Graphical Presentation and Classification for assessment of Groundwater Quality

presented by

Ravi Kiran JP Email : kiran.ravi382@gmail.com

Department of Environmental Science & Engineering

Indian School of Mines(ISM), Dhanbad Jharkhand- 826004

Source of this Paper:

Study on spatial distribution of geochemical characteristics in Groundwater of North Bengal using GIS and its evaluation using statistical and graphical techniques under NIH ROORKEE in association with MINISTRY OF WATER RESOURCES INDIA.

SR kumar, Scientist H, NIH Roorkee.

Assisted by Anshul Jain & Prashanth.

Ground Water

Water present in the subsurface environment of earth is called Groundwater, an important component of water resource systems.

Groundwater is the largest reservoir of fresh water that is readily available to humans( 90% of Earth’s fresh water).

Extracted from aquifers through pumping wells and supplied for domestic use, industry and agriculture.With increased withdrawal of groundwater, the quality of groundwater has been continuously deteriorating.

Groundwater as an integral part of Hydrological Cycle

Ground Water Quality Significance

Helps us understand the hydro-geologic system.

Indicates comingling of groundwater and surface water.

Helps us interpret groundwater flow dynamics

Delineates groundwater contamination.

Ground Water contamination

Sources of GW Pollution

Effects of Ground water Pollution

Ground water contaminated with bacteria, chemicals, pesticides, gasoline or oil can result in various human health problems, Ecological Imbalance etc.

It costs far less to prevent contamination than to clean up.

One Example: Landfill Effects

• Waste acts as rectors to form Toxic Products• These landfills also breeds harmful insects and organisms• Spreads contagious diseases• Ultimately Groundwater pollution

Groundwater resources Management by Water Classification

How?

Compare ions with ions using chemical equivalence

Making sure anions and cations balance

Use of diagrams and models.

Ground Water resourcesManagement by Water Classification

Why?

Helps define origin of the water

Indicates residence time in the aquifer

Aids in defining the hydrogeology

Defines suitability

Graphical Classification

Presentation of chemical analysis in graphical form makes understanding of complex groundwater system simpler and quicker.

The chemical parameters of groundwater play a significant role in classifying and assessing water quality.

The hydro chemical study reveals quality of water that is suitable for drinking, agriculture and industrial purposes

Contd..

Tables showing results of analyses of chemical quality of ground water may be difficult to interpret, particularly where more than a few analyses are involved.

To overcome this, graphical representations are useful for display purpose, for comparing analyses, and for emphasizing similarities and differences.

Graphical classifications can also aid in detecting the mixing of water of different compositions and in identifying chemical processes occurring as ground water moves (Todd, 1980).

Graphical Presentation and classification for assessment of GW Quality

Stiff DiagramStiff diagrams are graphical representation of water chemical analyses, first developed by H.A. Stiff in 1951.

A polygonal shape is created from three or four parallel horizontal axes extending on either side of a vertical zero axis. Cations are plotted in milliequivalents per liter on the left side of the zero axis, one to each horizontal axis, and anions are plotted on the right side.

Stiff patterns are useful in making a rapid visual comparison between water from different sources.

Stiff Diagram

Stiff Diagram –sample

Na

Ca

Mg SO4

HCO3

Cl

0

Typical Sample Diagram

ADVANTAGES

• Can help visualize ionically related waters from which a flow path can be determined, or;

• If the flow path is known, to show how the ionic composition of a water body changes over space and/or time.

DISADVANTAGE• Only one analysis per plot.

Horsetooth Dam, Colorado-Big Thompson Project, Ft. Collins, Colorado

Piper Trilinear Diagram

A piper diagram is a graphical representation of the chemistry of a water sample or samples.

The cations and anions are shown by separate ternary plots.

The apexes of the cation plot are calcium, magnesium and sodium plus potassium cations. The apexes of the anion plot are sulfate, chloride and carbonate plus bicarbonate anions.

