Transcript Contaminant Hydrogeology V

Гидрогеология Загрязнений
и их Транспорт в
Окружающей Среде
Yoram Eckstein, Ph.D.
Fulbright Professor 2013/2014
Tomsk Polytechnic University
Tomsk, Russian Federation
Fall Semester 2013
Subsurface
Environment
A Hidden Reserve: Groundwater
 Much of the global water, resides
below the surface of the Earth as
groundwater.
 Although in the subsurface, it has a
large impact on society and the
features that we see on the surface
of the Earth.
 In general, surface water gets into
the subsurface by infiltration.
The Winter Park, Florida sinkhole
Central-pivot irrigation utilizing
groundwater, Jordan
The Underground Reservoir
 Some precipitation enters the subsurface via infiltration.
 Soil properties and vegetation govern infiltration rate.
 Infiltrated water adds to soil moisture and groundwater.
 Soil moisture wets the soil.
 Some is wicked up by roots, some is evaporated.
The Underground Reservoir
 Some infiltrated water percolates to a deeper level.
 It is added to water that fills subsurface void spaces.
 This is groundwater.
Primary vs. Secondary
Porosity
 Primary Porosity – This
is the porosity of the rock
after it first lithifies/forms
based on the spaces between
grains.
 Fine grained sediment has a
lower porosity because the
little grains can fill in the
spaces.
 Crystalline rocks have very
low primary porosity.
 Secondary Porosity –
New pore space created in
the rock at some time after
the rock formed
 E.g. Joints, Faults,
Dissolution.
 Because of secondary
porosity any rock could
potentially have some
porosity.
Porosity vs. Permeability
 If solid rock completely
surrounds a water-filled pore,
then the water cannot flow.
 For groundwater to flow, pore
spaces must be interconnected.
 The ability of a rock to allow a
fluid to flow through an
interconnected network of
pores is called Permeability.
 If a rock has a high porosity, it
does not necessarily have a
high permeability. The pores
must have interconnected
conduits!
 E.g. porous cork, is nearly
impermeable
 Permeability depends on:
 Number of available conduits
 Size of conduits
 Straightness of conduits
Aquifers and Aquitards
 Hydrogeologists distinguish between rocks that transmit
water easily and rocks that do not easily transmit water.
 Aquifer – A rock that easily transmits water
 Aquitard – A rock that does not transmit water easily (i.e.
retards water motion)
 Aquifuge – A rock that does not transmit water at all
• Unconfined Aquifer – An
aquifer that has direct access to
the surface of the Earth
– Can be quickly recharged
by meteoric water
• Confined Aquifer – An aquifer
that is trapped below an
aquitard or aquifuge
Hydrogeologic Zones
 Unsaturated Zone / Vadose Zone – The portion of the
subsurface where some of the pores are filled with only air.
 Saturated Zone / Phreatic Zone – The portion of the
subsurface where the pores are completely filled with water.
 Water Table – The boundary between these two zones
How deep does
the saturated
zone go?
Hydrogeologist
s are not sure…
At some depth
(10-20km)
water is
utilized for
metamorphic
reactions.
Topography of the Water Table
 The water table is not a flat surface that never changes…
 It may have seasonal oscillations (wet dry seasons) and rise and fall
 Underneath mountains and hills, the water table follows a similar
but subdued shape
Perched Water Tables
 A locally present aquitard may create a Perched
Water Table, a localized phreatic zone (saturated)
above the regional water table.
Can form springs if
the perched water
table intersects
surface topography
Recharge and Discharge
 Groundwater flows downward in areas of Recharge, and upward
in areas of Discharge.
 But what causes groundwater to flow??
 Hydraulic Head: A measure of the potential energy
available to drive the flow of a given volume of groundwater.
 Groundwater flows from locations of high hydraulic head to low
hydraulic head.
Hydraulic Head and Hydraulic Gradients
 In an unconfined aquifer:
 Hydraulic head = the weight of the water above it. (Similar to air
pressure)
 Water will always flow from regions of high to low head
 In a confined aquifer:
 Hydraulic head is
measured by drilling holes
into the ground and
measuring the level to
which water fills the hole.
 Hydraulic Gradient: the
change in head from one
location to another.
Controls groundwater
velocity
Groundwater Discharge and Darcy’s Law
 Groundwater discharge:
 Henry Darcy (French Engineer), coined what we now call Darcy’s Law.
 If you know:
 the hydraulic gradient (Δh/j)
 the hydraulic conductivity (K)
 the area through which the water is flowing (A)
 Discharge = Q = K(Δh/j)A
• Sometimes we simplify this
and say that
• Discharge = Slope of Water
Table × Permeability
How Fast Does Groundwater Flow?
 Water in an ocean current ~ 3 km/hr (1.8 Mph)
 Water in a river - up to 30 km/hr (18 Mph)
 Groundwater – 0.01 - 1.4 m/day (~4-500 m/yr)
 Why so slow? - Conduits are very curved and small, so groudwater
must flow in a very crooked path and friction with conduit walls
slows it down.
