Final Report

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ACKNOWLEDGEMENT

We would like to convey our heartfelt gratitude to Prof. T. Kumar (Director, ISM),

Prof. B.C. Sarkar (HOD, Applied Geology), and Dr. A.K. Varma (Training In-

Charge) first of all, for the entire arrangement of the summer training program in

CMPDIL HQ, Ranchi.

We would like to take this opportunity to thank all the people involved in making

this summer training at CMPDI, Ranchi, a very fruitful assignment.

We would like to convey special thanks to Mr. S.K. Mitra [Director (T / ES)],

Mr. B. Kumar [HOD (HRD)], Mr. N. Ahmad [GM (Expl)], Mr. S.Nath [GM

(Geology)], Dr. H.K. Mishra [GM (Labs)], Mr. P. Prasad [Senior Manager

(Hydrogeology)] and Dr. R.K.Jain [GM (Geology)] of CMPDIL Head Quaters,

Ranchi, for their valuable guidance during the summer training program.

Date: 3rd

June, 2011 Poulomi Baksi

Place: Ranchi Shreyasi Das

Satavisha Ganguly

Sulekha Bhaya

Prasanta Ku. Mishra

Nikhil Marda

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INTRODUCTION

We, students of Applied Geology (M.Sc. Tech) of ISM, Dhanbad have done our summer training job at

CMPDI HQ (Central Mine Planning and Design Institute), Ranchi. The duration of this training was from

16th

May to 4th June, 2011.We are very thankful to Prof. T. Kumar (Director ISM), Prof. B.C.

Sarkar (HOD, Dept. of Applied Geology), and Dr. A.K. Varma (Training in-charge). We would like to

thank Mr. S. Nath, Mr.R.K.Jain , Mr. H.K. Mishra of CMPDIL for giving us such an opportunity and

guidance.

COAL INDIA AND ITS SUBSIDIARIES:

The mission of Coal India is to produce the planned quantity of coal which is found in Jharkhand, Bihar,

Orissa, M.P., A.P., Maharashtra, West Bengal, Assam, Sikkim states, efficiently and economically with

due regard to safety, conservation and quality. Coal India Limited has eight subsidiaries while seven of

them are engaged in coal mining operation and production of coal, CMPDI does all the prospecting,

exploration, preparation of Geological Reports, Project Reports, Mine planning and design works for all

the coal producing subsidiaries apart from many other activities.

Coal India Limited

Dankuni

Coal

Complex

(DCC)

North-Eastern

Coalfields (NEC)

0.86 b.t. 5mines

Margherita

(Assam)

Eastern

Coalfields

Ltd.

(ECL)36.63

b.t. 129

mine

Asansol

(W.B.)

Bharat Coking Coal

Ltd.(BCCL)

19.42 b.t. 92 mines

Dhanbad (Jharkhand)

Central Coalfields

Ltd.(CCL)

33.45 B.T. 54 mines

Ranchi (Jharkhand)

Northern

coalfields

Ltd.(NCL)

10.34 b.t.

10 mine

Singrauli

(UP)

South-eastern

Coalfields Ltd.

(SECL)

27.36 b.t.

73 mines

Bilaspur

(Chhatishgarh )

CMPDI

Ranchi

Mahanadi Coalfields

Ltd. (MCL) 46.22 b. t.

22 mines

Sambalpur(Orissa)

Western Coalfields

Ltd.(WCL)

8.65 B.T. 64 mines

Nagpur(Maharashtra)

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INDIAN COAL:

1. A total of 2,85,862 Millon Tonnes of geological resources of coal have so far been estimated in

India up to maximum depth of 1200m (as per GSI). Out of total resources, the Gondwana

coalfields account for 2,84,369 Mt (99.5%) while the Tertiary coalfields of North-eastern region

(Assam, Meghalaya) contribute 1493Mt (0.5%) of coal resources. The type wise and category

wise break up of Indian coal resources are given below:

Type of coal

Proved(Mt) Indicated(Mt) Inferred(Mt) Total(Mt) %Share

Prime Coking 4,614.35 698.71 0 5,313.06 1.99

Medium Coking 12,448.44 12,063.93 1,880.23 26,392.60 9.88

Semi-Coking 482.16 1,003.29 221.68 1,707.13 0.64

Non coking 87,797.69 109,614.09 35,312.63 232,724.41 87.09

Tertiary coal 477.68 89.68 506.02 1073.38 0.40

Total of all

type 1,14,001.60 1,37,471.10 34,389.51 2,85,862.21 100

2. The depth-wise and category-wise break-up of Indian coal resources is as follows:

Depth Range

(mt)

Proved (Mt) Indicated

(Mt)

Inferred(Mt) Total (Mt) %Share

0-300 89,263.57 68238.66 11756.89 169,259.12 59.21

300-600 9,349.62 55195.47 16556.53 81101.62 28.37

0-600 (jharia) 13,710.33 502.09 0.00 14,212.42 4.97

600-1200 1,678.08 13534.88 6,076.09 21289.05 7.45

Total 114001.60 137471.10 34389.51 285862.21 100.0

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Coal and its Characteristics:

Coalification

Coal is formed from plants and is a complex substance consisting of different constituents representing

several chemical compounds, is a readily combustible rock containing more than 50% by weight and

more than 70% by volume of carbonaceous material.

