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CHAPTER 5
HYDRO CHEMISTRY
5.1 GENERAL
The chemical composition of groundwater varies with many
complex factors. It depends on the size and geography of the aquifer which
yield water to any bore or open well. Groundwater quality can be affected by
the composition and solubility of rock or soil materials in the aquifer, water
temperature, partial pressure of carbon dioxide, acid-base reactions,
oxidation-reduction reactions, loss or gain of constituents as water percolates
through clay layers and mixing of groundwater from adjacent strata. The
extent of each effect is greatly influenced by the duration of the water within
the different subsurface environments. The hydro chemical analysis of water
samples can reveal the quality of the groundwater and its evolution.
5.2 QUALITY PARAMETERS FOR DRINKING PURPOSE
Water samples were collected from 73 locations in clean polythene
bottles during premonsoon and postmonsoon seasons and tested for major
physical and chemical parameters employing the standard methods given by
American Public Health Association (APHA 1998). pH was measured using
pH meter and electrical conductivity (EC) was measured using conductivity
meters. Total dissolved solids (TDS) were computed by gravimetric method.
Carbonate (CO3) and bicarbonate (HCO3) were estimated by titrating with
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H2SO4. Total hardness (TH) as CaCO3 and calcium (Ca) were analysed
titrimerically, using standard EDTA. Magnesium (Mg) was calculated from
Total hardness and calcium. Sodium (Na) and potassium (K) were measured
by a flame photometer. Chloride (Cl) was estimated by standard AgNO3
titration. Sulphate (SO4) and Nitrate (NO3) were analysed using a
colourimeter. Some samples are selected in random manner and tested at
different laboratories. The results are compared to verify the accuracy of the
tests. The quality of the groundwater for drinking purpose was assessed based
on the results of physical and chemical analyses. Its suitability for drinking
purpose is assessed from norms recommended in IS 10500:1991, for both
premonsoon and postmonsoon seasons.
5.2.1 Turbidity
The presence of suspended matters such as clay, organic, inorganic
and microorganisms make water turbid. (ASCE AWWA 1990) Attempts to
correlate turbidity with the concentration of suspended solids are impractical
due to their size, shape and their refractive indices, which are more important
for optical properties. The recent literatures on the subject of water borne
diseases have stressed very strongly the need to reduce turbidity as much as
possible. Viruses, Cysts and Micro organisms associate with suspended
particulate material of water create water borne diseases. It is therefore more
important to have a very low turbidity to qualify as safe drinking water
(Montgomery 1985).
5.2.2 pH
The negative logarithm of the concentration of hydrogen ions in
moles per litre is pH value of a solution. For example, in a pure water sample,
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the disassociated molar concentration of H +
(hydrogen) and OH –
(hydroxyl)
ions are equal, each being 10-7
moles per litre and it is equivalent to a pH of 7.
Hence if pH is less than 7, the water sample is acidic and if pH is higher than
7, the water sample is alkaline. Water with pH value equal to 7 is neutral. The
pH value is dependent on the carbon-di-oxide ~carbonate~bicarbonate
equilibrium. Alkalinity in drinking water will affect the mucous membranes
of human body (IS: 10500 1991). If the value of pH of water is below 6.5, it is
classified as acidic, if it is between 6.5 and 8.5, it is classified as neutral and if
it is above 8.5, it is classified as alkaline.
5.2.3 Total hardness
Hardness is the term relating to the concentrations of certain
metallic ions in water. Total hardness (TH) in natural water is primarily due to
the presence of calcium(Ca) and magnesium(Mg) ions. The relation between
TH, Ca and Mg is given in Equation (5.1). The presence of other ions and
trace elements are ignored for the calculation of TH due to their very poor
concentrations (Syed et al, 2002).
TH = 2.497 Ca + 4.115 Mg (5.1)
where, TH, Ca and Mg are measured in ppm.
Hardness is usually expressed as an equivalent concentration of
dissolved calcite (CaCO3) (APHA 1998). Hard water prevents formation of
lather until excessive soap is consumed and causes yellowing of fabrics and
toughening of vegetables. The classification of groundwater samples based on
hardness is summarized in Table 5.1.
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Table 5.1 Classification of groundwater samples based on hardness
after Tchobanoglous and Schroeder, (1985) and Viessman
and Hammer, (1998).
Total hardness, mg/L as Ca CO3 Classification
0-40 Soft
40-100 Moderately Hard
100-300 Hard
300-500 Very Hard
Above 500 Extremely Hard
5.2.4 Iron
Groundwater containing iron in soluble form (ferrous) is usually
clear and colorless when first drawn. Upon contact with air, they slowly cloud
and finally deposit a yellowish to reddish brown precipitate of ferric
hydroxide in water stored. Iron is an essential element with a suggested daily
intake of 14 mg. The drinking water contributes only a small fraction of daily
needs. For the reasons of aesthetics and taste the iron content in drinking
water is limited. Waters containing iron, stain porcelain fixtures and laundry.
The growth of bacteria in iron-bearing waters may cause pipe clogging
(Syed et al 2002).
5.2.5 Chloride
Chloride bearing rocks minerals and liquid inclusions with very
insignificant fraction of the rock volume are minor sources of chloride in
groundwater. Hence, the chloride content in groundwater is either from
atmospheric sources or from sea water intrusions. The chloride in
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groundwater is present as sodium chloride, but the chloride content may
exceed sodium due to the Base Exchange phenomenon. The presence of
calcium and magnesium chloride is rare in groundwater. Abnormal
concentrations of chloride may result due to pollution by sewage wastes and
leaching of saline residues in the soil (Karnath 1999). Large amount of
chloride along with high sodium concentrations can impart a salty taste to
water. Amounts above 1000 ppm may be physicologically unsafe. High
concentrations also increase the corrosiveness of water (NDWRHA 1993).
5.2.6 Total dissolved solids
Total dissolved solids (TDS) are a measure of the total amount of
dissolved minerals in water. The concentration of TDS in water will depend
on resident time of ground water in aquifers, local geological conditions,
climate and waste discharges (Syed et al 2002). Several processes may cause
an increase in the dissolved solids content of groundwater. These include
movement of groundwater through rocks containing soluble minerals, salt
concentration by evaporation and contamination due to waste water disposal
(Karnath 1999). TDS content beyond the permissible limit will decrease
palatability and may cause gastro intestinal irritation.
5.2.7 Calcium
Calcium is mostly derived from rocks. Calcium is the second major
constituent present in natural water after bicarbonate. It is required as a
nutrient for plants and is a required mineral for human and other animals.
Suggested daily intake is 800 mg for human. The deficiency of calcium may
cause Osteoporosis and its toxicity may cause kidney stones (Syed et al
2002). Excessive presence of calcium cause not only hardness in water but
also it causes encrustation in water supply structures (IS: 10500 1991).
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5.2.8 Sulphate
A wide range of sulphate content in groundwater is due to various
processes during its traverse through rock. Sulphates are also added in
groundwater by the application of sulphatic soil conditioners. Sulphide
minerals when oxidized give rise to soluble sulphates (Karnath 1999). High
concentration of sulphate in drinking water will make the people difficult to
consume. Sulphate rich water may cause laxative action. Medicinal or bitter
taste is produced in water if sulphate content is high (Syed et al 2002).
5.2.9 Nitrate
Nitrogen is a very minor constituent of the rocks. The average nitrate
content in rain water is reported to be 0.2 ppm. Part of the nitrate may be taken
inside the ground by plants before the rain water infiltrates below the root zone.
But the greatest contribution of nitrate to groundwater is from decaying organic
matter, sewage waste and nitrate fertilizers. Groundwater when not polluted
contains less than 5 ppm of nitrates. Nitrate is a non-essential contaminant with
no minimum daily requirement. Excessive content of nitrate in groundwater
may cause infant methemoglobinemia (Syed et al 2002).
5.2.10 Total alkalinity
Alkalinity maintains the pH within the limit. Alkalinity is due to the
presence of bicarbonate, carbonate ions, salts of silica, borate, phosphate,
organic acids and hydroxides. Concentration of alkalinity varies in
groundwater with respect to geographical location and character of the rocks
and soils. Sudden changes in alkalinity in streams are generally due to the
discharge of treated or untreated industrial wastes. Alkalinity results are
needed to calculate the lime and soda ash dosage for water softening and to
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determine the corrosive or scaling action of water. Excessive content of
alkalinity in water tastes unpleasant (IS: 10500 1991).
5.2.11 Fluoride
Flouride occurs in few types of rocks and slightly soluble in water.
Higher fluoride contents occur in aquifers. Both surface water and
groundwater may experience fluoride contamination from certain insecticides,
chemical wastes, airborne particles and gases from aluminum smelting plants.
Flouride is an essential constituent and is utilized in the structure of bones and
teeth. Suggested intake of fluoride per day for infants, children and adults are
0.6, 1.0 and 2.7 mg respectively. A deficiency in fluoride may result in
increased dental cavities. Large intakes of fluoride may cause dental fluorosis
and toxicity (Syed et al 2002).
5.3 DRINKING WATER QUALITY STANDARDS
The water quality limits prescribed by Bureau of Indian standard
specification (IS: 10500-1991) has been followed in this work for the
assessment of water quality. The limits given by IS 10500:1991 are
summarized in Table 5.2.
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Table 5.2 Limits for drinking as per IS 10500-1991
LimitsS.No Parameter Unit
Desirable Permissible
1. Turbidity NTU 5 10
2. pH -- 6.5 8.5
3. Total hardness mg/ L 300 600
4. Iron mg/L 0.3 1.0
5. Chlorides mg/L 250 1000
6 Total dissolved solids mg/L 500 2000
7. Calcium mg/L 75 200
8. Sulphate mg/L 200 400
9. Nitrate mg/L 45 100
10 Total alkalinity mg/L 200 600
11 Flouride mg/L 1.0 1.5
5.4 SPATIAL DISTRIBUTION
Spatial distribution study is an important tool to understand the
spatial distribution of ionic concentrations of hydro-chemical parameters. The
Spatial distribution provides pictorial representation of the spread of ionic
concentration. The sample locations are represented as point feature layer.
Each location is attributed with location identity, physical and chemical
content concentrations. The spatial distribution is presented in three
classifications namely very good, good and poor. The water quality parameter
whose content is within desirable limit is classified as very good and the
water quality parameter whose content is between desirable to permissible
limit is classified as good and the water quality parameter whose content is
above the permissible limit is classified as poor. The limits recommended by
IS: 10500 are followed to define classification.
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5.5 HYDRO CHEMICAL ANALYSIS OF GROUNDWATER
SAMPLES DURING PREMONSOON SEASON
The water samples are tested for physical and chemical parameters.
The results are compared with IS: 10500 recommendations. The chemical and
physical parameters above the permissible limits and below the desirable
limits are discussed here for the samples collected during premonsoon season.
5.5.1 Turbidity
The turbidity values of all the samples are shown in Figure 5.1. The
variations in turbidity values within desirable limit, above permissible limits
and within permissible limits in the study area are presented here in bar chart.
Figure 5.1 Turbidity values of all samples during premonsoon.
78 % of the total samples are free from turbidity contamination.
Out of 73 samples, 57 samples are free from turbidity hazard, 4 samples are
within the permissible limit. Turbidity is high in 12 samples of the study area.
Turbidity varies from 0 NTU to 80 NTU over the study area. The turbidity
has a maximum value of 80 NTU at the sample S17. The turbidity values of
the samples S13, S17, S18, S22, S25, S26, S30, S34, S45, S50, S59 and S63
exceed the permissible limit during premonsoon season.
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5.5.1.1 Spatial distribution of turbidity
The spatial distribution of turbidity values of samples is presented
by dark brown colour and it is shown in the Figure.5.2. From the spatial
distribution diagram, it is understood that the groundwater from the central
part of the study area has groundwater of poor quality with respect to turbidity
during premonsoon season. The distribution of groundwater of poor quality is
found over an area of 732.3 sq-kms, good quality is present over an area of
638 sq-kms and groundwater of very good quality is present over an area of
2034 sq-kms with respect to turbidity during premonsoon season.
Figure 5.2 Spatial distribution of turbidity values of premonsoon
samples
The rainfall during this period (July 2007) is higher than the rainfall
during postmonsoon season (March 2007). The increased turbidity content
during this season may be due to higher rainfall, low slope and rock types
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from surface and subsurface sources. The groundwater in central part of the
study area may have influenced these factors during this season.
5.5.2 pH
The pH values of all the samples are shown in Figure 5.3.The pH
values within the desirable limit, within the permissible limits and above the
permissible limits in the study area are presented here in bar charts. The
results of the chemical analysis revealed that none of the samples is either
neutral or acidic during premonsoon season.
Figure 5.3 pH values of all samples during premonsoon.
7 out of 73 samples collected from the study area are alkaline due
to high pH values above 8.5 and the remaining 66 samples are neutral. The
maximum pH value of the study area is 8.82 at the sample S35.The minimum
pH value of the study area is 7.23 at the sample S62. The variations in the pH
values among the groundwater samples are less and it is understood that the
pH of the groundwater during premonsoon season of the year 2007 was
almost same in the study area. The pH values of the samples S1, S4, S20, S24,
S35, S45 and S49 exceed 8.5 and the groundwater from these locations are
alkaline during premonsoon season.
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5.5.2.1 Spatial distribution of pH
The spatial distribution of pH values of these samples is presented
by dark violet colour and it is shown in the Figure 5.4. From the spatial
distribution diagram, it is understood that the some scattered areas of south
and central part of the study area, contains alkaline groundwater with respect
to pH during premonsoon season. The distribution of groundwater of acidic
quality is not found in any area, neutral quality is present over an area of 3378
sq-kms and groundwater of alkaline quality is present over an area of 26.3
sqkm with respect to pH during premonsoon season.
Figure 5.4 Spatial distribution of pH values of premonsoon samples
The amount of rainfall during premonsoon season (July) is more
than that of postmonsoon season. Increased infiltration due to rainfall may
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pass through carbonate rich rocks and subsequent dissolution of constituents
may be considered as the reason for the increase in pH value of the
groundwater samples in some illustrated portions in Fig 5.4 of the study area
during premonsoon season.
5.5.3 Total hardness
The differences in the TH values of the groundwater samples
during premonsoon season of the year 2007 are presented here in bar chart.
The TH values of all the samples are shown in Figure 5.5.
Figure 5.5 Hardness values of all samples during premonsoon
Out of 73 samples, 14 samples contain TH above permissible value
and 59 samples contain TH within permisible values. None of the water
samples collected in the study area is classified as soft water or moderately
hard. Out of 73 samples, 41 samples are classified as hard, 14 samples as very
hard and 17 samples as extremely hard. But 14 samples are classified as non
potable as per IS: 10500 standards due to TH values exceeding the
permissible limit of 600 mg/L. The maximum value of hardness is 1112 mg/L
as CaCO3 at the sample S61. The TH values of the groundwater samples S3,
S8, S13, S18, S26, S28, S29, S36, S52, S61, S65 and S67 exceed the
permissible limit during premonsoon season.
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5.5.3.1 Spatial distribution of TH
The spatial distribution of TH values of the premonsoon
groundwater samples is shown in the Figure 5.6. TH value above 600 mg/L
are presented by dark bluish green colour and categorized as poor, TH value
between 300 mg/L and 600 mg/L are categorized as good and below 300
mg/L are categorized as very good. The distribution of groundwater of poor
quality is found over an area of 206.5 sq-kms, good quality is present over an
area of 2008.8 sq-kms and groundwater of very good quality is present over
an area of 1189 sq-kms with respect to TH during premonsoon season.
Figure 5.6 Spatial distribution of TH values of premonsoon samples
Higher rainfall during premonsoon season has diluted the
concentration of harness and some parts of the study area contain
groundwater of poor quality. Rest of the area has very good to good category
of groundwater during premonsoon season. From the spatial distribution
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diagram, it is understood that the groundwater from some scattered areas in
central portion of the study area have groundwater of poor quality with
respect to TH during premonsoon season.
5.5.4 Iron
The iron values of all the samples are shown in Figure 5.7. Fe
content in groundwater samples within the desirable limit, within the
permissible limits and above the permissible limits in the study area are
presented here in bar chart.
Figure 5.7 Iron values of all samples during premonsoon
All the groundwater samples of study area contain iron within
permissible limit. Out of 73 samples, iron content is present in 15 samples
only. 58 samples do not contain iron. The sample S54 contains the maximum
iron content of 0.6 mg/L.Due to infiltration in premonsoon season, the values
Fe in the groundwater samples S25, S54 and S57 are above the desirable limit
but within the permissible during premonsoon season.
