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INTERNATIONAL JOURNAL OF ENVIRONMENTAL SCIENCES Volume 1, No 7, 2011

© Copyright 2010 All rights reserved Integrated Publishing Association

Research article ISSN 0976 – 4402

Received on May, 2011 Published on June 2011 1770

Groundwater quality and its suitability to agriculture – GIS based case study of Chhatna block, Bankura district, West Bengal, India

Nag.S.K 1 , Poulomi Ghosh 2 1 Professor, Department of Geological Sciences, Jadavpur University, Kolkata

2 Research Scholar, Department of Geological Sciences, Jadavpur University, Kolkata [email protected]

ABSTRACT

Water pollution is a major challenge amongst all other types of pollution. A number of factors like geology, soil, effluents, sewage disposal and other environmental conditions in which the water happens to stay or move and interact are responsible for this. The study has been made to find out the status of groundwater quality and its suitability in regards to irrigation purpose. A total number of 23 water samples from borewells have been collected for premonsoon 2009 and postmonsoon 2009 from Chhatna block, Bankura district, West Bengal, India. Water quality data used in the present study include Electrical Conductivity (EC), Total Dissolved Solids (TDS), Total Hardness (TH), Soluble Sodium Percentage (SSP), Residual Sodium Bicarbonate (RSBC/RSC) and Sodium Adsorption Ratio (SAR). From the results of analysis, it is revealed that the values of Sodium Adsorption Ratio indicate that, ground water of the area falls under the category of low sodium hazard. So, there is neither salinity nor toxicity problem of irrigation water, and hence the ground water can safely be used for longterm irrigation.

Keywords: Groundwater quality, SAR, SSP, GIS, Agriculture.

1. Introduction

Water is one of the most precious gifts of nature, whose presence is absolutely vital for the sustenance of life. Man has been drawing on this unique natural resource from times immemorial. Over the years growing demand for water by the varied needs of human society have actually threatened its existence. The demand for water has increased over the years with the increase in population and this has led to water scarcity in many parts of the world. The situation is aggravated by the problem of water pollution or contamination. India is heading towards a freshwater crisis mainly due to improper management of water resources and environmental degradation, which has led to a lack of access to safe water supply to millions of people. The freshwater crisis is already evident in many parts of India, varying in scale and intensity depending on the time of the year.

Water being a universal solvent, carries minerals in solution though present in small quantities. The quantity and composition of the dissolved minerals in natural water depend upon the type of rock or soil with which it has been in contact or through which it has passed and the duration it has been in contact with these rocks. Development of groundwater also provides opportunities taken to perfect its quality. Quality of groundwater may vary from place to place and from stratum to stratum. It also varies from season to season. The determination of suitability of groundwater would, therefore involve a description of the occurrence of the various constituents and their relation to the use to which water would be put. The water quality data also provides information about geologic history of rocks,

Groundwater quality and its suitability to agriculture – GIS based case study in Chhatna block, Bankura district, West Bengal, India

Nag.S.K , Poulomi Ghosh 1771 International Journal of Environmental Sciences Volume 1 No.7, 2011

groundwater recharge, discharge, movement and storage. Groundwater is being contaminated either from natural resources or from human activities. Residential, municipal, commercial, industrial and agricultural activities affect groundwater quality. Contamination of groundwater results in poor drinking water quality, loss of water supply, high cleanup cost, high cost in alternative water supply and potential health hazards. The present study aims to find out water quality which is becoming more and more important due to population explotion, increasing agriculture and improved standard of living, especially in developing countries. Water quality data utilized in the present paper for the analysis of groundwater chemistry of year 2009 premonsoon and postmonsoon seasons. Water quality data used in analyses include Electrical Conductivity (EC), Total Dissolved Solids (TDS), Total Hardness (TH), Soluble Sodium Percentage (SSP), Residual Sodium Bicarbonate (RSBC/ RSC) and Sodium Adsorption Ratio (SAR).

