Chapter 3

Question 1

Groundwater is

Answer 1

is an important and significant part of the hydrologic cycle. Yet, it remains a mystery to many people

Question 2

Groundwater is an important and significant part of the hydrologic cycle. Yet, it remains a mystery to many people. Because we

Answer 2

cannot see it directly, groundwater defies our experience of the land surface as a solid, rigid boundary marking the top of the earth

Question 3

In the vast majority of intermontane basins - ……………………-

Answer 3

the areas where groundwater exists in greatest quantity

Question 4

. In the vast majority of intermontane basins—the areas where groundwater exists in greatest quantity—groundwater

Answer 4

fills small, often microscopic pores between the grains of sediment

Question 5

Groundwater may occur in

Answer 5

tiny fractures and fissures of rocks hidden below the loose, or unconsolidated, surface sediments

Question 6

Groundwater may occur in tiny fractures and fissures of rocks hidden below the loose, or unconsolidated, surface sediments. To the naked eye

Answer 6

soils and rocks may appear next to impenetrable

Question 7

To the naked eye, soils and rocks may appear next to impenetrable. But most such materials are, in fact, a

Answer 7

microscopic universe full of empty spaces that can be occupied by water

Question 8

. But most such materials are, in fact, a microscopic universe full of empty spaces that can be occupied by water. When such water completely fills the void space of sediment pores or rock fractures, the pores or fractures are said to be

Answer 8

saturated

Question 9

When such water completely fills the void space of sediment pores or rock fractures, the pores or fractures are said to be saturated. In all but truly ……………………areas, the ground just beneath the land surface is ……………………..: water occupies only part of the pore space

Answer 9

swampy

aerated

Question 10

The boundary between ………………………….. and ………………………… is referred to as the water table.

Answer 10

vadose zone water (unsaturated)

groundwater

Question 11

The zone above the water table is referred to as the

Answer 11

“unsaturated zone” or “vadose zone

Question 12

The term “soil” describes

Answer 12

only the first three to six feet below the land surface that is exposed to weathering plant root growth, etc.

Question 13

In cold to moderate, humid climates, the vadose zone is commonly

Answer 13

identical to the soil layer

Question 14

In cold to moderate, humid climates, the vadose zone is commonly identical to the soil layer—that is, the water table is

Answer 14

less than 6 feet from the land surface

Question 15

In Mediterranean and semi-arid climates, it is not uncommon to have a …………… that is ……………………….

Answer 15

vadose zone that is several tens of feet thick.

Question 16

In Mediterranean and semi-arid climates, it is not uncommon to have a vadose zone that is several tens of feet thick. In some areas, this zone may even be

Answer 16

be several hundred feet thick.

Question 17

While the vadose zone is not a resource from which we can obtain water, it is an important

Answer 17

storage area, pathway, and potential barrier for pathogens, nutrients, or contaminants traveling within the water.

Question 18

To understand the occurrence of groundwater at a given site, one must understand the

Answer 18

local geology

Question 19

Geologists usually investigate local geology by studying

Answer 19

the type and age of the various sediment and rock layers

Question 20

Geologists usually investigate local geology by studying the type and age of the various sediment and rock layers. That information also provides

Answer 20

important clues about the characteristics of the groundwater system in an area.

Question 21

A geologic formation from which significant amounts of groundwater can be pumped for

Answer 21

domestic, municipal, or agricultural uses is known as an aquifer

Question 22

A geologic formation from which significant amounts of groundwater can be pumped for domestic, municipal, or agricultural uses is known as an aquifer. The term is relative: it means that a geologic unit

Answer 22

yields water relative to surrounding materials

Question 23

A geologic formation from which significant amounts of groundwater can be pumped for domestic, municipal, or agricultural uses is known as an aquifer. The term is relative: it means that a geologic unit yields water relative to surrounding materials, but

Answer 23

does not indicate that a specific amount of groundwater can be pumped.

Question 24

A small intermontane-valley aquifer yields

Answer 24

significantly more water than its surrounding hard rock (bedrock) formations.

Question 25

Aquifers sometimes are ...................... separated by......................... that permit...................................

Answer 25

vertically geologic formations little or no water to flow.

Question 26

The formation that acts as water barrier is called

Answer 26

aquitard

Question 27

The formation that acts as water barrier is called aquitard if it is

Answer 27

much less permeable than a nearby aquifer but still permits flow (e.g., sandy clay).

Question 28

aquiclude

Answer 28

If the water barrier is almost impermeable (e.g., clay) and forms a more or less formidable flow barrier between multiple levels of aquifers

Question 29

Aquifers can be of two major types

Answer 29

unconfined or confined

Question 30

In an unconfined aquifer, there is

Answer 30

no overlying aquitard or aquiclude

Question 31

Where multiple levels of aquifers exist,

Answer 31

the uppermost aquifer is typically unconfined

Question 32

Where multiple levels of aquifers exist, the uppermost aquifer is typically unconfined. Vertical recharge by

Answer 32

infiltration of rainwater or irrigation water downward to the unconfined aquifer is therefore not restricted

Question 33

The water table at the top of the unconfined aquifer can

Answer 33

migrate freely up and down depending on how much water is stored in the aquifer

Question 34

A confined aquifer, on the other hand, is “.........................” between ..........................................................