5.5.4.1 Spatial distribution of Fe
The spatial distribution of Fe values of these samples is presented
by dark pink colour and it is shown in the Figure 5.8. From the spatial
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distribution diagram, it is understood that Fe is seen in some scattered area in
west part of the study area during premonsoon season. The higher rainfall and
therby the higher infiltration during premonsoon season might have made the
iron contents to dissolve and might have mixed in the groundwater.
Figure 5.8 Spatial distribution of Fe values of premonsoon samples
From the geological studies, it is learnt that iron bearing formations
are not found in the study area. Hence it may be considered that leaching of
cast iron pipes of water supply system in these loacaltions is the cause for the
presence of iron in groundwater. The distribution of groundwater of poor
quality is not found in any area, good quality is present over an area of 46.5
sq-kms and groundwater of very good quality is present over an area of
3357.8 sq-kms with respect to Fe during premonsoon season.
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5.5.5 Chloride
The chloride values of all the groundwater samples are presented
here in bar chart. The chloride values within the desirable limit, within the
permissible limits and above the permissible limits are presented here. The
chloride values of all the samples are shown in Figure 5.9.
Figure 5.9 Chloride values of all samples during premonsoon
All the samples have chloride contents within the permissible limit.
52 samples have chloride contents below 250 mg/L and 21 samples contain
chloride between 250 mg/L and l000 mg/L. The chloride content of the study
area varies from 44 mg/L to 588 mg/L. The water sample S54 has a minimum
chloride content of 44 mg/L and the sample S13 has maximum chloride
content of 588 mg/L. The Cl values of the groundwater samples S3, S4, S8,
S13, S16, S18, S26, S27, S28, S29, S32, S36, S44, S45, S48, S52, S61, S65,
S67 and S69 are above the desirable limit but within the permissible during
premonsoon season.
5.5.5.1 Spatial distribution of Cl
The chloride bearing rock minerals are very minor consituets of
rocks. Hence it is presumable that the chloride content in groundwater is
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either from atmospheric sources or due to sea water intrusion. The evaporite
deposits in sedimentary rocks also give rise to high chloride content in
groundwater. Mostly chloride in groundwater is present as sodium chloride
but the chloride content may exceed sodium due to Base Exchange
phenomena and will be present in groundwater. Abnormal concentrations of
chloride in groundwater may result due to pollution by sewage wastes, salting
for some types of trees and leaching of saline residues in the soil (Karnath
1999). The spatial distribution of Cl values of premonsoon samples is
presented by dark algae green colour and it is shown in the Figure 5.10. The
distribution of groundwater of poor quality is not found in any area, good
quality is present over an area of 1176.3sq-kms and groundwater of very good
quality is present over an area of 2228sq-kms with respect to Cl during
premonsoon season.
Figure 5.10 Spatial distribution of Cl values of premonsoon samples
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As the chances for the presence of chloride content in groundwater
due to the above said reasons are equal, the higher infiltration during
premonsoon season weakened the chloride concentration. From the spatial
distribution diagram, it is understood that the groundwater from the central
part of the study area has groundwater with chloride contents within desirable
to permissible limit and the rest part has chloride content below the desirable
limit during premonsoon season.
5.5.6 Total dissolved solids
The TDS values of all the groundwater samples are presented here
in bar chart. TDS values within the desirable limit, within the permissible
limits and above the permissible limits are presented here in the figure.The
TDS values of all the samples are shown in Figure 5.11.
Figure 5.11 TDS values of all samples during premonsoon
20 samples of the study area contain TDS values below the
desirable limit and 47 samples contain TDS values within the permissible
limit. Six water samples contain higher content of TDS. The minimum value
of dissolved solids of the study area is found to be 252.7 mg/L at the sample
S59 and the maximum value is 3501 mg/L at the sample S13. The TDS values
of the groundwater samples S3, S8, S13, S18, S26 and S61 exceed the
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permissible limit during premonsoon season. From the figure, it can be
understood that the TDS content are widely varying across the study area.
5.5.6.1 Spatial distribution of TDS
Several processes may cause an increase in the dissolved-solids
content of groundwater. These include movement through rocks containing
soluble mineral matter, concentration by evaporation and contamination due
to pollutants. The spatial distribution of concentration of TDS values of these
samples is presented by dark blue colour and it is shown in the Figure 5.12.
Figure 5.12 Spatial distribution of TDS values of premonsoon samples
From the spatial distribution diagram, it is understood that the
groundwater from some scattered areas in central north and central south part
of the study area contain groundwater of poor quality with respect to TDS
during premonsoon season. The distribution of groundwater of poor quality is
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found over an area of 60.5sq-kms, good quality is present over an area of
3204.8sq-kms and groundwater of very good quality is present over an area of
60.5sq-kms with respect to TDS during premonsoon season.
5.5.7 Calcium
The Ca values of all the groundwater samples are presented here in
bar chart. Ca values within the desirable limit, within the permissible limits
and above the permissible limits are presented here in the figure.The calcium
values of all the samples are shown in Figure 5.13.
Figure 5.13 Calcium values of all samples during premonsoon.
Water samples from 47 locations of the study area contain calcium
within desirable limit. Samples from 21 locations contain calcium within the
permissible limit. Five water samples contain calcium above permissible
limit. The maximum calcium content of 253.6 mg/L is present in the sample
S61.The minimum calcium content of 20.4 mg/L is present in the sample S10.
The Ca values of the groundwater samples S3, S26, S61 and S65 exceed the
permissible limit during premonsoon season.
5.5.7.1 Spatial distribution of Ca
The spatial distribution of Ca values of these samples is presented
by blue colour and it is shown in the Figure 5.14. From the spatial distribution
diagram, it is understood that the groundwater from some scattered areas in
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central north, west and south part of the study area which contain
groundwater of poor quality with respect to Ca during premonsoon season.
The distribution of groundwater of poor quality is found over an
area of 26.3 sq-kms, good quality is present over an area of 1856 sq-kms and
groundwater of very good quality is present over an area of 1522 sq-kms with
respect to Ca during premonsoon season.
Figure 5.14 Spatial distribution of Ca values of premonsoon samples
5.5.8 Sulphate
The sulphate values of all the groundwater samples are presented
here in bar chart.Sulphate values within the desirable limit, within the
permissible limits and above the permissible limits in the figure presented
here.
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The sulphate values of all the samples are shown in Figure 5.15. 4
samples of the study area contain high sulphate concentrations. 17 samples
contain sulphate content within the permissible limit. The highest value of
sulphate content of the study area during premonsoon season is 522 mg/L and
it is collected from the sample S61.
Figure 5.15 Sulphate values of all samples during premonsoon
The lowest value of sulphate content is 29 mg/L and it is collected
from the sample S55. The SO4 values of the groundwater samples S18, S26
and S61 exceed the permissible limit during premonsoon season.
5.5.8.1 Spatial distribution of SO4
The spatial distribution of SO4 values of these samples is presented
by dark blue colour and it is shown in the Figure 5.16. From the spatial
distribution diagram, it is understood that the groundwater from some
scattered areas in central north, and centre part of the study area have
groundwater of poor quality with respect to SO4 during premonsoon season.
The distribution of groundwater of poor quality is found over an
area of 27 sq-kms, good quality is present over an area of 1045.3 sq-kms and
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groundwater of very good quality is present over an area of 2332 sq-kms with
respect to SO4 during premonsoon season.
Figure 5.16 Spatial distribution of SO4 values of premonsoon samples
5.5.9 Nitrate
The nitrate values of all the groundwater samples are presented
here in bar chart. Nitrate values within the desirable limit, within the
permissible limits and above the permissible limits are presented here in the
Figure 5.17 Nitrate values of all samples during premonsoon.
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Figure. The nitrate values of all the samples are shown in Figure 5.17. Sixty
samples of the study area contain nitrate within desirable limit. 13 samples
contain nitrate within the permissible limit. The maximum value of the nitrate
content of the study area is 92 mg/L and it is present at the sample S13. The
minimum value of the nitrate content of the study area is 5 mg/L and it is at
the sample S63. The NO3 values of the groundwater samples S3, S8, S13, S18,
S26, S29, S36, S48, S52, S61, S65, S67 and S69 are above the desirable limit
during premonsoon season.
5.5.9.1 Spatial distribution of NO3
The spatial distribution of NO3 values of these samples is presented
by dark brown colour and it is shown in the Figure 5.18. From the spatial
distribution diagram, it is understood that the groundwater from some
scattered areas of central part of the study area has groundwater with NO3
contents within desirable to permissible limit during premonsoon season.
Figure 5.18 Spatial distribution of NO3 values of premonsoon samples
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The distribution of groundwater of poor quality is found over an
area of 1sq-kms, good quality is present over an area of 528.3 sq-kms and
groundwater of very good quality is present over an area of 2875 sq-kms with
respect to NO3 during premonsoon season.
5.5.10 Total alkalinity
The TA values of all the groundwater samples are presented here in
bar chart. TA values within the desirable limit, within the permissible limits
and above the permissible limits are presented here in the figure.The total
alkalinity values of all the samples are shown in Figure 5.19.
Figure 5.19 Total alkalinity values of all samples during premonsoon.
Three samples of the study area contain alkalinity above the
permissible limit. 31 samples contain alkalinity within the permissible limit.
39 samples of the study area contain alkalinity below the desirable limit. The
maximum value of the alkalinity is present in the sample S13. The minimum
value of the alkalinity is present in the sample S63. The TA values of the
groundwater samples S8, S13 and S61 exceed the permissible limit during
premonsoon season.
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5.5.10.1 Spatial distribution of TA
The spatial distribution of TA values of these samples is presented
by red colour and it is shown in the Figure 5.20. From the spatial distribution
diagram, it is understood that the groundwater from few scattered areas in
centre part of the study area contain groundwater of poor quality with respect
to TA during premonsoon season.
Figure 5.20 Spatial distribution of TA values of premonsoon samples
The distribution of groundwater of poor quality is found over an
area of 19.3 sq-kms, good quality is present over an area of 2494 sq-kms and
groundwater of very good quality is present over an area of 891 sq-kms with
respect to TA during premonsoon season.
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5.5.11 Fluoride
Fluoride values of all the groundwater samples are presented here
in bar chart. Fluoride values within the desirable limit, within the permissible
limits and above the permissible limits are presented here.The fluorides
values of all the samples are shown in Figure 5.21.
Figure 5.21 Fluoride values of all samples during premonsoon
Forty one samples out of 73 samples collected from different
locations of study area contain fluoride of very less concentration. The
maximum fluoride content of the study area is present at the sample S2 and it
is found to be 1.2 mg/L and 32 samples of the study area have no fluoride
content in it. The F value of one groundwater sample S2 is marginally above
the desirable limit but it is within the permissible during premonsoon season.
5.5.11.1 Spatial distribution of F
The spatial distribution of F values of the study area is presented in
the Figure 5.22. From the spatial distribution diagram, it is understood that the
groundwater from considerable area of north central part and some scattered
areas of south central part of the study area have groundwater with F contents
within desirable to permissible limit during premonsoon season.
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Figure 5.22 Spatial distribution of F values of premonsoon samples
The distribution of groundwater of poor quality is not found in any
part of the study area, good quality is present over an area of 8.59 sq-kms and
groundwater of very good quality is present over an area of 3395.71 sq-kms
with respect to fluoride during premonsoon season.
5.6 HYDRO CHEMICAL ANALYSIS OF GROUNDWATER
SAMPLES DURING POSTMONSOON SEASON
The groundwater samples collected from all the 73 locations were
tested for physical and chemical parameters for postmonsoon season also. The
chemical and physical parameters of all the groundwater samples with respect
to IS: 10500 limits are compared and presented here for postmonsoon season.
106
5.6.1 Turbidity
The variations in turbidity values within desirable limit, above
permissible limits and within permissible limits in the study area are
presented here. The turbidity values of all the samples are shown in Figure
5.23.
Figure 5.23 Turbidity values of all samples during postmonsoon
Out of 73 samples, 53 samples contain turbidity below the desirable
limit. 10 samples contain turbidity within the permissible limit. Turbidity is
high in 10 samples of the study area. Turbidity varies from 0 NTU to 60 NTU
over the study area. The turbidity has a maximum value of 60 NTU at the
sample S35. The turbidity values of the samples S35, S43, S50, S53, S54,
S55, S56, S57, S58 and S59 exceed the permissible limit during postmonsoon
season.
5.6.1.1 Spatial distribution of turbidity
The spatial distribution of turbidity values is presented by dark
brown colour and it is shown in the Figure 5.24. The rainfall during
postmonsoon season (March 2007) is lower than the rainfall during
107
premonsoon season (July 2007). Since the rate of infiltration is low during
this period, the groundwater is not very turbid during this period.
Figure 5.24 Spatial distribution of turbidity values of postmonsoon
samples
From the spatial distribution diagram, it is understood that the
groundwater from the north part of the study area has groundwater of poor
quality with respect to turbidity during postmonsoon season. The distribution
of groundwater of poor quality is found over an area of 246 sq-kms, good
quality is present over an area of 505.3 sq-kms and groundwater of very good
quality is present over an area of 2653 sq-kms with respect to turbidity during
postmonsoon season.
108
5.6.2 pH
The pH values of all the samples are shown in Figure 5.25. The
variations in pH values are within the desirable limit or within the permissible
limits or above the permissible limits in the study area are presented here.
Figure 5.25 pH values of all samples during postmonsoon
2 samples of the total 73 samples collected from the study area are
alkaline and their pH values are above 8.5. The maximum pH of value of the
study area is 8.83 at the sample S66. The minimum pH of value of the study
area is 7.45 at the sample S35. The pH values of all the samples are shown in
Figure 5.25. The pH values of the samples S69, S71 and S73 exceed 8.5 and
the groundwater from these locations are alkaline during postmonsoon season.
5.6.2.1 Spatial distribution of pH
The spatial distribution of pH values of these samples is presented
by dark violet colour and it is shown in the Figure 5.26. From the spatial
distribution diagram, it is understood that the some scattered areas of north
part of the study area, contain alkaline groundwater with respect to pH during
postmonsoon season.
109
Figure 5.26 Spatial distribution of pH values of postmonsoon samples
The distribution of groundwater of Acidic quality is found over an
area of 1sq-kms, Neutral quality is present over an area of 23.3 sq-kms and
groundwater of alkaline quality is present over an area of 3380 sq-kms with
respect to pH during postmonsoon season.
5.6.3 Total hardness
The differences in the TH values of the groundwater samples are
during postmonsoon season of the year 2007 are presented here in bar chart.
The TH values of all the samples are shown in Figure 5.27. The classification
of water based on hardness is summarized in Table 5.1. Out of 73 samples, 27
samples are classified as hard, 17 samples as very hard and 29 samples as
extremely hard. The maximum value of hardness is 864 mg/L as CaCO3.at the
sample S26.
110
Figure 5.27 Hardness values of all samples during postmonsoon
The TH values of the groundwater samples S3, S7, S8, S9, S13,
S16, S17, S18, S19, S21, S25, S26, S27, S28, S29, S30, S32, S35, S36, S37,
S43, S45, S48, S61, S64, S65, S67, S69 and S72 exceed the permissible limit
during this season.
5.6.3.1 Spatial distribution of TH
The spatial distribution of TH values of these samples is presented
by dark bluish green colour and it is shown in the Figure 5.28. Rainfall is less
during postmonsoon season and it is not sufficient to dilute the concentration
of harness and some parts of the study area contain groundwater of poor
quality. Rest of the area has very good to good category of groundwater
during postmonsoon season.
From the spatial distribution diagram, it is understood that the
groundwater from considerable scattered part in central portion of the study
area have groundwater of poor quality with respect to TH during
postmonsoon season. The distribution of groundwater of poor quality is found
over an area of 737.3 sq-kms, good quality is present over an area of 2118 sq-
kms and groundwater of very good quality is present over an area of 549 sq-
kms with respect to TH during postmonsoon season.
111
Figure 5.28 Spatial distribution of TH values of postmonsoon samples
5.6.4 Iron
The iron values of all the samples are shown in Figure 5.29. Fe
content in groundwater samples within the desirable limit, within the
permissible limits and above the permissible limits in the study area are
presented here. Out of 73 samples, 3 samples contain iron content between
0.3 mg/L and 1.0 mg/L, 3 samples contain iron content above 1.0 mg/L, the
remaining 67 samples contain iron below 0.3 mg/L. Sample S35, contains
maximum iron content of 1.8 mg/L. The Fe values of the groundwater
samples S35, S54 and S57 exceed the permissible limit during postmonsoon
season.
112
Figure 5.29 Iron values of all samples during postmonsoon
5.6.4.1 Spatial distribution of Fe
The spatial distribution of Fe values of these samples is presented
by dark pink colour and it is shown in the Figure 5.30.
