groundwater hydrology slides

7/27/2019 groundwater hydrology slides

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HYDROGEOLOGY

VIKRANT SHARMA


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The thickness of the capillary

fringe varies depending on

the pore sizes in the medium.

In a silt or clay, the capillary

fringe can be more than a

meter thick, while the

capillary fringe in a coarse

gravel would be less than amillimeter thick.


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An Aquifer can be defined as a geological formation in which water

accumulates and may circulate, via its pores and fissures, thus enabling

humans to make use of it in economically viable quantities. (Custodio andLlamas, 1996)

Sustainable Groundwater Development


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Lithology

Unconsolidated Sedimentary rocksConsolidated Sedimentary rocks

Volcanic

Igneous

Metamorphic

Hydrostatic P of GW

Unconfined Aquifers

Confined Aquifers

Semi-Confined Aquifers

Depth of Aquifer

ShallowDeep (>300m)

Scale of StudyLocal

Regional

Basic Aquifer Classifications

Porosity

Single Porosity

Double Porosity


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An aquifer is defined as a saturated permeable geological unit that is

permeable enough to yield economic quantities of water to wells. The

most common aquifers are unconsolidated sand and gravels, but

permeable sedimentary rocks such as sandstone and limestone, and

heavily fractured or weathered volcanic and crystalline rocks can also beclassified as aquifers.

An aquitard is a geological unit that is permeable enough to transmit

water in significant quantities when viewed over large areas and long

periods, but its permeability is not sufficient to justify production wellsbeing placed in it. Clays, loams and shale are typical aquitards.

An aquiclude is an impermeable geological unit that does not transmit

water at all. Dense unfractured igneous or metamorphic rocks are typical

aquicludes. In nature, truly impermeable geological units seldom occur;

all of them leak to some extent, and must therefore be classified as

aquitards. In practice, however, geological units can be classified as

aquicludes when their permeability is several orders of magnitude lower

than that of an overlying or underlying aquifer.

*** These definitions are imprecise with respect to permeability.


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Aquifer Types


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Aquifer Types


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Unconsolidated Semi-consolidated

Sandstone Carbonate

VolcanicPlutonic

Principle Aquifer Rock Types


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Unconsolidated AquifersUnconsolidated deposits are geological formations formed by the accumulation of

particles that are transported by gravity, water, wind or ice, in riverbeds, lakeside or

marine settings. They usually comprise of sands and gravels of varying geological

origin. Fluvial deposits are made up of the alluvial materials of rivers and their terraces.Deltaic deposits accumulate at river mouths. In general such deposits are recent in

geological time. Its porosity is due to voids or space between the rock particles, or

single porosity.

Aquifers that are mapped as unconsolidated

sand and gravel can be grouped into four

broad categories:

basin-fill or valley-fill aquifers

blanket sand and gravel aquifers

glacial-deposit aquifers

stream-valley aquifers

All four types have intergranular porosity

and all contain water primarily under unconfined or water-table conditions.

Determination of depth, thickness and extension of

permeable deposits and confining layers.


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Ground water in unconsolidatedaquifers flows along relatively shortflow paths typical of local flow systems

Basin-fill aquifers typically haveintermediate flow systems

Thick basin-fill aquifers may supportregional flow system.

Likewise, the thick blanket sandsaquifers and alluvial aquifers canrepresent regional flow systems.

Unconsolidated

Aquifer Properties

Unconsolidated

Aquifer Flow Systems

The hydraulic conductivity ofunconsolidated aquifers is variable,depending on the sorting of aquifermaterials and the amount of silt andclay present, but generally it is high.

Aquifer thickness ranges from a fewmeters or tens of meters in the blanketsands to several hundred meters in the

basin-fill aquifers.

Unconsolidated sand and gravelaquifers are susceptible to

contamination because of theirgenerally high hydraulic conductivity.


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Semi-consolidated aquifers consist of sand interbedded with silt, clay, andminor carbonate.

The aquifers are typically of fluvial, deltaic, and shallow marine origin.

The varied depositional environments of these sediments have causedcomplex interbedding of fine and coarse-grained materials.

