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GEOLOGY

Paper: Hydrogeology and Engineering Geology

Module: Assessment of groundwater quality

Subject Geology

Paper No and Title Hydrogeology and Engineering Geology

Module No and Title Assessment of groundwater quality

Module Tag HG & EG VII

Principal Investigator Co-Principal Investigator Co-Principal Investigator

Prof. Talat Ahmad

Vice-Chancellor

Jamia Millia Islamia

Delhi

Prof. Devesh K Sinha

Department of Geology

University of Delhi

Delhi

Prof. P.P. Chakraborty


University of Delhi

Delhi

Paper Coordinator Content Writer Reviewer

Dr. Shashank Shekhar


University of Delhi

Delhi

Dr. Shashank Shekhar


University of Delhi

Delhi

Dr. S. P. Rai (Scientist F)

National Institute of

Hydrogeology (NIH)

Roorkee

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Table of Content

1. Learning outcomes

2. Introduction

3. Groundwater Quality

4. Groundwater Contamination and Pollution

5. Measurement and reporting of water quality parameters

5.1. Organoleptic and Physical Parameters

5.2. Chemical Parameters

5.3. Radioactive Substances

5.4. Bacteriological Parameters

6. Quality criteria for portable water

7. Quality criteria for irrigation water

7.1. Salinity

7.2. Sodium Adsorption Ratio (SAR)

7.3. Specific ion toxicity

8. Graphical representation of groundwater chemical quality

data

8.1. Trilinear Diagram (Hill-Piper plot)

8.2. Durov’s Diagram

8.3. C-S Diagram

9. Summary

10. Acknowledgement

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1. Learning outcomes

After studying this module, you shall be able to:

Understand groundwater water quality concept.

Appreciate the concept of groundwater contamination and pollution.

Get familiar with the way water quality parameters are measured and

reported.

Get familiar with quality criteria for portable and irrigation water.

Learn about the way chemical groundwater quality data is graphically

represented

2. Introduction

The groundwater all over the world has emerged as a potential source for domestic

and irrigation purposes. In this case, it becomes important to assess the quality of

groundwater before assigning it for domestic or irrigation purposes. We must realize

that the natural groundwater without any anthropogenic influences and will also

have a baseline concentrating of different dissolved solutes. These solutes are

primarily introduced in to the groundwater system by the process of sediment-

groundwater interaction. This natural groundwater quality varies from place to place

depending upon nature of soil, nature of subsurface lithology, climatic conditions

etc. The dissolved solids in groundwater can be divided in major ions, minor

constituents and trace elements. In general, the major ions of groundwater include

sodium, potassium, calcium, magnesium cations and bicarbonate, carbonate,

chloride and sulphate anions. The minor constituents include small amount of

dissolved solids like iron, manganese, fluoride etc. Besides many elements of the

periodic table are present in very small concentration in the groundwater and they

are referred to as trace elements. Further, at some places we can also find organic

compound in groundwater.

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3. Groundwater Quality

When we talk of groundwater chemistry it includes all the dissolved solids in the

groundwater system; popularly referred to as the total dissolved solids (TDS),

including organic compound and trace elements. While groundwater quality is much

more than groundwater chemistry which mainly includes chemical constituents of

groundwater. It also includes biotic constituents of groundwater like bacteria,

physical parameters like color, turbidity, odor etc. The issue here is which

parameters define groundwater quality and what is the standard for these parameters.

There is no universal definition. We must understand that water quality is defined in

perspective of its desired use. Thus, the water quality desired for drinking purpose

will need to be assessed for a set of parameters in comparison to the agreed standard

norm. Similarly, the water quality desired for irrigation purpose will need to be

assessed for a different set of parameters in comparison to the agreed standard norm

for irrigation water. Holistically we can assess the water quality in terms of physical,

chemical and bacteriological parameters for different uses.

