Hydrogeology Geology Dept, Anna University Elango, L 1 AG 9131 Hydrogeology AG 9131 Hydrogeology L. Elango L. Elango Professor Department of Geology Anna University, Chennai [email protected]www.elango.5u.com Reference text: Hydrogeology Groundwater - Freeze, R.A and Cherry, J.A, Groundwater Hydrology – David Keith Todd Groundwater -- H.M. Raghunath Weightage for Grading Weightage for Grading Attendance : 5% Tests (best 2 from 3) : 45% Final Exam : 50% Dept. of Geology Anna Uiversity
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Groundwater abstraction techniquesConstruction of wells – shallow and deep wells
Groundwater quality
Hydrology is the f
Hydrology
Hydrology and Hydrogeology
science of occurrence, movement and transport of water
H drogeologHydrogeology deals with the occurrence, distribution, movement of water and its constituents (quality of water) beneath the Earth's surface- that is groundwater
Hydrogeology
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Hydrogeology is an Hydrogeology is an interdisciplinary subjectinterdisciplinary subject
►►InvolvingInvolvingGeologyGeology
►►To answer To answer questions posedquestions posedGeologyGeology
►►Virtually every activity in the earth Virtually every activity in the earth i i k l d fi i k l d f
Life on earth is possible Life on earth is possible primarily because of the primarily because of the availability of water on it. The availability of water on it. The first form of life originated in first form of life originated in water.water.
sciences requires some knowledge of sciences requires some knowledge of groundwatergroundwater
►►Until the 1900 Until the 1900 –– focus on groundwater focus on groundwater as a resource as a resource –– (Still it is the important (Still it is the important
))resource)resource)►►In the past century In the past century –– Engineering and Engineering and
Environmental aspects Environmental aspects –– also become also become importantimportant
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Scope of HydrogeologyScope of Hydrogeology
►► Important resourceImportant resource
AgricultureAgriculture
IndustryIndustry
DomesticDomestic
Water Balance of the Earth Water Balance of the Earth Distribution of Water Volume
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Impo
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UNESCO, 2000
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Global Distribution of Water
Oceans
Ocean water: 97.2%Ocean water: 97.2%
Fresh water: 2 8%Fresh water: 2 8%
Groundwater – An important resourcert
ant
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Fresh Water
Distribution of Fresh Water
Ice/Glaciers
Fresh water: 2.8%Fresh water: 2.8%
Ice: 2.14%Ice: 2.14%
Groundwater: 0.61%Groundwater: 0.61%
Impo
rIm
por
Groundwater
Surface Water
Soil Moisture
Atmosphere
Surface water: 0.009%Surface water: 0.009%
Surface Moisture: 0.005%Surface Moisture: 0.005%
Atmosphere: 0.001%Atmosphere: 0.001%
Need for waterNeed for water
rtan
t re
sour
cert
ant
reso
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Impo
rIm
por
USEPA 1987
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rtan
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cert
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-GW is significantly less costly to develop than surface water.
Impo
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-GW is less susceptible to contamination than surface water
- quite often requires little or no treatment to be used as drinking water.
OBSERVED OBSERVED -- SIMULATED NITROGEN (NSIMULATED NITROGEN (N--NONO ) CONCENTRATION IN THE) CONCENTRATION IN THE
2017
0
2
4
6
N (m
g/kg
) ObservedSimulated
0
5
10
N (m
g/Kg
)
10
20
mg/
kg)
NONO33) CONCENTRATION IN THE ) CONCENTRATION IN THE UNSATURATED ZONEUNSATURATED ZONE
0N (
0
5
10
N (m
g/Kg
)
1.001.001.001.00
16 22 28 38 48 96Days after Transplantation
N (m
g/Kg
)
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►► Love canal in Niagra FallsLove canal in Niagra Falls►► Dug in 1890 for shipping/hydropower Dug in 1890 for shipping/hydropower
but not completedbut not completed►► Hooker chemical co dumped wastes (organicHooker chemical co dumped wastes (organic
Contaminant migration ...contd
►► Hooker chemical co. dumped wastes (organic Hooker chemical co. dumped wastes (organic chemicals, pesticides etc.,) from 1942 to 1953chemicals, pesticides etc.,) from 1942 to 1953
►► Covered with soil and soldCovered with soil and sold►► High rainfall in 1975High rainfall in 1975--76 eroded soil cover76 eroded soil cover►► Liquid wastes contaminated groundwaterLiquid wastes contaminated groundwater►► As wastes denser than As wastes denser than
water it could not water it could not penetrate soft claypenetrate soft clay
►► Health risks and source of contamination known Health risks and source of contamination known in 1978in 1978
Contaminant migration ...contd
in 1978in 1978►► Declared as federal emergencyDeclared as federal emergency►► School and homes evacuated School and homes evacuated ►► Cleaning up Cleaning up –– perimeter drain and groundwater perimeter drain and groundwater
intercepted, onsite treatment plant installedintercepted, onsite treatment plant installedThi i d h i l di iThi i d h i l di i►►This improved the environmental conditionThis improved the environmental condition
►► A clear A clear hydrogeologicalhydrogeological problem!problem!
