Soil Remediation Techniques at Uncontrolled Hazardous Waste Sites

Journal of the Air & Waste Management Association

ISSN: 1047-3289 (Print) (Online) Journal homepage: http://www.tandfonline.com/loi/uawm18

Soil Remediation Techniques at Uncontrolled Hazardous Waste Sites Robin Anderson , Richard E. Woodward , Sunil I. Shah , J. N. Hartley , Stephen C. James & Ronald C. Sims To cite this article: Robin Anderson , Richard E. Woodward , Sunil I. Shah , J. N. Hartley , Stephen C. James & Ronald C. Sims (1990) Soil Remediation Techniques at Uncontrolled Hazardous Waste Sites, Journal of the Air & Waste Management Association, 40:9, 1232-1234, DOI: 10.1080/10473289.1990.10466768 To link to this article: http://dx.doi.org/10.1080/10473289.1990.10466768

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Soil Remediation Techniques at Uncontrolled Hazardous Waste Sites

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Critical Review Discussion Papers The A&WMA Critical Review entitled "Soil Remediation Techniques at Uncontrolled Hazardous Waste Sites" was presented by Ronald C. Sims, Department of Civil and Environmental Engineering, Utah State University, Logan, Utah. Dr. Sims presented his review at the 83rd Air & Waste Management Association Annual Meeting, held in Pittsburgh, Pennsylvania in June 1990. Prepared discussions presented during the Critical Review session are published here, along with some closing remarks by Dr. Sims. Ronald Harkov, Chairman of the Critical Review Subcommittee of the Publications Committee, served as moderator of the 1990 A&WMA Critical Review session.

Prepared Discussion Robin Anderson U.S. Environmental Protection Agency Washington D.C.

I appreciate the opportunity to discuss Dr. Ronald Sims' critical review of soil remediation techniques of uncontrolled hazardous waste sites. Dr. Sims provides an excellent overview of treatment alternatives for soil contamination and proposes a conceptual methodology for site assessment and remedy selection and evaluation. Current practices at Superfund sites are consistent to a large extent with Dr. Sims' proposal. The degree to which his proposal is implemented is dependent on the information available, the complexity of the site, and the state of science. Remediating sites which pose current or potential future risks due to releases of hazardous substances and pollutants or contaminants involve complex scientific and policy issues. Today I will discuss how these issues impact our remedy selection process through a discussion of the statutory and regulatory requirements and remedial process. I will end my talk with a discussion of Dr. Sims' proposal as compared with the current Superfund practices. While Dr. Sims' review of the subject focused principally on a scientific evaluation of the processes involved, my discussion focuses on the policy framework in which decisions are made. Statutory and Regulatory Background

The Comprehensive Environmental Response Compensation, and Liability Act (CERCLA) of 1980 provided a statutory basis for addressing uncontrolled hazardous waste sites Copyright 1990—Air & Waste Management Association

1232

that pose a threat to human health and the environment.1 Congress revised CERCLA with the Superfund Amendments and Reauthorization Act (SARA) of 1986 adding new authorities and responsibilities to the program.2 The SARA amendments, among other new requirements, provide general rules for remedy selection, describe requirements for clean-ups, and emphasize long-term effectiveness and permanence. The National Oil and Hazardous Substances Pollution Act (NCP) provides the regulatory blueprint for implementation of the statute. It regulates EPA, other federal agencies', state's, and private parties' responses to releases. The NCP was revised this year (March 8,1990, FR 8666-8865) to incorporate changes in the program required by SARA and the Clean Water Act and to reflect the process which has evolved over the first ten years that the Superfund program has been in existence.3 The NCP details the program goal, expectations, and a process for remedy selection at Superfund sites which direct the site evaluation and ultimately the selection of remedy. The NCP states that the Superfund program goal is to utilize: " . . . remedial actions that protect human health and the environment, that maintain protection over time, and that minimize untreated wastes." The goal reflects CERCLA's increased emphasis on treatment when practicable to provide for a permanent and reliable solution. The NCP expectations discuss circumstances under which treatment, engineering and institutional controls are likely to be appropriate. They aid in streamlining the Superfund process but are not a substitute for the site-specific analysis to determine the extent to which treatment can practicably be used in a cost-effective manner. It is expected that remedies will generally include a treatment alternative that significantly reduces toxicity and/or mobility of the contaminants posing a significant threat, wherever practicable, to reduce the need for long-term manJ. Air Waste Manage. Assoc.

