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United States
Environmental Protection
Agency
Risk Reduction Engineering
Laboratory
Cincinnati OH 45268
Research and Development
EPA/600/S2-89/066 Apr. 1990
&ERA Project Summary
Technologies of Delivery or
Recovery for the Remediation of
Hazardous Waste Sites
L. Murdoch, B. Patterson, G. Losonsky, and W. Harrar
Remediating techniques that
involve recovering contaminants or
delivering treating material are
particularly attractive because they
can be less expensive and more
permanent than either containment
or excavation. A few delivery or
recovery techniques are In use today,
but on the horizon are new
technologies that offer improvements
in both the rate and the ultimate
effectiveness of remediation.
A review was conducted of In-situ
delivery or recovery techniques that
show promise for the remediation of
contaminated ground or groundwater.
Of the techniques reviewed, some
are currently being Investigated for
remedial actions: others show
promise but have yet to be investi-
gated for remedial purposes. Current
Investigations are funded chiefly by
the U.S. Environmental Protection
Agency (EPA) or other government
agencies. The promising
technologies have been drawn from
methods developed by the petroleum
or solution mining industries.
The review examined 17
technologies. Twelve are currently
being investigated in some way as
remedial techniques; four are from
the enhanced oil recovery industry,
and one from the solution mining
industry.
This Project Summary was
developed by EPA's Risk Reduction
Engineering Laboratory, Cincinnati,
OH, to announce key findings of the
research project that Is fully
documented In a separate report of
the same title (see Project Report
ordering Information at the back).
Introduction
Definitions
Delivery and recovery technologies are
processes that facilitate the transport of
materials either into or out of the
subsurface. Delivery technologies, in
general, involve transporting materials
into the subsurface. Liquids are the
principal phase in most delivery
operations, although some of the new
techniques allow either vapor or solid
phases to be delivered as well.
Recovery technologies, in general,
include any process to remove material
from the subsurface. Existing recovery
technologies used for remediation are
associated with fluid flows driven by
hydraulic gradients. Some innovative
technologies are driven by other types of
processes, such as thermal methods, as
well as processes to expedite recovery
by employing chemical reactions that
alter the behavior of contaminants.
An innovative delivery or recovery
technology is a process that offers some
improvement when compared with
existing methods. For hazardous waste
remediation, improvements either in the
rate of recovery or in the amount of
contaminants remaining in the subsurface
are considered valuable. Improvements
in delivery would occur with development
of a method to deliver an increased
volume of a liquid phase, or a method to
deliver vapor or solid phases.
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Limitations of Current
Technologies
Delivery and recovery techniques have
been used for many years to remediate
contaminated sites. Most currently used
techniques rely principally on pumping
from wells to recover contaminated
groundwater followed by treatment and
injection at delivery wells. These pump
and treat techniques reduce
concentrations to acceptable levels for
some contaminants under certain
saturated site conditions. But these
technologies are generally not applied to
tight formations where hydraulic
conductivities are less than 10-4 cm/sec.
Currently the delivery of remediating
materials is limited to injecting liquids
through wells. Methods of delivering
solid or vapor phases are for the most
part unavailable, although such methods
would facilitate some remedial actions.
Existing technologies are usually not
effective at sites with contaminants of low
water solubilities or those that are readily
adsorbed to soil. Current delivery or
recovery methods are also usually
ineffective for contaminated unsaturated
soils. Low hydraulic conductivities and
local stagnant zones in unsaturated
media inhibit the rates and ultimate
effectiveness of most delivery or
recovery technologies. Furthermore,
some current recovery methods applied
to the unsaturated zone require an
underlying impermeable barrier that
precludes their use at some sites.
Another problem not addressed by
current delivery and recovery
technologies is the presence in some
natural soils of preferred pathways of
high conductivity separated by blocks of
low conductivity. Delivery or recovery
from such soils is limited by rates of
diffusion through the soil matrix blocks to
the preferred pathways.
Procedures
The innovative technologies reviewed
were identified during a literature survey
of topics related to the remediation of
contaminated ground and groundwater,
enhanced petroleum recovery, and
solution mining. When published
descriptions were insufficient to
adequately describe a technology,
interviews were conducted with
researchers or developers.
Some of the technologies are currently
being investigated as possible
remediation methods, whereas others,
principally the ones from the petroleum
and mining industries, have yet to be
investigated. They may, however, offer
potential as remediation methods.
Results and Discussions
The 17 innovative methods of delivery
or recovery identified during the review
are listed in Table 1 and summarized
below.
Colloidal gas aphrons (CGA) are
microdispersions of gas in water.
Typically, a CGA dispersion is 60 to 70
volume percent gas occurring in the form
of minute bubbles or aphrons. The use
of gas aphrons has been suggested as a
technique to enhance the in-situ aerobic
biodegradation of dissolved and
dispersed organic contaminants. This
suggestion is based on laboratory
experiments showing that aphrons deliver
a much greater concentration of gas
when compared with other methods that
deliver gases dissolved in water.