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Leaking Gas TanksLeaking Gas TanksLNAPLLNAPL
Contaminant migration ...contd
Geological work of groundwaterGeological work of groundwater
Permeable pathways are controlled by Permeable pathways are controlled by distributions of geological materialsdistributions of geological materialsWhere groundwater is available as a Where groundwater is available as a resource is controlled by geology resource is controlled by geology
Permeable pathways are Permeable pathways are controlled by distributions controlled by distributions of geological materialsof geological materialsWhere groundwater is Where groundwater is available as a resource is available as a resource is controlled by geologycontrolled by geology
controlled by geologycontrolled by geologyContaminant transport in Contaminant transport in the subsurface is the subsurface is controlled by geology controlled by geology
►►Volcanic ProcessesVolcanic Processes::Igneous RocksIgneous Rocks: : Groundwater controls water Groundwater controls water content of magmascontent of magmasMetamorphic RocksMetamorphic Rocks: : Groundwater injected by Groundwater injected by j yj ymagmas can metamorphose magmas can metamorphose country rocks country rocks VolcanismVolcanism: Geysers are an : Geysers are an example of volcanic activity example of volcanic activity interacting with groundwaterinteracting with groundwater
EarthquakesEarthquakes: fluids control fracturing and fault : fluids control fracturing and fault movement, lubrication and pressuresmovement, lubrication and pressuresLandslidesLandslides: groundwater controls slope failure: groundwater controls slope failureLandformsLandforms: Valley development and karst : Valley development and karst topographytopography
Surface Water & GroundwaterSurface Water & Groundwaterare Related and Connected !are Related and Connected !
Local Water Divide
Sources of Groundwater
►Meteoric water derived from rainfall►Meteoric water- derived from rainfall►Connate water- fossil interstitial water►Magmatic water or Juvenile water- from hot
molten magma►Plutonic water- very deeper condition
( 5k )(>5km)►Volcanic water- shallow depths (<5km)►Metamorphic water- during metamorphism
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Vertical distribution of WaterVertical distribution of Water
SurfaceWater
SoilSoilMoistureMoisture
GroundwaterGroundwater
Unsaturated Zone – Zone of Aeration
Pores Full of Combination of Air and Water
Zone of Saturation
Pores Full Completely with Water
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Unsaturated Zone:
Soil and Groundwater ZonesSoil and Groundwater ZonesSoil and Groundwater ZonesSoil and Groundwater Zones
Water in pendular saturation
Water Table: where
Caplillary Fringe: Water is pulled above the water table by capilary suction
Saturated Zone: Where all pores are completely filled with water.
Phreatic Zone: Saturated zone below the water table
fluid pressure is equal to atmospheric pressure
The Water Table
Lies Roughly at theg yInterface Between the Unsaturated
Zone and the Saturated Zone
But How Do WeDefine the
Water Table?
