nagarajan et al., 2010

Environ Monit AssessDOI 10.1007/s10661-009-1279-9

Evaluation of groundwater quality and its suitabilityfor drinking and agricultural use in Thanjavur city,Tamil Nadu, India

R. Nagarajan · N. Rajmohan ·U. Mahendran · S. Senthamilkumar

Received: 9 April 2009 / Accepted: 3 December 2009© Springer Science+Business Media B.V. 2009

Abstract As groundwater is a vital source ofwater for domestic and agricultural activities inThanjavur city due to lack of surface water re-sources, groundwater quality and its suitability fordrinking and agricultural usage were evaluated.In this study, 102 groundwater samples were col-lected from dug wells and bore wells during March2008 and analyzed for pH, electrical conductivity,temperature, major ions, and nitrate. Results sug-gest that, in 90% of groundwater samples, sodiumand chloride are predominant cation and anion,respectively, and NaCl and CaMgCl are major

R. Nagarajan (B)Department of Science and Mathematics,School of Engineering and Science,Curtin University of Technology, CDT 250, 98009,Miri, Sarawak, Malaysiae-mail: [email protected],[email protected]: http://geonagarajan.googlepages.com

N. RajmohanDepartment of Waste Treatment and ConditioningResearch, Commissariat a l’energie atomique (CEA),Centre De Valrho/Marcoule,BP 1717F 30207 Bagnols-Sur-Cèze, Francee-mail: [email protected]

U. Mahendran · S. SenthamilkumarDepartment of Civil Engineering,Periyar Maniammai University,Thanjavur, Tamil Nadu, India

water types in the study area. The groundwa-ter quality in the study site is impaired by sur-face contamination sources, mineral dissolution,ion exchange, and evaporation. Nitrate, chloride,and sulfate concentrations strongly express theimpact of surface contamination sources such asagricultural and domestic activities, on ground-water quality, and 13% of samples have elevatednitrate content (>45 mg/l as NO3). PHREEQCcode and Gibbs plots were employed to evaluatethe contribution of mineral dissolution and sug-gest that mineral dissolution, especially carbonateminerals, regulates water chemistry. Groundwa-ter suitability for drinking usage was evaluatedby the World Health Organization and Indianstandards and suggests that 34% of samples arenot suitable for drinking. Integrated groundwatersuitability map for drinking purposes was createdusing drinking water standards based on a conceptthat if the groundwater sample exceeds any one ofthe standards, it is not suitable for drinking. Thismap illustrates that wells in zones 1, 2, 3, and 4 arenot fit for drinking purpose. Likewise, irrigationalsuitability of groundwater in the study region wasevaluated, and results suggest that 20% samplesare not fit for irrigation. Groundwater suitabilitymap for irrigation was also produced based onsalinity and sodium hazards and denotes that wellsmostly situated in zones 2 and 3 are not suitablefor irrigation. Both integrated suitability mapsfor drinking and irrigation usage provide overall

Environ Monit Assess

scenario about the groundwater quality in thestudy area. Finally, the study concluded thatgroundwater quality is impaired by man-madeactivities, and proper management plan is neces-sary to protect valuable groundwater resources inThanjavur city.

Keywords Groundwater quality ·Suitability maps · Contamination ·Thanjavur city · South India

Introduction

Due to the ever-increasing demand for potableand irrigation water and inadequacy of availablesurface water, the importance of groundwater isincreasing exponentially everyday. Further, about80% of the diseases and deaths in the devel-oping countries are related to water contamina-tion (UNESCO 2007). In recent days, Thanjavurcity is facing an acute shortage of good drink-ing water owing to poor quality of groundwa-ter except good potable water supplied by themunicipality. Hence, evaluation of groundwaterquality is a necessary and immediate task forpresent and future groundwater quality manage-ment in Thanjavur city due to the nonperennialnature of Cauvery River and frequent failure ofmonsoon. In addition, numerous studies concen-trated on groundwater quality monitoring andevaluation for domestic and agricultural activities(Al-Bassam and Al-Rumikhani 2003; Al-Futaisiet al. 2007; Elampooranan et al. 1999; Elango et al.1998, 2003; Jeevanandam et al. 2006; Pritchardet al. 2008; Rajmohan et al. 1997; Subramani et al.2005; Sujatha and Rajeshwara Reddy 2003). Maet al. (2009) evaluated water quality and iden-tified the source of water pollution in the Wuweibasin of Shiyang river in northwest China andreported high salinity and nitrate in groundwa-ter. These studies emphasized that groundwaterquality monitoring and evaluation is a neces-sary task to protect valuable groundwater sourcesand management. Generally, the concentrationsof dissolved ions in groundwater are governedby lithology, groundwater flow, nature of geo-chemical reactions, residence time, solubility of

salts, and human activities (Bhatt and Saklani1996; Karanth 1987; Nisi et al. 2008; Schot andVan der Wal 1992). Moreover, the groundwa-ter quality is mostly affected by either naturalgeochemical processes such as mineral weath-ering, dissolution/precipitation reactions, ion ex-change, or various man-made activities such asagriculture, sewage disposal, mining and industrialwastes, etc. The surface runoff from the agricul-tural field is one of the main sources for nutrientsand salinity in the groundwater, and occurrenceof nitrate and nitrite in the groundwater abovethe permissible limit is not conductive for thedrinking purpose (Lee et al. 2003; Rajmohan andElango 2005). Nitrate results mostly from sur-face contamination sources. Nitrate (>300 mg/l)poisoning may result in the death of livestockconsuming water (Canter 1997). In humans, acondition called methemoglobinemia, also knownas blue baby syndrome, results from the ingestionof high concentration of nitrate in its inorganicform. Nitrate contamination is strongly relatedto land use pattern and reported in several stud-ies throughout the world (Ator and Denis 1997;Elhatip et al. 2003; Jeong 2001; Kalkhoff et al.1992; Rajmohan et al. 2009). Further, groundwa-ter with low pH values can cause gastrointesti-nal disorder and this water cannot be used fordrinking purposes (Laluraj and Gopinath 2006).Total dissolved solids (TDS) values are also con-sidered as an important parameter in determiningthe usage of water, and groundwater with highTDS values is not suitable for both irrigationand drinking purposes (Fetters 1990; Freeze andCherry 1979). Like drinking, groundwater qualityis an important criterion to decide the water forirrigation activities. Several researchers evaluatedthe suitability of groundwater for irrigation usingvarious parameters, e.g., Na%, sodium absorptionratio (SAR), residual sodium carbonate (RSC),Wilcox, and US Salinity Laboratory (USSL) clas-sifications, etc. (Al-Bassam and Al-Rumikhani2003; Al-Futaisi et al. 2007; Elampooranan et al.1999; Elango et al. 1998, 2003; Jeevanandam et al.2006; Rajmohan et al. 1997; Subramani et al. 2005;Sujatha and Rajeshwara Reddy 2003).

