109

CHAPTER 7

IRRIGATION GROUNDWATER QUALITY

7.1 GENERAL

The exploitation of groundwater has increased greatly in the last

two to three decades in India, particularly for agriculture purpose, because

large parts of the area have little access to the surface water resources. Hence,

groundwater is used for irrigation and drinking purpose. The groundwater of

Tondiar basin is used for the domestic and agriculture purposes as the surface

water resources are limited. There has been increase in the demand for

groundwater agricultural practices and growth of the population. Groundwater

quality is strongly influenced by various hydrochemical processes as

discussed in the previous chapter. Increased agricultural activity in this region

is likely to have an impact on the groundwater quality. Groundwater is largely

contaminated by organic and inorganic pollutants in the rural area due the

modern agriculture, by way of application of agrochemicals. Hence, it is

necessary to determine the suitability of groundwater for the domestic and

irrigation purposes based on the presence of major ions, nutrients and trace

elements in the groundwater. There was no systematic variation in the quality

of groundwater throughout the study area, but the quality of the groundwater

is affected mostly where there is a human settlement, storage of the animal

waste and domestic waste.

The minimum, maximum and mean of the chemical analysis of

groundwater samples of this area during the months of May (summer) and

110

November (winter) 2006 is given Table 7.1. The concentration of Ca2+, Mg2+,

Na+, K+ HCO2-, Cl- increase from winter to summer month. NO3- and K+

concentration increase during the winter season due to the application of

fertilizer and shallow water table. Statistical data further confirms the role of

seasonal effect on the contributions of ions to the groundwater quality (Table

7.1).

Table 7.1 Min, max and aver concentration major ions in groundwater

Chemical Constituent (mg/l)

January 2006 (Winter) May 2006 (Summer)

Min Max Mean Min Max Mean

pH (no unit) 7.0 8.55 7.5 6.58 7.71 7.1

EC(μS/cm) 469 4531 1863 719 4844 2116

TH 154 761 338 155 826 340

Ca2+ 42 220 94 34 232 91

Mg2+ 4.8 59.4 25 9 68 27

Na+ 7.2 448 111 8.9 490 134

K+ 1 212 14 0.7 159 12.8

HCO2- 180 470 321 186 671 395

Cl- 22 638 192 26 899 218

SO42- 5 180 50 10 400 85

NO3- 4.5 62 20.83 4.0 43 17.50

7.2 DOMESTIC WATER QUALITY

Drinking water used for the domestic purpose should be free from

color, turbidity, odour, and micro-organisms. In most of the hydrogeological

conditions, groundwater can be put to direct use without treatment. The

domestic water quality indicates that a particular parameter may be useful at a

certain concentration but become toxic at higher concentration. According to

111

WHO (1984), about 80% of the disease prevalent are because of the

contaminated water. In the study area, the groundwater does not possess any

smell but there is some variation in taste. Drinking water specifications (Table

7.2) have been established by many organizations like ISI (1991), ICMR

(1975) and WHO (1984). The spatial distribution map of total dissolved solids

(TDS arrived from EC x 0.64) in Figure 7.1. Generally groundwater samples

in the study area is suitable for domestic purposes, except in Tondur,

Pennagar, Perumpoondi, Desur, C.M.Pudur, Melsithamur, Vallam,

Kongampattu, Indirasonkuppam, Elamangalam, Rettani, Vengathur and

Pelampattu where TDS is higher than the permissible limit of 1500 mg/l.

Hence, the water containing TDS more than 500 mg/l causes gastrointestinal

irritation (ISI, 1991) and about 80 % samples have TDS values above the

desirable limit of 500 mg/l. Most of the groundwater of this area is slightly

saline in nature with TDS greater than 1000 mg/l. Only in a few wells the

groundwater has TDS less than 1000 mg/l. Generally groundwater contains

TDS in more than 1000 mg/l make them unsuitable for ordinary water supply

purpose.