Hydraulic fracturing is a process of
cracking rock in the neighborhood of a
borehole. The cracks are formed by
injecting a fluid, usually water, at
pressures exceeding the confining stress
at the bottom of the borehole. Sand
pumped into the fracture at the time of its
creation holds the fracture open forming
a high-permeability channelway.
Hydraulic fracturing could be used to
increase the rates of either delivery or
recovery to contaminated soil or rock
from a well.
Radial well drilling is a technique used
to place horizontal wells radially outward
from a central borehole (4.5 inches in
diameter or larger). The horizontal radial
is cut by high velocity water pumped out
of a conical jet nozzle. The nozzle is fed
from the surface through steel tubing and
cuts a borehole with a diameter several
times larger than the tubing. Completed
radials can be used to enhance access,
for either delivery or recovery, to a
contaminated formation or aquifer for
groundwater control and in-situ treatment.
Ultrasonic vibration is used extensively
by soil scientists to disperse clay and silt
particles in the laboratory. Most
commercial ultrasonic probes contain a
transducer that converts electrical energy
to mechanical energy and results in a
mechanical disturbance of the sample.
Possible applications of ultrasonic
vibration to remedial actions include: (1)
dispersing clay particles clogging soil
pores adjacent to wells, (2) reducing
adsorption of contaminants onto the
surfaces of clays, and (3) eliminating
microorganisms clogging soil pores
adjacent to wells.
Kerfing (or borehole notching) is a
technique to cut a slot either normal or
parallel to the axis of a borehole. Kerfi
uses a high pressure jet of water, wa
with entrained air, water and bentonite,
water and an abrasive material to cut I
slot. Although recent interest in kerfi
has been as a technique to help stop I
migration of pollutants from uncontroll
waste sites, it may also have applicati
as a recovery technique.
Electro-kinetics (electro-osmos
occurs when a liquid migrates througr
charged porous medium under the acti
of an electric field. The electric field
applied through the anodes that cau
the cations to migrate through t
saturated medium towards the negativi
charged cathodes. Viscous drag of I
water molecules by the cations causes
net flow of water towards the cathodi
Basically, this is how the flow of wa
can be induced from the application of
electric field. Electro-kinetics has t
potential for delivering remediati
materials and recovering spent solutic
or contaminants, principally metals, frc
contaminated soil.
The jet-induced slurry method is
technique used to excavate an ore bo
at depth without removing t
overburden. A borehole-mining tool
lowered down a predrilled borehole. T
borehole-mining tool generates a hi<:
velocity hydraulic jet that erod
subsurface material and then pumps 1
slurry through a well to the surface
processing. This technology could of
the unique capability of recoveri
contaminated material from t
subsurface without removing t
overburden.
Carbon dioxide flooding is an enhanc
oil recovery technique. Carbon dioxide
injected into oil-bearing formations
maintain pressure and displace c
Carbon dioxide injection mobilizes oil
reducing oil viscosity and increasing 1
pressure in the reservoir. Carbon dioxi
flooding to recover groundwat
contaminants would likely be limited
applications where carbon dioxide
either dissolved in water or contained
aphrons. In either case, carbon dioxi
flooding could be used to decrease I
viscosity and increase the recovery
hydrocarbons.
Water-soluble polymers added
waterfloods are used to enhance
recovery. Water-soluble polymers c
used to decrease the viscosity contr
between the oil and fluids in waterfloc
or to homogenize reservoir permeabili
The homogenezation of permeability
one possible application of polymers
the recovery of contaminanl
Temporarily filling high-permeabil
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Table 1. Summary of the Development Status of Innovative Delivery or Recovery
Technologies
Delivery Recovery
Technology
General Remedial General Remedial
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
13.
14.
15.
16.
17.
Colloidal gas
aphrons
Hydraulic fracturing
Radial drilling
Ultrasonic methods
Kerfing
Electro-kinetics
Jet slurrying
Co2 injection
Polymer injection
Vapor extraction
Steam stripping
Hot-brine injection
In-situ combustion
Radio frequency
heating
Cyclic pumping
Soil flushing
Ground freezing
E"
E
E
NA
E
D
NA
NA
NA
NA
NA
NA
NA
NA
C
NA
NA
E
E
E
NA
E
D
NA
NA
NA
NA
NA
NA
NA
NA
C
NA
NA
A
A
D
A
A
A
A
A
A
A
A
C
A
D
A
A
A
NA
E
D
C
E
D
C
C
C
D
D
C
C
D
C
D
D
"Level of development
A - available fully proven and in routine use;
D - developed, passed bench- and pilot-scale testing;
E - emerging, research in progress;
C - conceptual, applicable but unevaluated;
NA - not applicable.
channelways with polymer gels could be
used to induce flow and transport
contaminants out of local zones of low
permeability.
Vapor extraction involves the recovery
of vapor-ladened air from unsaturated
soils by applying a vacuum at extraction
wells. The pore space of unsaturated
soils is composed of liquid and vapor
phases. Compounds with moderate to
high vapor pressures will be partitioned
more strongly into the vapor phase than
will compounds of lesser vapor pressure.
Vapor extraction techniques make use of
the strong partitioning by removing the
vapor phase from the soil through the
application of a vacuum at well points.
