INTERNATIONAL JOURNAL OF ENVIRONMENTAL SCIENCES Volume 2, No 2, Copyright 2010 All rights reserved Integrated Publishing Association

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1 INTERNATIONAL JOURNAL OF ENVIRONMENTAL SCIENCES Volume 2, No 2, 2011 Copyright 2010 All rights reserved Integrated Publishing Association Case Study ISSN Evaluation of water quality, Hydro-geochemistry of Confined and Unconfined aquifers and irrigation water quality in Digha Coast of West Bengal, India (A case study) Anirban Kundu Chowdhury 1, Srimanta Gupta 2 1- Department of Civil Engineering, Jadavpur University, Kolkata, West Bengal, India 2- Department of Environmental Science, the University of Burdwan, Burdwan, West Bengal, India anikc13@yahoo.co.in doi: /ijes ABSTRACT Evaluation of ground water quality and hydro-geochemistry of confined and unconfined aquifer (with respect to provisional guideline values of WHO 2004, geochemical classifications, ion exchange processes and mechanisms controlling ground water chemistry) and evaluation of surface water quality (with respect to different sodium hazards, Ca 2+ /Mg 2+ ratio and common phytotoxic anions) for irrigation purpose in a coastal area were the aims of the present study. Accordingly ground and surface water samples were collected from confined, unconfined aquifers and irrigation water tanks of Digha coast and its adjoining area of West Bengal, India in post-monsoon and pre-monsoon seasons. Quality of the water samples collected from the confined aquifer found satisfactory in comparison with water samples collected from the unconfined aquifer. Geochemical nature of confined aquifer was earth alkaline with increased portion of alkalis with prevailing bicarbonate, followed by chloro-alkaline disequilibrium type of ion-exchange process. Chemical weathering of rock forming minerals was the major driving force controlling confined aquifer water chemistry. Hydro-geochemistry of unconfined aquifer in post-monsoon season was alkaline with bicarbonate and sulfate-chloride and earth alkaline with increased portion of alkalis with prevailing bicarbonate where as in pre-monsoon season hydro-geochemistry of the unconfined aquifer shifted towards alkaline with sulfate and bicarbonate. Ion exchange process in this aquifer showed complete dominance of base exchange reaction in both the seasons. Chemical weathering and chemical weathering along with evaporation were the two major driving forces controlling the water chemistry of the unconfined aquifer in postmonsoon and pre-monsoon seasons respectively. RSC (residual sodium carbonate), %Na +, SAR (sodium adsorption ratio), Ca 2+ /Mg 2+ ratio and concentration of Cl -, B -, F - in irrigation water revealed that the majority of surface water samples were not good enough for irrigation in pre-monsoon season in comparison to that of post-monsoon season. Keywords: confined aquifer, unconfined aquifer, hydro-geochemistry, irrigation water 1. Introduction Coastal zones are the most densely populated areas in the world. However, these regions face many hydrological hazards like flooding due to cyclones and wave surge, and drinking water scarcity due to saline water intrusion in aquifers. Surface water bodies are also affected by sea spray in coastal areas, resulting increment in salt concentration in surface water. Primary effects of salt on soil productivity are governed by total electrolyte content and the sodium ion content, relative to the other major cations. Pore space in soil decreases in presence of excess sodium ion relative to calcium and magnesium ions in surface water due to the Received on September 2011 Published on November

2 displacement of the other adsorbed cations followed by swelling and dispersion of clays. Insufficient pore space in soil decreases its permeability and increases the potential of water logging (Tchobanogious et al., 1987). Number of studies on groundwater and surface water quality in coastal aquifers of India with respect to drinking and irrigation purposes have been carried out extensively by Central Ground Water Board, Geological Survey of India as embodied in various publications (Goswami, 1968 & 1973, Pathak, 1981, Das, 1991 and UNESCO, 1897). The present study was performed with an objective to evaluate ground water quality and hydro-geochemistry of confined and unconfined aquifer and surface water quality for irrigation purpose in a coastal area. 2. Study area (location & hydrology) The study area (Figure 1) is located between north latitudes & and east longitudes & in the southern part of East-Midnapur district of West Bengal (around Digha, a beach resort), India. Figure 1: Map of the study area The area is bordered by Bay of Bengal and is characterized by a number of tidal channels resulting in seawater encroachment at surface. Digha and its neighboring areas are underlain by newer alluvium showing alternate sequence of nearly horizontal sand, silt, and clay layers. The principal fresh water bearing confined aquifer occurs in the depth range of m below ground level, overlain by a moderately thick (20-30m) gray, sticky clay bed and 589

