Soils and Groundwater Flashcards
Liquid limit
moisture content at which a cohesive soil passes from liquid to plastic state
Plastic limit
moisture content at which a cohesive soil passes from plastic to semisolid state
Shrinkage limit
moisture content at which a cohesive soil passes from semisolid to solid state
Confined aquifer
bounded on top by a confining layer (aquitard), pressurizing the aquifer
Unconfined aquifer
upper level of aquifer is at atmospheric pressure
The surface of an unconfined aquifer is…
… the water table
Piezometric surface
imaginary level to which water in an aquifer would rise
Recharge area
area in which water seeps into the ground to supply a confined aquifer
Specific yield
percentage of an aquifer’s water that will drain due to gravity
Storage coefficient
volume of water that an aquifer gains/loses in response to a change in unit head
Hydraulic gradient
slope of the piezometric surface or water table
Hydraulic conductivity
ability of a material to transport water
Flow net
graph of flow lines and equipotential lines which aid in the calculation of flow rate
Flow line
line along which a water particle travels from upstream to downstream
Equipotential line
line along which potential head is equivalent
Total stress in soil is a combination of…
… pore water pressure and effective stress
Effective stress
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
Consolidation settlement
volume change in saturated clayey soils due to the expulsion of water occupied in the void spaces
Normally consolidated clay
present effective overburden pressure is the maximum it has experienced recently
The slope of the piezometric surface is _____ in the direction of flow
negative
Darcy velocity is less than true velocity because…
… the area through which groundwater flows (pore space) is much smaller than A
LNAPL
light non-aqueous phase liquids, lighter than water- migrate downwards until they encounter a physical barrier, then move
DNAPL
dense non-aqueous phase liquids, tend to sink to the bottom of surface waters and groundwater aquifers
Adsorption of contaminants to soil grains…
… slows the migration of the contaminant plume
Partition coefficient
describes a species’ preference for the soil or water phase
Retardation factor
measures how much a species is hindered relative to water flow
Tailing
the progressively slower rate of decline of dissolved contaminant concentration as pump-and-treat remediation continues