Figure 5.30 Spatial distribution of Fe values of postmonsoon samples
113
From the spatial distribution diagram, it is understood that the
groundwater of these sample locations which contain marginal Fe are seen in
some scattered area and they spread in north part of the study area during
postmonsoon season. The distribution of groundwater of poor quality is found
over an area of 17 sq-kms, good quality is present over an area of 240.3 sq-
kms and groundwater of very good quality is present over an area of 3147 sq-
kms with respect to Fe during postmonsoon season.
5.6.5 Chloride
The chloride values of all the groundwater samples are presented
here in bar chart. Chloride values within the desirable limit, within the
permissible limits or above the permissible limits are presented here. The
chloride values of all the samples are shown in Figure 5.31.
Figure 5.31 Chloride values of all samples during postmonsoon
2 samples of the study area contain chloride content above the
permissible limit. 38 samples have chlorides content below the desirable limit
and 33 samples contain chlorides between 250 mg/L and l000 mg/L. The
chloride content of the study area varies from 72 mg/L to 1316 mg/L. Sample
S63 has a minimum content of chloride 72 mg/L and the sample S13 has a
114
maximum chloride content of 1316 mg/L. The Cl values of the groundwater
samples S13 and S61 exceed the permissible limit during this season.
5.6.5.1 Spatial distribution of Cl
The spatial distribution of Cl values of these samples is presented
by dark algae green colour and it is shown in the Figure 5.32. From the spatial
distribution diagram, it is understood that the groundwater from the north part
of the study area has groundwater with chloride contents above the
permissible limit during postmonsoon season. The distribution of
groundwater of poor quality is found over an area of 13.3 sq-kms, good
quality is present over an area of 2452 sq-kms and groundwater of very good
quality is present over an area of 939 sq-kms with respect to Cl during
postmonsoon season.
Figure 5.32 Spatial distribution of Cl values of postmonsoon samples
115
5.6.6 Total dissolved solids
TDS values of all the groundwater samples are presented here in
bar chart. TDS values within the desirable limit, within the permissible limits
and above the permissible limits are presented here.The TDS values of all the
samples are shown in Figure 5.33. 9 samples of the study area contain TDS
content below the desirable limit and 38 samples contain TDS within the
permissible limit. 26 samples contain higher content of TDS. The minimum
value of TDS of the study area is 322 mg/L at the sample S63 and the
maximum value is 4767 mg/L at the sample S13. 9 samples of the study area
contain TDS content below the desirable limit and 38 samples contain TDS
within the permissible limit. 26 samples contain higher content of TDS. The
minimum value of TDS of the study area is 322 mg/L at the sample S63 and
the maximum value is 4767 mg/L at the sample S13.
Figure 5.33 TDS values of all samples during postmonsoon
116
5.6.6.1 Spatial distribution of TDS
The spatial distribution of TDS values of these samples is presented
by dark blue colour and it is shown in the Figure 5.34.
Figure 5.34 Spatial distribution of TDS values of postmonsoon samples
From the spatial distribution diagram, it is understood that the
groundwater from considerable area in central part of the study area contain
groundwater of poor quality with respect to TDS during postmonsoon season.
The distribution of groundwater of poor quality is found over an area of 989.3
sq-kms, good quality is present over an area of 2379 sq-kms and groundwater
of very good quality is present over an area of 36 sq-kms with respect to TDS
during postmonsoon season.
117
5.6.7 Calcium
Ca values of all the groundwater samples are presented here in bar
chart. Ca values within the desirable limit, within the permissible limits and
above the permissible limits are presented here.The Ca values of all the
samples are shown in Figure 5.35.
Figure 5.35 Ca values of all samples during postmonsoon
Groundwater samples from 39 locations of the study area contain
calcium below the permissible limit. Samples from 32 locations contain
calcium below the desirable limit. 2 water samples contain Ca content above
the permissible limit. Maximum content of Ca of value 255.3 mg/L is present
in the sample S2.The minimum value of Ca is 16 mg/L and it is present in the
sample S59. The Ca values of the groundwater samples S3 and S48 exceed
the permissible limit during this season.
5.6.7.1 Spatial distribution of Ca
The spatial distribution of Ca values of these samples is presented
by blue colour and it is shown in the Figure 5.36. From the spatial distribution
diagram, it is understood that the groundwater in small southern part of the
118
study area contain groundwater of poor quality with respect to Ca during
postmonsoon season. The distribution of groundwater of poor quality is found
over an area of 12.3 sq-kms, good quality is present over an area of 2852 sq-
kms and groundwater of very good quality is present over an area of 540 sq-
kms with respect to Ca during postmonsoon season.
Figure 5.36 Spatial distribution of Ca values of postmonsoon samples
5.6.8 Sulphate
The sulphate values of all the groundwater samples are presented
here in bar chart.Sulphate values within the desirable limit, within the
permissible limits and above the permissible limits are presented here.The
sulphate values of all the samples are shown in Figure 5.37.7 samples of the
study area contain sulphate concentration above the permissible limit. 28
samples contain within the permissible limit. The maximum value of sulphate
content is 517 mg/L in the sample S16 and the minimum value of the sulphate
119
content is 29 mg/L in the sample S63. 38 samples contain sulphate content
less than the desirable limit. The SO4 values of the groundwater samples S13,
S16, S18, S61, S64, S69 and S71 exceed the permissible limit during
postmonsoon season.
Figure 5.37 Sulphate values of all samples during postmonsoon
5.6.8.1 Spatial distribution of SO4
. The spatial distribution of SO4 values of these samples is
presented by dark blue colour and it is shown in the Figure 5.38. From the
spatial distribution diagram, it is understood that the groundwater from some
scattered areas in central north, and centre part of the study area contain
groundwater of poor quality with respect to SO4 during postmonsoon season.
The distribution of groundwater of poor quality is found over an area of 56.3
sq-kms, good quality is present over an area of 1872 sq-kms and groundwater
of very good quality is present over an area of 1476 sq-kms with respect to
SO4 during postmonsoon season.
120
Figure 5.38 Spatial distribution of SO4 values of postmonsoon samples
5.6.9 Nitrate
The nitrate values of all the groundwater samples are presented
here in bar chart. Nitrate values within the desirable limit, within the
permissible limits and above the permissible limits are presented here.The
nitrate values of all the samples are shown in Figure 5.39.
Figure 5.39 Nitrate values of all samples during postmonsoon
121
68 samples of the study area contain nitrate concentration below the
desirable limit. 5 samples contain nitrate within the permissible limit. The
maximum value of the nitrate content of the study area is 73 mg/L in the
sample S13. The minimum value of the nitrate content is 10 mg/L and it is
present in the samples S54, S59, S63. The NO3 values of the groundwater
samples S3, S13, S26, S30, and S61 are above the desirable limit but within the
permissible limits during postmonsoon season.
5.6.9.1 Spatial distribution of NO3
The spatial distribution of NO3 values of these samples is presented
by dark brown colour and it is shown in the Figure 5.40. From the spatial
distribution diagram, it is understood that the groundwater from some scattered
areas in south central part of the study area contain groundwater with NO3
content within desirable to permissible limit during postmonsoon season. The
distribution of groundwater of poor quality is not found in any area, good
quality is present over an area of 947.3 sq-kms and groundwater of very good
quality is present over an area of 2457 sq-kms with respect to NO3 during
postmonsoon season.
122
Figure 5.40 Spatial distribution of NO3 values of postmonsoon samples
5.6.10 Total alkalinity
TA values of all the groundwater samples are presented here in bar
chart. TA values within the desirable limit, within the permissible limits and
above the permissible limits are presented here.The total alkalinity values of
all the samples are shown in Figure 5.41.
Figure 5.41 Total alkalinity values of all samples during postmonsoon
123
6 samples of the study area contain alkalinity above the
permissible limit. 39 samples contain alkalinity within the permissible limit.
28 samples of the study area contain alkalinity below the desirable limit. The
maximum value of the alkalinity is present in the sample S36. The
maximum value of the alkalinity is 712 mg CaCO3/L. The minimum value
of the alkalinity is present in the sample S59. The minimum value of the
alkalinity is 64 mg CaCO3/L. The TA values of the groundwater samples
S13, S26, S30, S35, S36 and S61 exceed the permissible limit during
postmonsoon season.
5.6.10.1 Spatial distribution of TA
The spatial distribution of TA values of these samples is presented
by red colour and it is shown in the Figure 5.42. From the spatial distribution
diagram, it is understood that the groundwater from few scattered areas in
centre north part and one small portion from south part of the study area
contain groundwater of poor quality with respect to TA during postmonsoon
season.
124
Figure 5.42 Spatial distribution of TA values of postmonsoon samples
The distribution of groundwater of poor quality is found over an
area of 43.3 sq-kms, good quality is present over an area of 2953 sq-kms and
groundwater of very good quality is present over an area of 408 sq-kms with
respect to TA during postmonsoon season.
5.6.11 Fluoride
Fluoride values of all the groundwater samples are presented here
in bar chart. Fluoride values within the desirable limit, within the permissible
limits and above the permissible limits are presented here.The fluoride values
of all the samples are shown in Figure 5.43.
125
Figure 5.43 Fluoride values of all samples during postmonsoon
4 samples out of 73 samples collected from the study area contain
fluoride above the desirable limit of 1 mg/L. A maximum fluoride content of
1.4 mg/L is present in the samples S12 and S49 and 8 samples do not contain
fluoride. The F value of 4 groundwater samples S7, S12, S13 and S49 are
above the desirable limit but it is within the permissible during postmonsoon
season.
5.6.11.1 Spatial distribution of F
The spatial distribution of F values of these samples is presented by
in the Figure 5.44. From the spatial distribution diagram, it is understood that
the groundwater from considerable area of north central part and some
scattered areas of south central part the study area contain groundwater with F
contents within desirable to permissible limit during postmonsoon season.
The distribution of groundwater of poor quality is not fount in any
part of the study area, good quality is present over an area of 351.3 sq-kms
and groundwater of very good quality is present over an area of 3053 sq-kms
with respect to fluoride during postmonsoon season.
126
Figure 5.44 Spatial distribution of F values of postmonsoon samples
5.7 QUALITY OF GROUNDWATER FOR IRRIGATION
Early irrigation water quality criteria including USSL (1954) have
received strong criticism from the users. It was argued that it was neither
possible nor correct to define clear cut boundaries between different classes of
irrigation water. Because the ionic composition of the water was considered
and the soil properties, salt tolerance of plant species, climatic conditions and
existing irrigation and agronomic practices followed in a region were not
considered. A third class irrigation water in one region may be second or first
quality in another region. Therefore, a general awareness has now reached
among the users, to use water quality criteria as a general guideline. The
awareness has also been reached to consider plant, soil and climatic
conditions to evaluate the final water quality (Kirda 1997).
127
5.7.1 Irrigation hazard
There are two different types of salt problems exist due to irrigation
water. The first type is associated with the salinity and the second type is
associated with the sodium. Soils may either be affected by salinity or by both
salinity and sodium (Fipps 1914).
5.7.1.1 Salinity hazard
Water with high salinity is toxic to plants and poses a salinity
hazard. Soils with high levels of salinity are called saline soils. High
concentrations of salt in the soil can result in a physiological drought
condition. That is, the field may appear to have plenty of moisture but plants
wilt, because the roots are unable to absorb the water. Water salinity is
usually measured by TDS (Fipps 1914). If TDS content in irrigation water is
below 450 mg/L, there is no restriction to use such water for irrigation
purpose and if the TDS content is above 2000 mg/L in irrigation water, severe
restrictions are to be followed to use such water for irrigation (Ayers and
Westcot 1994).
5.7.1.1.1 TDS values of irrigation water during premonsoon season
TDS values of all the groundwater samples are presented here in
bar chart. Excessive amounts of TDS in irrigation water affect plants and
agriculture soil physically and chemically thus reducing productivity. The
physical effects are to reduce osmotic pressure in plant cell and thus
preventing water to reach plant leaves and branches. The chemical effects
disrupt plant metabolism (Yesilnacar and Gulluoglu 2009). Hence regulations
on irrigation water are mandatory to preserve plant and soil. The TDS values
of all the samples for premonsoon season are shown in Figure 5.45.
128
Figure 5.45 TDS values of premonsoon samples with for irrigation
purpose
14 samples of the study area contain TDS values below 450 mg/L
and the groundwater from these sample locations have no restriction for
irrigation use during premonsoon season. 6 samples contain TDS values
above 2000 mg/L during premonsoon season and the groundwaters from these
sample locations have severe restrictions for irrigation use. The representing
samples of high TDS content are S3, S8, S13, S18, S26 and S61. 91.8 % of
the study area did not pose any restriction on its groundwater for irrigation
use whereas 8.2 % of the study posed restriction on its groundwater for
irrigation use during premonsoon season of the year 2007. These 6 sample
locations are not in same locality but spread across the central part of the
study area from north to south directions.
5.7.1.1.2 TDS values of irrigation water during postmonsoon season
The TDS values of all the postmonsoon groundwater samples are
presented here in bar chart.8 samples of the study area contain TDS values
below 450 mg/L and the groundwater from these sample locations have no
restriction for irrigation use during postmonsoon season. 26 samples contain
TDS value above 2000 mg/L during postmonsoon season and the
groundwaters from these sample locations have severe restrictions for
129
irrigation use. The representing samples of high TDS content are S3, S7, S8,
S9, S13, S16, S17, S18, S25, S26, S27, S28, S29, S30, S32, S35, S36, S37,
S45, S48, S61, S64, S65, S67, S69 and S72.
Figure 5.46 TDS values of postmonsoon samples with for irrigation
purpose
The TDS values of all the samples for postmonsoon season are
shown in Figure 5.46. 64.4 % of the study area did not pose any restriction on
its groundwater for irrigation use whereas 35.6 % of the study posed
restriction on its groundwater for irrigation use during the postmonsoon
season of the year 2007. These 26 sample locations are not in same locality
but spread across the central part of the study area from north to south
directions except few samples.
5.7.1.2 Sodium hazard
Excessive content of sodium in irrigation water will have effects on
soil and it will cause sodium hazard. The four different indices to assess the
presence excessive sodium are presented here. They are (i) Sodium absorbtion
ratio (SAR), (ii) Residual Sodium Carbonate (RSC), (iii) Soluble Sodium
Percent (SSP) and (iv) Exchangeable Sodium Percentage (ESP).
130
5.7.1.2.1 SAR
SAR is widely used to assess excessive sodium in irrigation water.
It is calculated from the ratio of sodium to calcium and magnesium. The latter
two ions are important since they tend to counter the effects of sodium. (Fipps
1914). SAR gives a clear idea about the absorbtion of sodium by the soils.
Also it is a better measure to understand the reactions of irrigation water with
the soil. The irrigation water with high SAR values will make the soil to
tighten up. The water quality for irrigation based on SAR is summarized in
Table 5.3. The expression for SAR is given as below in Equation (5.2), in
which the concentrations are expressed in meq/L
SAR = Na / ((Ca+Mg)/2)1/2
(5.2)
Table 5.3 Water quality for irrigation based on SAR as per IS: 2296 -
1963
SAR Water Quality
0-10 Excellent
10-18 Good
18-26 Fair
> 26 Poor
5.7.1.2.1.1 SAR values of the premonsoon samples
The SAR values of all the premonsoon groundwater samples are
presented here in bar chart.SAR values of all 73 samples of the study are
below 10, the groundwater from all sample locations is excellent in quality for
irrigation. The minimum value of SAR of the study area is found to be 1.128
at the sample S54 and the maximum value is 9.9882 at the sample S12. The
SAR values of all the samples during premonsoon season are shown in
Figure 5.47.
131
Figure 5.47 SAR values of premonsoon samples
The study area is free from sodium hazard in premonsoon season.
All the groundwater samples have SAR value less than 10 and also the value
of SAR is less than 6 in 70 samples of the study area during this season.
Diluted concentration of chemical elements in the groundwater due to higher
rainfall during this season may be the reason for low SAR value in the
groundwater samples.
5.7.1.2.1.2 SAR values of the postmonsoon samples
SAR values of all the postmonsoon groundwater samples are
presented here in bar chart. SAR values of 71 samples of the study are less
than 10, the groundwater from these sample location are excellent in quality
for irrigation. SAR values of 2 samples are between 10 and 18, the
groundwater quality of these sample locations is good. The minimum value of
SAR of the study area is found to be 2.01 at the sample S54 and the maximum
value is 13.65 at the sample S12. The SAR values of all the samples during
postmonsoon season are shown in Figure 5.48.