The present study was carried out to evalu-ate the groundwater quality and its suitability fordomestic and agricultural activities in Thanjavur


city, Tamil Nadu, India, as the groundwater isthe only major source of water for agriculturaland domestic purposes due to the lack of surfacewater.

Study area

The study region is Thanjavur city, which is lo-cated 300 km far from Chennai, in the CauveryDelta Zone of eastern part of Tamil Nadu, India(Fig. 1). The city extends between North lati-tudes 10◦ 8′–10◦ 48′ and east longitudes 79◦ 09′–79◦ 15′ with an altitude of 59 m, and it has anaverage elevation of 2 m. The study region hasan area of 36.31 km2 and being developed in the

adjacent villages. Total population in the studysite is about 226,830 (Census of India 2001). TheCauvery delta zone has a tropical climate, andthe average annual rainfall in Thanjavur city is1,114 mm. The average temperature in this regionvaries between 36.6◦C and 32.5◦C in summer andbetween 23.5◦C and 22.8◦C during winter, respec-tively. The most important economic activity ofthis area is agriculture, and the major crops arepaddy, sugarcane, coconut, plantain, etc. The ir-rigation system is mostly feed by the groundwateras well as the canal system (Grand Anaicut Canal)in this Cauvery delta area. It consists of grandand upper anaicuts across the Cauvery River. Thisgreat system of canals is covering the whole deltain the districts of Thiruchirapalli and Thanjavur.

Fig. 1 Sampling wellslocation and zonesclassification inThanjavur city


The total length of the canal exceeds 6,000 km,and 400,000 ha of land is being irrigated.

Geology and hydrogeology

Figure 2 illustrates the geology of the study site.The area consists of alluvial flood plain and in-cludes paleochannel deposits, sandstone, gravels,and patches of kankar formations which belong tothe Tertiary to Quaternary age (Tamil Nadu Agri-cultural University 2002–2004). The study areaconsists of two distinct formations namely Quater-nary alluvial flood plain deposits in the northernpart and Miocene sediments in the southern partof the study area. The alluvial thickness rangesfrom 30 to 400 m. The alluvial soil is clayey-textured with 40–45% of clay fraction particu-larly montmorillonite, which has good capacity foradsorption and retention of water and plant nu-trients (Tamil Nadu Agricultural University 2002–

2004). The Cretaceous Formations occur as smallpatch in the southwestern sides but not within thestudy area. These formations have a very thicklateritic cap, consisting of impure argillaceousand calcareous clay. The Pliocene formations areformed to occur on the southeastern side of Than-javur town overlying the Miocene formations.This formation includes sand, variegated clay, andgravel. The water level fluctuates between 10.50and 23.00 m during summer and between 6.15and 10.90 m during winter. Thickness of shallowaquifer ranges from 10 to 30 m and deep aquiferranges from 60 to 120 m.

Methodology

Thanjavur city was divided into ten zones basedon Panchayat wards for administration purposes.In this study, we have considered the same ad-ministration zones for groundwater sampling and

Fig. 2 Geology of thestudy area


further discussion. In the study area, 102 boreand dug wells were selected for groundwater sam-pling based on field survey. Figure 1 shows thegroundwater sampling locations and administra-tion zones. Groundwater samples were collectedduring March 2008 and analyzed for major ionsand nitrate. The groundwater samples were col-lected in 2-l high-density polyethylene contain-ers prewashed with 1:1 HCl and rinsed three tofour times before sampling using sampling water.Collected samples were transported to laboratorywithin the same day and stored at 4◦C. Sam-ples for laboratory analysis were filtered in thelaboratory in the same day through 0.45-μm cel-lulose membranes prior to the analyses. Ground-water samples for cation analysis were acidified topH < 2 with several drops of ultrapure HCl inthe laboratory. Groundwater samples were ana-lyzed based on standard methods (APHA 1995).Electrical conductivity (EC) and pH were mea-sured in the field immediately after the collectionof the samples using portable field meters. Theanalyses were carried out in the Regional WaterTesting Laboratory, TWAD Board, Thanjavur.In the laboratory, Na and K were analyzed byflame photometer, and Ca, Mg, Cl, and alkalinity(HCO3) were estimated by titration. Sulfate andnitrate were analyzed using spectrophotometer.Measurement reproducibility and precision foreach analysis were less than 2%. The analyticalprecision for the total measurements of ions waschecked again by calculating the ionic balanceerrors and was generally within ±5%.

The geochemical computer code PHREEQC(Parkhurst and Appelo 1999) with thermody-namic database PHREEQC and WATEQ4F wasused to calculate the distribution of aqueousspecies and mineral saturation indices. In addi-tion, groundwater quality data were employed tocreate integrated groundwater quality maps.

Results and discussion

General water chemistry

The hydrochemistry of groundwater for all thezones is given in Table 1 with minimum, maxi-mum, mean, and standard deviation values. The

chemical composition of the groundwater samples(n = 102) in the study region shows a wide range.The EC in the study region is varied from 190 to6,000 μS/cm with an average of 1,101 μS/cm (n =102). The TDS ranged from 133 to 4,200 mg/l witha mean value of 783 mg/l. According to the TDSclassification, 29.4% of the groundwater samplesbelong to the brackish type (TDS > 1,000 mg/l),and the remaining comes under freshwater cate-gory (TDS < 1,000 mg/l; Freeze and Cherry 1979).Among the cations, the concentrations of Na, K,Ca, and Mg ions ranged from 18 to 740, 1 to 60, 12to 240, and 3 to 154 mg/l with an average valueof 133, 8, 67, and 20 mg/l, respectively. Cationchemistry indicates that 94% of the samples areNa > Ca > Mg > K, while the remaining 6% ofsamples are Ca > Na > Mg > K. The dissolvedanions such as alkalinity, Cl, SO4, and NO3 lie inbetween 40 and 688, 28 and 1,660, below detectionlimit (BDL) and 133, and 2 and 176 mg/l withan average value of 196, 204, 44, and 23 mg/l,respectively. The pH of the groundwater samplesin the study area varies from 6 to 9.6 with an aver-age value of 7.1 which indicates that the dissolvedcarbonates are predominantly in the HCO3 form(Adams et al. 2001). About 62% of samples showthe pH variation between 7 and 8.2, indicating analkaline nature.