3 underlain by another 8-10m thick grayish clay bed which laterally grades into sandy clay at places. The aquifer is protected against any large-scale saline water intrusion at depth because of the clay layers which also have probable extensions under the sea (Choudhury et al., 2001). The aquifers overlying and underlying these clay beds generally contain brackish water as indicated electrical logs and by chemical analysis data (Bhattacharya et al., 1996). The near-surface aquifers formed by the dune sand alternating with thin clay and gravelly clay beds down to 25-30m below ground level are also fresh water bearing except locally. 3. Materials and Method Forty-eight (24 2) water samples (nine confined aquifer water samples, eight unconfined aquifer water samples and seven surface water samples from ponds and irrigation water tanks of study area) were collected from the study area in post-monsoon 2005 and pre-monsoon The sampling stations are shown in Figure 1. Influence of temporal variation in confined aquifer hydro-geochemistry is less significant because of its confining nature and restricted recharge. Water quality of the samples and hydro-geochemistry of confined aquifer were evaluated by averaging the analytical data of water samples collected in both the seasons. Water quality of the samples and hydro-geochemistry of unconfined aquifer were assessed on the basis of analytical data of water samples collected separately in pre-monsoon and post-monsoon seasons. Two water samples were collected from each of the four sampling stations and the analytical data were averaged during reporting. Physical parameters like ph and electrical conductivity (EC) were determined by Systronics ph meter (Model 169) and Systronics EC meter (Model 306) respectively. Total dissolved solids (TDS) and total suspended solids (TSS) were determined by gravimetric method and turbidity (TUR) was determined by nephlometric turbidity meter. Chemical parameters like sulfate (SO 4 - ) was determined by colorimetric method, whereas, total hardness (TH), Cahardness (Ca-H), calcium (Ca 2+ ) and magnesium (Mg 2+ ) were determined by standard EDTA titrimetric method. Carbonate (CO 3 2- ) and bicarbonate (HCO 3 - ) were estimated by titrating with H 2 SO 4. Chloride (Cl - ) was determined by argentometric titration method. Sodium (Na + ) and potassium (K + ) had their measurement by flame photometric method. Fluoride (F - ) was measured by ion selective electrode. Rest of the chemical parameters like total iron (T-Fe), phosphate (PO 4 3- ), nitrate nitrogen (NO N), molybdate reactive silica (MR-Si), molybdate non-reactive silica (MNR-Si), and boron (B - ) were measured by colorimetric method. All the analytical methodologies including sample collection, had been carried out following Standard Methods for the Examination of Water and Wastewater, published by AWWA, APHA and WPCF (1998) together. 4. Results and discussion 4.1 Water quality of confined and unconfined aquifer samples Statistical summary of analytical data of the water samples collected from confined and unconfined aquifer are described in Table 1 and Table 2. Table 1: Descriptive statistical summary of the analytical data (confined aquifer) Parameters Range Average SD ph T EC

4 TSS BDL TDS TUR TH Ca-H Ca Mg Na K T-Fe PO Cl NO - 3 -N CO HCO SO MR-Si MNR-Si All unites have their measurement in mg/l except, T is expressed in C, EC is expressed in µscm -1 at 25 C, TUR is expressed in NTU, TH and Ca-H are expressed in mg/l as CaCO 3, SD=standard deviation, BDL = below detection level Table 2: Descriptive statistical summary of the analytical data (unconfined aquifer) Parameters Post-monsoon Pre-monsoon Range Average SD Range Average SD ph T EC TSS BDL TDS TUR TH Ca-H Ca Mg Na K T-Fe PO Cl NO - 3 -N CO 3 BDL BDL BDL BDL BDL BDL - HCO SO MR-Si

