• Air Sparging - Injection of gas (usually air or oxygen) under pressure
into well(s) installed within the saturated zone to volatilize contaminants dissolved
in groundwater,
present as non-aqueous phase liquid, or sorbed to the soil matrix. Volatilized
contaminants migrate upward and are removed upon reaching the vadose zone, typically
through soil vapor extraction. Most applicable for volatile organic contaminants
in relatively moderate to high permeability geologic materials.
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Blast-Enhanced Fracturing - A technique used at sites with fractured
bedrock
formations to improve the rate and predictability of recovery of contaminated
groundwater by creating "fracture trenches" or highly fractured areas
through detonation of explosives in boreholes (shotholes). Blast-enhanced fracturing
is distinguished from hydraulic or pneumatic fracturing in that the latter technologies
do not involve explosives, are generally conducted in the overburden, and are
performed within individual boreholes.
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• Directional Wells - Encompasses
horizontal wells. Trenched or directly
drilled
wells installed at any non-vertical inclination for purposes of ground-water
monitoring or remediation. Especially useful when contaminant plume covers a
large area and has linear geometry, or when surface obstructions are present.
This technology can be used in the application of various remediation techniques
such as ground-water and/or non-aqueous phase liquid extraction, air sparging,
soil vapor extraction, in situ bioremediation, in situ flushing, permeable reactive
barriers, hydraulic and pneumatic fracturing, etc.
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Ground-Water Recirculation Wells - Encompasses in situ vacuum,
vapor, or air stripping, in-well vapor stripping, in-well aeration, and vertical
circulation
wells. Creation of ground-water circulation "cell" through injection
of air or inert gas into a zone of contaminated ground-water through center of
double cased stripping well which is designed with upper and lower double screened
intervals. Injection of air creates "airlift pumping system" due to
density gradient, causing ground-water with entrained air bubbles to rise and
partition volatile contaminants from dissolved to vapor phase. Water exits upper
screen beneath a divider, where vapors are drawn off through annular spaces between
well casings by vacuum pump, and ground-water re-enters the contaminated zone,
where it is again drawn into the stripping well. In this manner, ground-water
is recirculated through the stripping well until remediation goals are met. Several
commercial types of in-well vapor stripping exist which strive to make the general
process most efficient, or to use the process to enhance bioremediation or metals
fixation by taking advantage of the circulation cell development. Most applicable
to volatile organic contaminants; modifications of the basic remedial process
are proposed for application to semivolatile organic compounds, pesticides and
inorganics. May be used in unconfined or confined aquifers; process has been
applied to geologic materials of wide ranging permeability.
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• Hydraulic and Pneumatic Fracturing
- Techniques to create enhanced fracture
networks
to increase soil permeability to liquids and vapors and accelerate contaminant
removal. Especially useful for vapor extraction, biodegradation and thermal treatments.
Hydraulic fracturing involves injection 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. The gel biodegrades, leaving a highly permeable sand-filled lens that
may be up to 60 feet in diameter. Pneumatic fracturing involves injection of
highly pressurized air into consolidated sediments to extend existing fractures
and create a secondary fracture network. Most applicable for unconsolidated sediments
or bedrock.
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• In Situ Flushing - Also
known as injection/recirculation or in situ soil washing. General injection or
infiltration of a solution into a zone of contaminated
soil/groundwater,
followed by downgradient extraction of groundwater and elutriate (flushing solution
mixed with the contaminants) and above ground treatment and/or re-injection.
Solutions may consist of surfactants, cosolvents, acids, bases, solvents, or
plain water. Any variety of configurations of injection wells, directional wells,
trenches, infiltration galleries and extraction wells or collection trenches
may be used to contact the flushing solution with the contaminated zone. Excellent
understanding of the hydrogeologic regime for potential projects is essential;
best applied to moderate to high permeability soils. May be used for variety
of organic contaminants, including non-aqueous phase liquid; may have application
to some inorganic contaminants.
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• In Situ Stabilization/Solidification -
Also known as in situ fixation, or immobilization. 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 (solidification), or their mobility is reduced through
chemical reaction (stabilization). Excellent understanding of the hydrogeologic
regime for potential projects is essential; best applied to moderate to high
permeability soils; may be used for variety of organic and inorganic contaminants.