The two ternary plots are then projected up onto a diamond. The diamond is a matrix transformation of a graph of the anions and cations

Figure: Classification of hydrochemical facies using the Piper plot.

In Piper diagrams the concentrations are expressed as %meq/L.

% meq/l

A- Calcium type B- No Dominant typeC- Magnesium type D- Sodium and potassium typeE- Bicarbonate type F- Sulphate typeG- Chloride typeSubdivision of the diamond Characteristics of corresponding subdivisions of diamond-shaped fields1-Alkaline earth (Ca2++Mg2+) exceeds alkalies (Na++K+).2- Alkalies exceed alkaline earths.3- Weak acids (CO2-

3+HCO-3) exceed Strong acids (SO2-

4+Cl-).4- Strong acids exceed weak acids. 5- Magnesium bicarbonate type.6- Calcium-chloride type. 7- Sodium-chloride type. 8- Sodium-Bicarbonate type. 9- Mixed type (No cation-anion exceeds 50%).

ADVANTAGES• Many water analyses can be plotted on the same diagram.• Can be used to classify waters by hydrochemical facies.• Can be used to identify mixing of waters.

• Can track changes through space and temporal

relationships.

DISADVANTAGES• Concentrations are renormalized. • Cannot easily accommodate waters where other cations or

anions may be significant

Plotting a Piper Diagram

Cations Anions

GroundwaterFacies

Ca

Mg

Na + K HCO3 + CO3 Cl

SO4C

a + MgS

O4 +

Cl

HC

O3 +

CO

3

Na + K

Plotting a Piper DiagramC

alci

um-M

agne

sium

Sodi

um-P

otas

sium

Chloride-Sulphate

Bicarbonate

Bicarbonate-C

hloride-Sulphate

Chloride-Sulpahte-B

icarbonateC

alci

um-S

odiu

mSo

dium

-Cal

cium

Cations Anions

Plotting on a Piper Diagram

Ca

Mg

Na + K HCO3 + CO3 Cl

SO4C

a + Mg

SO4 +

Cl

HC

O3 +

CO

3

Na + K

Classification

Ca

Mg

Na + K HCO3 + CO3 Cl

SO4

Ca + M

g

SO4 +

Cl

HC

O3 +

CO

3

Na + K

Grouping of waters on the Piper Diagramsuggests a commoncomposition and origin.

Red: Ca-Mg-SO4

Yellow: Ca-Mg-Na-Cl-SO4

APPLICATION

Schoeller Diagram

A Schoeller Diagram is a semi-logarithmic diagram of the concentrations of the main ionic constituents in water (SO4, HCO3, Cl, Mg, Ca, Na/K) in equivalents per million per kg of solution (mEq/kg).

• Concentrations of each ion in each sample are represented by points on six equally spaced lines and points are connected by a line.

• The diagram gives absolute concentration, but the line also gives the ratio between two ions in the same sample.

Schoeller Diagram

Key note:

Because of logarithmic scale, if a straight line joining the two points of two ions in one water sample is parallel to another straight line joining the other two points of the same two ions in another water sample, the ratio of the ions in both analyses is equal.

Studies that use Schoeller Diagram

cations anions

[sem

i-log

arit

hmic

axi

s]

Durov’s Double Triangular DiagramDescription/ Type of data : a composite plot consisting of 2 ternary diagrams where the cations of interest are plotted against the anions of interest (data is normalized to 100%); sides form a binary plot of total cation vs. total anion concentrations (this plot can be contoured); expanded version includes TDS (mg/L) and pH data added to the sides of the binary plot to allow further

comparisons. • Primary: Cations (i.e. Na + K, Ca and Mg) and Anions

(i.e. Cl, HCO3 and SO4), and total cations vs. total anions only.

• Expanded: TDS and pH added

Applications

To graphically illustrate cation/anion concentrations, relative to TDS and pH.