Table7.2. Standards for drinking Water

Chemical

Constituents

(mg/l)

ISI (1991) ICMR(1975) WHO(1984)

Highest

desirable

Limit

Maximum

permissible

Limit

Highest

desirable

Limit

Maximum

permissible

Limit

Highest

desirable

Limit

Maximum

permissible

Limit

pH (units) 7.0 – 8.5 6.5 – 9.2 6.5 – 8.5 6.5 – 9.2 7.0 – 8.5 6.5 – 9.2

TDS 500 1500 500 1500 500 1500

TH 300 600 300 600 100 500

Ca2+ 75 200 75 200 75 200

Mg2+ 30 100 50 100 50 150

Cl- 250 1000 250 1000 200 600

SO42- 150 400 200 400 200 400

112

Figure 7.1 Spatial distribution pattern of Total Dissolved Solids (mg/l)

of groundwater (May 2006)

The groundwater analysis of January 2006 plotted in the Durov’s

(1956) diagram is shown in Figure 7.2. Most of the groundwater samples fall

in the category C which is moderate quality from domestic purpose.

TDS (mg/l)

1500

2000

500

2500

3000

1000

300

May 2006

113

Figure 7.2 Durov’s classification of groundwater (January 2006)

7.3 WATER HARDNESS

Water hardness primarily depends on the amount of calcium and

magnesium present in groundwater. Water hardness in most groundwater

naturally occur due to weathering of limestone, sedimentary rock and calcium

bearing minerals. Hardness can also occur due to the application of lime to

soil in agricultural areas. Calcium and magnesium along with their sulphates,

chloride, bicarbonates and carbonates makes the water hard in nature. Safe

limit of hardness suggested by ISI (1983) for drinking water is 300 mg/l. Hard

water is unsatisfactory for household cleaning purpose, hence water-softening

process for removal of harness needed. Hard water is due to the unpleasant

taste. Hard water is generally believed to have no harmful effect on human

beings. Hard water leads to incidence of urolithiosis, anencephaly parental

mortality, some types of cancer and cardio-vascular disorder (WHO 1984).

114

Greater incidences of cardio-vascular diseases are reported to be more

confined to the area of soft water than hard water (Crawford, 1972). Hardness

is one of the important properties of groundwater because of its characteristics

influences on development of scales in water heaters, distribution pipes and

well pumps, boilers and cooking utensils and requires more soap for washing

clothes (Todd 1980; Hem 1991). The classification of the groundwater based

on hardness (Matthess 1982) and the representing wells are given in Table

7.3. Hardness of groundwater in the study area ranges from 154 to 761 mg/l

with an average value of 338 mg/l during winter season as shown in the Table

7.2. Majority of the groundwater samples fall in the hard water to very hard

category with allowable limit of total hardness for drinking water of 500 mg/l.

This may due to the geological formation of the rocks. In some agricultural

lands where fertilisers are applied to the land, excessive hardness may

indicate the presence of other chemicals such as nitrate.

Table 7.3 Classification of groundwater based on hardness (Matthness

1982) Hardness

Classification

Hardness as

CacO3 (mg/l)

Representing Wells

Very Soft 0-50 Nil

Soft 50-150 Nil

Average 150-250 2,3, 12,13,19,21,23,29,36,38,39

Hard 250-500 1,4,5,7,9,10,11,14,15,16,17,20,22,24,26,

Very Hard >500 6,8,18,27,28,30,31,32,33,34,35,37,40,41,42,

43,44,45.

7.4 IRRIGATION WATER QUALITY

The groundwater of the study area is extensively used for irrigation

in this area. The suitability of groundwater for irrigation depends upon the

mineral constituents present in the water. Irrigation water of good quality is

115

essential to maintain the soil crop productivity at a higher level. Water used

for irrigation always contains measurable quantities of dissolved substances,

which are generally called as the salts. The salts should contain small amounts

of dissolved solids originating from dissolution or weathering of the rocks.

EC and Na play a vital role in suitability of water for irrigation. Higher salt

content in irrigation water causes an increase in soil solution osmotic pressure

(Throne and Peterson 1954), which makes difficult for the plant root to

extract water for osmosis. The osmotic pressure is proportional to the salt

content or salinity hazard. The various salts present in the irrigation water not

only affect the plant growth directly, also affect the soil structure,

permeability and aeration which indirectly affect the plant growth (Mohan

and others 2000). The total concentration of soluble salts in irrigation water

can be classified into low (C1), medium (C2), high (C3) and very high (C4)

salinity zones and the values are shown in the Table 7.4. Higher EC in water

creates a saline soil. The important chemical parameters for judging the

degree of suitability of water for irrigation is sodium content or alkali hazard

which is expressed using EC, Sodium adsorption Ratio (SAR) and Sodium

Percentage, Residual Sodium Carbonate (RSC).