Accordingly, some aquifers are thin and local whereas others are thick andmay extend over hundreds of square kilometres.

The Ravenscrag Formation is a Saskatchewan example of a semi-consolidated aquifer.

Semi-consolidated Aquifers


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Semi-consolidated

Aquifer Properties

Semi-consolidated

Aquifer Flow Systems

Porosity is intergranular, and thehydraulic conductivity of the aquifers ismoderate to high.

The aquifers form thick extensivewedges of sediment.

Wedges tend to dip away fromtopographically high erosional sourceareas.

Aquifer thicknesses can reach severalhundred metres.

Numerous local aquifers can be grouped intoa few regional aquifer systems that containgroundwater flow systems of local,intermediate, and regional scale.

In topographically high recharge areasaquifers are unconfined but become

confined in the downdip direction. Discharge is by upward leakage to shallower

aquifers or to saltwater bodies in coastalareas.

Because flow is sluggish near the ends ofregional flow paths, the aquifers commonly

contain unflushed saline water in theirdeeply buried, downdip extremities.


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Consolidated Sedimentary RocksConsolidated sedimentary rocks are made of sediments that have

become consolidated by compaction or diagenesis processes, which

reduce the space occupied by the voids. On the basis of their porositythey can be classified as double porosity aquifers as is the case of

sandstones with primary and or interstitial porosity and secodary

porosity mainly due to fracturing in karstic aquifers as limestones

and dolomites, secondary porosity is due to fracturing and chemical

dilution processes.

Origin (Detritic)

Conglomerates

Sandstones

Clays

Chemical

Limestone (Carbonates)

Dolomites (Carbonates)

Chalk (Carbonates)

Marls

Organic

Carbons

Natural

Hydrocarbons

One of the main targets in the study of such aquifers is to localize the

fractured and voided areas.

S d t A if


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Sandstone Aquifers

Secondary openings, such as joints and fractures, along with beddingplanes, typically transmit most of the groundwater in bedrocksandstone aquifers.

Sandstone retains only a small part of the intergranular pore space that

was present before the rock was consolidated.

Compaction and cementation greatly reduce the primary pore space.


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Sandstone Aquifer

Properties

Sandstone Aquifer

Flow Systems

The hydraulic conductivity ofcemented sandstone aquifers is lowto moderate.

Transmission is primarily throughfractures although primary porosity

may continue to contribute tostorage.

Because bedrock sandstones extendover large areas, these aquifers canoften provide large amounts of

water.

Sandstone aquifers in the Prairies arehorizontal to gently dipping.

Because they are commonly interbedded withsiltstone or shale, most of the water in theseaquifers is under confined conditions.

Groundwater flow systems in relatively thinsandstone aquifers are local to intermediate.

Regional, intermediate, and local flow arepresent in the sandstone aquifers westernCanada.

Many extensive sandstone aquifers containhighly mineralized water at depths of only afew hundred meters.

C b t A if


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Carbonate Aquifers

The most important are the carbonate rocks among the consolidated

sedimentary rocks. Chalk, limestone and dolomites they vary considerably

in density, porosity and permiability - some are considered to be confining

units, whereas others are among the most productive aquifers known. Most of the carbonate-rock aquifers consist of limestone, but dolomite and

marble locally yield water.

Carbonate rocks originate as sedimentary deposits in marine environments.

Compaction, cementation, and dolomitization processes act on the depositsas they undergo lithification and greatly change their porosity and

permeability.


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Carbonate Aquifer

Properties

Carbonate Aquifer

Flow Systems

The principal post-depositional change incarbonate rocks is the dissolution of partof the rock by circulating, slightly acidicgroundwater.

Solution openings in carbonate rocksrange from small tubes and widenedjoints to caverns that may be tens of

meters wide and hundreds to thousandsof meters in length.

Where they are saturated, carbonaterocks with well-connected networks ofsolution openings yield large amounts ofwater to wells that penetrate the openings

The undissolved rock between the largeo enin s ma be almost im ermeable.

