United States
Environmental
Protection Agency
Office of Emergency and
Remedial Response
Washington, DC 20460
9203.1-16
PB 94-963271
EPA 540/R-94/043
August 1994
Common Cleanup Methods
At Superfund Sites
&EPA
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INTRODUCTION
This booklet contains one page fact sheets on some of the common clean-up
methods used at hazardous waste sites across the nation. It is meant to help you
understand more about the various treatment methods.
It answers such questions as: What is the type of clean-up method? How
does it work?, Where is it used most?, and What are the reasons for using it?
The treatments discussed in this booklet are:
Activated Carbon Treatment
Air Stripping
Bioremediation
Capping
Excavation
Groundwater Monitoring
Immobilization
In Situ Vitrification
Incineration
Leachate Collection
Pump and Treat
Soil Washing
Thermal Desorption
If you have more questions about the clean-up methods mentioned in this
booklet or would like more information on the U.S. Environmental Protection Agency's
Superfund hazardous waste cleanup program, please call the Superfund Hotline at
1-800-424-9346 or 1-800-535-0202.
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3
EPA Facts About
Activated Carbon Treatment
June 1992
What is activated carbon treatment?
The process of activated carbon treatment makes
use of a particular physical attribute of the
chemical carbon. Carbon has the ability to adsorb,
or grab onto passing organic molecules and hold
them in pores within the carbon granule. Organic
molecules are those that contain carbon and are
usually associated with natural processes. When a
waste stream containing orgrnic contaminants is
pumped through a filter of carbon granules, a large
portion of the contaminant becomes trapped in the
pores. Essentially the same process is used in the
filter of most household aquariums.
After a certain length of time, all the surface area
inside the pores is used up and the filter is said to
be saturated or spent. At this point, the carbon in
the filter must be replaced or regenerated. This
regeneration is usually accomplished by heating
the carbon and passing an air stream through it.
The heat loosens the organic molecules, and they
are swept away by the air stream. The freed
organic molecules are subsequently collected and
treated or destroyed.
Most hazardous waste treatment applications use
adsorption units that contain granular activated
carbon (GAC). Figure 1 presents the essential
parts of the GAC treatment method.
(CONTAMWATED
LIQUID)
CIBE»T£D WATERi
SPENT CARBON
I Schematic Diagram of Fixed-Bed GAC System
What is adsorption?
Adsorption is the adherence (ability to stick to) of one
substance to the surface of another by physical or
chemical processes. The treatment of waste streams
using the adsorption process is essentially a method of
transferring and concentrating the contaminants from the
waste stream to another material. The most commonly
used material is activated carbon in granule form.
Activated carbon granules are highly porous (full of
holes). Adsorption takes place on the walls of these
pores because of an imbalance of forces on the atoms of
the walls. The adsorption of organic molecules serves to
balance these forces.
Adsorption treatment usually involves pumping the waste
stream through a container (normally columns) of
activated carbon granules. Relatively large spaces
between granules (voids) ensure that the waste stream is
allowed to move through the column and contacts many
granules. The treated waste stream leaves the column
with reduced concentrations of contaminants. It can be
directed into a series of these columns; each column
removing more and more of the contaminant. Some
duplication is built into the system to allow for some
columns to be taken out of service while the activated
carbon is replaced or regenerated. This allows the
operation to proceed with minimal delays. The activated
carbon in each column will eventually become saturated
and can be disposed of in approved landfills, or
regenerated as mentioned above.
What is the value of GAC?
Activated carbon is an effective and reliable means of
removing organic contaminants. It is suitable for
treating a wide range of organics over a broad
concentration range. The use of several carbon
adsorption columns at a site can provide considerable
flexibility. Several columns can be arranged in series
(one after the other) to increase the service life between
regeneration of any particular column. They can also be
arranged in parallel so that a maximum volume can be
treated at any one time. The piping between columns
would allow for one or more column to be taken out of
service to be regenerated while the other columns
continue to work.
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The most obvious maintenance consideration associated
with activated carbon is the regeneration of the saturated
carbon for re-use. Regeneration must be performed for
each column as it becomes saturated so that the carbon
can be restored as close as possible to its original
condition. If regeneration is not used, the carbon can be
disposed of in an approved landfill. Most other
operations and maintenance procedures are minimal for
this technology if appropriate automatic controls have
been installed.
F%*re 2 Arrangement of Carbon Adsorption Columns
What are the applications of granular activated
carbon (GAC)?
Activated carbon is a well developed technology which is
widely used in the treatment of hazardous waste streams.
It is especially well suited for the removal of organic
contaminants from liquid wastes.
Some metals and inorganic chemicals may also be
removed from a waste stream with some success,
including antimony, arsenic, bismuth, chromium, tin,
silver, mercury, cobalt, zirconium, chlorine, bromine, and
iodine.
Carbon adsorption is generally accepted for use in the
control of volatile organic compounds (VOCs), hydrogen
sulflde, and some radioactive elements such as iodine,
krypton, and xenon. VOCs are organic compounds that
evaporate rapidly when heated or disturbed in any way.
The odor that surrounds us when we pump gasoline into
the tank is a good example. Carbon adsorption can also
be used to control sulfur oxides, nitrogen oxides, and
carbon monoxide.
Carbon adsorption is widely used in industry for air
pollution and odor control. Often these systems are
operated in association with a recovery and re-use
program for the contaminants.
Adsorption by activated carbon has a long history of use
as a treatment for municipal, industrial and hazardous
wastes. The relative effectiveness of carbon adsorption
is related to the chemical composition and molecular
structure of the contaminant.
What is the technology of GAC?
Carbon is an excellent adsorbent material because of its
large porous surface area. This area is made up of many
different surfaces which are highly attractive to many
different kinds of contaminants. Regular carbon is made
into activated carbon through a process that produces an
extensive network of internal pores.
The process of adsorption takes place in three steps.
First, the contaminant moves to the external surface of
the activated carbon granules. It then moves deeper into
the pore structure. Finally, a physical or chemical bond
forms between the contaminant and the internal carbon
surface.
What process residuals result from GAC?
The main residual produced from an activated carbon
system is the spent carbon which contains the hazardous
contaminants. When the carbon is regenerated, the
contaminants are released from the carbon and must be
recovered or destroyed. If the carbon cannot be
economically regenerated, it must be treated and
disposed of in an approved landfill.
For more information about Activated Carbon
Treatment you may contact EPA at the following
address:
U.S.Environmental Protection Agency
ATTN: Superfitnd Hotline
401 M Street, S.W.
Washington, D.C. 20460
1-800-424-9346 or 1-800-535-0202
The Infomutkm in thlt fact sheet wit compiled from the EP>
nular Activated Carton Treatment. October 1991
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EPA Facts About
Air Stripping
What is air stripping?
Air stripping is a process used to remove volatile
or certain semi-volatile organic compounds from
contaminated groundwater or surface water.
Organic compounds are those that contain carbon
and are usually associated with life processes.
Volatile organic compounds, or VOCs as they are
called, are chemicals which iend to vaporize
rapidly when heated or disturbed in any way. An
example would be the gasoline fumes that you
smell as you fill the tank on your car. In air
stripping, these vapors are transferred from the
water in which they were dissolved into a passing
air stream. This air stream can be further treated
to allow for the final collection and re-use or
destruction of the VOCs.
How does air stripping work?
Air stripping is used to remediate (clean up)
groundwater or surface water that has been contaminated
by VOCs. This method of remediation is often
accomplished in a packed tower that is attached to an air
blower. This "packed tower" is simply a large metal
cylinder that is packed with material. The water stream
is pumped into the top and the air stream is pumped
into the bottom. The material in the tower is designed
to force the water stream to trickle down through
various channels and air spaces. Meanwhile, the air
stream is being forced into the bottom and flows upward,
exiting at the top. This is called "counter-current" flow.'
As the two streams flow past each other, the VOCs tend
to vaporize out of the disturbed water stream and are
collected in the air stream.
Figure 1 presents a diagram of the air stripping process.
The contaminated surface water or groundwater is
pumped from its source and is collected in large pre-
treatment storage tanks. The water is then pumped into
the top of the tower and leaves from the bottom. It is
collected and sent on to be treated further if this is
necessary. The air stream is also collected and treated to
remove or destroy the VOCs.
