples indicated no salinity issue (SAR < 6) and rest 3.05 and 1.29% of samples indicated medium (SAR in 6–9 range) and severe salinity problems (SAR > 9), respectively. Sites with SAR in 6–9 range are listed in Table 4 under Bmedium problems^ column. It is observed that only one site in semi-arid zone and few more sites in arid zone have SAR in 6–9 range. Contour map of Fig. 5 also indicated regional picture of the type of SAR, adjusted SAR, and SCAR to be adopted for identifying sodium hazard. Wilcox and US salinity diagrams Classification of water for irrigation purpose depends on sodium ion (% Na) and total salt content (EC). Groundwater is classified based on % Na and EC, defined as Wilcox diagram (Wilcox 1948) as shown in Fig. 6a. Wilcox diagram revealed that all the samples of humid

Arab J Geosci (2017) 10:171

Page 15 of 20 171

a100

b

90

28

Medium ( S2)

60 50

10

0

Low (S1)

Unsuitable

20

Doubtful to Unsuitable

Excellent to Good

30

Good to Permissible

40

1000 2000 3000 4000 5000 6000 Electrical Conductivity (EC, µS/cm)

24 Sodium (Alkalinity) Hazard (SAR)

High ( S3)

Permissible to Doubtful

70

0

Arid Semi-arid Sub-humid Humid

30

26

80

Percentage Sodium (% Na)

32

Vey High (S4)

Arid Semi-arid Sub-humid Humid

22 20 18 16

C3S3

14 12

C4S3

10

C3S2

8 6

C1S1

4

C2S1

C3S1

C4S2

2

7000

C4S1

0 100

1000

10000

Salinity Hazard (EC) Low (C1)

Medium (C2)

High (C3)

Very High (C4)

Fig. 6 Groundwater quality identification using a Wilcox diagram and b US salinity diagram

and sub-humid zones lied in Bexcellent to good^ class of irrigation suitability. Most of the samples from semi-arid and arid zones belonged to excellent to good and Bgood to permissible^ classes. Few samples in semi-arid zone had EC in 2250–4000 μS/cm range and lied in Bdoubtful to unsuitable^ category for irrigation purpose. Very few samples in arid zone had EC > 4000 μS/cm and are classified as Bunsuitable^ for irrigation purpose. US salinity laboratory diagram classifies water into low, medium, high, and very high categories based on EC and SAR. Low, medium, high, and very high salinity hazard are denoted as C1, C2, C3, and C4, respectively, while those of sodium hazard are denoted as S1, S2, S3, and S4, respectively. Semi-logarithmic plot gives the ranges for 16 classes of water developed from different combinations of 4 classes for sodium hazard and 4 classes for salinity hazard. US salinity diagram for Upper Godavari basin, plotted in Fig. 6b, illustrated that the water samples from humid and sub-humid zones lied in C1S1, C2S1, and C3S1 indicating low–high salinity hazard (EC) and low sodium alkaline hazard (SAR). These waters could be used for irrigation in almost all types of soil with little danger of development of exchangeable sodium and salinity. On the other hand, groundwater from semi-arid zone indicated high EC with low SAR (C3S1 category) and samples from arid zone suffered from high (C3) to very high (C4) salinity hazard. Use of such water in irrigation is harmful to soil and thereby would result in low permeability and poor cultivability. These waters are suitable for plants having good salt tolerance and it restricts suitability for irrigation, especially in soils with restricted drainage. Very few samples in arid zone had medium sodium alkalinity (SAR) hazard, i.e., fall in C3S2 and C4S2 categories (Fig. 6b).

Suitability for irrigation—CO3 and HCO3 Residual sodium carbonates and bicarbonates Excess sum of CO3 and HCO3 in groundwater over the sum of Ca and Mg also influence the suitability/ unsuitability of groundwater for irrigation. This excess sum is computed as residual sodium carbonate (RSC) and residual sodium bicabonate (RSBC). RSC is considered to be superior to SAR as a measure of sodicity, particularly at low salinity levels. If water contains CO3 and HCO3 in excess of Ca and Mg, then it is likely to perceptible Ca displayed by exchange reactions. The result is an increase in sodium hazard of water. This excess quantity, denoted by RSC, is determined by the formula as below (Raghunath 1987) RSC ¼ ðCO3 þ HCO3 Þ–ðCa þ MgÞ