5 MNR-Si All unites have their measurement in mg/l except, T is expressed in C, EC is expressed in µscm -1 at 25 C, TUR is expressed in NTU, TH and Ca-H are expressed in mg/l as CaCO 3, SD=standard deviation, BDL = below detection level Table 3 describes that,100% of the water samples collected from confined aquifer were found within safe limit as per with the provisional guideline values of WHO 2004 with respect to ph, TDS, TH, Na +, T-Fe, Cl -, NO N, and SO 4 2- point of view. ph of all the water samples collected from unconfined aquifer in post-monsoon and pre-monsoon seasons were found within the safe limit. TDS of 100% water samples in the post-monsoon season and 50% samples in the pre-monsoon season were found safe. Regarding the values of TH, Na +, T-Fe, Cl -, NO N, and SO , 75, 50, 75, 100 and 100 % samples in post-monsoon season and 75, 75, 50, 50, 100 and 100 % samples in pre-monsoon season were found safe. Table 3: Distribution of water samples within the drinking water standards collected from confined and unconfined aquifers Physical and chemical parameters (mg/l) WHO standards for drinking water, 2004 (maximum permissible limit) Confined aquifer Samples within safe limit (%) Unconfined aquifer Samples within safe limit, in postmonsoon (%) Sample within safe limit, in premonsoon (%) ph T EC TSS TDS TUR Ca Mg Na K TH Ca- H T-Fe Cl NO - 3 -N PO CO HCO SO MR-Si MNR-Si All unites have their measurement in mg/l except, T is expressed in C, EC is expressed in µscm -1 at 25 C, TUR is expressed in NTU, TH and Ca-H are expressed in mg/l as CaCO 3 592

6 4.2 Hydro-geochemistry of the aquifers The hydro-geochemical facies Piper (Piper 1944) graphical representation method was used to assess the nature of hydrogeochemistry of both the aquifers. Plots of analytical data (Figure 2) of the water samples collected from confined aquifer clustered in the divisions 1, 3 and 5 of Piper diagram, which showed that alkali earths exceed alkalis, weak acid exceeds strong acids and carbonate hardness (secondary alkalinity) exceeds 50% (Table 4) type of hydro-geochemistry. Figure 2: Piper diagram plot of the water samples collected from confined aquifer Table 4: Geochemical classification of water samples collected from confined and unconfined aquifers Area subdivisions in Piper s diagram Confined aquifer Unconfined aquifer Samples clustered in area subdivision (%) Samples clustered in area subdivision in post-monsoon (%) Samples clustered in area subdivision in pre-monsoon (%) 1. Alkali earths exceed alkalis Alkalis exceeds alkaline earths 3. Weak acids exceed strong acid 4. Strong acids exceed weak acid 5. Carbonate hardness (secondary alkalinity) exceeds 50% 6.Non carbonate hardness

