Hydrochemistry of groundwater from Tuticorin District ...

EnviroGeoChimica Acta (2014) 1(2):172-179 ORGINAL ARTICLE

ISSN: 2348 – 7259

Hydrochemistry of groundwater from Tuticorin District, Tamil Nadu, India C.Singaraja • S.Chidambaram • P. Anandhan • C.Thivya • R. Thilagavathi Received: 20 Jan 2014/ Accepted: 23 Mar 2014 ©EnviroGeoChimica Acta

Abstract: The study area being a hard rock terrain with minimal rainfall and large extraction of groundwater for domestic, irrigational and industrial purposes have threatened the groundwater environment both in the conditions of quality and quantity. Hence an attempt has been made to classify the major geochemical process activated for controlling the ground water chemistry. Groundwater was generally alkaline with higher EC values. The dominance of anions and cations were of the order of Cl->HCO3->SO42->H4SiO4>NO3->Fand Na+>Ca2+>Mg2+>K+. The plot for Na+/Clto EC indicates Na+ released from silicate weathering and Cl- from anthropogenic activities. The plot for Ca2++Mg2+ to SO42- + HCO3-, indicates ion exchange process. Thermodynamic plot indicates that groundwater is in equilibrium with kaolinite, muscovite and chloride minerals. In general, water chemistry is guided by complex weathering process, ion exchange. Saturation index of Carbonate and Sulphate minerals indicates under saturation to oversaturation and Silicate minerals were at equilibrium to oversaturation state. P. Anadhan, Department of Geology, Presidency College, Chennai, Tamilnadu, India, C.Singaraja • S.Chidambaram • C.Thivya • R. Thilagavathi. Department of Earth Sciences Annamalai University, Annamalai Nagar-608002, India. Corresponding author Email: [email protected]

Kew words: Hard rock terrain• Geochemical process• Silicate weathering Introduction Groundwater quality assessment is in advance importance, due to passionate urbanisation, industrialization and agricultural activities

putting the soil and groundwater to greater risk of contamination (Ackah et al., 2011; Thilagavthi et al., 2012; Singaraja et al., 2013b). Natural waters, having a contact with different chemical variations of rocks, inevitably gain a specific composition. Geochemical processes occurring within the groundwater and reactions with aquifer minerals have a profound effect on water quality. These geochemical processes are responsible for the seasonal and spatial variations in groundwater chemistry. The geochemical properties of groundwater depend on the chemistry of water in the recharge area as well as on different geochemical processes that are taking place in the subsurface. The quality of water along the course of its underground movement is therefore dependent on the chemical and physical properties of surrounding rocks, the quantitative and qualitative properties of through - flowing water bodies, and the products of human activity (Maththess, 1982). Demarcating the character of the groundwater in varied space, was proved to be an important technique in solving different geochemical problems (Back and Hanshaw,1965; Srinivasamoorthy et al., 2011; Singaraja et al., 2013b). The calculation of mineral saturation index and thermodynamic equilibrium studies initiated by (Garrels and Christ, 1965) to decipher the possible reactant, product minerals, indication of the equilibrium state of groundwater and the surrounding material. The study area gains its own importance by its location in hard rock terrain, frequent failure in monsoon, highly industrialized and urbanized zone all of which contributes for a proper assessment of the chemical quality of groundwater in the study area. 172


Study area Area chosen for study this is Thoothukudi districts, situated in the southeast coast of Tamil Nadu, India (Fig.1). The study area falls in the latitudinal and longitudinal extensions of 8° 19’ to 9° 22’ N and 77° 40’ to 78° 23’ E. It covers a total area of about 4590.54 Sq.Km. Geologically the study area is mainly composed of Hornblende Biotite Gneiss, Alluvial marine and Charnockites in the west. The quartzite formations are also found as scattered patches in the study area. There are minor representation of Cretaceous formation and Granitic intrusion in the eastern part and Fluvial marine in coastal region of the study area. A few streams originate in the hillocks within the district and confluences directly with the sea after flowing about 10 to 20 km. Vaipar, Tambraparani and Karamanaiyar are the major rivers draining the district. All the rivers are ephemeral in nature and run off is generated in heavy rainfall period only. The Tamirabarani River flows along the central part towards the south eastern part of the study area and as a result the southern part is more fertile with the distributaries channels of the river. The northern part of the study area is mainly dependent on the rain fed irrigation practices (Gangai and Ramachandran, 2010; Singaraja et al., 2012b). The southwest monsoon rainfall is highly erratic and summer rains are negligible. Fig 1 Sampling location and Geology map of the study area