ð4Þ

where, all concentrations are in milliequivalents per liter. Good irrigation practices make it possible to use marginal RSC water for irrigation. Excessive RSC causes soil structure to deteriorate with soil–water movement restricted. At places, where CO3 is not measured or HCO3 is dominant than CO3, residual sodium bicarbonates (RSBCs) are used in place of RSC to check for suitability of groundwater. Oladeji et al. (2012) defined RSBC as HCO3–Ca. Water samples with high RSBC value tend to have relatively high pH values. Therefore, land irrigated with such water becomes infertile owing to deposition of NaCO3 (Eaton 1950). Irrigation water with RSC/RSBC <1.25 meq/L are Bsafe for irrigation,^ and those in range of 1.25–2.5 meq/L are

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Bmarginally suitable^ for irrigation and should be used with some treatment. Zones with groundwater having RSC/RSBC >2.5 meq/L are unfit for irrigation. RSC in groundwater of Upper Godavari basin is observed to vary from −2 to 0 meq/ L in humid and sub-humid zones. Higher variation in RSC (−18 to 4 meq/L) is observed in semi-arid and arid zones. It is observed that 93% of the study area has RSC < 1.5 meq/L and, hence, suitable to marginally suitable for irrigation. Further, percentage of samples with RSC < 1.5 meq/L reduced from 95 to 91% as transit from humid to arid zone. Mean values of RSBC computed at each of the sampling site are plotted as contour plot in Fig. 7. Contour plot indicated that majority of the humid and sub-humid zones have normal (RSBC <0.75 meq/L) and low alkaline (0.75 < RSBC < 1.25 meq/L) groundwater. Groundwater in these zones of low alkalinity could only be used for irrigation with pre-treatment. Some regions in semi-arid and arid zones indicated medium alkaline (2.5 < RSBC <5 meq/L) groundwater and is unfit for irrigation. Contour map showed the central region as high alkaline zone, where groundwater should not be used for irrigation.

Permeability index - PI Soil permeability is affected by long-term use of irrigation water and is influenced by Na, Ca, Mg, and HCO3 contents of the soil. Permeability index is defined as (Doneen 1964) PI ¼

pffiffiffiffiffiffiffiffiffiffiffiffiffi Na þ HCO3 *100 Ca þ Mg þ Na

ð5Þ

where concentrations of all ions are in milliequivalents per liter. Water samples are classified as class I if PI >75% and as class II if PI ranged in 25–75%. PI is computed for each of the water samples and observed that 1129 samples have PI in 25–75% range, falling in class II. Only 12 sampling sites are in class I category with PI >75%. Figure 8 shows scatter plot between PI and RSC/ RSBC indicating that most of the samples are in class II while some are in class I, indicating the suitability of groundwater in most of the regions for irrigation.

Fig. 7 Suitable and unsuitable zones for irrigation based on residual sodium bi-carbonate (RSBC)

Arab J Geosci (2017) 10:171

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Fig. 8 Scatter plot between permeability index (PI) and residual sodium carbonate (RSC)

Arid Semi-arid Sub-humid Humid

Class I

0.9 0.8

0.5 0.4

Normal Water

0.3 0.2 0.1

Safe for Irrigation Non alkaline water -20

-18

-16

Kelly’s ratio - KR Level of Na measured against Ca and Mg is known as Kelley’s ratio (KR), based on which irrigation water can be rated (Kelly 1951). KR is expressed as KR = Na / (Ca + Mg). Concentration of Na in irrigation water is considered to be in excess, thereby making the water unsuitable, if KR > 1. Hence, water samples with KR < 1 are considered to be suitable for irrigation (Kelly 1951). KR calculated for all water samples of study area ranged from 0.05 to 12.81 mg/L. According to KR values, about 76% of groundwater samples fall in good quality of the water category for irrigation purpose. Sites in semi-arid and arid zones with mean KR > 1 are listed in Table 4. Management practices should be adopted in these sites for reducing higher concentrations of Na. Magnesium hazard - MgAR Magnesium content of water is considered as one of the most important qualitative criteria in determining the quality of water for irrigation. Ca and Mg maintain a state of equilibrium in most waters, but increasing amount of Mg in water will increase the salinity of the water and therefore decline the crop yield (Joshi et al. 2009). Magnesium absorption ratio (MgAR) is a measure of excess Mg, i.e., magnesium hazard, defined as MgAR ¼

Mg *100 Ca þ Mg

ð6Þ

where, all concentrations are in milliequivalents per liter. Samples having MgAR >67% are not acceptable for irrigation. MgAR is computed for all the water samples of the study, and it is observed that 69% of the samples fall under permissible category, i.e., have MgAR < 67%. Sites with mean MgAR > 67%, which are unsuitable for irrigation, are listed