 Hydrogeologists measure flow in some regions by injecting tracers
(a dye, radioactive element, or bacteria) and monitor its movement.
 Some
groundwater may
emerge after
months or years,
but some may not
emerge for
thousands to tens
of thousands of
years.
Wells – How We Get To Groundwater
 Since water is important to society, access
to groundwater is important.
 We access groundwater through wells and
springs (where groundwater percolates
out at the surface of the Earth).
 An ordinary well penetrates to a depth
below the water table where an aquifer
allows access to flowing water. We then
either pump it out (right) or manually pull
up the water (below).
Well Drawdown & Cones of Depression
 If a well pumps out water faster than it is replaced by normal
groundwater flow, it draws down the water table in what is
called a Cone of Depression.
 Cones of depression can make
nearby wells temporarily dry.
 So when drilling a well, drillers
must consider both the flow rate in
the aquifer and the pumping rates
of nearby wells.
Artesian Wells
 In some places, groundwater does not need to be pumped out of a well; if
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water freely flows out of the well it is called a flowing artesian well.
To see why this happens, lets look at a city water supply and water towers.
Cities first pump water from the local aquifer/source into a high reservoir
tank.
This high tank is connected to the houses in town by a network of
underground pipes.
The pressure in the elevated tank provides the push to make water rise out
of the pipes of town. The level to which the water will rise is called the
Potentiometric Surface.
• Therefore, the water
company doesn’t have to
pump water to your house,
just to the raised tower.
• So if you are on city water,
you are likely getting it
because you have an artesian
connection to the city water.
Artesian Wells in Nature
 An artesian well can occur in nature when a well penetrates a
confined aquifer that is under great pressure.
 If the potentiometric surface is above ground, the well will be a
flowing artesian well.
 If the potentiometric surface is above the water table, but below
the ground, it will be a non-flowing artesian well.
Springs – What Conditions Cause
Them to Form?
 Spring – A location where groundwater is discharged
from the ground
 The springs can form in various hydrologic scenarios
Springs – What Conditions Cause
Them to Form?
• Note that an Artesian Spring is a
natural feature while and artesian
well is drilled by man.
Oasis...Mirage or Geology?
 Folded aquifers and faults can cause an
Oasis to form.
 These are important stops for people
traveling across the Sahara.
 Faults can bring deep water up to the
surface of the Earth forming a hot spring.
Karst Landscapes and Groundwater
 Groundwater can dissolve
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calcite bearing rocks such
as limestone.
When CO2 mixes with
water is makes a weak acid
called carbonic acid that
speeds this process.
Over time, changes in the
water table may form
complex networks of
caves.
If a large cave becomes
near to the surface of the
Earth (usually by erosion),
it can collapse forming a
sinkhole.
Terrain dominated by
sinkholes is called Karst
Landscape or Karst
Topography.
How Does Groundwater Flow
Through
Limestone?
 Although limestone is
nearly impermeable,
it is commonly
jointed.
 The joints provide a
secondary porosity
and allow
groundwater to flow
through.
Karst Landscapes
http://www.youtube.com/watch?v=YH5j_okckkY
http://www.youtube.com/watch?v=n0op-h7yT2s&feature=fvwrel
Arecibo Observatory, Puerto Rico
Groundwater…Infinite or Finite?
 Although on scales of tens of thousands of years,
groundwater is renewable, if usage is high, it can
be a big problem on scales of years to hundreds of
years.
An Industrial
well, lowers
the water
table and
dries up a
river
Groundwater Problems
 Large wells can
change the
direction of
groundwater flow
moving
contaminants into
unsafe places.
Groundwater Problems
 Saltwater is more
dense than
freshwater so it
stays below the
fresh water table.
 Pumping and
drawdown can
cause saltwater
influx into what
would naturally
be freshwater
aquifers.
Groundwater Problems
 Saltwater influx is a huge problem in Florida.
Groundwater Problems
 Groundwater pressure holds
grains of rock apart.
 When water is removed, the
once wet layer may become
compacted, causing
subsidence above the aquifer.
Methods for classification of
groundwater contamination sources
Classification Examples
By way of release Discharge sources; transport
sources
By origin
Domestic sources; agricultural
sources
By chemical type Heavy metals; hydrocarbons;
pesticides
By location
Above ground surface; below
surface
By character
Point, diffuse, and line sources
Potential sources of groundwater
contamination by character of discharge
CATEGORY I: sources designed to discharge
substances
 Subsurface percolation (septic tanks, cesspools)
 Injection wells
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Hazardous waste
Non-hazardous waste (brine disposal, drainage)
Artificial recharge
Solution mining
Enhanced recovery
 Land applications
 Waste water (e.g., spray irrigation)
 Waste water by-products (e.g., sludge)
 Hazardous waste and non-hazardous waste (brine)
Potential sources of groundwater
contamination by character of discharge
CATEGORY II: sources designed to store, treat,
and/or dispose substances
 Landfills
 Industrial hazardous waste
 Industrial non-hazardous waste
 Municipal sanitary landfills
 Surface impoundments
 Hazardous liquid waste
 Non-hazardous liquid waste (e.g., brine, sludge)
 Mining waste tailings
 Material stockpiles (coal, salt, etc.)
