chapter 3 part 2 Flashcards
Tests on Illinois water gave ages of
50 to more than 100 years
Tests on Illinois water gave ages of 50 to more than 100 years. (Beyond 100 years, the tritium concentrations …………………………..)
could not be measured accurately
Tests on Illinois water gave ages of 50 to more than 100 years. (Beyond 100 years, the tritium concentrations could not be measured accurately.) These ages are generally in keeping with the …………………… when all the ……………………… in each area are considered
anticipated values
hydrologic factors
water must travel through …………………….. before becoming groundwater
various strata
water must travel through various strata before becoming groundwater. Below the surface it
moves first through the subsoil (the belt of soil water)
water must travel through various strata before becoming groundwater. Below the surface it moves first through the subsoil (the belt of soil water), ……………………………. , the ………………………… and finally into …………………
the intermediate layer,
the capillary fringe
and finally into the groundwater bed.
A
B
C
D
E
F
G
H
I
J
water must travel through various strata before becoming groundwater. Below the surface it moves first through the subsoil (the belt of soil water), the intermediate layer, the capillary fringe and finally into the groundwater bed.
These layers vary
in depth and are not too sharply defined
These layers vary in depth and are not too sharply defined. In fact, there is a ……………………. from one to another
gradual transition
These layers vary in depth and are not too sharply defined. In fact, there is a gradual transition from one to another until
the ground water level or zone of saturation is reached
These layers vary in depth and are not too sharply defined. In fact, there is a gradual transition from one to another until the ground water level or zone of saturation is reached
Even after water moves into the ………………………….. much of it may still return to the …………………..
topsoil and subsoil
atmosphere
Even after water moves into the topsoil and subsoil, much of it may still return to the atmosphere either through
evaporation or transpiration
Even after water moves into the topsoil and subsoil, much of it may still return to the atmosphere either through evaporation or transpiration. Water is held in the subsoil by
molecular attraction
Water is held in the subsoil by molecular attraction. It is only after
sufficient water has accumulated here that it begins to seep downward under the pull of gravity
It is only after sufficient water has accumulated here that it begins to seep downward under the pull of gravity. The subsoil may extend down
50 feet
It is only after sufficient water has accumulated here that it begins to seep downward under the pull of gravity. The subsoil may extend down 50 feet. It supplies the water needed for
the growth of vegetation
It is only after sufficient water has accumulated here that it begins to seep downward under the pull of gravity. The subsoil may extend down 50 feet. It supplies the water needed for the growth of vegetation. Consequently, it is extremely important to
farmers
Water in the intermediate belt is generally considered in
“dead storage.”
Water in the intermediate belt is generally considered in “dead storage.” To all intents and purposes it is
suspended and does not flow into wells
Water in the intermediate belt is generally considered in “dead storage.” To all intents and purposes it is suspended and does not flow into wells. This belt varies from a
hairsbreadth to several hundred feet.
Below lies the capillary fringe. The thickness of this capillary fringe depends on its
composition
Below lies the capillary fringe. The thickness of this capillary fringe depends on its composition. In silty materials it may extend down for
several feet
Below lies the capillary fringe. The thickness of this capillary fringe depends on its composition. In silty materials it may extend down for several feet. In coarse, gravelly materials it may go down
less than an inch
Below lies the capillary fringe. The thickness of this capillary fringe depends on its composition. In silty materials it may extend down for several feet. In coarse, gravelly materials it may go down less than an inch. Even in this capillary fringe, water will
still not enter well systems
Below lies the capillary fringe. The thickness of this capillary fringe depends on its composition. In silty materials it may extend down for several feet. In coarse, gravelly materials it may go down less than an inch. Even in this capillary fringe, water will still not enter well systems. It is only when it reaches the …………………………….. that it may be …………………….
zone of saturation
drawn back up to the surface by wells
Capillary action, where water
touches a solid
Capillary action, where water touches a solid, capillary action causes the water at that point to
rise higher than that portion of its surface not in contact with the solid
Capillary action is due to
adhesion, cohesion and surface tension
Capillary action is due to adhesion, cohesion and surface tension. Capillarity is one of the causes of water’s
rising in the sail as in the capillary fringe
This zone of saturation forms a huge
natural reservoir
This zone of saturation forms a huge natural reservoir that feeds
springs and streams in addition to our wells.
