CRS Report: 91-713 - Treatment Technologies at Superfund Sites

The Comprehensive Environmental Response, Compensation. and Liability Act of 1980 (CERCLA), commonly known as Superfund, authorizes the Federal Government, through the Environmental Protection Agency (EPA), to clean up hazardous waste sites. There are currently about 1,200 sites on Superfund's National Priorities List, with remedial costs expected to be around $40 billion.

After a site is discovered and appropriate authorities are notified, a preliminary assessment is conducted to determine if there is a threat to human health or the environment. If warranted, investigators then carry out a site inspection, taking samples, collecting data, and ultimately rating its hazard potential. Sites that score high enough are placed on the National Priorities List for cleanup. Next, the remedial investigation/feasibility study (RI/FS) is carried out. The RI/FS process involves a detailed definition of problems at the site, determining the necessary response, evaluating potential remedies, and reviewing the cost effectiveness of each remedy. If, at any time, the site presents an imminent hazard to public health or the environment, EPA may undertake an emergency removal action.

The main body of this report offers a basic description of widely used and demonstrated cleanup technologies, as well as some innovative undemonstrated technologies.

Biological treatment uses living organisms to degrade, stabilize, and destroy organic contaminants. The wastes provide energy and carbon for the microorganisms, which may be indigenous or imported. Microbes with superior degradative capabilities may be prepared through genetic alteration and/or selective enrichment techniques. Nutrients and oxygen are supplied to the contaminated zone for aerobic bioremediation. For anaerobic treatment another substance, such as nitrate or sulfate, takes the place of oxygen. Another group of microorganisms, methanotrophs, needs methane and air to break down the contaminants.

The objectives in using mobile chemical treatment technologies are to immobilize, to mobilize for extraction, or to detoxify the contaminants. The chemical treatments examined are soil flushing, soil washing, solvent extraction, chemical reduction-oxidation, neutralization, and dehalogenation.

Thermal treatment technologies accomplish one or more of three goals: detoxifying hazardous waste by destroying organic compounds, reducing the volume, and converting wastes to solids by vaporizing water and other liquids in the waste. Technologies reviewed are infrared incineration, rotary kiln incineration, fluidized bed incineration, vitrification, wet air oxidation, low temperature thermal stripping, and in-situ radio frequency.

The objectives of physical treatments are to immobilize wastes, detoxify them, or render them less harmful. They often produce residues that require further treatment prior to disposal. The physical treatments discussed are in-situ vacuum extraction, steam stripping, four stabilization/solidification techniques, in-situ vitrification, and air stripping.

The research presented in this report was performed by Alborz A. Wozniak, under the supervision of Mark Reisch.

TABLE OF CONTENTS

Introduction
Cleaning up Superfund Sites
Biological Treatment
-- In-Situ Bioremediation
Chemical Treatment
-- Soil Flushing
-- Soil Washing
-- Solvent Extraction
-- Chemical Reduction-Oxidation
-- Neutralization
-- Dehalogenation
-- Technology Comparison
Thermal Treatment
-- Infrared Incinerators
-- Rotary Kiln Incinerators
-- Fluidized Bed Incinerators
-- Vitrification
-- Wet Air Oxidation
-- Low Temperature Thermal Stripping
-- In-Situ Radio Frequency
-- Technology Comparison
Physical Treatment
-- In-Situ Vacuum Extraction and Steam Stripping
-- Stabilization/Solidification
-- -- Cement-Based Techniques
-- -- Silicate-Based Techniques
-- -- Thermoplastic-Based Techniques
-- -- Surface Microencapsulation
-- In-Situ Vitrification
-- Air Stripping
-- Technology Comparison
Glossary of Environmental Terms
Appendix A: Technology Case Studies

Figure 1 In-Situ Bioremediation
Figure 2 In-Situ Soil Flushing
Figure 3 Soil Washing System
Figure 4 Chemical Extraction
Figure 5 Glycolate Dechlorination
Figure 6 Infrared Thermal Treatment
Figure 7 Rotary Kiln Incineration
Figure 8 Fluidized Bed Incineration
Figure 9 Wet Air Oxidation
Figure 10 Low Temperature Thermal Stripping
Figure 11 In-Situ Vacuum Extraction
Figure 12 In-Situ Vitrification

Table 1 Bioremediation Summary
Table 2 Redox Agents and Waste
Table 3 Chemical Technology Comparison
Table 4 Thermal Treatment Comparison
Table 5 Physical Treatment Comparison

Table A Technology Case Studies

INTRODUCTION

Hazardous waste generation and the consequent disposal of it have become one of the most prominent environmental issues of the Nation. The United States produces 250 million tons of hazardous substances a year, or the equivalent of one ton per person. (1) In the Resource Conservation and Recovery Act (RCRA) of 1976, hazardous waste is defined as:

Improper treatment, storage, and disposal of these wastes has had both short-term and long-term effects on human health and the ecosystem. For decades, hazardous waste was abandoned at many sites around the Nation. In 1980, Congress passed the Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA), commonly known as Superfund. This Act was the first major response to the problem of abandoned and uncontrolled hazardous waste sites. The Act authorized $1.6 billion to finance the cleanup of abandoned hazardous waste sites and allowed the Environmental Protection Agency to recover cleanup costs. CERCLA was later renewed and expanded by the Superfund Amendments and Reauthorization Act (SARA) of 1986, which provided an $8.5 billion budget through 1991. (3) SARA established a strong preference for permanent remedies at Superfund sites and set schedules for beginning cleanup work and studies. The Congress directed the U.S. Environmental Protection Agency (EPA) to promote the development of alternative and innovative treatment technologies for use in Superfund response actions. (4) There are currently about 1,200 sites on Superfund's National Priorities List, with remedial costs expected in the $40 billion range.

This report provides a basic description of potentially applicable treatment technologies at Superfund sites, their strengths and limitations, and their current status in the Superfund program. The report includes information on widely used and demonstrated technologies as well as some innovative undemonstrated treatment technologies. The appendix contains a glossary of environmental terms used in the report. Also attached is a table of case studies of selected Superfund sites with descriptions of the contaminants, technologies applied during the remediation process, the status of the site, and estimated costs of the entire project.

CLEANING UP SUPERFUND SITES

To determine the appropriate treatment technology to be applied at a Superfund site, it is necessary to first identify and characterize the problem that requires treatment. EPA has implemented procedures for responding to and remedying the uncontrolled releases of hazardous wastes. This section provides a brief description of the cleanup methodology. These steps are general and do not cover the entire hazardous substance response. For more detailed information, the reader can refer to the National Contingency Plan (NCP) (40 CFR Part 300).