7.4.1 Electrical Conductivity

Electrical Conductivity (EC) is a measure of the degree of the

mineralization of the water, which is dependent on rock water interaction, and

thereby the residence time of the water in the rock (Eaton, 1950). EC of the

irrigation water becomes one of the important parameters to evaluate the

overall chemical quality of groundwater and it is being used to compare the

waters with one other in any region. Based on EC the water could be

classified as tasteless, sweet, brackish, saline and brine. As groundwater

moves and stays for a longer time along its flow path the increase in total

dissolved concentration and major ions normally occurs. It has been noticed

116

in many groundwater investigations that the groundwater in recharge area is

characterized by a relatively low EC than the groundwater in the discharge

area it is higher (Freeze and Cheery, 1979).

Figure 7.3 Spatial distribution pattern of Electrical Conductivity

(μS/cm) (May 2006)

Excellent

Good

Permissible

Unsuitable

LEGEND

Electrical Conductivity

Doubtful

117

Hence, irrigation water with high EC will affect the root zone and

water flow, due to high osmotic pressure. The United States Salinity

Laboratory has established a guideline for grouping of irrigation water based

on EC (U.S. Salinity Laboratory 1954). Groundwater of this area is grouped

based on these guidelines in Table 7.4 with corresponding well numbers

against each class. This shows that due to high EC the groundwater is not

suitable for irrigation in certain locations as specified in Table 7.4. However,

even in these areas groundwater can be used for irrigation with suitable

precautions as given in the Table 7.4. Similarly the regional variation of

Electrical conductivity of the groundwater as shown in Figure 7.3 falls in

permissible to doubtful in nature (May 2006).

118

Table 7. 4 USDA salinity laboratory (January 2006)

TDS (mg/l) EC in Μs/cm

at 25° C

SalinityClass Potential injury and necessary management for use in irrigation water

Representing Wells

119

7.4.2 Relation between SAR AND EC The SAR and EC values of water samples of the study area are plotted

in the widely used diagram for evaluating waters for irrigation purposes suggested

by the U.S.Salinity Laboratory (1954). This plot is shown in Figure 7.4. In this

USSL diagram (1954) waters of the study area are classified into C2, C3 and C4

types on the basis of salinity hazard and S1, S2, S3 types on the basis of sodium

hazard. The plot of the data on the US salinity diagram is shown for premonsoon

and postmonsoon seasons. This shows that there is slight improvement in the

water quality after the monsoon. This means in general they are classified as

satisfactory for irrigational use in almost all types of soils. Moderate and bad

quality types are due to enrichment of Na+ and EC concentrations. From (Table

7.5) it is found that most of samples fall in moderate water quality and few

samples 6, 8, 16, 17, 18, 25, 26, 27, 28, 30, 33, 35, 37 and 42 are undesirable for

irrigation. The causes of unsuitability are due to storage due to bedrock formation,

agriculture activities, storage of animal waste and local pollution of the villages.

The USSL diagram has shown both the premonsoon and postmonsoon period. The

good water can be used for irrigation in almost all types of soils. The moderate

waters can be used to irrigate salt-tolerant and semi-tolerant crops under favorable

drainage conditions. The bad waters are generally undesirable for irrigation and

should not be used on clay soils of low permeability. Bad waters, however, can be

used to irrigate plants of high salt tolerance, when grown on salty soils to protect

against under decline of fertile lands. The relative tolerance of crops to salt

concentration (After Sharma and Chawla 1977) is given in Table 7.7.