7 (secondary salinity) exceeds 50% 7.Non carbonate alkali (primary salinity) exceeds 50% 8. Carbonate alkali (primary alkalinity) exceeds 50% 9. No one cation anion pair exceeds 50% From another point of view 100% of the plots clustered in Type-I (Ca+Mg-CO 3 +HCO 3 ) facies of the Piper s diagram. This might be attributed to hydro-geochemistry of the confined aquifer was mainly controlled by dissolution of carbonate minerals (Al-Agha 2005). Plots of analytical data of the water samples collected from unconfined aquifer clustered in the divisions 1,2,3,4,5,7,9 of Piper diagram (Figure 3) in post-monsoon season, representing equal dominance of alkaline earths and alkali, dominance of weak acid, carbonate hardness, non carbonate alkali and dominance of no one cation anion pair. Plots of analytical data of the water samples collected from the same aquifer in pre-monsoon seasons clustered in the divisions of 1,2,3,4,5,6,7 which indicated equal dominance of alkaline earths and alkali, dominance of strong acids, equal dominance of carbonate hardness and non carbonate hardness and dominance of non carbonate alkali (Table 4) type of hydro-geochemistry. In post-monsoon season 50% plots clustered in Type-I facies and another 50% of the plots clustered in Type-II (Na+K-Cl+SO 4 ) facies of Piper diagram, this might be attributed to saline water contamination in unconfined aquifer system through the tidal channels. In premonsoon season Type-I facies represented by 25% plots, Type-II facies represented by 50% plots, while 25% samples represents no pair up Facies (alkaline water with bicarbonate and sulfate). No pair up facies is characterized by the mixing of different types of water (Al-Agha 1995). Figure 3: Piper diagram plot of the water samples collected from unconfined aquifer Ion-exchange process in the aquifers The ion exchange between the ground water and its host environment during residence or travel can be understood by studying the chloro-alkaline indices i.e., CA-I [(Cl - -Na + +K + )/Cl - ] and CA-II [(Cl - -Na + +K + )/(SO HCO 3 - +CO NO 3 - )]. 100% of the water samples collected 594

8 from confined aquifer had CA-I and CA-II value negative and 100% of water samples collected from unconfined aquifer in both post-monsoon and pre-monsoon seasons had positive CA I and CA II values. Negative chloro-alkaline indices is due to chloro-alkaline disequilibrium (host rocks are the primary source of dissolved solids in cation-anion exchange reaction) and positive chloro-alkaline indices is due to base exchange (Na + and K + ions in water are exchanged with Mg 2+ and Ca 2+ ions) reaction (Schoeller, 1965 & 1967) Mechanism controlling ground water chemistry Gibbs s diagrams representing the ratios of [Na + :(Na + + Ca 2+ )] and [Cl - :(Cl - + HCO 3 - )] as a function of TDS, are widely employed to assess the functional source of dissolved chemical constituents, such as precipitation dominance, rock dominance and evaporation dominance (Gibbs, 1970). Gibbs s plot (Figure 4) of analytical data of the ground water samples collected from confined aquifer clustered at the region of rock dominance. This might be attributed to chemical weathering of rock forming minerals is the major driving force in controlling ground water chemistry. Figure 4: Gibb s diagram plot of the water samples collected from confined aquifer Figure 5: Gibb s diagram plot of the water samples collected from unconfined aquifer 595

9 Gibbs s diagram plot (Figure 5) of analytical data of the water samples collected from unconfined aquifer indicated that the chemical weathering of rock forming minerals were dominant in post-monsoon season while, evaporation and chemical weathering both running simultaneously in the pre-monsoon season. 4.3 Analysis of irrigation water samples Sodium hazards Values of residual sodium carbonate (RSC), percentage sodium (%Na + ) and sodium adsorption ratio (SAR) of the collected samples are described in Table 5. RSC is a measurement that compares the concentration of Ca 2+ and Mg 2+ to HCO 3 - and CO It also determines when Ca 2+ and Mg 2+ (macro nutrients) precipitation can occur in the soil and results in additional Na + dominance of soil cation exchange sites. RSC may be explained as follows (Hydrology Project Training Module, 2002) RSC, meq/l = [HCO CO 3 2- ] [Ca 2+ + Mg 2+ ] (1) Places Table 5: Results of physicochemical analysis of surface water samples Post-monsoon EC RSC % Na + SAR Cl - B - F - Dakkhinsimulia Jagadishpur Alankarpur Purbamukundapur Kantaboni Fatepur Gopalpur Pre-monsoon Dakkhinsimulia Jagadishpur Alankarpur Purbamukundapur Kantaboni Fatepur Gopalpur EC is expressed in µscm -1 at 25 C, RSC and Cl - in meq/l, B - and F - in (mg/l) Where, all the cations and anions are expressed in meq/l. The USDA (United States Department of Agriculture) has established guidelines (Bulletin No. 197) for modifying water quality classification based on RSC. RSC level less than 1.25meq/l is considered safe, where as water with RSC of meq/l is within marginal range and RSC value of 596