Usually the problem is discovered by citizens, or State or local government officials. Upon discovery of the site, the officials notify the National Response Center (NRC), which in turn designates an On-Scene Coordinator (OSC) for the site. It is the responsibility of the OSC to notify the Governor of the State affected by the release.

After the discovery of the release, the OSC acts immediately in assessing the problem. The OSC gathers such information as: the identification of the waste; the nature of the release; the quantity of waste; and the size of the site. Based on information provided by the OSC, the Agency for Toxic Substances and Disease Registry (ATSDR) of the Department of Health and Human Services (HHS) evaluates the threat to public health. During this period, the OSC tries to determine the parties responsible for the problem.

If the preliminary report shows that a threat is posed to human health, inspectors sample the contaminated zones, collect data, and rate its hazard potential. By analyzing the samples, the inspectors gain a better understanding of the nature of the contaminant, its constituents, and the extent of toxicity. In general, a site inspection provides the following information: it helps distinguish between serious releases that pose a threat to the public health and those that do not; it assesses the threat to neighboring communities and ecosystems; and it ranks the site on the National Priorities List (NPL) if it is sufficiently severe. Prior to a site inspection, however, the OSC reviews the conditions of the contaminated area to determine if it is safe for a site visit. Some sites may pose a health danger to the inspectors who would be sampling in the area.

The NPL contains the worst abandoned or uncontrolled waste sites around the Nation. This list is updated at least once a year. There are three general methods for adding a site to the NPL. First, there is the Hazard Ranking System (HRS), which is a set of conditions and requirements that determine the seriousness of the contamination. Second, each State designates its top priority site for the National Priorities List. Finally, during the site inspection, the inspectors may determine that a release poses a serious health threat and EPA determines that it would be more cost-effective to list the site on the NPL than to use other authorities to respond +o the release.

In accordance with section 105 of CERCLA, the EPA has established a process by which, upon the discovery of a release, data are collected, the necessary response is determined, remedies are evaluated, and the cost effectiveness of each remedy is reviewed. This process is known as the remedial investigation/feasibility study (RI/FS) process. During an Rl, scientists and technicians collect data and evaluate the site characteristics. Concurrently, the FS team makes decisions regarding remedial solutions based on the facts and data the RI group is collecting. RI tasks include:

During the feasibility study, the remedial investigation report is carefully studied and technologies are selected for the cleanup of the release. The steps of an FS are:

Site characteristic (e.g. soil permeability, contamination depth), waste characteristics (e.g. biodegradability, solubility, volatility, quantity), and technology limitations (e.g. performance record, operation and maintenance problems.)

The EPA may take short-term removal action at any time if the site is found to present an imminent hazard to public health or the environment. The factors affecting the determination of appropriateness of a removal action are listed below.

Technology selection begins once the site parameters and waste characteristics have been defined. The treatment technologies reviewed in the following report are categorized into biological, chemical, thermal and physical processes. Each technology is generally applicable to treating specific wastes. This report, however, is not a guide for selecting a technology for remediation of a hazardous waste site. It merely provides a basic understanding of some of the technologies used during the remediation process.

BIOLOGICAL TREATMENT

Biological treatment is the process of utilizing naturally occurring living organisms to degrade, stabilize and destroy organic contaminants. These microorganisms use the waste as their source of energy and carbon. Biological treatment technologies are restricted to organic wastes, and therefore have limited application. It is appropriate at this point to review some principles of biological processes. (The reader may find it helpful to refer to the glossary which begins on page 44 for technical terms with which s/he is not familiar.)

All living organisms require a source of energy and carbon to be able to develop and reproduce. Many organisms (autotrophic) get their carbon from inorganic compounds (such as CO2), while other organisms (heterotrophic) use organic compounds to get their carbon. Aerobic and anaerobic metabolic pathways are used by microorganisms to degrade organic waste. During aerobic respiration, the organism utilizes oxygen to break down complex organic compounds into simple inorganic salts, carbon dioxide and water. These microorganisms require an electron acceptor (oxygen in the case of aerobic), nutrients such as nitrogen (N) and phosphorous (P), and other trace elements. Some common aerobic bacteria are Pseudomonas, Arthrobacter, and Flavobacterium. Various microorganisms require different conditions for optimal growth. For example, anaerobic bacteria break down organics in the absence of oxygen. These bacteria utilize other molecules (such as nitrates) as the electron acceptor. (5)

One form of biological treatment that has gained popularity at CERCLA sites is in-situ bioremediation. In-situ bioremediation (also known as bioreclamation) is the process of altering and controlling environmental conditions in order to enhance the metabolic activity of the microorganisms which degrade organic contaminants. Before using this technology, many factors must be taken into consideration.

Waste and site characteristics dictate the applicability of bioremediation. One of the most important characteristics of the waste is its biodegradability. Microorganisms can either directly use the contaminated waste and gain energy and carbon from it; or, with the help of another substance they can co-metabolically break down the contaminated waste. The biodegradability of a waste can be measured in the laboratory through BOD(5)/COD tests. BOD (biological oxygen demand) (6) is a test through which contaminants can be categorized according to their biodegradability. COD (chemical oxygen demand) is a measure of the oxygen required to oxidize all compounds in water, both organic and inorganic. Site conditions can also determine the feasibility of bioreclamation. Some of the more important subsurface conditions that control the activity of microorganisms are: (7)

As mentioned above, some factors can be controlled while others may not. Often, a site contains microflora that can biodegrade the waste. However if useful organisms are not present in the contaminated zone, non-indigenous microorganisms may be added. Microbes with superior degradative capabilities may be prepared through genetic alteration and/or selective enrichment techniques.

Generally the following steps are taken to characterize and prepare a site for in-situ bioremediation: (8)

After preparation of the site and characterization of the waste, the bioremediation process may begin. During aerobic bioremediation, oxygen must be supplied to the contaminated zone continuously. There are different methods of achieving this task. Typical sources of oxygen are air, pure oxygen, hydrogen peroxide (H(2)O(2)), and ozone (0(3)). Pure oxygen and ozone are usually too expensive, and air does not contain enough oxygen. Therefore, the most common source of oxygen used in the field is H(2)O(2). Whatever source is chosen, oxygen is fed continuously to the site through a system of injection wells or infiltration galleries. The injection system can operate in either continuous or batch mode. Nutrients that are pumped into the contaminated zones are seldom injected continuously. Nutrients are pumped before oxygen (simultaneous injection can cause excessive microbial growth around the injection point and therefore plug the formation). Within the contaminated zone, the microorganisms degrade the organic waste using the oxygen and nutrients provided by the wells. Upon degradation, excess nutrients are collected by the use of recovery (production) pumps. During the operation, the concentrations of contaminants and nutrients, and microbial growth are monitored by wells placed between the injection and recovery wells. Figure 1 shows a typical aerobic in-situ bioremediation operation.