132
Figure 5.48 SAR values of postmonsoon samples
The study area is free from sodium hazard in postmonsoon season
as well. All the groundwater samples have SAR value less than 18 and also
the value of SAR is less than 10 in 71 samples of the study area during this
season. But all the samples contain higher value of SAR when compared with
the premonsoon season.
5.7.1.2.2 Residual sodium carbonate (RSC)
In waters containing high concentrations of bicarbonate, there is a
tendency for calcium and magnesium to precipitate as carbonates. This
reaction does not complete under ordinary circumstances but it would
continue. And hence, the concentrations of calcium and magnesium are
reduced and the relative proportion of the sodium is increased. The relative
abundance of sodium due to abundant presence of bicarbonate and carbonate
influence the suitability of water for irrigation purposes. This excess presence
of bicarbonate and carbonate is denoted as Residual Sodium Carbonate (RSC)
and is determined by the formula given in Equation (5.3) (Richards 1954).
RSC = (HCO3 + CO3) – (Ca + Mg) (5.3)
133
where, the concentrations are expressed in epm. If the RSC exceeds 2.5 epm,
the water is generally unsuitable for irrigation. If the value is between 1.25
and 2.5 epm, the water is of marginal quality, while values less than 1.25 epm
indicate the water is probably safe (Karnath 1999).
5.7.1.2.2.1 RSC values of premonsoon samples
The RSC values of all the premonsoon groundwater samples are
presented here in bar chart. RSC values of all 73 samples of the study are
below 1.25 epm. The minimum value of RSC of the study area is found to be
-11.265 epm at the sample S25 and the maximum value is 1.097 epm at the
sample S19. The RSC values of all samples are shown in Figure 5.49.
Figure 5.49 RSC values of premonsoon samples
The study area is free from the risk of precipitation of calcium and
magenesium as carbonates in premonsoon season. And hence the chances for
sodium accumulation in soil due to the presence of carbonates in irrigation
water is nil during premonsoon season. RSC values in 66 groundwater
samples are negative and hence, they can be considered as if they are well
safe against the accumulation of excessive sodium in this season The
groundwaters from 7 sample locations contain poisitive RSC values but less
134
than 1.25 epm. The RSC values in premonsoon samples are higher than the
RSc values of postmonsoon season.
5.7.1.2.2.2 RSC values of postmonsoon samples
The RSC values of all the postmonsoon groundwater samples are
presented here in bar chart. RSC values of all 73 samples of the study are
below 1.25 epm. The minimum value of RSC of the study area is found to be
–8.035 epm at the sample S48 and the maximum value is 0.9423 epm at the
sample S66. The RSC values of all samples are shown in Figure 5.50.
Figure 5.50 RSC values of postmonsoon samples
The study area is free from the risk of precipitation of calcium
and magenesium as carbonates in postmonsoon season. And hence the
chances for sodium accumulation in soil due to the presence of carbonates in
irrigation water is nil during postmonsoon season. RSC values in 66
groundwater samples are negative and hence, they can be considered as if
they are well safe against the accumulation of excessive sodium in this season
as well. The groundwaters from 7 sample locations contain positive RSC
values but less than 1.25 epm. The lower rate of infiltration in postmonsoon
season may be considered as the cause for lower concentrations of
bicarbonates and carbonates and hence reduced values of RSC during
postmonsoon season.
135
5.7.1.2.3 Soluble sodium percent (SSP)
Soluble sodium percent is defined as the ratio of sodium in epm
between total cations in epm as given by the Equation (5.4).
SSP = (Na / (Ca +Mg + K+Na)) x 100 (5.4)
where, the concentrations are expressed in epm. Water with SSP greater than
60 percent may result in sodium accumulations that will cause a breakdown in
the soil’s physical properties (Fipps 1914).
5.7.1.2.3.1 SSP values of premonsoon samples
The SSP values of all the premonsoon groundwater samples are
presented here in bar chart. The SSP values of the premonsoon samples show
that 6 samples of the study area contain SSP values above the permissible
limit. The SSP values of all premonsoon samples are shown in Figure 5.51.
The minimum value of SSP is 29.7 epm in the sample S52 and the maximum
value is 68.4 epm in the sample S10.
Figure 5.51 SSP values of premonsoon samples
136
The representing samples which have SSP above 60 percent are
S9, S10, S11, S12, S13 and S14. 8.2 % of the samples have the risk sodium
accumulations due to SSP and the remaining 97.2 % of the samples have no
risk of sodium due to increase in SSP during premonsoon season. The
increased infiltration during premonsoon season and the consequent dilution
of concentration of ions in the groundwater may be considered as the cause
for the sodium accumulation risk free locations.
5.7.1.2.3.2 SSP values of postmonsoon samples
The SSP values of all the postmonsoon groundwater samples are
presented here in bar chart. SSP values of the postmonsoon samples show that
17 samples of the study area contain SSP values above the permissible limit.
The SSP values of all postmonsoon samples are shown in Figure 5.52. The
minimum value of SSP is 42.9 epm in the sample S13 and the maximum
value is 69.3 epm in the sample S49.
Figure 5.52 SSP values of postmonsoon samples
The representing samples which have SSP above 60 percent are
S1, S12, S22, S23, S29, S49, S50, S56, S57, S58, S59, S62, S63, S66, S68,
S71 and S73. 23.3 % of the samples have the risk sodium accumulations due
137
to SSP and the remaining 76.7 % of the samples have no risk of sodium due
to increase in SSP during postmonsoon season. The infiltration due to rainfall
was not sufficient during this season to dilute the concentration of ions in the
groundwater and it may be considered as the cause for the sodium
accumulation risks in 17 sample locations.
5.7.1.2.4 Exchangeable sodium percentage (ESP)
Excessive sodium content in water renders it unsuitable for soils
containing exchangeable Ca and Mg ions. If the percentage of Na to (Ca +
Mg + Na) is considerably above 50 in irrigation waters, soils containing
exchangeable calcium and magnesium will take up sodium in exchange for
calcium and magnesium causing de-flocculation and impairment of the tilth
and permeability of soils (Karnath 1999).
5.7.1.2.4.1 ESP values of premonsoon samples
The ESP values of all the premonsoon groundwater samples are
presented here in bar chart. ESP values of the premonsoon samples show that
23 samples of the study area contain ESP value above the permissible limit.
The remaining 50 samples contain ESP values within the desirable limit. The
minimum value of ESP of the study area is 30.8 epm at the sample S52 and
the maximum value is 71.9 epm at the sample S14. The ESP values of all
samples are shown in Figure 5.53.
The representing samples which have ESP above 50 percent are
S1, S6, S9, S10, S11, S12, S13, S14, S16, S17, S19, S21, S22, S23, S24, S35,
S68, S69, S70, S71, S72 and S73. 31.5 % of the samples have the risk sodium
accumulations due to ESP and the remaining 68.5 % of the samples have no
risk of sodium due to increase in ESP during premonsoon season.
138
Figure 5.53 ESP values of premonsoon samples
The increased infiltration during premonsoon season and the
consequent dilution of concentration of ions in the groundwater may be
considered as the cause for the sodium accumulation risk free locations due to
ESP in premonsoon season.
5.7.1.2.4.2 ESP values of postmonsoon samples
The ESP values of all the postmonsoon groundwater samples are
presented here in bar chart. The ESP values of the postmonsoon samples
show that 61 samples of the study area contain ESP value above the
permissible limit. The remaining 12 samples contain ESP values within the
desirable limit. The minimum value of ESP of the study area is 45.2 epm at
the sample S41 and the maximum value is 72.7 epm at the sample S68. The
ESP values of all samples are shown in Figure 5.54.
The representing samples which have ESP below 50 percent are
S4, S7, S12, S14, S19, S20, S21, S41, S42, S43, S54 and S69. 83.6 % of the
samples have the risk sodium accumulations due to ESP and the remaining
16.4 % of the samples have no risk of sodium due to increase in ESP during
postmonsoon season.
139
Figure 5.54 ESP values of postmonsoon samples
The infiltration due to rainfall was not sufficient during this season
to dilute the concentration of ions in the groundwater and it may be
considered as the cause for the sodium accumulation risks in 61 sample
locations due ESP in postmonsoon season.
5.8 CLASSIFICATIONS OF GROUND WATER SAMPLES FOR
IRRIGATION USE
The suitability of groundwater for irrigation purpose is also known
from the following methods of classifications.
1. USSL classification
2. Doneen’s classification
3. Wilcox’s classification.
5.8.1 USSL classification
Irrigation water quality criteria developed by US Salinity
Laboratory has received wide acceptance in many countries (USSL 1954).
The notations C1, C2, C3, C4 and S1, S2, S3, S4 represents the low, medium,
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high and very high salinity and alkali hazard. The diagram is divided into 16
divisions by which the water can be categorized as good, moderate and bad
for irrigation.
5.8.1.1 USSL classification of groundwater samples during
premonsoon season
The classification of groundwater for irrigation based on USSL
diagram shows the presence of 5 combination indices of sodium and salinity
hazards in premonsoon samples. These combinations and their respective
categories are summarized in Table 5.4.The USSL diagram for the
premonsoon samples are shown in Figure 5.55.
Figure 5.55 USSL diagram for premonsoon samples
141
Table 5.4 Classification of groundwater samples based on USSL
diagram for premonsoon seasons
ClassificationSuitability for
irrigation
Number of samples during
premonsoon season
C2-S1 Good 23
C3-S1 Good 21
C3-S2 Moderate 15
C4-S2 Moderate 13
C4-S4 Bad 1
From USSL classifications of premonsoon groundwater samples, it
is found that 31.5 % of groundwater samples are medium salinity and low
sodium water category, 28.8 % of groundwater samples are high salinity and
low sodium water category, 20.5% of groundwater samples are high
salinity and medium sodium water category, 17.8% of groundwater samples
are very high salinity and medium sodium water category and 1.4% of
groundwater samples are very high salinity and very high sodium water
category. In general, 60.3% of groundwater samples are good, 24.6% of
groundwater samples are moderate and 1.4% of groundwater samples are bad
for irigation purposes during premonsoon season.
5.8.1.2 USSL Classification of groundwater samples during
postmonsoon season
The classification of groundwater for irrigation based on USSL
diagram shows the presence of 5 combination indices of sodium and salinity
hazard in postmonsoon samples. These combinations and their respective
categories are summarized in Table 5.5. The USSL diagram for the
postmonsoon samples is shown in Figure 5.56.
142
Figure 5.56 USSL diagram for postmonsoon season
Table 5.5 Classification of groundwater samples based on USSL
diagram for postmonsoon seasons
ClassificationSuitability for
irrigation
Number of samples during
postmonsoon season
C2-S1 Good 21
C3-S1 Good 20
C3-S2 Moderate 16
C4-S2 Moderate 15
C4-S4 Bad 1
From USSL classifications of postmonsoon groundwater samples,
it is found that 28.8 % of groundwater samples are medium salinity and low
sodium water category, 27.4 % of groundwater samples are high salinity and
low sodium water category, 21.9% of groundwater samples are high
salinity and medium sodium water category, 20.5% of groundwater samples
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are very high salinity and medium sodium water category and 1.4% of
groundwater samples are very high salinity and very high sodium water
category. In general, 56.2% of groundwater samples are good, 42.4% of
groundwater samples are moderate and 1.4% of groundwater samples are bad
for irigation purposes during postmonsoon season.
5.8.2 Doneen’s classification
Doneen (1966) proposed a concept called "permeability index" (PI)
to assess probable influence of water quality on physical properties of soils.
The PI can be calculated using the expression given in Equation (5.5) where
ion concentrations are given in me1-l.
PI = (Na + HCO3) / Cations (5.5)
The major portion of the study area consists of red soil. Alluvial
soil is present along the river banks. Clay loam is also present in some portion
of the study area (PWD 2001). As the permeability of the soils of study area
are less than 2 cm h-1
, Doneen’s chart of part (a) is used. In Doneen’s chart,
the values of PI and TDS are plotted along x and y axes respectively. In
general, water for irrigation propose is good if it is of the class I and class II
of Doneen classification.
5.8.2.1 Doneen classification of groundwater samples for premonsoon
season
The classification of water samples based on Doneen’s diagram
shows that 23 samples belong to class 1, 49 samples belong to class 2 and 1
sample belong to class 3 during premonsoon season. The Doneen’s diagram
for premonsoon sample is shown in Figure 5.57.
144
Figure 5.57 Groundwater samples plotted on Doneen’s diagram for
premonsoon season
From Doneen classification of prmonsoon samples, it is found that
31.5% of the groundwater samples are of the class I, 67.1% of the
groundwater samples are of the class II and 1.45% of the groundwater
samples are of the class III. In general, 98.6% of the groundwater samples are
of good quality and have maximum permeability of 75% and 1.4% of the
groundwater samples are of moderate quality and have a maximum
permeability of 25 %.
145
5.8.2.2 Doneen’s classification of groundwater samples for
postmonsoon season
The classification of water samples based on Doneen’s diagram
shows that 21 samples belong to class 1, 43 samples belong to class 2 and 9
samples belong to class 3 during postmonsoon season. The Doneen’s diagram
for postmonsoon sample is shown in Figure 5.58.
Figure 5.58 Groundwater samples plotted on Doneen’s diagram for
postmonsoon season
From Doneen classification of prmonsoon samples, it is found that
28.8% of the groundwater samples are of the class I, 58.9% of the
groundwater samples are of the class II and 12.3% of the groundwater
samples are of the class III. In general, 87.7% of the groundwater samples are
of good quality and have maximum permeability of 75% and 12.3% of the
groundwater samples are of moderate quality and have a maximum
permeability of 25 %.
146
5.8.3 Wilcox’s classification
Wilcox classified groundwater used for irrigation purpose based on
electrical conductivity and percentage of sodium content (Wilcox 1955). In
Wilcox chart, the values of electrical conductivity and percentage of sodium
content are plotted on x and y axes respectively. The percentage of sodium
content is calculated by the expression given in Equation (5.6).
Sodium percent (Na %) = ( (Na + K ) / ( Ca + Mg + Na + K )) x 100 (5.6)
5.8.3.1 Wilcox’s classification of groundwater samples for premonsoon
season
The classification of water samples based on Wilcox classification
shows that 33 samples belong to very good to good category, 22 samples
belong to good to permissible category, 5 samples belong to permissible to
doubtful category,8 samples belong to doubtful to unsuitable category and 5
samples belong to unsuitable category during premonsoon season. Wilcox
classification for premonsoon samples is shown in Figure 5.59.
From Wilcox’s classification for the premonsoon samples, it is
found that 45.2% of groundwater samples are of good quality and they can be
used for irrigation purposes with out any risk to soil and plant. 31.1 % of
groundwater samples are of moderate quality and good to permissible
category, salinity is little high among these samples. 6.8% of groundwater
samples are of permissible to doubtful category, sodium content is high
among these samples. 11% of groundwater samples are of doubtful to
unsuitable category, salinity is high among these samples. 6.8% of
groundwater samples are of unsuitable category, salinity is very high among
these samples.
147
Figure 5.59 Groundwater samples plotted on Wilcox’s diagram for
premonsoon season
5.8.3.2 Wilcox’s classification of groundwater samples for postmonsoon
season
The classification of water samples based on Wilcox classification
shows that 10 samples belong to very good to good category, 12 samples
belong to good to permissible category, 15 samples belong to permissible to
doubtful category,13 samples belong to doubtful to unsuitable category and
23 samples belong to unsuitable category during postmonsoon season. The
Wilcox classification for postmonsoon samples is shown in Figure 5.60.
148
Figure 5.60 Groundwater samples plotted on Wilcox’s diagram for
postmonsoon season
From Wilcox’s classification for the premonsoon samples, it is
found that 13.7% of groundwater samples are of good quality and they can be
used for irrigation purposes with out any risk to soil and plant. 16.44 % of
groundwater samples are of moderate quality and good to permissible
category, salinity is little high among these samples. 20.55% of groundwater
samples are of permissible to doubtful category, sodium content is high
among these samples.17.8% of groundwater samples are of doubtful to
unsuitable category, salinity is high among these samples. 31.51% of
groundwater samples are of unsuitable category, salinity is very high among
these samples.
149
5.9 CONTROLLING MECHANISM OF HYDRO CHEMISTRY
Rain and snow are the major sources of recharge to groundwater.
The quality of groundwater is altered due to various processes such as
chemical reactions, surface influences, etc. The causes that produce changes
in groundwater quality are discussed here.