Peat undergoes transformation through physical and chemical changes brought about by continued

subsidence, increasing pressure and temperature leading generally to the formation of the coal series. The

coal series generally expressed as peat, lignite, sub-bituminous, bituminous and anthracite develops

mainly due to enrichment of carbon and decrease of volatile matter, decrease of moisture, increase in

calorific value and increase in reflectance of vitrinite. The moisture content however marginally decreases

in anthracite. This process of physical-chemical changes is also known as “Coalification” and indicative

of the maturity of “Rank” of coal.

Coal Constituents:

Just as a rock composed of several minerals so is the coal composed of several organic constituents

termed as mecerals, the organic equivalent of minerals. The mecerals can be divided into three groups-

Vitrinite (termed as Huminite for peat and Lignite essentially woody materials), Exinite (Liptinite derived

mainly from spores, resins and cuticles), Inertinite (derived mainly from oxidized plant materials).

Mecerals are normally intermixed and occur as groups termed as „Micro-litho type” which are mainly

four types and they are Vitrain, Durain, Clarain, Fusain.

Coking and Non-Coking Coal:

Some coals on heating suitably swell and fuse to form a hard and porous mass called Coke which can

provide concentrated heat and withstand a huge pressure. Such coals are known as coking coal which is

extensively used in metallurgical industries. Coals lacking this property are called as Non-coking coal and

used in power, railway, fertilizer and other industries.

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EXPLORATION

Coal India Ltd. has eight subsidiaries in which seven are production companies (ECL, BCCL,

CCL, WCL, SECL, NCL & MCL) and one is Mine Planning and Design company - CMPDI

(Central Mine Planning and Design Institute). Head quarter of CMPDI is situated in Ranchi and

it has seven Regional Institutes (R.I. s). The location of the Regional Institutes is RI 1 Asansol

(ECL), RI 2 Dhanbad (BCCL), RI 3 Ranchi (CCL), RI 4 Nagpur (WCL), RI 5 Bilaspur (SECL),

RI 6 Singrauli (NCL) and RI 7 Bhubaneswar (MCL).

Our summer training program was held in CMPDI HQ, Ranchi for 21 days. In CMPDI, mine

planning and design works are carried out mainly, apart from many activities related to Civil

Engineering, Electrical & Mechanical Engineering, Coal Technology & Lab, Exploration,

Geomatics, Coal Bed Methane, Finance, Information &Communication Technology, Personnel

& Administration, Town Engg. & CM Division.

GEOLOGICAL SURVEY OF INDIA (GSI) has already done the geological mapping and has

given us the Formational details of the coal bearing horizons in almost all the coalfields of India.

The investigations of GSI are a continuing process establishing the coal bearing Formations

which is still going on.

STAGES OF EXPLORATION

Preliminary Regional Detailed Developmental

Investigation Exploration Exploration Exploration

PRELIMINARY INVESTIGATION:

First of all survey work is carried out. It includes the location of the block (latitude, longitude),

i.e. the relative position of the block in the coal field is earmarked. Its location and distance with

respect to adjacent explored block and/or existing mines is determined. Accessibility, objective

of exploration, likely period of investigation, area of the block in sq.km are required to be

determined. In virgin areas, the help of satellite imagery and aerial photograph is needed. At this

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stage, 1-2 boreholes are drilled. Before proceeding for further investigation, factors considered

for the design of exploration programme are to be assessed. These factors include the geology of

the area, nature of the deposit, degree of confidence required, schedule, accessibility, inputs like

density of boreholes, diameter, target seam, depth of drilling, quantum of drilling etc., are to be

determined.

REGIONAL EXPLORATION:

In this case, the block is regionally explored. Here boreholes are drilled at 800m-1km apart.

These days, 1 km interval is chosen. Based on the data generated after drilling, litholog plotting,

sampling, construction of seam structure etc, seam correlation with the help of logs is carried out.

At this stage an idea about the presence or absence of fault, fault types, throw, lithology, number

and thickness of the seams etc are obtained.

Almost all the coalfields of India except the coalfield of Assam are suffered by normal faults.

DETAILED EXPLORATION:

Here boreholes are drilled at 400m interval which is suggested by “The Bureau of Indian

Standard” by which the influence of coal is up to 200m from the known point. This is evidenced

from the Gondwana coalfields where up to 200m from the known point, there is no significant

variation between the lithological and other characteristic features. At this stage structural

modeling is carried out. Here the reserves are accessed as Proved Reserve.