Methodology A total of 100 Ground water samples were collected during PRM (Pre-Monsoon), covering the enter litho units of the study area. The sample were filtered 0.45 m Millipore filters and immediately stored in polyethylene bottles and analyzed for major and minor cations and anions using standard procedures (APHA, 1995). pH, Total Dissolved Solid (TDS) and electrical conductivity (EC) were measured in situ. The samples collected were analyzed for major cations like Ca2+ and Mg2+ by titrimetric; Na+ and K+ by flame photometry (CL 378); anions, Cl- and HCO-3 by titrimetric; and SO2-4, PO-4, and H4SiO4 by spectrophotometry (SL 171 minispec). Nitrate (NO3) were analyzed by using ion sensitive electrode. Fluoride was analyzed using Orion fluoride ion electrode model (94-09, 96-09). The analytical precision for the measurements of ions was determined by calculating the ionic balance error that varies by about 5–10%. TDS/EC ratio is 0.50/1.0 (with excess of anions in water). Results and Discussion The average geochemical behavior of groundwater in the study area shows that Cl>HCO-3>SO2-4>H4SiO4>NO-3>PO-4 >F- trend of anions and that of cations is N Na+>Ca2+>Mg2+>K. The findings and their comparison with World Health Organization (WHO) health-based drinking water guidelines (2004) are presented in Table 1. The data revealed a considerable variation in the water samples with respect to their chemical composition. Groundwater of the region is generally acidic to alkaline with pH ranging from 6.80 to 9.20 during PRM. The EC values ranges from 308.80 to 28140µS/cm during PRM. The TDS values ranges from 194.50mgl-1 to 16685.61mgl-1. Na+ concentration varies from 14.80mgl-1 to 4488 mgl-1 with an average of 441.62mgl-1. Na+ is also attributed to be released by weathering of the sodic feldspar. Ca2+ concentration ranges from 4mgl-1 to 1600mgl-1 with an average of 100.54mgl-1. The concentration of magnesium in groundwater 173


samples in the study area varies from 4.80mgl-1 to 1248mgl-1 with an average of 78.12mgl-1K+ is higher in both seasons due to weathering of feldspar and presence of clay minerals in the aquifer matrix. Cl- concentration ranges from 35.45mgl-1 to 10812.25mgl-1 with an average of 915.82mgl-1 Higher Cl- concentration may also be due to the due to leaching from upper soil layers derived from industrial and domestic activities (Srinivasamoorthy et al., 2008). HCO-3 was higher in the study area may be due to action of CO2 upon the basic material of soil and

lithology. SO2-4 values ranges from 0.50mgl-1 to 456 mgl-1 with average 71.85mgl-1 may be due to action of leaching and anthropogenic activities in a metamorphic environment by release of sulfur gases from industries and urban utilities get oxidized and enter into the groundwater system (Saxena 2004).The concentration of PO-4 shows that lesser. Fluoride was higher in the study area 3.2 mgl-1. NO-3 value ranges from 0.51mgl-1 to 148mgl-1. In general, increase of nitrate in groundwater may be an indicator of bacterial pollution (Sundaray et al., 2009).