June 1992
^^••••^••••i
The air stripper is an example of a liquid-gas contactor.
The most efficient type of liquid-gas contactor is the
packed tower. Inside the packed tower, the packing
material provides more surface area for the water stream
to form a thin film on. This allows much more of the
air stream to come into contact with the water stream.
Selecting packing material that maximizes this wetted
surface area will improve the efficiency of the air
stripper. Smaller packing material sizes generally
increase the area available for stripping arid improves the
transfer process. Once the packing material has been
selected, it can be packed in two different ways. First, it
could simply be dumped into the top of the tower to fill
it up. This is called random packing. In the second
method, the packing material is arranged on trays
attached at certain levels inside the tower. These trays
are made of metal gauze, sheet metal, or plastic. This is
called structured packing. Random packing is generally
less expensive, but the structured packing allows for
easier maintenance.
There are several variations of the packed tower. In one,
the "cross-flow tower", the water stream flows down
through the packing in the same way as the counter-
current tower. The air stream, however, is pulled across
the water by a fan, instead of being forced upward
through the tower. The "coke tray aerator" is a simple,
low maintenance process that doesn't use a blower for
the air stream. The water stream is simply allowed to
trickle through several layers of trays. This produces a
large surface area in contact with the surrounding air.
Another method, "diffused aeration stripping", uses
basins instead.of a tower. The water stream flows either
from the top to bottom of the basin or from one side to
the other while air is dispersed from the bottom of the
basin and allowed to "bubble-up" through the water.
These fine bubbles tend to disturb the liquid and carry
some of the VOCs away when they leave the liquid at
the top. Finally, "rotary air stripping" uses the centrifugal
force caused by a rotating cylinder instead of gravity to
pull the liquid through the packing material. The use of
centrifugal force seems to be more efficient because the
liquid is spread in thinner layers over the packing
material. The revolving motion also tends to disturb the
liquid a great deal. Both of these factors increase the
efficiency of this type of air stripper. The biggest
advantage, however, is the smaller size of the device. A
small rotary device can strip the same amount of water
as a much larger packed tower.
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Liquid
*—*; Stripper
• Otlgoi
Mm ffaninoiw
Rtcycte
Treated Liquid
Figure 1 Schematic Diagram of Air Stripping System
What are the applications of air stripping?
Air stripping is used to remove volatile organic
contaminants from liquids. These organic compounds
include 1,1,1-trichloroethane, trichloroethylene,
dichloroethylene, chlorobenzene, and vinyl chloride.
Stripping is only partially effective in some cases. In
these cases, stripping must be followed by another
process to remove the remaining contaminant. The
equipment used in air stripping is relatively simple,
allowing for quick start-up and shut-down. The modular
design of packed towers allows for easy maintenance.
These factors make air stripping well suited for
hazardous waste site operations.
An important factor to consider when looking at air
stripping as a remediation option is the air pollution
impact. The gases generated during an air stripping may
require the collection and treatment of the waste air
stream. Often, computer modeling of the air stripper is
required before operations can begin. These models are
used to predict the stripper impact on the surrounding
atmosphere.
How well does air stripping work?
Air stripping has been successfully used to treat water
that has been contaminated with volatile organic
compounds (VOCs) and semi-volatile compounds. Air
stripping has been shown to be capable of removing up
to 98 percent of VOCs and up to 80 percent of certain
semi-volatile compounds. The method is not suitable for
the removal of some low-volatility compounds, metals, or
inorganic contaminants. Air stripping has commonly
been used with pump-and-treat methods for treating
contaminated groundwater. In this method, the
groundwater is removed from the ground by pumps,
treated in the packed tower and often returned to the
same area.
Where have air strippers been used?
An air stripping system was installed at the Sydney Mine
site in Valrico, Florida. The packed tower was 42 feet
tall, four feet in diameter, and contained a 24-foot
section of packing material. The packing material was
3.5-inch diameter (baseball-sized) polyethylene balls.
The average water flow rate was 150 gallons per minute.
Air stripping was also used at a municipal well site in
the city of Tacoma, Washington. Five towers were
installed in this operation. Each tower was 12 feet in
diameter and was packed with one-inch saddle shaped
packing material to a depth of 20 feet. The average
water flow was 700 gallons per minute for each tower.
The towers consistently removed 94 to 98 percent of the
contaminants.
Are residues generated by air stripping?
The primary residues created with air stripping systems
are the waste gas coming from the top of the tower and
the treated water coming from the bottom. The gas is
released to the atmosphere only after it is treated to
remove or destroy the contaminants. The treated water
may require further treatment if it contains other
contaminants that were not removed during the air
stripping. If the water requires further, it is treated on-
site or stored for transportation to another treatment
facility. Once an acceptable level of contaminants has
been removed from the water, it can either be sent to a
sewage treatment facility, released to a surface water
body, or returned to its source if it was removed from
the ground.
For more information about Air Stripping, you
may contact EPA at the following address:
U.S. Environmental Protection Agency
ATTN: Superfund Hotline
401 M Street, S.W.
Washington, D.C. 20460
1-800-424-9346 or 1-800-535-0202
The information in tbis fact sheet was compiled from Engineering Bulletin, Air Stripping of AoueoiM Solution*. October, 1991.
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EPA Facts About
Bioremediation
June 1992
What is bioremediation?
Bioremediation - a process that uses microorganisms
to transform harmful substances into nontoxic
compounds - is one of the most promising new
technologies for treating chemical spills and
hazardous wastes.
This process uses naturally occurring microorganisms,
such as bacteria, fungi, or yeast, to degrade harmful
chemicals into less toxic or nontoxic compounds.
Toxic substances are poisonous or hazardous, and can
have harmful qualities. Microorganisms, like all
living organisms, need nutrients (such as nitrogen,
phosphate, and trace metals), carbon and energy to
survive. Microorganisms break down a wide variety
of organic (carbon-containing) compounds found in
nature to obtain energy for their growth. Many
species of soil bacteria, for example, use petroleum
hydrocarbons as a food and energy source,
transforming them into harmless substances
consisting mainly of carbon dioxide, water, and fatty
acids. Bioremediation harnesses this natural process
by promoting the growth of microorganisms that can
degrade contaminants and convert them into
nontoxic by-products.
When microorganisms are exposed to contaminants,
they tend to develop an increased ability to degrade
those substances. For example, when soil bacteria
are exposed to organic contaminants, new strains of
bacteria often naturally appear that break down these
substances to obtain energy.
How does bioremediation work?
One bioremediation technique known as In situ
Bioremediation is used to treat wastes "in-place" without
removing the contaminated soil or water. This technique
can be used to treat contamination in the top 6 to 12
inches of soil by tilling the soil to provide aeration and by
adding nutrients and water to stimulate bacterial growth.
Treatment of contamination at depths up to 40 feet usually
requires the installation of injection wells to deliver
nutrients and oxygen to support microbial activity.
Another bioremediation technique treats soil or water in
either a compost pile or a bioreactor. In composting, highly
biodegradable materials, such as wood chips, are combined with
a small percentage of biodegradable wastes. This creates
conditions for accelerated degrading of the wastes. A
bioreactor, or closed vessel, is used to mix contaminated soil or
sludge with water, nutrients, and oxygen to create a slurry (a
thin mixture of water and soil). The water and soil are
separated following treatment and the cleaned soil is distributee
on the site. Contaminated solids can be placed in a lined bed
with nutrients, moisture and oxygen added to promote
decomposition. Leachate and air emission produced during
degradation of the waste are collected and treated.
What chemicals and sites are best suited to
bioremediation?
Bioremediation has been used for nearly two decades to
degrade petroleum products and hydrocarbons. It is a
potentially effective treatment technique for many of the
10,000 to 15,000 oil spills that occur each year. In
addition, approximately 15% of the nation's underground
tanks that store petroleum, heating oil, and other
materials are leaking. Many more underground tanks
may begin to leak in the next 5 to 10 years.
Bioremediation may be suitable for cleaning up soil and
ground water at many of these sites as well.
Wood preserving sites represent another promising
application of bioremediation. The estimated 700 wood
preserving plants located in the U.S. use more than
495,000 tons of creosote per year. Creosote leaking from
holding tanks and wood treatment areas can seep into the
soil and groundwater. Microorganisms that degrade
creosote are currently the focus of extensive research
efforts by EPA
Why do some biodegradable organic chemicals
persist in the environment?