2. Study Area

The Chhatna Block, one of the western blocks of Bankura district, borders the western most Puruliya district of West Bengal. Regionally, the area constitutes the extreme eastern fringe of the Ranchi Plateau and further east gradually merges with the depositional fluvial terraces of Dwarkeswar – Kangsabati Rivers (Figure 1).

Figure 1: Index Map of the Study Area

The area is characterized by gently undulating, to rolling topography with enclosures of erosional remnants such as inselbergs/hillocks (e.g., Shushunia hill in the eastern part of the block). The regional southeasterly slope is exemplified by the Dwarakeswar River which flows from northwest to southeast, almost dividing the Chhatna block into two equal halves. The overall drainage pattern of the area is parallel to subparallel and is mainly controlled by geological structural elements. The country rock of the area is Chhotanagpur granite gneiss



with enclaves of metasedimentaries. Major portion of the block is chracterised by the presence of skeletal soil, at places lateritic also, excepting the valley fills. Chhatna is located 13 km from Bankura town on the BankuraPurulia road. Susunia is 10 km northeast of Chhatna. The climate, especially in the upland tracts to the west, is much drier than in eastern or southern Bengal. From the beginning of March to early June, hot westerly winds prevail, the thermometer in the shade rising to around 45°C (113°F). The monsoon months, June to September, are comparatively pleasant. The total average rainfall is 1,494.4 mm, the bulk of the rain coming in the months of June to September. In the 2001 census, Chhatna community development block had a total population of 169,141 of which 85,562 were males and 83,579 were females.

2.1 Data used

1. Survey of India toposheets of the study area (73 I/15, 73 I/16 and 73 M/3) in 1:50,000 scale.

2. Satellite Imagery (IRSIB, LISSII) 3. Chemical Analyses data of the collected water samples

3. Methodology

For analyzing the chemical aspects of groundwater in the study area, bore wells (23 Nos.) spreading well over the Chhatna block has been considered. Samples have been collected during 2009 (Premonsoon, April) and (Postmonsoon, November) periods.

Table1a: Water Quality data used in the present study (Pre monsoon)

Location Name EC (µs/cm)

TDS (mg/L) TH SSP RSBC SAR

P 1 Dubrajpur More 340 218 74.85 17.95 2.77 0.38 P 2 Satyatan Primary School 190 122 41.28 25.12 0.98 0.43 P 3 Dwarkeswar River Bed 180 115 53.50 21.07 0.73 0.39 P 4 Teghari 1850 1184 156.02 13.78 0.17 0.40 P 5 Gara 1940 1242 152.88 14.13 0.39 0.41 P 6 Suburdih 130 83 29.89 28.01 1.53 0.43 P 7 Kamalpur 480 307 74.07 17.02 5.57 0.35 P 8 Sukhnibash 450 288 63.77 25.44 1.02 0.55 P 9 Jhatipahari 590 378 80.34 17.98 0.85 0.39 P 10 Morgaboni 220 141 48.57 22.73 1.65 0.41 P 11 Kharbona 590 378 96.73 17.35 10.85 0.41 P 12 Saluni 240 154 48.24 25.16 0.51 0.47 P 13 Tilna 770 493 124.73 10.65 1.93 0.27 P 14 Jorehira 900 576 131.24 12.06 1.15 0.31 P 15 Dhaban 1260 806 131.22 14.99 7.70 0.40 P 16 Hapania 1120 717 120.12 17.31 2.19 0.46 P 17 Kanudi 170 109 38.23 22.93 1.37 0.37 P 18 Bhagbanpur 220 141 44.37 20.37 1.08 0.34 P 19 Hutgram 220 141 44.10 24.27 1.74 0.43 P 20 Chaitor 780 499 130.77 10.41 1.48 0.27 P 21 Goaldanga 880 563 122.86 13.27 0.17 0.34 P 22 Jhumki 120 77 14.73 46.38 1.51 0.66 P 23 Jorthal 460 980 48.03 19.23 3.63 0.33