Anaerobic treatment is an alternative method of biorestoration. During anaerobic metabolism, another electron acceptor (e.g., nitrate, sulfate) plays the part of oxygen. Nitrates, for example, have been used, and have proven more cost effective and efficient due to the fact that they are more water soluble.

Another group of microorganisms that are being used is methanotrophs. Alone, these organisms are unable to break down the organic waste; rather, they rely on methane molecules and/or halogenated methanes for indirect degradation of the contaminants. Methane and air are supplied to these organisms to allow them to co-metabolically break down the contaminants.

Bioremediation is an innovative treatment technology. Between 1982 and 1989, 37 percent of all technologies used for source control at Superfund sites were innovative technologies. Bioremediation was selected or used at 22.5 percent of those sites. (9) The advantages and disadvantages of biological treatment are tabulated in Table 1. For an example of the in-situ bioremediation technology, see Appendix A.

Technology	Advantages	Disadvantages
In-situ bioremediation	Cost-effective technology.	Complex wastes can inhibit biological activity.
	Fairly broad applicability for organic wastes.	Applicability limited by site conditions.
	Large volumes of soil may be treated.	Difficult process to monitor for cleanup efficiency.
	Likely to be supported by the public since it is viewed as a natural process.	Better understanding and optimization of the science required.

CHEMICAL TREATMENT

The technologies described in this section are mobile chemical treatment technologies that are used for the cleanup of uncontrolled hazardous waste sites. In general, chemical treatments alter the structure of the waste constituents to render them less hazardous than their original form. The objectives in using chemicals and chemical reactions are to either immobilize, mobilize for extraction, or detoxify the contaminants. A chemical technology may achieve one or all of the above tasks. Before describing any of the treatments in detail, a few points must be emphasized.

One way of separating contaminants from the soil is through "soil flushing," also referred to as "solvent flushing," "ground leaching," or "solution mining." (10) The process includes injection of a water-based solution into the contaminated zone in order to scrub the contaminants from the soil. Applied to unexcavated soils, the process removes contaminants in two ways: either by dissolving them in the flush solution, or by concentrating them into a smaller volume of soil. In the former, the contaminated solution is pumped to the surface and treated by conventional wastewater treatment methods. In the second method, the contaminants are first concentrated into a smaller region through the use of particle size separation. Organic and inorganic contaminants tend to stick to clay and silt soil particles. Contaminants, by reason of volubility or through chemical reactions, become mobile and can be packed into a smaller zone. To enhance mobility, ponds and sprinklers may be used. Control measures, including naturally occuring phenomena such as clay containing layers, may be required to prevent migration of the contaminants into the groundwater. After collecting the contaminants in a small zone, an extraction unit pumps the waste into a treatment system. After treatment, the groundwater is reinjected, creating a closed loop. Flush solution added during the process must be removed before reinjection. Figure 2 shows a simple in-situ flushing system. This technology is often used for removal of volatile organic contaminants.

Two factors determine the effectiveness of soil flushing, one is the contaminant type and the other is the soil type. Generally soil flushing is most effective on coarse sand and gravel. The type of contaminant dictates the solution that is used in the flushing system. There are five classes of potential solutions: 1) water, 2) acids-bases, 3) complexing and chelating agents, 4) surfactants, and 5) certain reducing agents. Some organic and inorganic contaminants are readily solubilized in water. Certain metals or heavy organics are insoluble in water, and other solvents such as acids and bases must be used to extract the contaminants. It is desirable to use weaker acids, since acids can themselves be toxic. Sodium dihydrogen phosphate (NaH(2)PO(4)) and acetic acid (CH(3)COOH) are examples of stable weak-acid solutions frequently used.

Of all the flushing solutions, one of the most promising is surfactants. Surfactants (surface-active-agents) are a class of soluble compounds that enhance the solubilization and emulsification of other chemicals, and therefore increase the efficiency of removal. The major types of surfactants are anionic, cationic, nonionic, and amphoteric. Each type of surfactant has specific applications. Anionic surfactants are the largest group in terms of usage and importance. They are water soluble, chemically stable, and non-biodegradable. Due to these characteristics, they are popular as detergents and wetting agents. (11) Although surfactants show a promising future, there is still a great deal of research and pilot-scale testing that needs to be done on surfactant applications to hazardous waste sites. In-situ soil flushing is innovative and can have great success in sites contaminated by only a few chemicals. Two Superfund sites are applying in-situ flushing for remediation of soils contaminated with metals such as chromium, nickel and mercury. The Lipari landfill site in New Jersey is scheduled for completion in July, 1991. (12)

Another technique for extracting contaminants from soil using a liquid medium is soil washing. In this system, the soil is excavated and fed through a mobile treatment unit as shown in Figure 3. Before treatment the soil is sent through a screen to remove larger non-soil material. The waste then enters a soil scrubber, where it is sprayed with a washing fluid. The types of washing solvent are similar to those mentioned earlier in soil flushing, and choice is dictated by the type of contaminant and soil. The output of the scrubber is generally in two phases. Coarse grain and sand particles are separated, rinsed, and dewatered. Fine-grained particles with most of the contaminants still attached to them (due to the fact that wastes tend to stick to the smaller particles) enter a chemical extractor, where contaminants are removed. In the extractor, washing fluid is injected countercurrently to the soil flow. The contaminants are collected with the washing solvent at one end, and the remaining soil is dewatered and returned to the site. The solvent fluid is treated, cleaned, and recycled. (13)

Soil washing can be applied to a wide variety of contaminants such as halogenated solvents, aromatics, heavy metals, and PCBs. Similar to soil flushing, this technology is site specific and its effectiveness depends on the waste and soil characteristics. EPA has selected soil washing as one of the source control remedial technologies to be used at seven CERCLA sites. Appendix A provides more detailed information on soil washing.