5.9.1 Factors influencing groundwater quality
The percolating rain water contains small amount of dissolved
solids and gases such as carbon dioxide, sulphur-dioxide and oxygen. As the
precipitation infiltrates through the soil, biologically-derived carbon dioxide
reacts with the water to form a weak solution of carbonic acid. The reaction of
oxygen with reduced iron minerals is an additional source of acidity in
groundwater. The slightly acidic water dissolves soluble rock material,
thereby increasing the concentrations of chemical constituents’ such as
calcium, magnesium, chloride, iron, and manganese. As groundwater moves
slowly through an aquifer, the composition of water continues to change by
the addition of dissolved constituents (Freeze and Cherry, 1979). A longer
residence time will increase concentrations of dissolved solids. Because of
short residence time, groundwater in recharge areas often contain lower
concentrations of dissolved constituents.
Dissolved carbon dioxide, bicarbonate, and carbonate are the
principal sources of alkalinity or the capacity of solutes in water to neutralize
acid. Atmospheric and biologically-produced carbon dioxide, carbonate
minerals and biologically-mediated sulphate are carbonate contributors to
alkalinity. Noncarbonated contributors to alkalinity are hydroxide, silicate,
150
borate and organic compounds. Alkalinity helps to buffer natural water so that
the pH is not greatly altered by addition of acid. Calcium and magnesium are
the major constituents responsible for hardness in water. Their presence is the
result of dissolution of carbonate minerals such as calcite and dolomite. The
weathering of feldspar and clay is the source for sodium and potassium in
groundwater. Sodium and chloride are produced by the solution of halite
which occurs in the form of grains dispersed in unconsolidated and bedrock
deposits. Chloride also occurs in bedrock cementing material and connate
fluid inclusions (Hem 1991).
Cation exchange is often a modifying influence of groundwater
chemistry. The most important cation exchange processes are sodium-
calcium and sodium- magnesium. Concentrations of sulphide, iron and
manganese depend on amount of dissolved oxygen, pH, minerals available for
solution, amount of organic matter, and microbial activity and geology and
hydrology of the aquifer system. Mineral source of sulphate can include
pyrite, gypsum, barite and celestite. Oxidation-reductions constitute an
important influence on concentrations of both iron and manganese. High
dissolved iron concentrations can occur in groundwater when pyrite is
exposed to oxygenated water or ferric oxide or hydroxide minerals when in
contact with reducing substances (Hem, 1991). Natural concentrations of
nitrate-nitrogen in groundwater originate from the atmosphere and from the
living and decaying organisms. High nitrate levels can result from leaching of
industrial chemicals or decaying organic matter such as animal waste or
sewage.
151
5.9.2 Hydro chemical facies
Hydrochemical facies are defined as water chemistry properties of
distinct zones within an aquifer (Freeze and Cherry 1979). The nature and
distribution of hydro chemical facies can provide information about how
groundwater quality changes within and between aquifers. Trilinear diagrams
are used to graphically illustrate the relationship between the most important
dissolved constituents in a group of groundwater samples.
A scheme for describing hydro chemical facies presented by
Walton (1970) with tri-linear diagram is shown in Figure 5.61. It is based on
the methods used by Piper (1984). This method is based on the dominance of
certain cations and anions in solution.
Figure 5.61 Piper’s tri linear diagram
152
Table 5.6 Basic hydro chemical facies
S.No Hydro chemical
facies
Nature
1 Primary hardness Combined concentrations of calcium,
magnesium and bicarbonate exceed 50 percent
of the total dissolved constituent load in meq/L.
Such waters are generally considered hard and
are often found in lime stone aquifers or
unconsolidated deposits containing abundant
carbonate minerals.
2 Secondary
hardness
Combined concentrations of sulphate, chloride,
magnesium and calcium exceed 50 percent of the
total concentration.
3 Primary salinity Combined concentrations of alkali metals,
sulphate and chloride are greater than 50 percent
of the total concentration. Very concentrated
waters of the hydro chemical facies are
considered brakish or saline.
4 Primary
alkalinity
Combined sodium, potassium and bicarbonate
concentrations exceed 50 percent of the total
concentration. These waters generally have low
hardness in proportion to their dissolved solids
concentrations (Walton 1970).
5 No specific
cation- anion pair
No specific cation-anion pair exceeds 50 percent
of the total dissolved constituent load. Such
water will result from multiple mineral
dissolutions or mixing of two chemically distinct
groundwater bodies.
Cations are expressed as percentage of total cations in meq/L and
plotted as single point in lower left triangle while anions are similarly
expressed as percentage of total anions and plotted as a single point in lower
right triangle. These two points are then projected into the central diamond
shaped area. Distinct hydro chemical facies are defined by specific
combinations of dominant cations and anions. Fundamental interpretations of
153
the chemical nature of a water sample are based on the location of the
projection in the diamond field. If no single cation or anion in water sample
meets this criterion, the water has no dominant ion in solution. The various
interpretations of chemical nature of water are summarized in Table 5.6.
5.9.2.1 Hydrochemical facies based on Piper’s diagram for premonsoon
samples
Cation-Anion concentrations of the groundwater samples of
premonsoon season are plotted on tri-linear diagram for the analysis of
hydrochemical facies. The Piper diagram for premonsoon samples is shown in
Figure 5.62.
Figure 5.62 Piper’s tri-linear diagram for premonsoon season
154
Hydrochemical facies of the premonsoon samples
1. No specific cation anion pair: The facies of no specific cation-
anion pair is found in 43 samples of the study area.
2. Primary salinity: Facies of primary salinity exists in 28
samples. Very concentrated waters of these sample locations
are considered as saline.
3. Primary hardness: One sample out of seventy three samples
consist hydro chemical facies of this type. Water from this
location generally considered hard.
4. Secondary hardness: One sample of the study area consist
facies of this type. In this sample combined concentrations of
anions exceed 50 % of the total dissolved solids.
Cation types in premonsoon samples
1. Sodium or Potassium type: Na or K type cation is present in
30 samples during premonsoon season. This shows that the
concentration of these cation exceed by 50 % than other
cations in these 30 samples.
2. No dominant type: 43 number of samples during premonsoon
season contain no dominating cation. That is, none of the
cations in these 43 samples exceed 50 % of the concentration
of other cations of the solution.
Anion types in premonsoon samples
1. Choride type: Cl type cation is present in 18 samples during
premonsoon season. This shows that the concentration of these
anion exceed by 50 % than other anions in these 18 samples.
155
2. Bicarbonate type: HCO3 type anion is present in 1 sample
during premonsoon season. This shows that the concentration
of this anion exceed by 50 % than other anions in this sample.
3. No dominant type: 54 number of samples during premonsoon
season contain no dominating anion. That is, none of the
anions in these 54 samples exceed 50 % of the concentration
of other anions of the solution.
5.9.2.2 Hydrochemical facies based on Piper’s diagram for postmonsoon
samples
Cation-Anion concentrations of the groundwater samples of
premonsoon season are plotted on trilinear diagram for the analysis of
hydrochemical facies. The Piper diagram for premonsoon samples is shown in
Figure 5.63.
Figure 5.63 Piper’s tri-linear diagram for postmonsoon season
156
Hydro chemical facies of the postmonsoon samples
1. Primary salinity: Facies of primary salinity exists in 65
samples. Very concentrated waters of these sample locations
are considered as saline.
2. No specific cation-anion pairs: The facies of no specific cation-
anion pair exist in 8 samples of the postmonsoon season.
Cation types in postmonsoon samples
1. Sodium or Potassium type: Na or K type cation is present in
67 samples during postmonsoon season. This shows that the
concentration of these cation exceed by 50 % than other
cations in these 67 samples.
2. No dominant type: 6 number of samples during postmonsoon
season contain no dominating cation. That is, none of the
cations in these 45 samples exceed 50 % of the concentration
of other cations of the solution.
Anion types in postmonsoon samples
1. Choride type: Cl type cation is present in 31 samples during
postmonsoon season. This shows that the concentration of this
anion exceed by 50 % than other anions in these 31 samples.
2. Bicarbonate type: HCO3 type anion is present in 5 samples during
postmonsoon season. This shows that the concentration of these
anion exceed by 50 % than other anions in these 5 samples.
3. No dominant type: 37 number of samples during postmonsoon
season contain no dominating anion. That is, none of the
anions in these 37 samples exceed 50 % of the concentration
of other anions of the solution.
157
5.9.3 Gibb’s plot
Gibb’s (1970) attempted to predict the contributions of atmospheric
precipitation, rock weathering and evaporation to water chemistry using a plot
of total dissolved salts (TDS) against Na/(Na + Ca) or Cl/(Cl + HCO3). He
had also proposed a diagram to understand the relationship of the chemical
components of water from their respective aquifer lithologies. Three distinct
fields, namely precipitation dominance, evaporation dominance and rock
dominance are shown in the Gibb’s diagram. The Gibb’s ratios are calculated
with the expressions given in Equation (5.7) and in Equation (5.8).
Gibb’s Ratio I (for anion) = Cl / (Cl+HCO3) (5.7)
Gibb’s Ratio II (for cation) = Na+K / (Na+K+Ca) (5.8)
Gibb’s ratios for the samples of the study area are plotted against
their respective TDS as shown in Figure 5.64 to know whether the
groundwater chemistry is due to rock dominance, evaporation dominance or
precipitation dominance.
Water chemistry in the central part of the “boomerang” is
dominated by weathering of silicate minerals. Samples in the upper part of the
boomerang represent progressive evaporation resulting in an increase in TDS
and enrich the water in Na while depleting in Ca. The lower part of the
diagram represents water from precipitation, which would have lower
concentrations of TDS. However, some samples fall outside the boomerang
region that encompasses water of the earth's surface.
158
Figure 5.64 Gibb’s plot
5.9.3.1 Gibb’s plot for groundwater samples of premonsoon season
The plots of Gibb’s ratio for anions and cations of all groundwater
samples during premonsoon season are shown in Figure 5.65.
Figure 5.65 Gibb’s plot for premonsoon season
159
Gibb’s ratio I: Controlling mechanisms of anions in premonsoon samples
a. Rock dominance: The mechanism controlling the
hydrochemistry of anions of 56 samples during premonsoon
season is rock dominance. They occupy the place in central
part of the Gibb’s diagram.
b. Evaporation dominance: The mechanism controlling the
hydrochemistry of anions of 14 samples during premonsoon
season is evaporation dominance. They occupy the upper part
of the Gibb’s boomerang diagram.
b. Surface influences: The mechanism controlling the
hydrochemistry of anions of 3 samples during premonsoon
season is surface influences. They occupy the outer part of the
Gibb’s boomerang diagram.
Gibb’s ratio II: Controlling mechanisms of cations in premonsoon
samples
a. Rock dominance: The mechanism controlling the
hydrochemistry of 50 samples during premonsoon season is
rock dominance. They occupy the place in central part of the
Gibb’s diagram.
b. Evaporation dominance: The mechanism controlling the
hydrochemistry of 15 samples during premonsoon season is
evaporation dominance. They occupy the upper part of the
Gibb’s boomerang diagram.
b. Surface influences: The mechanism controlling the
hydrochemistry of 8 samples during premonsoon season is
surface influences. They occupy the outer part of the Gibb’s
boomerang diagram.
160
5.9.3.2 Gibb’s plot for groundwater samples of postmonsoon season
The plots of Gibb’s ratio for anions and cations of all groundwater
samples during postmonsoon season are shown in Figure 5.66.
Figure 5.66 Gibb’s plot for postmonsoon season
Gibb’s ratio I: Controlling mechanisms of anions in postmonsoon
samples
a. Rock dominance: The mechanism controlling the
hydrochemistry of anions of 39 samples during postmonsoon
season is rock dominance. They occupy the place in central
part of the Gibb’s diagram.
b. Evaporation dominance: The mechanism controlling the
hydrochemistry of anions of 31 samples during postmonsoon
season is evaporation dominance. They occupy the upper part
of the Gibb’s boomerang diagram.
b. Surface influences: The mechanism controlling the
hydrochemistry of anions of 3 samples during postmonsoon
season is surface influence. They occupy the outer part of the
Gibb’s boomerang diagram.
161
Gibb’s ratio II: Controlling mechanisms of cations in postmonsoon
samples
a. Rock dominance: The mechanism controlling the
hydrochemistry of 31 samples during postmonsoon season is
rock dominance. They occupy the place in central part of the
Gibb’s diagram.
b. Evaporation dominance: The mechanism controlling the
hydrochemistry of 34 samples during postmonsoon season is
evaporation dominance. They occupy the upper part of the
Gibb’s boomerang diagram.
b. Surface influences: The mechanism controlling the
hydrochemistry of 8 samples during postmonsoon season is
surface influence. They occupy the outer part of the Gibb’s
boomerang diagram.
5.10 RAINFALL AT THE SAMPLE LOCATIONS
The annual rainfall data obtained from the rain gauge stations are
attributed in the GIS software ArcView 3.2a. The rainfall values at the sample
locations are arrived with the help of interpolation grids generated using the
software. The annual rainfall of a year is the total rainfall obtained by the
summation of monthly rainfall in a year from January to December. The total
rainfall for the premonsoon season (July) of the year 2007 is calculated from
the summation of monthly rainfall from July 2006 to June 2007 and the total
rainfall for the postmonsoon season (March) of the year 2007 is calculated
from the summation of monthly rainfall from July 2006 to February 2007.
162
5.10.1 Rainfall during premonsoon season
The rainfall during the year 2007 was taken for the study. The total
rainfall during premonsoon season at the sample locations of the study area are
graphically shown in Figure 5.67. The maximum rainfall during the premonsoon
season (July) of the study area was 939 mm and the maximum rainfall was
recorded at the sample location 9. The minimum rainfall during the premonsoon
season was 512 mm and the minimum rainfall was recorded at the sample S18.
The average rainfall during the premonsoon season was 680 mm.
Figure 5.67 Rainfall during premonsoon season at the sample locations
5.10.2 Rainfall during postmonsoon season
The total rainfall during postmonsoon season at the sample
locations of the study area are graphically shown in Figure 5.68. The
maximum rainfall during the postmonsoon season (March) of the study area
was 723 mm and the maximum rainfall was recorded at the sample location 9.
The minimum rainfall during the postmonsoon season was 431 mm and the
minimum rainfall was recorded at the sample location 18. The average rainfall
during the postmonsoon season was 550 mm.
163
Figure 5.68 Rainfall during postmonsoon season at the sample locations
The rainfall during premonsoon season is invariably higher at all
the sample locations than during postmonsoon season. At the same time, the
concentrations of TDS are lower during premonsoon season than during
postmonsoon season. Hence, it may be considered that the rate of infiltration
has a definite influence in reducing TDs content in groundwater.
5.11 SUBSURFACE PARAMETERS OF THE SAMPLE LOCATIONS
The subsurface parameters such as soil, geology and
geomorphology of the sample locations are known from GIS overlay of
thematic maps and sample locations using ArcView 3.2a. The respective
parameters are summarized in Table 5.7.