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Capillary FringeCapillary Fringe
Surface tension Surface tension –– sediments retain watersediments retain water
Depends on Surface area:Depends on Surface area:smaller grains smaller grains –– higher surface area higher surface area –– higher surface tensionhigher surface tension
Capillary Fringe
Zone above water table that is effectively saturated
Water Held by Tension
Capillary Rise Related
Capillarity Due to Adhesion of Water to a Surface
Capillary Rise Related to Size of Pores
Smaller the Pore, The Larger the Capillary Rise
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Soil waterSoil waterDepth up to which the root zone extends
Depth up to which the atmospheric conditions has an influence
Intermediate/Gravitational water – zone between soil water and capillary fringe
AQUIFERSAQUIFERS►Aquifer is derived from the Latin term meaning water
bearer. ►Lithologic unit or collection of units capable of yielding
water to wells
►An aquifer is not:A geological formation,A permeable geologic unitA permeable geologic unit,A porous medium, orA petroleum reservoir
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AQUIFERSAQUIFERS
Consolidated or unconsolidated geologic unit (material, stratum, or formation) or set of connected units that yields a significant (economic) quantity of water of suitable quality to wells in usable amountsto wells in usable amounts.
AQUIFER TypesAQUIFER Types►unconfined (or water-table) - the upper surface
of the aquifer is the water table. Water-table if di tl l i b t t daquifers are directly overlain by an unsaturated
zone or a surface water body. ►Water table separates saturated and
unsaturated zones
hi h bilit lhigh permeability layers near the surface
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AQUIFER TypesAQUIFER Types►confined (or artesian) - an aquifer that is
immediately overlain by a low-permeability it ( fi i l ) A fi d if dunit (confining layer). A confined aquifer does
►► Permeable material overlain by Permeable material overlain by relatively impermeable materialrelatively impermeable material
►► Piezometric or potentiometric Piezometric or potentiometric surfacesurface
►►Water level in the piezometer is Water level in the piezometer is a measure of water pressure in a measure of water pressure in the aquiferthe aquifer
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AQUIFER TypesAQUIFER Types►perched - a local, unconfined aquifer at a
higher elevation than the regional unconfined aquifer An unsaturated zone is presentaquifer. An unsaturated zone is present between the two unconfined aquifers.
AQUIFER TypesAQUIFER Types►Leaky or semi confined- an aquifer that
receives recharge via cross-formational flow through confining layersthrough confining layers.
►Leaky confining unit (K is too low to be an aquifer, but great enough to permit significant flow through the layer)
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Other geological formations!Other geological formations!
►Aquitard (flow through the layer is signifcant on a regional scale or over very long (e.g., geologic) time scales) sandy clay
►Aquifuge (no K and no n) massive rock
►Aquiclude (no/very less K) clay►Aquiclude (no/very less K) clay
How water occurs in How water occurs in beneath ground surface?beneath ground surface?
S b lid iS b lid i►► Spaces between solid grains Spaces between solid grains –– PoresPores►► FracturesFractures►► Measure of pore volume Measure of pore volume -- PorosityPorosity►► Measure of water yield Measure of water yield –– Specific YieldSpecific Yield►► Measure of water retention Measure of water retention ––
Specific Retention Specific Retention
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Porosity
%% 100%100%VVVVn% =n% =n% = porosity (expressed as a percentage)n% = porosity (expressed as a percentage)VVVV = volume of the void space= volume of the void spaceVVTT = total volume of the material (void + rock)= total volume of the material (void + rock)
Volume of water that a permeable unit will absorb or expel from storage per unit surface area per unitstorage per unit surface area per unit change in head.
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Storage CoefficientThe storage coefficient (S) consists of two components:
water released from compressibility of aquiferpore fluid draining of the aquifer
S = SsbSs = specific storage (1/L)b = saturated thickness (L)S < 0.005
For confined aquifers, there is no draining of the pores, so all storage comes from the compressibility component
For unconfined aquifers, most of the water is from draining, contribution from compressibility is very small
S = Sy + Ssbb = saturated thickness (L) Sy = specific yieldSs = specific storage (1/L) usually, Sy >> Ssb
S ~ Sy S: 0.02 to 0.30
Specific Storage (Ss)
Amount of water per unit volume of a saturated formation that is stored or expelled from storage owing to compressibility of the mineral skeleton and pore
Elastic storage coefficient
compressibility of the mineral skeleton and pore water per unit head change (unit=1/L)
Ss = ρwg(α + nβ)ρw = density of water
α = compressibility of aquifer skeletong = acceleration of gravity
S = Ssb
α compressibility of aquifer skeletonn = porosity
β = compressibility of water
What contributes more to storage, compressibility of water or compressibility of matrix?