Chemical extraction technologies are used to separate hazardous waste contaminants from sludges and soils. These processes do not detoxify the waste, but merely separate them from the medium thereby making it easier to treat the waste through other processes. Solvent extraction systems are generally applied to organic contaminants such as polychlorinated biphenols (PCBs) and volatile organic compounds (VOCs). There are currently two types of systems that have been tested and used at Superfund sites. (14)

BEST is a mobile solvent extraction unit that separates contaminants into three fractions: oil (with organics), water, and solids. In this process, a secondary or tertiary amine (usually triethylamine, or TEA) solvent is mixed with the waste slurry at low temperatures in a mixing tank. The chemical principle behind the solvent extraction process is that at low temperatures the TEA can be completely mixed with water, forming a homogeneous mixture. The solvent is able to break the water-oil-solid bonds, extracting the organics from the solid particles. The flow from the mixing tank is centrifuged in order to separate the solids from the liquids. The solids are then sent to another mixing tank, where they are washed with solvents and centrifuged a second time. Finally, the solid stream is sent to a dryer where the solvent is vaporized and recycled to the mixing tank. If the dried solids contain heavy metals, they require further treatment before disposal. The liquid stream from the centrifuge which contains the oily wastes is sent through a series of heat exchangers. The water is stripped from the oil-solvent. Then, the oil-solvent is decanted and stripped; the solvent is recycled and the oil is either recycled or disposed (Figure 4). Some technology considerations that may affect the use of the BEST solvent extraction system are:

Critical fluid solvent extraction units use liquefied gases to extract organic contaminants from the soil. In this technology, liquefied gases such as carbon dioxide and propane are mixed with waste under pressure. These gases are capable of dissolving large quantities of organics. Again, like BEST the solvent-organic phase that is formed is decanted and sent through a pressure vessel where the gases are separated and recycled, and the extracted organics are collected. (15) An important requirement for operation is that the soil must be pumped into the unit in a slurry. Also, soil is screened prior to entry in order to exclude particles larger than 0.25 inch.

The chemical reduction-oxidation (redox) process is employed to destroy waste or render it less toxic. It is frequently used with other treatment methods such as soil flushing or chemical precipitation. Redox treatments are most commonly used in treating watery waste containing heavy metals.

In redox reactions, oxidizing agents are usually mixed with the waste. Although the process is simple, there are specific requirements. The reagents are added to a mixing tank with specific pH adjustments, chemical additions, and rapid mixing. The process must provide adequate contact time between the reactants and the contaminants. The conditions in the tank may be monitored by oxidation-reduction potential (ORP) electrodes. Table 2 lists some common redox agents and some wastes that can be treated via redox reactions. Selection of the appropriate redox agent and the type of reaction depends on the contaminants, the feasibility of delivery, and environmental safety.

A technology frequently used to treat contaminated groundwaters is neutralization. Neutralization can be used as a pretreatment to other treatments such as bioremediation, redox processes, or precipitation. It can also stand as a final waste treatment process. Neutralization involves the injection of acids or bases to the waste solution in order to adjust the pH of the mixture to between 5 and 9. Sodium hydroxide, lime, and sulfuric acid are some the most common reagents added to neutralize wastes. The products of the neutralization reactions are water and different salts that usually precipitate.

One of the largest classes of contaminants and hazardous compounds is halogenated aromatic compounds. They contaminate soils, sludges, and sediments. Dehalogenation is the process of removing the halogen from the rest of the pollutant through a chemical reaction. This process renders the waste less toxic, permitting other treatment technologies to remedy the waste. Chemical dehalogenation technologies discussed in this section are alkaline metal hydroxide/polyethylene glycol (APEG) and an innovative process called potassium polyethylene glycolate (KPEG).

In the APEG treatment process, the contaminated waste must first be excavated and moved to an off-site unit. Figure 5 presents the treatment process of glycolate dehalogenation. During the first stage of the process, the waste and the reagents are well mixed. As with other chemical treatments, the contaminated soil must be in a slurry form. The homogeneous mixture is then passed to a vessel where the temperature is raised to about 150·C, and decomposition of the waste takes place. The reaction time can be anywhere from 1 to 5 hours depending on the concentration and type of contaminants. During the batch process, water vapor that is produced is collected at the top, condensed and treated to remove any volatile compounds that it may contain. After the complete decomposition of the waste, the treated material goes to a separator where the reagent is removed and recycled while the soil continues into a washer unit. At this stage, the soil is physically mixed and the rest of the reagents are removed with water. The soil is further dewatered and collected. The soil's pH is analyzed and adjusted through neutralization before returning it to the site. The water containing waste constituents is sent to a wastewater treatment process. (16)

When potassium is used as the alkaline metal in the reagent, the process is referred to as KPEG. In this process, the halogen atoms are displaced by the PEG molecules and combine with potassium to produce salts. The KPEG reagent is very air and water sensitive, and therefore the process must take place under nitrogen blankets at high temperatures. The KPEG process increases the volume of wastewater that must be further treated. Common processes that follow a KPEG treatment are chemical oxidation, biodegradation, or incineration. (17)

EPA has selected dehalogenation for cleanup at three Superfund sites. All three sites have soils contaminated with PCBs and none of the projects is yet complete. Glycolate dehalogenation, however, has been successfully field tested on small scales on various waste types at numerous CERCLA sites.

The chemical processes described may be combined or used individually as treatment alternatives. Since all these technologies alter the chemical structure of the waste, they are very waste specific. Each technology has certain strengths and limitations in its applicability to the contaminated soils. Table 3 summarizes some of the advantages and disadvantages of each chemical treatment process.

Technology	Advantages	Disadvantages
Soil Flushing	Costs are relatively low. Great success on soils with few contaminants.	Effectiveness limited to soils with few hazardous materials. Limited application if soil characteristics are unfavorable.
Soil Washing	Effective on gravel, treats wide variety of wastes. Removes 90-99% of organics, in closed-treatment unit. Cost effective and favorably viewed by the public.	Ineffective on soils containing silt and clay. Limited by complex waste mixtures. Additives may be hazardous and difficult to remove.
Solvent Extraction BEST	Separation efficiencies greater than 98% Produces dry solids, and reduces waste volume. Waste does not require heating.	Uses flammable solvent, requiring safety measures. Requires pH adjustment.
CF System	90% removal efficiency on PCB contaminated soils.	Treatment limited to halogenated organics.
Dehalogenation	Toxicity reduction of target contaminants. Short treatment time, and relatively low operational and maintenance costs.	By-products may require further treatment.

THERMAL TREATMENT

One class of treatment technologies that presents a potentially permanent solution to the problem of many hazardous wastes is thermal treatment. In general, thermal treatments accomplish three goals: detoxify hazardous waste by destroying organic compounds contained in the waste; reduce the volume of the wastes; and convert wastes to solids by vaporizing water and other liquids the wastes may contain. Any single thermal technology does not necessarily achieve all three goals. In recent years incineration treatment has been increasingly used. With the restrictions placed on land disposal, thermal destruction processes are becoming a more viable option.