A number of environmental conditions may slow down or stop
the biodegradation process. Some reasons for this are: (1) the
concentration of the chemical may be so high that it is toxic to
the microorganisms; (2) soil (or other contaminated media)
conditions may be too acidic or alkaline; (3) the
microorganisms may lack sufficient nutrients (such as nitrogen,
phosphorous, potassium, sulfur, or trace elements), which they
need to use the chemical as a food source; (4) moisture
conditions may be unfavorable; or (5) the microorganisms may
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lack the oxygen, nitrate, or sulfate they need to use the
chemical as an energy source.
In many instances, these environmental conditions can be
altered to enhance the biodegradation process. By altering
the types of microorganisms present, nutrients, and climatic
conditions (i.e., pH, moisture, temperature and oxygen
levels) microbial degradation can be enhanced.
What are some reasons we use bioremediation?
Bioremediation can be an attractive option for many
reasons: (1) It is an ecologically sound, "natural" process.
New strains of bacteria which most efficiently break down
organic wastes often appear naturally. As a result, the
population of these strains explodes, propelling the
"breaking down of hazardous wastes" or bioremediation
process forward. When soil bacteria are exposed to
organic contaminants, they tend to develop an increased
ability to degrade those substances. These bacteria can
increase in numbers when a food source (the wastes) is
present. When the contaminant is degraded, the microbial
population naturally declines; (2) Instead of merely
transferring the contaminants from one place to another,
for example, to a hazardous waste landfill, bioremediation
destroys the target chemicals - residues from the biological
treatment are usually harmless products; (3) It is usually
less expensive than other technologies; and (4)
Bioremediation can often be accomplished where the
problem Is located. This eliminates the need to transport
large quantities of contaminated waste off site and the
potential threats to health and the environment that can
arise during such transport
For more information about Bioremediation, please
contact EPA at the following address:
17.5. Environmental Protection Agency
ATTN: Superfitnd Hotline
401M Street, S.W.
Washington, D.C. 20460
1-800-424-9346 or 1-800-535-0202
GLOSSARY
Bioreactor: Any dosed vessel to which hazardous wastes
are combined with bacteria, nutrients, moisture and
oxygen ia proportions which will produce optimal,
biological actiwly for the purpose ot degrading the wastes
into harmless, eon-toxic substances.
Compost Pile: An open area to which hazardous wastes
are blenled with a mixture of organic matter, nutrients,
Moisture and oxygen for the purpose of degrading
(breaking down) the wastes and rendering them harmless.
Creosote: A complex mixture of over 200 individual
cheoicais, including some substances known to cause
cancer, used ia the preservation of wood,
Injection Wells: A hole sunk into the ground for the
purpose of pumping tt£^-4als to an area below the
surface of the ground. Nutrients, oxygen or water eaa be
delivered to an underground area to which
bwrernediarton fe being performed.
Leachate: A oadfttamtoated 14t|oM that results from water
collecting contaminants as it trickles through wastes,
agrkniltural pesticides, or fertilizers. Leaching can cause
hazardous substances to enter the soil, surface water, or
groandwater.
''MicrobM~Activty:'n& Wologiteal action of
ia which substances are consumed
these
living organisms to produce energy and food, to
bioremediation, hazardous materials arc physically or
chemical transformed into non-toxic substances.
.**W.VWAV\^. \\AIA WAW^wS-*'-''^ s \S VA J f A X
Microorganisms: Microscopic animal 6f plant organism;
viruses, <*&
*fee «o« sft m ft> break ft
into sfflalitr particles and to mix organic matter, minerals
and other soil additives into surface soil- In
fei&ismedtei&a, tffitog Is performed to increase the
•mount of soil exposed to the air (oaygen) and la
merging of microorganisms, nutrients and
The iaXotm»tk» conUiaed in thk fact iheet WM compiled faun UndenitendiM Btoreroeduitioo: A Guidebook for atizem. a publication of the US.
Eovirau»eaui Frotecik* Agemy, Februiiy, 1991. Thufactshe&focumontheanpactofhmtrdouswcutaonhwnmhet^hou^^
impact* OH the environment, including plena and animals.
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EPA Facts About
Capping
June 1992
What is capping?
Capping is a process used to cover buried waste
materials to prevent migration (movement) of the
contaminants. This migration can be caused by
rainwater or surface water moving over or through
the site, or by the wind blowing over the site.
Caps are generally made of a combination of ^uch
materials as synthetic fibers, heavy clays, and
sometimes concrete. The caps are designed to
meet several goals. First, they must minimize the
movement of water through the wastes, by
efficiently draining the site after rain showers.
Second, they should be easily maintained. Third,
caps should be resistant to damage caused by
settling. Finally, they should be capable of
funnelling away as much water as the underlying
filter or soils are capable of handling. This will
prevent standing water. A variety of cap designs
and cap materials are available.
What are the applications of capping?
Capping is required when contaminated materials are to
be left in place at a site. It is used when the
underground contamination is so extensive that it
prohibits excavation and removal. It may also be used if
the removal of wastes from the site would pose a greater
threat to human health and the environment than simply
leaving them in place.
Capping is often used in combination with groundwater
extraction (removal) or containment technologies to
reduce and, if possible, prevent contaminant migration.
Groundwater monitoring wells are often used in the area
where a cap has been installed to detect any unexpected
migration of the wastes. A gas collection system should
always be a part of a cap when wastes may generate
gases. Capping is also associated with surface water
controls such as ditches, dikes, and berms. These
structures are used to receive rainwater drainage from
the cap.
What are the long-term maintenance
requirements?
All caps require periodic inspection for settlement,
standing water, erosion, or disturbance by deep-rooted
plants. In addition, the groundwater monitoring wells
usually associated with caps need to be sampled
periodically (to monitor for migration) and maintained.
However, the long-term maintenance requirements are
usually more economical than many other alternatives.
Caps generally have a minimum design life of 20 years
when a synthetic liner is the only barrier to outside
liquids. This period can be extended to over 100 years
when the synthetic liner is supported by a non-porous
base, such as clay and the contaminants are above the
water table. Proper maintenance will extend the life of
the cap even longer. Rigid barriers such as concrete are
subject to cracking and chemical deterioration.
However, these cracks can be exposed, cleaned, and
repaired with relative ease. Concrete covers may have a
design life of about SO years, except when they are used
to cap caustic or physically unstable landfill areas.
A final cap should be inspected on a regular basis for
signs of erosion and settlement Maintenance of the
final cap should be limited to periodic mowing of the
vegetation to prevent any deep-rooted plants from
growing, and to deny cover to burrowing animals. Any
signs of settling should be addressed immediately by
removing the soil cover to inspect and repair the affected
areas.
What are the types of cap design?
The primary purpose of a cap is to minimize
contact between rain or surface water and the
buried waste. Two types of caps that serve this
purpose are:
• Multi-layered Caps - This type of cap
generally has three layers; vegetation,
drainage, and water-resistant. The vegetation
layer prevents erosion of the soils of the cap.
The drainage layer channels rainwater away
from the cap and keeps water from collecting
on the water-resistant layer which covers the
waste.
• Single-layer Caps - This type of cap can be
constructed of any material that resists the
penetration of water. The most effective
single-layer caps are made of concrete or
asphalt. Single-layer caps are not usually
acceptable unless there are valid reasons for
not using a multi-layered cap.
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What installation factors must be considered?
The first layer of a multi-layered cap is the foundation
layer. It should be composed of soil materials that are
structurally capable of supporting the weight of the
finished cap. The foundation material should be spread
over the wastes in six-inch increments and compacted.
Structural stability tests should be run on each increment
to assure uniformity.
The water-resistant layer should be placed in six-inch
increments and compacted with a bulldozer or other
heavy equipment The thickness of the water-resistant
layer should be at least two feet, but should be increased
if settling is expected in the underlying wastes. A
synthetic liner should be placed and sealed according to
the manufacturers specifications. The liner should be at
least 20 mils thick. (One mil is equal to one-thousandth
of an inch.) A thicker liner should be used if more than
a few inches of settling is expected.
The drainage layer should also be placed in six-inch
increments and should be at least one foot thick. If the
drainage layer is placed directly over the liner, it must be
free of sharp objects that could puncture the liner.