Where carbonate rocks are exposed at landsurface, solution creates karst topography,characterized by little surface drainage,sinkholes, blind valleys, sinking streams, andkarst towers (mogotes).

Because water enters the carbonate rocks

rapidly through sinkholes and other largeopenings, any contaminants in the water can

spread rapidly through the aquifers.

Regional, intermediate, and local ground-

water flow systems are present in carbonate

aquifers but most near-surface carbonates tend

to provide only local and intermediate systems.


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P t A if Ch t i ti


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Parameters: Aquifer Characterization

Three conditions are necessary for the existence and use of an aquifer:1: The rock must be able to store water (Aquifer Storage Property)

2: The water has to be able to circulate through the rock (Aquifer Flow Property)3: There must be water replenishment (Aquifer Recharge)

*** Water removal

The amount of water held in a rock depends upon itsporosity. Porosity is

controlled by the grain size and shape, the degree of sorting, the extent of

chemical cementation and the amount of fracturing.

Solid density: s = Msolids/Vsolids

Bulk density: b= Msolids/Vtotal

Simple Cubic Body-Centered Cubic Face-CenteredCubicn = 0.48 n = 0. 26 n = 0.26

total

pores

V

Vn

total

solidstotal

V

VVn

total

solids

V

Vn 1

s

bn

1


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Porosity that has developed after the rocks have formed is termed

secondary porosity to distinguish it from intergranular or primary

porosity. Secondary porosity typically results from two main causes:fractures associated with joints, along bedding-planes, tectonic joints and

faulting (although where fault gouge has been produced or secondary

mineralization has occurred along the fault plane, groundwater

movement will be restricted rather than enhanced), and karst processesthat dissolve the limestone aquifers.

Dolomitization of limestones (i.e. the replacement of calcium ions with

magnesium) also increases porosity because the magnesium ion is

smaller than the calcium ion that it replaces by as much as 13 per cent.However, the dolomite crystals are usually very small, producing tiny

pore spaces, and are unevenly distributed through the rock, resulting in

only small increases in the hydraulic conductivity.

Aquifer Storage Property: Porosity


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E l ti f A if P ti


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Evaluation of Aquifer PropertiesPorosity (Grain Size)In unconsolidated materials, the size of the mineral grains is a key

characteristic of the material. The distribution of grain sizes determineshow much pore space is available to hold water, and how easily water is

transmitted through the material.

E l ti f A if P ti


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Evaluation of Aquifer PropertiesGrain Size Distribution

Sieve Analysis

Evaluation of Aquifer Properties


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Evaluation of Aquifer PropertiesGrain Size DistributionHydrometer Analysis

L1

L2

L



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Evaluation of Aquifer PropertiesGrain Size Distribution



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Evaluation of Aquifer PropertiesParticle ShapeThe shape of particles present in a soil mass is equally as important asthe particle size distribution because it has significant influence on the

physical properties of a given soil. However, not much attention is paid

to particle shape because it is more difficult to measure.

Bulky: Bulky particles are mostly formed by mechanical weatheringof rock and minerals. Geologists use such terms as angular, sub-angular,

rounded and sub-rounded.

Flaky: Flaky particles have very low sphericity usually 0.01 or less. These particles are predominantly clay minerals.

Needle Shaped: Needle-shaped particles are much less commonthan the other two particle types. Examples of soils containing needle-

shaped particles are some coral deposits and attapulgite clays.


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Parameters: Aquifer Storage


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The proportion of voids in relation to the total volume of rock considered

is evaluated by the total porosity n. But some voids may not be

connected with other voids, and the fluid inside that is trapped; itsvolume proportion is named trapped porosity nt. Trapped porosity is

abundant in karstic and hard-rock aquifers. In unconsolidated sediments

and in sandstones , the role of nt is negligible and can be disregarded

usually.


How much of the stored water of the

aquifer is available for pumping?

Real Question



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The amount of interconnected pore space that is available for fluid flow

and advective transport is termed the effective porosity ne. The main

application field of ne is contaminant-transport modeling according toadvective-dispersive equation. ne is high in well-sorted sands and/or

gravels; and in clayey rock types. ne is low in poorly sorted deposits such

as glacial tills.