DEVELOPMENTAL EXPLORATION:

In India, this stage is followed wherever it is required. It helps in day-to-day planning and quality

control. In TISCO, this practice is followed. The main objective of this stage is to Prove Incrop,

faults and the heat affected zones, etc.

DRILLING: -. In the case of drilling, mainly diamond core drilling is used. There are two types

of drilling methods. One is by using single tube core barrel and another is by using double tube

core barrel. In coal industry mainly the use double tube core barrel is adopted. For the drilling,

mainly diamond bits and TC bits are used. During drilling operation CMPDI mainly uses NQ

core size .Sometimes they use the BQ core size as and when required due to boreholes

conditions.

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CORE RECOVERY: - For the area prescribed acceptable norm for core recovery percentage

are 90% and 70% in non coal and coal horizons respectively in general and 70% and 50% in non

coal and coal horizons of soft and friable nature especially in northeastern regions. Core recovery

in both coal and non coal cores obtained by drilling in the block satisfy this norm with some

exceptions.

RECORDING OF DRILLING DATA: - After the drilling carried out the drilling data is

recorded as follows-

For example- (Figs in metres)

From To Extrapolated

Depth

Recovery Lithology

123.00 123.40 0.40 0.20 Coal

123.40 123.70 0.30 0.25 Shaly coal

123.70 124.10 0.40 0.40 Carbshale

124.10 124.70 0.60 0.45 Coal

124.70 125.40 0.70 0.50 Sand stone

125.70 126.00 0.60 0.35 Coal

LOGGING:

The data obtained by drilling is used in plotting the lithologs using the RF of 1:500 in general.

This gives an idea about the lithotypes associated with the seam/s. After litholog plotting seam

structure is plotted in which RF of 1:50 is used in general as per detailed chemical analysis

whether it is coal, shaly coal or carbshale.

SAMPLING:

The core logs obtained by drilling are sampled and sent for band by band analysis. The coal

cores are arranged in the boxes in book pattern. Here taking into account as per the visual

logging C1, C2, C3, etc are indicated for coal and shaly coal and D1, D2, D3 etc are indicated for

carbshale. Then the borehole no. and box number are written on the box. e.g.,CMBT-167/Box

No-5 and dispatched to the respective laboratories for band by band analysis.

On obtaining the band by band analysis of the seams of the respective boreholes, seam

structure is plotted on RF 1:50 considering the ash% + Moisture % i.e., for coal (upto35%), shaly

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coal (35%-50%) and carbonaceous shale (>50% - 75%) are marked. Then making the roof-floor

corrections to eliminate unviable carbshale, the seam depths are defined. The seams defined in

this manner is subjected to overall analysis i.e., at 40 degree centigrade and 60% relative

humidity. Approximately 50% of boreholes are determined by Overall analysis. The rest 50% are

calculated by using the software CEMGEODOC produced by CMPDI. The useful heat values

thus arrived from the overall analysis data are utilized for the estimation of the grade of the

respective seams.

SEAM CORRELATION:

Correlation of seams is done with the help of lithologs. Significance of fault is of much

importance. Fault are determined by evidence in the boreholes, i.e. when some strata is missing,

brecciated strata or the presence of slickensides etc., then it is evidenced that there may be a

fault. Fault can also be determined by Inference, i.e. unusual difference in the level of roof and

floor of the seam/s on either side of the fault. The observations of some boreholes passing

through the fault and some are adjacent to it helps in „Stitching‟ the fault alignment.

Overall Advice for seams defined:

Floor contour plan is done using the FRL (Floor Reduced Level) value of the boreholes

by means of 3-point method.

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Roof Contour Plan: The same procedure is followed for Roof Contour Plan as that of

Floor Contour Plan using the RRL (Roof Reduced Level) value.

ISOCHORE MAP: - Isochore map is drawn by using the vertical thickness of the coal seam

as encountered in the borehole.

ISOPARTING MAP: - Parting is the difference between the floor of one coal seam and the

roof of another coal seam. By using the isoparting line we draw isoparting map which is mainly

used in opencast mine.

ISOEXCAVATION MAP: - This gives an indication of total coal available and total OB

presents in terms of the thickness.

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QUALITY-

Quality evaluation of coal is most important for rational utilization of this valuable commodity.

To suit the requirement of various industries, which requires a particular variety of coal, proper

characterization of coal is important before being used. Before going to further ahead in Quality it is

needed to define the calorific value and UHV (Useful Heat Value).

Calorific value-It is the heat liberated by its complete combustion with oxygen. It is expressed as Btu/lb

(British Thermal Unit/Pound) or Kcal/Kg (Kilo Calorie/Kilogram).

