Title: 11: Groundwater
111 Groundwater
- Water resources
- Geologic Agent
2Hydrogeology Defined
Water
Earth
- 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
3Hydrogeology 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.
4Hydrogeology Defined Water??Earth Interactions
- Geology controls groundwater flow
- Permeable pathways are controlled by
distributions of geological materials. - E.g., Artesian (confined) aquifer
5Hydrogeology Defined Water??Earth Interactions
- Geology controls groundwater flow
- Permeable pathways are controlled by
distributions of geological materials. - Groundwater availability is controlled by
geology.
6Hydrogeology 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.
7Hydrogeology 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.
8Hydrogeology 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.
9Hydrogeology 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?
10Hydrogeology 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.
11Darcys Law Answers the fundamental questions of
hydrogeology.
- What controls
- How much groundwater flows?
- How fast groundwater flows?
- Where groundwater flows?
12Darcys Law
- Henry Darcys Experiment (Dijon, France 1856)
Darcy investigated ground water flow under
controlled conditions
A
Q Volumetric flow rate L3/T
A Cross Sectional Area (Perp. to flow)
Dx
Q
K The proportionality constant is added to form
the following equation
K units L/T
13Calculating Velocity with Darcys 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 HWD/t av
- a the area available to flow
- D the distance traveled during t
- v Average linear velocity
- In a porous medium a An
- A cross sectional area (perpendicular to flow)
- n porous For media of porosity
- Q Anv
- v Q/(nA)q/n
v
Vw
a
H
w
D
14Darcys Law (cont.)
- Other useful forms of Darcys Law
- Used for calculating Volumes of groundwater
flowing during period of time
- Volumetric Flux
- (a.k.a. Darcy Flux or
- Specific discharge)
- Used for calculating Q given A
Q
A
- Used for calculating average velocity of
groundwater transport - (e.g., contaminant
- transport
Q
q
A.n
n
- Assumptions Laminar, saturated flow
15Darcys Law Application
- 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?
This is a hypothetical example based on a
composite of a few real cases
16Application (cont.)
Water flows between ponds through the saturated
fine sand barrier driven by the head difference
Pond 1
Pond 2
W 1510 ft
Outfall
Overflow
Elev. 658.74 ft
Elev. 652.23 ft
Dx 186
Sand
17Application (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 Darcys Law
assumption) - Parallel flow (so you can use 1-D Darcys law)
- Formulate a mathematical representation of your
conceptual model that - Meets the assumptions and
- Addresses the objectives
M Q C
Q?
v?
M?
18Application (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?
M Q C
M?
19Ground Water Zones
- Degree of saturation defines different soil water
zones
20Soil 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
22Bedrock Hydrogeology
- Hydraulic Conductivity of bedrock is controlled by
- Size of fracture openings
- Spacing of fractures
- Interconnectedness of fractures
23Porosity 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, lt5)
30
5
1
24Porosity 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
25Porosity and Permeability
- Permeability is not proportional to porosity.
30
Table 11.1
5
1
26The Water Table
- Water table the surface separating the vadose
zone from the saturated zone. - Measured using water level in well
Fig. 11.1
27Ground-Water Flow
- Precipitation
- Infiltration
- Ground-water recharge
- Ground-water flow
- Ground-water discharge to
- Springs
- Streams and
- Wells
28Ground-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)
29Natural 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
30Natural 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
31Effects of Pumping Wells
- Pumping wells
- Accelerates flow near well
- May reverse ground-water flow
- Causes water table drawdown
- Forms a cone of depression
32Effects 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
33Effects 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
34Ground-Water/ Surface-Water Interactions
- Gaining streams
- Humid regions
- Wet season
- Loosing streams
- Humid regions, smaller streams, dry season
- Arid regions
- Dry stream bed
35Confined Aquifers
36Confined Aquifers
37Ground-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
38Ground-Water Contamination
- Leaking Gasoline
- Floats on water table
- Dissolves in ground water
- Transported by ground water
- Contaminates shallow aquifers
39Ground-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
40Ground-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
41Ground 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
42Ground Water Action
- Karst Topography
- Caves
- Sink holes
- Karst valleys
- Disappearing streams
- Giant springs
43Ohio 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.
44Wisconsin 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.
45English 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.
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