11: Groundwater Water resources Geologic Agent. Earth materials Rock Sediment (Soil) Fluids (Water)...

11: Groundwater

Water resources Geologic Agent

Earth materials• Rock• Sediment (Soil)• Fluids (Water)

Geologic processes• Form,• Transform and• Distribute (redistribute) Earth materials

Water is a primary agent of many (all?) geologic processes

Hydrogeology DefinedHydrogeology DefinedWater Earth

Hydrogeology Defined Water EarthHydrogeology Defined Water EarthInteractions go both ways GeologyGroundwater

Geology controls flow and availability of groundwater because

Groundwater flows through the pore spaces and/or fractures

Groundwater geologic processes.

InteractionsInteractions

Hydrogeology Defined WaterEarth InteractionsHydrogeology Defined WaterEarth InteractionsGeology controls groundwater flow

Permeable pathways are controlled by distributions of geological materials. E.g., Artesian (confined) aquifer

Shale

ShaleSandstone


Permeable pathways are controlled by distributions of geological materials.

Groundwater availability is controlled by geology.


Permeable pathways are controlled by distributions of geological materials.

Groundwater availability is controlled by geology. Subsurface contaminant

transport in is controlled

by geology.

Geology controls groundwater flow Permeable pathways are controlled by

distributions of geological materials. Groundwater availability is controlled by geology. Subsurface contaminant

transport in is controlled

by geology.

Hydrogeology Defined WaterEarth InteractionsHydrogeology Defined WaterEarth Interactions

Groundwater controls geologic processes Igneous Rocks:

Groundwater controls water content of magmas.

Metamorphic Rocks: Metasomatism (change in composition) is controlled by superheated pore fluids.

Volcanism: Geysers are an example of volcanic activity interacting with groundwater.

Hydrogeology Defined WaterEarth InteractionsHydrogeology Defined WaterEarth InteractionsGroundwater controls geologic processes Landforms: Valley development and karst topography are

examples of groundwater geomorphology. Landslides: Groundwater controls slope failure. Earthquakes: Fluids control fracturing, fault movement,

lubrication and pressures.

Hydrogeology SubdisciplinesHydrogeology Subdisciplines

Water resource evaluation What controls how much

groundwater is stored and can be safely extracted?

What controls where groundwater comes from and where it flows?

What controls natural water quality: natural interactions with geological materials control the chemistry of groundwater?

How can we protect groundwater recharge areas and groundwater reservoirs from contamination and depletion?

Water resource evaluation What controls how much

groundwater is stored and can be safely extracted?

What controls where groundwater comes from and where it flows?

What controls natural water quality: natural interactions with geological materials control the chemistry of groundwater?

How can we protect groundwater recharge areas and groundwater reservoirs from contamination and depletion?

Hydrogeology SubdisciplinesHydrogeology Subdisciplines Contaminant Hydrogeology

Anthropogenic effects: degradation of water quality due to human influences (contamination)

How fast are dissolved contaminants carried by groundwater?

Transport pathways of contaminants: Where are sources of contamination impacting the groundwater, where are the going and what are the destinations?

Remediation (clean-up) of contaminants dissolved in the groundwater.

PotentiometricSurface

What controls: How much groundwater

flows? How fast groundwater

flows? Where groundwater

flows?

Darcy’s Law Answers the fundamental questions of hydrogeology.

Darcy’s LawHenry Darcy’s Experiment (Dijon, France 1856)

AQxQhQ ,1, AQxQhQ ,1,

xhAKQ

xhAQ

xhAKQ

xhAQ

xQ

Q: Volumetric flow rate [L3/T]

Darcy investigated ground water flow under controlled conditions

h

h1 h2

h

x

h1

Slope = h/x ~ dh/dx

hx

h2

x1 x2

K: The proportionality constant is added to form the following equation:

K units [L/T]

A

: Hydraulic Gradientxhh

A: Cross Sectional Area (Perp. to flow)

Calculating Velocity with Darcy’s Law Q= Vw/t

Q: volumetric flow rate in m3/sec Vw: Is the volume of water passing through area “a” during t: the period of measurement (or unit time).

Q= Vw/t = H∙W∙D/t = a∙v a: the area available to flow D: the distance traveled during t v : Average linear velocity

In a porous medium: a = A∙n A: cross sectional area (perpendicular to flow) n: porous For media of porosity

Q = A∙n∙v v = Q/(n∙A)=q/n

Vw

v

Darcy’s Law (cont.)