10 water sample 2.50meq/l or greater is considered too high making the water unsuitable for irrigation use. In post-monsoon and pre-monsoon seasons 42.9% and 28.6% samples respectively had RSC value less than 1.25meq/l. In pre-monsoon season 14.9% samples had RSC value greater than 2.5meq/l. In post and pre-monsoon seasons 57% samples had RSC value negative which may be attributed to excess Ca 2+ and Mg 2+ in irrigation water. Percentage sodium (%Na + ) in irrigation water samples is also widely used to evaluate suitability of the sample for the purpose (Wilcox, 1948). It is computed with respect to relative proportions of cations present in water, where the concentrations of ions are expressed in meq/l using the following equation %Na + = [(Na + + K + ) / (Ca 2+ + Mg 2+ + Na + + K + )] 100 (2) %Na + ranged from 21.8% to 80.8% with a mean 56.4% in post-monsoon season and 62.4% in pre-monsoon season. Analytical data of the irrigation water samples collected in premonsoon and post-monsoon season were plotted in the Wilcox s diagram (Wilcox 1948). In the Wilcox s diagram EC is plotted against %Na + (Figure 6). In post-monsoon season 71.4% of the samples were excellent to good for irrigation and 28.6% samples were unsuitable for irrigation where as in pre-monsoon season 28.6% of the samples were excellent to good, and 28.6% samples were good to permissible and 42.8% samples were found unsuitable for irrigation. Figure 6: Wilcox s diagram plot of the surface water samples Sodium adsorption ratio (SAR) indicates the effect of relative cation concentration on sodium accumulation in soil. Thus SAR is a more reliable indicator for determining these effects than %Na +. SAR is calculated using the following equation SAR = Na + / [(Ca 2+ + Mg 2+ ) / 2] 0.5 (3) 597

11 where, ions are expressed as meq/l. The potential for sodium hazard increases in water with higher SAR values. The SAR should not be much higher than 20 and preferably less than 10. SAR value ranged from 0.4 to 43.7 with a mean 6.0 in the post-monsoon and 15.5 in the premonsoon seasons. EC and Na + play a vital role in suitability for irrigation water. High salt content in irrigation water causes an increase in soil solution osmotic pressure. The salts besides affecting the growth of plants directly also affect the soil structure, permeability and aeration which indirectly affect plant growth. Total concentration of soluble salts in irrigation water can be classified into low (EC less than 250μscm -1 ), medium ( μscm -1 ), high ( μscm -1 ) and very high (greater than 2250μscm -1 ). According to classification of irrigation water diagram (After US Salinity Laboratory Staff 1954) the above mentioned classes are designated as C 1 (low-salinity water), C 2 (medium-salinity water), C 3 (highsalinity water) and C 4 (very high-salinity water) respectively. These are also called salinity hazard. Another hazard mentioned in the same diagram is sodium hazard. These are classified as low sodium (S 1 ), medium sodium (S 2 ), high sodium (S 3 ) and very high sodium (S 4 ) water having SAR value less than 10, 10 18, and greater than 26 respectively. In post-monsoon season C 1 S 1 (low salinity low sodium water) represented 28.6% of the collected irrigation water samples (Figure 7). This class of water could be used for irrigation on most crops in most soils with little likelihood that soil salinity will develop and with little danger of developing harmful levels of sodium. C 2 S 1 (medium salinity low sodium water) represented 42.8% of the collected irrigation water samples. This class of water could be used if a moderate amount of leaching occurs with little danger of developing harmful levels of sodium. C 4 S 4 (very high salinity very high sodium water) represented 28.6% of the collected irrigation water samples, which were not at all suitable for irrigation under ordinary conditions but it may be used occasionally under very special circumstances (practically these class of water is used in shrimp cultivation). In pre-monsoon season C 2 S 1 and C 4 S 4 represented 28.6% and 42.8% of collected irrigation water samples. C 3 S 1 (high salinity low sodium water) represented 28.6% samples. This class of irrigation water cannot be used on soils with restricted drainage otherwise harmful level of sodium may develop. Figure 7: US Salinity Laboratory Staff diagram plot of the surface water samples 598