Filter fabric should be placed above the drainage layer to
prevent the soil from the vegetation layer from clogging
the drainage pores. The pore size of this layer should be
large enough to allow for proper drainage, but small
enough to prevent the soil from moving into the
drainage layer.
The vegetation layer should be at least two feet thick to
accommodate root penetration. It should be spread
evenly and not overly compacted. The vegetation should
be non-woody plants, preferable grasses, which will
require low maintenance.
How "good" is capping?
Capping is a reliable technology for sealing off
contamination from the aboveground environment and
significantly reducing underground migration of wastes
away from the site. Caps can be constructed over
virtually any site, and can be completed relatively quickly
if the ground is not frozen or saturated with water. The
soils and other material for capping are readily available
In most areas of the country. Standard road construction
equipment is used in this method of remediation.
The performance of a properly installed, multi-layered
cap is generally excellent for at least the first twenty
years of service. Proper monitoring and maintenance
will extend the useful life of the cap even longer.
Capping is an attractive alternative when excavation
and/or treatment is not cost-effective or protective of
human health and the environment.
FINAL
COVER
CLAY LINER
INDIFFERENT IATE9/"
LEVELING LAYER
SURFACE
SEALING
Figwe 1 Infiltration Control Technologies
For more information about Capping, you may
contact EPA at the following address:
U.S. Environmental Protection Agency
ATTN: Superfund Hotline
401 M Street, S.W.
Washington, D.C. 20460
1-800-424-9346 or 1-800-535-^202
Th« Mnmntinn mnuingd in thi« fact iheet was compiled from Superfund Innovative Technology Evaluation, a publication of the U.S. Environmental
Protection Agency, November 1990.
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EPA Facts About
Excavation
June 1992
What is excavation?
Excavation is the removal of contaminated
material from a hazardous waste site using heavy
construction equipment. This equipment is the
same type of equipment that might be seen at road
building projects such as backhoes, bulldozers, and
front loaders. On certain sites, specially designed
equipment may be used to prevent the spread of
contaminated waste.
How does excavation work?
The first step in excavation involves the sampling of the
contaminated area. Typically a grid is laid out on the
ground so that sampling locations can be identified.
Drilling equipment is used to take samples of the soil
and groundwater at each location identified by the grid.
Samples are taken at several different depths in the same
location so that a vertical, as well as horizontal, map of
the contamination can be pieced together. Special
sensing equipment can be used to identify the nature of
contamination on sites that are suspected of holding
wastes in metal drums. Historical records such as
photographs, eye witness accounts from past employees,
and the contamination's effects on vegetation can also be
used to pinpoint the area to be excavated.
Once the area of contamination is fully mapped, the
actual removal of material can begin. Excavation is
accomplished by digging up the contaminated materials
and loading them onto trucks for hauling. If on-site
remediation of "cleanup* treatment is used, the excavated
waste may be taken to a staging area for treatment such
as soil washing. The soil is then returned to its original
location for use as backfill. If off-site treatment is
required, the trucks will be properly covered and marked.
The trucks will then haul the soil to the treatment
location. After the soil is cleaned, it may be returned to
the site to be used as backfill.
In cases where hazardous wastes have been buried in the
ground, it may be necessary to remove a layer of soil
prior to excavating the waste. This layer, called
overburden, is removed and set aside in a clean area to
await replacement to its original location.
Soil testing is accomplished in the walls and bottom of
the excavated area to ensure that all contaminated soil
has been removed. Large volumes of soil next to the
waste area may have been contaminated by leaching.
Leaching occurs when rain, surface or groundwater
flowing through the soil carries some of the
contaminants away from the original source and into
neighboring areas. Excavation proceeds until the
cleanup goals are met. The concentrate a of waste
materials in surrounding areas should no longer
represent a threat to human health, wildlife and natural
habitats, or groundwater supplies.
In some cases, the leaching process may have carried the
contaminants vertically downward into an aquifer. An
aquifer is an underground rock and soil formation that
is capable of holding large amounts of water. To carry
out excavation in areas where the contaminants has
entered the aquifer, it may br necessary to install a
vertical barrier around the excavation site (see Figure 1).
The water in the site area is then pumped out so that
the soil can be more easily removed. The water that is
removed from the site will probably need to be treated
before it can be returned to the soil or discharged to a
sewage treatment plant. The vertical barrier will be
removed once the site is backfilled, to allow the aquifer
to return to its original state.
Excavation of hazardous wastes or contaminated
materials must be carefully planned. This planning will
include operations to minimize the spread of
contamination to clean areas of the site. Once
excavation equipment is in a contaminated area, it must
remain there until the work is completed. The
equipment must be thoroughly cleaned and
decontaminated prior to leaving the site.
Fieme 1: Excavation Below The Water Table Showing Vertical Barrier
-------
How is monitoring well sampling performed?
The sampling of monitoring wells is usually done by
trained field personnel from the testing laboratory or by
groundwater consultants. In general, a sample is taken
only after the pH, electrical conductivity, and
temperature of the water being pumped from the well
have stabilized. (pH is a numerical measure of the
relative acidity of the water; zero to seven indicate
decreasing acidity, seven to fourteen indicate increasing
alkalinity, while seven is considered neutral.)
How is contaminant movement predicted?
In many instances of groundwater contamination, the
ability to predict how the contaminant plume will behave
in the future can only be based on the results of
expensive drilling and sampling programs. Many
scientists interested in the movements of contaminants
in groundwater believe that it will soon be possible to
use mathematical modeling techniques to estimate the
spread of a particular contaminant and its concentration
at any point in the plume.
How are the locations of monitoring wells
determined?
Once the general limits of the plume have been
identified, several monitoring wells are installed in or
near the plume. The purpose of these monitoring wells
is to:
• Determine the properties of the rock formation
in which the contamination is found and the
surrounding aquifers.
• Determine the level of groundwater of all
aquifers in the area.
• Provide samples of groundwater for the
detection of contaminants.
• Monitor the movement of the contaminant
plume.
Usually one monitoring well is located near the center of
the plume in the path of the groundwater as it moves
away from the site. Another is installed farther away,
but in the path of the plume. Background conditions are
recorded from a third monitoring well that is located in
an uncontaminated area (see Figure 3).
The most difficult decision is usually not where to place
the monitoring well, but at what depth the samples
should be taken. Selection of the most appropriate
depths depend on the characteristics of both the
contaminant and the aquifer or soil surrounding the site.
The design of the well and sampling plan are extremely
important if meaningful and accurate information
concerning the extent of contamination is to be obtained.
Proper placement of the monitoring wells is also
important and must be based on accurate information
concerning the pattern of groundwater flow and the type
of contamination.
EXPLANATION
Uporodient monitoring
will
Londfill monitoring
well
Downgrodient monitorng
well
ffgmic 3c Typical Arrangement of Monitoring Wells
For more information about Groundwater
Monitoring, please contact EPA at the following
address:
TJ.S. Environmental Protection Agency
ATTN: Superfund Hotline
401M Street, S.W.
Washington, D.C. 20460
1-800-424-9346 or 1-800-535-0202
Tfce Monn«Uoo coouiaed in thk fact sheet wa. compiled from Sunerfiind Innovative Technology Evaluation (SITEt. a publication of the U.S.
envlroomenU] Protection Agency, November 1991.
-------
EPA Facts About
Immobilization
June 1992
What is immobilization?
Immobilization is a treatment process used to
prevent migration (movement) of toxic and
hazardous chemicals from soil slurries and waste
sludges from spreading to the surrounding
environment. This process binds the hazardous
chemicals into immobile (insoluble) forms,
binding them in an insoluble mass which
minimizes the surface area of the waste
chemicals exposed to migration through leaching.
Leaching is caused when water, either surface
water or groundwater, moves through wastes
(much as water percolates through coffee
grounds) picking up contaminants.
How does immobilization work?
Immobilization involves solidification and stabilization
processes in which chemicals, reagents, and cement-like
binding materials are mixed with contaminated soil to
render the waste immobile and inactive. Solidification
results in a monolithic block of treated waste with high
structural rigidity. Stabilization results in either
reducing the toxic effects of the treated waste or
limiting its solubility. The application of
immobilization to contaminated soil results in a high-
strength, non-leaching block that can be placed into
the ground without double liners or covering caps.