GIS software package TNT mips 7.4 is used to map and analyse the data for the evaluation of groundwater data. Water quality data used in the study include Electrical Conductivity (EC), Total Dissolve Solids (TDS), Total Hardness (TH), Soluble Sodium Percentage (SSP), Residual Sodium Bicarbonate (RSBC/ RSC) and Sodium Adsorption Ratio (SAR) (Table 1a and 1b)

Table1b: Water Quality data used in the present study (Post monsoon)

Location Name EC (µs/cm)

TDS (mg/L) TH SSP RSBC SAR

P 1 Dubrajpur More 700 257 83.78 3.19 1.93 0.06 P 2 Satyatan Primary School 300 135 169.98 6.25 0.61 0.17 P 3 Dwarkeswar River Bed 300 122 133.49 5.71 0.12 0.14 P 4 Teghari 3400 1365 302.73 2.90 1.46 0.10 P 5 Gara 2400 948 259.33 1.67 0.10 0.05 P 6 Suburdih 300 130 214.53 3.96 1.18 0.12 P 7 Kamalpur 900 334 115.61 7.95 3.43 0.19 P 8 Sukhnibash 900 333 106.41 13.79 0.33 0.33 P 9 Jhatipahari 900 327 90.93 14.11 1.95 0.31 P 10 Morgaboni 500 177 226.72 5.19 0.76 0.16 P 11 Kharbona 1300 495 167.11 8.91 2.40 0.25 P 12 Saluni 300 130 208.57 6.65 2.37 0.21 P 13 Tilna 1300 182 376.94 3.30 2.78 0.13 P 14 Jorehira 1500 588 404.32 3.94 4.97 0.16 P 15 Dhaban 1400 549 109.06 14.61 0.77 0.36 P 16 Hapania 2000 835 79.77 18.16 4.14 0.40 P 17 Kanudi 300 104 218.87 6.73 1.43 0.21 P 18 Bhagbanpur 400 144 278.30 3.77 2.78 0.13 P 19 Hutgram 400 153 555.91 2.86 7.68 0.14 P 20 Chaitor 1100 442 125.19 10.17 2.25 0.25 P 21 Goaldanga 1500 542 107.06 10.44 0.65 0.24 P 22 Jhumki 300 110 75.47 9.77 0.62 0.19 P 23 Jorthal 2500 1008 93.52 12.03 4.52 0.26

4. Results and Discussion

Access to safe drinking water remains an urgent necessity, as 30% of urban and 90% of rural households still depend completely on untreated surface or groundwater (Rakesh Kumar 2005). While access to drinking water in India has increased over the past decade, the tremendous adverse impact of unsafe water on health continues (WHO/UNICEF 2004). It is now generally recognized that the quality of groundwater is just as important as its quantity. All groundwater contains salts in solution that are derived from the location and past movement of the water. The quality required of a groundwater supply depends on its purpose; thus, needs for drinking water, industrial water, and irrigation water varies widely. To establish quality criteria, measures of chemical, physical, biological, and radiological constituents must be specified, as well as standard methods for reporting and comparing results of water analyses. Dissolved gases in groundwater can pose hazards if their presence goes unrecognized. The uniformity of groundwater temperature is advantageous for water supply and industrial purposes, and underlying saline ground waters are important because they offer potential benefits. Study of ground water resources cannot be considered to be complete without any knowledge about its physical and chemical character and quality – its stability and usability or otherwise for such specific uses as irrigation, industry and drinking



purposes. Several properties both physical and chemical were studied in the laboratory, either by chemical experiment or with the aid of instrument like atomic absorption spectrophotometer.

4.1 Electrical Conductivity (EC)

Conductivity is the measure of capacity of a substance to conduct the electric current. Electrical conductivity or specific conductance is the reciprocal of resistance in ohms measured between the opposite faces of 1 cm 3 usually expressed at 25 o C. Specific conductance is expressed in mhos/cm. Most of the salts in water are present in their ionic forms and capable of conducting current and conductivity is a good indicator to assess groundwater quality. The quality standards for drinking water have been specified by the World Health Organisation (WHO) in 2004. It has provided the permissible and desirable limits of various elements in groundwater, Table – 2.

