1. 11: Groundwater
Water resources
Geologic Agent

2. Hydrogeology Defined Water Earth Earth materials Geologic processes
Rock
Sediment (Soil)
Fluids (Water)
Geologic processes
Form,
Transform and
Distribute (redistribute) Earth materials
 Water is a primary agent of many (all?) geologic processes

3. Hydrogeology Defined Water Earth
Interactions 
Interactions go both ways
GeologyGroundwater
Geology controls flow and availability of groundwater because
Groundwater flows through the pore spaces and/or fractures
Groundwater  geologic processes.

4. Hydrogeology Defined WaterEarth Interactions
Geology controls groundwater flow
Permeable pathways are controlled by distributions of geological materials.
E.g., Artesian (confined) aquifer
Shale
Sandstone

5. Hydrogeology Defined WaterEarth Interactions
Geology controls groundwater flow
Permeable pathways are controlled by distributions of geological materials.
Groundwater availability is controlled by geology.

6. Hydrogeology Defined WaterEarth Interactions
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.

7. Hydrogeology Defined WaterEarth 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.

8. Hydrogeology Defined WaterEarth Interactions
Groundwater 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.

9. Hydrogeology 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?

10. Hydrogeology 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.

11. Darcy’s Law Answers the fundamental questions of hydrogeology.
What controls:
How much groundwater flows?
How fast groundwater flows?
Where groundwater flows?
Potentiometric
Surface

12. Henry Darcy’s Experiment (Dijon, France 1856)
Darcy’s Law
Henry Darcy’s Experiment (Dijon, France 1856)
Darcy investigated ground water flow under controlled conditions h1 h2 A Dh
Q: Volumetric flow rate [L3/T] h x h1
A: Cross Sectional Area (Perp. to flow) Dx Q
K: The proportionality constant is added to form the following equation:
Controlled laboratory experiment designed to investigate what controls the flow rate (e.g. through a dam)
Experiment
A saturated porous medium is placed in a “column”
(this could just as easily be vertical and was in Darcy’s experiment but this orientation, horizontal flow, is more familiar to us hydrogeologists)
A method of measuring the dependent variable, volumetric flow rate, Q
A method of individually changing the variables that were hypothesized to control flow (the dependant variable)
Manometers can be thought of as wells (but you know that you need more than two wells to calculate groundwater flow rates and directions)
discuss proportionalities
Introduce hydraulic gradient as the slope of head with distance,
Slope at a point is the derivative of the functional relationship between h and x
In reality we use delta h/delta x
Negative sign results from the fact that head decreases in the direction of flow, I.e. when the slope (hydraulic gradient is negative flow id in the positive x direction)
Dimensional analysis shows that the units of K are [L/T] (this is not a velocity but can be thought as a quantitative measure of how easily water flows through the porous media
: Hydraulic Gradient
Slope = Dh/Dx
~ dh/dx Dh Dx h2 x1 x2
K units [L/T]

13. 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 v a Vw H w D

14. Darcy’s Law (cont.) Other useful forms of Darcy’s Law = = =
Used for calculating Volumes of groundwater flowing during period of time
Volumetric Flow Rate
Volumetric Flux
(a.k.a. Darcy Flux or
Specific discharge) Q
Used for calculating Q given A = A
Volumetric Flux: Volumetric flow per unit area (e.g. Rainfall depth is a volumetric flux, R*A=Q) q*A
The volumetric flux is easy to calculate once you have measured (or approximated) the hydraulic gradient and measured or estimated q
In order to calculate velocity you need to account for porosity because the same flow is squeezed through the percentage of pore space represented by the porosity therefor the velocity is greater than the volumetric flux by a factor of 1/n
Once you’ve calculated q you cal calculate Q by multiplying by the cross sectional area (A: the area perpendicular to the flow vector)
and you can calculate v by dividing by n (measured or approximated)
Ave. Linear
Velocity Q q
Used for calculating average velocity of groundwater transport
(e.g., contaminant
transport = =
A.n n
Assumptions: Laminar, saturated flow

15. Darcy’s Law Application
Settling Pond Example*
A company has installed two settling ponds to:
Settle suspended solids from effluent
Filter water before it discharges to stream
Damp flow surges
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?
5000 ft
652
658 N
Pond 1
Pond 2
The company wanted to discharge sediment laden water into Pond 1 and have the water filter through a sand dike before it discharges into the stream
This brings up the first question: How much water could they discharge without overflowing Pond 2?
The upper settling pond is separated from the lower pond by 186 ft of sand
The maximum elevation of Pond 1 is 658 ft and the outlet of Pond 2 is at an elevation of 652
If Pond 1 becomes contaminated with a dissolved contaminant it will flow towards Pond 2 at a rate roughly equivalent to the average groundwater velocity
Once we figure out this velocity (given the distance of travel) it can be used to get a worst case calculation of the time of arrival of the advective front
Once the contamination reaches Pond 2 the volumetric flow rate of the groundwater
*This is a hypothetical example based on a composite of a few real cases