Pressure gradients are established within
the soil to induce convective air flow
through the porous media. The process
appears to be limited to those
contaminants that exhibit significant
volatility at ambient temperatures.
In-situ steam stripping is a method
intended to recover highly volatile and
also moderately low vapor pressure
organic compounds from contaminated
soil. The steam is injected into the
contaminated soil through wells where it
releases heat to the soil when it
condenses. The steam has two main
functions: it vaporizes the contaminants
tat would be immobile at ambient
iemperatures and it becomes the
transport medium for the vaporous
materials. The rate of vaporization and
transport of these compounds increases
with increasing soil temperature following
contact with the steam.
Hot-brine injection is being developed
to recover natural gas from solid and
liquid gas-hydrate deposits. Hot-brine
injection increases both the temperature
and salinity of a reservoir thereby
promoting dissociation reactions that
drive solid or liquid gas-hydrates into a
vapor phase and water for easier
recovery. Hot-brine injection could be
used at uncontrolled hazardous waste
sites to recover certain contaminants
whose dissociation temperatures
decrease with an increasing salinity of
pore fluid. The applicability of this
method will require a salinity dependence
on the dissociation temperature of the
contaminant species to be recovered.
In-situ combustion methods are used to
recover crude oil from tar sands and
other deposits of viscous hydrocarbons.
In-situ combustion uses an injection and
production well system to create and
migrate a thermal front through an oil-
bearing formation. As the front advances
and the formation temperature increases,
lighter oil fractions are mobilized through
volatilization and reduced viscosity.
Similar techniques could possibly be
used to recover hydrocarbons from
uncontrolled hazardous waste sites.
Radio-frequency (RF) heating was
developed in the 1970's for the thermal
recovery of hydrocarbons. Electro-
magnetic energy is applied to the
contaminated soil through bound-wave
exciter electrodes. In this way molecular
agitation rather than thermal conduction
is used to heat the soil. RF heating
techniques may have two general
applications as a remedial technique: (1)
thermal vaporization and recovery of
contaminants with low boiling points and
(2) the improvement of reaction rates
between contaminants with high boiling
temperatures and applied reagents.
Cyclic pumping is a delivery or
recovery technique that systematically
varies rates of either injection or
extraction. Pumps are turned on during
an active cycle and turned off during a
rest cycle. The rest cycle allows time for
diffusion between high-permeability path-
ways and the low-permeability blocks
between them. Treating solutions diffuse
from the pathways into the blocks, or
contaminants diffuse from the blocks to
the pathways. The active cycle is
designed to deliver the minimum volume
of nutrients or reactants or to remove the
maximum possible concentration of
reaction products. The optimization of
pumping practices has the potential to
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reduce remediation costs at hazardous
waste sites by minimizing pumping costs.
In-situ soil flushing is a technology
designed to accelerate the movement of
a contaminant through unsaturated
materials. The efficacy of soil flushing is
related to two processes: (1) the increase
in hydraulic conductivity that
accompanies an increase in water
content of unsaturated soil and (2) the
engineering of treatment solutions to the
composition of the contaminants and the
contaminated medium. A treatment
solution is applied to the soil and allowed
to percolate downward and interact with
contaminating chemicals. Contaminants
are mobilized and transported downward
to a saturated zone where they are
pumped to the surface.
Ground freezing is a technique with the
potential to migrate and concentrate
solutes. When pore water freezes slowly,
crystals of nearly pure ice form, and any
dissolved species are concentrated in
pockets or thin films of liquid around solid
particles. The film around the particles
can be very mobile allowing ion
movement to occur through diffusion.
Artificial ground freezing potentially can
concentrate contaminants ahead of
freezing fronts reducing the volume of
contaminated soil at a site and thereby
facilitate remediation.
Conclusions
Innovative technologies of delivery and
recovery offer a range of potentially
valuable new methods of remediati
contaminated sites. Furth
investigations that would develop t
appropriate technologies to a level
routine field application should certaii
enhance the remediation of sor
problematic uncontrolled hazardo
waste sites.
The full report was submitted
fulfillment of Work Assignment 1-11
Contract No. 68-03-3379 by t
University of Cincinnati under t
sponsorship of the U.S. Environmen
Protection Agency.
L Murdoch, B. Patterson, G. Losonsky, and W. Harrar are with the University of
Cincinnati, Cincinnati, OH 45221.
Kenneth Dotson was the Work Assignment Manager.
The complete report, entitled "Technologies oj Delivery or Recovery for the
Remediation of Hazardous Waste Sites,"nprder No. PB90-156 2251 AS;
Cost: $23.00 subject to change) will be avvfable only from:
National Technical Information Service
5285 Port Royal Road
Springfield, VA 22161
Telephone: 703-487-4650
For further information, Michael Roulier can be contacted at:
Risk Reduction Engineering Laboratory
U.S. Environmental Protection Agency
Cincinnati, OH 45268
United States
Environmental Protection
Agency
Center for Environmental Research
Information
Cincinnati OH 45268
Official Business
Penalty for Private Use $300
EPA/600/S2-89/066
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