Environmental Engineering Reference
In-Depth Information
zone typically does not occur as migrating air
bubbles, with the exception of within homoge-
neous, highly permeable formations of uncon-
solidated course sand and gravel deposits. IAS
enhances physical or biological attenuation pro-
cesses and physical attenuation by volatilizing
polycyclic hydrocarbons (PHCs) adsorbed to the
formation matrix and stripping those dissolved
in groundwater. IAS stimulates aerobic biodeg-
radation of absorbed and dissolved-phase PHCs
amenable to metabolism. Physical processes are
a more significant attenuation mechanism for
volatile PHCs, whereas biological processes are
a more significant attenuation mechanism for
PHCs of low volatility and varying aqueous solu-
bilities.
water through center of double-cased stripping well
which is designed with upper and lower double-
screened intervals.
Hydraulic and Pneumatic Fracturing
Techniques to create enhanced fracture net-
works to increase soil permeability to liquids
and vapors and accelerate contaminant re-
moval. The technique is especially useful for
vapor extraction, biodegradation, and thermal
treatments. Hydraulic fracturing involves injec-
tion of high pressure water into the bottom of a
borehole to cut a notch; a slurry of water, sand
and thick gel is pumped at high pressure into
the borehole to propagate the fracture from the
initial notch.
Blast-Enhanced Fracturing
A technique used at sites with fractured bedrock
formations to improve the rate and predictabil-
ity of recovery of contaminated groundwater by
creating “fracture trenches” or highly fractured
areas through detonation of explosives in bore-
holes (shotholes). Blast-enhanced fracturing is
distinguished from hydraulic or pneumatic frac-
turing in that the latter technologies do not in-
volve explosives, are generally conducted in the
overburden, and are performed within individual
boreholes.
In situ Flushing
The technique is also known as injection/recircu-
lation or in situ soil washing. General injection
or infiltration of a solution into a zone of con-
taminated soil/groundwater, followed by down
gradient extraction of groundwater and elutriate
(flushing solution mixed with the contaminants)
and above-ground treatment and/or reinjection.
Solutions may consist of surfactants, cosolvents,
acids, bases, solvents, or plain water.
In situ Stabilization/Solidiication
The technique is also known as in situ fixation,
or immobilization. The process of alteration of
organic or inorganic contaminants to innocuous
and/or immobile state by injection or infiltration
of stabilizing agents into a zone of contaminated
soil/groundwater. Contaminants are physically
bound or enclosed within a stabilized mass (so-
lidification), or their mobility is reduced through
chemical reaction (stabilization).
Directional Wells
Encompasses horizontal wells, trenched or di-
rectly drilled wells are installed at any nonver-
tical inclination for purposes of groundwater
monitoring or remediation. This technology can
be used in the application of various remediation
techniques such as groundwater and/or nonaque-
ous phase liquid extraction, air sparging, soil
vapor extraction, in situ bioremediation, in situ
flushing, permeable reactive barriers, hydraulic
and pneumatic fracturing, etc.
Permeable Reactive Barrier
Encompasses passive barriers, passive treatment
walls, treatment walls, or trenches. An in-ground
trench is backfilled with reactive media to pro-
vide passive treatment of contaminated ground-
water passing through the trench. Treatment wall
is placed at strategic location to intercept the con-
taminant plume and backfilled with media such
as zero-valent iron, microorganisms, zeolite,
Groundwater Recirculation Well
This technique encompasses in situ vacuum, vapor,
or air stripping, in-well vapor stripping, in-well
aeration, and vertical circulation wells. Creation of
groundwater circulation “cell” through injection of
air or inert gas into a zone of contaminated ground-
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