120

Figure 7.4 USSL Classification of groundwater during pre and postmonsoon

Table 7.5 Integrated Classification of groundwater

Groups USDA Classes Number of Wells Irrigation water classes

Premonsoon Postmonsoon Group I C1-S1,C2-S1 2 2 Suitable to use

Group II C1-S2,C2-S2, C3-S1,C3-S2

29 30 Conditionally suitable water

Group III C1-S3,C1-S4, C2-S3,C2-S4, C3-S3,C3-S4, C4-S1,C4-S2, C4-S3,C4-S4

14 13 Unsuitable

121

Table 7.6 Relative tolerance of crops to salt concentration

Salt-Sensitive Semi-tolerant High-tolerant

Gram, Moong, peas Rice, Wheat, Millets, Maize, Tomato,

Cabbage, Potato, onion, Mango,

Banana, Pears, Apple, orange, Lemon

Sugarcane, cotton, Mustard,

Sugarbeet, Tobacco, Barley

7.4.3 Sodium percentage

Sodium is important in classifying irrigation water, because sodium

reacts with soil thereby reducing the permeability. Percent sodium in water is a

parameter computed to evaluate the suitability of water quality for irrigation

(Wilcox 1948). The %Na is computed with respect to relative proportions of

cations present in water, where the concentrations are expressed in meq/l using the

formula

Soil containing large proportions of sodium with carbonate as the

predominant anions termed to alkali soil, whereas with chloride or sulphate as the

predominant cations termed as saline soil. Neither soil will support plant growth.

The percentage sodium computed for the postmonsoon and premonsoon period of

January 2006 and May 2006. Generally, %Na+ should not exceed 60% in

irrigation waters. In the Table 7.8 shows the most of groundwater samples fall

under the category of good to permissible quality during the premonsoon season.

A few samples fall under excellent and doubtful category. The Figure 7.5 indicates

the effect of monsoon rains on the irrigation water quality of the region. That is the

irrigation water quality improves in the post monsoon period. Groundwater

samples of the study area are plotted in the Wilcox’s diagram (Wilcox 1955) for

%Na+ = (Na+ +K+ ) X 100

(Ca2+ + Mg2+ +Na+ + K+)

122

the classification of groundwater for irrigation, wherein EC plotted against %Na

(Figure 7.5).

Table 7.7 Suitability of irrigation water based on sodium percent

Representing Wells in this category

Na% Suitability for

irrigation

Postmonsoon

(January 2006)

Premonsoon

(May 2006)

80 Unsuitable Nil Nil

The water samples of this area falls in all categories, however majority

of samples fall under good to permissible region. As explained earlier the

monsoon recharge results in the improvement of irrigation water quality. The

agricultural yields are observed to be generally low in lands irrigated with water

belonging to doubtful to unsuitable and doubtful. This is probably due to the

presence of sodium salts, which cause osmotic effects in soil plant system

123

Figure 7.5 EC Vs Sodium percent (Wilcox diagram)

7.4.4 Residual sodium carbonate

The quantity of bicarbonate and carbonate in excess of alkaline earth

(Ca +Mg) also influences the suitability of water for irrigation purposes. Residual

sodium carbonate (RSC) is frequently used to assess the water quality for

irrigation purpose, was not applied in present day. The RSC value is computed,

where ions are expressed in meq/l using the following formula.

RSC = (CO3 + HCO3) – (Ca + Mg)

The variation in RSC of the study area during pre and post monsoon

period is given in Table 7.8. However with respect to RSC all samples are within

the safe quality categories for irrigation this indicates that water is suitable for

irrigation purpose. From the table it is found that well no 36 is not suitable for

both seasons. This is clearly found from field studies the occurrence of alkaline

124

white patches of the soil. Further, continued usage high RSC will result in burning

of leaves of plants, affects crop yield. Similarly irrigation with high RSC water in

the fine textured soil will result in the development of alkali soil.

Table 7.8 Suitability of irrigation water based on residual sodium carbonate

Residual Sodium Carbonate of sample in this category

RSC (meq/l) Suitability for

irrigation

Premonsoon

Total wells

Postmonsoon

Total wells

2.5 Unsuitable 4 1

7. 4.5 Potential Salinity

This is defined as the chloride concentration and plus half of the

sulphate concentration. Doneen (1954) pointed out that the suitability of water for

irrigation is not dependent on the concentration of soluble salts. Doneen (1962) is

of the opinion that low solubility salts precipitated in the soil and accumulate with

each excessive irrigation, whereas the concentration of highly soluble salts

increases the salinity of soil. The potential salinity of water samples ranges from

2.5 to 27.85 with a mean of 8.50. The huge amount of potential salinity is due to

the presence of chlorides. From the Figure 7.6 shows the well nos. 33 with high

salinity and this well is surrounded by plantation crops like Casuarinas which is a

salt resistant plant should be cultivated in this region of high groundwater EC.