Other useful forms of Darcy’s Law

QA =

QA.n =

qn =

Volumetric Flux (a.k.a. Darcy Flux or

Specific discharge)

Ave. Linear

Velocity

Used for calculating

Q given A

Used for calculating average velocity of groundwater transport

(e.g., contaminant

transport Assumptions: Laminar, saturated flow

Volumetric Flow RateUsed for calculating Volumes of groundwater flowing during period of time

Darcy’s Law Application

Settling Pond Example*

Questions to be addressed:

How much flow can Pond 1 receive

without overflowing? Q?

How long will water (contamination)

take to reach Pond 2 on average?v?

How much contaminant mass will enter Pond 2 (per unit time)?

M?

A company has installed two settling ponds to:Settle suspended solids from effluent Filter water before it discharges to streamDamp flow surges

*This is a hypothetical example based on a composite of a few real cases

5000 ft

652658

0

N

Pond 1

Pond 2

Application (cont.)

W1

510

ft

x =186

Pond 1 Pond 2

Outfall

Elev.=658.74 ft

Elev.=652.23 ft

Q? v? M?

K

x =186 ft

b=8.56 ft

Water flows between ponds through the saturated fine sand barrier driven by the head difference

Sand

Clay

h=6.51 ft

ContaminatedPond

b

xNot to scale

Overflow

Application (cont.)

Develop your mathematical representation(i.e., convert your conceptual model into a mathematical model) Formulate reasonable assumptions

Saturated flow (constant hydraulic conductivity)

Laminar flow (a fundamental Darcy’s Law assumption)

Parallel flow (so you can use 1-D Darcy’s law) Formulate a mathematical representation of your conceptual model that:

Meets the assumptions and Addresses the objectives

M = Q CM = Q CQ? v? M?

Application (cont.)

Collect data to complete your Conceptual Model and to Set up your Mathematical Model The model determines the data to be collected

Cross sectional area (A = w b) w: length perpendicular to flow b: thickness of the permeable unit

Hydraulic gradient (h/x) h: difference in water level in ponds x: flow path length, width of barrier

Hydraulic Parameters K: hydraulic tests and/or laboratory tests n: estimated from grainsize and/or laboratory tests

Sensitivity analysis Which parameters influence the results most strongly? Which parameter uncertainty lead to the most uncertainty in the results?

xh

AKQ

xh

AKQ

xh

nK

v

xh

nK

v

M = Q CM = Q C

Q?

v?

M?

Ground Water ZonesGround Water Zones Degree of saturation

defines different soil water zones

Unsaturated Zone:

Saturated Zone: Where all pores are completely filled with water. Phreatic Zone: Saturated zone below the water table

Water in pendular saturation

Water Table: where fluid pressure is equal to atmospheric pressure

Soil and Groundwater ZonesSoil and Groundwater Zones

Caplillary Fringe: Water is pulled above the water table by capilary suction

Ground water and the Water cycle Infiltration Infiltration capacity Overland flow Ground water

recharge GW flow GW discharge

Bedrock Hydrogeology

Hydraulic Conductivity of bedrock is controlled by

Size of fracture openings Spacing of fractures Interconnectedness of fractures

Porosity and Permeability

Porosity: Percent of volume that is void space.

Sediment: Determined by how tightly packed and how clean (silt and clay), (usually between 20 and 40%)

Rock: Determined by size and number of fractures (most often very low, <5%) 1%

5%30%

Porosity and Permeability

Permeability: Ease with which water will flow through a porous material Sediment: Proportional to

sediment size GravelExcellent SandGood SiltModerate ClayPoor

Rock: Proportional to fracture size and number. Can be good to excellent

Excellent

Poor

Porosity and Permeability Permeability is not

proportional to porosity.

Table 11.1

1%

5%30%

Water table: the surface separating the vadose zone from the saturated zone.