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agement. The principal threat is defined as liquids, high concentrations of toxic compounds, and highly mobile materials. High concentrations of toxic chemical are anticipated to be those wastes which are two to three orders of magnitude above levels that allow for unrestricted use and unlimited exposure. The NCP clarifies the use of engineering and institutional controls. Engineering controls include containment technologies such as capping and slurry walls to prevent the migration of contaminants. Institutional controls include deed restrictions to limit the future use of the site to prevent exposure. Engineering controls will be considered for wastes that pose a relatively low long-term threat or where treatment is impracticable. Institutional controls are expected to be used frequently to mitigate short-term impacts and to supplement engineering controls for long-term management. Institutional controls will not be used as a substitute for treatment or engineering controls unless such measures are impracticable. The NCP, in the preamble and the regulation, states that protection of human health and the environment may be achieved through a range of alternatives. Innovative technologies will be considered when those technologies offer the potential for comparable or superior treatment, fewer adverse affects, or lower cost for similar performance. The NCP further established a treatment guideline of 90 percent or greater reduction of the concentration or mobility of contaminants of concern. Remediation goals will be set, taking into consideration site-specific factors and Agency guidelines and goals. Remedial Process

The NCP provides a systematic process that factors in the program goal and expectations and allows consideration and balancing of site-specific factors in remedy selection. The process consists of a site characterization phase called the remedial investigation (RI) and a remedial alternative investigation phase termed the feasibility study (FS).4 The RI and FS are generally performed in a simultaneous manner due to their interactive nature. The remedy is selected based on the RI/FS and comments received from the public on the proposed plan. The final decision is documented in the Record of Decision (ROD). The purpose of the RI is to collect data necessary to adequately characterize the site to support the identification and evaluation of remedial alternatives. The RI includes field investigations, treatability studies, and a baseline risk assessment to identify the extent of the problems and to support the identification and analysis of alternatives. The purpose of the FS is to ensure that appropriate remedies are developed and evaluated in such a manner that a decision may be made on the appropriate alternative. The development and evaluation of alternatives are scaled for the complexity of the site and the action under study. The identification of a preferred alternative and final selection of remedy is determined from an analysis of the nine evaluation criteria identified in the NCP (40 CFR 300.430(f)(l) (ii) Threshold Criteria 1. Overall protection of human health and the environment; 2. Compliance with applicable or relevant and appropriate requirements (ARARs); Primary Balancing Criteria 3. Long-term effectiveness and permanence; 4. Reduction of toxicity, mobility, or volume through treatment; 5. Short-term effectiveness; 6. Implementability; 7.

Cost;

September 1990

Volume 40, No. 9

Dr. Harkov, on left, and Dr. Sims

Modifying-Criteria 8. State acceptance; and 9. Community acceptance. As noted above, the criteria are categorized into three groups: threshold criteria, primary balancing criteria, and modifying criteria. Remedial alternatives must satisfy the threshold criteria of protection and compliance with ARARs (or justify a waiver) to be eligible for selection. Remedial alternatives are then compared with each other based on their relative performance with regards to the primary balancing criteria. The long-term effectiveness and the degree to which the toxicity, mobility or volume is reduced through treatment are two of the most crucial balancing criteria since they focus on treatment and permanence, principal themes of SARA. Finally, state and community acceptance of the alternatives are considered as the modifying criteria. Evaluation of Dr. Sims' Review

Dr. Sims identified the critical issues and research needs concerning soil remediation as establishing clean-up criteria and improving our understanding of technologies and their capability to meet these goals. Specific areas on which we need to focus our research efforts include: • Improved understanding of multi-contaminant fate and transport to aid in the establishment of realistic cleanup criteria. • Identification of critical site characterization information needed to predict technology performance. • Demonstration of innovative technologies (e.g., biodegradation) and technology train capabilities and understanding of factors affecting performance. • Identification of implementation issues (e.g., volatile emissions) and viability of engineering solutions. Although we have come a long way in our understanding of the science and have broken new ground in melding that science with public policy, the scientific basis of our decisions is inexact. This is due to a combination of a lack of scientific knowledge and the need to assume some risks in the decision process so that we may expedite remediation to the extent possible. We are often limited in our ability to fully characterize a site, as Dr. Sims proposes. Dr. Sims' proposed methodology for characterizing sites and evaluating remedies involves integrated data collection activities to support site characterization, risk assessment, remedy evaluation and selection, and performance monitoring. The proposal as outlined is that which is utilized in the Superfund program. The Agency strives to maximize data collection to support both the RI and the FS simultaneously. However, the Agency also recognizes the need to balance the desire for definitive site characterization with the desire to 1233