UHV-Useful Heat Value to grade coal, can be determined by the following formula as follow:-

[8900-138(Ash + Moisture) kcal/kg.].

CHARACTERIZATION OF COAL:-

Coal has been readily combustible rock containing more than 50% by weight and more than 70% by

volume of carbonaceous material including inherent moisture, formed from compaction and indurations

of variously altered plant material.

Difference in the kind of plant material defines Coal type. Range of impurities define Coal grade. These

are main characteristics of COAL.

CLASSIFICATION OF COAL:-Depending upon coking property coal has two classifications. One is for

coking coal and another is for non coking coal.

FOR COKING COAL:-Some coals on heating suitably swell and fuse to form a hard and porous mass

called coke which can provide concentrated heat and withstand some pressure. Such coals are called

Coking coals. It is extensively used in metallurgical industries.

GRADE ASH% SPECIFIC GRAVITY

Steel Grade I Up to 15 1.42

Steel Grade II 15-18 1.44

Washery Grade I 18-21 1.46

Washery Grade II 21-24 1.50

Washery Grade III 24-28 1.53

Washery Grade IV 28-35 1.58

Inferior >35 1.65

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FOR NON-COKING COAL:-Coal lacking the properties of coking coal is non-coking coal. Its

classification is as follows.

ASH%+MOISTURE% GRADE UHV

SP.GRAVITY

(K.Cal/Kg)

< 20 A >6200 1.40

20-24 B >5600-6200 1.45

24-29 C >4940-5600 1.50

29-34 D >4200-4940 1.55

34-40 E >3360-4200 1.58

40-47 F >2400-3360 1.68

47-55 G >1300-2400 1.75

>=55 UNGRADED <1300

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PROXIMATE ANALYSIS

By proximate analysis the moisture (water content), ash (mineral content), volatile matter (Gaseous

components) are determined in the laboratory as weight percentage. Hundred minus the sum total of these

gives the fixed carbon. It reflects the utilization potential.

FC = 100 – (Moisture + Ash + Volatile Matter)

ULTIMATE ANALYSIS

It consists of the determination of the percentage of elements (viz; carbon, nitrogen, sulphur and oxygen)

present in coal by weight.

SPECIAL TESTs

FOR COKING COAL=>

a) Caking Index= Inert Material/ (Unit weight of coal in a mixture totaling 25 grams which on

carbonization gives a coherent mass capable of supporting a load of 500 gms.)

It gives an idea about the coking property of coal.

b) Swelling Index=It gives the Swelling nature of coal during carbonization. It measures the volume

increase of coal when unit mass of coal is heated under specific condition and numbered from 1

to 9 by reference to a series of standard profiles.

c) LTGK Coke type: The nature, shape, size of the cock pencil formed in the standard

L.T.G.K.(Low Temperature Grey King) retort and designated by alphabets A,B,C,D.E,F,G.G1 to

G8 gives an indication of the coking potentiality of the coal, for use in metallurgical industries.

d) Plastometric Test=

i. Giesler‟s Plastometric test

It determines the temp. Where coal softens, attain the maximum fluid state and

resolidifies by rotating a small paddle inside a coal mass at a constant torque

when coal is being heated and by measuring the rate of rotation of paddle as

number of dial division per minute.

ii. Sapoznikov‟s Petrographic study

The coal sample is heated from the bottom at the constant pressure of 1 kg/cm2

from top. The maximum thickness of the layer of plastic mass formed after the

temp raises above 3000c measures indirectly the maximum fluidity (ddpm) of

Giesler‟s Plastometric test.

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e) Petrographic study= It is the visual examination of a polished section of coal under microscope under

reflected light. This study has gained importance now a day because the relevance of the determination of

the parameter s has a great impact on the quality of coal.

FOR NON-COKING COAL=>

a) Gross calorific value=It is the heat liberated by its complete combustion with oxygen. It is

expressed as Btu/lb (British Thermal Unit/Pound) or Kcal/Kg (Kilo Calorie/Kilogram).

b) Ash fusion temperature=When heated the coal ash commens to soften at substantially lower

temp, before melting. Three points are determined the fusion range of coal ash which are initial

deformation temp.(IDT),Hemispherical temperature(HT),Flow temperature(FT).

c) Ash Analysis=Here various acidic/basic constituents present in coal ash in the form of oxide. It

provides the corrosive nature of coal ash when used in power plants and allied industries.

d) Hard grove Grind ability Index (HGI) =It indicates the relative grind ability of coal. It helps to

provide information on the choice of the type of pulverized required in the industries.

e) Trace element Study=Trace elements in coal is derived from the original plant material, from

mineral matter washed to the coal swamp, from atmospheric deposition and from surface and

underground water flowing into the swamps.

f) Mineralogical Study=Coal is composed of organic and inorganic constituents have play a specific

characterization of coal. X-ray diffractometry (XRD) is most direct technique for determination

of mineral type, because it measures X-ray diffracted from a unique phase crystal structure.