12 4.3.2 Ca 2+ /Mg 2+ ratio Ca 2+ /Mg 2+ ratio of the 57.14% of collected irrigation water samples in post-monsoon and 71.43% of collected irrigation water samples in pre-monsoon were less than one. It indicated that, these were Mg 2+ dominated water. In Mg 2+ dominated water the potential effect of Na + may be slightly increased (FAO, 1994) might be due to Mg 2+ induced Ca 2+ deficiency caused by high levels of exchangeable Mg 2+ in soil. Ca 2+ appears to reduce possible toxicities due to other ions like Na +, Mg 2+ in the root environment. If the Ca 2+ /Mg 2+ ratio is near or less than one, the uptake and translocation of Ca 2+ from soil-water to the above-ground parts of the growing crop is diminished due to antagonistic effects of high Mg 2+ or competition for absorption sites to such an extent that less Ca 2+ is absorbed Concentration of common phytotoxic anions Values of concentration of common phytotoxic anions (Cl -, B - and F - ) of the collected samples are described in Table 5. In the irrigation water the most common toxicity is from Cl -. Cl - is not adsorbed or held back by soils, therefore it moves readily with the soil-water, is taken up by crops, moves in the transpiration stream, and accumulates in leaves. If the Cl - concentration in the leaves exceeds the tolerance of the crops, injury symptoms develop such as leaf burn or drying of leaf tissue. With sensitive crops, these symptoms occur when leaves accumulate from 0.3 to 1.0% Cl - on a dry weight basis, but sensitivity varies among these crops. Usual range of chloride in irrigation water is 0 30meq/l (FAO, 1994). In the collected irrigation water samples Cl - concentration ranged between 0.70 and meq/l with mean values of 12.96meq/l and meq/l in post and pre-monsoon seasons respectively % of the irrigation water samples collected in post-monsoon and 57.14% of the irrigation water samples collected in pre-monsoon were found within the usual range. B - is an essential micronutrient for plant growth. Surface water rarely contains enough B - to be toxic. Boron toxicity symptoms normally show first on older leaves as yellowing, spotting, or drying of leaf tissue at the tips and edges. Most crop toxicity symptoms occur after B - concentrations in leaf blades exceed mg/kg (dry weight), but not all sensitive crops accumulate B - in leaf blades (FAO, 1994). According to United States Salinity Laboratory (USSL, 1954) boron sensitive, boron semi tolerant and boron tolerant crops can withstand approximately B - concentrations up to 1.25, 2.5 and 3.75mg/l respectively. Safe B - concentration ranges are less than mg/l, less than mg/l and less than 1 3 mg/l respectively for boron sensitive, boron semi tolerant and boron tolerant crops (Rowe et al., 1995). In the collected irrigation water samples B - concentration ranged between 0.19 to 0.57mg/l with mean values of 0.24 mg/l and 0.36 mg/l in post and pre-monsoon seasons respectively. All the irrigation water samples collected in both the seasons had B - concentrations well below the values required for boron sensitive crops. F - in the soil is generally not harmful. But F - on plant surfaces may be harmful to plants and grazing animals. USDA 2008 recommended 1mg/l maximum concentrations of F - in irrigation water. F - concentration in the collected irrigation water samples ranged between 0.12 to 0.56mg/l with mean values of 0.19 mg/l and 0.41 mg/l in post and pre-monsoon seasons respectively. This implied the irrigation waters are safe from F - point of view. 599