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implement protective remedies in an expeditious manner. The Agency will perform a site characterization sufficient to support the remedial response envisioned but which may not result in an extended study of the site. The Agency may limit data gathering and streamline the RI/FS particularly where site problems are straight forward such as in situations involving a selected group of chemicals or where remediations options are limited. A streamlined approach may also be appropriate in cases where an interim action may be taken to eliminate or reduce the risk posed while additional studies progress to evaluate alternatives for the final remedy. The concept of "mass balance" is a key component in Dr. Sims' methodology. The idea presented is that we need a thorough understanding of the fate and transport of contaminants in order to ascertain the route of exposure and to select the appropriate technology to remediate the site. The extent to which mass balance is currently applied on a site specific basis is determined by nature of the constituents, the type of remediation appropriate for the site, and the limitations in our scientific understanding. The term "mass balance" connotes that we have a fairly complete knowledge of the fate of materials. In light of the fact that even well studied above-ground treatment processes have not afforded the research community mass balance closure, it is highly unlikely that we will achieve this for most technologies or complex sites in the near term. However, the concept of mass balance is an ideal which we should strive to

Prepared Discussion

Richard E. Woodward ENSR Consulting and Engineering Houston, Texas

I commend Dr. Sims on compiling this summary of treatment technologies and his associated interpretations. His treatment of this subject has elucidated deficiencies in the currently available technology, provided an effective conceptual framework for remediation and supplied some selection criteria for remediation technologies. This is an important start for comparing remedial technologies for the unsaturated zone and will be a useful reference for selecting remedial approaches and for developing treatment trains. Physical, chemical and biological approaches to remediation have been presented as individual techniques and as components of a treatment train. Because of my training and experience in biotechnology, I feel best qualified to address those technologies which deal with bioremediation alone or as part of a treatment train. Consequently my review will be limited to the bioremediation aspects of Dr. Sims presentation. Since this paper is the first strawman on the topic of the remediation of soil in the unsaturated zone, it tends to discuss the topic and related technologies as ideal systems. Actual application to the real world will differ substantially, especially given the lack of homogeneity of field conditions. 1234

achieve as we make decisions on a site specific basis to the extent that it is feasible. For example, we need to understand if volatilization or other treatment (e.g., biodegradation) is the principal route of removal if we are to select and design a remediation process which will effectively remove the contaminants. Mass balance is expected to become increasingly achievable as our scientific knowledge improves. References 1. P.L. 96-510; 42 U.S.C. Sec. 9601 et. seq. 2. P.L. 99-499; 42 U.S.C. Sec. 9601 et. seq. 3. U.S. EPA, "National Oil and Hazardous Substance Pollution Contingency Plan; Final Rule," FEDERAL REGISTER, Vol. 55, No. 46 Page 8666-8865, March 8,1990. 4. U.S. EPA, "Guidance for Conducting Remedial Investigations and Feasibility Studies under CERCLA (Interim Final)", Office of Emergency and Remedial Response, EPA/540/G-89/004, Oct. 1988. .

Robin Anderson is the Acting Section Chief, Regional Operations Section, U. S. Environmental Protection Agency, Washington, D. C. 20460.

