CHAPTER 17
Each of the vertical arrows added onto this diagram represents a well. Which is most likely to be unsuccessful in producing water?
1
Consider chromium contamination in a groundwater sample. At first, nothing is known of the chromium source, the groundwater characteristics, or the extent of the plume. Rank in order the process for tracking the contamination and its remediation, with the first step on top.
1. Determine the geology of the site and water table. 2. Determine the direction of the flow of groundwater. 3. Determine possible sources of the chromium behind the plume. 4. Drill wells in front of the plume of contamination and extract contaminated groundwater 5. Process contaminated groundwater
The layer that would act as an aquitard is the ______.
3. Mud and clay
How much water recharged the Ogallala aquifer in 2000? How much water was removed during 2000? How much water is expected to recharge in 2050? How much water is expected to be pumped in 2050?
500; 2,000; 500; 1,800 to 1,000 m3/year
From the choices below, select all the places or rock types that would be good aquifers.
Cavernous limestone Highly fractured rocks of nearly any type Most sandstone Poorly cemented sand and gravel
What is the trend of storage in the Ogallala aquifer, and what is its cause?
Dewatering is compacting the sediments. Storage is decreasing.
Which of the following would be information that a geophysical survey could provide to a geologist?
Electrical conductivity measurements Measurements in the variation of gravity Magnetism measurements
How are springs affected by faulting?
Faults provide a permeable pathway for groundwater movement to the surface
If a well has a cone of depression associated with it because of overpumping of the groundwater, what is a possible consequence?
Groundwater, which may contain pollutants, will flow toward the cone of depression and cause a polluted well.
Which of the following are considered common groundwater contaminants?
Hazardous microbes Hazardous chemicals
Which of the following are specifically human-made or human-induced substances that can contaminate groundwater?
Human wastes Agricultural wastes Insecticides
Which of the following choices best describes what happens to the flow of groundwater if a cone of depression is formed?
Instead of flowing in one direction, groundwater flows toward the cone of depression from all directions.
What is the main use of the water pumped from the Ogallala Aquifer?
Irrigation
Which of the following are characteristics of the Ogallala aquifer?
It is an unconfined aquifer. The western part is expected to be totally depleted by 2050. It has been overpumped.
What will happen to sewage contamination that flows through sandstone as compared to flowing through cavernous limestone?
It will be naturally filtered in the sandstone.
Which of the following are common sources of groundwater contamination?
Landfills Factories Service stations
Which of the following are natural substances that can contaminate groundwater?
Lead and arsenic from mineralized rocks Sulfur
Choose all of the possible pathways, direct or indirect, for contaminants to get into groundwater.
Leaking storage ponds Accidental spills into waterways Accidental spills onto the ground Fumes and particles from smokestacks
Select all the geologic settings where springs could occur.
Limestone aquifers Unconformities Faults
Which of the following geologic materials usually has the highest permeability?
Loosely cemented gravel and sand
Which section of the Ogallala aquifer has the greatest saturated thickness and thus the most water?
Northern
The most important aquifer in the United States that sits under the High Plains from South Dakota to Texas is called the ______.
Ogallala aquifer
______ sits above the main water table where a lens of impermeable rock blocks and collects water infiltrating into the ground.
Perched water
What property of a rock, as modeled in this image, is the primary control on the rate of ground water flow?
Permeability
Choose the three properties that control the rate of groundwater flow through rocks.
Permeability of the rock materials Steepness of the water table Porosity of the rock materials
Using the diagram, if you were a geologist looking for water, which area would you drill an exploratory well into?
Permeable sands
What settings are groundwater typically found in?
Pore spaces Caves Fractures
Which of these is the last step taken in a groundwater investigation?
Remediation of contamination
Which of the following materials would serve as an aquitard?
Shale
Using the figure of a contour map of groundwater locations, determine the general direction of the groundwater flow.
South
Which of the following would not be information collected by a hydrogeologist?
The final intended use of the groundwater
Why does the Ogallala aquifer have an uneven base?
The land was eroded before the deposition of the sediments now holding the aquifer.
From the diagram of the slope of a water table, select the correct answer from the following choices.
The long arrow on the diagram represents the highest hydraulic gradient.
What happens to the sediments that are in and below the dewatered zone of an aquifer?
The sediments become compacted.
What might happen to a losing stream as the water passes from flowing over hard, impermeable rocks to flowing over more permeable rocks?
The stream will lose more water to the subsurface and might disappear.
Which way is the water flowing in the area indicated by the circle?
To the right
True or false: Volatile organic compounds as contaminants is groundwater can be detected by the gases they emit.
True
True or false: The percentage of rock or sediment that consists of voids or openings is a measurement of a rock's ability to hold water.