164
Table 5.7 Subsurface parameters of the sample locations
Sample. No Soil type Geology Type Geomorphology Type
1 Red Gneissic Rock Shallow pediment
2 Red Gneissic Rock Shallow pediment
3 Alluvial Gneissic Rock Flood plain
4 Red Gneissic Rock Shallow pediment
5 Black Dolonite Plateau
6 Red Alluvium Shallow pediment
7 Red Charnockite Shallow pediment
8 Black Alluvium Shallow pediment
9 Black Alluvium Shallow pediment
10 Black Charnockite Shallow pediment
11 Red Charnockite Structural hill
12 Black Charnockite Shallow pediment
13 Red Gneissic Rock Shallow pediment
14 Red Gneissic Rock Shallow pediment
15 Red Gneissic Rock Shallow pediment
16 Red Gneissic Rock Shallow pediment
17 Black Gneissic Rock Plateau
18 Red Gneissic Rock Shallow pediment
19 Alluvial Alluvium Flood plain
20 Alluvial Alluvium Flood plain
21 Alluvial Gneissic Rock Flood plain
22 Red Gneissic Rock Shallow pediment
23 Brown Gneissic Rock Shallow pediment
24 Red Gneissic Rock Shallow pediment
25 Red Gneissic Rock Flood plain
26 Alluvial Gneissic Rock Shallow pediment
27 Red Gneissic Rock Shallow pediment
28 Red Gneissic Rock Shallow pediment
29 Alluvial Gneissic Rock Shallow pediment
30 Red Gneissic Rock Shallow pediment
31 Red Gneissic Rock Shallow pediment
32 Red Gneissic Rock Shallow pediment
33 Red Gneissic Rock Structural hill
34 Black Charnockite Shallow pediment
35 Black Gneissic Rock Shallow pediment
36 Black Gneissic Rock Shallow pediment
37 Red Charnockite Shallow pediment
38 Red Gneissic Rock Plateau
39 Red Charnockite Bazada zone
165
Table 5.7 (Continued)
40 Red Charnockite Bazada zone
41 Red Charnockite Plateau
42 Hill Charnockite Structural hill
43 Red Charnockite Shallow pediment
44 Black Gneissic Rock Shallow pediment
45 Black Charnockite Shallow pediment
46 Black Charnockite Structural hill
47 Red Gneissic Rock Shallow pediment
48 Red Gneissic Rock Shallow pediment
49 Red Gneissic Rock Shallow pediment
50 Red Gneissic Rock Flood plain
51 Red Gneissic Rock Shallow pediment
52 Red Gneissic Rock Shallow pediment
53 Alluvial Gneissic Rock Flood plain
54 Red Granitoid gneis P Shallow pediment
55 Alluvial Gneissic Rock Flood plain
56 Red Gneissic Rock Shallow pediment
57 Brown Gneissic Rock Shallow pediment
58 Red Gneissic Rock Flood plain
59 Alluvial Gneissic Rock Flood plain
60 Red Gneissic Rock Shallow pediment
61 Red Alluvium Shallow pediment
62 Red Charnockite Shallow pediment
63 Brown Alluvium Flood plain
64 Brown Gneissic Rock Shallow pediment
65 Red Charnockite Structural hill
66 Alluvial Gneissic Rock Shallow pediment
67 Red Gneissic Rock Shallow pediment
68 Red Gneissic Rock Shallow pediment
69 Red Gneissic Rock Shallow pediment
70 Red Gneissic Rock Shallow pediment
71 Red Granitoid gneiss P Shallow pediment
72 Red Gneissic Rock Shallow pediment
73 Brown Gneissic Rock Shallow pediment
166
Table 5.8 Water quality test results of premonsoon samples
Sam
ple
ID
Tu
rbid
ity
( N
TU
)
EC
(
µm
ho
/cm
TD
S
( m
g/
L )
pH
Tota
l alk
ali
nit
y a
s
mg
Ca
CO
3/
L
Tota
l h
ard
nes
s as
mg
Ca
CO
3/
L
Ca
(m
g /
L)
Mg
(m
g /
L)
Na
(m
g /
L)
K
(mg
/ L
)
Fe
(mg
/ L
)
NO
3
(mg
/ L
)
Cl
(m
g /
L)
F (
mg
/ L
)
SO
4
(mg
/ L
)
PO
4
(mg
/ L
)
S1 0 1017 712 8.67 156 252 62.7 30.1 136.7 24.4 0.1 19 180 0 128 0
S2 2 760 532 7.82 120 184 50 25.2 83.7 20 0.2 14 132 1.2 84 0
S3 1 3160 2212 7.86 528 864 202.5 113 367.2 39.4 0.1 48 504 0 346 0
S4 0 1845 1292 8.12 264 412 57 57.7 224.6 47.1 0 30 320 0 259 0
S5 1 718 503 8.1 116 204 21 22 84.4 16.4 0 12 122 0 92 0
S6 1 503 352 8.43 112 120 25.7 11.8 66.3 4.7 0.1 11 72 0.4 52 0
S7 0 1964 1375 8.25 436 536 110 62 199.5 30.1 0.2 35 180 0.7 270 0
S8 1 3180 2226 7.9 706 768 182.3 102.7 316.4 33.6 0 60 428 0.4 364 0
S9 0 1827 1279 8.23 348 440 95.6 51.5 242.2 30.9 0 28 316 0 180 0.1
S10 1 1151 806 8.1 216 176 35 38 160.8 24.6 0 21 182 0.2 140 0
S11 8 729 510 8.03 152 112 20.4 10.6 105.3 10.2 0 12 112 0.6 74 0
S12 0 770 539 8.21 100 120 26.6 16 106.5 17.7 0 15 124 0.7 97 0
S13 24 5000 3500 8.15 916 784 42.2 84 690 60 0 92 588 1 513 0
S14 6 1410 987 7.65 212 220 44.5 23.9 225.3 33.5 0 28 248 0.2 182 0
S15 1 1086 760 8.31 188 156 31 36 156.2 23.1 0 19 184 0.4 126 0
S16 1 2720 1904 8.15 416 628 159.6 97 313.2 37.8 0 32 452 0.6 382 0
S17 80 1588 1112 8.05 332 368 69.2 43.4 201.9 38.5 0 27 224 0.6 192 0.1
S18 60 3120 2184 7.95 516 724 168.5 100 341.4 63.6 0.3 60 420 0 404 0.2
167
Table 5.8 (Continued)
Sam
ple
ID
Tu
rbid
ity
( N
TU
)
EC
(
µm
ho
/cm
TD
S
( m
g/
L )
pH
Tota
l alk
ali
nit
y a
s
mg
Ca
CO
3/
L
Tota
l h
ard
nes
s as
mg
Ca
CO
3/
L
Ca
(m
g /
L)
Mg
(m
g /
L)
Na
(m
g /
L)
K
(mg
/ L
)
Fe
(mg
/ L
)
NO
3
(mg
/ L
)
Cl
(m
g /
L)
F (
mg
/ L
)
SO
4
(mg
/ L
)
PO
4
(mg
/ L
)
S19 0 1506 1054 8.41 336 340 45 47 177.3 37 0 27 243 0.2 172 0
S20 1 959 671 8.62 264 224 42.1 27.1 93.5 11.7 0 19 100 0 91 0
S21 4 1524 1067 8.22 424 352 67.3 36.8 164.5 14.6 0 28 156 0.2 158 0
S22 60 1137 796 8.33 284 260 50 32 148 16 0.1 23 176 0 64 0.1
S23 0 690 483 8.07 172 152 34 16 96 6 0 11 112 0 42 0
S24 1 630 441 8.57 104 140 25.1 17 79.8 4.8 0 13 96 0 49 0
S25 50 1492 1044 7.62 360 432 92 51.2 156 16.4 0.5 27 176 0 169 0.3
S26 64 3610 2527 8.25 512 988 244.5 149.1 399.2 49.9 0 69 564 0.2 474 0
S27 1 1965 1376 7.93 256 512 123.5 69.6 233.8 8.2 0 35 312 0.4 216 0
S28 1 2150 1505 8.23 296 644 131.5 81 232.6 36.2 0 41 332 0.8 176 0
S29 0 2800 1960 7.92 412 739 174.2 100 253.7 51.9 0.1 51 312 0.6 362 0
S30 40 1461 1023 8.15 256 384 75.2 47 174 22 0.3 29 196 0.6 166 0.2
S31 1 651 456 7.88 120 164 42.8 21.1 73.7 11.9 0 11 124 1 49 0
S32 1 1975 1383 8.14 224 496 118.4 73.4 225.7 36.4 0 38 320 0.8 236 0
S33 1 806 564 8.1 108 200 48.4 24.7 89.6 13.4 0 14 132 0.6 70 0
S34 24 1038 727 8.41 200 256 55.5 35.5 125.4 17.9 0 21 172 0.4 106 0
S35 1 669 468 8.82 140 168 37 18.3 84.4 10.1 0 11 124 0.6 41 0
S36 0 2800 1960 8.09 360 712 194 119 324 62 0 53 532 0.4 366 0
168
Table 5.8 (Continued)
Sam
ple
ID
Tu
rbid
ity
( N
TU
)
EC
(
µm
ho
/cm
TD
S
( m
g/
L )
pH
Tota
l alk
ali
nit
y a
s
mg
Ca
CO
3/
L
Tota
l h
ard
nes
s as
mg
Ca
CO
3/
L
Ca
(m
g /
L)
Mg
(m
g /
L)
Na
(m
g /
L)
K
(mg
/ L
)
Fe
(mg
/ L
)
NO
3
(mg
/ L
)
Cl
(m
g /
L)
F (
mg
/ L
)
SO
4
(mg
/ L
)
PO
4
(mg
/ L
)
S37 1 1639 1147 8.22 360 412 87.6 48.7 188.4 26.6 0 30 188 0 226 0S38 1 875 613 7.56 156 220 50.2 32.4 104.1 14.2 0 18 160 0 79 0
S39 1 774 542 8.28 148 196 48.3 24.6 82.1 11.3 0 13 124 0 66 0
S40 1 1024 717 7.56 196 248 58.6 37.5 112.3 17 0 20 172 0.4 100 0
S41 0 710 497 7.83 136 176 42.1 21 83.4 11 0 12 124 0.2 56 0
S42 2 1138 797 8.41 176 280 62.1 39.4 148.3 18.3 0.2 23 204 0.6 122 0.1S43 1 1654 1158 7.51 320 436 89.6 50 194.2 23.8 0 29 188 0.8 226 0
S44 1 1572 1100 7.59 236 400 91 57 211 27.8 0 30 292 0 183 0
S45 76 1416 991 8.69 216 384 93.7 51.7 171.1 25.7 0 26 252 0.4 154 0.1
S46 2 816 571 7.42 164 212 47.3 30.6 83.5 13.9 0 17 128 0.6 72 0S47 1 720 504 7.73 148 184 44.5 22.4 77.8 11.2 0.1 12 116 0 60 0
S48 2 2700 1890 8.08 468 796 189 115.8 288 45.6 0.1 51 416 0 338 0
S49 2 675 473 8.65 124 192 45.3 23 82.8 10.9 0 12 128 1 52 0
S50 60 588 412 8.49 96 168 38.8 25.6 69.1 10.9 0.2 13 100 0.6 74 0.1
S51 1 1132 792 7.94 212 324 76 41.3 134 17.9 0 20 192 0 116 0S52 0 2640 1848 8.49 364 856 238 145.4 244.1 49.1 0 50 492 0 335 0
S53 1 473 331 8.16 76 152 43.2 21 46.2 7.7 0 8 80 0 58 0
S54 4 362 253 7.45 56 116 24.7 17 32 5.7 0.6 9 44 0 42 0.5
S55 7 416 291 8.15 68 132 37.2 17.5 40.2 7.5 0 6 84 0 29 0
S56 0 463 324 7.67 76 148 35.1 23.4 43.8 8.8 0 10 72 0 57 0
169
Table 5.8 (Continued)
Sam
ple
ID
Tu
rbid
ity
( N
TU
)
EC
(
µm
ho
/cm
TD
S
( m
g/
L )
pH
Tota
l alk
ali
nit
y
as
mg
Ca
CO
3/
L
Tota
l h
ard
nes
s as
mg
Ca
CO
3/
L
Ca
(m
g /
L)
Mg
(m
g /
L)
Na
(m
g /
L)
K
(mg
/ L
)
Fe
(mg
/ L
)
NO
3
(mg
/ L
)
Cl
(m
g /
L)
F (
mg
/ L
)
SO
4
(mg
/ L
)
PO
4
(mg
/ L
)
S57 1 1026 718 7.89 164 328 85.3 46.4 110.3 19.8 0.5 18 172 0 137
S58 1 482 337 7.69 72 156 35.2 23.4 40.4 9.5 0 11 60 0 60
S59 10 360 252 8.12 56 112 30.5 13.7 35.8 7.1 0 5 56 0 43 0
S60 1 610 427 7.45 100 184 65.5 42.8 7.8 12.1 0 12 92 0 79 0
S61 1 3680 2576 8.41 612 1112 253.6 147.8 404.7 67.4 0 68 494 0.6 522 0
S62 0 923 646 7.23 140 280 66.2 42.1 97.4 18.3 0 19 168 0.4 88 0
S63 40 365 256 8.12 52 112 32.2 14.5 36.5 7.5 0 5 64 0 41 0
S64 1 1894 1326 8.02 284 572 135.4 83.6 223.3 36 0 36 340 0.6 226 0
S65 1 2600 1820 7.73 352 788 218.3 125.7 276.9 54.3 0 48 504 0.6 324 0
S66 1 606 424 8.47 92 180 42.4 27.8 59.2 12.3 0 13 92 0 74 0
S67 1 2640 1848 7.92 400 784 198.3 114.2 266.4 55.8 0.1 47 392 0 366 0
S68 1 606 424 7.72 96 136 30.3 20.5 78.2 11.8 0 12 104 0.4 74 0.1
S69 2 2450 1715 8.41 340 560 142.3 80.7 327.4 49.4 0 45 460 0 305 0
S70 1 852 596 7.92 128 196 42.3 27.5 112.5 15.8 0 18 136 0 112 0
S71 1 670 469 8.65 100 152 37.7 18.3 80.8 13.5 0 12 124 0.6 51 0
S72 2 1017 712 8.22 152 228 49.1 31.6 128.4 20.1 0 20 176 0.4 102 0
S73 1 480 336 7.73 72 108 28.5 12.7 60.8 13.8 0 8 96 0.4 41 0
170
Table 5.9 Water quality test results of postmonsoon samples
Sam
ple
ID
Tu
rbid
ity
( N
TU
)
EC
(
µm
ho
/cm
TD
S
( m
g/
L )
pH
Tota
l alk
ali
nit
y a
s
mg
Ca
CO
3/
L
Tota
l h
ard
nes
s as
mg
Ca
CO
3/
L
Ca
(m
g /
L)
Mg
(m
g /
L)
Na
(m
g /
L)
K
(mg
/ L
)
Fe
(mg
/ L
)
NO
3
(mg
/ L
)
Cl
(m
g /
L)
F (
mg
/ L
)
SO
4
(mg
/ L
)
PO
4
(mg
/ L
)
S1 0 1931 1352 7.62 216 316 71 33 272 27.6 0 24 256 0 283 0
S2 4 1029 720 7.9 172 228 54 20 126 10.4 0.5 15 164 1 67 0
S3 1 4370 3059 7.78 516 736 255.3 112 392 64 0 49 836 0 274 0
S4 0 2120 1484 7.63 432 492 109 51 196 18 0 26 276 0 167 0
S5 0 1017 712 8.3 180 252 58 20 116 6.3 0 15 121 0 74 0.5
S6 0 735 515 8.1 156 164 48 13 84 15 0 13 132 0.6 46 0
S7 7 2890 2023 8 392 656 159 81 296 84.7 0.5 34 548 1.2 167 0
S8 0 3720 2604 7.72 476 712 180 98 420 36.3 0 41 716 0.8 256 0
S9 0 3280 2296 7.73 424 684 164 79 356 76.1 0 39 496 0 326 0
S10 0 1801 1261 8.4 312 372 87 39 190 15.2 0 23 236 0.4 153 0.3
S11 0 1638 1147 7.73 272 336 82 40 174 47.9 0 22 248 1 173 0
S12 4 1215 851 8.1 296 312 62 26 132 6.1 0.2 17 124 1.4 75 0
S13 1 6810 4767 7.87 696 828 123 78 900 270 0.1 73 1316 1.2 474 0
S14 0 2115 1960 7.7 452 330 67 36 256 132 0 42 372 0.4 273 0
S15 0 2750 1925 7.78 468 584 131 59 316 24.8 0 33 392 0.6 228 0.7
S16 3 3430 2401 8.24 484 680 162 75 384 69.6 0 40 416 1 456 0
S17 0 3970 2779 8.1 552 732 160 70.5 528 30 0 45 536 0 517 0
S18 0 3240 2268 7.93 472 652 149 64 435 46.3 0 37 428 0.6 447 0
171
Table 5.9 (Continued)
Sam
ple
ID
Tu
rbid
ity
( N
TU
)
EC
(
µm
ho
/cm
TD
S
( m
g/
L )
pH
Tota
l alk
ali
nit
y
as
mg
Ca
CO
3/
L
Tota
l h
ard
nes
s
as
mg
Ca
CO
3/
L
Ca
(m
g /
L)
Mg
(m
g /
L)
Na
(m
g /
L)
K
(mg
/ L
)
Fe
(mg
/ L
)
NO
3
(mg
/ L
)
Cl
(m
g /
L)
F (
mg
/ L
)
SO
4
(mg
/ L
)
PO
4
(mg
/ L
)
S19 1 2850 1995 7.75 456 644 153 70 292 28 0 32 412 0.4 242 0
S20 0 1480 1036 8.25 348 362 68 35 130 20 0 20 168 0 72 0
S21 0 2790 1953 7.93 452 628 134 70 264 56 0 30 348 0.8 314 0.67
S22 1 2560 1792 7.88 416 556 151 69 268 99.6 0.1 31 416 0.6 332 0
S23 0 1276 893 8.08 164 192 52 13 184 15.6 0 18 216 0 116 0
S24 0 1045 732 7.95 152 184 45 16 156 15..5 0 15 200 0.4 83 0
S25 6 2960 2072 7.91 468 636 159 62 312 50.7 0.3 35 332 0.4 369 0
S26 2 4440 3108 8.2 664 864 189.6 85 544 63 0.1 69 756 0.2 336 0
S27 1 3130 2191 7.72 476 692 139.5 67 425 9.9 0 36 456 0.8 274 0
S28 5 2960 2072 8.12 456 632 146.8 68.2 324 52.2 0.2 35 392 0.8 316 0
S29 1 3140 2198 8.03 512 660 154.8 71.7 328 54.3 0.2 31 480 1 223 0.3
S30 6 4320 3024 8.13 652 708 168.8 79.2 330 164 0.2 48 632 1 352 0
S31 2 1061 743 7.73 148 236 67.3 19 116 23 0.1 16 164 1 92 0
S32 0 3200 2240 7.75 492 684 165.7 77.5 332 68.3 0 37 516 0.8 236 0
S33 2 1375 963 7.69 228 312 78.4 29.5 150 23.2 0.1 19 196 0.6 123 0
S34 2 1965 1376 8.39 332 432 111 37.3 216 30.1 0.1 25 236 0.6 224 0
S35 60 3240 2268 7.45 676 652 143.6 67.9 356 37.4 1.8 37 436 1 264 0
S36 2 3780 2646 7.73 712 728 168 63.5 415 53.2 0.2 42 512 0.4 316 0
S37 1 3030 2121 7.46 536 676 153.6 60.3 405 23.6 0.1 34 424 0.2 328 0
172
Table 5.9 (Continued)
Sam
ple
ID
Tu
rbid
ity
( N
TU
)
EC
(
µm
ho
/cm
TD
S
( m
g/
L )
pH
Tota
l alk
ali
nit
y
as
mg
Ca
CO
3/
L
Tota
l h
ard
nes
s
as
mg
Ca
CO
3/
L
Ca
(m
g /
L)
Mg
(m
g /
L)
Na
(m
g /
L)
K
(mg
/ L
)
Fe
(mg
/ L
)
NO
3
(mg
/ L
)
Cl
(m
g /
L)
F (
mg
/ L
)
SO
4
(mg
/ L
)
PO
4
(mg
/ L
)
S38 1 1460 1022 7.83 192 264 66.8 21.3 198 17 0 20 220 0.4 152 0
S39 1 1041 729 8.49 132 164 37 13.9 152 7.2 0 15 176 0.4 81 0
S40 1 1323 926 7.72 168 332 77.9 32.9 172 19.2 0 18 228 0.6 114 0
S41 1 1092 764 7.93 204 296 71.7 37 112 31.4 0 16 136 0.6 172 0
S42 1 1874 1312 7.89 356 452 107.9 41.2 196 19.7 0.1 24 192 1 217 0
S43 13 2820 1974 7.67 416 660 147 70 284 36 0 32 416 1 270 0
S44 4 2640 1848 7.63 452 592 134 61 276 36 0.6 42 356 1 232 0
S45 5 3010 2107 7.77 516 628 142 65 316 40 0.3 35 458 0.8 174 0
S46 2 1037 726 7.62 128 192 46 18 126 16 0.1 15 136 0.8 139 0
S47 0 1005 704 8.13 116 176 46.3 17.2 120 26.4 0 14 176 0.4 82 0
S48 1 3740 2618 8.45 440 816 205.1 92.6 415 97.5 0.1 40 652 0.4 324 0.28
S49 1 1191 834 8.08 196 156 28.6 13.1 188 18.6 0 17 172 1.4 94 0
S50 18 890 623 8.03 152 128 24.5 9.8 136 22.9 0.3 14 136 1 52 0
S51 1 1895 1327 7.78 264 412 105.9 41.7 236 50.7 0.2 24 392 0.8 114 0
S52 2 2780 1946 8.04 444 536 112.9 53.6 344 21 0.1 30 362 0.6 287 0
S53 20 579 405 8.2 84 120 31.7 11.6 64 12.2 0.2 11 84 0.2 57 0.8
S54 30 467 327 8.28 72 112 31.2 9.3 49 9.2 1.3 10 76 0.2 28 0.6
S55 16 538 377 8.07 80 92 27.5 4.7 68 5 0.1 11 84 0.2 35 0.5
S56 18 577 404 8.48 92 84 16.4 7.8 87 11.8 0.2 12 92 0 38 0.7
173