Regulatory Issues

Dr. Sims has provided a good review of the current regulatory status affecting remediation in the unsaturated zone and the historical perspective leading to its implementation. His presentation has stimulated several questions: 1. The relatively age-old question remains: "How clean is clean?" and continues to be an issue with both federal and state regulatory agencies. 2. Will the trend toward lower and lower decontamination objectives continue as our ability to detect contaminants in the soil matrix continues to improve and our remedial options continue to expand? 3. Would you agree that the trend toward risk assessment based decontamination objectives will continue and perhaps expand? 4. Will remedial technology developments begin to drive regulators toward lower decontamination objectives? Remediation Systems

Three remediation systems were discussed: in situ treatment, prepared bed and in vessel treatment. As the database expands for these treatment systems, a "soil profile" should appear that will allow candidate soils to be evaluated against each treatment approach. A ranking system could then direct the remediator to the best technology. A matrix summarizing the: • innate soil characteristics (bulk density, cation exchange capacity, pH, macro, secondary and micro nutrient levels, pore size, permeability, etc.), • contaminant characteristics (as outlined in the Critical Review), and • specific remediation treatment systems would provide useful guidance in technology selection. J. Air Waste Manage. Assoc.

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Conceptual Approach to Soil Remediation

The concepts of mass balance/materials balance need to be put in the proper perspective in relation to remediation technology. Mass balance is essential for validating the application of a candidate technology for a given site, contaminant matrix and waste mixture. It is inappropriate and unrealistic to apply mass balance to field demonstrations, for the following reasons: 1. Field systems are frequently poorly defined both in terms of contaminant volume and specific chemical constituents; both are subject to sampling error and bias, 2. Field systems are open and subjected to the perturbations of the weather, such perturbations directly effect volumes and may effect the rate of remediation indirectly, 3. Total accountability from a mass balance perspective will not eliminate the need for the frequent monitoring and analysis required of any field scale demonstration to assure compliance with ARARs and to verify ultimate decontamination objectives, 4. Pursuit of mass balance in a field demonstration rapidly drives the demonstration to the level of a research and development project, generally not justified from a cost perspective.

Robin Anderson, James N. Hartley, and Sunil I. Shah

One approach to improving models is to model smaller components of the system. Models could be fine-tuned to reflect the three dimensional characteristics of the unsaturated soil zone. An improved vadose zone model would individually address the three sub-zones: upper belt, intermediate belt and lower belt introduced earlier. Many of the three dimensional spatial models commonly used to model air toxics could be directly applied to the spatial relationships in the soil systems.

Reaction Kinetics

Dr. Sims has provided an excellent summary and explanation of three key models for evaluating reaction kinetics: o zero order kinetics • first order kinetics • the hyperbolic rate model (Michaelis-Menton kinetics). However, the underlying tone of this discussion implies that mineralization of organic compounds is required for effective bioremediation. Verification and monitoring of the models by respirometry and/or the release of specific ions (Cl~, Br", So4=, NO3~) supports this preoccupation with mineralization. Two problems exist with the use of mineralization to verify completion of the bioremediation process: 1. in most cases, listed constitutents comprise less than 2 percent of the organic compounds present; 98 percent of the organic carbon at many sites is not listed or monitored by specific compound! As degradation progresses, nonlisted, larger molecular weight organics like kerogen can be degraded into smaller, listed organics. Likewise listed organics can be removed from the listed by transformation without the production of carbon dioxide. 2. there is no precedent in the area of wastewater treatment of the use of mineralization to verify bioremediation. Indeed, wastewater treatment is based on the concept of rapid transformation of organics into microorganism bodies and/or slimes which are then removed by the clarifier. Only after the biomass is consolidated by clarification is mineralization a consideration. Biomass from a wastewater treatment plant is mineralized by a variety of processes including: extended aerobic digestion, composting, or anaerobic digestion. Models

Models can provide effective prediction of the performance of remediation systems. Their real limitation lies in their failure to deal with the heterogeneity of field conditions. Generally, the definition of field conditions are only as good as the sampling program. Biased or limited sampling will distort the data used to run a model and consequently distort the results of the model. September 1990

Volume 40, No. 9

Toxicity

Measurement of toxicity initially and during the remediation of uncontrolled hazardous waste sites has been the focus of considerable misunderstanding by both the regulated and regulating community. Unlike toxicity measurements used for listing specific organic constituents or for risk assessment; the application of toxicity measurements to remediation is not: 1. extrapolated to human health, and 2. related to established toxicological values like exposure limits (TLV, STEL, IDLH), dose response or measurements of acute or chronic toxicity. The application of toxicity to remediation relates to changes in toxicity and is therefore a measurement of relative toxicity. Relative toxicity is a useful indicator of the overall health of the microbial system. The toxicity bioassay is used directly to estimate the loading capacity of a soil system (Mathews and Bullich, 1985). When used in conjunction with a standard chemical death curve of the indigenous microorganisms, relative toxicity can be used to estimate the tolerance of the microbes to toxicity during remediation. This toxicity limit is useful in regulating mixing and/or the introduction of waste into an operating system without jeopardizing the viability of the biomass.