True Reason: This property is called porosity.
Which of these would make the poorest aquifer?
Unfractured granite
The water table has ______.
a shape similar to that of the land surface lying above it
As the water table drops, the upper section of the original aquifer is now ______ the water table and is dewatered.
above
The pore spaces in the unsaturated zone of the subsurface are filled with ___________. The pore spaces in the saturated zone are filled with ___________.
air; water
A large body of permeable, saturated material through which groundwater can flow well enough to yield sufficient volumes of water to wells and springs is a(n) ____________.
aquifer
If you were looking for a steady supply of groundwater, you'd be looking for a(n) ______.
aquifer
What name is used for any type of rock that retards the flow of water in an aquifer?
aquitard
What natural contaminant has contaminated million of wells in Bangladesh?
arsenic
The term ______ means that the groundwater is in a confined aquifer and under enough water pressure that the water will rise some amount within a well.
artesian
The term ____________ means that groundwater is confined and rises in a well because it is under pressure.
artesian
The water level in a well drilled into an unconfined aquifer will be _______ the aquifer.
at the same level as in
The Ogallala aquifer is located ______.
beneath an area extending from South Dakota to the panhandle of Texas
Which of the materials listed has a low permeability and often a high porosity, actually swelling in volume as it absorbs excess water?
clay
A wetland can form in an area that is not associated with a high-water table if that area is underlain by ______.
clay-rich deposits
The first step in constructing a water table contour map is to ______.
collect and plot the elevations of the water table in all available wells in an area
The figure shown here is associated with well drilling and represents data collected from a drill ___________.
core OR log
If groundwater is removed from an aquifer by overpumping, a cone of ___________ will form.
depression
As the water table ______, the upper section of the original aquifer is now above the water table and is said to be dewatered.
drops
The groundwater in this image is encountering a less permeable rock as it flows to the left, but is making its way to the ground surface along the ____________.
fault
Subsidence occurs when groundwater is overpumped from an aquifer. In areas with nonporous rock, such as granite, which cannot be compacted, ______ develop.
fissures
When groundwater is overdeveloped, subsidence of the land may occur. In areas with unconsolidated sediments, compaction occurs, whereas in areas of solid bedrock, ________________ in the rock develop in order to accommodate the change in surface elevation.
fissures
When groundwater is overdeveloped, subsidence of the land may occur. In areas with unconsolidated sediments, compaction occurs, whereas in areas of solid bedrock, ______________ in the rock develop in order to accommodate the change in surface elevation.
fissures, fractures, cracks OR joints
The arrows drawn perpendicular to the contour lines on the contour map shown indicate the direction of the groundwater flow. In this example, the groundwater is ______.
flowing down the slope of the water table from higher contours to lower ones
Groundwater found in crystalline rock such as granite usually moves through ___________ instead of pore spaces.
fractures
Most groundwater is found in three settings: pore spaces, ___________, and subterranean caves.
fractures
A part of a stream that receives water from the inflow of groundwater is called a(n) __________ stream.
gaining
A stream that receives water from the inflow of groundwater is called a ______.
gaining stream
The part of a stream that receives water from the inflow of groundwater is called a(n) _____________ stream. The part of a stream that loses ____________ to outflow is called a losing stream.
gaining; water
Some volatile organic compounds can be detected by hydrogeologists in the field or labs because of the ______ emitted from the groundwater and/or soil samples.
gases
Farms, ranches, and commercial orchards are contributors to contamination of ______________ by using various chemicals such as pesticides, fungicides, and fertilizers that are not completely used when applied and then infiltrate the ground surface.
groundwater
Hydrogeologists collect information such as depth, amount, setting, direction of flow, and quality to understand the behavior of ___________.
groundwater
Lakes and rivers are often found in topographic lows where _____________ is expressed as surface water.
groundwater
Subsidence is the lowering of the elevation of the ground surface due to excessive pumping of ______________.
groundwater
Accidental spills on the surface, leaking underground storage tanks, and deep disposal wells are the sources of contaminants that pollute ____________.
groundwater OR aquifers
A cone of depression will form if ______.
groundwater is overpumped from an aquifer
Materials with high porosity usually have __________ permeability.
high
Clay has ______ porosity and ______ permeability.
high to low
Rocks and sediments with clasts that are well-sorted and well-rounded have porosity ___________. Rocks and sediments that are angular and poorly sorted have porosity ___________.
high; low
The slope of a water table is also called the ______.
hydraulic gradient
Groundwater on either side of a groundwater divide flows ______.
in opposite directions
A well should ______ the water table in order to effectively be able to draw water to the surface.
intersect or be below
Saltwater ______________ occurs if groundwater wells are overpumped along coastlines.