Both EC and chloride have high standard de-viation compared to other parameters and sug-gest that water chemistry is not homogeneous inthe study region and regulated by distinguishedprocesses. Moreover, the nitrate concentrationindicates that 13% of samples exceed 45 mg/l,and 11% of samples lie between 25 and 45 mg/l.The concentrations of chloride and nitrate firmlyevidence the influences of surface contaminationsources such as agricultural activities (irrigationreturn flow, fertilizers, and farm manure) and do-mestic wastewaters (septic tank leakage, sewagewater, etc.) in the study region. However, alkalin-ity concentration (196 ± 129, mean ± SD) revealsthe influences of mineral dissolution on waterchemistry in the study region.

Processes regulating water quality

Zone-wise groundwater quality data (Table 1) in-dicate that zones 2, 3, and 4 have high concentra-


Table 1 Statistical summary of groundwater quality data in Thanjavur City

TDS EC pH TH Ca2+ Mg2+ Na+ K+ NO−3 Alk Cl− SO2−

4

Zone 1 Min 560 800 7.2 160 48 5 84 4 2 180 112 33Max 1,400 2,000 7.9 512 152 32 264 12 11 478 352 120Mean 977 1,395 7.5 310 93 19 169 7 7 299 234 64SD 292 417 0.2 108 35 9 59 3 3 89 81 28n 10 10 10 10 10 10 10 10 10 10 10 10

Zone 2 Min 504 720 6.7 88 24 7 92 6 8 120 140 10Max 4,200 6,000 9.6 1,240 240 154 740 60 102 688 1,660 133Mean 1,413 2,018 7.8 383 104 34 265 17 52 394 357 66SD 981 1,402 0.7 289 55 39 186 15 35 151 425 39n 12 12 12 12 12 12 12 12 12 12 12 12

Zone 3 Min 168 240 6.5 74 20 6 20 1 5 50 40 8Max 2,100 3,000 7.9 540 180 62 368 32 176 540 504 120Mean 1,023 1,461 7.3 264 89 25 167 11 51 294 226 62SD 539 770 0.5 120 51 16 111 9 49 144 131 37n 10 10 10 10 10 10 10 10 10 10 10 10

Zone 4 Min 749 1,070 6.2 224 56 19 95 6 17 160 156 28Max 1,253 1,790 7.6 500 131 48 220 16 56 324 384 90Mean 1,099 1,570 6.6 390 104 31 166 11 39 210 304 69SD 192 275 0.5 88 25 10 34 3 12 48 87 25n 10 10 10 10 10 10 10 10 10 10 10 10

Zone 5 Min 420 600 7.1 156 40 12 65 3 8 122 86 23Max 805 1,150 7.5 170 48 15 174 12 21 160 272 44Mean 535 764 7.4 163 42 13 98 6 16 137 137 33SD 160 229 0.1 6 3 1 46 4 4 13 77 7n 10 10 10 10 10 10 10 10 10 10 10 10

Zone 6 Min 308 440 7.0 120 29 11 46 1 13 76 66 BDLMax 721 1,030 8.0 186 44 19 144 10 18 160 232 38Mean 432 617 7.4 149 37 14 70 4 15 118 109 18SD 120 172 0.3 23 6 3 29 3 2 30 47 11n 10 10 10 10 10 10 10 10 10 10 10 10

Zone 7 Min 322 460 6.4 110 26 10 51 3 2 68 66 15Max 903 1,290 8.0 312 82 26 148 10 18 170 316 45Mean 459 655 7.5 159 42 13 73 5 12 113 120 28SD 164 234 0.6 57 16 5 28 2 6 31 71 10n 10 10 10 10 10 10 10 10 10 10 10 10

Zone 8 Min 175 250 6.1 72 25 3 24 1 3 60 36 14Max 1,470 2,100 7.6 480 136 42 248 12 11 260 488 108Mean 655 935 6.6 228 63 17 104 5 7 131 189 45SD 427 610 0.4 146 39 13 69 4 3 57 166 27n 10 10 10 10 10 10 10 10 10 10 10 10

Zone 9 Min 133 190 6.0 50 12 4 18 1 5 40 28 BDLMax 1,610 2,300 7.0 500 120 48 256 16 13 270 574 48Mean 587 838 6.6 178 45 16 102 5 9 123 178 19SD 508 725 0.3 148 36 14 91 5 3 84 182 18n 10 10 10 10 10 10 10 10 10 10 10 10

Zone 10 Min 189 270 6.0 84 24 6 24 1 4 52 40 8Max 1,029 1,470 8.1 350 84 34 220 12 18 160 356 108Mean 528 754 6.7 171 46 14 88 5 11 100 151 35SD 276 394 0.7 85 20 9 57 4 5 40 104 33n 10 10 10 10 10 10 10 10 10 10 10 10Min 133 190 6.0 50 12 3 18 1 2 40 28 BDLMax 4,200 6,000 9.6 1,240 240 154 740 60 176 688 1,660 133


Table 1 (continued)

TDS EC pH TH Ca2+ Mg2+ Na+ K+ NO−3 Alk Cl− SO2−

4

Total Mean 783 1,119 7.1 242 67 20 133 8 23 196 204 44SD 548 783 0.6 158 42 17 104 8 26 129 191 32n 102 102 102 102 102 102 102 102 102 102 102 102

tions of major ions, nitrate, and EC. Especially,groundwater samples in zone 2 are extremelyaffected by surface contamination sources be-cause the average chloride (357 mg/l) and nitrate(52 mg/l) concentrations are very high comparedto other zones. Regional groundwater qualitymaps, prepared by GIS, also apparently illustratethat wells in zone 2 contain elevated concentrationof TDS, nitrate, and Cl (Fig. 3). Like nitrate andCl, a similar trend is observed in other major ionsand in EC. Further, zones 3 and 4 also expresshigh concentrations of most of the ions next tozone 2. Alkalinity generally represents dissolutionof carbonate and silicate minerals. However, it isalso very high in zones 2, 3, and 4 (Table 1). Theaverage concentrations of alkalinity in zones 2,3, and 4 are 394, 294, and 210 mg/l, respectively.This observation suggests that the water chemistryin these zones (2, 3, and 4) could be affected byinfiltration of wastewater originating from surfacecontaminations sources, which causes dissolutionof carbonate and silicate minerals indirectly.