Treatability Studies

The purpose of the treatability study should be to validate the chosen technology for application to a specific site. In this respect, mass balance determinations are completely appropriate. A second and independent part of the treatability study involves optimization of the conditions required to stimulate bioremediation initially and to sustain activity during treatment. Only after optimization of the treatment conditions, can effective and realistic estimates of the reaction kinetics be made. 1235

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Approaches to Bioremediation

The science of microbial ecology and the related manipulation of the microenvironments to favor those populations effective at degrading wastes has developed rapidly in the past decade. During the bioremediation of mixed wastes, there are dramatic changes in the population diversity and environmental factors driving that diversity. The following four approaches to bioremediation listed by Dr. Sims can be used alone or in combination in various sequences to expedite remediation: 1. Enhanced biochemical mechanisms: stimulation of indigenous microbial populations, 2. Bioaugmentation: the addition of exogenous organisms, (Sayler and Blackburn, 1989), 3. Cell free enzyme preparations, and 4. Vegetative uptake and assimilation. The major aspects of microbial enhancement, bioaugmentation and vegetative assimilation were addressed in the review. However the area of cell free extracts and enzyme preparations were overlooked. Cell free systems offer tremendous opportunities over living systems because they: • are generally insensitive or much less sensitive to toxicity than living systems, • do not require the life support systems (electron acceptors, pH, nutrients, cometabolites, attachment surfaces, etc.) required by whole cells, • are generally more mobile in percolating water and consequently subject to better redistribution than whole cell systems. Treatment systems employing cell free preparations offer exciting opportunities to direct hazardous waste metabolism, improve degradation kinetic and lower attainable decontamination objectives by the following approaches: • Pretreatment to reduce toxicity prior to more complete treatment with whole cells, • Focused treatment of specific organics to avoid the production of toxic intermediates or end products (e.g., TCE and other difficult-to-treat halogenated organics), • Pretreatment to prime a contaminant for further biodegradation via a preferred metabolic pathway (e.g., specific ring cleavage). Samples

The reliability of degradation experiments based on the destruction of contaminants spiked into a soil sample rather than those adsorbed over time is controversial. Typically, spiked samples exhibit much faster degradation kinetics than samples containing contaminants tightly sorbed to the soil matrix over time. The use of spiked soils to estimate degradation kinetics can therefore result in the over optimistic estimation of degradation rates. Treatment Trains

Early treatment trains were designed with physical or chemical pretreatment prior to bioremediation. With recent advances in biotechnology, biotreatment can be used prior to physical or chemical treatment to reduce volumes and concentrate the constituents for the next process. Advances in all three areas of technology justify a reassessment of the order of cars in the treatment train and the development of strategies for establishing the optimum order. Mixed wastes complicate the selection of treatment train components and many questions remain to be answered. Should the order of treatment be based on the most recalcitrant component of the waste mixture? Will today's regulatory climate increase the number of cars in the treatment train? 1236

Richard E. Woodward

Additional Comments

Additional agency databases that address bioremediation include the WERL database (Dostal, 1988) and QSAR database (Moore et al, 1990). Other databases relevant to remediation of uncontrolled hazardous wastes in the unsaturated zone should be included in the critical review. These databases will be useful in constructing and verifying: • treatment models, • treatment trains, and • soil profiles for assessing treatment technologies. The role of anaerobic treatment systems needs to be clarified. Generally, anaerobic systems exhibit slow degradation kinetics, are sensitive to biomass volume and generate reduced intermediates and end products that may produce high relative toxicity values in aerobic bioassays. In anaerobic systems, facultative organisms may provide more flexibility for utilizing oxidative and reductive metabolic pathways for bioremediation than obligate anaerobes. Conclusions