Table 5.9 (Continued)
Sam
ple
ID
Tu
rbid
ity
( N
TU
)
EC
(
µm
ho
/cm
TD
S
( m
g/
L )
pH
Tota
l alk
ali
nit
y a
s
mg
Ca
CO
3/
L
Tota
l h
ard
nes
s as
mg
Ca
CO
3/
L
Ca
(m
g /
L)
Mg
(m
g /
L)
Na
(m
g /
L)
K
(mg
/ L
)
Fe
(mg
/ L
)
NO
3
(mg
/ L
)
Cl
(m
g /
L)
F (
mg
/ L
)
SO
4
(mg
/ L
)
PO
4
(mg
/ L
)
S57 42 1469 1028 7.98 152 216 47.5 24.8 196 31.2 1.4 20 232 0.6 165 0
S58 12 555 389 7.95 80 88 19.2 8.2 74 1.7 0 12 84 0.2 37 0.4
S59 20 486 340 7.73 64 76 16 5.9 79 11.8 0.1 10 80 0.2 35 0.3
S60 2 840 588 7.65 132 156 34 12.7 94 19.7 0.1 14 120 0.6 67 0
S61 6 5800 4060 7.72 684 852 163.5 78.3 800 164.7 0.1 64 1164 1 416 0
S62 1 1280 896 7.85 156 176 39 17.5 196 18.4 0.1 18 228 1 129 0.5
S63 0 460 322 8.35 72 88 18.2 7.8 66 1 0 10 72 0.2 29 0.4
S64 8 2950 2065 8.03 532 616 127.8 67.3 316 31.3 0.1 35 236 1 432 0
S65 7 3300 2310 8.27 564 732 162 79 348 44 0 39 436 1 367 0
S66 1 765 536 8.83 92 100 30 6 99 26 0.1 13 112 0.6 86 0
S67 5 3470 2429 8.13 528 760 168 82 388 48 0.1 40 664 1 312 0
S68 0 745 526 8.4 84 96 26 8 116 16 0 12 96 0.8 127 0
S69 3 3000 2100 8.51 468 728 190.7 84 328 89.7 0 34 436 0.4 432 0
S70 0 1143 800 7.85 156 212 55.4 21.7 138 31.4 0 16 136 0.8 192 0.4
S71 0 700 490 8.7 92 104 31.1 8.6 94 18.5 0 12 116 1 416 0
S72 8 3060 2142 8.4 436 628 163.6 74.9 356 104.9 0.1 34 516 1 129 0
S73 0 599 419 8.58 76 92 23.9 9.8 79 17.8 0 11 104 0.2 29 0
174
5.12 RESULTS AND DISCUSSION
The discussion on results of various studies to evaluate the quality
of groundwater for drinking and irrigation purposes and to study the
controlling mechanism of groundwater hydrochemistry is presented here.
5.12.1 Quality of groundwater for drinking purpose
The quality of groundwater samples are estimated for both physical
and chemical parameters based on IS 10500:1991. The water quality
parameters of premonsoon and postmonsoon groundwater samples are
presented here for a comparative analysis. It is found that the water quality
parameters vary between the seasons. The extent of these seasonal variations
of the water quality parameters are explained separately.
5.12.1.1 Turbidity
In some of the samples, the values of turbidity are higher in
postmonsoon season and lower in premonsoon season and vice versa. 21
samples have shown higher turbidity values during postmonsoon season and
lower during premonsoon season. 14 samples have shown turbidity values
higher in premonsoon season and lower in postmonsoon season.
Figure 5.69 Turbidity values during premonsoon and postmonsoon seasons
175
But 6 samples contain turbidity value above the desirable limit and
beyond the permissible limit in both the seasons. The values of turbidity for
both the seasons are shown in Figure 5.69.
5.12.1.2 pH
Invariably all the samples of the study area contain pH value 6.5
during both the seasons. 30 numbers of samples have shown higher pH values
during postmonsoon season and lower during premonsoon season. 43
numbers of samples have shown higher pH values during premonsoon season
and lower during postmonsoon season. But 3 numbers of samples contain pH
value above 8.5 in both the seasons. The values of pH for both the seasons
with the desirable and permissible limits are shown in Figure 5.70.
Figure 5.70 pH values during premonsoon and postmonsoon seasons
5.12.1.3 Total hardness
44 samples have shown high TH values during postmonsoon season
and low during premonsoon season. 29 samples have shown high TH values
during premonsoon season and low during postmonsoon season. But 12
samples contain TH value beyond permissible limit in both the seasons. The
values of TH for both the seasons with desirable and permissible limits are
shown in Figure 5.71. None of the water samples collected in the study area is
classified as soft water or moderately hard during both seasons.
176
Figure 5.71 TH values during premonsoon and postmonsoon seasons
5.12.1.4 Iron
All the samples of study area are safe against iron content. 31
samples have shown higher iron values during postmonsoon season and lower
during premonsoon season. 7 samples have shown higher iron values during
premonsoon season and lower during postmonsoon season. But 35 samples
contain nil or very low value of iron content in both the seasons. The values
of iron for both the seasons with desirable and permissible limits are shown in
Figure 5.72.
Figure 5.72 Iron values during premonsoon and postmonsoon seasons
5.12.1.5 Chloride
61 samples have shown higher chloride values during postmonsoon
season and lower value during premonsoon season. 9 samples have shown
higher chloride values during premonsoon season and lower value during
177
postmonsoon season. 3 samples have no change in their chloride content
during both the seasons. But 2 samples contain chloride value above
permissible limit only in postmonsoon season. The values of chloride for both
the seasons with desirable and permissible limits are shown in Figure 5.73.
Figure 5.73 Chloride values during premonsoon and postmonsoon
seasons
5.12.1.6 Total dissolved solids
6 samples have shown higher TDS values during postmonsoon
season and lower value during premonsoon season. These 6 samples have
TDS content above the permissible limit during premonsoon season also. No
samples have shown higher TDS values during premonsoon season and lower
value during postmonsoon season. But 20 samples contain TDS value above
the permissible limit only in postmonsoon season. The values of TDS for both
the seasons with desirable and permissible limits are shown in Figure 5.74.
Figure 5.74 TDS values during premonsoon and postmonsoon seasons
178
5.12.1.7 Calcium
45 samples have shown higher calcium values during postmonsoon
season and lower values during premonsoon season. 28 samples have shown
higher calcium values during premonsoon seaon and lower value during
postmonsoon season. But only one sample contains calcium value above the
permissible limit in post and premonsoon seasons. The values of calcium for
both the seasons with desirable and permissible limits are shown in Figure 5.75.
Figure 5.75 Calcium values during premonsoon and postmonsoon
seasons
5.12.1.8 Sulphate
45 samples have shown higher sulphate values during postmonsoon
season and lower value during premonsoon season. 27 samples have shown
higher sulphate values during premonsoon season and lower value during
Figure 5.76 Sulphate values during premonsoon and postmonsoon seasons
179
postmonsoon season. But 3 samples contain high sulphate value in both
premonsooon and postmonsoon seasons. The values of sulphate for both the
seasons with desirable and permissible limits are shown in Figure 5.76.
5.12.1.9 Nitrate
None of the samples of the study area contain nitrate content above
the permissible limit. 49 samples have shown higher nitrate values during
postmonsoon season and lower value during premonsoon season. 20 samples
have shown higher nitrate values during premonsoon season and lower value
during postmonsoon season. But 4 samples contain same nitrate value in both
postmonsoon and premonsoon seasons. The values of nitrate for both the
seasons with desirable and permissible limits are shown in Figure 5.77.
Figure 5.77 Nitrate values during premonsoon and postmonsoon seasons
5.12.1.10 Total alkalinity
56 samples have shown higher values of total alkalinity during
postmonsoon season and lower values of total alkalinity during premonsoon
season. 16 samples have shown higher total alkalinity values during
premonsoon season and lower total alkalinity values during postmonsoon
season. But 2 samples contain same total alkalinity value in post and
premonsoon seasons. The values of total alkalinity for both the seasons with
desirable and permissible limits are shown in Figure 5.78.
180
Figure 5.78 TA values during premonsoon and postmonsoon seasons
5.12.1.11 Fluoride
57 samples have shown higher fluoride values during postmonsoon
season and lower value during premonsoon season. 2 samples have shown
higher fluoride values during premonsoon season and lower value during
postmonsoon season. But 14 samples contain same fluoride value in post and
premonsoon seasons. The values of fluoride for both the seasons with
desirable and permissible limits are shown in Figure 5.79.
Figure 5.79 Total Fluoride during premonsoon and postmonsoon
seasons
181
5.12.2 Suitability of groundwater quality parameters for drinking
purpose
The suitability of groundwater during premonsoon and
postmonsoon seasons for drinking purpose with respect to IS 10500:1991 are
summarized here. The water quality parameters show lower values in their
concentration during premonsoon samples when compared with their values
during postmonsoon samples. The higher rate of dissolution due to rainfall
during the month of July (premonsoon season) can be taken into consideration
for the lower content of water quality parameters in groundwater samples of
premonsoon season.
The value of turbidity is high in more number of premonsoon
samples than in postmonsoon samples. The higher rate of dissolution due to
rainfall during the month of July (premonsoon) is the one of the reasons for
the presence of insoluble sediments in groundwater which has risen the value
of turbidity in premonsoon samples.
The increase in pH of premonsoon samples can be reasoned out
with the following fact. The temperature during premonsoon season (July) is
lower than the temperature during postmonsoon season (March), this change
in temperature can be taken into account for the imbalance in carbon dioxide-
carbonate-bicarbonate equilibrium and it would influence pH value of the
groundwater. No relaxation is permitted in pH value of drinking water.
Higher pH will impart bitter/ soda taste to drinking water. The groundwater
samples with higher pH may be treated by the addition of white vinegar or
citric acid (IS: 10500 1991). pH values of 3 groundwater samples are above
the permissible limit during both premonsoon and postmonsoon seasons. The
groundwater from these sample locations may be used after the treatment
suggested by IS: 10500.
182
TH values of 39.7 % of postmonsoon samples and 19.17 % of
premonsoon samples are above the permissible limits.TH values of 16.44%
samples remain high during both the seasons. The groundwater of theses
sample locations will cause scales in utensils and poor lather with soaps. This
shows the presence of dissolved calcium or magnesium from soil and aquifers
minerals containing limestone or dolomites. The groundwater of these sample
locations may be treated with water softener or ion exchanger or reverses
osmosis (IS: 10500 1991).
Iron content in 3 samples of postmonsoon season are high above
the permissible limits. But none of the samples during premosoon season has
iron content above permissible limits. The higher rate of dissolution due to
rainfall during the month of July (premonsoon) is considered here as the cause
for the reduction in iron concentrations of premosnoon samples. Higher
concentrations of iron will impart metallic taste and brackish colour to the
groundwater. Leaching of cast iron pipes in water distribution system is the
one of the major source for iron in drinking water. Oxidizing filters and green
sand mechanical filters may be used to reduce iron concentrations in
groundwater (IS: 10500 1991). This technique may be used at these 3 sample
locations during postmosnoon season if the groundwater used for drinking
purpose is objectionable due to accumulation of iron concentrations.
Chloride content in 2 samples of postmonsoon season are high
above the permissible limits. But none of the samples during premosoon
season has chloride content above permissible limits. The higher rate of
dissolution due to rainfall during the month of July (premonsoon) is
considered here as the cause for the reduction in chloride concentrations of
premosnoon samples. Higher concentrations of chloride in groundwater will
impart salty taste and it will bring high blood pressure to the users. Fertilizers,
industrial wastes and minerals in aquifer are the major sources for chloride in
183
ground water. Reverse osmosis, distillation and activated carbon methods
may be adopted to reduce chloride concentrations in groundwater (IS: 10500
1991). This technique may be used at these 2 sample locations during
postmosnoon season if the groundwater used for drinking purpose is
objectionable due to accumulation of chloride concentrations.
TDS values of 26 postmonsoon samples and 6 premonsoon samples
are above the permissible limits. Groundwater with high TDS concentrations
will have sediments, cloudy colour and hardness. Also, groundwater with
high TDS will have salty or bitter taste. The sources for high TDS content are
the presence of livestock wastes, septic system wastes, landfills and dissolved
minerals from soil and aquifers. TDS values of 6 samples remain high during
both the seasons. The groundwater of these sample locations may be treated
with reverses osmosis, distillation and deionization by ion exchanger
processes (IS: 10500 1991).
Calcium content in 5 samples of premonsoon season and 2 samples
of postmosoon season are high above the permissible limits. Carbonates and
sulphates of calcium are abundantly present in most of the rocks and its
solubility is found in all groundwater. Dissolution of calcium carbonate
continues as long as the quantity of percolating water is high (Karnath 2001).