125

0

5

10

15

20

25

30

1 3 5 7 9 11 13 15 17 19 21 23 25 27 29 31 32 34 36 38 40 42 44

Well Nos

Pote

ntia

l Sal

inity

Figure 7.6 Potential Salinity of groundwater

7.4.6 Sodium adsorption ratio

The SAR is used to estimate the sodicity hazard of the water, the

sodium adsorption ratio (SAR) is used to predict the danger of sodium

accumulation in soil. Excess sodium in water produces the undesirable effects of

changing soil properties and reducing soil permeability and soil structure (Kelly,

1957). Hence, the assessment of sodium concentration is necessary while

considering the suitability for irrigation. The sodium or alkali hazard in irrigation

water is recommended by USSL which takes into account of the relative activity

in the exchange reaction with soil as expressed in terms of ratio known as SAR

(Sodium Adsorption Ratio). SAR is calculated by the following formula,

SAR = [Na+/√Ca2++Mg2+/2

The concentration is expressed in meq/l. While high salt content (EC) in

waters leads to development of saline soil, high sodium content (SAR) leads to

126

development of an alkaline soil. SAR can indicate the degree to which irrigation

water tends to enter cation-exchange reaction in soil. Sodium replacing adsorbed

calcium and magnesium is a hazard as it causes damage to the soil structure and

becomes compact and develops permeability problems. This will support little or

no plant growth. SAR is an important parameter for the determination of the

suitability of irrigation water because it is responsible for the sodium hazard

(Todd, 1980). The groundwater of the study area are classified with respect to

SAR values (Richard 1954) (Table 7.9). According to the above classification, the

SAR values in the study area range from 0.73 to 10.9 meq/l and the samples of the

study area have been classified as there is no danger of sodium consideration in

soil as per SAR. If the SAR values are greater than 9, the irrigation water will

cause permeability problems on shrinking and swelling in clayey soils (Saleh et

al., 1999). The higher the SAR values in the water, the greater the risk of sodium.

Table 7.9 Sodium adsorption ratio

Sodium adsorption ratio of sample in this category

SAR Suitability for irrigation Premonsoon

Total wells

Postmonsoon

Total wells

26 Unsuitable Nil Nil

7.4.7 Kelly’s ratio

Based on Kelly’s ratio waters are classified for irrigation. Sodium

measured against Calcium and Magnesium was considered by Kelly (1957) to

calculate this parameters. A Kelly’s ratio of more than one indicates an excess

level of sodium in waters. Therefore, water with the Kelly’s ratio less than one is

127

suitable for irrigation, while those with a ratio more than three are unsuitable for

irrigation. Kelly’ ratio of groundwater of the study area varies from 1.07 to 7.62

with an average 3.50 in the premonsoon while in the postmonsoon it varies from

0.65 to 6.07 with an average of 3.05. Therefore according to the Kelly’ ratio, all

the water samples are in the category of doubtful-unsuitable for irrigation as

shown in Figure 7.7.

Figure 7.7 Spatial distribution pattern of Kelly’s ratio (July 2006)

7.4.8 Permeability index

The soil permeability is affected by long term use of irrigation water as

it influenced by sodium, calcium, magnesium, and bicarbonate content of the soil.

Kelly's ratio

1

3

0

Legend

Permissible

Doubtful

Unsuitable

128

Doneen (1964), WHO (1989) gave a criterion for assessing the suitability of

groundwater for irrigation based on the permeability index (PI). Where

concentrations are in meq/l.

PI = (Na++√HCO3-)100

(Ca2+ + Mg2+ + Na+)

Accordingly, the permeability index is classified under class 1 (>75%), class

11(25-75%) and class 111(

129

The study area hazard of irrigation water sodium on soil infiltration

must be determined from SAR/EC interactions as shown in Figure 7.9 (Ayers and

Westcott 1985). From the Figure it is found most of water plot in the region of no

reduction in rate of infiltration. However, a few samples plot in the other regions.