In order to understand the chemical character-istics of groundwater in the study region, ground-water samples were plotted in Piper trilineardiagram (Piper 1944) using AquaChem software(Fig. 4). Figure 4 displays that groundwater sam-ples are classified as various chemical types onthe Piper diagram. The dominant water typesare in the order of NaCl > CaMgCl > mixedCaNaHCO3 > CaHCO3. However, most of thesamples are clustered in NaCl and CaMgCl seg-ments. Water types (CaMgCl and NaCl) suggestthe mixing of high-salinity water caused fromsurface contamination sources such as irrigationreturn flow, domestic wastewater, and septic tankeffluents, with existing water followed by ion ex-change reactions. However, mixed CaNaHCO3

and CaHCO3 water types express mineral dissolu-tion and recharge of freshwater. In addition withPiper diagram, Gibbs plots were also used to gainbetter insight into hydrochemical processes suchas precipitation, rock–water interaction, and evap-oration on groundwater chemistry in the study

79.11 79.12 79.13 79.14 79.15 79.16 79.17 79.18

79.11 79.12 79.13 79.14 79.15 79.16 79.17 79.18

10.7310.74

10.7510.76

10.7710.78

10.7910.8

10.8110.82

10.7310.74

10.7510.76

10.7710.78

10.7910.8

10.8110.82

< 50

150 - 200

50 - 100

100 - 150

Legend

Zone I

Zone II

Zone III

Zone VIZone V

Zone IV

Zone VII

Zone IX

Zone VIII

Zone X

NO3 mg/l

79.11 79.12 79.13 79.14 79.15 79.16 79.17 79.18

79.11 79.12 79.13 79.14 79.15 79.16 79.17 79.18

10.7310.74

10.7510.76

10.7710.78

10.7910.8

10.8110.82

10.7310.74

10.7510.76

10.7710.78

10.7910.8

10.8110.82

< 200

600 - 800

200 - 400

400 - 600

800 - 1000

1000 - 1200

1200 - 1400

1400 - 1600

Legend

1600 - 1660

Zone I

Zone II

Zone III

Zone VIZone V

Zone IV

Zone VII

Zone VIII

Zone IX

Zone X

Cl mg/l

79.11 79.12 79.13 79.14 79.15 79.16 79.17 79.18

79.11 79.12 79.13 79.14 79.15 79.16 79.17 79.18

10.7310.74

10.7510.76

10.7710.78

10.7910.8

10.8110.82

10.7310.74

10.7510.76

10.7710.78

10.7910.8

10.8110.82

> 500

1500 - 2000

500 - 1000

1000 - 1500

2000 - 2500

2500 - 3000

3000 - 3500

3500 - 4000

4000 - 4200

Legend Zone I

Zone II

Zone III

Zone IV

Zone V

Zone VI

Zone VII

Zone VIII Zone X

Zone IX

TDS mg/l

Fig. 3 Spatial distribution of TDS, nitrate, and chloride in the study region


Fig. 4 Piper trilineardiagram shows thechemical character ofgroundwater samples

Ca Na+K HCO3 Cl

Mg SO4

80 60 40 20

20

40

60

80

20

40

60

80

20

40

60

80

20 40 60 80

80

60

40

20

SO4 +

Cl

Na

+K H

CO 3

CaHCO3

Mixed CaNaHCO3

NaCl

Mixed CaMgCl

Ca+M

g

region (Fig. 5). Gibbs (1970) demonstrated that ifTDS is plotted against Na/(Na + Ca), this wouldprovide information on the mechanism control-

ling chemistry of waters. Figure 5 displays thatgroundwater samples were plotted mostly in therock–water interaction zone and few samples in

Fig. 5 Mechanismscontrolling groundwaterchemistry—Gibbs plots

1

10

100

1000

10000

100000

0.0 0.2 0.4 0.6 0.8 1.0

(Na+K)/(Na+K+Ca)

TD

S (

mg

/l)

1

10

100

1000

10000

100000

0.0 0.2 0.4 0.6 0.8 1.0

Cl/(Cl+Alk)

TD

S (

mg

/l)

Precipitation

Evaporat

ion

Precipitation

Evaporat

ion

Rock water interaction Rock water interaction


the evaporation zone. This observation suggeststhat dissolution of carbonate and silicate mineralsare mostly controlled the groundwater chemistryin the study region. However, few samples plot-ted in the evaporation zone reveal that surfacecontamination sources, for example irrigation re-turn flow, seem to be affected the groundwaterquality in the study region. Both Piper and Gibbsplots suggest that water chemistry is regulatedby mixing of salinity water, caused by surfacecontamination sources, with existing water, ionexchange reactions, mineral dissolution, and pos-sibly evaporation.

Ion exchange process

The evolution of groundwater towards a Na-richtype generally occurred by the precipitation ofcalcite and/or cation exchange. In contrast, Ca–Cl-type water is commonly produced by reverseion exchange reaction (Na + Ca-Clay = Na-Clay + Ca). Both cation exchange and reverseion exchange are encouraged by aquifer mate-rials, especially montmorillonite, which leads tothe release of Na or Ca into groundwater andadsorption of Ca or Na, respectively (Alison et al.1992; Blake 1989; Cerling et al. 1989; Foster 1950).As Piper plot indicates the possibility of ion ex-change reactions, Schoeller chloroalkaline indiceswere employed to understand the ion exchangereactions. The ion exchange reactions betweenthe groundwater and its host environment duringresidence or travel can be understood by studyingthe chloroalkaline indices; chloroalkaline indices1 and 2 (CAI 1 and CAI 2) are calculated for thegroundwater samples of the study region using thefollowing relations (Schoeller 1965, 1967).