-14

-12

-10 -8 -6 -4 Residual Sodium Carbonate (RSC)

Medium Alkaline Water

Permeability Index (PI, %)

0.6

Class II

Marginally Suitable – Low Alkaline Water Unsuitable for Irrigation

0.7

Suitable for Irrigation

0 -2

0

2

4

in Table 4. The table indicated that certain zones of semi-arid and arid zones are subject to magnesium hazard. Hence, different criteria had been adopted to analyze the control of climatic gradient on water chemistry and to check the suitability of groundwater for different purposes.

Conclusions Groundwater chemistry analyzed along Upper Godavari basin in this study is observed to be controlled by geogenic, hydrological, climatic (rain-fed), and anthropogenic factors. Piezometer and rain gauge observations are considered for 3–4 years at 456 sampling sites, belonging to ∼45 taluks of three districts in the basin. This secondary data is supported with few samples collected from eight different observation wells across the basin. Four climatic zones are defined based on mean annual rainfall (MAR)—humid (MAR > 1600 mm), sub-humid (MAR as 1000–1600 mm), semi-arid (MAR as 600–1000 mm), and arid (MAR < 600 mm). Pollution percentage is adopted as elimination criteria with higher percentages (55–75%) observed in arid and semi-arid zones and lower percentages in humid and sub-humid (20–40%) zones. Major hydrogeochemical observations of this study area are as follows: &

&

Piper’s diagram indicated evolution of Ca(Mg)HCO3 composition (zone 1) into mixed Ca(Mg)Cl(SO4) type (zone 5a), while some of the samples belonging to arid and semi-arid zones evolved from Ca(Mg)HCO3 composition (zone 1) to Na(K)ClSO4. Samples from humid and sub-humid zones tended towards carbonate pole while those from semi-arid and arid zones tended towards silicate pole due to high Na in dry regions.

171

&

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Ca and Mg varied from 4.8 to 800 mg/L and from 1.2 to 401.44 mg/L, respectively. Ca exceeded Mg due to its multiple sources—carbonate nodules, weathering reactions, agricultural inputs, etc.

&

Suitability of groundwater in the basin for drinking purposes indicated based on different parameters, that:

&

&

&

&

&

&

Groundwater in humid and sub-humid zones lied in Bsoft water^ (TH < 60 mg/L) and Bmoderately hard water^ (TH in 60–120 mg/L) categories, while semi-arid and arid zones lied in Bhard water^ (TH in 120–180 mg/L) and Bvery hard water^ (TH > 180 mg/L) categories, possibly due to the presence of dissolved carbonates. Range of Cl is 7–390 mg/L in humid and sub-humid zones, indicating groundwater to be within desirable and permissible limits, while semi-arid and arid zones indicated that higher Cl concentrations, 1224 and 2440 mg/L, respectively, are unsuitable for drinking. Higher Ca concentrations in semi-arid and arid zones could possibly cause gastro-intestinal irritation and other health issues, while high Mg water has adverse effects on domestic usage. Small belt along Godavari river and at the Paithan dam had higher TDS (1000–3000 mg/L). AhKo, AhRar, AhNe, and AhPar of Ahmednagar districts and tourist spots of Aurangabad district (AuPa, AuAu) indicated higher TDS (1500–3000 mg/L), where groundwater is impotable. One village of Rahuri taluk (AhRar) of Ahmednagar district indicated TDS > 3000 mg/L, where water is suitable neither for drinking (bad in taste) nor for irrigation and needed immediate attention. As per WQI, 98% of water samples are observed to be suitable for drinking purpose and rest 2% of the samples are severely polluted and unfit for drinking. NIg (NIg05), NSu (NSu02, NSu04, NSu06), and NTr (NTr02, NSu09) of humid zone and some sites in NPe (NPe02, NPe03) of subhumid zone had WQI > 80 and are severely polluted. NIg06, NIg09, and NIg12 of NIg and NTr01of NTr in humid zone and NPe04 of NPe in sub-humid zone had WQI ranging from 50 to 80, classified as moderately polluted. High WQI index in these individual sites is due to urbanization, domestic sewage from open drains, increase in tourism in Nasik (NNa) and Triambakeswar (NTr) taluks, and possible contamination from external sources along Kalwan river in Surgana (NSu) and Peint (NPe) taluks.