Incineration of hazardous waste is the process of destroying the waste through application of high temperature. A variety of organic wastes can be treated in solid, liquid, or gaseous forms by subjection to temperatures as high as 3000 degrees F. Thermal treatment may be either incineration, which is combustion in the presence of oxygen, or pyrolysis, which is the breakdown of chemical bonds at high temperatures (usually in the absence of oxygen). The end products of a thermal process are ash, gases such as CO2 and NOX, and water. This section describes some innovative technologies that are commercially available or have potential application in the remediation of CERCLA sites. Thermal treatments can be divided into high temperature (greater than 1000 degrees F) and low temperature technologies. Infrared incineration, rotary kiln incineration, fluidized bed incineration, and vitrification are high temperature processes. Wet air oxidation, low temperature thermal stripping, and in-situ radio frequency are categorized as low temperature thermal technologies.

Organic compounds can be broken down to simpler, less harmful matter through the use of near-infrared radiation. Temperatures produced using electric energy can pyrolytically decompose organic contaminants. Shirco Infrared Systems has developed a mobile thermal processing system that uses electrically powered silicon carbide rods to create high temperatures that will combust organic waste. A simplified version of the process is presented in Figure 6. Waste is fed through a furnace on a woven wire belt and exposed to temperatures as high as 1850 degrees F. Air is blown into the system at specific locations to supply oxygen. Ashes formed in the bottom of the chamber are collected and transported to an ash cooling system. The ashes are analyzed for PCB contamination before discard. Gases formed in the primary chamber are directed to a secondary chamber (afterburner) where they are further heated to complete destruction of the hazardous waste. Finally, the emissions are treated in an emission control system that contains a venturi scrubber and a packed tower scrubber. (18)

Infrared incineration is commonly used for solids and soil containing organic waste. However, this technology is not recommended for liquid or slurry waste. Variables that determine the rate of incineration and can therefore affect the cost of the process are: temperature, residence time, waste thickness on the belt, and the air flow rate in the primary chamber. Optimizing such variables can minimize the operating costs. In 1987, EPA conducted two evaluations of a system developed by Shirco Infrared Systems. Although it is no longer being commercially manufactured, it has been used at Superfund sites by remediation firms which had previously purchased it.

A rotary kiln is a slightly inclined cylindrical refractory-lined shell that is rotated at slow speed and is used to heat materials such as ceramics. The kilns used for waste treatment help facilitate mixing of waste with combustion air, promote movement of waste through the vessel, and assure complete destruction of waste by exposing all of the surfaces to oxidation. The design of the rotary kiln can vary based on the type of waste and treatment requirements. In this section the most basic kiln incinerator is described. (19) The system consists of a kiln, an afterburner, and emission control units. Contaminants are injected into the high end of the kiln along with auxiliary fuels as needed by the process. The heating value of the waste will dictate the fuel needed. Rotating the kiln causes the waste to slowly pass through the chamber. The retention time within the kiln can be anywhere between several minutes to one hour or more. The combustion products are ashes, waste gases, and scrubber waste water. Ashes are removed from the bottom of the kiln and gases are treated in a second burner. After further combustion, the gases are sent through a cleaning system before they are returned to the atmosphere. A schematic of the process is shown in Figure 7.

Rotary kiln incinerators can treat solid, liquid, and gaseous wastes. The temperature in the kiln varies from 1500-2900 degrees F, (20) depending on the waste. Wastes that contain substantial inorganic contaminants are not recommended for this treatment process. Also, the shape of the waste can play a crucial role in the effectiveness of the kiln. Spherical and/or cylindrical wastes can roll through the kiln with little combustion. Rotary kiln incinerators are commercially available, both mobile and fixed, and have been used at Superfund sites.

Fluidized bed combustion (FBC) involves the combustion of fuel in a bed of solid particles that has been fluidized (that is, held in suspension) by the injection of air at high velocity from beneath the bed. The system consists of a cylindrical vertical refractory-lined vessel containing a bed of inert granular material such as sand or a perforated metal plate (Figure 8). Air is introduced from the bottom of the column and rises vertically, fluidizing the bed at a minimum critical velocity. (21) The waste, along with the auxiliary fuel can be pumped into the bubbling bed, where combustion occurs. The heat is transferred from the bed (temperatures can vary from 1400-1600 degrees F) to the waste. Because of long retention time and heavy combustion, solid particles become light and small enough to travel upward in the column. This separation allows the volatile gases to be sent to a secondary reaction chamber for further combustion. The resulting gases then pass through air pollution control equipment and are released into the atmosphere. Many types of wastes, including halogenated and non-halogenated organics, may be treated using fluidized bed incineration. The waste can be in solid, slurry, or liquid form. However, a careful study of the chemical and physical characteristics of waste is required. Many problems are encountered if the waste is very dense. High density wastes will not mix well and optimum combustion will not occur. Also, if chlorinated wastes are present, sorbents such as lime must be added to the bed in order to absorb acidic gases that are released.

A variation of the fluidized bed incinerator is the circulating bed combustor (CBC). This system employs high air velocities (10-30 ft/sec) and circulating solids to create a larger and better combustion zone. The approach results in a greater combustion rate and a higher retention of the acidic vapors. Gases are separated from heavier particles in a solid separation cyclone and are recycled back to the combustor. The process does not require an afterburner, and can operate at lower temperatures. One of the advantages of circulating beds as compared to fluidized beds is the reduction in emissions of gases such as CO(2) and NO(x). Ogden Environmental Services has constructed a CBC unit to burn PCBs. A test burn/treatability study of the waste from a Superfund site was conducted and pilot-scale demonstration results are being reviewed by the EPA.

Vitrification, i.e. glassification, is the treatment, under high temperatures, of hazardous wastes so that their chemical and physical characteristics change, rendering them an immobilized mass. The destruction of the waste occurs in a reactor chamber which consists of two sections. The upper section accepts the waste via gravity feed and contains gases (CO(2), H2) emitted from the destruction of the organics and other products of pyrolysis. The lower portion of the chamber contains the melts from siliceous compounds and metals. Temperature in the chamber can reach as high as 3000 degrees F. The waste is fed by conveyor to the top portion of the reactor. The gases that are produced during the reaction are drawn from the top of the chamber by a fan and treated by an air emission unit. The solid portion of the waste is separated from the bottom of the chamber in the form of glass. Vitrification presents a permanent solution to some hazardous waste problems. The hazardous waste constituents in the residue are minimal and require no further treatment. Westinghouse Electric Pyrolyzer is a vitrification process (sometimes referred to as plasma incineration) developed for destruction of hazardous waste solids containing organics and water concentrations as large as 10 and 25 percent respectively. This process destroys organics in the absence of oxygen. A prototype of the process was tested at a Superfund site in 1986. (22)

Wet air oxidation is the process of breaking down oxidizable inorganic and organic waste in a high-temperature, high-pressure, aqueous environment. (23) The process is categorized as a low-temperature thermal treatment. The reactor conditions are usually at a temperature of 350-650 degrees F and a pressure of 300-3000 pounds per square inch. Waste is pumped into the system and mixed with compressed air. The mixture is then passed through a heat exchanger, and into a reactor. Within the reactor, the oxygen in the air reacts with the waste. The oxidation reaction liberates more heat. After the reaction is complete, the gas and liquids are separated, and the liquid is passed through a heat exchanger, heating the incoming material. Again the gas and liquid streams are separated and discharged through control valves. The effluents are further treated since they may contain small organic compounds such as acetaldehyde, acetone, acetic acid and methanol in the gas and oxidized liquid. Carbon adsorption and biological treatments are commonly used for further remediation. Figure 9 illustrates the wet air oxidation process. This technology has not yet been applied to a Superfund site, although several sites have been studied for suitability.

