Hydrogeology Lecture 1
description
Transcript of Hydrogeology Lecture 1
93-482:
Hydrogeological Engineering
Summer 2012
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Hydrogeology
• Hydrogeology
– study of the laws of occurrence and
movement of subterranean water
• Geohydrogeology
• Contaminant Hydrogeology
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Groundwater Contamination Cases • Walkerton May 2000
• Woburn Case – Civil Action
– Contamination of TCE near W.R. Grace's Cryogenic plant and J.J. Riley's (Beatrice Foods) tannery, MA.
• Pacific Gas and Electric Company, California
– contamination of drinking water with hexavalent chromium, also known as chromium (VI), in the southern Calif. Town of Hinkley
• Amherstburg – Arsenic Contamination
• Ville Mercier in Quebec;
• Highway de-icing salt problem in Nova Scotia;
• industrial effluents in Elmira, Ontario;
• various pesticides in the Prairie provinces;
• industrial contamination in Vancouver, British Columbia
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Questions to be Addressed?
• What is groundwater?
• Why is it important?
• Where does it come from?
• How does it move?
• How much can we take for water supplies?
• What is its role in transporting contaminants?
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Objectives
• To impart knowledge on fundamentals of groundwater hydrology, contaminant transport and remediation
• To train students on applying the fundamentals to real world problems
• To equip the students with some of the techniques and tools required for practicing profession in hydrogeology
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Hydrological Cycle
Todd and Mays (2005)
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What is Groundwater?
• Subsurface water that occurs beneath the water table in
soils and geologic formations that are fully saturated
• found underground in the spaces between particles of
rock and soil, or in crevices and cracks in rock.
• flows slowly through water bearing formations (aquifers)
at different rates.
• In places where groundwater has dissolved limestone to
form caverns and large openings, its rate of flow can be
relatively fast but this is exceptional
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Todd and Mays (2005)
Groundwater
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Why is it important?
Groundwater is a major link in the hydrologic cycle
Areas of interest
1. Fluid Motion
Flow rates, direction and amounts
Important for transport of chemical substances/
contamination studies
2. Storage
Amount of fluid available in pore/fractures to exploit.
Involves porosity and compressibility
Important for water resources evaluation, land subsidence
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Groundwater Use in Canada
• Almost nine
million (30.3%)
Canadians
depend on
groundwater
http://www.ec.gc.ca/wate
r/en/nature/grdwtr/e_
sixmil.htm
http://www.ec.gc.ca/WATER/images/nature/grdwtr/a5f6e.htm
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Alfonso Rivera, Chief
Hydrogeologist, 2006
Groundwater Use in Canada
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World Water Supply - Groundwater
http://www.ec.gc.ca/water/images/nature/grdwtr/a5f7e.htm
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How Old is Groundwater?
• Residence time varies from as little as days or weeks to
as much as 10,000 or more years
• By comparison, average turnover time of river water is
about two weeks
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Hydrologic Cycle
Todd and Mays (2005)
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Hydrologic Cycle
Reference???
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Published by AAAS W. M. Alley et al., Science 296, 1985 -1990 (2002)
Hydrological Cycle - Water Fluxes
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Hydrological Cycle
Todd and Mays (2005)
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Groundwater Hydrology –
Its Connection to Mass Transport
• Groundwater flow transports the solutes
and/or contaminants along with it.
• Mechanisms
– Advection
– Dispersion
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Todd and Mays (2005)
Local vs Regional Groundwater flow
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Local vs Regional Groundwater flow
Todd and Mays (2005)
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Definitions
• Aquifer
– Saturated permeable geologic unit that can
transmit significant quantities of water under
ordinary hydraulic gradients
• Confined Aquifer
• Unconfined Aquifer
• Semi-Confined Aquifer
• Aquitard
• Aquiclude
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Definitions
• Aquifer
• Aquitard
– Beds of lower permeability in the stratigraphic sequence that contain water but do not yield water to pumping wells
– Generally referred to as low permeability formations overlie major aquifers
– Aquifer and aquitard separation is ambiguous
• Aquiclude
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Definitions
• Aquifer
• Aquitard
• Aquiclude
– Saturated geologic unit that is incapable of
transmitting significant quantities of water
under ordinary hydraulic gradients
– e.g., Clays
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Confined-Unconfined Aquifers
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Confined-Unconfined Aquifers
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Confined-Unconfined Aquifers
• Unconfined Aquifers –Also water table aquifer
an aquifer in which water table forms the upper
boundary
– Water level – water table
• Confined aquifers – confined between two
aquitards
– Potentiometric surface
– Concept of potentiometric surface is valid in
horizontal flow in horizontal aquifers
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Aquifers
Todd and Mays, 2005
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Recharge-Discharge Areas
• Process by which some of the water from rainfall and melting snow seeps into the soil and percolates into the saturated zone
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Todd and Mays (2005)
Gaining and Losing Streams
Todd and Mays (2005)
Losing Gaining
Streams
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Basic Material Properties of
Media and Fluid
• Media – Porosity (n), permeability (k) and
compressibility (α)
• Fluid – Density (ρ), dynamic viscosity (μ) and
Compressibility (βw)
• Others are derived….
– Hydraulic Conductivity (K), Specific Storage (Ss);
Transmissivity (T) and Storativity (S) in confined
aquifers; Transmissivity (T) and specific yield (Sy) in
unconfined aquifers etc.
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Physical Properties and Principles
• Porosity – void volume/total volume
• Effective porosity – amount of
interconnected pore space available for
fluid flow
• Permeability – Ease with which fluid can
move through a porous rock
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Todd and Mays (2005)
Types of Pore Spaces
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Todd and Mays, 2005
Porosities of Different Porous Media
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Particle Sizes of Different Soils
Todd and Mays, 2005
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Capillary Rise
Todd and Mays, 2005
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Specific Yields
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Summary
• Introduction to Hydrogeology
• Aquifer, Aquitard, Aquiclude
• Confined and Unconfined aquifers
• Recharge and discharge areas
• Gaining and Losing streams
• Properties – Porosity, Effective porosity, Permeability
• Specific Yield