Often the immobilized product has structural strength
sufficient to help protect itself from further fracturing,
thereby preventing increased leaching. Environmental
damage is significantly reduced as the hazardous
chemicals are encapsulated in a solid block.
Solidification and stabilization processes have two key
components: the chemical reactants and the mixing
equipment. The chemicals typically include portland
cement, lime, fly ash, clay, silicates, and a proprietary
chemical. The proprietary chemical is supposed to
react with the metals and organics to form insoluble
compounds and to prevent the organic constituents
from interfering with the pozzolanic (cement)
reactions.
WATER TANK
8UW
StLO
FIXED MASS
CMW REAGENT
MOONGAND
CONTROL PLANT
PERIMETER CUTOFF
WALL (OPTIONAL)
BERM
Figure 1: Typical In Situ Immobilization Ptocess
-------
How are agents mixed with contaminated
soils?
Effective mixing is required whether the waste and
chemicals are mixed in situ or above ground in tanks,
drums, pits, or mills. Without thorough mixing, the
chemicals cannot immobilize the hazardous onstituents.
Immobilization for soils can be achieved by the
injection method for wastes below ground or in a
specially designed mill above ground for excavated
contaminated soil. In the injection method.
immobilization agents (cement, fly ash or patented
additives ) are injected into the waste materials in a
liquid or slurry form. Figure 1 shows a typical "in situ"
or in place immobilization process. Injection can be
achieved by pumping the immobilization reagent inside
a porous tube to the required depth. In above ground
application, the excavated contaminated material is
screened to remove pieces larger than one inch and
stored in a feed hopper. A conveyor belt moves it
from the feed hopper to the weight feeders where it is
measured. The homogenizer mixes the wastes with
water to achieve the desired moisture content. The
wetted material then moves to a pug mill, where it is
thoroughly mixed with reagents. After the material is
blended, it is discharged and allowed to harden. The
final product is a solidified mass of soil.
What are typical solidification and
stabilization methods and common uses?
Cement-based fixation process treats sludges and soils
containing metals, radioactive wastes, and solid organic
wastes (plastics, resins, tars) by the addition of large
amounts of siliceous materials combined with cement
to form a dewatered, stabilized solidified product.
Soluble silicates are added to accelerate hardening and
containment Larger amounts of dissolved sulfate salts
or metallic anions, such as arsenate and borates, will
hamper solidification. Organic matter, lignite, silt, or
clay in the wastes will increase setting time.
Pozzolanic-based fixation process treats sludges and
soils containing heavy metals, waste oils, solvents, and
low-level radioactive wastes, onsite by the addition of
large amounts of pozzolanic materials (fly-ash, lime)
combined with cement to form a dewatered stabilized,
solidified product. Materials such as borates,
sulphates, and carbohydrates, interfere with the
process.
Vitrification is a process that uses a very high
temperature to convert hazardous wastes into a glass-
like substance. The process is carried out by inserting
large electrode into contaminated soils containing
significant levels of silicates. Graphite on the surface
connects the electrodes to the soil. A high current of
electricity passes through the electrodes and graphite.
The heat causes a melt that gradually works downward
through the soil. Some organic contaminants are
volatilized and escape from the soil surface as gases,
and must be collected by a vacuum system. Inorganic
and some organics are trapped in the melt, which as it
cools, becomes a form of obsidian (gemstone like) or
very strong glass. When the melt is cooled, it forms a
stable noncrystalline solid.
GL08SA&V
Proprietary Chemical: Reagents used to the
iMmofeilzafioii process which have been
developed uaidir » protected patent These
chemicals improve ta* effectiveness of (he
process.
Sludges:' A »ga»£«DiJtf waste product generated
lr or water ttwawart processes sncfc &
Toxic:, A poisonous or hazardous substance.
vaporized or
For more information about Immobilization,
please contact EPA at the following address:
U.S. Environmental Protection Agency
ATTN: Super/and Hotline
401M Street, S.W.
Washington, D.C. 20460
1-800-424-9346 or 1-800-535-0202
The information cootained in this fact sheet was compiled from Supetfund Innovative Technology Evaluation, a publication of the U.S. Environmental
Protection Agency, November 1990.
-------
EPA Facts About
In Situ Vitrification
June 1992
What is in situ vitrification?
In situ vitrification (ISV) is the process of melting
waste and soils or sludges "in place" to bind the
waste into a glassy, solid mass resistant to leaching.
This mass is more durable than either granite or
• marble. This thermal process destroys organic
(carbon-containing) pollutants and immobilizes ai.d
traps inorganic pollutants. ISV technology is based
on extremely high temperatures, in the range of
2,900°F to 3,600°F, to electrically melt soil or
sludge. It destroys organic pollutants bypyrofysis,
chemically decomposing the substances through
heat Although the process was initially developed
to stabilize previously disposed radioactive wastes,
it may also be used to destroy or immobilize many
organic and inorganic chemical wastes, such as
heavy metals, PCBs, process sludges, and plating
wastes.
Vitrification technology converts contaminated
soils, sediments, and sludges into glass-like
substances, rendering them non-toxic. Inorganic
and toxic wastes are chemically bonded through
heat into glass and are changed chemically to a
non-toxic form.
How does in situ vitrification work?
In the ISV process, large electrodes are inserted into the
soil to the desired treatment depth. Because soil typically
has a low electrical conductivity, flaked graphite and small
glass fragments may be placed on the soil surface between
the electrodes to provide a started path for electric
current. The electric current passes through the electrodes
and begins to melt soil at the surface. As the current
flows, the soil is heated to 2900-3600°r, wb;-,h is well
above a typical soil's melting temperature. This melting
process continues to grow downward, at a rate of 1 to 2
inches per hour using the above temperature ranges.
Placement of electrodes in tt. soil may vary to encompass
a total melt volume of 1,000 tons and a maximum width of
30 feet. A diagram of a typical ISV treatment process
stages is shown in Figure 1.
The pyrolyzed by-products migrate to the surface of the
melt zone, where they ignite in the presence of oxygen. A
hood placed over the melt zone to collect both the organic
and inorganic gases, drawing the escaping gases into a
treatment system before release to the atmosphere.
Convective currents (heat-driven) within the melt zone
uniformly mix the materials in the soil. When the electric
current ceases, the molten volume cools and solidifies.
POROUS GLASS
FRIT STARTER
ELECTRODES
VITRIFIED SOL/WASTE
Figure 1: Stages of a Typical In situ Vitrification Process
-------
What conditions are required?
Two conditions must be met to successfully vitrify
soils, sediments, and sludges: (1) the development
of glass compositions tailored to the waste being
treated; and (2) the development of a glass melting
technology that can convert the waste and additives
into a stable glass without producing toxic
emissions. Specific site characteristics must be
considered in determining the appropriateness of
ISV. In the event that feasibility tests indicate
problems in the soil electrical conductivity or
vitrification, sand, soda ash, or glass frit (fragments)
can be mixed with the soil to improve the process.
Generally, ISV can treat contaminated soils which
are not more than 5 to 10 percent uiganic materials
by weight and not more than 5 to 15 percent
inorganic materials by weight.
Soil moisture is an important factor in the
operation of the ISV process. More electrical
power and time are required to evaporate the water
as soil moisture increases. A combination of high
soil permeability (excessive air space in soils) and
the presence of groundwater can significantly
increase the cost of ISV. The process will work
with fully saturated soils; however, the water in the
soil must be driven off through evaporation before
the soil will begin to melt. If the soil moisture is
being recharged by an aquifer, there is an additional
economic impact. Engineered barriers, which block
groundwater from entering the treatment area, may
be required to vitrify soils below the water table.
The environmental impact of the escaping gases
must also be addressed when considering ISV. A
hood must be placed over the processing area to
collect volatiles (wastes compounds which can
vaporize rapidly as gases and present an exposure
risk through inhalation) driven off during start-up,
combustion gases, and steam and convey them into
a gas treatment system.
What benefits can ISV provide?
ISV eliminates the need for excavation, processing,
and reburial of the hazardous compounds, and
minimizes worker exposure to the contaminants.
The process produces a stable, glassified mass that
has excellent long-term durability and an extremely
low leach rate, requiring little or no site
monitoring.