The higher rate of dissolution due to rainfall during the month of July
(premonsoon) is considered here as the reason for the presence of higher
calcium content in 5 premonsoon samples. Higher concentrations of calcium
in groundwater will impart poor lathering and deterioration of the quality of
clothes. Incrustation of pipes and scale formation will be seen in water supply
system. Calcium values of 1 sample remain high during both the seasons. The
groundwater of this sample location may be treated with water softener ion
exchanger or reverses osmosis during premonsoon season to reduce the
effects of higher calcium content (IS: 10500 1991).
184
Sulphate values of 7 postmonsoon samples 4 of premonsoon
samples are above the permissible limits. Groundwater with high sulphate
concentrations will have bitter medicinal taste, scaly deposits. Also,
groundwater with high sulphate will have laxative effects. The sources for
high sulphate content are the presence of animal sewage, septic systems,
sewages, industrial wastes and natural deposits or salts. Sulphate values of 3
samples remain high during both the seasons. The groundwater of these
sample locations may be treated with reverses osmosis, distillation and by ion
exchanger processes (IS: 10500 1991).
TA values of 6 premonsoon samples and 2 postmonsoon samples
are above the permissible limits. Alkalinity influences the pH value of the
water. TA values of 2 samples remain high during both the seasons. The
groundwater from these locations contain may be treated with proper
neutralizing agent (IS: 10500 1991) before use.
Nitrate and Flouride contents in all 73 samples are within
permissible limits during both premonsoon and postmonsoon seasons. The
groundwater quality assessment of the study area and the representing
samples which exceed the concentration limits are summarized in Table 5.10.
Table 5.10 Suitability assessment of groundwater
No of samples exceeding the
permissible limitS.
No
Water quality
ParametersPremonsoon Postmonsoon
Representing samples
exceeding
the permissible limits
during both the seasons.
1 Turbidity 12 10 S25,S30,S45,S50,S55,S59
2 pH 7 3 S66,S69,S71
3 TH 14 29S3,S8,S13,S16,S18,S26,S28,
S29,S48,S61,S65,S67
4 Iron Nil 3 Nil
5 Chloride Nil 2 Nil
6 TDS 6 26 S3,S8,S13,S18,S26,S61
7 Calcium 5 2 S3
8 Sulphate 4 7 S13,S18,S61
9 Nitrate Nil Nil Nil
10 TA 6 2 S13,S61
11 Fluoride Nil Nil Nil
185
The samples S3, S8, S13, S18, S26 and S61 contain high
concentrations in more number of chemical parameters during both
premonsoon and postmonsoon seasons. Hence, the groundwaters from these
locations are to be used after proper treatment. However, the samples which
are turbid may be used for drinking purpose after filtering or boiling.
5.12.3 Quality of groundwater for irrigation purpose
The quality of the groundwater for irrigation purpose is analyzed
and assessed by evaluating the chances of irrigation hazards. The
classification of groundwater of the study area for irrigation purpose during
premonsoon and postmonsoon season are carried out in this work. The
irrigation hazard is evaluated separately as salinity hazard and sodium hazard.
5.12.3.1 Salinity hazard
The presence of high salts in irrigation water will produce salinity
hazard. It is evaluated with the help of TDS content in irrigation water. The
TDS content in premonsoon and postmonsoon groundwater samples are
present here to assess salinity hazard.
Figure 5.80 TDS values of all samples for irrigation use during
premonsoon and postmonsoon seasons
186
26 numbers of samples contain TDS value above the permissible limit
in postmonsoon season and 6 numbers of samples contain higher values of TDS in
premonsoon season. 20 numbers of samples become fit during premonsoon season
while they are unfit during postmonsoon season. 8 numbers of samples contain
TDS value less than 450 mg/L during postmonsoon season but this number has
increased to 14 in premonsoon season due to dissolution after rainfall. 39 samples
contain TDS value within desirable to permissible limit during postmonsoon
season and this number has increased to 53 during premonsoon season. The values
of TDS content in all the sample locations during premonsoon and postmonsoon
seasons are shown in Figure 5.80.
5.12.3.2 Sodium hazard
Irrigation water containing large amounts of sodium is dangerous to
soil and it leads to a situation called as sodium hazard. Continued use of water
having high sodium leads to a breakdown in the physical structure of the soil.
Sodium is adsorbed and becomes attached to soil particles. The soil becomes
hard and compact when dry and increasingly impervious to water penetration.
Fine textured soils, especially those high in clay, are most subject to this action.
The values of SAR, RSC, SSP and ESP will help to assess the sodium
accumulation in soil due to irrigation water. The values of theses indices of
premonsoon and postmonsoon groundwater samples are tabulated in Table 5.11.
Influences for salinity are found more in postmonsoon samples than
in premonsoon samples. Indices of sodium accumulations reveal that sodium
accumulation rates remain almost same during both the seasons. The
influences of salinity hazard and sodium hazard are less in premonsoon
season. And hence, the sensitive and susceptible crops are less prone to the
effects of groundwater used for irrigation in premonsoon season than in
postmonsoon season.
187
Table 5.11 The values of indices of sodium accumulation
Indice
sRange Effects
No of
premonsoo
n samples
No of
postmonsoo
n samples
0-10 Excellent for irrigation use 72 71
10-18 Good for irrigation use 1 2
18-26 Fair for irrigation use 0 0SAR
> 26 Poor for irrigation use 0 0
<1.25 epmWater is safe for irrigation
use.72 73
1.25-2.5
epm
Water is of marginal quality
for irrigation use.0 0RSC
>2.5 epm Water is unsuitable for
irrigation use
1 0
< 60 % Safe against sodium
accumulations63 54
SSP
>60 % Not safe against sodium
accumulations
10 19
,< 50% Exchangeable calcium and
magnesium will not take up
sodium for exchange
16 16
ESP
> 50 % Exchangeable calcium and
magnesium will take up
sodium for exchange
57 57
USSL classifications, Doneen classifications and Wilcox
classifications of irrigation water during premonsoon season and
postmonsoon season are summarized in Table 5.12, Table 5.13 and Table
5.14 respectively.About 98 % of the groundwater samples of the study are of
good to moderate in quality for irrigation purposes during both the seasons as
per USSL classification. Groundwater quality for irrigation is good during
premonsoon season when compared with post-monsoon season as per
Wilcox’s classifications. Doneen’s permeability indices reveal that the
probable long time effect of groundwater used for irrigation purposes are
not significant as most of the groundwater samples are of class I and class II
during both the seasons.
188
Table 5.12 Classification of groundwater samples based on USSL
diagram
Classification
Suitability
for
irrigation
No of samples
during premonsoon
season
No of samples
during postmonsoon
season
C2-S1 Good 23 21
C3-S1 Good 21 20
C3-S2 Moderate 15 16
C4-S2 Moderate 13 15
C5-S4 Bad 1 1
Table 5.13 Groundwater classes for irrigation use according to Doneen
diagram
Water ClassNo of samples
during premonsoon season
No of samples
during postmonsoon
season
Class 1 23 21
Class 2 49 43
Class 3 1 9
Table 5.14 Groundwater classes for irrigation use according to Wilcox
diagram
Water Class No of samples
during premonsoon
season
No of samples
during postmonsoon
season
Very Good to Good 33 10
Good to permissible 22 12
Permissible to Doubtful 5 15
Doubtful to Unsuitable 8 13
189
USSL classification is carried out with the help of both salinity and
sodium hazards. And hence, USSL classification is considered as more
important than any other classifications. In general, the groundwater quality
for irrigation use during premonsoon season (July) is better than during
postmonsoon season (March) in the study area.
5.12.4 Controlling mechanism of hydro chemistry
The phenomenon which alters the groundwater chemistry during
traverse through the substratum can be studied from hydrochemical facies
with the help of Piper’s diagram. The dominant mechanism which plays role
in altering the groundwater chemistry can be studied graphically with the help
of Gibb’s plot. The observations made using these two studies are present
here to understand the controlling mechanisms of premosoon and
postmonsoon groundwater samples of the study area.
5.12.4.1 Hydrochemical facies
There exists a significant change in the hydro-chemical facies in the
groundwater samples during the study period of premonsoon and
postmonsoon seasons. The premonsoon season of the syudy period was July
2007. The predominant hydrochemical facies of this season was of the type
“No specific cation-anion pair”. This is represented by 58.9 % of the total
samples. The other hydro chemical facies present during premonsoon season
was of the type “Primary salinity”. This is represented by 38.4 % of the total
samples. 2.7 % of the remaining samples exhibit facies of “Hardness types”.
The postmonsoon season of the study period was March 2007. The
predominant hydrochemical facies of this season was found to be “Primary
salinity”. This facies is found in 89.04% of the total samples. The other
hydrochemical facies is of the type “No specific cation-anion pair”. This is
represented by 10.6 % of the total samples. The comparative status of
hydrochemical facies of premonsoon and postmonsoon seasons is
summarized in Table 5.15.
190
Table 5.15 Hydrochemical facies (Piper’s diagram)
S.NoHydro Chemical
Facies
No of premonsoon
samples
No of postmonsoon
Samples
1 Primary Hardness 1 0
2 Secondary Hardness 1 0
3 Primary salinity 28 65
4 Primary alkalinity 0 0
5 No specific cation-
anion pair
43 8
The results observed from hydrochemical facies show that the
presence of primary salinity is decreased to 28 number of premonsoon
samples from 65 number of samples of postmonsoon samples. At the same
time, the hydrochemical facies of type “No specific cation-anion pair” is
found more in premonsoon season than in postmonsoon season. This shows
that the presence of combined concentrations is more during premonsoon
season. The dissolution of minerals in percolating water may be considered as
one of the reasons for these wide variations in hydrochemical facies of the
groundwater samples between these two seasons. It can also be interpreted
from the results that the groundwater is passing through soluble rocks and the
rock dominance is the controlling groundwater chemistry in the study area.
5.12.4.2 Gibb’s ratio
The cross plots between TDS and Gibb’s ratios I and II are
separately used here to evaluate the contributions of atmospheric
precipitation, rock weathering, and evaporation in anions and cations of
premonsoon and postmonsoon groundwater samples. The mechanisms which
dominate the water chemical composition of premonsoon and postmonsoon
samples are summarized in Table 5.16.
191
Table 5.16 Mechanisms controlling the groundwater chemistry
(Gibb’s diagram)
No of premonsoon
samples
No of postmonsoon
samples
Mechanism
controlling
groundwater
chemistryAnions Cations Anions Cations
Rock dominance 56 50 39 31
Evaporation
dominance
14 15 31 34
Precipitation
dominance
0 0 0 0
Earth’s surface
influence
3 8 3 8
From the results obtained, it is found that the rock dominance is
predominant controlling mechanism of anions and cations of grooundwater in
premonsoon samples. The infiltrations are high during premonsoon season (July).
These higher infiltrations have diluted the TDS content of premonsoon samples
and the effects of salt concentrations in groundwater are also reduced.
From Gibb’s diagram, the controlling mechanism of cations of
groundwater during postmonsoon season is evaporation dominance and the
controlling mechanism of anions of groundwater is rock dominance. Since the
temperature in postmoonsoon season (March) is higher than the premonsoon
season (July), the rate of evaporation is also high during postmosnoon season.
From these analyses, it may be interpretated that the higher values of TDS
concentrations in postmonsoon samples are due to the influences of
evaporation. The earth surface influence is also found in the mechanisms
controlling the groundwater chemistry of anions in 3 different samples and of
cations in 8 different samples during both the seasons.
192
5.12.5 Hydro meteorology
The rainfall and groundwater level are considered here as a major
hydro meteorological parameter to study the groundwater quality. The annual
rainfall data and groundwater level for one decade from 1998 to 2007 are taken
here to understand the rainfall and groundwater level variations in this period.
5.12.5.1 Rainfall
The rainfall was low in the year 2002 when compared with the other
years of the period considered. The rainfall in the year 2005 was high during
this decade. The rainfall hydrograph for this period is shown in Figure 5.81.
(Source: State Groundwater and Surface Water Resources Data Centre, Chennai)
Figure 5.81 Rainfall hydrograph
5.12.5.2 Water level
The well hydrograph from 16 observation wells for the period from
1998 to 2007 is presented in Figure 5.82. The groundwater level from the year
1998 to 2002 was not varying in noticeable difference. The groundwater level
during the year 2004 was very low when compared with the other years of the
period.
193
(Source: State Groundwater and Surface Water Resources Data Centre, Chennai)
Figure 5.82 Well hydrograph
From the rainfall and groundwater level study, it is understood that
the groundwater level in the year 2004 has gone lower due to very poor
rainfall during the year 2002. The groundwater level started rising after the
good rainfall in the year 2005. This shows the recharge potential of the study
area is good. The depletion in groundwater level in the year 2004 was due to
the poor rainfall.
5.12.5.3 Rainfall and TDS content in premonsoon and postmonsoon
seasons
The variations in TDS content at the sample locations with the
rainfall are presented here to discuss the influence of rainfall in the dissolution
of TDS content in the groundwaters of the study area. The total rainfall from
premonsoon season of the year 2006 (July) to premonsoon season of the year
(July) 2007 is considered here to estimate the seasonal variations in TDS
content between the seasons of the year 2007. The chart showing the
194
variations in rainfall at the sample locations during premonsoon and
postmonsoon seasons is given in Figure 5.83
Figure 5.83 Rainfall at sample locations during premonsoon and
postmonsoon season of the year 2007
The rainfall during premonsoon season (July) in all sample
locations were higher than the rainfall during postmonsoon(March) season of
the year 2007. The higher rate of rainfall during premonsooon season may be
taken as the cause for better groundwater quality during premonsoon season
than the groundwater quality during postmonsoon season. The influence of
rainfall on the groundwater quality can further be discuused with the values of
TDS content and rainfall. The values of rainfall and TDS at the rain gauge
stations are taken for the comparison here. The values are summarized in
Table 5.17.
195
Table 5.17 TDS and rainfall during premonsoon and postmonsoon
seasons
Premonsoon (July 07) Postmonsoon (March 07)Rain Gauge
Stations Rainfall
mm
TDS
mg/L
Rainfall
mm
TDS
mg/L
Mohanur 659 1292 560 1484
Senthamangalam 939 1279 723 2296
Namakkal 686 760 609 1925
Paramathi 512 2184 431 2268
Rasipuram 802 727 644 1376
Belukurichi 601 1147 551 2121
Komarapalayam 690 1326 562 2065
Tiruchengode 580 469 434 490
At rain gauge station Mohanur, the rainfall in March 07 was 560
mm and it was increased to 659 mm in July 07. The increased rainfall has
made TDS to decrease from 1484 mg/L in March 07 to 1292 mg/L in July 07.
At the rain gauge station Senthamangalam, the rainfall in March 07 was 723
mm and it was increased to 939 mm in July 07. The TDS content was
decreased from 2296 mg/L in March 07 to 1279 mg/L in July 07. At rain
gauge station Namakkal, the rainfall in March 07 was 609 mm and it was
increased to 686 mm in July 07. The TDS content was decreased from 1925
mg/L in March 07 to 760 mg/L in July 07. At rain gauge station Paramathi,
the rainfall in March 07 was 431 mm and it was increased to 512 mm in July
07. The TDS content was decreased from 2268 mg/L in March 07 to 2184
mg/L in July 07.
At rain gauge station Rasipuram, the rainfall in March o7 was 644
mm and it was increased to 803 mm in July 07. The TDS content was
196
decreased from 1376 mg/L in March 07 to 727 mg/L in July o7. At rain gauge
station Belukurichi, the rainfall in March o7 was 551 mm and it was increased
to 601 mm in July 07. The TDS content was decreased from 2121 mg/L in
March 07 to 1147 mg/L in July 07. At rain gauge station Komarapalayam, the
rainfall in March o7 was 562 mm and it was increased to 690 mm in July 07.
The TDS content was decreased from 2065 mg/L in March 07 to 1326 mg/L
in July 07. At rain gauge station Tiruchengode, the rainfall in March 07 was
434 mm and it was increased to 580 mm in July 07. The TDS content was
decreased from 490 mg/L in March 07 to 469 mg/L in July 07.
The variation of TDS values with rainfall for premonsoon and
postmonsoon seasons is shown in Figure 5.84 for the selected rain gauge
stations of the study area. The changes in TDS content with repect to the
changes in rainfall at the raingauge stations are shown here in bar chart for
better visualization of the changes. The same pattern changes are found in all
stations. From this, it is understood that the higher rainfall reduces the TDS
content in groundwater.
Figure 5.84 Variations in TDS content and rainfall during
premonsoon and postmonsoon season the year 2007