4. Groundwater Contamination and Pollution

At this stage, it is desired that we understand the term ‘groundwater contamination

and pollution’. They are very often used synonymously. Many a times groundwater

contamination is referred to geogenic source while pollution is exclusively assigned

to anthropogenic source. In literary perspective the word ‘contaminate’ means

making something dirty or impure by adding a substance that may be dangerous,

while the word ‘pollute’ means “adding dirty or harmful substance to land, air,

water etc. so that it is no longer pleasant or safe to use” (Oxford dictionary 8th

edition). It emerges out from here that loosely these two term terms can be used as

synonyms. Since literary meaning of pollution also emphasizes on the fact that

during pollution the addition of harmful substance to water, air etc. makes it no

longer safe. Therefore, if we want to be more specific we can say that groundwater

contamination can be from both natural (geogenic) or human induced

(anthropogenic) sources. While groundwater pollution is a stage when groundwater

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contamination has crossed the safe limits of the desired use. Since historically most

of the groundwater pollution was attributed to human activity, in due course of time

the use of groundwater pollution was generally restricted to human induced activity

leading to occurrence of certain parameters beyond safe limits of the desired use.

We must also be very clear here that a groundwater, which is polluted for drinking

purposes with respect to certain parameters, might be only contaminated for

irrigation uses. Technically the sediment groundwater interaction leading to

dissolution of solids and its addition to groundwater below desirable limits for

drinking purposes is also an act of groundwater contamination.

5. Measurement and reporting of water quality parameters

The water quality parameters are estimated following the standard protocols

formulated by Bureau of Indian Standards (BIS) in India. The analysis is finally

reported by laboratory in unit as given below.

5.1 Organoleptic and Physical Parameters

Colour: Reported in Hazen Unit. Hazen unit basically quantifies colour

to a numeric value, which is then used for comparison.

Odour: It is sensed physically and should be agreeable to a normal

human being.

Taste: Again, it is sensed physically and should be agreeable to a normal

human being.

Turbidity: Reported in Nephelometric Turbidity Unit (NTU). NTU is

basically quantification of scattered light at 90 degree from the incident

light beam.

pH: It is measure of negative logarithm to base 10 of the hydrogen ion

concentration in moles per liter. It is used for expressing acidity or

alkalinity of the solution.

5.2 Chemical Parameters

The chemical parameters are mostly reported from a laboratory in term of mg/liter.

For pesticides and some trace elements, it can also be represented as micro

gram/liter. The interrelationship amongst different units of measurements is:

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Milligram per liter (mg/l) ≃ parts per million (ppm) (Ayers & Westcot 1985)

Mill equivalent per liter (me/l) = mg/l ÷ equivalent weight (Ayers & Westcot 1985)

Where Equivalent weight = Formulae weight ÷ charge (after Todd 1980)

5.3 Radioactive Substances

The parameter used for quantifying the concentration of radioactive substances

in water is Becquerel/liter (Bq/l). Becquerel quantified radioactivity of a

substance.

5.4 Bacteriological Parameters

The bacteriological parameters with regards to BIS drinking water standards

specifies that the organism shall not be detectable in any 100 ml sample.

6. Quality criteria for portable water

Since water is a basic necessity for life, the quality criteria for drinking and

irrigation uses has been adopted at various institutional levels. The World Health

Organization (WHO) prepares a detailed guideline for drinking water quality. The

acceptable standards vis-à-vis microbial aspects, chemical aspects, physical aspects

like taste, appearance, odour and radiological aspects have been formulated. A

detailed look can be had at weblink:

http://www.who.int/water_sanitation_health/publications/gdwq4-with-add1-chapters/en/

(accessed 12-07-2017). It is not desired to memorize all of them but one should be

aware about availability of the list of standards and they can be referred on the basis

of requirement. On account of socio-economic and geologic variations across the

world, each country has suitably modified the WHO standards and adopted local

standards. In context of India, the Bureau of Indian standards has prepared a detailed

guideline giving specifications for drinking water. The guideline is exhaustive and

has detailed specifications for organoleptic and physical parameters; chemical

parameters and bacteriological parameters. The specification booklet by Bureau of

Indian standard is available from their office on payment basis. Some government

organization has one or other version of the specification on their website (For e.g.

http://www.who.int/water_sanitation_health/publications/gdwq4-with-add1-chapters/en/

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http://cgwb.gov.in/Documents/WQ-Standards.pdf (accessed 11-07-2017). It

becomes important to study theses parameters as their occurrence in drinking water

beyond permissible limits has serious and damaging effect on human health. Here as

an example we show with help of Fig.1 the damages a polluted groundwater with

respect to certain parameters causes on human health.