Table 1 Comparison of groundwater quality with standards

pH TDS EC Ca2+ Mg2+ Na+ K+ FClHCO3NO3SO42-

Table 1 Comparison of groundwater quality with standards Ionic ratio Study area ranges % of sample exceed the permissible limit WHO (2004) PRM PRM 6.5 - 8.5 6.3 - 9.2 5 500 - 1000 194.5 - 23699.2 35 1400 306.8 - 37500 53 100 4 - 1600 21 50 4.8 - 1248 31 200 14.8 - 6847 31 20 0.4 - 520 14 1.5 0 - 3.3 30 250 35.45 - 13846 53 125 -350 12.2 - 536.8 6 50 0.47 - 148 2 250 0.5 - 456 6

Mechanisms controlling the groundwater chemistry The results from the water analysis were used as a tool to identify the process and mechanisms affecting the chemistry of groundwater from the study area. Gibbs (1970) plot is used to determine the mechanism controlling the water chemistry (Fig. 2). The Samples represents in rock dominance and precipitation zones indicating chemical weathering of rock-forming minerals and evaporation are the primal factors influencing the groundwater quality suggesting

precipitation induced chemical weathering along with dissolution of rock forming minerals. Ionic ratio The relationship between Na+ + K+ and total cations (TZ+) of the area indicate that the majority of samples are plotted above the 1:1 line indicating the increase of silicate weathering in the geochemical processes, which contributes mainly sodium and potassium ions to the groundwater (Stallard and Edmond, 1983; Sarin et al., 1989) (Fig. 3a). 174


The (Ca+Mg) versus TZ+ plot (Fig. 3b) lie far below the equiline with average equilibrium ratio of 0.40 to 0.35 indicating the contribution of alkalis (Na+ and K+) as like that of alkaline earth (Ca2+ and Mg2+) due to leaching from silicate weathering, from the aquifers of the study area. The scatter diagram of Ca2+ + Mg2+ versus SO2-4 + HCO-3 show that (Fig. 4a), majority ground water samples in both the seasons fall below the equiline (Zone 1), indicating that silicate weathering was the primary process involved in the evolution of groundwater (Datta and Tyagi, 1996). If bicarbonate and sulfate are dominating than calcium and magnesium, it reflects that silicate weathering was dominating and, therefore, was responsible for the increase in the concentration of HCO3- in groundwater (Elango et al., 2003; Rajmohan and Elango, 2004). This indicates that carbonate weathering is not the main source for ions in groundwater; whereas few samples fall on above the equiline (Zone 2), indicating that carbonate weathering is effect in the ground water. In this reaction, carbonic acid (CO2 and water) and calcium carbonate in soil react to form bicarbonate and calcium ion. It is also evident that Ca2++Mg2+ verses HCO3- (Fig 4b ) show that most of the groundwater samples fall on below the equiline due to the silicate weathering process. If HCO3- are dominating than Ca2++Mg2+ may be due to the increase of HCO3- in groundwater (Elango et al., 2003). Similarly, the Na+ versus Cl- (Fig. 5a) plot shows most of the groundwater samples lie above the 1:1 trend line. The excess of Na+ can be attributed to silicate weathering (Stallard and Edmond, 1983) from feldspars or due to anthropogenic activities like waste water. It is also may be due to Samples having a Na+/Cl- ratio (Fig. 5b) indicate excess sodium, which might have come from silicate weathering. If silicate weathering is a probable source of sodium, the water samples would have HCO3- as the most abundant anion (Rogers, 1987). This is because of the reaction of the feldspar minerals with the carbonic acid

in the presence of water, which releases HCO3 (Elango et al., 2003).

Fig 2 Gibbs plot depicting the mechanism controlling the groundwater chemistry of the study area

Fig 3 Plot for relationship of ions (A-B) 175


Thermodynamic stability Thermodynamic plotting of [K+]/H+ for the groundwater in major litho units in the study area are plotted on the stability diagram as a function of [H4SiO4]. In plot for Ca, the samples(Fig.6A) clusters in Ca Montmorllionite field indicating impact of dilution. In the plot for Magnesium (Fig.6B) majority of the samples are shifted from Kaolinite Field to Chlorite field due to theincrease in concentration of Mg2+ may be indicate that the shift of samples between two Fields i.e Kaolinite and Chlorite due to forward or reverse nature of reaction (Chidambaram,2007). The samples irrespective of seasons are stable with Kaolinite field and few represented samples exhibit high Mg. Hence, these samples fall in Chlorite Stability Field. Chlorite+10H+=Kaolinite+5Mg2++H4SiO4+5H2O

Fig 4 Plot for relationship of ions (A-B)

Fig 5 Plot for relationship of ions (A-B)