Table – 2: Classification of Irrigation Water based on Electrical Conductivity

Water Class

EC (micromohs/cm

)

Salinity Significance

Excellent <250 Water of low salinity is generally composed of higher proportions of calcium, magnesium and bicarbonate ions.

Good 250 750 Moderately saline water having varying ionic concentrations

Permissible 750 2250 High saline waters consist mostly of sodium and chloride ions.

Doubtful > 2250 Water containing high concentration of sodium, bi carbonate and carbonate ions has high pH.

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1500

1800

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600

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1800

2400

3000

micromohs/cm

Figure 2a: Specific conductance map of the study area (Premonsoon 2009)

Figure 2b: Specific conductance map of the study area (Postmonsoon 2009)



Here values range from 120 1940 micromhos/cm in premonsoon and in postmonsoon 300 3400 micromhos/cm. During pre monsoon period the EC was observed maximum in Gara (1940 micromhos/cm) and minimum in Jhumki (120 micromhos/cm) (Figure 2a)and in post monsoon maximum value observed in Teghari (3400 micromhos/cm) and minimum is recorded in many places viz. Dwarkeswar river, Satayatan Primary School, Suburdi, Saluni, Kanudi, Jhumki i.e. 300 micromhos/cm. (Figure 2b)

4.2 Total Dissolve Solids (TDS)

Total dissolved solids in a water sample include all solid materials in solution, whether ionized or not. It does not include suspended sediments, colloids or dissolved gases. TDS is numerical sum of all dissolved solids obtained by this method does not coincide completely with the material originally in the solution. Dissolved gases which may have an important bearing on the character of water originally are driven off. The concentration of total dissolved solids (TDS) in groundwater has been determined directly by weighing the solid residue obtained by evaporating a measured volume of filtered sample to dryness.

In the drying process the bi – carbonate is converted to carbonate with the loss of carbon – dioxide and water and thus is lost. Some of the solid salts deposited may be volatilized at the drying temperatures. Some water may deposit residues containing water of crystallization not driven off at the drying temperatures. Its general acceptance level is 500mg/l. But WHO has set allowable limit of 1500mg/l. In the study area the TDS varies from 77 – 1242mg/l in pre monsoon maximum value is recorded at Gara and minimum value at Jhumki and in post monsoon it varies from 104 – 1365mg/l, maximum and minimum values are recorded at Teghori and Kanudi respectively. (Figures 3a and 3b) Table 3

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Figure 3a: Total Dissolve Solids concentration map of the study area (Pre monsoon 2009)

Figure 3b: Total Dissolve Solids concentration map of the study area (Postmonsoon 2009)



Table 3: Classification of groundwater based on TDS [Carroll ,1962]

Water Class TDS (mg/l)

Fresh Water 0 to 1,000

Brakish Water 1,000 to 10,000

Saline Water 10,000 to 1,00,000

Brine 1,00,000

On the basis of the above table it can be stated that the study area’s water belong to Fresh water to Brakish water class.

4.3 Total Hardness

Hardness results from the presence of divalent metallic cations of which Calcium (Ca) and Magnesium (Mg) are the most abundant in groundwater. These ions react with soap to form precipitates and with certain anions present in the water to form scale. The hardness in water is derived from the solution of carbon di oxide released by bacterial action in the soil, in percolating rain water. Hardness HT is customarily expressed as the equivalent of the Calcium carbonate. Thus,

HT = Ca X Ca

CaCO 3 + Mg X Mg

CaCO 3

Where HT, Ca and Mg are measured in milligrams per liter and the ratios in equivalent weights.

The degree of hardness in water is commonly based on the classification listed in Table. 4.

