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BESC 402 EXAM 2 QUESTIONS AND ANSWERS
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BESC 402 EXAM 2 QUESTIONS AND ANSWERS
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BESC 402 EXAM 2 QUESTIONS ANDANSWERS
Saturated/Saturation - Answer -when all the pore space in a soil or rock is filled with
water table, phreatic zone.
Unsaturated - Answer -when the pore space is less than completely filled with water,
and partially filled with air
Vadose Zone - Answer -when water from rainfall, snowmelt, rivers, and lakes percolates
through the cracks and pores of soil and rock, it passes through this geological zone,
which is also considered the unsaturated zone
Groundwater - Answer -Water in the vadose and saturated zone. This water is held
between grains under tension (negative pressure) by capillary forces (from the water,
capillary action).
Root zone - Answer -plant utilize soil water that is shallow, within the saturated zone
Capillary fringe - Answer -subsurface layer in which groundwater seeps up from a water
table by capillary action to fill pores, water pressure is negative.
Aquifers - Answer -geological deposit, stratum, succession of strata that contain and
transmit groundwater. discharge is leaving the aquifer, recharge is entering the aquifer.
Confined aquifers - Answer -completely saturated and under pressure from overlying
strata
Unconfined aquifer - Answer -Water table as an upper boundary, these are more
vulnerable to contamination from activities on the ground because they are shallow,
while confined aquifers are thought to be protected by the low permeability aquitards.
HOWEVER, contamination can occur from wells or recharge areas.
Aquitards - Answer -geologic strata interlayered with aquifers tend to impede, or stop,
the movement of groundwater.
Plume - Answer -shape of the dissolved contaminant mass in groundwater.
Phreatic Zone: - Answer -saturated zone
, Vadose Zone: - Answer -unsaturated zone
Water Table: - Answer -boundary between the saturated zone and the unsaturated
zone.
An underground storage tank leaked the solvent TCE into the ground. The water table is
20 feet below the surface. The soil is mostly sandy until about 28 feet below the surface
where a 2 ft layer of low permeability clay is found before a return to mostly sandy soil.
Describe the movement you might expect to see for the mass of TCE in the subsurface
over time and describe the different phases of the TCE during its movement. - Answer -
TCE is a DNAPL, which can migrate as a separate liquid phase, dissolved phase, and a
vapor phase, and will sink since it is heavier than water.
How do characteristics of COCs affect the ease of remediation? - Answer -Volatile,
Solubility, and Reactivity
What characteristics of the subsurface geology and hydrology contribute to the level of
difficulty of remediation? - Answer -Clay contains micropores and has a low
permeability, making it difficult for COC to pass through, but once saturated, it is difficult
to get the COC out. Sand has macropores, making it permeable and easier for the COC
to be removed.
In addition to advection, dispersion, and diffusion, retardation plays a role in
contaminant movement. Explain what is meant by retardation - Answer -Refers to a
decrease in the contaminant migration velocity caused by sorption.
Advection: - Answer -Mass transport due to flowing groundwater, main process driving
the movement of solutes from one location to another downgradient location. Implying,
the contaminants move at the same velocity as the flowing groundwater.
Dispersion: - Answer -The spreading of the contaminant plume from highly concentrated
areas to less concentrated areas. strongly impacts the shape of the plume
Diffusion: - Answer -Weakly impacts the shape of the plume.
Absorption: - Answer -the adhesion of contaminated molecules to certain types of
particles in an aquifer. Another process that removes contaminants from the flowing
mass in groundwater. For inorganic, ionic substances, adsorption occurs as cation
exchange between dissolved ions in groundwater and loosely bound ions of certain
silicate minerals such as CLAYS and Zeolites (alkali & alkaline earth metals). Iron and
manganese oxide particles are also capable of absorbing dissolved or complexed metal
ions. THE ABSORPTION PROCESS IS dependent on the Temperature and pH in the
groundwater-aquifer system.
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