The critical review provided by Dr. Sims represents a milestone in the compilation and integration of technologies available for remediation of hazardous wastes in the unsaturated soil zones. Because of the dynamic nature of remediation technology, this topic should be addressed periodically. It is clear that the role of biotechnology will expand rapidly as the pressure to destroy wastes, rather than store them, increases. Integration of biological, physical and chemical technologies into treatment trains to reduce costs, expedite remediation and lower attainable decontamination objectives will continue to a major challenge for site remediators and regulators. References

1. K. A. Dostal, "WERL Treatability Database," Risk Reduction Engin. Lab., USEAP, Cincinnati, OH, 1988 2. J. E. Mathews, A. A. Bullich, "A toxicity reduction test system to assist predicting land treatability of hazardous wastes," in Hazardous and Industrial Solid Waste Testing: Fourth Symposium, STP-886, J. K. Petros, Jr. et al. Eds. American Society of Testing and Materials, Philadelphia, PA, 1981, p. 176. 3. S. A. Moore, J. D. Pope, J. T. Barnett, Jr., L. A. Suarez, "Structure-Activity Relationships and Estimation Techniques for Biodegradation of Xenobiotics," Envirn. Res., Res. Dev., U. S. EPA, Athens, GA 30613, pp. 90-149857,1990. 4. G. S. Sayler, J. W. Blackburn, "Modern Biological Methods: The Role of Biotechnology," in Biotreatment of Agricultural Wastewater, CRC Press, Inc. Chapt. 5, p. 63-71,1989.

Richard E. Woodward is Vice President, Bioremediation, ENSR Consulting and Engineering, 750 West Second Ave., Suite 100, Anchorage, AK 99501.

J. Air Waste Manage. Assoc.

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To visualize the soil system we want to remediate, consider whether the target VOC resides in gas phase, water, and/ or soil (Figure 2). To predict total VOC mass, the following mass balance calculations are applied: where:

VACUUM

Mtotal = Mgas + Mliquid + MS0U Mgas = /(MH 2 O; Muquid; H) + Mevapomtion Ms0n = /(MH 2 O; Muquid; Kd) + Mfree uquid

•»:*:-:->: GAS PHASE >»:->:

The expression used to determine the VOC distribution between liquid and gas is as follow: Cgas = H*Cuquid @ equilibrium

Cgas = VOC concentration in gas phase Cuquid = VOC concentration in liquid phase H = Henry's constant. Henry's constant is an index of the partitioning of a chemical between dissolved and gaseous phases. Correlations based on Henry's Law constant can be used to give indications of the relative VOC recovery potential, but in a multicomponent system, it becomes a function of concentration of all species present in solution and therefore the relationship becomes much more complex. Downloaded by [37.187.118.56] at 18:29 30 January 2016

where:

H2O Separator

Figure 1.

Activated Carbon to reclamation disposal

Typical Vacuum Gas Extraction System.

The relationship between the VOCs in the soil solid and liquid is based on adsorption equilibrium models. The simplest expression is:

Figure 2.

Predicting SGE performance.

where:

Y,- = mole fraction of component i PT = total pressure of gas phase Pi = partial pressure of component i. This contribution is rarely calculated or reported in the literature. The distribution of VOC between two liquids should be experimentally measured since present prediction techniques are poor for any polar compounds in water. Prediction of multi-component solubility in water or any other solvent requires sophisticated computer algorithms. As you can see from the above expressions, there are ways to theoretically determine a mass balance under equilibrium conditions. However, as with most other in situ soil treatment techniques, equilibrium conditions do not exist, making our ability to use the mass balance approach difficult to nearly impossible. However, by following the general mass balance approach that Dr. Sims suggests, better insight into the remediation process can be obtained even though an in situ mass balance probably cannot be determined. The soil processes and chemical mechanisms that can influence the performance of any in situ remediation technique should be identified and evaluated. The mass balance approach is a good starting point as long as it is recognized that the equations used to determine distribution of chemicals are for equilibrium conditions which rarely exist during remediation. Overall Dr. Sims' paper is a useful introduction to a complex and growing field. It is apparent that a lot of thought and work went into preparation of this paper. I commend Dr.' Sims for his effort and hope that he will continue to pursue his approach to soil remediation.