Table 4: Hardness classification of water (after Sawyer and McCarly 1967)

Hardness, mg/l as CaCO3

Water class

0 – 75 Soft 75 150 Moderately Hard

150 – 300 Hard Over 300 Very hard

Its general acceptance level is 300mg/l. But WHO has set allowable limit of 600mg/l. In my study area the Hardness varies from 60 – 1190 mg/l. It is within limit everywhere except in the Teghari and Gara having more than 1000 mg/l, Dhaban has 840 mg/l and Satyatan Primary School has 870 mg/l in pre monsoon(Figure. 4a) and in post monsoon Hardness varies from 120 – 1070 mg/l., in the Teghari, Gara and Jorthal having values of hardness respectively 1070 mg/l, 750mg/l, and 800 mg/l.(Figure 4b) which are above allowable limit and indicating very hard water.



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mg/l

4.4 Soluble Sodium Percentage (SSP)

SSP is used to evaluate sodium hazard. SSP is defined as the ratio of sodium to the total cation. Water with a SSP greater than 60% may result in sodium accumulations that will cause a breakdown in the soil’s physical properties (Khodapanah et al.2009). SSP has been calculated by the following equation (Todd, 1980):

SSP = ) (

100 ) ( K Na Mg Ca

x K Na + + +

+ ………….. (1)where, all the ions are expressed in meq/L.

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6 8 10 12 14 16 18 20 22 24 26 28 30 32 34 36 38 40 42 44

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1 2

3 4 5 6 7 8

9 10 11 12 13 14 15 16 17 18

The Soluble Sodium Percentage (SSP) values were found from 10.41 meq/L at Chaitor to 46.38 meq/L at Jhumki and average was 19.51 meq/L in pre monsoon time (Figure. 5a) and in post monsoon time it varies between 1.67 meq/l at Gara to 18.15 meq/l at Hapania and

Figure 4a: Hardness map of the study area (Premonsoon 2009)

Figure 4b: Hardness map of the study area (Postmonsoon 2009)

Figure 5a: Soluble Sodium Percentage map of the study area (Premonsoon 2009)

Figure 5b: Soluble Sodium Percentage map of the study area (Postmonsoon 2009)



average was 7.65 meq/l (Figure 5b).

4.5 The Residual Sodium Bicarbonate (RSBC)

RSBC/ RSC have been calculated according to Gupta and Gupta (1987):

RSBC = HCO3Ca……………………… (2) where, RSBC and the concentration of the constituents are expressed in meq/L.

The residual Sodium Bicarbonate (RSBC) value of the water samples were found in between 0.17 mg/l and 10.85 mg/l at Teghari and Kharbona respectively in pre monsoon(Figure. 6a) and in post monsoon it varies 7.68 mg/l (at Hutgram) to 4.52 mg/l (at Jorthal) (Figure 6b). The positive RSBC value indicates that dissolved calcium and magnesium ions less than that of carbonate and bicarbonate contents.

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4.6 Sodium Absorption Ratio (SAR)

When water high in sodium, is applied to soils, some of sodium is taken up calcium and magnesium. The action is called Base Exchange and a result of this; the physical characteristics of the soil are altered. Clay that carries a good excess of calcium and magnesium ions tills easily and has good permeability. If it takes up sodium, it becomes sticky and slick when wet and has a very low permeability. It shrinks, when dry into hard clods which are difficult to break. High concentration of sodium salts develops alkali soil in which little or no vegetation can grow. If the irrigation water contains calcium and magnesium ions in quantity that equals or exceeds the quantity of sodium, a sufficient concentration of calcium or magnesium will be retained on clay particles of the soil to maintain good permeability. Such waters serve well for irrigation even through the total mineral content may be quite high. Sodium percentage exceeding 50% was taken as a warning of sodium hazard. However, in 1954, the U.S. Salinity Laboratory proposed that sodium percentage idea be replaced by a significant ratio termed the Sodium Adsorption ratio or S.A.R. because it has a direct relation

Figure 6a: Residual Sodium Bicarbonate map of the study area (Premonsoon 2009)

Figure 6b: Residual Sodium Bicarbonate map of the study area (Postmonsoon 2009)



with the adsorption of sodium by soils. This ratio has been calculated by the following equation given by Richards (1954) as:

SAR =

2 Mg Ca

Na +

……….. (3)

Where, all the ions are expressed in meq/L.