Hence, it is concluded that the groundwater has moderate salt content and the

groundwater can be utilised for irrigation based on the capacity of infiltration.

7. 9 Plot of SAR Vs EC interactions

7.4.9 Magnesium hazard

Generally calcium and magnesium maintain a state of equilibrium in

groundwater. More magnesium present in waters affects the soil quality

converting it to alkaline and decreases crop yield. Szabolcs and Darab (1964)

proposed magnesium hazard (MH) value for irrigation water as given

MH = Mg/ (Ca + Mg) x 100

Where the are concentrations in meq/l.

130

MH > 50 is considered harmful and unsuitable for irrigation for irrigation purpose.

In generally groundwater samples have minimum value of 16.77 meq/l, maximum

value of 52.65 meq/l and average 32.65 meq/l. The spatial distribution of

magnesium hazard in groundwater as shown in Figure 7.10 indicates that almost

all the samples are with the range of less than 50 meq/l and suitable for irrigation.

Figure 7.10 Spatial distribution magnesium hazard (meq/l)

Magnesium Hazard

10-20

20-30

30-40

40-50

>50

Legend

131

7.5 NUTRIENTS AND TRACE ELEMENTS

As the study area is an intensive agriculture region, there is a possibility

of contamination of the groundwater by the inorganic fertiliser. Hence, the

groundwater samples were analysed for the concentration of nutrients and trace

elements to study the impact of agriculture and rocks formations.

7.5.1 Nitrate

The spatial variation of nitrate concentration in the groundwater of the

study area varies below detection limit to 45 mg/l (Figure 7.11). The nitrate

concentration in the groundwater samples varies between 4 mg/l to 43 mg/l with

an average of 17.5 mg/l. Thus it is within the recommended limit 45 mg/l

suggested for drinking water (ISI 1983; WHO 1984). Considering the intensive

agricultural activities and the application of the man-made and natural fertiliser in

this area, groundwater concentration of nitrate is reasonably less. Agricultural

activities, including both fertilizer nitrate and nitrate derived from increased

mineralization of soil nitrogen through cultivation, are the major sources for

nitrate in groundwater (Jackson and Sharma 1983, Flipse et al 1985). There is no

known geological source for nitrate for its presence in groundwater of this area.

The wells near agricultural land have high concentration due to irrigation return

flow.

Hence, fertilisers are considered to be the principle source of nitrates in

this area under intensive agriculture. The types of fertiliser that are in use in this

area are organic and inorganic chemicals. Organic fertiliser includes solid and

liquid manure, slurry and composite and inorganic fertiliser which are applied in

higher proportion than organic fertiliser. The commonly applied inorganic

fertiliser are urea, di-ammonium phosphate, ammonium sulphate, superphosphate,

132

Nitrate

20

010

30

40

Legend

potassium chloride, ammonium chloride and potash. Generally, people assume

that crop yield increases with higher fertiliser application without considering the

thickness and absorbing capacity of soil in the study area. From the study it is

found that groundwater of the basin is affected by nitrate due to the application of

fertiliser for agricultural purpose.

Figure 7.11 Spatial distribution of nitrate (mg/l) in groundwater (March

2006)

133

7.5.2 Boron

The spatial distribution (Figure 7.12) of boron in groundwater samples

varies from 0.43 to 0.76 mg/l with average of 0.66 mg/l. Boron is essential to

plants and it helps in the growth when it is present in a very small amount for

irrigation. Boron concentration of about 1 mg/l is good for the plants, but if it is

above 2 mg/l is injurious to the crops. The injury appears as a burning and

browning of the leaf top followed by yellowing of the margin. Boron

concentration in this area is within the permissible limit.

7.5.3 Silica

The regional distribution of silica (Figure 7.13) concentration in

groundwater varies between 10.8 mg/l to 39 mg/l and the concentration varies

seasonally. However, in most of the wells, high concentration of silica is observed

in the summer season due to the lowering of the water table. The concentration of

SiO2 decreases the due to the rise in water level. Silica concentration is

comparatively high in the central part of the basin, due the presence of composite

gneissic rocks. Exner and spalding (1979) reported that silica concentration in

groundwater is controlled by mineral solubility. Rock weathering is a major source

for high concentration of silica in the study area.