This zone of saturation forms a huge natural reservoir that feeds springs and streams in addition to our wells. Its thickness varies from
two to hundreds of feet
This zone of saturation forms a huge natural reservoir that feeds springs and streams in addition to our wells. Its thickness varies from two to hundreds of feet, depending on
local geologic conditions
In general, the contours of the water table parallel
the surface contours
In general, the contours of the water table parallel the surface contours. However, the water table goes deeper
under high elevations and rises nearer to the surface under lower elevations
At ………………………………., the surface and water table elevations coincide
springs and flowing streams
Groundwater is abstracted from
beneath the earth’s surface
Groundwater is abstracted from beneath the earth’s surface using methods similar to the
oil industry
Wells are drilled into
aquifers and pumps
Wells are drilled into aquifers and pumps are used to bring
groundwater to the surface
In some cases groundwater may naturally flow
out of a well
In some cases groundwater may naturally flow out of a well, which is known as
artesian flow
The existence of artesian flow is not necessarily an indication of
high well or aquifer yield
The existence of artesian flow is not necessarily an indication of high well or aquifer yield.
It is a physical phenomenon reflecting ……………….
aquifer conditions
It is a physical phenomenon reflecting aquifer conditions whereby groundwater is
trapped below an impermeable layer
It is a physical phenomenon reflecting aquifer conditions whereby groundwater is trapped below an impermeable layer, in conjunction with
recharge at a higher level
It is a physical phenomenon reflecting aquifer conditions whereby groundwater is trapped below an impermeable layer, in conjunction with recharge at a higher level. Alternatively it can be caused when
groundwater intercepts very impermeable material or a boundary
It is a physical phenomenon reflecting aquifer conditions whereby groundwater is trapped below an impermeable layer, in conjunction with recharge at a higher level. Alternatively it can be caused when groundwater intercepts very impermeable material or a boundary, forcing flow to
the surface
The first challenge for someone looking to use groundwater is to
locate a viable source
The first challenge for someone looking to use groundwater is to locate a viable source, particularly if
large quantities are required such as for crop irrigation
The first challenge for someone looking to use groundwater is to locate a viable source, particularly if large quantities are required such as for crop irrigation. Domestic supplies are more widely available because
only smaller volumes are needed
Domestic supplies are more widely available because only smaller volumes are needed, which can often be
pumped at low rates to storage tanks
The subsurface mapping of geological formations and the location of old stream channels can help
build a picture of how an area has been formed and where groundwater may be found
…………………………………………………. and ……………………………………….. can help build a picture of how an area has been formed and where groundwater may be found
The subsurface mapping of geological formations and the location of old stream channels
The most frequently used and reliable descriptor of underground strata and groundwater are
drilling contractor’s records commonly referred to as well logs
The most frequently used and reliable descriptor of underground strata and groundwater are drilling contractor’s records commonly referred to as well logs. Well logs describe the
material that was encountered during drilling
The most frequently used and reliable descriptor of underground strata and groundwater are drilling contractor’s records commonly referred to as well logs. Well logs describe the material that was encountered during drilling and general details such as
yield information and physical dimensions
The most frequently used and reliable descriptor of underground strata and groundwater are drilling contractor’s records commonly referred to as well logs. Well logs describe the material that was encountered during drilling and general details such as yield information and physical dimensions. The well logs also show
the results of the test pump
Locating groundwater is a
science and an art
Locating groundwater is a science and an art. It requires a basic knowledge of ………………….., as well as, ……………………… and ……………….
hydrogeology, as well as, observation and inquiry
As mentioned early, groundwater flows from
a recharge area to a discharge point
As mentioned early, groundwater flows from a recharge area to a discharge point. Generally, the discharge point is at a
lower elevation than the recharge area
As mentioned early, groundwater flows from a recharge area to a discharge point. Generally, the discharge point is at a lower elevation than the recharge area. So, groundwater generally flows from a
higher elevation to a lower elevation
Discharge points may be a
spring or the bed of a river or stream
Discharge points may be a spring or the bed of a river or stream. Groundwater may also discharge along
the shore of a lake or beneath a lake or ocean
Discharge points may be a spring or the bed of a river or stream. Groundwater may also discharge along the shore of a lake or beneath a lake or ocean. So, we may find groundwater closer to
the surface if we drill near streams, rivers or lakes
Groundwater generally follows the
contours of the surface of the ground
Groundwater generally follows the contours of the surface of the ground. We may be more successful locating groundwater if we
drill a well at the bottom of a low point
Groundwater generally follows the contours of the surface of the ground. We may be more successful locating groundwater if we drill a well at the bottom of a low point, such as a ………….. rather than
such as a ravine, rather than at the top of a mountain
Groundwater generally follows the contours of the surface of the ground. We may be more successful locating groundwater if we drill a well at the bottom of a low point, such as a ravine, rather than at the top of a mountain.
Generally we want to look at the lower elevations of the
surrounding topography, like in valleys, basins, or ravines, and also near rivers, streams, lakes, or ponds.