16. Application (cont.) W Q? v? M? Dh=6.51 ft K
Water flows between ponds through the saturated fine sand barrier driven by the head difference
Pond 1
Pond 2
Outfall
1510 ft W
Overflow
Elev.= ft
Elev.= ft
Sand
Dx =186
Q? v? M? K
Dx =186 ft
b=8.56 ft W
Two settling ponds were dug in 10 ft of sand, bottomed on low permeability clay.
Two settling ponds, different levels, separated by an earthen barrier
Start with conceptual model
Clay
Dh=6.51 ft
Contaminated
Pond b Dx
Not to scale

17. Application (cont.) Develop your mathematical representation Q? v? M?
(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
Any mathimatical model requires assumptions in order to represent an infinitely complex natural system with a set of mathematical equations
This is a bit of an art because technically you need to develop a more complex model and demonstrate that the simplifications do not significantly effect the results
If you understand the limits of the model you can make more appropriate assumptions Q? v? M?
M = Q C

18. 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 (Dh/Dx)
Dh: difference in water level in ponds
Dx: 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? Q? v?
The mathematical model is helpful in that it will dictate what information you need to collect
Cross sectional area (perpendicular to flow): A=b*w
Hydraulic gradient: Dh: head difference between ponds, Dx flow pathlength
Discuss sensitivity analysis
The accuracy of the model results depends on 1) how well your assumptions represent reality and 2) how accurately you have determined the parameters of the model.
M = Q C M?

19. Ground Water Zones
Degree of saturation defines different soil water zones

20. Soil and Groundwater Zones
Unsaturated Zone:
Water in pendular saturation
Caplillary Fringe: Water is pulled above the water table by capilary suction
Water Table: where fluid pressure is equal to atmospheric pressure
Saturated Zone:
Where all pores are
completely filled with water.
Phreatic Zone: Saturated zone below the water table

21. Ground water and the Water cycle
Infiltration
Infiltration capacity
Overland flow
Ground water recharge
GW flow
GW discharge

22. Bedrock Hydrogeology
Hydraulic Conductivity of bedrock is controlled by
Size of fracture openings
Spacing of fractures
Interconnectedness of fractures

23. 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%)
30% 5% 1%

24. Porosity and Permeability
Permeability: Ease with which water will flow through a porous material
Sediment: Proportional to sediment size
GravelExcellent
SandGood
SiltModerate
ClayPoor
Rock: Proportional to fracture size and number. Can be good to excellent
Excellent
Poor

25. Porosity and Permeability
Permeability is not proportional to porosity.
30%
Table 11.1 5% 1%

26. The Water Table
Water table: the surface separating the vadose zone from the saturated zone.
Measured using water level in well
Fig. 11.1

27. Ground-Water Flow Precipitation Infiltration Ground-water recharge
Ground-water discharge to
Springs
Streams and
Wells

28. Ground-Water Flow Velocity is proportional to
Permeability
Slope of the water table
Inversely Proportional to
porosity
Fast (e.g., cm per day)
Slow (e.g., mm per day)

29. Natural Water Table Fluctuations
Infiltration
Recharges ground water
Raises water table
Provides water to springs, streams and wells
Reduction of infiltration causes water table to drop

30. 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

31. Effects of Pumping Wells
Accelerates flow near well
May reverse ground-water flow
Causes water table drawdown
Forms a cone of depression

32. Effects of Pumping Wells
Gaining
Stream
Pumping wells
Accelerate flow
Reverse flow
Cause water table drawdown
Form cones of depression
Water Table
Drawdown
Low well
Dry Spring
Cone of
Depression
Gaining
Stream
Low well
Low river
Pumping well

33. Effects of Pumping Wells
Dry well
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
Losing
Stream
Dry well
Dry well
Dry river

34. Ground-Water/ Surface-Water Interactions
Gaining streams
Humid regions
Wet season
Loosing streams
Humid regions, smaller streams, dry season
Arid regions
Dry stream bed

35. Confined Aquifers

36. Confined Aquifers

37. 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

38. Ground-Water Contamination
Leaking Gasoline
Floats on water table
Dissolves in ground water
Transported by ground water
Contaminates shallow aquifers

39. 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

40. 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

41. 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

42. Ground Water Action Karst Topography Caves Sink holes
Karst valleys
Disappearing streams
Giant springs

43. 1861: Frazier v. Brown English Rule in Ohio
Ohio Groundwater Law
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.”

44. Wisconsin 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.
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.”

45. English 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.”
Today: Lingering effects of English Rule
It is very difficult to prove cause and effect to be defensible in court.