Following the ISV process, there is a significant volume
reduction in the amount of contaminated material. The
percentage of removal of contaminated organic material is
approximately 99.999%; inorganic material is permanently
i .nmobilized.
A melting unit which uses electricity rather than fossil
fuels as the heat source helps to limit the emissions
associated with these fuels. Since molten glass is a good
conductor, the electrodes melting the waste can do so
under a thick blanket of the molten glass. This blanket
essentially forms a scrubber for volatile emissions. In
contrast, fossil fuels melters have large, exposed molten
glass surface areas from which hazardous constituents caa
vaporize into the ambient air. Typical experience with
commercial electric melters has shown that the loss of
inorganic volatile constituents, which are high in fossil fuel
melters is significantly reduced. Because of its low
emission rate and small volume of exhaust gases, electric
melting is a promising technology for incorporating high-
level nuclear waste into a stable glass.
C&OSSAfcY
In situ Vitrification: Hi6 process of weltuig
and soil* or slod^s "fe-pfcee* to bind &e*»ste in
a glassy, solid resistant to leaching,
tyofysis:
fceat
H£F or water treatment processes.
For more information about In situ Vitrification,
please contact EPA at the following address:
U.S. Environmental Protection Agency
ATTN: Superfund Hotline
401M Street, S.W.
Washington, D.C. 20460
1-800-424-9346 or 1-800-535-0202
The Information contained in thii fact sheet was compiled from In situ Vitrification, a publication of the U.S. Environmental Protection Agency,
RcjkmV.
-------
EPA Facts About
Incineration
June 1992
What is incineration?
Incineration is one of the technologies available to
treat hazardous wastes. It can destroy organic
compounds in wastes such as dioxins and
porychlorinated biphenyls (PCBs). Incinerators can
hi ndle many forms of waste, including contaminated
soils, sludges, solids and liquids. Some incinerators
provide for the recovery of energy.
Incineration, however, destroys onlyorganicsubstances,
it is not effective in the treatment of inorganic
substances such as hydrochloric acid, salts, and metals.
How does incineration work?
Incineration is accomplished by using high temperatures
(between 1600°F and 2500°F) to degrade contaminants.
Toxic chemicals can be reduced to the basic elements
(hydrogen, carbon, chlorine, nitrogen, etc). These combine
with oxygen to form non-toxic substances such as water
(hydrogen and oxygen), carbon dioxide (carbon and oxygen),
and nitrogen oxides (nitrogen and oxygen). Inert ash,
organic-free paniculate matter, hydrogen chloride, and small
concentrations of organic materials may also be present in
the combustion gas. Properly done, high-temperature
incineration is an effective, odorless, and smokeless process.
What happens to the residues produced by
incineration?
f. .
The U.S. Environmental Protection Agency (EPA)
incinerator regulations assume that ajl ash and
particulates removed from the stack and the bottom of
the burner unit are hazardous. Accordingly, they must
be disposed of at a RCRA-p, rmitted facility, (The
Resource Conservation and Recovery Act, or RCRA,
as it is called, is the law that regulates the handling of
hazardous wastes). In addition, scrubber water must
meet the Clean Water Act standards before it can be
discharged to surface waters.
Can highly toxic wastes be destroyed by
incineration?
A common misconception is that the more toxic the
chemical, the more difficult it is to bum. Although some
chemical compounds are more difficult to destroy by
incineration than others, ease of thermal decomposition is not
related to ioxicity. EPA research has demonstrated that
destruction of organic wastes occurs independent of toxicity.
This is encouraging news, because it means that chemicals
ranging from complex pesticides to PCBs, benzene and dioxin
all break down under heat; provided that specific conditions
are met.
Are the wastes completely destroyed by
incineration?
No incinerator can destroy 100 percent of the
hazardous wastes fed into it Small amounts are
released into the atmosphere through the incinerator
stack or are mixed with the ash. EPA requires that
each incinerator meet stringent performance standards.
A standard of 99.99 percent has been set for
destruction and removal of all hazardous wastes
processed in incinerators. For PCBs and dioxin-listed
wastes, the standard is 99.9999 percent or that only
one pound of an organic compound may be released to
the air for every 1,000,000 pounds fed into the
incinerator. When operated property, hazardous waste
incinerators can meet or exceed these requirements
which have been developed to protect human health
and the environment.
What are the advantages of incineration?
Incineration offers a permanent solution to much of our
hazardous waste problem by destroying wastes that would
otherwise require space in a landfill. Incineration has proven
effective in the destruction of aU organic compounds, usually
accomplishing well over 99% reduction of organics.
-------
Hew does EPA know that standards are being
met?
EPA requires "trial burns" to demonstrate the
effectiveness of each incinerator. The incinerator is
fed measured volumes of various hazardous wastes
which are representative samples of the wastes
expected to be incinerated during normal operations.
The trial burn is designed to test the performance of
the incinerator unit under the most demanding
operating conditions the unit may experience. For
each test batch, EPA selects up to six compounds
known to be the most concentrated and most difficult
to incinerate. If the operators of the incinerator
cannot demonstrate a destruction and removal efficiency
of 99.99 percent, the waste feed used during the trial
burn cannot be accepted for processing by the unit
The results of the trial burn are used to establish
conditions under which each permitted facility must
operate. The permit defines such operating thresholds
as; the maximum carbon monoxide level in stack gases,
maximum feed rates, minimum combustion
temperature, maximum combustion gas velocity, etc.
Essentially, these conditions are designed to deliver a
•complete burn" of the hazardous waste by ensuring
optimal operating circumstances. Safeguards are
required which cut off the waste feed when these
circumstances do not meet the stated permit
conditions.
are taken. Finally, accurate recordkeeping and reporting on
the operation of the incinerator are required.
Which agency regulates incinerators?
All hazardous waste incinerators are regulated by EPA or
state agencies acting under authority of EPA Incineration
is one of the final steps in the cradle to grave regulatory
management system created by Congress under RCRA
legislation.
All owners and operators of incinerators are required to
submit information on the design, operation, and future
closure of the incinerator. They must also submit information
on their financial capacity to cover the closing of the unit
and liability for bodily injury or property damage to third
parties. The permittee must specify what analyses will be
done for all hazardous wastes prior to incineration to ensure
that the wastes are suited to the technology. Security
measures, such as installation of a fence around the
incinerator and adequate surveillance, are also required.
Owners aad operators must develop and follow a written
inspection schedule to assess the overall safety of the
incinerator facility, and they must employ trained personnel
They are also required to prepare an action plan for
emergencies and ensure that emergency prevention measures
Cradle to Gravel EPAteq»iK» hazardous satwtances to
'be" tracked from the time of prodwStton to final
disposal or destruction. „ / \
,- •"/,-»•.
Destruction and Removal Efficiency: A measure
-------
EPA Facts About
-zs Leachate Collection
June 1992
What is leachate?
Leachate is a liquid that has passed through
buried waste and, as a result, contains dissolved
or finely suspended solid matter and microbial
waste products. This solid matter and waste
products may consist of organic and inorganic
substances, groundwater or infiltrating surface
water moving through solid wastes can produce
leachate. Leachate may leave the fill at the
ground surface as a spring or percolate through
the soil and rock that underlie and surround the
waste.
Why is leachate collection important?
This feet sheet only applies to leachate collection under
the U.S. Environmental Protection Agency (EPA)
Superfund program. It does not apply to Resource
Conservation and Recovery Act, Subtitle C and
Subtitle D facilities where the design and monitoring
requirements are much more stringent than reflected
here.
Leachate is perhaps the most significant problem in the
pollution of groundwater. Leachate develops at
sanitary landfills by groundwater or surface water
filtering through the solid waste. Leachate is a highly
complex mixture of soluble, insoluble, organic, and
bacteriological contaminants in a water-based solution.
Bacteriological contaminants are usually filtered from
the leachate after traveling through several feet of most
soils. Suspended solids, however, travel greater
distances, creating groundwater pollution.
As water passes through the cover material and down
through buried wastes in our landfills, it picks up solids
and dissolves some portion into solution. Leachates
generated by the disposal of hazardous wastes may
include high concentrations of such heavy metals as
mercury, cadmium, and lead; tanc substances such as
barium and arsenic; organic compounds, including
chlorinated solvents, aromatic hydrocarbons, and
organic esters; and various corrosive, ignitable or
infectious materials. Landfill leachates degrade
groundwater quality by introducing hazardous
constituents as well as biological contamination.