134

Figure 7.12 Spatial distribution of boron (mg/l) in groundwater (March

2006)

7.5.4 Fluoride

Fluoride is an essential element for maintaining normal development of

healthy teeth and bones. Deficiency of Fluoride in drinking water below 0.6 mg/l

contributes to tooth caries. An excess of over 1.2 mg/l causes fluorosis (ISI 1983).

High intake of fluoride results in physiological disorders, skeletal and dental

fluorosis, thyroxine changes and kidney damages (Latha et al., 1999). Bedrock

Boron

0

0.50

0.751.0

0.25

Legend

135

Silica

0

10

20

30

40

Legend

containing fluoride minerals is generally responsible for high concentration of this

ion in groundwater (Handa, 1975; Bardsen and others 1996). It is a common

constituent in most of the soil and rocks. The concentration of the fluoride in

groundwater of the basin varies between 0.08 to 0.3 mg/l in the month of

November 2006. All the samples exhibit suitability of this water for drinking

based on the concentration of F. The spatial distribution of fluoride concentration

in groundwater is shown in Figure 7.14. The concentration of the fluoride is within

the permissible limit of 1.5 mg/l drinking water (ISI, 1991; WHO, 1994).

.

Figure 7.13 Spatial distribution of silica (mg/l) in groundwater (March 2006)

136

Fluoride

0

0.1

0.2

0.3

0.4Legend

Figure 7.14 Spatial distribution of fluoride (mg/l) in groundwater

(November 2006)

7.5.5 Chromium

The concentration of chromium in the groundwater samples ranges from

0.12 mg/l to 0.67 mg/l with an average concentration of 0.49 mg/l. Out of 45

samples analysed almost all the samples exceed the desirable limit of 0.05 mg/l

and permissible limit of 0.1 mg/l as per BIS (2003) as shown in Figure 7. 15.

High concentration of Cr may therefore be due to their dissolution from the rock

137

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

1 3 5 7 9 11 13 15 17 19 21 23 25 27 29 31 33 35 37 39 41 43 45

Well No

Cr (m

g/l)

material. This is possible because between the pH range of 5 to 13, chromium

dissolve from Cr2O3 (Hem, 1985). Thus Kerbyson and Schandorfn (1966)

reported that granite or metamorphic rocks in Ghana contain upto 0.03% of

Cr2O3and also the aquifer materials contain mica, hornblende and feldspar which

contain elevated level of chromium and Fe. Thus this basin contains hard rock

crystalline formations contain the higher concentration of chromium in almost all

the wells with the pH ranges from 6.5 to 8.5. The source of chromium in the area

is from the weathering of granite and subsequent leaching of ultrbasic rocks.

Chromium is highly toxic and in higher concentration it can be carcinogenic

(Swayer and MacCarty 1978).

Figurer 7.15 Chromium concentration in groundwater of all wells

138

0

0.005

0.01

0.015

0.02

0.025

1 3 5 7 9 11 13 15 17 19 21 23 25 27 29 31 33 35 37 39 41 43 45Well No

Cu (m

g/l)

7.5.6 Copper

The copper in the groundwater ranges from 0 to 0.022 mg/l with an

average of 0.0099 mg/l. These values are within the desirable limit 0.5 mg/l and

permissible limit 1.5 mg/l of BIS (2003). Figurer 7.16 shows that the copper in the

groundwater samples related to agriculture practices. Furthermore, other potential

source of copper to agriculture land includes the application of pesticides. Copper

is essential for plant and animal metabolism, their limited occurrence in

groundwater is useful from the point of view water quality.

Figure 7.16 Copper concentrations in groundwater of all wells

7.5.7 Zinc

The zinc concentration falls below the desirable limit of 5 mg/l. Zinc is

essential element for plants metabolisms, their limited occurrence in groundwater

is useful from the point of view of water quality. Zinc occurs only in a few wells,

while in the rest of the wells it is absent. Zinc in the groundwater of this area

139

ranges from 0 to 0.372 mg/l. Agriculture activity is the major source for high

concentration of zinc in groundwater of the study area. Similar result was

observed by Pawer and Nikumbh (1999) in Behedi basin, Maharastra.