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MAJOR COALFIELDS IN INDIA

In India, all the coal is explored and produced by the Coal India Limited, a Navaratna Company of Indian

Government. Coal India has 7 production unit and one R&D unit. These total 8 units discovered the

India‟s major coal fields.

In India, there are 20 major coal fields. These are the following-

I. Raniganj Coalfield

II. Jharia Coalfield

III. East Bokaro Coalfield

IV. West Bokaro Coalfield

V. Ramgarh Coalfield

VI. South Karanpura Coalfield

VII. North Karanpura Coalfield

VIII. Daltonganj Coalfield

IX. Hutar Coalfield

X. Singrauli Coalfield

XI. Sohagpur Coalfield

XII. Korba Coalfield

XIII. IB river Coalfield

XIV. Talcher Coalfield

XV. Pench-Kanha-Tawa Valley Coalfield

XVI. Wardha Valley Coalfield

XVII. Rajmahal Coalfield

XVIII. Godavari Valley Coalfield

XIX. North Eastern Region Coalfield

XX. Namchik- Namphuk Coalfield

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Basics of Ground Water Hydrology

1. Introduction

Water is the essence of life which is essential for the survival of all living beings i.e. humans, animals and

plants. Water is a principal element that influences the economic, agricultural and industrial growth of

mankind. Since the olden times Ground water has been a major dependable source for domestic and

irrigation use. During the past few decades it is also being extensively used for industrial purposes. The

water resources can be distinctly classified into two categories -1).Surface water. 2).Ground water. The

water on the earth‟s surface is nearly 70% and the remaining is land surface. The Oceans contain 97.25%

of the total global water and remaining 2.5% is fresh water. The distribution of total fresh water is as

follows:- Ice caps and Glaciers :-68.9%, Ground water:-29.9%, Lakes & Rivers:-0.3%, soil moisture:-

0.005%, atmosphere:-0.001%, streams & rivers:-0.0001%, Soil moisture, swamp

water etc:- 0.9%.

2. Hydrologic Cycle

The water of the earth circulates in the three media namely hydrosphere, atmosphere and the upper part of

lithosphere. The circulation of water from the oceans to the atmosphere, from the atmosphere to the

lithosphere and from lithosphere to the oceans, occurring through complex and inter-dependent processes

including precipitation, runoff, ground water flow, evaporation and transpiration is called as the

hydrologic cycle. The water evaporates from the oceans, rivers, streams, lakes and other water bodies and

forms a part of the atmospheric moisture. This moisture when it moves to low temperature areas is

condensed and precipitates as rain, snow or hail. The water that reaches the ground is dissipated in several

ways. It may be evaporated, transpired by plants, infiltrated in the ground or flow as surface runoff into

streams, rivers or the oceans. The hydrologic cycle is an important natural phenomenon on Earth; it is the

driving force behind most other natural processes.

Fig 1: Hydrological Cycle

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3. Hydrogeology

Hydrogeology is a branch of earth science that is concerned with the mode of occurrence, distribution,

movement and chemistry of water occurring in the subsurface in relation to the geological environment.

SUBSURFACE WATER: The water in the rocks existing in the liquid, solid or gaseous state is called

subsurface water. The subsurface water can be divided into ground water or phreatic water, vadose water

and internal water. Ground water occurs in the zone of saturation in which all interconnected voids are

filled with water that is under hydrostatic pressure. The upper surface of this zone of saturation is termed

as water table. The zone of aeration lies between the ground surface and the water table. The zone of

aeration contains the vadose water which includes water held in the interstices of capillary dimensions.

Depending on the origin and source the subsurface water is classified as connate water if the water

occurring in the rock formation was entrapped during the deposition of the rock, meteoric water if it was

derived from atmospheric precipitation and as juvenile water if it is derived from the

interior of the earth. The geology, topography, climate, drainage and vegetation control the form and

configuration of zone of aeration and also control the position of water table. Water bearing and water-

yielding properties of the zone of aeration mainly govern the percolation of water to the zone of

saturation. There may be two or more zones of saturation in some areas. Where there is an impermeable

rock in the zone of aeration, the downward movement of water may be hindered resulting in the saturation

of interstices of the rocks above the impermeable barrier. Water in such zones of saturation is termed as

perched ground water.

3.1 Hydraulic Properties of Rocks

The important hydraulic properties of rocks are a) Porosity and b) Permeability.