VEGETATION
TOPSOIL
CLAV LINER
UNDirFERENTIATED
LEVELING
SURFACE
SEAtlNG
WASTE
: Leachate Control Technologic*
What causes leachate?
Leachate is produced when the infiltration of
precipitation and other sources of water is applied to
the landfill surface which exceed the combined of
runoff, evapotronspiration, and soil moisture storage.
All these are natural cycles which prevent the water
from traveling downward though the soil. For
example, the net inflow to an area of buried hazardous
wastes (called percolation) is absorbed by the wastes
until the absorption capacity of the buried wastes is
reached. As a result, if additional water infiltrates into
the waste, it will accumulate as leachate or discharge to
the groundwater beneath the wastes.
-------
How soon after the burial of wastes is
leachate produced?
The appearance of leachate at a landfill from the initial
time the waste was deposited may be delayed by as
much as 20 years. Therefore, any short-term study of
leachate may not adequately establish the magnitude of
the problem. This is dependent on the soil
characteristics at the landfill. Leachate may enter the
groundwater or overflow onto the surface (like a bath
tub overflowing) depending on the permeability of the
underlying soil. While soil permeability has no effect
on leachate generation, it is controlled by the
permeability (the rate of water loss) of the material
which covers the waste. Sites with good covers should
not generate leachate, even though the site may be
underlain by permeable and porous soils.
What is a leachate collection system?
A leachate collection system generally consists of
Strategically placed perforated drain pipe bedded and
backfilled with drain rock. This system resembles a
french-drain which is often installed in residential
property to promote drainage. The system can be
installed completely around the perimeter of the
landfill or a network or grid of collection pipes can be
installed. The collection system is drained to a sump
from which the leachate is withdrawn by pumping.
The configuration of the collection pipe network varies
depending on the amount of water which can be
allowed to build up in the wastes. For Superfund sites,
the minimum collection system should extend
completely around the perimeter of the site to provide
absolute control of the level to which leachate can rise
on this critical boundary. It should be noted that this
method should never be used for a RCRA Subtitle C
or Subtitle D facility where the height of the rise of
accumulating leachate on the liner must not exceed one
foot
What level of maintenance and monitoring is
required?
Landfill leachate control systems must include facilities
for (1) the monitoring of leachate levels at the base of
the landfill, and (2) the withdrawal of leachate to
prevent build-up of a fluid level that would promote
unacceptable migration (movement) of leachate from
the waste site. The current state-of-the-art in landfill
design uses sumps or excavated basins located at low
points on the base of the landfill to which a leachate
control system or to the surface of the fill provides the
means for removing the leachate from the sump in
addition to providing a Veil" in which the leachate
levels can be measured. Leachate sumps are filled with
drain rock (large stone) that provides the necessary
storage capacity (pore space) while also providing the
water movement characteristics necessary to produce
flow to the sump pumping location.
GLOSSARY
Evapoiranspiration: £ wfcoess to which green
plants iftove «itet fro» the gmun4 and release
ft to the atmosphere as vntet vapor,
Superfund Program:' 'The program operated
wader tke legislative authority of the
Comprehensive Environmental »<*P<>nsf»
totttt*easatk>& and Liability Act ol 1980
(CERCLA), as aasended by the Stiperfond
Amendments awl fteauihorizaifcm Act of 1986
(SARA) that fcu«fe the EPA solid waste
eaergeaey and tea|-teaB wsaoval and rentediai
Toxic: Acting *s a j*oisoBoa& or hazardous
sB&ftwM^iaving pofcoaous or harmful qualities.
For more information about Leachate
Collection, please contact EPA at the following
address:
U.S. Environmental Protection Agency
ATTN: Superfund Hotline
401M Street, S.W.
Washington, D.C. 20460
1-800-424-9346 or 1-800-535-0202
Ttw tafonn»tioti cooulned in thk fact sheet was compiled from the o,wn,pu .
m^ntou.WMteSite* September 1985; C.mde toTeehnioJRe**^ frr theDerip. of 1 and nbpc^F«dl.t^D«»nber 1988,
Guidance Focun^Final Coven on Hazardous Waste Landfill* and Sinface ImnoiiBdmeote. July 1989.
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s
EPA Facts About
Pump-and- Treat
June 1992
What is the pump-and-treat method?
The pump-and-treat method is the most common
remedial (cleanup) technology used in purifying
contaminated aquifers. These aquifers are natural,
underground rock formations that are capable of
storing large amounts of water. The pump-and-treat
process usually includes three steps. First, the
contaminated groundwater is recovered from the
aquifer through recovery wells. Second, the
recovered water is treated. Finally, the treated water
is discharged and the contaminants are disposed of.
Groundwater collection systems are designed to
capture contaminated groundwater by removing it
from the aquifer. These collection systems are also
used to prevent the spread of contamination. As the
contaminated groundwater is recovered from the
aquifer, the contamination is prevented from moving
deeper into the aquifer or spreading into surrounding
clean aquifers.
Why not simply treat water at the well?
Another form of the pump-and-treat process, called well-
head treatment, is sometimes used when drinking water
wells are contaminated. In some cases, it has been found
to be cost-effective to continue to recover contaminated
groundwater, but to remove the contaminants before
delivering it to users.
There are several variations of this approach. At some
sites, the source of the contamination is known and an
auxiliary recovery system has been installed. This auxiliary
system is intended to cleanup the contaminated aquifer or
may operate simply to prevent further spread of
contamination. The contaminated water is drawn away
from the drinking water well and redirected. In other
cases, the source of contamination is not known and the
well-head treatment system may be the only practical
alternative.
The system may use a variety of tools to move and redirect
groundwater, including extraction wells, injection wells, dram
intercepts, and barrier walls. Extraction wells are designed
to pump groundwater out of the aquifer and to redirect the
remaining water. Injection wells use the opposite method;
pumping water into an aquifer to change its flow patterns.
Drain intercepts are surface features that are designed to
capture and redirect the groundwater flow. Barrier walls
may be installed in the cleanup area to create physical
barriers to groundwater flow.
Why do we want to pump groundwater?
The treatment of a contaminated aquifer, or "aquifer
restoration", is not the only goal of groundwater extraction
systems. Another goal is the contr~' of contaminant
migration (movement). Groundwater pumping techniques
involve the active management of groundwater to contain
or remove contaminants. These techniques can also be
used to adjust the groundwnter level so that no migration
will occur.
The area of contaminated groundwater associated with a
site is called a plume, and is the groundwater equivalent of
smoke from a fire. A water barrier may be constructed by
causing the water in an aquifer to move in such a way as to
prevent the plume from moving toward a drinking well.
Pump-and-treat technology is used to construct these water
barriers to prevent off-site migration of contaminants. In
most aquifer restoration systems, plume containment is
listed as secondary goal. It is usually necessary to establish
control of contaminant migration if the aquifer is to be
cleaned up. Exceptions to this general rule are sites where
the aquifer can restore itself naturally by discharging to
surface water bodies or through chemical or biological
degradation (breaking down) of the groundwater
contaminants to render them harmless to human health and
the environment
Control of groundwater contamination involves one or
more of four options: (1) containment of a plume; (2)
removal of a plume after the source of contamination has
been removed; (3) reduction of groundwater flow to
prevent clean groundwater from flowing through a source
of contamination, or to prevent contaminated groundwater
from moving toward a drinking well; and (4) prevention of
a plume by lowering the water table beneath a source of
contamination.
Why do we use pump-and-treat?
Groundwater collection and treatment has proven effective
over a wide range of site conditions and contaminants.
Well collection systems can remove groundwater from the
great depths. In addition, the costs associated with this
technology are generally moderate.
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What makes soil washing a good treatment
technology?
Soil washing can significantly reduce the volume of
contaminated soil that must be treated by more costly
technology. In addition, a wide variety of chemical
wastes can be removed from soils using soil washing.
Removal efficiencies, that is the percent of wastes
removed, depend on the type of waste present as well
as the type of soil. Volatile organic compounds, or
VOCs, are those compounds that contain carbon and
are usually associated with life processes. These
compounds, such as gasoline, evaporate quickly when
heated or disturbed in any way. This type of
compound can usually be removed with 90 to 99
percent efficiency. Semi-volatile o-janics are harder to
remove, but with addition of the proper surfactant,
removal efficiencies are normally in the 40 to 90
percent range.