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Permeable Reactive Barriers - Encompasses passive barriers,
passive treatment walls, treatment walls, or trenches. An in-ground trench is
backfilled with reactive
media to provide passive treatment of contaminated ground-water passing through
the trench. Treatment wall is placed at strategic location to intercept the contaminant
plume and backfilled with media such as zero-valent iron, microorganisms, zeolite,
activated carbon, peat, bentonite, limestone, saw dust, or other. The treatment
processes which occur within the treatment wall are typically contaminant degradation,
sorption or precipitation. Applicable to wide range of organic and inorganic
contaminants; choice of media for treatment wall is based on specific contaminant.
Hydrogeologic setting is critical to application; geologic materials must be
relatively conductive and a relatively shallow aquitard must be present to provide
a "basement" to the system. Ground-water flow should have a high degree
of preference, and ground-water quality must support the desired reaction without
imposing additional loading of the reactive media or creating undesirable by-products.
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• Thermal Enhancements -
Use of steam, heated water, or radio frequency
(RF) or
electrical resistance (alternating current or AC) heating to alter temperature-dependent
properties of contaminants in situ to facilitate their mobilization, solubilization,
and removal. Volatile and semivolatile organic contaminants may be vaporized;
vaporized components then rise to the vadose zone where they are removed by vacuum
extraction and treated. Steam best applied to moderate to high permeability geologic
materials; RF and AC heating may be applied to low permeability, clay-rich geologic
materials as the clay will preferentially capture the RF or AC energy. Excellent
understanding of hydrogeologic conditions essential for all applications. May
be used for variety of organic contaminants and non-aqueous phase liquid; may
have application to some inorganic contaminants.
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• Treatment Train - the sequential
use of unique remediation technologies
to treat
the same volume of contaminated soil or groundwater.
Biological Treatment.
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• Bioslurping - Use of vacuum-enhanced
pumping to recover light, non-aqueous phase liquid (LNAPL) and initiate vadose
zone remediation through bioventing.
In bioventing,
air is drawn through the impacted vadose zone via extraction wells equipped with
low vacuums to promote biodegradation of organic compounds.
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• Intrinsic Bioremediation -
Natural, non-enhanced microbial degradation of organic constituents by which
complex organic compounds are broken down to
simpler, usually
less toxic compounds through aerobic or anaerobic processes. For environmental
application, documentation that current biodegradation rates are sufficient to
control or degrade a contaminant plume or zone without creation of unacceptable
risk to human health or the environment must be demonstrated.
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• Monitored Natural Attenuation -
Encompasses intrinsic bioremediation. Reliance on a variety of physical, chemical,
or biological processes (within
the context
of a carefully controlled and monitored site cleanup approach) that, under favorable
conditions, act without human intervention to reduce the mass, toxicity, mobility,
volume, or concentration of contaminants in soil or groundwater.
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• Phytoremediation - The general use of plants to remediate environmental
media
in situ. Includes rhizofiltration (absorption, concentration, and precipitation
of heavy metals by plant roots), phytoextraction (extraction and accumulation
of contaminants in harvestable plant tissues such as roots and shoots), phytotransformation
(degradation of complex organic molecules to simple molecules which are incorporated
into plant tissues), phytostimulation or plant-assisted bioremediation (stimulation
of microbial and fungal degradation by release of exudates/enzymes into the
root zone), and phytostabilization (absorption and precipitation of contaminants,
principally metals, by plants). May or may not involve periodic harvesting
of
plants, depending upon method utilized. Applicable to a wide range of organic
and inorganic contaminants; most appropriate for sites where large volumes
of ground-water with relatively low concentrations of contaminants must be remediated
to strict standards. Most effective where ground-water is within ten feet of
the ground surface, and soil contamination is within three feet of the ground
surface.
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• Treatment Train - the sequential use of unique remediation technologies
to treat
the same volume of contaminated soil or groundwater.
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• Electrokinetics - An in situ process involving application of low intensity
direct electrical current across electrode pairs implanted in the ground on
each side
of a contaminated area of soil, causing electro-osmosis and ion migration.
Contaminants migrate toward respective electrodes depending upon their charge.
Process may
be enhanced through use of surfactants or reagents to increase contaminant
removal rates at the electrodes. Process separates and extracts heavy metals,
radionuclides,
and organic contaminants from saturated or unsaturated soils, sludges, and
sediments. Especially unique due to ability to work in low permeablility soils
as well as
high permeability soils; applicable to a broad range of organic and inorganic
contaminants.
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