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Aquifer Compressibility:
1. Compressibility of Water2. Compressibility of Porous Medium
In the saturated zone the head create pressure which affect the arrangement of mineral grains as well as density of water in the voids
The expansion of mineral skeleton and pressure areThe expansion of mineral skeleton and pressure are directly proportional (elasticity).
The contraction of water in aquifer and the pressure created by head is inversely proportional.
Think of a tyreFilled with air under pressure
When we release itit is still filled with airSystem is elastic
If pressure increasesSkeleton Water
If pressure increases, Mineral skeleton will expand
Water will contract
If pressure drops,
PExpansion of mineral skeleton and pressure -> directly proportional (elasticity). Contraction of water in aquifer and pressure created by head -> inversely proportional.
Expansion of Water
Compaction of the Aquifer Skeleton
p p ,Mineral skeleton will contract
Water will expandP
When PumpingReduce the Pressure
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Clay 10-6 to 10-8
Sand 10-7 to 10-9
Gravel 10-8 to 10-10
Shale 10-9 to 10-10
Compressibility of Geologic Materials (m2 N-1)
asin
g
Shale 10-9 to 10-10
Sandstone 10-10 to 10-11
Limestone 10-10 to 10-11
Igneous/Metamorphic 10-11
Water 4.4 x 10-10
Dec
rea
Discharge of groundwaterfrom a spring in California.
Springs generally emerge atth b f hill l
Springs
the base of a hillslope.Some springs produce water
that has traveled for manykilometers; while others emitwater that has traveled onlya few meters.
Springs represent placeswhere the saturated zone(below the water table)comes in contact with theland surface.(from Keller, 2000, Figure 10.8)
S. Hughes, 2003
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Groundwater Table and Occurrence
In Arid Areas: Water table flatter
In Humid Areas: Water Table Subdued Replica of Topography
Subdued replica of topographyWater Table Mimics the Topography
Need gradient for flow
Discharge occurs in topographically low sites
Need gradient for flowIf water table flat – no flow occurringSloping Water Table – Flowing Water
Particle Size Distribution Particle Size Distribution GraphGraph
Tectonic valleys — Intermontane basins
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Water in Rock MaterialWater in Rock Material
M t f th i d t hi kM t f th i d t hi kMost of the igneous and metamorphic rocks Most of the igneous and metamorphic rocks are very dense with interlocked texture. are very dense with interlocked texture.
The rocks therefore have extremely low The rocks therefore have extremely low permeability and porosity. permeability and porosity.
Some clastic sedimentary rocks, typically Some clastic sedimentary rocks, typically d t b d bld t b d blsandstones, can be porous and permeable. sandstones, can be porous and permeable.
Weathered rocks can also be porous and Weathered rocks can also be porous and permeable.permeable.
►►conglomerateconglomerate►►High porosity, high permeabilityHigh porosity, high permeability
►►LimestoneLimestone►►high porosity and low permeabilityhigh porosity and low permeability
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Groundwater as a Geologic Groundwater as a Geologic AgentAgent
Groundwater as a Geologic Groundwater as a Geologic AgentAgent
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Groundwater as a Geologic Groundwater as a Geologic AgentAgent
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LimestoneLimestone
Igneous rocksIgneous rocks
Groundwater percolates downward through Groundwater percolates downward through the regolith which is a layer of weatheredthe regolith which is a layer of weatheredthe regolith which is a layer of weathered the regolith which is a layer of weathered rock, alluvium, rock, alluvium, colluviumcolluvium and soil to and soil to fractures in underlying bedrock. fractures in underlying bedrock.
►►HydraulicHydraulic►►Hydraulic Hydraulic Conductivity Conductivity of bedrock is of bedrock is controlled bycontrolled by
Size of fracture openingsSize of fracture openingsSpacing of fracturesSpacing of fracturesInterconnectedness of fracturesInterconnectedness of fractures
Geologic origin of aquifersGeologic origin of aquifers
Todd (1996)Todd (1996)
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is a graph showing changes in the discharge of a river over a period of
Hydrograph
discharge of a river over a period of time.
