Soils and Groundwater

Question 1

Liquid limit

Answer 1

moisture content at which a cohesive soil passes from liquid to plastic state

Question 2

Plastic limit

Answer 2

moisture content at which a cohesive soil passes from plastic to semisolid state

Question 3

Shrinkage limit

Answer 3

moisture content at which a cohesive soil passes from semisolid to solid state

Question 4

Confined aquifer

Answer 4

bounded on top by a confining layer (aquitard), pressurizing the aquifer

Question 5

Unconfined aquifer

Answer 5

upper level of aquifer is at atmospheric pressure

Question 6

The surface of an unconfined aquifer is…

Answer 6

… the water table

Question 7

Piezometric surface

Answer 7

imaginary level to which water in an aquifer would rise

Question 8

Recharge area

Answer 8

area in which water seeps into the ground to supply a confined aquifer

Question 9

Specific yield

Answer 9

percentage of an aquifer’s water that will drain due to gravity

Question 10

Storage coefficient

Answer 10

volume of water that an aquifer gains/loses in response to a change in unit head

Question 11

Hydraulic gradient

Answer 11

slope of the piezometric surface or water table

Question 12

Hydraulic conductivity

Answer 12

ability of a material to transport water

Question 13

Flow net

Answer 13

graph of flow lines and equipotential lines which aid in the calculation of flow rate

Question 14

Flow line

Answer 14

line along which a water particle travels from upstream to downstream

Question 15

Equipotential line

Answer 15

line along which potential head is equivalent

Question 16

Total stress in soil is a combination of…

Answer 16

… pore water pressure and effective stress

Question 17

Effective stress

Answer 17

sum of the vertical components of the forces developed at the points of contact of the solid particles per unit cross section of the soil mass

Question 18

Consolidation settlement

Answer 18

volume change in saturated clayey soils due to the expulsion of water occupied in the void spaces

Question 19

Normally consolidated clay

Answer 19

present effective overburden pressure is the maximum it has experienced recently

Question 20

The slope of the piezometric surface is _____ in the direction of flow

Answer 20

negative

Question 21

Darcy velocity is less than true velocity because…

Answer 21

… the area through which groundwater flows (pore space) is much smaller than A

Question 22

LNAPL

Answer 22

light non-aqueous phase liquids, lighter than water- migrate downwards until they encounter a physical barrier, then move

Question 23

DNAPL

Answer 23

dense non-aqueous phase liquids, tend to sink to the bottom of surface waters and groundwater aquifers

Question 24

Adsorption of contaminants to soil grains…

Answer 24

… slows the migration of the contaminant plume

Question 25

Partition coefficient

Answer 25

describes a species’ preference for the soil or water phase

Question 26

Retardation factor

Answer 26

measures how much a species is hindered relative to water flow

Question 27

Tailing

Answer 27

the progressively slower rate of decline of dissolved contaminant concentration as pump-and-treat remediation continues