7.5.8 Nickel

The concentration of nickel is found in the groundwater is normally

from 0 to 0.034 mg/l. In most of the wells nickel is absent. The concentration of

nickel in drinking water is normally less than 0.02 mg/l (WHO 1993). High

concentration of nickel as both soluble and soluble compounds is now considered

to be a human carcinogen when related to pulmonary exposure (WHO 1993).

Generally, lower concentration of nickel is observed in the study area.

7.5.9 Manganese

The manganese in the groundwater ranges from 0.01 to 0.67 mg/l. The

permissible limit of manganese is 0.3 mg/l. as per BIS (2003). Agriculture

practices, fertiliser use, sewage and animal waste disposal contribute significant

amount of manganese to the groundwater of the study area and there is no

geological source. Similar results were observed by Pawar and Nikumbh (1999) in

the Bedi basin, Maharastra. Manganese is also essential element and is readily

absorbed by plants. This might be toxic at higher concentration and is usually

unpalatable in terms of taste, odour and discoloration of food (Figure 7.17).

Almost all the wells are within the limit and only the well no. 44 has exceeded the

limit and close to the well there is animal storage waste and also village sewage

pit, which would have resulted in this elevated concentration.

140

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

Mn

( mg/

l)

1 3 5 7 9 11 13 15 17 19 21 23 25 27 29 31 33 35 37 39 41 43 45

Well No

Figure 7.17.Manganese concentration in groundwater of all wells

7.5.10 Lead

The concentration of lead is almost absent in all the wells except the

well no 1 where concentration is very low (0.005 mg/l). The concentration of lead

in natural water increases mainly through the anthropogenic activities (Goel

1997). Lead is extensively used some of the pesticides such as lead arsenate.

Table 7.10 Classification of Trace elements in the groundwater

Concentration

Of Trace

metals (mg/l)

Minimum Maximum Average BIS (2003)

Permissible

limit (mg/l)

Wells

exceeding

limit

Cr 0.122 0.669 0.4889 0.10 45 wells

Cu 0 0.022 0.0099 1.50 Nil

Zn 0 0.372 0.0275 15 Nil

Ni 0 0.034 0.0014 0.20 Nil

Mn 0.001 0.67 0.0679 0.30 1

Pb 0 0.005 0.05 Nil

141

7.6 SOURCES FOR NUTRIENTS AND TRACE ELEMENTS

From the groundwater studies it gives us preliminary information about the sources of nutrients and trace elements in the study area. Nutrient and trace metals in the groundwater of this area are mainly due to the agriculture activities, local pollution of the villages and rock formation. The nutrients like nitrate seeps from the agriculture land to the wells due to the fertilization of crop lands. The concentration of nitrate increases slightly with rise in water table during the monsoon and concentration decreases during the summer period. Silica is high in groundwater due to rock weathering of silicate minerals. The fluoride is from the country rocks like hornblende biotite gneiss and charnockite but the ionic concentration is within the limit, since no man made pollution is noticed in this area. Intensive and long term irrigation in the area is probably another factor that causes weathering and leaching of fluoride from soils/weathered rocks. The boron in groundwater occurring naturally, although its distribution varies widely among aquifers, also boron in groundwater also comes from over application agricultural fertiliser, improper manure management practice and storage of animal manure. Groundwater pollution has many sources in common, such as fertiliser, pesticides and animal waste in the rural area. Groundwater or the study area is permissible to unsuitable for domestic and irrigation purpose, except in a few locations where EC is high, the Na%. SAR and RSC. The source of trace elements in the groundwater is related to agricultural practices, included application of fertiliser, pesticides, rural sewage and the geological formation of the rocks due to the weathering of rocks, from which the released trace elements. However, the trace element chromium has been found at higher level than the permissible limits and is probably most harmful to the human beings. The remaining elements are within the limit. The seasonal variation in groundwater quality is due to agriculture and domestic activities through infiltration and percolation during monsoon. The groundwater in this basin is moderate quality suitable for irrigation and domestic purpose. The overall quality of the groundwater in the study area is controlled by agriculture and lithology.