Measured using water level in well

The Water Table

Fig. 11.1

Precipitation Infiltration Ground-water

recharge Ground-water flow Ground-water

discharge to Springs Streams and Wells

Ground-Water Flow

Velocity is proportional to Permeability Slope of the water

table Inversely

Proportional to porosity

Ground-Water Flow

Fast (e.g., cm per day)

Slow (e.g., mm per day)

Infiltration Recharges ground

water Raises water table Provides water to

springs, streams and wells

Reduction of infiltration causes water table to drop

Natural Water Table Fluctuations

Reduction of infiltration causes water table to drop Wells go dry Springs go dry Discharge of rivers

drops Artificial causes

Pavement Drainage

Natural Water Table Fluctuations

Pumping wells Accelerates flow

near well May reverse

ground-water flow Causes water table

drawdown Forms a cone of

depression

Effects of Pumping Wells

Pumping wells Accelerate flow Reverse flow Cause water

table drawdown Form cones of

depression Low river

GainingStream

GainingStream

Pumping well

Low well

Low well

Cone of Depression

Water TableDrawdown

Dry Spring


Dry river

Dry well


Dry well

Dry well

LosingStream

Continued water-table drawdown May dry up

springs and wells May reverse flow

of rivers (and may contaminate aquifer)

May dry up rivers and wetlands

Ground-Water/ Surface-Water

Interactions

Gaining streams Humid regions Wet season

Loosing streams Humid regions, smaller

streams, dry season Arid regions

Dry stream bed

Confined Aquifers

Ground-Water Contamination

Dissolved contamination travels with ground water flow

Contamination can be transported to water supply aquifers down flow

Pumping will draw contamination into water supply

Ground-Water Contamination Leaking Gasoline

Floats on water table

Dissolves in ground water

Transported by ground water

Contaminates shallow aquifers

Ground-Water Contamination Dense solvents

E.g., dry cleaning fluid (TCE)

Sinks past water table

Flows down the slope of an impermeable layer

Contaminates deeper portions of aquifers

Ground-Water Contamination Effects of pumping

Accelerates ground water flow toward well

Captures contamination within cone of depression

May reverse ground water flow

Can draw contamination up hill

Will cause saltwater intrusion

Ground Water Action

Ground water chemically weathers bedrock E.g., slightly acidic

ground water dissolves limestone

Caves are formed Permeability is increased Caves drain Speleothems form

Ground Water Action Karst Topography

Caves Sink holes Karst valleys

Disappearing streams Giant springs

Ohio Groundwater LawOhio Groundwater Law

1843: Acton v. Blundell “English Rule”

The landowner can pump groundwater at any rate even if an adjoining property owner were harmed.

1843: Acton v. Blundell “English Rule”

The landowner can pump groundwater at any rate even if an adjoining property owner were harmed.

1861: Frazier v. Brown English Rule in Ohio

Groundwater is “…occult and concealed…” and legislation of its use is “…practically impossible.”

1861: Frazier v. Brown English Rule in Ohio

Groundwater is “…occult and concealed…” and legislation of its use is “…practically impossible.”

Wisconsin Groundwater LawWisconsin Groundwater Law

1903: Huber v. Merkel

English Rule in Wisconsin

A property owner can pump unlimited amounts of groundwater,

even with malicious harm to a neighbor.

1903: Huber v. Merkel

English Rule in Wisconsin

A property owner can pump unlimited amounts of groundwater,

even with malicious harm to a neighbor.

1974: Wisconsin v. Michels Pipeline Constructors Inc.

English Rule Overturned

Landowners no longer have

“an absolute right to use with impunity all water that can be pumped from the subsoil underneath.”

1974: Wisconsin v. Michels Pipeline Constructors Inc.

English Rule Overturned

Landowners no longer have

“an absolute right to use with impunity all water that can be pumped from the subsoil underneath.”

English Rule Overturned in OhioEnglish Rule Overturned in Ohio

1984: Cline v. American Aggregates English Rule overturned in Ohio

Justice Holmes: “Scientific

knowledge in the field of hydrology has advanced in the past decade…” so it

“…can establish the cause and

effect relationship of the tapping of underground water to the existing water level.”

1984: Cline v. American Aggregates English Rule overturned in Ohio

Justice Holmes: “Scientific

knowledge in the field of hydrology has advanced in the past decade…” so it

“…can establish the cause and

effect relationship of the tapping of underground water to the existing water level.”

Today: Lingering effects of English Rule

It is very difficult to prove cause and effect to be defensible in court.

Today: Lingering effects of English Rule

It is very difficult to prove cause and effect to be defensible in court.

11: Groundwater Water resources Geologic Agent. Earth materials Rock Sediment (Soil) Fluids (Water)...

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