Fig.1 A schematic drawing to show the effect of polluted drinking water on human

body (Source: http://www.neerwater.com/images/men.jpg, accessed 11-07-2017).

http://cgwb.gov.in/Documents/WQ-Standards.pdf

http://www.neerwater.com/images/men.jpg

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7. Quality criteria for irrigation water

Plants are sensitive to the water quality used for irrigation; the crop yield depends on

the type of water used for irrigation purpose. The main parameters identified for

assessing water quality for irrigation purposes (Ayers & Westcot 1985) are: Salinity;

Sodium Adsorption Ratio (SAR) and specific ion toxicity (Sodium, chloride,

Boron). These parameters are briefly discussed below:

7.1. Salinity: Very high salinity in irrigation water adversely affects plant

growth. The salinity of water is measured by total dissolved solids,

generally expressed as mg/l. The total dissolved solids in water control the

electrical conductivity of water. Now a days hand held devices are available

for estimation of the electrical conductivity of the water. Todd (1980)

elucidates and approximates Logan (1961) and Richard’s (1954)

relationship between TDS and electrical conductivity. It mentions that for

water having electrical conductivity in the range of 100 to 5000 micro

Siemens/cm the relationship is:

1 mg/l = 1.56 micro Siemens/cm

Since measurement of electrical conductivity is quite easy, most of the time

the water quality consideration with respect to salinity is discussed in terms

of electrical conductivity. Different agencies and workers have discussed in

detail about tolerance of crops vis-à-vis salinity of irrigation water. However,

the most holistic consideration with regards to suitability of irrigation water

can be taken when salinity is examined vis-à-vis Sodium Adsorption Ratio

(SAR). This can be easily done using C-S diagram. The detailed discussion

on Sodium Adsorption Ratio and C-S diagram follows further in text.

7.2. Sodium Adsorption Ratio (SAR): The sodium content relative to calcium

and magnesium content of the irrigation water controls the rate of

infiltration of water to the root zone of crops (Ayers & Westcot 1985). It has

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also been elucidated further by Todd (1980) that the soil permeability gets

reduced by reaction of sodium with the soil.

SAR = Na

√Ca+Mg/2 (Ayers & Westcot 1985)

It is to note here that all the cationic concentrations are in meq/liter.

7.3. Specific ion toxicity: In this category, we have toxicity primarily by

chloride, sodium and boron ions. What happens that circumstantially if the

concentration of these ions crosses the critical limit of the crop, the yield

reduces drastically? The water needs to be assessed vis –a – vis tolerance of

specific crops with regards to concentration of these ions in irrigation water.

8. Graphical representation of groundwater chemical quality data

Graphical representation of groundwater chemical quality data:

The chemical quality of groundwater is appreciated better by graphical

representation. In the very beginning, we must understand that mostly in graphical

representation the major ion concentration (that is Na, K, Mg, Ca, CO3, HCO3, SO4,

Cl) is used. Further, while plotting these concentrations are mostly in milli

equivalents per liter (meq/liter). The graphical representation of groundwater quality

data started by using bar graphs, circular diagram etc. However, limitation of these

plotting were that they could not represent substantial number of analysis for one

synoptic view. Piper (1944) improved upon Hill (1940) to produce trilinear diagram

for representation of major ion chemistry of groundwater. A similar plot with more

flexibility was proposed by S.A Durov and reported by Zaporozec (1972). Besides

Richards (1954) proposed a diagram for classification of irrigation water. The

diagram has Electrical conductivity on x-axis and SAR on y-axis and thus it is also

referred to as C-S diagram. Below we will briefly discuss about the important

graphical plots mentioned above.

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8.1. Trilinear Diagram (Hill-Piper plot): This is one of the most useful

diagrams for graphical representation of groundwater quality data (Fig.2). It

has unique advantage that large number of data can be plotted on a single

diagram. It also helps in ascertaining hydrochemical facies of groundwater.

The hydrochemical facies refers to a cation and anion concentration within a

distinct zone (Back 1961, Freeze and Cherry 1979). Prior to plotting a data,

the concentration of major ions is converted in terms of meq/l. Then the

cations are tabulated as percentage of total cations and similarly the anions

are tabulated as percentage of total anions. The percentage value of each

cation is plotted on the cation triangle on the left and percentage value of

each anion is plotted on the anion triangle on the right (Fig.2). The data

from cation and anion triangles are projected to the central diamond shaped

area as shown by dotted lines. In this way, huge number of data can be

plotted and the hydrochemical facies variation can be identified.