Chemical Waste Management has developed one of the few low-temperature thermal desorption processes, which they call the X*TRAX system. The system operates with indirect heating at temperatures between 200-900 degrees F. The X*TRAX system is designed to remove organic contaminants from soils, sludges and other solid media. (24) The basic principle behind the system is the application of heat to the waste in the presence of water, so as to drive off the organics with the water and leave behind a dry solid with little or no organic content. The required conditions for the wastes are: organics with boiling points less that 800 degrees F, less than 10% total organics, and less than 60% moisture. (25) The system is not applicable for the removal of heavy metals. The X*TRAX system consists of an externally-fired rotary kiln dryer and a gas handling trailer (Figure 10). Contaminated solids or sludges are fed into the dryer and heated to 500-800 degrees F. The resulting volatilized water and organic mixture is directed from the dryer to the gas treatment system by a nitrogen carrier gas. Organics and water vapor are removed in a stepwise fashion through cooling and condensing stages. The nitrogen carrier gas is reheated and recycled. In the process, the following three factors are adjusted to control the removal of contaminants: the feed rate, the dryer temperature, and the residence time in the dryer.

Currently, Chemical Waste Management has three X*TRAX systems available: laboratory, pilot, and full-scale. Laboratory test results achieved 97.9% removal efficiency for soils contaminated with 805 ppm PCBs. The full-scale X*TRAX system was completed in 1990, and is being used to remediate a PCB-contaminated soil at a CERCLA site. (26)

The In-Situ Radio Frequency (IRF) process is very similar to heating in a microwave oven. IRF uses low electromagnetic wave energy to heat the soil and destroy the waste. IRF is not a new process, rather it has been under development since the mid-1970s. Radio frequency wave energy is applied to the ground by the use of exciters and ground electrodes. The soil is heated in a range of 200 to 1000 degrees F. The contamination area is covered with a blanket to capture the vaporized contaminants such as volatile organic compounds. In order to further enhance the efficiency of the system, a vacuum can be applied to the hollow electrodes to remove vaporized organics. An additional treatment unit is placed on-site to treat the collected vapors, usually by incineration or carbon adsorption. Typically radio frequency treatments are limited to volatile organic compounds such as chlorinated solvents and petroleum hydrocarbons. (27) This treatment is not effective for the removal of metals. Radio frequency heating was demonstrated by the Air Force in Wisconsin. The technology was applied to a 500 cubic foot volume of soil for 12 days. A 97 percent removal efficiency of semivolatile hydrocarbons was observed, along with a 99 percent removal of volatile aromatics. In-situ radio frequency is considered a potential enhancement of the vacuum extraction process discussed in the next section.

Almost all thermal technologies can be used as a final treatment for selected hazardous waste problems. They provide almost complete destruction of the toxic components in the waste matrix, plus a substantial reduction or even elimination of liabilities and risks. (28) However, each technology has its own strengths and limitations. Table 4 compares some of the apparent advantages and disadvantages of each thermal technology.

Technology	Advantages	Disadvantages
General Thermal Treatments	Effective in treating variety of wastes. Reduces volume. Destroys organic waste with efficiency of 99.9%.	Relatively expensive technology. Public resistance is high. Volatile metals can cause stack emission problems.
Infrared Incineration	Applicable to wide variety of solids.	Not appropriate for liquid or slurry wastes. Volatile metals can cause stack emission problems.
Rotary Kiln Incineration	Least preprocessing requirements and can accept debris up to 12". Well-developed and proven, extensive operating experience.	The process has long setup time and requires large gas volume. Susceptible to thermal shock, requiring careful maintenance. Volatile metals can cause stack emission problems.
Fluidized Bed Incineration	Operates at lower temperature, reducing fuel costs. Simple design and long life of incinerator. Minimal NO(x) formation reducing emission control costs.	Difficulty in removing residual from the bed. Relatively slow throughput capacity (3 ton/hour). Volatile metals can cause stack emission problems.
Wet-Air Oxidation	Potentially cost-effective if applicable to waste.	Limited to liquid or sludge waste (organics and oxidizable inorganics). Volatile metals can cause stack emission problems.
Low-Temperature Thermal Stripping	Tests show 97.9% PCB removal efficiency. No combustion byproducts.	Not applicable to waste with high moisture and organics. Not applicable to heavy metals
In-Situ Radio Frequency	Potentially 2 to 4 times cheaper than excavation and incineration.	More research is required to verify effectiveness in-situ. Volatile metals can cause stack emission problems.

PHYSICAL TREATMENT

The basic objective of physical treatment is the manipulation of the physical properties of the wastes in order to immobilize them, detoxify them, or render them less harmful. Some of these technologies may apply physical forces to the waste to separate it from its medium. The chemical characteristics of the hazardous waste remain constant during physical treatment. Physical treatment often produces residues that require further treatment prior to disposal. Chemical or thermal technologies may be applied to these residues in order to dispose of them in an environmentally safe manner.

Volatile organic compounds (VOCs) in the soil can be separated and removed from the contamination zone in a hazardous waste site. one technology which has been successful in removing VOCs from the soil is vacuum extraction. By creating a pressure gradient using vacuum pumps, the volatile compounds in the soil percolate and diffuse through the air spaces between the soil particles toward the pumps. The contaminated air in the soil is drawn by the vacuum and replaced by fresh air from the surface. Upon extraction, the contaminated air is treated and released into the atmosphere. The basic components of the system include production wells, monitoring wells, vacuum pumps and an emission control system (Figure 11). The production wells are drilled into the contaminated zone with monitoring wells around them to observe the air pressure in the soil. After the VOCs are removed by the vacuum pumps, they are processed by a liquid-vapor separator. The vapor is then treated by activated carbon or catalytic oxidizer. The liquid portion which still contains VOCs is treated through an aeration unit designed to evaporate the VOCs. The vaporized VOCs are treated and released to the atmosphere. This process does not require excavation and is not limited by depth.