CAI 1 = Cl− − (Na+ + K+)

/Cl− (1)

CAI 2 = Cl− − (Na+ + K+)

/SO2−4 + HCO−

3

+CO2−3 + NO−

3(All values are expressed

in milliequivalent per liter)

(2)

If the index values are negative, Na+ and K+ions in the aquifer materials are exchanged withMg2+ and Ca2+ ions in water whereas a reverse

process will give a positive value (Cl > Na + K).During this process, the host rocks are the primarysources for dissolved solids in the water. Schoeller(1965, 1967) indices indicate that all samples inthe study region have positive values except a fewsamples and explain that reverse ion exchangereaction is dominant in the study region. But ina few sites where the values are negative, thissuggests the influences of normal ion exchangereactions.

Ef fect of mineral dissolution and surfacecontamination sources

As per the geology, soil information, and Gibbsplots, mineral dissolution is one of the ma-jor processes regulating water chemistry in thestudy region. Dissolution of carbonate mineralsseems to largely affect the water chemistry be-cause kankar formation is observed in the studysite. Saturation indices (SI) of carbonate (calcite,dolomite), sulfate (gypsum, anhydrite) minerals,and halite were calculated using PHREEQC. Sat-uration indices of calcite vary between −3 and 1(Fig. 6) while SI value of dolomite ranges from−5 to 2. SI values of sulfate minerals and halitesuggest that groundwater samples are highly un-dersaturated with respect to gypsum (SI < −2),anhydrite (SI < −2), and halite (SI < −6). Thisobservation reveals that influences of sulfate min-erals and halite are not significant on groundwa-ter chemistry, and there is no known geologicalinformation about the occurrence of sulfate min-erals and halite in the study region. However,application of gypsum (fertilizer) in the irrigationfield may contribute sulfate content in groundwa-ter through irrigation return flow. Likewise, NaClsalt from domestic wastewater can affect waterchemistry by infiltration.

Saturation indices of carbonate minerals (cal-cite, dolomite) show that these are varying withgroundwater zones (Fig. 6). Groundwater samplesmay be classified into three groups: oversaturated(SI > 0), saturated (SI ≤ 0), and undersaturated(SI < −1). Figure 6 illustrates that wells locatedin zones 1, 2, and 3 come under group 1 (SI > 0).Wells existing in zones 4, 5, 6, and 7 are classifiedas group 2 (SI ≤ 0) whereas wells situated in theremaining zones (8, 9, and 10) come under group


Fig. 6 Variation ofselected parameters withrespect to well numbers

-6

-5

-4

-3

-2

-1

0

1

2

3

0 10 20 30 40 50 60 70 80 90 100

Calcite Dolomite

Sat

ura

tio

nIn

dic

es

0

500

1000

1500

2000

2500

0 10 20 30 40 50 60 70 80 90 100

TD

S(m

g/l)

0

100

200

300

400

500

600

700

800

0 10 20 30 40 50 60 70 80 90 100

Alk

alin

ity

(mg

/l)

020406080

100120140160180200

0 10 20 30 40 50 60 70 80 90 100

020406080

100120140160180200

0 10 20 30 40 50 60 70 80 90 100

Cal

ciu

m(m

g/l)

Nit

rate

(mg

/l)

Well number


3 (SI < −1). The variation of carbonate mineralssaturation in the study site may be due to threemajor reasons: (1) variation in the occurrence ofcarbonate minerals, (2) external sources of Ca,Mg, and alkalinity entering into the groundwatersystem by recharge process, and (3) infiltration ofwastewater, originating from surface contamina-tion sources, enhances the dissolution of carbon-ate minerals existing in the aquifer materials. Inthe study region, there is no heterogeneity in geo-logical formation, which ruled out the first reason.Moreover, Fig. 6 also shows that total TDS andcalcium behave similarly, and group 1 followed bygroup 3 wells have high concentrations comparedto group 2. Other major ions (Mg, Na, K, Cl, andSO4) also express similar trend like calcium andTDS. However, alkalinity and nitrate are contraryto other ions, and these are very high in group 1wells compared to groups 2 and 3 wells. These ob-servations suggest that alkalinity in group 1 wellsmay originate from surface contamination sourcesin addition with carbonate mineral dissolution(Adams et al. 2001). Generally, alkalinity can en-ter the aquifer from the dissolution of carbonateminerals, soil CO2, or from the bacterial degrada-tion of organic material (Jeong 2001). In this studysite, alkalinity can also come from surface conta-mination sources such as bacterial degradation oforganic material, anthropogenic CO2 gas causedfrom municipal wastes dumped in the unlineddumping sites, and oxidation of organic materialsleaked from old latrines and sewage systems inthe study area (Clark and Fritz 1997). Hence,the second and third reasons are more reliablefor oversaturation of groundwater with respect tocarbonate minerals in group 1 wells because theinfluences of domestic wastewater and irrigationreturn flow are apparently observed in zones 2–4which enhances saturation of carbonate mineralsin the study region.

As mentioned earlier, the study region is cov-ered by both urban and agricultural activities.The study area is mostly irrigated with paddycrops. Hence, application of fertilizers and irri-gation return flow may also affect the ground-water quality in the study region. It is stronglyobserved in potassium, sulfate, and nitrate. Gen-erally, potassium is retained with aquifer material,especially in clay formation, and several studies