Answer 34

sandwiched | an aquiclude above and an aquiclude or aquitard (e.g., bedrock) beneath

Question 35

As a result of “backpressure”, water in the confined aquifer is

Answer 35

pressurized

Question 36

As a result of “backpressure”, water in the confined aquifer is pressurized. Due to the pressure, the water level in a borehole drilled into a confined aquifer will

Answer 36

rise significantly above the top of the aquifer

Question 37

An artesian well occurs where the

Answer 37

pressure is so large that the water level in a well drilled into the confined aquifer rises above the land surface

Question 38

. An artesian well occurs where the pressure is so large that the water level in a well drilled into the confined aquifer rises above the land surface—in other words,

Answer 38

the well flows freely (if opened) without pumping.

Question 39

. An artesian well occurs where the pressure is so large that the water level in a well drilled into the confined aquifer rises above the land surface—in other words, the well flows freely (if opened) without pumping. Note that a confined aquifer

Answer 39

does not have a water table—it is completely filled with groundwater.

Question 40

. By definition, a perched water table is

Answer 40

a saturated groundwater zone separated from the aquifer below by a zone that is unsaturated or aerated

Question 41

Springs form whereSprings form where

Answer 41

a water table intersects with the land surface

Question 42

Springs form where a water table intersects with the land surface. This may occur in

Answer 42

in a depression of the land surface, particularly on hillsides

Question 43

Springs form where a water table intersects with the land surface. This may occur in a depression of the land surface, particularly on hillsides. It can also occur where

Answer 43

two geologic (rock) formations outcrop at the land surface, if the lower one is less permeable than the upper one

Question 44

A spring also may form when

Answer 44

back pressure forces water to the surface through a sinkhole, fracture, joint, or fault zone that acts as a conduit for water movement

Question 45

The size, shape, regularity, and continuity of the pore space will determine

Answer 45

how much water can be extracted or stored in the subsurface, how fast water can move through the pore space, and how contaminants are distributed within the subsurface.

Question 46

Groundwater fills

Answer 46

the entire pore space, but not all of that groundwater will be available for pumping

Question 47

Groundwater fills the entire pore space, but not all of that groundwater will be available for pumping. Some pores may be

Answer 47

entirely isolated from the rest of the pores. Other pores may be so fine that water molecules are held tightly to the soil, particle, or mineral surfaces by adhesion (magnet-like forces on the surface of water molecules that attract them to the surfaces of mineral grains, especially clay).

Question 48

Adhesion .........................................

Answer 48

immobilizes water molecules

Question 49

Even if pores are not fine enough for adhesion

Answer 49

capillary forces can hold water back against gravity drainage

Question 50

Different sediments and rocks not only have different ......................... but also ............................................

Answer 50

effective porosities, but also different specific yields

Question 51

............................................. also have relatively high effective porosities

Answer 51

Clay, silt and fine sand

Question 52

The period of time since groundwater fell as rain can now be estimated by a technique based on

Answer 52

the amount of tritium found in groundwater

Question 53

Tritium is a

Answer 53

radioactive isotope of hydrogen,

Question 54

Tritium is a radioactive isotope of hydrogen, believed to be formed

Answer 54

in the atmosphere from the action of cosmic rays on ordinary hydrogen

Question 55

Tritium is a radioactive isotope of hydrogen, believed to be formed in the atmosphere from the action of cosmic rays on ordinary hydrogen. Thus, tritium is found in

Answer 55

all atmospheric water, such as rain and snow

Question 56

. As a radioactive material, tritium

Answer 56

gradually decays or decomposes into simpler substances

Question 57

As a radioactive material, tritium gradually decays or decomposes into simpler substances, and has a known

Answer 57

"half-life" of 12'/2 years. That is, one half of the radioactive form is dissipated in 12 1/2 years. An additional half is lost in the succeeding 121/2 years, and so on until the amount remaining is too small to be measured.

Question 58

Isotopes

Answer 58

forms of atoms of an element which differ in their masses

Question 59

Isotopes: forms of atoms of an element which differ in their masses, due to

Answer 59

variations in the numbers of mass particles in their nuclei

Question 60

Hydrogen has three known isotopes: the most common form has

Answer 60

only a proton (a relative mass of one and a single positive electrical charge) in its nucleus

Question 61

a second isotope known as

Answer 61

"deuterium" has one proton and a neutron (neutral in charge and also with a relative mass of one) in its nucleus, and thus a relative mass of two

Question 62

a third isotope known as

Answer 62

"tritium" has two neutrons and a single proton in its nucleus, and thus has a relative mass of three.

Question 63

As the approximate amount of tritium originally present in

Answer 63

water as it fell as rain is known and the amount remaining can be measured, the length of time underground can be calculated unless the amount remaining is too small to be detected by the instruments currently available.

Question 64

Tests of this type on deep well water from several locations in Nebraska indicated underground water ages of about

Answer 64

14 to 61 years