Steam stripping is one of the more recent innovative technologies used for removal of VOCs. This technology uses a drilling rig and a process train. The drills contain two concentric pipes. The inner pipe carries steam at 450 degrees F and 450 pounds per square inch gauge (psig) while the outer pipe conveys air at 300 degrees F and 250 psig. (29) The delivery tool injects steam and hot air to depths of almost 30 feet. The steam heats the soil causing the chemicals to vaporize. The contaminated vapor is collected in a metal box at the surface and piped to the process train. In the process train, the evaporated chemicals are first condensed. The condensed water is then separated through distillation and filtered through activated carbon beds. The contaminants recovered by the process are taken to an incineration unit and destroyed by a thermal treatment technology.

Both vacuum extraction and steam stripping technologies are being used at Superfund sites. Vacuum extraction has been used at three Superfund sites. Among the innovative technologies used for source control during 1982-1989 period, vacuum extraction was selected 32% of the time (the highest percentage). (30) Steam stripping has been demonstrated at CERCLA sites for removal of VOCs in the soil, with efficiencies greater than 85% observed.

In many cases, the most economical and environmentally sound method of remediation of hazardous wastes is to secure them on the premises where they were disposed. The main danger posed by the wastes is that they can be transported in the groundwater, surface water, or air and contaminate the surrounding environment. To remedy this problem, the contaminants must be stabilized and immobilized. By addition of certain chemical agents and rigorous mixing of the soil, the waste can be fixed or stabilized. Mobility is reduced through the binding of the hazardous constituents within a solid matrix, reducing permeability and surface area available for the release of toxic components. The final result is a monolithic block of waste with high structural stability. Although solidification is applicable to solid, liquid or sludge waste, the following qualities are required if it is to be used as a remediation alternative:

The actual mechanism of binding depends on the chemical agents used and the characteristics of the waste. Before a stabilization process begins it is important to study the chemical and physical characteristics of the waste and consider some of the pretreatment requirements such as ease and cost of operation and the method of disposal. Solidification processes are categorized based on the chemical agents used in the process. Typical solidification/ stabilization techniques are listed below.

Usually common construction materials like portland cement plus additives are introduced in proportions equal to or greater than the amount of waste to form a rigid concrete-like mass. This process is best applied to heavy metal contaminants with a stable pH.

Data suggest that addition of silicates to lime or cement can result in a wider range of material being stabilized. Other proprietary additives can cause the binding of organics to the solid matrix, increasing the durability of the end product.

Sometimes the characteristics of the waste allow the use of plastic material such as asphalt, paraffin and polyethylene in the solidification process. When the waste is fixed within a plastic matrix, it becomes more water resistant and less biodegradable than untreated waste.

Hazardous waste can be physically sealed in an organic binder or resin. The binding material acts as an impermeable jacket protecting the waste from leaching and mobility. Microencapsulation can be applied to solids and sludges. Thus far, this technique has been applied mainly to inorganics; however, methods to solidify organics are under development.

Solidification/stabilization processes are currently being used at Superfund sites. Several vendors have successfully demonstrated their processes at different CERCLA sites. The Soliditech, Inc. process was demonstrated in 1988, treating soils contaminated with PCBs and heavy metals. (31) In order to understand the long term reliability of stabilization processes, treated sites are being monitored and technical evaluation reports are published regularly.

In-situ vitrification (ISV) is the process of melting the contaminated wastes and soil or sludge in place, using electrical power for heat, to form a stable crystalline structure with very low leaching characteristics. As discussed previously in the vitrification process under the thermal treatment section, the basic concept is to destroy organic contaminants by pyrolysis under extreme temperatures. ISV is considered by many a solidification/stabilization process. (32)

ISV uses a square array of four electrodes inserted into the ground to establish a current in the medium and heat the soil. Usually flaked graphite and glass frit are placed between the electrodes to conduct the initial current (due to the fact that soil is a poor conductor of electricity). Temperature in the soil rises to a range of 1600-2000 degrees F. As the soil melts, the organic contaminants vaporize and pyrolyze (Figure 12). The pyrolysis byproducts move toward the surface and combust in the presence of oxygen. The gases are captured in a hood placed over the heated zone, and sent to an emission control unit. Inorganics in the soil are either melted and incorporated in the matrix, or vaporized and collected at the surface by the hood. Upon completion of the process, the system is shut off, fresh soil is placed on top of the vitrified zone, and the soil is allowed to cool. Several months are required for the soil to reach ambient temperatures. (33) ISV is a costly process and has not yet been applied to a CERCLA hazardous waste site. However, it is in the design stage at the Ionia City Landfill, Michigan.

Air stripping is a mass transfer process in which volatile contaminants in a dilute aqueous waste stream are transferred to gas. This technology is generally applied to groundwater or wastewater contaminated with low levels of volatile organic Air stripping is accomplished in a packed tower equipped with an air blower. The waste stream flows downward through the column while the air flows countercurrently and is exhausted at the top. The volatile organics move from the liquid to the gas. The contaminated air is run through an emission control unit before it is recycled or released to the atmosphere. Air stripping is most effective when combined with another process. (34) Restrictive waste characteristics are low volatility and high volubility, metals and inorganics.

Some physical treatments such as in-situ vitrification can probably be used as a complete remediation process of a contaminated site. However, technologies like air stripping are combined with other processes to remedy a hazardous waste site. The applicability of a technology depends on the site's parameters and waste characteristics. Therefore, in deciding upon a remediation technology it is necessary to compare the site and waste specifications against the strengths and limitations of each technology. Table 5 outlines some of the advantages and disadvantages of physical treatment technologies described in this report.

Technology	Advantages	Disadvantages
In-Situ Vacuum & Steam Extraction	Demonstrated effectiveness in removing VOCs. Relatively simple and reliable technology. Treatment costs are low.	Process limited to volatile compounds. Uneven treatment may occur due to non-homogeneous soil.
Stabilization/Solidification
Cement-Based:	Relatively low cost technology. Use of readily available material.	End product not acceptable for disposal without secondary containment. Weight & volume of final products is twice the original, increasing costs.
Silicate-Based:	Can stabilize a wider range of material compared to cement-based.	End product not acceptable for disposal without secondary containment. Oil and grease plus material such as calcium sulfate can interfere with bonding process.
Thermoplastic:	Lower leaching rate and less volume compared to cement-based techniques. Little affected by water or microbial attacks.	Certain wastes are incompatible with this technique, limiting its application. High equipment and energy costs.
Micro-encapsulation	Waste material is completely isolated from leaching solution. Material for encapsulation very tough, nonbiodegradable, chemically stable & flexible.	Energy intensive and a costly process. Binding resins expensive.
In-Situ Vitrification	Potentially the greatest degree of containment compared to all other technologies. Successfully tested for treatment of radioactive hazardous waste. Potential to destroy all contaminant groups.	High energy demands and very costly. Requires off-gas collection and treatment.
Air Stripping	Combined with activated carbon, very effective in removing contaminants from groundwater.	Alone, only partially effective; must be followed by other treatment technology. High energy costs.