reported very low concentration in groundwater(Sarin et al. 1989; Subba Rao 2002). In the studyregion, potassium is generally less than 8 mg/l(average) except in zones 2, 3, and 4 (K > 11 mg/l,average; Table 1). This observation suggests thatpotassium concentration in zones 2, 3, and 4 isentered into the groundwater system from exter-nal sources in addition with mineral dissolutionbecause there is no heterogeneity in geology. Likepotassium, the average sulfate concentration isless than 45 mg/l in the study region except wellsin zones 1, 2, 3, and 4 where SO4 > 60 mg/l(Table 1). Application of potassium fertilizers(Potash (KCl) and NPK (nitrogen–phosphorus–potassium, mixed fertilizer) and gypsum seemsto be contributed well in potassium and sulfateconcentrations in addition with domestic waste-water (sewage, septic tank effluent, etc). Likepotassium and sulfate, nitrate also illustrates verylarge variation with respect to zones (Table 1,Fig. 3). The average nitrate is generally less than16 mg/l except in zones 2, 3, and 4 (Table 1). Theaverage concentrations in zones 2, 3, and 4 are 52,51, and 39 mg/l, respectively. Generally, nitrateoriginates from distinguished processes such asirrigation practice, organic material oxidation, soilmineralization, urban contamination, etc. (Elhatipet al. 2003; Jeong 2001; Subba Rao 2002). In thestudy region, infiltration of domestic wastewater,septic tank effluents, irrigation return flow, fertil-izer (mainly urea), and farm manure are the majorsources for nitrate in groundwater. The study areais dominantly covered by old settlements, andconstructed septic tanks in this settlement area areolder than a decade. Hence, leakage of effluentfrom these septic tanks is one of the major sourcesfor nitrogen.

Evaluation of groundwater quality

Drinking usage

The analytical results have been evaluated to as-certain the suitability of groundwater in the studyarea for domestic and agricultural purposes basedon the World Health Organization (WHO 1993)and Indian Standards (1991; Table 2). The averagevalues of individual parameters of groundwater


Tab

le2

Ran

gein

conc

entr

atio

nof

chem

ical

para

met

ers

ofth

est

udy

area

and

com

pare

dw

ith

WH

Oan

dIn

dian

Stan

dard

sfo

rdr

inki

ngpu

rpos

es

Wat

erqu

alit

yW

HO

(199

3)In

dian

stan

dard

No.

ofsa

mpl

esex

ceed

the

stan

dard

sC

once

ntra

tion

Und

esir

able

effe

ctpr

oduc

edpa

ram

eter

s(I

S10

500,

1991

)in

the

stud

yar

eabe

yond

max

allo

wlim

itH

ighe

stac

cept

Max

allo

wab

leH

ighe

stM

axA

ccor

ding

toA

ccor

ding

tolim

it(m

g/l)

limit

desi

rabl

epe

rmis

sibl

eW

HO

(199

3)(I

SI19

91)

TD

S50

01,

500

500

2,00

013

,18,

21,2

9,92

21,2

913

3–4,

200

Tas

te,g

astr

oint

esti

nal

(avg

.771

)ir

rita

tion

pH6.

58.

56.

5–8.

56.

5–9.

511

116–

10(a

vg.7

)T

aste

effe

cts

muc

usm

embr

ane

and

wat

ersu

pply

syst

emT

H(a

sC

aCO

3)10

050

030

060

08,

21,2

921

50–1

,240

Enc

rust

atio

nin

wat

er(a

vg.2

39)

supp

lyan

dad

vers

eef

fect

ondo

mes

tic

use

Ca2+

7520

075

200

12,2

112

,21

12–1

,132

(avg

.76)

Mg2+

5015

030

100

2121

3–15

4(a

vg.1

9)N

a+–

200

–20

01,

4,7,

12,1

5,16

,1,

4,7,

12,1

5,16

,18

–748

18,2

0,21

,28,

29,3

0,18

,20,

21,2

8,29

,30,

(avg

.137

)36

,79,

85,8

7,92

,94

36,7

9,85

,87,

92,9

4K

+–

12–

–13

,15,

18,2

0,21

,28,

1–60

(avg

.8)

29,3

0,36

,40,

92N

O− 3

45–

4545

13,1

4,15

,18,

21,2

3,13

,14,

15,1

8,21

,23,

2–17

6(a

vg.2

2)B

lue

baby

dise

ases

24,2

7–29

,32,

40,4

1,24

,27–

29,3

2,40

,41

inch

ildre

nC

l−20

060

025

01,

000

2121

28–1

,660

Salt

yta

ste

indi

cate

s(a

vg.1

99)

pollu

tion

SO2− 4

200

400

200

400a

Nil

Nil

0–13

3(a

vg.4

4)C

ause

gast

roin

test

inal

irri

tati

onw

hen

Mg

and

Na

sulf

ate

Uni

ts=

mg/

l,ex

cept

pHa U

pto

400

mg/

lifM

gdo

esno

texc

eed

30m

g/l


Table 3 Classification of groundwater based on TDS(Davies and DeWiest 1966)

TDS Water type Percentage

Up to 500 Desirable for drinking 42500–1,000 Permissible for drinking 28<3,000 Useful for irrigation 99>3,000 Unfit for drinking and irrigation 1

are within the permissible limit when comparedto the WHO (1993) and Indian Standard (1991)whereas individual samples are having higherconcentration which have shown in the table bycomparing WHO and Indian standards. Accord-ing to the Freeze and Cherry (1979), 70.6% ofsamples are considered as freshwater type. Inthe classification based on Davies and DeWiest(1966), 42% of samples are desirable for drinkingand 28% of samples are considered as permissiblefor drinking purposes based on TDS (Table 3).Among the cations, sodium is the most dominantcation in groundwater. Sodium concentration ofmore than 50 mg/l makes the water unsuitablefor domestic use. Hardness is an important cri-terion for determining the usability of water fordomestic, drinking, and many industrial supplies(Karanth 1987). Hardness can be classified astemporary due to carbonate and bicarbonates orpermanent due to sulfate and chlorides of calciumand magnesium. Total hardness varies between50 and 1,240 with an average of 239 mg/l. Thegroundwater with total hardness (TH) value lessthan 75 mg/l is considered as soft. According to theclassification using total hardness, 20% of ground-water samples show moderate quality and 75%come under hard to very hard category (Table 4).A very low percentage, about 4.90%, of samplesshows good quality. Hard water is mainly an es-thetic concern because of the unpleasant taste. Italso reduces the ability of soap to produce latherand causes scale formation in pipes and on plumb-