For example, using samples IC and AAS data, we can plot the ion concentrations, then calculate the TDS from our specific conductivity field measurements, and use the pH field measurements. Because we sampled at several locations (i.e. causeway, pond, etc.), we can use those as data groups to see if there are any spatial variations in water chemistry , and if so, could they be related to a different TDS content, different pH, or both

The intersection of lines extended from the two sample points on the triangle to the central rectangle gives a point that represents the major-ion compositions on a percentage basis. From this point, lines extending to the adjacent scaled rectangles provide for representations of the analyses in terms of two parameters selected from various possibilities, such as total major-ion concentrations, total dissolved solids, ionic strength, specific conductance, hardness, total dissolved inorganic carbon,

or pH.

Durov SA, 1948, Natural waters and graphic representation of their composition

Collins bar Diagram

Display of concentrations (not ratios) for individual samples

But as it is a cumulative chart the values are not readily apparent

Total height ~ reflects TDS

Easier to compare samples than pie charts

Collin bar Diagram

Collin Bar Diagram

These are vertical bar diagrams. Each sample is represented by two bars, one for cations and other for anions. The height of each bar is proportional to the total concentration of cations or anions in meql-1.

The concentration of cations and anions can be plotted either in absolute values or as the percentage of total epm.

The Collin’s bar chart was used to show the concentration of various major ions of the analyzed samples.

The cations are represented as Ca2+, Mg2+, Na+, K+, and the anions as Cl-, SO4

2- and CO32-, HCO3

2- .

Gibb’s DiagramMany aspects of the over all mechanism are still poorly understood of Ground water. Therefore, Gibb's suggested a graphical diagram to understand the water chemistry relationship of the chemical components of the water from the respective aquifers, such as chemistry of the rock types, chemistry of the precipitated water and rate of evaporation.

Based on Gibbs variation (ratio – I) i. e. anions dominant and Gibbs variation (ratio – II) i. e. cation dominant nature, the groundwater samples of the area are plotted separately against respective values to know the nature of the groundwater chemistry of the area .

Gibb’s Diagram

Gibb’s Diagram

The Gibbs plot depicted that the chemistry of waters were modified by chemical weathering piloted by precipitation as the major factor controlling the chemistry of the sub-surface waters

It illustrates the three major mechanisms that regulate the chemistry of the world's water:

(1) Evapo-concentration

(2) selective mineral precipitation

(3) rainfall of variable composition

Stuyfzand Classification

A new hydrochemical classification of water types.

This subdivides the most important chemical water characteristics at 4 levels. The primary type is determined based on the chloride content (Table I).

The type is determined on the basis of an index for hardness (Table II). The classification into subtypes is determined based on the dominant cations and anions.

Finally, the class is determined on the basis of the sum of Na, K and Mg in meq/l, corrected for a sea salt contribution.

Primary Classification (Table I)

Fresh water Class Code Chloride (mg/L)

Very oligohaline G <5

Oligohaline G 5-30

Fresh F F 30-150

Fresh-brackish f 150-300

Brackish B 300-1000

Brackish-salt b 1000 – 10,000

Index of Hardness (Table II)Hardness Code Hardness (Ca+Mg)

meq/L

Very soft * 0-0.5Soft 0 0.5-1.0Moderately Hard 1 1-2Hard 2 2-4Very Hard 3 4-8Extremely Hard 4 8-16Extremely Hard 5 16-32Extremely Hard 6 32-64Extremely Hard 7 64-128Extremely Hard 8 128-256Extremely Hard 9 >256

Conclusion

It provides a quick processing and interpretation of a lot of complete water analysis and a short, concise presentation of the results in graphical form makes understanding of complex. groundwater system simpler and quicker.

This study illustrated the usefulness of multivariate statistical techniques in the water quality assessment and identification of pollution sources.

Accuracy assessment of the classification process using different classification algorithms is always recommended for the assessment of Ground water quality.

A graphical classification approach by using geochemical analysis of the ground water in order to estimate potential quality of the groundwater resources.

Conclusion