Parameters: Aquifer StorageA small part of the water can be attached by molecular forces to the walls

of the grains (within 0.0002 mm from surface), and its proportion to the

total volume of rock is called bound waterb; the rest of the water iscalledfree waterf.

For saturated conditions soil moisture content (theta) is equal to porosity,

theta(m) is mobile water theta(MRS) is soil moisture deciphered by MRS.


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Methods for Obtaining Effective Porosity

Tables

Aquifer Flow Property

Usually, hydraulic conductivity, and to a much lesser extent dispersivity,

are the focus of field and laboratory data-collection efforts for models

that are based on the advectiondispersion equation (ADE). A third

hydraulic parameter required for transport modeling is effective porosity.

For aquifer simulations, it has become common practice to estimate

effective porosity from ones experience or the literature. Effective

porosity is not often evaluated because it has a small range of variability

compared with hydraulic conductivity and dispersivity.

Values from the tables can vary substantially from the actual values.

Hence we can use the tables for an initial guess, however these values

could be inefficient and/or inaccurate.


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Effective porosity is sometimes obtained from other measured parameters, such as

specific yield, or total porosity minus specific retention or residual water content. This

is not correct. Specific yield and effective porosity are two different parameters. Thesetwo parameters have in fact comparable values for coarse rock materials (because

specific retention is small) where Sy ne. However in fine grained rocks and

particularly in clayey materials, Sy is low while ne is high so the Sy differs substantially

from ne.

Effective porosity defined in context of transport is different from effective porosity that

pertains to drainage and capillary processes.


Tables


Texture

class

Sampl

e size

Total

porosity

Residual

(bound)

Effective

porosity

Pore-size

Distribution

Specific

retention (Sr)

Wilting

point

Specific

yield

Saturated

hydraulic


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class e size

[cm3]

porosity

n

[cm3/cm3]

(bound)

water

content b

[cm3/cm3]

porosity

ne

[cm3/cm3]

Distribution

arithmetic

mean

retention (Sr)

water retained

at 33 kPa

[cm3/cm3]

point

water

retained at

1500 kPa

[cm3/cm3]

yield

estimated

from

Sy = n Sr

[cm3/cm3]

hydraulic

conductivity

K [cm/h]

Sand 762 0.437(0/374-0/500)

0.020

(0.01-0.039)

0.417

(0.354-0.480)

0.694

(0.298-1.090)

0.091

(0.018-0.164)

0.033

(0.007-0.059)

0.346 23.56

Loamy

sand

338 0.437(0.368-0.506)

0.035(0.003-0.067)

0.401(0.329-0.473)

0.553(0.234-0.872)

0.125(0.060-0.190)

0.055(0.019-0.091)

0.312 5.98

Sandy

loam

666 0.453

(0.351-0.555)

0.041

(-0.024-0.106)

0.412

(0.283-0.541)

0.378

(0.140-0.616)

0.207

(0.126-0.288)

0.095

(0.031-0.159)

0.246 2.18

Loam 383 0.463(0.375-0.551)

0.027

(-0.020-0.074)

0.434

(0.334-0.534)

0.252

(0.086-0.418)

0.207

(0.195-0.345)

0.117

(0.069-0.165)

0.193 1.32

Silt loam 1206 0.501(0.420-0.582)

0.015

(-0.028-0.058)

0.486

(0.394-0.578)

0.234

(0.105-0.363)

0.330

(0.258-0.402)

0.133

(0.078-0.188)

0.171 0.68

Sandy

clay

loam

498 0.398

(0.332-0.464)

0.068

(-0.001-0.137)

0.330

(0.235-0.425)

0.319

(0.079-0.559)

0.255

(0.186-0.324)

0.148

(0.085-0.211)

0.143 0.30

Clay

loam

366 0.464

(0.409-0.519)

0.075

(-0.024-0.174)

0.390

(0.279-0.501)

0.242

(0.070-0.414)

0.318

(0.250-0.386)

0.197

(0.115-0.279)