13 5. Conclusion Quality of the water samples collected from the confined aquifer found satisfactory in comparison with water samples collected from the unconfined aquifer. It was concluded from the Piper diagram plot that hydro-geochemistry of confined aquifer was earth alkaline with increased portion of alkalis and with prevailing bicarbonate. Chloro alkaline disequilibrium type of ion exchange process was found in confined aquifer. Chemical weathering of rock forming minerals was the major driving force controlling ground water chemistry as represented by Gibbs diagram plot. Hydro-geochemistry of unconfined aquifer in postmonsoon season was alkaline with bicarbonate and sulfate-chloride and earth alkaline with increased portion of alkalis with prevailing bicarbonate where as in pre-monsoon season hydro-geochemistry of the unconfined aquifer shifted towards alkaline with sulfate and bicarbonate. Ion exchange process in unconfined aquifer was found base exchange type in both the seasons. According to Gibbs s diagram plot chemical weathering of rock forming minerals in post monsoon season and chemical weathering along with evaporation in premonsoon season were the major driving force controlling hydro-geochemistry of unconfined aquifer. RSC, %Na +, SAR, Ca 2+ /Mg 2+ ratio, concentration of Cl -, B -, F - in irrigation water along with US Salinity Laboratory s and Wilcox s diagrams suggested that the majority of surface water samples were not good for irrigation during pre-monsoon season in comparison to post-monsoon season. 6. References 1. Al-Agha M.R (2005), Hydro-geochemistry and carbonate saturation model of groundwater, Khanyounis Governorate-Gaza Strip, Palestine, Environ Geol, 47, pp Al-Agha M.R (1995), environmental contamination of groundwater in the Gaza Strip, Environ. Geol, 25, pp AWWA, APHA, WPCF (1998), standard methods for the examination of water and wastewater. American Public Health Association, Washington DC 4. Bhattacharya B.B., and Chakladar S (1996), selection of tube well sites for Digha water supply scheme for P.H.E.D, Govt. of West Bengal, Technical Report No Choudhury K., Saha K. D., and Chakraborty P (2001), geophysical study for saline water intrusion in a coastal alluvial terrain, J. appl. Geophys., 46(3), pp Das S (1991), Hydrogeological features of Deltas and Estuarine tracts of India, Geol.Soc.of India, 22, pp FAO (1994), water quality for agriculture, Food and Agriculture Organization of the United Nations, Rome 8. Gibbs R.J (1970), mechanisms controlling world water chemistry, Science, 17, pp

14 9. Goswami A.B (1968), geochemical aspects of groundwater in the near surface aquifer at Digha, Midnapur district, West Bengal, Jour. Indian Geohydrology, 4(1). 10. Goswami A.B (1973), application of tidal method in determining aquifer characteristics in Digha coast of West Bengal, India, Proc. Int. Symp. on Development of Groundwater Resources, 1(II). 11. Hydrology Project Training Module, Version: 05/11/02, Pathak B. D (1981), estimation of changes in the salt and fresh water balance in Deltas, Estuaries and Coastal zones due to structural works and groundwater exploration, Bull.C.G.W.B. Tech. Sr.H. No Piper A.M (1944), a graphic procedure in the geochemical interpretation of water analyses. Trans. Am. Geophy. Union, 25, pp Rowe D.R., and Abdel-Magid M. I (1995), handbook of Wastewater Reclamation and Reuse, CRC Press, Inc., pp Schoeller H (1965), qualitative evaluation of groundwater resources. In: Methods and techniques of groundwater investigations and development, UNESCO, pp Schoeller H (1967), geochemistry of groundwater. An international guide for research and practice, UNESCO, chap 15, pp Tchobanoglous G., and Schroeder ED (1987), water quality. Addison-Wesley Publishing Company, Reading 18. UNESCO (1987), groundwater problems in coastal areas, Studies and Reports in hydrology, Series No United States Department of Agriculture (2008), assessing Water Quality for Human Consumption, Agriculture, and Aquatic Life Uses, Natural Resources Conservation Service, Environment Technical Note No. MT-1 (Rev. 1) 20. US Salinity Laboratory Staff (1954), diagnosis and improvement of saline and alkali soils, US Department of Agricultural soils, US Department of Agricultural Hand Book 60, Washington, DC 21. USDA Bulletin No. 197, 1914, US Department of Agriculture. Washington 22. WHO (2004), guidelines for drinking water quality. World Health Organization, Geneva 23. Wilcox, L. V (1948), the quality of water for irrigation use, US Department of Agricultural Technical Bulletin 1962, Washington 601