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
Hydrogeology Defined WaterEarth InteractionsHydrogeology Defined WaterEarth InteractionsGeology controls groundwater flow
Permeable pathways are controlled by distributions of geological materials.
Groundwater availability is controlled by geology.
Hydrogeology Defined WaterEarth InteractionsHydrogeology Defined WaterEarth InteractionsGeology 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.
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
Effects of Pumping Wells
Dry river
Dry well
Effects of Pumping Wells
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
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.