Table 4 Classification of the groundwater based onhardness

Total hardness Water classification Percentage(as CaCO3, mg/l) of wells

<75 Soft 575–150 Moderately hard 20150–300 Hard 47>300 Very hard 28

ing fixtures. Magnesium is one of the constituentsresponsible for hardness of water. Further, highermagnesium concentration may be cathartic anddiuretic (WHO 1997). Also, the values of mag-nesium combined with sulfate act as laxative tohuman beings. The maximum permissible andhighest desirable limit given by the WHO (1993)and Indian Standard Institute (Indian StandardInstitution 1991) is 100 and 30 mg/l, respectively.The magnesium ranges between 3 and 154 mg/lwith an average of 20 mg/l (n = 102, Table 1).Most of the samples are within the permissiblelimit. Sulfate is one of the least toxic anions,even though dehydration is observed at high con-centrations. Indian Standard Institution (1991)suggested that highest desirable and maximumpermissible limit of sulfate is 200 and 400 mg/l,respectively. If the limit of sulfate exceeds, it maycause gastrointestinal irritation and laxative effectat higher level (WHO 1993). Sulfate values in thestudy area vary from BDL to 133 mg/l with anaverage of 44 mg/l (n = 102, Table 1). Mostly,all the samples show sulfate content within therecommended limit.

Integrated groundwater suitability map fordrinking purposes in the study site is created bycombining all the quality parameters, e.g., TDS,TH, pH, Na, K, Ca, Mg, Cl, SO4, and NO3 (Fig. 7).This map is produced based on the concept thatif the groundwater samples exceed the recom-mended limits (Indian Standard Institution 1991;WHO 1993) of any one of the parameters, theyare not suitable for drinking usage. In the studyregion, 34 wells (34% in total wells) exceed anyone of the drinking water standards recommendedby WHO (1993) and Indian Standard Institu-tion (1991) which are not suitable for drinkingpurpose.

Irrigational suitability

In the study region, the surface water facilityfor irrigation is available only for a limited timeor season due to frequent failure of monsoon.For other seasons, irrigation mainly depends ongroundwater. Irrigational suitability of groundwa-ter in the study site was evaluated by EC, SAR,RSC, USSL classification, Na%, and Wilcox dia-gram. The total content of soluble salts such as Na


Fig. 7 Integratedgroundwater suitabilitymap for drinking in thestudy region

79º8’0”E 79º10’0”E

79º8’0”E 79º10’0”E

10º4

4’0”

N

10º4

6’0”

N

10º4

8’0”

N

10º4

4’0”

N

10º4

6’0”

N

10º4

8’0”

N

Suitable

Unsuitable

Highly unsuitable

to Ca and Mg and its relative proportion affect thesuitability of groundwater for irrigation. The ECand Na concentration are important in classifyingirrigation water. According to Richards (1954),the irrigation water is classified into four groupssuch as low (EC = <250 μS/cm), medium (250–750 μS/cm), high (750–2,250 μS/cm), and very high(2,250–5,000 μS/cm) salinity. High EC in waterleads to formation of saline soil, whereas highNa content in water causes alkaline soil. In ad-dition, SAR and RSC are used to evaluate thegroundwater quality for irrigation. The irrigationwater containing a high proportion of sodium will

increase the exchange of sodium content of thesoil, affecting the soil permeability, and the tex-ture makes the soil hard to plough and unsuitablefor seedling emergence (Trivedy and Goel 1984).Features that generally need to be considered forevaluation of groundwater suitability for irriga-tion are salinity, sodium percentage, and SAR.The sodium or alkali hazard in the use of water forirrigation is expressed by determining the SAR,and it was estimated by the equation:

SAR = Na/[(

Ca + Mg)/2

]0.5

Units are expressed in milliequivalent per liter

Table 5 Classification ofthe groundwater qualityaccording to the USDAmethod

Sodium hazard Salinity hazardLow C1 Medium C2 High C3 Very high C4

Low S1 5 (4.9%) 40 (39.2%) 36 (35.3%) 0Medium S2 0 0 17 (16.7%) 1 (0.98%)High S3 0 0 0 2 (1.96%)Very high S4 0 0 0 0


Fig. 8 USSLclassification ofgroundwater samples

0

2

4

6

8

10

12

14

16

18

20

22

24

26

28

30

100 750 10000

SPECIFIC CONDUCTANCE (µs/cm at 25°C)

SO

DIU

MA

DS

OR

PT

ION

RA

TIO

(SA

R)

32

LOW

ME

DIU

MH

IGH

V.H

IGH

250 2250 5000

2 3 4 5 6 7 88 9 1000 2 3 4 5000 10000100

S1

S2

S3

S4

LOW MEDIUM HIGH V.HIGH V.V.HIGH

C1 C2 C3 C4 C5

The calculated values of SAR in the study areavary between 0.97 and 9.17 (Table 5). A moredetailed analysis, however, with respect to the ir-rigation suitability of the groundwater, was madeby plotting the data on the diagram of the USSalinity Laboratory of the Department of Agri-culture (United States Salinity Laboratory 1954).

According to this classification, low-salinity water(<200 mg/l) may be used for all types of soils(Fig. 8). The groundwater of the study area fallsinto the good to moderate category (Fig. 8; Ta-ble 6). Overall, 76% of samples fall in C2S1 andC3S1 fields, indicating medium- to high-salinityand low-alkalinity water which can be used for

Table 6 Relation between SAR and EC of the groundwater samples in the study area

SAR EC Water class Sample number Salinity hazard

<10 250 Excellent 25, 73, 84, 88, 90 (4.90%) Low250–750 Good 11, 26, 43–49, 53, 54, 56–68, 70–72, 74, 75, 80, 81, 83, Medium

86, 91, 93, 98–102 (39.2%)751–2,250 Fair 1–10, 12, 14–17, 19, 20, 22–24, 27, 28, 30–42, 50–52, High

55, 69, 76–79, 82, 85, 87, 89, 94–97 (51%)>2,250 Poor 13, 18, 21, 29, 92 (4.90) Very high


irrigation, where moderate amount of leachingoccurs and moderate permeability with leachingsoil. Besides, 18% of samples fall in C3S2 field,indicating high salinity and medium sodium haz-ard, which restrict its suitability for irrigation.Classification of groundwater based on salinityhazard (EC) and SAR is presented in Table 6.It is found that only five samples are unsuitablefor irrigation purposes. High salinity and mediumhazard type of water in fine-textured soil of highcation exchange capacity, especially under lowleaching conditions, unless gypsum is present inthe soil, presents appreciable sodium hazard. Butit may be used on coarse-textured or organic soilswhich have good permeability. The rating of watersamples in relation to salinity and sodium hazardreflects that the high sodium ion concentration inthe water at some of the stations may produceharmful levels of exchangeable sodium in the soil.