3.1.1 Porosity: The portion of the rock (or) soil not occupied by the solid rock material may be occupied by air (or)

ground water. These spaces are known as voids, interstices, pores/pore spaces. The porosity is the

measure or property of the interstices present in the formation. It is defined as the ratio of the volume of

voids to the total volume and

can be expressed as a percentage or as decimal fraction. Porosity is usually of two types a) primary

porosity and b) secondary porosity. Primary porosity is the inherent character of a rock which is

developed during the formation of the rock itself. In semi-consolidated (sedimentary) rocks and

unconsolidated (alluvial) formations, porosity is of primary nature and is due to the inter-granular space.

In volcanic rocks, the primary porosity is due to the presence of gas cavities (vesicles) and also lava tubes

and lava tunnels. Vesicular and scoriaceous lavas have high primary porosity. Secondary porosity is the

induced character and is developed subsequent to the formation of rocks. It is characteristic of

consolidated and semiconsolidated formations and it is introduced by weathering, fracturing and jointing

in hard rocks and dissolution of minerals in carbonate rocks (Limestone‟s and Dolomites). Joints and

fracture may induce secondary porosity in sandstone already possessing primary porosity.

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Individual pores in a fine-grained material like clay are extremely small but the total pore space is usually

large. While clay formation has large water holding capacity, water can not readily move through the tiny

pores and hence is not aquifer even though it may be saturated with water. In semi-consolidated

(sedimentary) and unconsolidated (loose sediments) formations, the porosity of formation is controlled by

the size, shape, sorting, distribution, packing

of particles and degree of cementation. In consolidated formations (hard rocks), the porosity is dependent

on the size of the individual fractures, joints and other openings; the extent, spacing and the pattern of

fracturing or on the

nature of solution channels.

3.2 Relation Between Texture and Porosity:

Fig. 2 a) If the grains that make up a rock are mostly spherical in shape, then the

rock is said to have well sorted arrangement and hence have greater

porosity.

Fig. 2 b) On the other hand, if the grains of a rock are not uniform, then the

smaller grains will fill up spaces between the larger ones and hence

poorly sorted and the porosity is less.

Fig. 2 c) Well-sorted sedimentary deposit consists of pebbles that are themselves

porous, so that the deposit as a whole has a very high porosity.

Fig. 2 d) Well sorted sedimentary deposit, whose porosity has been diminished

by the deposition of mineral matter in the interstices.

Fig. 2 e) Rock rendered porous by solution.

Fig. 2 f) Rock rendered porous by fracturing.

3.2.2 Packing:

Fig 3: Arrangement of Grains in Cubic and Rhombic packing

The geometrical arrangement of grains or the types of packing also affects porosity. In cubic packing, the

porosity is as high as 48% while in rhombic packing it is as low as 26%.

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3.2.3 Shape: Regarding the shape of grains, it is seen that angularity tends to increase porosity. Cementation and

compaction reduces porosity. In unconsolidated alluvial formations, the porosity at deeper levels is less

due to greater compaction. In volcanic rocks, the porosity decreases with the deposition of secondary

minerals in vesicles in the form of amygdule.

3.2.4 Effective Porosity: The holes in the rocks may be connected or disconnected. The term effective porosity refers to the amount

of interconnected pore spaces available for fluid flow and it is expressed as the ratio of volume of

interconnected voids to total volume of rocks.

3.2.5 Permeability: The pores or openings in the rocks may be connected or disconnected normally or randomly distributed,

interstitial or planar rock like feature. Larger openings are usually associated with larger permeability. It

is not only the size of

openings that determine the permeability. The connection between the openings also plays an important

role. Thus the degree of connectivity of the pores governs the permeability of the rock. The effective

porosity is more closely related permeability than its total porosity.

The permeability of porous medium is the ease with which a fluid can flow through the medium and is

measured by the rate of flow in suitable units. In other words, permeability characterizes the ability of a

porous medium to transmit a fluid or water. It is a factor governing how a rock will act as a source of

water for a well. On

the basis of permeability, the rocks are classified into permeable, semi-permeable and impermeable

(impervious).

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4. Water Bearing Formations The water bearing properties of various geological formations can be classified on the basis of their

hydraulic properties. The best known classification is based on rock porosity and permeability is as

follows:

AQUIFER: - An aquifer is defined as a saturated geological formation that is permeable enough to yield

significant quantities of water to wells and springs. Thus, a porous and permeable water bearing

formation is called an aquifer. The terms "water bearing formation/stratum" and "ground water

reservoir" are synonyms for the aquifer. The granular unconsolidated sedimentary formations like gravel

and sand form potential aquifers.

AQUICLUDE: - It is a saturated formation through which virtually no water is transmitted. Aquicludes

may have high porosity but relatively have very low permeability and hence do not yield appreciable

quantities of water to wells. In other words, a highly porous and an impervious (that does not transmit

water at all)

geological formation is called an aquiclude e.g. clay and shale.

