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