Successful removal of metals and pesticides, both of
which are less soluble (harder to dissolve) in water,
Often require the use of acids or the chelating agents
mentioned above. The process can be used for the
treatment of soils contaminated with wood-preserving
chemicals (e.g., pentachlorophenol and creosote);
organic solvents; electroplating residues (e.g., cyanide
and heavy metals); organic chemicals production
residues; pesticides; and petroleum residues.
Soil washing is most effective in treating sand and
gravel soils that have been contaminated with VOCs.
It is also effective in treating soils that have been
contaminated with inorganic compounds such as
metals.
Finally, soil washing provides a closed system that
allows operators to control the environment
immediately surrounding the treatment facility and
minimize the chance of contaminating clean areas at
the site. The equipment involved is mobile and,
therefore, can be moved to the site. This prevents the
possibility of the spread of contamination during
transportation to another treatment facility.
Is soil washing a cure-all?
In some cases, soil washing can deliver the performance
needed to reduce contaminant concentrations to
acceptable levels. In other cases, soil washing may
need to be combined with other technologies. It can
be cost-effective as a first step in a series of treatments
because it reduces the amount of material that
subsequent steps must process. It is also useful in
converting the excavated soil into a more uniform
consistency that can be more easily treated with other
processes.
Contaminated fine particles of clay and sludges
resulting from soil washing may require further
processing using accepted treatment technologies in
order to permit safe disposal. The used wash water
may also require treatment to meet safe discharge
standards prior to release into the environment. Any
vapor emissions from the waste preparation area and
washing unit must be collected and, if necessary,
treated to meet regulatory standards.
How do we know sofl washing will work?
Thorough testing is required to determine if soil
washing will be effective and safe at a given site. The
entire process is evaluated, from excavation to final
disposal of all the soil and wash water. If the test
results are promising, smell-scale demonstrations are
normally conducted before full-scale operations are
begun. ^
Fif«e 2 Debris Washing Process
For more information about Soil Washing,
please contact EPA at the following address:
U.S. Environmental Protection Agency
ATTN: Superfund Hotline
401 M Street, S.W.
Washington, D.C 20460
1-800-424-9346 or 1-800-535-0202
The information contained in this fact sheet was compiled from Technology Fact Sheet: Soil Washing, a publication of the US. Environmental
Protection Agency, July, 1991.
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EPA Facts About
Thermal Desorption
June 1992
What is thermal desorption?
Thermal desorption is a low-temperature heat line
separation process designed to remove organic
contaminants from soils and sludges.
Contaminated soils are heated at relatively low
temperatures (200°F to 900°F) so that only those
contaminants with low boiling points will vaporize
by turning into a gas. ^liese vaporized
contaminants removed from the soils or liquids are
collected and treated. Thermal desorption is not
an incinerator system, and no hazardous
combustion by-products are formed. Thermal
desorption technology is useful in treating organic
contaminants that become gases at relatively low
temperatures. These contaminants include volatile
organic compounds (VOCs), polychlorinated
biphenyls (PCBs), and some polynuclear aromatic
hydrocarbons (PAHs).
How does thermal desorption technology work?
Thermal desorption is a three step process: first, the soil
is heated to vaporize the contaminants; next, the
vaporized contaminants are treated; and, finally, the
treated soil is tested. The contaminated soil is heated at
temperatures between 200° F and 900° F to reduce the
chance that the organic contaminants will ignite. Four
different methods of heating the soil are available. Each
method is described below:
(1) b-pboe stem extractkm (Figure 1): The
contaminated soil is left in place white steam is pumped
through the ground. The contaminants vaporize to a gas
form, move through the air spaces in the soil, and the
gases are collected by a vacuum. Since steam, and not a
flame, is used to vaporize the contaminants, there is no
risk that the organic contaminants will ignite and form,
hazardous combustion by-products.
(2) Direct heatug This heating method is like heating
with a gas oven in your home. A disadvantage of this
heating method is that the flame is in direct contact with
the contaminants, and therefore, increases the chances
that the contaminants will burn and form hazardous
combustion by-products.
(3) Indirect heating: The contaminated soil is placed in
a kiln-type furnace. The outside of the kiln is heated
using fuel oil, and the heat is transferred through the
kiln's metal surface to the soil. Since the soil is enclosed
in the kiln, the fuel's combustion by-products and the
vaporized contaminants do not mix.
(4) Oxygen free heating: The soil is placed in a
container which is sealed to avoid any contact between
the soil and oxygen in the air. The outside of the
container is heated using a burner system, and the
contaminants vaporize. Without air, the risk of forming
combustion by-products is virtually eliminated.
What happens once the contaminants are
vaporized?
Once vaporized, the contaminants can be treated
in the same manner regardless of which heating
method is used. The vaporized contaminants may
be cooled and condensed into a liquid, which is
then placed in drums for treatment or disposal.
The vaporized contaminate may also be treated
using a carbon filtration system to meet applicable
federal, state, and local air emission standards.
Once thermal desorption is completed using one
of the four heating methods described above, the
soil is tested to verify that all contaminants have
been removed. The moisture content is adjusted
to eliminate dust particles and produce a solid that
is ready to be placed and compacted in its original
location. The organic contaminants and water
vapor driven from the solids are transported out of
the dryer by a nonreactive nitrogen gas. The inert
gas flows through a duct to the gas treatment
system, where organic vapors, water vapors, and
dust particles are removed from the gas. This gas
treatment system is made up of a high-energy
scrubber in which dust particles and 10 to 30
percent of the organic contaminants are removed.
The gases then pass through two heat exchangers,
where they are cooled to below 40°F. Most of the
remaining water and organic vapors are condensed
to liquids in the heat exchangers. The cleaned soils
and sludges can be returned to the site as backfill.
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Why consider thermal desorption?
Thermal desorption has a high success rate in removing
volatile organic compounds (VOCs). VOCs are
chemicals which tend to vaporize easily into the air,
creating an exposure hazard by inhalation. Existing
equipment is capable of treating up to 10 tons of
contaminated soil per hour. In addition, since thermal
desorption operates at low temperatures, the risk of
VOCs and other organic contaminants burning and,
consequently, forming hazardous gaseous emissions is
reduced. Finally, the low temperatures require less fuel
than other treatment technologies, and so this method is
less costly.
What kinds of waste can be treated by thermal
desorption?
This technology was developed primarily for on-site
remediation (clean-up) of soils contaminated with
organic contaminants. The process can remove and
collect volatiles, semi-volatiles, and PCBs, and has been
demonstrated on a variety of soils ranging from sand to
very heavy clays. Filter cakes from water treatment
processes and pond sludges have also been successfully
processed. In most cases, volatile organics are reduced to
below 1 part per million (ppm) and frequently to below
the levels which the laboratory can detect.
Thermal desorption cannot be used to treat heavy
metals, with the exception of mercury. Tars and heavy
pitches cannot be processed using this technology
because they create materials handling problems.
GLOSSARY
Heat Exchangers: A chamber used to add or
remove heat; a common example is a car radiator
which uses water (coolant) to accept the heat of
your car's engine wA releases this heat to the
atmosphere 9$ the heated water passes through the
exposed aetel chamber* (fias) of the radiator. An
air conditioner works on a similar principle,
f / ;
Scrubber: M aur poUtttion device that uses a spray
ol water (or reactant) or a dry process ( such as
filters or tjentnlwgal scrubbers) to trap pollutants
in gaseous emissions.
Sludges: A semi-solid waste product generated
ftbm air or water tteatmeot processes.
For more information about Thermal Desorption,
please contact EPA at tue following address:
U.S. Environmental Protection Agency
ATTN: Super/and Hotline
401 M Street, S.W.
Washington, D.C. 20460
1-800-424-9346 or 1-800-535-0202
CONOCMOH
(FuflhM tiMMMtl or dfcpoMQ
TMATtO
KM.
•OLTOTtO
POM
COMTAMMAMT*
figatc 1; Thermal Dcsorptkm Process Following Soil Excavation
The Information contained in this fact sheet was compiled from A Citizen's Guide: Thermal Desorption. a publication of the U.S. Environmental
Protection Agency, November, 1991.
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