Chapter 16

Question 1

Precipitation results (3)

Answer 1

Run-off, evapotranspiration, recharge (infiltration)

Question 2

Groundwater

Answer 2

Water that infiltrates the subsurface into pore spaces between rock grains and caves. It is 90% of the earth’s freshwater.

Question 3

Groundwater residence time

Answer 3

280 years

Question 4

Soil moisture

Answer 4

Infiltrated water that stays closest to the surface.

Question 5

Saturation/phreatic zone

Answer 5

Zone where all the pores/fractures of rocks are filled with water. This is true groundwater.

Question 6

Water table

Answer 6

The top of the saturation zone with a variable depth that is deeper below hills and reaches the surface at rivers, lakes and swamps. It is influenced by variation in rock type, folds and faults.

Question 7

Capillary fringe

Answer 7

Water at the top of the water table.

Question 8

Vadose/aeration zone

Answer 8

Water above the water table.

Question 9

Porosity

Answer 9

Fraction of rock volume that consists of voids.
Φ = Voids Volume/Total Volume

Question 10

Primary porosity in rocks

Answer 10

Porosity structures present when the rock was formed

Question 11

Secondary porosity in rocks

Answer 11

Porosity structures developed after rock formation.

Question 12

Porosity of sediment

Answer 12

Poorly sorted sediment will have pores filled with finer material, resulting in lower porosity. Porosity is reduced when sediment is lithified to form a sedimentary rock.
Doesn’t depend on size of grains if they are similar, but instead depends on packing structures.

Question 13

Porosity of basalt and Karst limestone

Answer 13

0.05-0.50

Question 14

Porosity of sandstone

Answer 14

0.05-0.30

Question 15

Porosity of limestone and dolomite

Answer 15

0-0.20

Question 16

Porosity of shale and fractured crystalline rock

Answer 16

0-0.10

Question 17

Porosity of dense crystalline rock

Answer 17

0-0.05

Question 18

Porosity of gravel

Answer 18

0.25-0.40

Question 19

Porosity of sand

Answer 19

0.25-0.50

Question 20

Porosity of silt

Answer 20

0.35-0.50

Question 21

Porosity of clay

Answer 21

0.40-0.70

Question 22

Permeability

Answer 22

How easily fluid can flow through a rock.
Porosity (%) = specific yield (%) + specific retention (%)

Question 23

Specific yield

Answer 23

The fraction of groundwater that will drain under influence of gravity.

Question 24

Specific retention

Answer 24

The fraction of groundwater that will be retained.

Question 25

Aquitard

Answer 25

An impermeable layer that hinders or prevents groundwater flow. (EX: clay, shale)

Question 26

Aquifer

Answer 26

Permeable layer that holds enough groundwater to be a useful source (EX: sandstone or coarse clastic sedimentary rocks)

Question 27

Relationship between porosity and permeability

Answer 27

Permeability increases as porosity increases. If the porosity stays constant, and pore size decreases, the permeability will decrease due to increased resistance and frictional effects.
Porosity decreases with depth as sediment gets compacted.

Question 28

Hydraulic gradient

Answer 28

Rate of change of head with distance

Question 29

Darcy’s law

Answer 29

Describes groundwater flow and hydraulic conductivity
V = Kh/ФL

V = groundwater velocity
K = permeability coefficient
h = head (difference in elevation)
Ф = porosity
L = horizontal distance

Question 30

Springs

Answer 30

Perched water tables that are at different heights than the main one. Found where there are permeability variations caused by faults.

Question 31

Hot springs

Answer 31

Springs 6-9°C above the mean annual air temperature

Question 32

Geysers

Answer 32

Produce regular “eruptions” of hot water and need very specific subsurface structure

Question 33

Drawdown

Answer 33

The lowering of water table due to withdrawal of water

Question 34

Cone of depression

Answer 34

The area of drawdown that forms around a well to level the water table because groundwater flows relatively in response to extraction from the aquifer.

Question 35

Confined aquifer

Answer 35

Aquifer bounded above and below by aquitards.

Question 36

Unconfined aquifer

Answer 36

Aquifer overlain by permeable rocks and soil. Pressure increases by elevation changes.

Question 37

Artesian well

Answer 37

When water in a confined aquifer rises to a level above the aquifer.

Question 38

Environmental Problems Caused By Groundwater Extraction (5)

Answer 38

1. Overproduction
2. Surface subsidence
3. Groundwater contamination
4. Seawater intrusion
5. Urbanization and reduction of infiltration

Question 39

Safe total dissolved solids (TDS) levels

Answer 39

500 mg/L / 0.5 g/L

Question 40

Hard water

Answer 40

Water with a substantial amount of dissolved calcium and magnesium.

Question 41

Geological Effects of Groundwater Flow (2)

Answer 41

Erosion and deposition

Question 42

Caves

Answer 42

Form at or just below the water table within the zone of saturation. Carbonic acid allows limestone to be dissolved.

Question 43

Stalactites

Answer 43

Hang from the ceiling

Question 44

Stalagmites

Answer 44

Grow from the floor

Question 45

Stalactites and stalagmites mnemonic

Answer 45

The ‘mites go up and the ‘tites come down.

Question 46

Karst topography

Answer 46

Dissolving of bedrock (limestone, marble, gypsum) to create sinkholes, sinking streams, caves, springs, etc…