intrusion
The main use of the water from the Ogallala aquifer is for ________________ of rangeland and agricultural land.
irrigation
The shape of the water table ______.
is a subtle expression of the land surface above it
Unconformities, faults, and ______ are geologic settings for springs.
limestone aquifers
Materials with low porosity usually have __________ permeability.
low
When contamination enters groundwater, it typically ______.
moves along with the flowing groundwater down the slope of the water table
In the figure, the lake marked by the letter A is called a perched lake and is above the water table. The lake marked by the letter C is said to be ______.
nearly at equilibrium with the water table
A spring is a place where water flows naturally from rock ______.
onto the land surface
A perched lake may remain permanent if the inflow of water is at least equal to the _____________ of water.
outflow, loss, depletion, OR discharge
The capacity of a rock to transmit a fluid is ___________.
permeability
The rate of groundwater flow is strongly controlled by the ____________ of the rock type.
permeability
The term given to the shape of contamination as it follows the flow of groundwater is ______________.
plume
When contamination enters groundwater, it moves along with the direction of the groundwater. The contamination takes on a particular shape called a ______.
plume
Groundwater exists in the ___________ spaces between sediment grains.
pore
Groundwater found in sediment usually moves through ______.
pore spaces
The percentage of rock or sediment that consists of voids or openings and is a measure of a rock's ability to hold water is its ___________.
porosity
A part of a stream that ______ water from the inflow of groundwater is called a gaining stream. The part of a stream that ______ water to outflow to groundwater is called a losing stream.
receives; loses
Infiltration of surface water into the groundwater system is one type of ______ that replenishes lost water.
recharge
The term that describes the replenishment of groundwater either naturally or by human processes is groundwater __________.
recharge
A drill log represents information about ______.
rock layers and presence or absence of water
If groundwater wells along coastlines are overpumped, then ______.
saltwater intrusion occurs
Groundwater ______ are taken from wells by geologists to analyze for hazardous chemicals and microbes.
samples
Contamination from the sewage outfall of a septic tank will be filtered if it passes into an area of ______ rather than an area of cavernous ______.
sandstone; limestone
The volume of water in the Ogallala aquifer can be estimate from its ___________ thickness.
saturated
Which of these geologic materials has the lowest permeability?
shale
A stream might disappear if it was first flowing over ______ but then changed to flowing over ______.
solid granite; fractured limestone
A place where water flows naturally out from rock onto the land surface is a(n) ___________.
spring
The three important controls of how quickly water flows through rocks are porosity of the materials, permeability of the materials, and the _______________ of the water table.
steepness, gradient OR slope
The dropping of the ground surface elevation due to the effects of overpumping is called ___________.
subsidence
The top of the saturated zone, as marked by the dashed line in the illustration, is called the water _____________.
table
Contamination typically flows with the groundwater down the slope of the water _____________.
tables
A perched lake is above the water table. If a perched lake is to remain permanent, then ______.
the amount of inflow of water must be equal to or greater than the amount of outflow and losses to evaporation
Surface water can soak into the subsurface and become part of the groundwater if ______.
the surface material is permeable the water table is deep enough so there is an unsaturated zone into which the water can seep
This geophysical data is used to assess the ______ in a basin. This information is then used groundwater in the basin.
thickness of sediments
The water table is the ______.
top of the zone of saturation
Permeability refers to the capacity of a geologic material to ______.
transmit fluid
The most common type of aquifer is a(n) ______ aquifer, in which the water-bearing unit is open to Earth's surface and atmosphere. A(n) ______ aquifer is separated from Earth's surface by rocks of low permeability.
unconfined; confined
The type of aquifer that has the water-bearing unit open to Earth's surface and atmosphere is a(n)__________ aquifer (A), whereas a(n) _________ aquifer(B) is separated from Earth's surface by low permeability rocks.
unconfined; confined
The permeability of a rock layer on which perched water sits is ______.
very low
The first step in constructing a contour map of a(n) ____________ table is to collect and plot the elevations of all of the available wells in an area.
water
In an effort to reduce diseases spread through drinking of surface water in Bangladesh, more than 10 million wells were installed to provide clean drinking water from aquifers. Which of the following is the current leading cause of disease in Bangladesh?
water contamination
Sediments in and below a dewatered area of an aquifer become compacted because ______.
water pressure drops and the pore spaces are closed
Most lakes mark where the ___________ ____________ intersects and rises above the land surface.
water table
Wetlands can form near lakes at the same level as the ____________ table. In other cases, wetlands can be perched at higher elevations where clays or other low-__________ materials trap precipitation and runoff and slow infiltration.
water; permeability
Rocks and sediments that have ______ clasts have higher porosity than those that do not.
well-rounded and well-sorted