Unit Hydrograph TheoryUnit Hydrograph Theory
►►The unit hydrograph is the response of the The unit hydrograph is the response of the watershed to 1 unit of excess runoffwatershed to 1 unit of excess runoffwatershed to 1 unit of excess runoff watershed to 1 unit of excess runoff distributed uniformly over the entire distributed uniformly over the entire watershedwatershed
1 inch (English units)1 inch (English units)1 mm (Metric units)1 mm (Metric units)
http://www.tcnj.edu/~horst/classes.htm
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Unit Hydrograph TheoryUnit Hydrograph Theory
Unit Hydrograph vs Storm Hydrographs
100
150
200
250
300
350
400
Flow
0
50
100
0 5 10 15 20 25 30
Time
Significance of Unit HydrographSignificance of Unit Hydrograph
►►Watersheds response to a given amount of Watersheds response to a given amount of excess precipitation is just a multiplier ofexcess precipitation is just a multiplier ofexcess precipitation is just a multiplier of excess precipitation is just a multiplier of the unit hydrographthe unit hydrograph
►►Use unit hydrograph as a basis to determine Use unit hydrograph as a basis to determine the storm hydrograph from any given the storm hydrograph from any given rainfall distributionrainfall distribution
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ExampleExample
►►Given the following rainfall distributionGiven the following rainfall distribution
Time Precipitation
1 0.5
2 3
3 1.5
4 0.2
►►The watershed will respond as followsThe watershed will respond as follows
http://www.tcnj.edu/~horst/classes.htm
ExampleExample
Incremental Storm Hydrographs
200
300
400
500
Flow
Time Precipitation
1 0.5
2 3
3 1.5
4 0.2
0
100
0 5 10 15 20 25 30 35
Time
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ExampleExample
Incremental + Final Storm Hydrograph
00
200
300
400
500
Flow
0
100
0 5 10 15 20 25 30 35
Time
Unit Hydrograph DerivationUnit Hydrograph Derivation►► A unit hydrograph is derived from historical rainfall and A unit hydrograph is derived from historical rainfall and
runoff datarunoff data
►► The volume of water produced by the storm (area under The volume of water produced by the storm (area under the hydrograph curve) divided by the area of the the hydrograph curve) divided by the area of the watershed equals depth of excess precipitationwatershed equals depth of excess precipitation
►► The ordinates of the storm hydrograph are divided by this The ordinates of the storm hydrograph are divided by this depth to obtain the unit hydrographdepth to obtain the unit hydrographdepth to obtain the unit hydrographdepth to obtain the unit hydrograph
►► Timing must be taken into consideration (STiming must be taken into consideration (S--curve curve technique to adjust timing)technique to adjust timing)
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Role of Geological Structures on Groundwater Occurrence & Flow
Attitude of formationsAttitude of formations
Joints and Faults
Folds
Igneous intrusions
Attitude of formations
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Artesian AquifersArtesian Aquifers
“artesian”
GW under pressure due to dipping layers
Non-flowing
Free-flowing
A. Although the contaminated water has traveled more than 100 m before reaching Well 1, the water moves too rapidly through the limestone to be purified.
B. As the discharge from the septic tank percolates through the sandstone, it is
ifi d i l ti l h tpurified in a relatively short distance.
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Folds Folds
Axis weak zonezoneOasisdesert spring
Joints and Faults
Weak zones
Increase porosity and K
Increase rate of weathering
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±Igneous Intrusives
±
LegendDykes
Igneous Intrusives
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Impact of dykesImpact of dykes
113
Impact of dykesImpact of dykes
114
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Land subsidence Land subsidence
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KARSTKARSTKarst Topography
A. GW percolates through limestone along joints and bedding planes. Dissolution creates and enlarges caverns at and below the water table.
B Si kh l f h thB. Sinkholes form when the roof of a cavern collapses. Surface streams may disappear down sinkholes and reappear as springs.
C. As time passes, caverns grow larger and the number and size of sinkholes increase. Collapse of caverns and coalescence of sinkholes form larger, flat-floored depressions (solution valleys). Eventually dissolution may remove most of the limestone from the area, leaving only isolated remnants (towers).
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KARSTKARST Guilin CHINA
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GW ErosionGW ErosionCaverns form as a result of dissolution of carbonate rocks below the water table