Fig. 2 Trilinear diagram for representation of major ion chemistry of

groundwater (After Piper 1944)

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8.2. Durov’s Diagram: The diagram proposed by Durov (Fig.3) has again two

cation and anion triangles, and in place of central diamond, area there is a

square. Like in a Trilinear plot here again major cations and anions are

converted in terms of meq/l and then percentage of each action with respect

to total cation and percentage of each anion with respect to total anion is

tabulated. These percentage values of the cations and anions are then plotted

in their respective triangles. Further, these plots can be projected to central

square area as shown by blue line in Fig.3. In extended Durov’s diagram the

square can be extrapolated blow and to its right for plotting two more

additional parameters.

Fig. 3 A prototype of Durov’s diagram (after Zaprorozec 1972).

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8.3. C-S Diagram: The C-S diagram (Fig.4) is used for classification of

irrigation water. Here on logarithmic x-axis, we plot electrical conductivity

in terms of micro Siemens/cm and on arithmetic y-axis, we plot SAR. The

x-axis helps in assessing salinity hazard and the y-axis helps in assessing

sodium hazard. The whole plot area is divided in to low, medium, high and

very high category with respect to sodium and salinity hazard. The location

of the sample on plot helps in assessing suitability of water for irrigation

purpose. In general, as we move towards higher values of sodium or salinity

hazard, the unsuitability of irrigation water increases.

Fig. 4 C-S diagram for classification of irrigation water (after Richards 1954).

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9. Summary

Groundwater quality encompasses groundwater chemistry, biotic

constituents of groundwater like bacteria, physical parameters like colour,

turbidity, odour etc.

The water quality is defined in perspective of its desired use like drinking or

irrigation.

Groundwater contamination is any addition to groundwater system either

from natural (geogenic) or human induced (anthropogenic) sources. While

groundwater pollution is a stage when groundwater contamination has

crossed the safe limits of the desired use.

Water quality parameters are estimated following the standard protocols

formulated by Bureau of Indian Standards (BIS) in India and similarly in

other parts of the world.

The different water quality parameters have defined units of reporting. Like

Hazen unit for colour, milli and micro gram per liter for chemical

constituents and Becquerel/liter for radioactive substances.

Pollution of drinking water adversely affects human body and its part.

The quality criteria of irrigation water mainly involves assessment of

salinity, sodium adsorption ratio and specific ion toxicity.

For holistic assessment of groundwater quality data graphical plots like

Trilinear diagram, Durov’s diagram and C-S diagram can be used.

The C-S diagram is specifically designed for assessment of irrigation water

quality data.

10. Acknowledgements

The content of the module is individual intellectual propriety of the content writer. It

is likely to be used in future for textbook etc. on the topic by the content writer

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Multiple Choice Questions-

1. C-S diagram is used for classification of

(a) Irrigation water

(b) Drinking water

(c) Industrial water

(d) None of the above

Ans: a

2. C-S plot is a semi logarithmic plot where

(a) X-axis is logarithmic

(b) Y-axis is arithmetic

(c) Both a and b


Ans: c

3. A C4-S4 category of water indicating very high salinity and Sodium Adsorption

Ratio is

(a) Good for irrigation uses

(b) Bad for irrigation uses

(c) Both a and b


Ans: b

4. While plotting data in Durov’s diagram the percentage of cations is estimated by

(a) Dividing the particular cation concentration with summation of all cation

concentration in meq/l

(b) Dividing the particular cation concentration with summation of all ions


(c) Dividing values in meq/l with equivalent weigh


Ans: a

5. While plotting data in Durov’s diagram the percentage of anions is estimated by

(a) Dividing the particular anion concentration with summation of both

cation and anion concentration in meq/l

(b) Dividing the particular anion concentration with summation of all ions


(c) Dividing values in meq/l with equivalent weigh


Ans: d

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6. Trilinear diagram has an advantage that

(a) A large number of data can be plotted

(b) The hydrochemical facies can be visually distinguished on the plot

(c) Both a and b

(d) None of the above.

