Chapter 17 Groundwater

What percentage of groundwater use goes to public supply?

21

What percentage of the Earth's total freshwater is in the form of groundwater?

30.1%

A typical rate of groundwater flow for many aquifers is approximately ________.

4 cm/day

What percentage of Earth's liquid freshwater is in the form of groundwater?

96%

Which of the following is not a factor that will influence infiltration of groundwater? A) Acidity of precipitation B) Steepness of the slope C) Nature of surface material D) Intensity of rainfall

Acidity of precipitation

Which of the following materials is most readily dissolved by water? A) Clay minerals B) Silica C) Feldspars D) Calcite

Calcite

Which acid, found in most groundwater, is responsible for most karst topography worldwide?

Carbonic

________ is a term used to describe how the water table around a pumping well becomes lowered and roughly conical in shape as water is taken from the subsurface.

Cone of Depression

______ is a period of abnormally dry weather that persists long enough to produce a significant hydrologic imbalance.

Drought

Aquitards are made of high-conductivity materials such as clay.

F

Clay's porosity is low, but its permeability is high, which means that it has a high specific yield.

F

Geysers are mostly found in coastal locations far from plate tectonic boundaries.

F

Stalactites grip tightly to the floor of a cave whereas stalagmites hang from the ceiling.

F

Unlike rivers and streams, groundwater does not act as an erosional agent.

F

Wells are drilled into the subsurface to remove water from the unsaturated zone.

F

Which of the following materials would make the best aquifer? A) Gravel B) Sandstone C) Clay D) Gneiss

Gravel

Which nineteenth-century scientist developed the following equation that determines the discharge of an aquifer? Q= KA(h1-h2)/D

Henri Darcy

In order for an aquifer to be useful for reliable water extraction, what kind of porosity and permeability should it have?

High porosity, high permeability

What force pushes groundwater from pore space to pore space when below the water table?

Hydraulic gradient

Which countries/regions outside the United States are famous for their geothermal activity?

Iceland, New Zealand, Japan, and Siberia

What is permeability?

Interconnectedness of pore space in a material

Which of the following uses the largest percentage of the Earth's groundwater? A) Mining B) Hydroelectric power C) Irrigation D) Public consumption

Irrigation

Why is the aquitard a necessary part of any groundwater system?

It serves like the bottom of a bucket, allowing water in the aquifer above to be held in place.

California's Central Valley is an important agricultural area for U.S. fruit and vegetable production. Because of the semiarid climate there, farmers must irrigate their crops. Which environmental problem do you anticipate as a result?

Land subsidence

What geologic process is responsible for warming the water at nonvolcanic locations such as Hot Springs National Park, Arkansas, and Warm Springs, Georgia?

Normal geothermal gradient as groundwater circulates at depth

Which of the following characteristics is not true of groundwater? A) Has a constant temperature year round B) Rarely contains suspended sediment C) Short droughts do not affect the supply D) Only occurs underground as large lakes

Only occurs underground as large lakes

In what spaces or voids does most groundwater reside?

Pore space and fractures

What is the term used to describe the hypothetical line the water in a confined aquifer would rise to if it weren't trapped?

Potentiometric surface

What is the source of much of water in geothermal features such as geysers and hot springs?

Precipitation

________ is when groundwater is being replenished. ________ is when groundwater is flowing back toward the surface.

Recharge; Discharge

Which environmental issue most commonly affects groundwater aquifers in coastal or island areas?

Saltwater contamination

What mineral substance makes up most geyser deposits?

Sinter

Which of the following materials would be the best natural filter, removing contaminants from groundwater over a long period of time? A) Fractured granite B) Slightly clayey sand C) Conglomerate D) Mica schist

Slightly clayey sand

________ is the portion of groundwater that is retained as a film on particle and rock surfaces and in tiny openings in the subsurface.

Specific retention

What groundwater feature forms where the water table intersects with the Earth's surface, creating a natural outflow of groundwater?

Spring

Why do geysers spout periodically and then go quiet?

Steam builds up in empty chambers and is released, thus relieving pressure

If gravity pulls infiltrating water downward, what force allows water to be pulled upward at the capillary fringe?

Surface Tension

Caves, as formed from dissolution, are most commonly formed in limestone, but are occasionally found in other rock types, like gypsum.

T

Except where a water table is at the surface, we cannot observe it directly.

T

Freshwater is less dense than saltwater

T

Groundwater is considered a nonrenewable resource in any location where it is not replaced at the same rate as it is withdrawn.

T

Groundwater migrates from areas of high pressure to areas of low pressure.

T

Lakes and streams are surface expressions of the water table.

T

Most caverns are created at or near the water table

T

The majority of groundwater occurs in pores and cavernous spaces.

T

The water in the majority of wells cannot rise above the level of the water table on its own.

T

The water table generally undulates with the ground surface. It is low where the ground surface is low and high where the ground surface is high.

T

When precipitation occurs over a forest, only 25% of the water will make it through the canopy to the forest floor, where other factors may affect how much will infiltrate.

T

While on vacation, you visit a local Imax theater and see a movie about cave diving in the Yucatan Peninsula. In one of the caves, which is currently filled with water, you notice the divers swimming past some stalactites and stalagmites. If the water table is now above the level of the ceiling of the cave, what does the presence of the cave decorations indicate about past water table levels?

The water table was much lower, and the features were formed by water dripping from the ceiling into an air-filled chamber.

Which household function has the highest daily water consumption?

Toilets

What geologic process is responsible for the geothermal features in Yellowstone National Park?

Volcanic activity

How will the water table respond when there is a drought?

Water table will fall.

How will the water table respond if part of it goes from being a dry spring to a wet spring?

Water table will rise.

Which of the following regions is famous for its artesian wells? A) Central Illinois B) Florida C) Western South Dakota D) Coastal Maine

Western South Dakota

The ________ is the point in the subsurface where 100% of the pore spaces are filled with water.

Zone of Saturation

A perched water table is normally located ________ the main aquifer and is an aquifer that is ________ than the main aquifer.

above; smaller than

The general term used to describe cave deposits is ________.

dripstone

To be a gaining stream, the elevation of the water table must be ________ than that of the surface of the stream.

higher

A water tower sending water into your home is most like a ________ artesian well and if your pipes were not sealed ________.

nonflowing; water would flow out of them

Some of the water that soaks into the ground from the surface does not travel far because it is held by molecular attraction as a surface film on soil particles. This near-surface zone is called the zone of ________.

soil moisture