Geophysical methods of locating groundwater are technological ways of determining conditions below the ground surface without actually
drilling a hole
Each of these geophysical techniques measures a specific
physical property of the rock or sediment
Each of these geophysical techniques measures a specific physical property of the rock or sediment such as the
earth’s electrical resistance, electrical conductance, density, and magnetic properties
Each of these geophysical techniques measures a specific physical property of the rock or sediment such as the earth’s electrical resistance, electrical conductance, density, and magnetic properties. Changes in these properties can be related to
changes in the type of sediment or rock, potential for aquifers, and in some cases groundwater quality.
However, each of these geophysical methods has
limitations
However, each of these geophysical methods has limitations. These techniques cannot, by themselves, determine the
presence and location of an aquifer
However, each of these geophysical methods has limitations. These techniques cannot, by themselves, determine the presence and location of an aquifer. Data developed by geophysical methods must be compared with
nearby known geology to be accurately interpreted.
Electrical Resistivity
A resistivity survey measures the electrical resistance to a current induced into the ground
The ………………………….. or …………… depends on many factors
electrical resistance of sediment
rock
The electrical resistance of sediment or rock depends on many factors such as
particle size, porosity, density, mineral and chemical composition, and moisture level
The electrical resistivity of a particular formation depends on many factors and these have been discussed in detail earlier. Generally fine grained material such
clays or silts
The electrical resistivity of a particular formation depends on many factors and these have been discussed in detail earlier. Generally fine grained material such as clays or silts have
low resistivity
The electrical resistivity of a particular formation depends on many factors and these have been discussed in detail earlier. Generally fine grained material such as clays or silts have low resistivity, whereas ……………………………. have high resistivity
sands or gravels
Dry formations have ……………… resistivity compared to
high
material lying beneath the water table
Water quality also affects
affects resistivity with saline water or water with higher concentrations of dissolved minerals having relatively low resistivity
Water contained within clay units is generally
highly mineralised
Water contained within clay units is generally highly mineralised, which contributes to its
low resistivity
It involves inducing a known electrical current into the ground via
two electrodes
It involves inducing a known electrical current into the ground via two electrodes, and evaluating the
resistivity of the ground material based on the measured potential difference in two other electrodes
Electric resistivity is a relatively
cheap method
Electric resistivity is a relatively cheap method and suited to
the gravel type aquifers
Electric resistivity is a relatively cheap method and suited to the gravel type aquifers, although the results it provides are a
simplification of nature
Earth resistivity is the
resistance of rock or soil to the passage of electric current
A
B
C
D
The following represents
electrical resistivity method
Electrical resistivity method
The method relies on different rock types having different
resistivity values
The method relies on different rock types having different resistivity values depending on their
density, porosity, water content and the quality of the water
The method relies on different rock types having different resistivity values depending on their density, porosity, water content and the quality of the water.
Thus the resistivity values are directly related to
the physical properties of the medium
Thus the resistivity values are directly related to the physical properties of the medium. Therefore this method is good for assessing the
bulk properties of different layers below the surface.
Clay minerals and water are good conductors of
current and exhibit low resistivity values
Clay minerals and water are good conductors of current and exhibit low resistivity values, whereas air is a
poor conductor
Clay minerals and water are good conductors of current and exhibit low resistivity values, whereas air is a poor conductor. If the pores are filled with water, the formation will be
least resistive
Clay minerals and water are good conductors of current and exhibit low resistivity values, whereas air is a poor conductor. If the pores are filled with water, the formation will be least resistive, particularly if it contains
saline groundwater
If the pores are filled with water, the formation will be least resistive, particularly if it contains saline groundwater. If the gravels are dry or empty they will be
very resistive
If the gravels are dry or empty they will be very resistive, but will be slightly less resistive if there is
a silt or clay matrix
If the gravels are dry or empty they will be very resistive, but will be slightly less resistive if there is a silt or clay matrix. An interpretation of resistivity soundings provide an indication of
the sub-surface sediments and the associated groundwater characteristics
. An interpretation of resistivity soundings provide an indication of the sub-surface sediments and the associated groundwater characteristics. However, it isn’t a …………………., and relies on a ……………………………….
direct measure
high degree of interpretation
Seismic Refraction
A seismic refraction survey measures how fast a “shockwave” travels through the ground
Because the waves travel at …………………… speeds
different
Because the waves travel at different speeds depending upon the
the density of the material they pass through, the timing of their arrival at the geophone
Because the waves travel at different speeds depending upon the density of the material they pass through, the timing of their arrival at the geophone can be interpreted to reveal something about the
density of materials at different depths.