The plot (Fig. 7 A) of Na falls in the Kaolinite and Na Montmorllionite stability field, indicating Na– Feldspar incongruent dissolution produces Kaolinite (Jacks, 1973). The sources of Na in the system may be due to weathering of Plagioclase weathering, ion exchange. The plot of K silicates (Fig. 7B) indicates majority of the samples fall in Kaolinite Field and Muscovite then distributed of the samples fall in the Muscovite and Kaolinite Fields. The diagram delineates stability field of Clay minerals that co-exist in matrix phase at a constant composition of water during chemical reaction of rock and water. It is evident that movement of chemical composition from Muscovite to Kaolinite has released Silica. Hence, H4SiO4 has increased in groundwater (Chidambaram et al., 2007) during the process of migration of the composition towards Kfeldspar. It can be understood from that there are two different path ways of thermodynamic stability migration Pathway 1: Gibbsite Kaolinite K-Feldspar Pathway 2: Gibbsite Muscovite K- Feldspar The main process that governs the migration of the compositional pathways is the availability of K+ ions. It is noticed that the First Pathway is more significant in the study area. Minor 176


representations of the samples show representations of the Pathway-2. Majority of the samples are dominantly stable with the KFeldspar field. This is may be due to migration of ions during weathering, ion exchange or other anthropogenic impacts.

Fig. 7 Thermodynamic stability plot for (A) Na and (B) K System

Fig 6 Thermodynamic stability plot for (A) Ca, (B) Mg System

Disequilibrium indices Disequilibrium indices log (IAP/KT) was calculated by WATEQ4F geochemical model for the minerals and other solids stored in the model data bank for which the dissolved constituents are reported in groundwater analysis. Disequilibrium indices of log (IAP/KT) indicate: if the groundwater is in thermodynamic equilibrium, the log (IAP/KT = 0), and when it is oversaturated log (IAP/KT > 0) and during under saturated log (IAP/KT < 0) with respect to certain solid phases (Trusdell and Jones, 1973; Drever, 1988). The different states of Silicate minerals like crystalline, cryptocrystalline and amorphous forms are represented by Crystobalite and Chalcedony respectively (Fig 8). All the Carbonate minerals vary from saturated to over saturation in the study area which is indicated by excess input of Ca and Mg ions mainly derived from silicate weathering process (Srinivasamoorthy et al., 2012).

Fig 8 Variation of Saturation index of different Silicate minerals with H4SiO4 for samples collected during PRM 177


Conclusions The groundwater of Tuticorin District is a inimitable example for the impact of weathering, ion exchange and anthropogenic process controlling water chemistry. The chemical composition of groundwater of the study area is strongly influenced by rock water interaction, dissolution and deposition of silicates group of minerals. Weathering of silicate minerals controls the major ion chemistry of calcium, magnesium, sodium and potassium. The ion exchange and reverse ion exchange controls the water chemistry of the study area. Thermodynamic plot indicates may be due to migration of ions during weathering, ion exchange or other anthropogenic impacts in the study area. SI of minerals indicates that Ca and Mg ions mainly derived from silicate weathering process. In general, water chemistry is guided by lithological influences on water chemistry by complex weathering process, ion exchange. References Ackah M, Agyemang O and Anim AK (2011) Assessment of groundwater quality for drinking and irrigation: irrigation: the case study of Teiman-Oyarifa Community, Ga East Municipality, Ghana. Proceedings of the International Academy of Ecology and Environmental Sciences, 1(3-4): 186-194. APHA (1995) Standard methods for the examination of water and waste water, 19th edition, APHA, Washington DC, USASS. Back W and Hanshaw B (1965) Chemical Geohydrology Advances in Hydroscience (Back W, Hanshaw B, eds).Academic Press, USA. Chidambaram S, Vijaykumar V and Srinivasamoorthy K (2007) A Study on Variation in Ionic compostion of Aqueous system in different litho units around perambalur region Tamilnadu. Journal geological society of India, vol.70. 1061-1069. Datta PS, Tyagi SK (1996) Major ion chemistry of groundwater in Delhi area: chemical weathering processes and groundwater regime. J Geol Soc India, 47:179–188.

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