Ans: c

7. On a Trilinear plot the hydrochemical facies refers to

(a) A cation and anion concentration within a distinct zone

(b) Trace element concentration within a distinct zone

(c) Pesticide concentration within a distinct zone

(d) Partial pressure of carbon dioxide

Ans: a

8. The formulae for Sodium Adsorption Ratio (SAR) is

(a) SAR = Na/K

√Ca+Mg/2

(b) SAR = Ca+Mg

√Na/2

(c) SAR = Na

√Ca+Mg/2

(d) SAR = Na

√Na+Ca+Mg/2

Ans: c

9. Soil permeability

(a) Gets enhanced by reaction of sodium with the soil

(b) Gets neutralized by reaction of sodium with the soil

(c) Gets extremely enhanced by reaction of sodium with the soil

(d) Gets reduced by reaction of sodium with the soil

Ans: d

10. Mostly specific ion toxicity in irrigation water relates to

(a) Toxicity by chloride, sodium and boron ions

(b) Toxicity by Sodium, Potassium and calcium ions

(c) Toxicity by Magnesium, Calcium and Potassium ions


Ans: a

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11. The concentration of radioactive substances in water is measured in terms of

(a) Milligram/liter (Mg/l)

(b) Becquerel/liter (Bq/l)

(c) Miliequivalence/liter (Meq/l)


Ans: b

12. The total dissolved solids can also be estimated

(a) By measuring only Sodium ion concentration in water

(b) By measuring only total anion concentrations in water

(c) By measuring trace element concentration in water

(d) By measuring electrical conductivity of the water

Ans: d

13. Unit Milligram per liter (mg/l) is approximately equal to

(a) Unit parts per billion (ppb)

(b) Unit parts per million (ppm)

(c) Unit Milli equivalent per liter (me/l)


Ans: b

14. We can estimate Milli equivalent per liter by dividing Milligram per liter with

(a) Total charge of the ions

(b) Total Formulae weigh only

(c) Cationic concentration only

(d) Equivalent weigh

Ans: d

15. We can estimate equivalent weigh by

(a) Dividing formulae weight with charge

(b) Dividing charge with formulae weigh

(c) Dividing charge with ion weigh


Ans: a

16. The measurement of turbidity is reported in

(a) Halophytic Turbidity Unit (HTU)

(b) Phreatophytic Turbidity Unit (PTU)

(c) Xerophytic Turbidity Unit (XTU)

(d) Nephelometric Turbidity Unit (NTU)

Ans: d

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17. The measurement of colour is reported in

(a) Hazen Unit

(b) Flozen Unit

(c) Trojan Unit

(d) Grazen Unit

Ans: a

18. Groundwater pollution is a stage when groundwater contamination has

(a) Started from anthropogenic sources

(b) Crossed the safe limits of the desired use

(c) Started from geogenic source


Ans: b

19. Technically the sediment groundwater interaction leading to dissolution of solids

and its addition to groundwater below desirable limits for drinking purposes is

(a) In no way groundwater contamination

(b) Always an act of pollution

(c) Also an act of groundwater contamination with respect to drinking use


Ans: c

20. The major ions of groundwater necessarily includes all of these

(a) Sodium, Potassium, Barium, Helium, Bicarbonate, Borates, Chloride

and Arsenic anions

(b) Strontium, Beryllium, Calcium, Magnesium, Phosphate, Carbonate,

Chloride and Nitrate anions

(c) Sodium, Aluminum, Iron, Magnesium, Rubidium, Fluoride, Chloride

and Sulphate anions


Ans: d

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Suggested Readings:

1. Todd, David Keith and Mays, Larry W., (2011), Groundwater Hydrology, 3rd

Edn., Wiley India Pvt. Ltd., New Delhi.

2. Ayres, R. S. and Westcot, D. W. (1985), Water quality for agriculture. FAO

Irrigation and Drainage Paper 29 Rev. 1. Food and Agricultural

Organization, Rome, 1, p.74.

3. Back, William (1961). Techniques for mapping of hydrochemical facies. US

Geol Surv Prof Pap, 424, 380-382.

4. Freeze, R. A., & Cherry, J. A. (1979). Groundwater (p. 604), 1st Edn., New

Jersey: Prentice Hall Inc. Englewood cliffs.

5. Hill, R. A. (1940). Geochemical patterns in Coachella valley. Eos,

Transactions American Geophysical Union, 21(1), 46-53.

6. Logan, J. (1961). Estimation of electrical conductivity from chemical analyses

of natural waters. Journal of Geophysical Research, 66(8), 2479-2483.

7. Piper, A. M. (1944). A graphic procedure in the geochemical interpretation

of water‐analyses. Eos, Transactions American Geophysical Union, 25(6),

914-928.

8. Richards, L. A. (1969). Diagnosis and improvement of saline and alkali soils.

United States Department of Agriculture; Washington.