HAZARDOUS WASTE MANAGEMENT 457
Air Sparging Air sparging is the further development of
soil vapor extraction, wherein that process is extended so that
soils and groundwater in the capillary fringe can be effec-
tively treated. Air sparging involves injecting air or oxygen
into the aquifer to strip or flush volatile contaminants from
the groundwater and saturated soils. As the air channels up
through the groundwater, it is captured through separate vapor
extraction wells and a vapor extraction system. The entire
system essentially acts as an in-situ air stripper. Stripped,
volatile contaminants usually will be extracted through soil
vapor extraction wells and usually require further treatment,
such as vapor phase activated carbon or a catalytic oxida-
tion treatment unit. This technology is effective when large
quantities of groundwater must be treated, and can provide
an efficient and cost-effective means of saturated zone soil
and groundwater remediation.
The biological degradation of organic contamination
in groundwater and soil is frequently limited by a lack of
oxygen. The speed at which these contaminants are degraded
can be increased significantly by the addition of oxygen in
either solid or liquid form. Air sparging is often combined
with in-situ groundwater bioremediation, in which nutrients
or an oxygen source (such as air or peroxide) are pumped
into the aquifer through wells to enhance biodegradation of
contaminants in the groundwater.Oxygen Enhancement/Oxidation In this in-situ process,
hydrogen peroxide is used as a way of adding oxygen to
low or anoxic groundwater, or other oxidative chemicals are
added as an oxidant to react with organic material present,
yielding primarily carbon dioxide and water. The application
of this technology is typically through the subsurface injec-
tion of a peroxide compound. It has been injected as a liquid,
above the plume, and allowed to migrate downward through
the contaminated plume. Alternately, it has been placed as a
solid in wells located at the downgradient edge of the plume;
in this fashion it can act as a contamination “barrier,” limiting
the potential for contaminated groundwater to move offsite.
As the organic contaminated groundwater moves through the
high oxygen zone, the contaminant bonds are either broken,
or the increased oxygen aid in the natural biodegradation of
the compounds.
The process is exothermic, causing a temperature
increase in the soils during the process. This acts to increase
the vapor pressure of the volatile organic compounds in the
soil, and subsequently increases volatilization of the con-
taminants. This process can be utilized in connection with
a soil vapor extraction and/or sparging system to improve
remediation time frames.
It does not act, however, on the soil groundwater vadose
zone. This may not be a critical flaw, however, since the strate-
gic placement of the wells may positively impact the contami-
nant concentrations adequately to meet cleanup standards.Dual Phase Extraction Dual phase extraction is an effec-
tive method of remediating both soils and groundwater in
the vadose and saturated zones where groundwater and
soil are both contaminated with volatile or nonvolatilecompounds. It is frequently used for contaminant plumes
with free floating product, combined with known contami-
nation of the vadose zone. This technique allows for the
extraction of contaminants simultaneously from both the
saturated and unsaturated soils in-situ. While there are
several variations of this technique, simply put, a vacuum
is applied to the well, soil vapor is extracted and ground-
water is entrained by the extracted vapors. The extracted
vapors are subsequently treated using conventional treat-
ment methods while the vapor stream is typically treated
using activated carbon or a catalytic oxidizer.
The process is frequently combined with other technolo-
gies, such as air sparging or groundwater pump-and-treat to
minimize treatment time and maximize recovery rate.Chemical Oxidation and Reduction Reduction/oxidation
reactions chemically convert hazardous contaminants to
nonhazardous or less toxic compounds that are more stable,
less mobile and/or inert. The oxidizing agents typically
used for treatment of hazardous contaminants are ozone,
hydrogen peroxide, hypochlorites, chlorine and chlorine
dioxide. These reactions have been used for the disinfec-
tion of water, and are being used more frequently for the
treatment of contaminated soils.
The target contaminant group for chemical reduction/oxi-
dation reactions is typically inorganics, however hydrogen
peroxide has been used successfully in the in-situ treatment
of groundwater contaminated with light hydrocarbons.Other Technologies Many other technologies are being
applied with increasing frequency. The following is only a
very brief description of several that have promise.- Surfactant enhanced recovery Surfactant flushing
of non-aqueous phase liquids (NAPL) increases
the solubility and mobility of the contaminants in
water, so that the NAPL can be biodegraded more
easily in the aquifer or recovered for treatment
aboveground via pump-and-treat methods. - Solvent extraction Solvent extraction has been
successfully used as a means of separating haz-
ardous contaminants from soils, sludges and
sediments, and therefore reducing the volume
of hazardous materials that must be treated. An
organic chemical is typically used as a solvent,
and can be combined with other technologies,
such as soil washing, which is frequently used
to separate, or classify, various soil particles into
size categories. The treatment of the concentrated
waste fraction is then treated according to its spe-
cific characteristics. Frequently, the larger volume
of treated material can be returned to the site. - Bioremediation using methane injection The method
earlier described for the injection of hydrogen per-
oxide into wells has also been successfully utilized
using methane. It is claimed that this bioremedia-
tion process uses microbes which co-metabolize
methane with TCE and other chlorinated solvents,
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