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0.22 0.24 0.26 0.28 0.3 0.32 0.34 0.36 0.38 0.4 0.42 0.44 0.46 0.48 0.5 0.52 0.54 0.56 0.58 0.6 0.62 0.64

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0.04 0.06 0.08 0.1 0.12 0.14 0.16 0.18 0.2 0.22 0.24 0.26 0.28 0.3 0.32 0.34 0.36 0.38 0.4

The result shows that concentration of sodium (Na + ) was in the range of 5.22 mg/l (at Bhagabanpur) to 11.57 mg/l (at Hapania) in pre monsoon period and 1.27 mg/l (at Dubrajpur) – 8.58 mg/l (at Dhaban) in post monsoon period. Sodium Adsorption Ratio (SAR) also influences infiltration rate of water. So, low SAR is always desirable. In the studied samples, SAR values were ranged between 0.27 (at Tilna) and 0.66 (at Jhumki) in pre monsoon (Figure 7a) and in post monsoon it varies in between 0.05 (at Gara) – 0.40 (at Hapania) (Figure 7b).

4.6.1 U.S. Salinity Laboratory Water Classification

The standard U.S. Salinity Diagram gives direct indication of the salinity and alkalinity hazards. According to this diagram the irrigation waters have been classified into 20 different groups each having specific properties.

Conductivity classes

Low Salinity Water (C1): Water in this class can be used for irrigating most of the crops on almost any soil type with little likelihood of developing soil salinity.

Figure 7a: Sodium Absorption Ratio map of the study area (Premonsoon 2009)

Figure 7b: Sodium Absorption Ratio map of the study area (Postmonsoon 2009)



Moderate Salinity Water (C2): Water in this class can be used for irrigating all but extremely saltsensitive plants if grown on soils of high to medium permeability. For soils of low permeability, some leaching precautions and at times proper selection of plants with moderate salt tolerance may be necessary.

MediumHigh Salinity Water (C3): Water in this class should be used only on soils of moderate to good permeability. Regular leaching is often needed to prevent serious salinity. Plants of moderate to good salt tolerance should be selected in such cases.

High Salinity Water (C4): Water in this class can be used for irrigation on soils of good permeability and where special leaching is provided to remove excess salt.

Very High Salinity (C5): Water is generally undesirable for irrigation and should be used only on highly permeable soils with frequent leaching and with plants of high salt tolerance.

Sodium classes

Low Sodium Water (S1): Water in this class can be used on almost all types of soils with little danger of accumulation of harmful amount of exchangeable sodium.

Figure 8: U.S. Salinity Diagram

Medium Sodium Water (S2): This water presents appreciable sodium hazard in soils of high clay content especially when leaching conditions are not adequate. This water may be used on coarsegrained soils with good permeability.



High Sodium Water (S3): Water will tend to cause harmful sodium accumulation in most non gypsiferous soils and will require special soil management. Good drainage, high leaching, and organic matter additions for improving the physical conditions of the soil are necessary for success with these waters. Chemical amendments may be used for exchangeable sodium replacement except for waters of very high salinity, in which case the use of amendments will not be feasible.

Very High Sodium Water (S4): Water will be generally unsatisfactory for irrigation purposes except at low and perhaps medium salinity where the use of gypsum or other amendments may be feasible. Considerable leaching is required.

Thus the point when plotted on the diagram (Figure 8) gives the classification of the water sample in two letter figures. C1, C2, C3 etc., represent water classes with increasing salinity hazards and S1, S2, S3. etc., represent water classes for increasing hazards of exchangeable sodium accumulation in irrigated soil. Good quality waters are taken as those falling C1S1 and C2S1 groups. Water falling C1S2, C2S2, C3S2 and C3S1 are taken as moderate waters; whereas waters belonging to groups other than these are considered as bad waters.