 Illegal dumps
Potential sources of groundwater
contamination by character of discharge
CATEGORY II: sources designed to store, treat,
and/or dispose substances (continued)
 Radioactive disposal sites
 Low-level radioactive disposal sites
 High-level radioactive disposal sites
 Low-level & long half-lives radioactive materials
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Above-ground storage tanks
Under-ground storage tanks
Mobile containers
Material stockpiles (coal, salt, etc.)
Illegal dumps
Graveyards
Potential sources of groundwater
contamination by character of discharge
CATEGORY III: sources designed to retain
substances during transport or transmission;
discharge by accident or negligence
 Pipelines
 Overland transport
Potential sources of groundwater
contamination by character of discharge
CATEGORY IV: sources discharging substances
as a consequence of other planned activities
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Irrigation practices (e.g., return flow)
Fertilizer application
Pesticide/herbicide application
De-icing salt application
Animal feeding operations (feedlots)
Urban runoff
Percolation of atmospheric contaminants
Mining effluents
Potential sources of groundwater
contamination by character of discharge
CATEGORY V: sources providing conduit or
inducing discharge through altered flow
patterns
 Production wells
 Water wells
 Oil/gas wells
 Geothermal and heat recovery wells
 Construction excavations
Potential sources of groundwater
contamination by character of discharge
CATEGORY VI: naturally occurring sources;
discharge created or exacerbated by human
activity
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Groundwater-Surface water interaction
Natural leaching
Saltwater intrusion
Salt- or brackish-water upconing
Summary of groundwater
contamination sources by origin (1)
Category Source type Usual
Normal
character location
Natural
sources
Inorganic
substances
Trace metals
Radionuclides
e.g., sea water
intrusion
Organic
Oil/gas
compounds
deposits
Microorganisms Diffuse
Near intrusions
Near acidic
intrusions
Shallow to
moderate depth
Shallow to
moderate depth
Summary of groundwater
contamination sources by origin (2)
Category Source type Usual
Normal
character location
Agriculture
and
forestry
Fertilizers
Pesticides
Animal waste
Diffuse
Diffuse
Diffuse/point
Animal feedlots Point
Irrigation return
flow
Diffuse
Stockpiles
Point
Surface
Surface
Surface & zone
unsaturated
Surface
Surface
Surface
Surface & zone
unsaturated
Summary of groundwater
contamination sources by origin (3)
Category Source type Usual
Normal
character location
Urbanisation
Solid waste sites Point
Wastewater,
effluent
Salvage and
junk yards
Leaking storage
tanks
Runoff, leaks,
spills
Point
Point
Point
Line and
point
Surface & zone
unsaturated
Surface & zone
unsaturated
Surface & zone
unsaturated
Surface & zone
unsaturated
Surface & zone
unsaturated
Summary of groundwater
contamination sources by origin (4)
Category Source type Usual
Normal
character location
Mining &
Industry
Mine tailings
Mine water
Solid waste
Wastewater,
effluent
Injection wells
Spills, leaks
Point
Surface & zone
unsaturated
Point and line Various
Point
Surface & zone
unsaturated
Surface & zone
Point and line unsaturated
Point
Below water
table
Point
Surface
Summary of groundwater
contamination sources by origin (5)
Category Source type Usual
Normal
character location
Water
Well-field
Mismanage- design
ment
Upconing
Seawater
Faulty well
construction
Abandoned
wells
Irrigation
practices
Point
Below water table
Point
Below water table
Line
Below water table
Point
Below water table
Diffuse
Surface
Summary of groundwater
contamination sources by origin (6)
Miscella Source type Usual
Normal
neous
character location
Miscellanea
Airborne
sources
Diffuse
Surface water
Line
Transport sector Point and
line
Natural
Point and
disasters
line
Cemeteries
Point
Surface
Below water table
Surface & zone
unsaturated zone
Surface & zone
unsaturated zone
Unsaturated zone
World Health
Organisation
(WHO) Drinking
Water Quality
Guidance 2011
Editors: WHO
Number of pages: 564
Languages: English
ISBN: 978 92 4 154815 1
http://www.who.int/water_sanitation_health/publi
cations/2011/dwq_guidelines/en/index.html
Selected leachate components in
municipal waste disposal sites
(Source: U.S. EPA, 1977)
Component Range (mg/l) Component Range (mg/l)
BOD (5 days)
81 – 33,360 Magnesium
17 – 15,600
COD
40 – 89,520 NH4
0 – 1,106
Copper
0 – 9.9 Zinc
0 – 370
Chloride
Iron (total)
TDS
Arsenic
Chromium
Fluoride
4.7 – 2,500 Lead
0 – 2,820 Sodium
584 – 44,900 Sulfate
0.01 Nitrate
0.05 Selenium
1.5 Cadmium
0.01
0 – 7,700
1 – 1,558
50
0.01
0.003