GLOSSARY OF ENVIRONMENTAL TERMS

Some of the following terminologies are taken from: U.S. Environmental Protection Agency Office of Communications and Public Affairs. Glossary of Environmental Terms and Acronym List. 19R1002. December 1989.

Aerobic: Life or processes that require, or are not destroyed by, the presence of oxygen.

Anaerobic: Life or processes that require, or are not destroyed by, the absence of oxygen.

Aromatic: Pertaining to or characterized by the presence of at least one benzene ring.

Autotrophic organism: An organism capable of synthesizing organic nutrients from inorganic substances.

Biodegradable: The ability to break down or decompose rapidly under natural conditions and processes.

Bioremediation: The manipulation of living systems to bring about desired chemical and physical changes in a confined and regulated environment.

BOD (Biochemical Oxygen Demand): The amount of dissolved oxygen in water consumed in five days by biological processes breaking down organic matter.

Chelating agent: An organic compound in which atoms from more than one coordinate bond with metals in solution.

COD (Chemical Oxygen Demand): A measure of the oxygen required to oxidize all compounds in water, both organic and inorganic.

Cometabolism: Alteration of a non-nutrient material requiring the presence of another readily transformable compound.

Decantation: A method for mechanically dewatering a wet solid by pouring off the liquid without disturbing the underlying sediment.

Dehalogenation: Removal of the halogen atom from a substance by chemically replacing it with hydrogen or hydroxide ions in order to detoxify the substances involved.

Denitrification: The anaerobic biological reduction of nitrate nitrogen to nitrogen gas.

Distillation: The act of purifying liquids through boiling, so that the steam condenses to a pure liquid and the pollutants remain in the concentrated residue.

Emulsification: The process of dispersing one liquid in a second immiscible liquid.

Fluidized bed: Suspension of finely divided solids by a rising current of air or other fluids.

Halogen: Any of a group of five chemically related nonmetallic elements that includes bromine, fluorine, chlorine, iodine, and astatine.

Heterotrophic organism: An organism that obtains nourishment from the breakdown of organic matter.

Hydraulic conductivity: A measure of the rate at which water flows through a unit cross section under unit hydraulic gradient. Also known as permeability coefficient.

Incineration: Treatment technology involving destruction of waste by controlled burning at high temperatures.

Inorganic compound: Chemical compounds that do not contain carbon as the principal element (except carbonates, cyanides, and cyanates).

Leachate: A liquid that results from water collecting contaminants as it trickles through wastes, agricultural pesticides or fertilizers.

Leaching: The process by which soluble constituents are dissolved and carried down through the soil by a percolating fluid.

Methanotrophs: A group of organisms that depend on methane or methane-carrying substances as their source of energy and carbon.

Monolithic: Constructed from a single crystal or other single piece of material.

Organic compound: Chemical compounds containing carbon as their principal element.

Osmosis (osmotic): The tendency of a fluid to pass through a permeable membrane (such as the wall of a living cell) into a less concentrated solution so as to equalize the concentrations on both sides of the membrane.

Oxidation: 1. The addition of oxygen which breaks down organic waste or chemicals such as cyanides, phenols, and organic sulfur compounds in sewage by bacterial and chemical means. 2. The chemical process whereby electrons are removed from a molecule.

Packed tower: A pollution control device that forces dirty air through a tower packed with crushed rock or wood chips while liquid is sprayed over the packing material. The pollutants in the air stream either dissolve or chemically react with the liquid.

Polychlorinated Biphenyls (PCBs): A group of toxic, persistent chemicals used in transformers and capacitators for insulation purposes and in gas pipeline systems as lubricants. Its manufacture was stopped in 1976 in the U.S.

Reagent: A substance, chemical, or solution used in the laboratory to detect, measure or otherwise examine other substances, chemicals or solutions.

Surfactant: A soluble compound that reduces the surface tension of liquids, or reduces interfacial tension between liquids or a liquid and a solid.

Vitrification: Thermal treatment in which the chemical and physical characteristics of the waste are transformed such that the treated residues containing hazardous material are immobilized in a glass-like mass.

Volatile Organic Compound (VOC): Any organic compound which participates in atmospheric photochemical reactions except for those designated by the EPA as having negligible photochemical reactivity.

In evaluating the technologies available for remediation of the hazardous waste sites, consideration is given to the site specific circumstances (type of waste, site characteristics) and the status of the technologies as they develop over time. Since most of the uncontrolled hazardous waste sites are contaminated with more than one type of waste, different technologies are applied to the site for remediation purposes. Table A evaluates six sites where Superfund cleanups are currently underway. The table first presents a site description, followed by a list of technologies used during remediation of the site and present estimated costs of the project.

The data in Table A is obtained from Records of Decision (ROD) Annual Report: FY 1989. The reader can refer to ROD-89 for further case studies.

Site Name Location	Key Contaminants	Treatment Technology	Costs
Koppers (Oroville Plant), CA	Soil and groundwater contaminated with VOCs, including toluene, xylene, and benzene.	In-situ bioremediation of 110,000 cubic yards of soil. 200,000 cubic yards of soil remedied by soil washing. Pumping and treatment of 22,000,000 cubic yards of groundwater.	$77.7 million (present worth)
Re-Solve, MA	Soil, sediment and GW contaminated with VOCs and organics, including PCBs.	Excavation with KPEG dechlorination and onsite placement of 22,500 yd(3) of soil; GW pumping and treatment using air stripping and carbon adsorption with reinjection.	$6.45 million (present worth)
Pinette's Salvage Yard, ME	Soil and GW contaminated with VOCs, PCBs and metals including lead.	Excavation and offsite incineration of 300 yd(3) of soil containing PCBs. Onsite solvent extraction of 1,900 yd(3) of soil contaminated with PCBs and other organics.	$4.367 million (present worth)
Tyson's Dump, PA	Soil and bedrock contaminated with VOCs.	In-situ vacuum extraction of 30,000 yd(3) of soil contaminated with VOCs including benzene and toluene.	$10.2 million (present worth)
W.R. Grace (Acton Plant), MA	Sediment, soil, and sludge contaminated with VOCs, other organics, and metals such as arsenic.	Excavating and incineration offsite of highly contaminated soils; solidification/stabilization of less contaminated soils, followed by disposal in the landfill and capping the landfill.	$7.058 million total costs

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Treatment Technologies at Superfund Sites