&

&

&

&

Suitability of groundwater for irrigation purpose can be justified based on different indices computed, which indicated that:

&

&

&

Humid, sub-humid, semi-arid, and arid zones of the basin had Na ranging from 5 to 102, 2.3 to 218, 2 to 917, and 2.1

to 1268 mg/L, respectively; higher Na (∼1200 mg/L) attributed to cation exchange, human activities, and repeated use of water in irrigated lands Very high concentrations of K (120–703.1 mg/L) observed in semi-arid and arid zones, mainly due to potash fertilizers applied in agricultural areas Humid and sub-humid zones indicated SSP < 60% and, hence, suitable for irrigation. NDe10 of Deola (NDe); NSi17 and NSi27 of Sinnar (NSi); AuGa01 of Gangapur (AuGa);AuPh14 of Phulambari (AuPh); AuPat08 of Pathardi (AuPat); and AhNe16 of Newasa (AhNe) taluks in semi-arid zone had SSP > 60%, while NNad24, AhKo17, AhKo14, AhShrr06, and AhKa19 sites in arid zone had SSP > 60% and, hence, regions in semi-arid and arid zone are unsuitable for irrigation purpose. EC ranged from 60 to 10,000 μS/cm in the study area, with 56 samples classified as low saline (EC < 250 μS/ cm), 583 samples as medium saline (250 < EC < 750 μS/ cm), 926 samples as high saline (750 < EC < 2250 μS/ cm), and 207 samples as very high saline (EC > 2250 μS/ cm). High salinity waters cannot be used on soil with restricted drainage. SAR varied from 0.07 to 18.67 meq/L with 95.65% of samples indicating no salinity issue (SAR < 6) while 3.05% of samples indicating increase in salinity problems (SAR in 6–9 range) and 1.29% of samples indicating severe salinity problems (SAR > 9) in some regions. Wilcox diagram revealed that all the samples of humid and sub-humid zones lied in excellent to good class for irrigation suitability while most of the samples from semi-arid and arid zones belonged to excellent to good and good to permissible classes with few samples in semi-arid zone having EC in doubtful to unsuitable category for irrigation purpose (2250–4000 μS/cm range). Very few samples in arid zone had EC > 4000 μS/cm, i.e., unsuitable for irrigation purpose Humid and sub-humid zones lied in C1S1, C2S1, and C3S1 indicating low–high salinity hazard (EC) and low sodium alkaline hazard (SAR). Thus, groundwater is suitable for irrigation in almost all types of soil with little danger of development of exchangeable sodium and salinity. On the other hand, groundwater from semi-arid zone indicated high EC with low SAR (C3S1 category) and those samples from arid zone suffered from high (C3) to very high (C4) salinity hazard. Very few samples in arid zone had medium SAR, i.e., fell in C3S2 and C4S2 categories. RSC varied −2 to 0 meq/L in humid and sub-humid zones with higher variations of 18 to 4 meq/L in semi-arid and arid zones. Percentage of samples with RSC < 1.5 meq/L reduced from 95 to 91% as transit from humid to arid zone. Humid and sub-humid zones had normal (RSBC < 0.75 meq/L) and low alkaline (0.75 < RSBC

Arab J Geosci (2017) 10:171

& &

< 1.25 meq/L) carbonates, low alkaline to be used for irrigation with pre-treatment. Some regions in semi-arid and arid zones had medium alkaline (2.5 < RSBC < 5 meq/L) groundwater and is unfit for irrigation. Around 1129 samples had PI in 25–75% range, falling in class II, and few samples belonged to class I category with PI >75%. KR ranged from 0.05 to 12.81 mg/L with about 76% of groundwater samples are categorized into good quality for irrigation purpose.

Hence, majority of the humid and sub-humid zones indicated low alkaline groundwater, while arid and semi-arid zones indicated normal to alkaline groundwater. Regions with high alkalinity, as indicated by various contour maps, should be supplied with treated groundwater for both irrigation and drinking purposes. Acknowledgements Our special thanks to Groundwater Surveys and Development Agency (GSDA), Pune, for providing us with the necessary data for this research work. This organization is part of the Water Resource Department, Government of Maharashtra, India, and but for their data, this research and analysis would have been impossible. We are also thankful to the Indian Meteorological Department (IMD, Pune) for providing rainfall information for the three districts of our concern. We gratefully acknowledge the support and encouragement received from College of Engineering Pune (COEP) to complete this work. We are also thankful to the editor and reviewers for giving suggestions which have markedly improved the manuscript.

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