4.7 GIS Map based on Water Quality Parameters

Parameter indices like EC, RSC, SAR, SSP for rating groundwater quality and its sustainability in irrigation are taken for preparation of GIS map (Table 5). The pre monsoon and post monsoon water quality map of groundwater of the study area is good to poor for irrigation purposes.

In Dhaban, Shushunia, parts of Jhantipahari, Kamalpur and Dubrajpur area having good water which is suitable for the irrigation where as Goaldanga, Chaitor area having poor water

Figure 9a:Water Quality map of the study area (Premonsoon 2009)

Figure 9b: Water Quality map of the study area (Postmonsoon 2009)



quality which is not suitable for irrigation during pre monsoon (Figure 9a) and Shushunia, Jorthal and Shburdhi area are good for the irrigation but parts of Jhantipahari, Kanudi, Sukhnibash, Teghori having poor water quality which is not suitable for irrigation during post monsoon (Figure.9b).

Table 5: Water Quality Classification for irrigation after Ayers and Westcot (1985), Eaton (1950), Wilcox (1955) and Todd (1980)

To bring out the changes clearly between pre monsoon and post monsoon water quality in a visual format, the groundwater quality maps generated for the two periods (pre monsoon 2009 and post monsoon 2009) were combined to make a Normalized Difference Index (NDI) map.

A Normalized Difference map is obtained with values ranging from 1 to 1.

Figure 10: Normalized Difference Map of the study area

Category EC (µs/cm ) RSC (meq/l) SAR SSP Sustainability

for Irrigation

I <250 <1.25 <10 <20 Excellent

II 250 – 750 1.25 – 2.5 10 – 18 20 – 40 Good

III 750 – 2250 >2.5 18 – 26 40 – 80 Fair

IV >2250 >26 >80 Poor



Values close to 1 indicate the maximum difference between the two maps while values close to 1 indicate areas with minimum difference between the two maps. The normalized difference map was calculated using the Raster Combine – Predefine tool in TNT mips 74.

In Chhatna Block, Dhaban, Jorthal, parts of Jhantipahari, Dubrajpur, Kamalpur, Shburdhi, Goaldanga Chaitor, Hapania and Hutgram area showing maximum changes in water quality and rest of the area shows no changes in water quality during the period. (Figure 10)

5. Conclusion

1. It is evident from the whole sample set that the SAR value is excellent in all the samples. Hence, our findings strongly suggest that all the abstracted groundwater samples from the study area were suitable for irrigation.

2. In U.S Salinity diagram all the samples fall under “Good Water” zone. But nearly 45% sample of the study area fall under high salinity zone (EC=750 µ mhos /cm) such water should not be used on soils with restricted drainage (Jain et al, 2000).

3. The Normalized Difference Map clearly demarcates the regions in the study area that have undergone maximum changes in water quality during the period. Changes in groundwater quality over a period of few years to tens of years may be primarily caused by (1) changes in long term hydraulic phenomenon that effect groundwater recharge, (2) variations in the recharge rate and water quality of the pollution sources, and (3) changes in water level and direction of groundwater movement (Schmidt 1977).

Acknowledgments

The author (SKN) is gratefully acknowledges the financial support from Centre of Advanced Study (CASPhase IV), Department of Geological Sciences, Jadavpur University in conducting the field work related to this work. The other author (Poulom Ghosh) is thankful to University Grants Commission, New Delhi and Jadavpur University also for providing the UGC Research Fellowship in Science for Meritorious Student 20072008 to her.

6. References

1. Ayers. R.S., and Westcot D.W, (1985), Water quality for Agriculture. FAO Irrigation and Drainage. 29 (1), pp 1 – 109.

2. Carroll. D., (1962), Rainwater as a chemical agent of geologic processes – A review, U.S. Geological Survey Water – Supply Paper 1535 – G, pp 18.

3. Eaton. F.M., (1950), Significance of carbonate in irrigation waters. Soil Science., 69(2), pp 123134.

4. Gupta,S. K. and Gupta,I. C. (1987). Management of Saline Soils and Water. Oxford and IBH Publication. Co. New Delhi, India. 399.

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