0.146 0.20

Silty

clay

loam

689 0.471

(0.418-0.524)

0.040

(-0.038-0.118)

0.432

(0.347-0.517)

0.177

(0.039-0.315)

0.366

(0.304-0.428)

0.208

(0.138-0.278)

0.105 0.20

Sandy

clay

45 0.430

(0.370-0.490)

0.109

(0.013-0.205)

0.321

(0.207-0.435)

0.223

(0.048-0.398)

0.339

(0.245-0.433)

0.239

(0.162-0.316)

0.091 0.12

Silty

clay

127 0.479

(0.425-0.533)

0.056

(-0.024-0.136)

0.423

(0.334-0.512)

0.150

(0.040-0.260)

0.387

(0.332-0.442)

0.250

(0.193-0.307)

0.092 0.10

Clay 291 0.475(0.427-0.523)

0.090

(-0.015-0.195)

0.385

(0.269-0.501)

0.165

(0.037-0.293)

0.396

(0.326-0.466)

0.272

(0.208-0.336)

0.079 0.06

Lubczynski, M.W. and Roy, J., 2007. Use of MRS for hydrogeological system parametrization and modeling. Table 1 Boletin Geologico y Minero pp 514


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Lab Measurements I Tracer Column Testing

Aquifer Flow PropertyFor traditional solute-transport modeling, effective porosity (ne) can be defined as the

ratio between Darcy flux and seepage velocity, where q is experimental Darcy flux(specific discharge) and v is seepage velocity (or velocity of a conservative tracer).

Advective and dispersive processes are active

within the pore spaces designated as effective

porosity.


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Lab Measurements I Tracer Column Testing


Assuming it is a chemical and physical

equilibrium transport, we use this ADE

(Advection Dispersion Equation).

Assuming no retardation, the traditional column

testing approach can

utilize the analytical

solution of a one-

dimensional version of

the above ADE.

The relative concentration point (c/co=0.5) describes solute moving at

the average velocity and for a nonreactive tracer c/co=0.5 should occur

when one pore volume of solution has flowed from the column. Using

the measured elapse time, t0.5 at c/co=0.5, the known column length, L,

and experimental Darcy flux, q, the effective porosity can be calculated.


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Methods for Obtaining Effective PorosityLab Measurements II CMR Approach to Column Testing



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Tables

Lab Experiments

Tracer Tests (CXTFIT)

MRS (50 m 60000; 100 m 90000; 150 m 130000)


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Storage

Storativity

Evaluation of Aquifer PropertiesHydraulic Properties

The amount of water held in a rock depends upon itsporosity. Porosity is

controlled by the grain size and shape, the degree of sorting, the extent ofchemical cementation and the amount of fracturing.

The hydraulic properties can be measured in the field or laboratory but can also be assessed in

general terms by consideration of the overall aquifer geology.

The amount of interconnected pore space that is available for fluid flow

is termed the effective porosity.

Porosity does not provide a direct measure of the amount of water thatwill drain out of the aquifer because some of the water will remain in the

rock, retained around individual grains by surface-tension forces. That

part of the groundwater that will drain from the aquifer is termed the

specific yield, andthe part that is held in the aquifer is called thespecific

retention.



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Evaluation of Aquifer PropertiesHydraulic Properties

Groundwater Flow

The hydraulic properties can be measured in the field or laboratory but can also be assessed in

general terms by consideration of the overall aquifer geology.

Hydraulic Conductivity

Hydraulic conductivity depends on both the properties of the aquifer and the

density and viscosity of the water. - concentrations of dissolved minerals andtemperature - increase in water temperature from 5C to about 30C, will

double the hydraulic conductivity and will double the rate of groundwater flow.

Not a problem in deep aquifers. In some shallow aquifers in areas of climate

extremes or in particular situations involving waste hot water and industrial

effluent the flow rates may be affected by the temperature. Hence always takethe temperature of pumped water in the field tests.

The property of a rock that controls the hydraulic conductivity is its intrinsic

permeability (k), and is constant for an aquifer regardless of the fluids flowing

through it, applying equally well to oil, gas and water. Intrinsic permeability

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