AQUITARD:- Aquitard is a saturated formation that has low permeability and yields water slowly in

comparison to the adjoining aquifers. In other words, aquitards are rock layers that are partly impervious

and transmit water at a lower rate than aquifer

(e.g.) sandy clay. Most aquitards do yield some water but usually not enough to meet even the modest

demand.

AQUIFUGE :- It is a formation which is neither porous nor permeable and hence neither stores nor

transmits water (e.g.) massive igneous and sedimentary rocks (compact limestone).

4.1 Types of Aquifers A further classification of aquifers in an area can be made on the basis of their location in the ground

water basin, and the position of their associated water levels.

Aquifers are of three types: a) Unconfined b) Confined c) Leaky

4.1.1 Unconfined Aquifers: An unconfined aquifer is not overlain by any confining layer but it has a confining layer at the bottom.

The upper surface is defined by the water table and it is in direct contact with the atmosphere. Water in a

well penetrating an unconfined aquifer is under atmospheric pressure and therefore does not rise above

the water table. The

water table in unconfined aquifers is free to rise and fall. Rises and falls in the unconfined aquifer

correspond to changes in the volume of water in storage within aquifer. It is also referred to as water table

or phreatic aquifer. The water table in unconfined aquifers is often termed as phreatic water level.

Movement of the ground

water is in direct response to gravity (Fig. 4).

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Fig. 4: Confined and Unconfined Aquifer

4.1.2 Confined Aquifers A confined aquifer is bounded above and below by an aquiclude, which is impermeable to water flow. It

has an overlying confining layer. Water in the confined aquifer occurs under pressure, which is usually

more than the atmospheric pressure, so that if a well taps the aquifer, the water level will rise above the

top of the aquifer

i.e. above the base of the overlying confining bed. It will rise up to an elevation at which it is in balance

with the atmospheric pressure. If this elevation is greater than that of the land surface at the well, the

water will flow from the well and such wells are termed artesian or flowing wells. The confined aquifers

have only an indirect or

distant connection with the atmosphere. The imaginary surface, conforming to the elevations to which

water will rise in wells penetrating confined aquifers is known as the piezometric surface or

potentiometric surface. It coincides with the hydrostatic pressure levels of the water in the aquifer (Fig.

4.).

4.1.3 Leaky or Semi-confiend Aquifers: It is an aquifer whose upper and lower boundaries are bounded by aquitards. As the aquitards are semi-

permeable, it may slowly transmit appreciable water to or from adjacent aquifers. For example, a water

bearing formation may be overlain by an aquitard, which permits water to move slowly upward out of the

aquifer or vertically

downward into the aquifer depending upon the hydrostatic head in the aquifer. Where the aquitard is

under the aquifer, water may be lost to or gained from the rocks below. Confined aquifers that loose or

gain waters from the surrounding formations are called leaky confined aquifers.

4.1.4 Perched Aquifers: It is a type of an unconfined aquifer (Fig. 5). Sometimes, an impermeable bed of clay or silt may be

present in some areas above the regional water table within the vadose zone or zone of aeration. This

impermeable barrier intercepts downward movement of water and causes some of it to accumulate in the

interstices of the rocks present above

the stratum. Thus, a zone of saturation of limited areal extent is locally formed with in the zone of

aeration i.e. a small water-bearing zone sometimes exists between the main water table and the ground

surface. This zone is called the perched ground water zone and the aquifer is called a perched aquifer.

The upper surface of the ground

water in this case is called a perched water table. Depending on the climatic conditions, a perched water

table may be permanent or seasonally intermittent. The perched aquifer has limited thickness and areal

extent

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Fig. 5: Perched Aquifers

4.2 Aquifer Properties Besides porosity and permeability there are several parameters that are related to the flow of water

through the aquifers and confining layers. The important parameters are transmissivity and storage

coefficient which are known as „Formation Constants”.

4.2.1 Transmissivity: The overall capacity of an aquifer to transmit water is dependent on the thickness and hydraulic

conductivities of the components parts of the aquifer. It is, therefore, a product of average hydraulic

conductivity and saturated thickness of the aquifer.

T Kb (T= transmissivity in m2/day, K= hydraulic conductivity in m, b = thickness of the aquifer)

Transmissivity is defined as the rate of flow of water in cubic meters per day, through a vertical strip of the

aquifer of one meter wide (unit width) and extending through the entire saturated thickness of the aquifer

under a hydraulic gradient of (100% unit hydraulic gradient) at a temperature of 15.6C.

4.2.2 Co-Efficient of Storage/Storativity (S): The capacity of an aquifer to store water is expressed as a coefficient designated as S. The head in the

aquifer changes when the water is either stored or released indicating a change in the storage volume

within the aquifer. Storativity is defined as the volume of water that an aquifer releases or takes in to

storage per unit surface area of the

aquifer per unit change in component of the head normal to that surface. Thus storativity is equal to the

amount of water removed from each vertical column of aquifer of height m and unit basal area when the

head declines by one unit (Fig. 7).