In all natural waters, percent of sodium contentis a common parameter to assess its suitability

for agricultural purposes (Wilcox 1948). Sodiumcombined with carbonate can lead to the forma-tion of alkaline soils, while sodium combined withchloride forms saline soils. Both these soils do nothelp plant growth. Na% was calculated using thefollowing equation.

Na% = Na × 100Ca + Mg + Na + K

A maximum of 60% sodium in groundwater isallowed for agricultural purposes (Ramakrishna1998). Percentage of sodium calculated forgroundwater in the study region is plotted againstspecific conductance in Wilcox diagram (Fig. 9).Figure 9 shows that 45 samples are excellent togood; 32 samples are good to permissible; 19 sam-ples are permissible to doubtful; and six are doubt-ful to unsuitable. RSC index of water samples in

Fig. 9 Irrigationalsuitability of groundwaterin the study region—Wilcox diagram

Sod

ium

per

cent

age

0

10

20

30

40

50

60

70

80

90

100

0 1000 2000 3000 4000

Electrical Conductivity (µS/cm) at 25°C

Exc

elle

nt to

goo

d

Goo

d to

per

mis

sibl

e

Dou

btfu

l to

unsu

itabl

e

Uns

uita

ble

Permissible toDoubtful


Fig. 10 Groundwatersuitability map forirrigational purposes inthe study region Excellent

Good

Unsuitable

Highly Unsuitable

79º8’0”E 79º10’0”E

79º8’0”E 79º10’0”E

10º4

4’0”

N

10º4

6’0”

N

10º4

8’0”

N

10º4

4’0”

N10

º46’

0”N

10º4

8’0”

N

the study site is estimated by the equation (Eaton1950)

RSC = (CO−−

3 + HCO3) − (

Ca++ + Mg++),

units are expressed in milliequivalent per liter

Lloyd and Heathcote (1985) have classified irri-gation water based on RSC as suitable (<1.25),marginal (1.25–2.5), and not suitable (>2.5). Ac-cording to RSC values, 96% of groundwater sam-ples are suitable for irrigation, and 3% of samplesare marginal, and the remaining is not suitable forirrigation.

Overall, groundwater suitability map for irri-gational activities for the study region is pro-duced based on irrigational quality parameterssuch as EC and SAR (Fig. 10). This map is createdbased on the same classification like USSL clas-sification (excellent (C1S1), good (C2S1, C3S1),unsuitable (C3S2), highly unsuitable (C4S3, C4S2,C5S3)). This image will provide the insight ofcurrent groundwater quality scenario and helps

groundwater planners and government sectors forpresent and future groundwater management.

Summary and conclusions

Groundwater quality and its suitability for drink-ing and agricultural use in Thanjavur city areevaluated since groundwater is a major source ofwater for domestic and agricultural activities inthe study site due to lack of surface water re-sources. For this study, 102 groundwater sampleswere collected from dug and bore wells duringMarch 2008 and analyzed for pH, electrical con-ductivity, temperature, major ions, and nitrate.Results suggest that, in 90% of groundwater sam-ples, sodium and chloride are the predominantcation and anion, respectively, in the study area.Further, Piper plot also indicates that NaCl andCaMgCl water types are dominant in the studyarea. Electrical conductivity and chloride con-centration show large variations and have high


standard deviation, which suggests that waterchemistry is not homogenous and regulated bydistinguished processes. The groundwater qualityin the study site is influenced by surface contami-nation sources, mineral dissolution, ion exchange,and evaporation. Nitrate and chloride concen-trations strongly express the impact of surfacecontamination sources such as agricultural anddomestic activities, and 13% of samples have ele-vated nitrate content (>45 mg/l as NO3). Besides,groundwater wells in zones 2, 3, and 4 have highconcentration of potassium and sulfate, which alsoevidences the impact of surface contaminationsources especially application of fertilizers andfarm manures. Influences of mineral dissolutionwas evaluated by PHREEQC and Gibbs plotsand suggest that mineral dissolution, especiallycarbonate minerals, regulate water chemistry. Sat-uration indices of carbonate minerals reveal thatrecharge of wastewater from surface contamina-tion sources enhances saturation of carbonateminerals. Chloroalkaline indices indicate that re-verse ion exchange reaction is a dominanceprocess in the study region. Groundwater suit-ability for drinking usage was evaluated by WHOand Indian standards and proposes that 34% ofsamples are not suitable for drinking. Integratedgroundwater suitability map for drinking purposeswas created using TDS, TH, pH, Na, K, Ca,Mg, Cl, SO4, and NO3, based on a concept thatif the groundwater sample exceeds the recom-mended limit of any one of these parameters, itis not suitable for drinking usage. Further, thismap illustrates that wells in zones 1, 2, 3, and 4are not fit for drinking purpose. Likewise, irri-gational suitability of groundwater in the studyregion was evaluated using quality parameters,e.g., EC, SAR, RSC, USSL classification, Na%,and Wilcox diagram. Result suggests that 20%samples are not fit for irrigation. Groundwatersuitability map for irrigation was also producedbased on salinity and sodium hazard and expressesthat wells mostly existing in zones 2 and 3 arenot suitable for irrigation. Both integrated suit-ability maps for drinking and irrigation usage giveoverall scenario about the groundwater quality inthe study area. Further, these maps will help forpeople who are dedicated to groundwater qual-ity management and planning. Overall, the study

concluded that groundwater quality is impairedby man-made activities, and proper managementplan is necessary to protect valuable groundwaterresources in Thanjavur city.

Acknowledgements The third author is indebted to theVice-Chancellor, Principal, and Head of the Civil De-partment, Periyar Maniyammai University, Thanjavur,India for their constant support during his master de-gree. The author appreciates Dr. M. V. Prasanna, Dr.M. Jeevananthanm, and Mr. Kannan for their help in thepreparation of the maps.

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