S = Volume of water / (Unit area) (Unit head change ) = m3 / (m2) (m)

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Fig. 7: Diagram illustrating storage coefficient of confined aquifers

Storatitivity is non-dimensional. In confined aquifer, storatitivity is a result of compression of the aquifer

and expansion of the contained water a result of reduced pressure due to pumping. The value of S ranges

from 0.00001 (10-5) to 0.001 (10-3) for confined aquifers.

4.2.3 Specific Yield (Sy): The capacity of the rock to drain water under the force of gravity is termed specific yield.. It is defined as

the volume of water released or stored per unit surface area of the aquifer per unit change in the head

normal to that surface.

When water is drained from a saturated material by gravity force, only part of the total volume stored in

its pores is released. The quantity of water that a unit volume of material will give up when drained by

gravity is the specific yield. The part of water that is not removed by gravity drainage is held against the

force of gravity by

molecular attraction and capillary. The quantity of water that a unit volume of aquifer retains when

subjected to gravity drainage is called its specific retention.

4.3 Well Hydraulics Water wells are used for the extraction of ground water for domestic, municipal, industrial and irrigation

needs. Flow towards a well has been termed Radial Flow.

4.3.1 Definition of Terms: 1. Static Water Level (SWL):- The level at which the water level stands in a well before pumping is called static water level. It is generally expressed as the distance from the ground surface to the water level in a well. For example, when the SWL is 15m, it means that the water stands 15 meters below the ground surface or measuring point when there is no pumping.

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2. Pumping Water Level (PWL):- This is the level at which water stands in a well when pumping is in progress. This level is variable and changes with the quantity of water being pumped. The pumping water level is also called the dynamic water level. 3. Drawdown (s):- It is the difference between the static water level and the pumping water level. Drawdown affects the yield of the well. 4. Residual Drawdown (s'):- After pumping is stopped, the water level rises and approaches the SWL observed before pumping began. During water level recovery, the distance between the recouping water level and the initial SWL is called residual drawdown. 5. Recovery:- This the amount by which the water level in a well has risen at a given time after pumping ceased. Thus, it is the difference between the residual drawdowns after the given time and drawdowns when pumping stopped. When the water level returns to the SWL, recovery is said to be complete. 6. Pumping Rate (Discharge):- This is the volume of water per unit time discharged from a well by pumping. This is also called the well yield. It can be measured in liters per minute (lpm). Other units employed are cubic meter per hour (m3/h) and cubic meter per day (m3/day).

4.3.2 Ground Water Flow

Turbulent flow

Two basic types of flow occur in ground water with one more prevalent than the other. The water in the

interstices of the permeable rocks in the zone of saturation is, as a rule, move very slowly and steadily.

This slow and steady kind of movement is called the laminar flow. It is also known as streamline (or)

viscous flow. In each thread of laminar movement there is an endless procession of particles of water, and

each particle of water moves in a regular path without crossing or intersecting those of others. That means

there is no intermixing individual threads /layers. (Fig. 9)

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4.3.3 Radial Flow to Wells

CONE OF DEPRESSION:- When a well is pumped, water is removed from the aquifer and the water

table is lowered and hydraulic gradient is established resulting in convergent or Radial flow towards the

well. The distance between static water level and the pumping water level is called drawdown. A

drawdown curve shows the

variation of drawdown with distance from the well. In three dimensions, the drawdown curve describes a

conic shape known as cone of depression. The water surface assumes approximately the shape of an

inverted cone with PWL as apex and the base conforming to the original SWL. The perimeter of the cone

of depression defines the area of influence and the radius of base of the cone is referred as the radius of

influence (R). Radius of influence is the horizontal distance from the center of a well to the limit of the

cone of depression. As more and more water is pumped out of the well, the area of influence keeps

expanding indefinitely till a position is reached when the rate of discharge from the well equals to the rate

of recuperation from the storage of the well. It is at this instant that the cone of depression is stabilized

and the well is in equilibrium condition. In a formation with high transmissivity, the

cone of depression is shallow with flat sides and has a large radius. In a formation with low

transmissivity, the cone is deep with steep sides and has a small radius.

STEADY-STATE FLOW:- Flow is said to be under steady or equilibrium state when the magnitude and

direction specific discharge remain constant with time.

Steady-state flow implies that the position of the piezometric surface and the hydraulic gradient remain

unchanged. There is no addition to or withdrawal from the storage of the aquifer, and equilibrium

conditions have been reached between recharge and discharge.

NON-STEADY STATE FLOW:- Flow is said to be under non-steady, also called unsteady or non-

equilibrium or transient state when the magnitudes or direction of specific discharge changes with time.

Changes in storage of the aquifer are involved in non-steady flow. Non-steady state flow is described with

respect to boundary and

initial conditions.