Csoil = Kd*CH2O

where: Kd = the distribution in coefficient. This model is valid in many water-soil systems but not all. It inherently assumes close to a static condition. The relationship between the VOC in the soil solid and gas is based on simple evaporation at equilibrium. Yi = Pi/PT

Prepared Discussion Stephen C. James U. S. Environmental Protection Agency Cincinnati, Ohio

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J. N. Hartley is Program Manager, Environmental Restoration, Battelle Environmental Management Operations, P.O. Box 999, Richland, Washington, 99352.

I would like to congratulate Dr. Ronald Sims on his fine effort to discuss and present an important issue that definitely has a variety of opinions from various technical experts in the field. Dr. Sims chose the subject of soil remediation, which is a very complex technical area worthy of an entire Journal issue. Dr. Sims did an excellent job of presenting an overview of soil remediation in a single article. J. Air Waste Manage. Assoc.

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The Hazardous Waste Action Coalition, in their publication entitled "The Hazardous Waste Practice: Technical & Legal Environment," correctly points out that the uncertainties in hazardous waste engineering are far greater than those assumed in conventional engineering projects. The solutions to many of the problems encountered in the cleanup of hazardous waste sites are not yet clearly defined. In general, there is a very limited data base on technologies that may be applicable to these problems. We do know that the solution to many of the existing problems begins with controlling the source of the contamination. It is here that we turn our attention to soil remediation. A historical view at the Superfund Records of Decision (RODs) for past years shows that control treatment remedies have steadily increased each year. From the years 1987 to 1989, treatment options such as biodegradation, soil flushing, vacuum/vapor extraction, thermal desorption, soil washing, and chemical treatment have increased in the percentage of treatment technologies specified, while the percentage of high temperature thermal and solidification/stabilization options have shown a decrease. These technologies may be applicable to the treatment of contaminated soils. Currently for the treatment of soils both excavation and treatment and in situ options are available. Current treatment technologies have come from the development of a new technology or the adaptation of an existing technology to the hazardous waste field. In either case, supporting systems (such as material handling, delivery systems, etc.) need to be closely integrated with the selected treatment system. Because of the volumes of contaminated, soil to be treated, high throughput/low-cost systems are required. Technologies with special requirements, such as extensive feed preparation, may not be economically feasible. The development of new technologies follows a process using 1) initial concept development; 2) research and development, including bench/laboratory testing; 3) pilot testing; 4) field demonstration; and commercialization. During each of these stages, important questions concerning the intended use of the technology (including waste matrix, contaminant levels, desired treatment effectiveness, etc.) need to be addressed. This is, in essence, the application of data quality objectives to the process of treatment technology development. Through a process of research and testing* commercialization and use of the treatment technology will be realized. Dr. Sims presented an excellent overview of a very broad subject area. He also conducted an excellent review of the existing literature. In the critical review, Dr. Sims presents

several issues/concepts. Two of these, chemical mass balance and treatability studies, are of interest. As most are aware, the various contaminants and the level of these contaminants present in contaminated soils at a hazardous waste site will vary widely. This is one reason why the treatment of these contaminated soils may involve treatment trains to eventually remediate the site. In estimating a mass balance or in conducting treatability studies, one is collecting data from very controlled laboratory experiments using actual waste from the hazardous waste site. Because of the above and other numerous reasons, field demonstrations and/or actual use of technologies during site remediation do not operate under the ideal conditions that can be controlled in the laboratory. Many times I have observed or been involved in field demonstrations or ongoing remediations at Superfund sites. During this field work, problems that could not have been anticipated by laboratory experiments or studies always have occurred. Primary among these are changing feed characteristics (contaminants, contaminant levels, soil properties, etc.) which can result in changing the feed preparation process, operating parameters of the technology, and control of emissions/residues from the. technology. To date, we have not been able to complete a mass balance on any of the technologies which we are evaluating under the Superfund Innovative Technology Evaluation Program. However, demonstrations of the technologies in the field under actual conditions have provided the Environmental Protection Agency (EPA) and the technology developer with invaluable information on the performance of their technology and where problem areas with the operation of their technology/ process exist. Treatability studies are an important aspect of technology development and evaluation. They indicate that the waste is or is not applicable to the proposed treatment technology and can provide information of the optimal level of treatment effectiveness that the technology can achieve. It is important to recognize that treatability studies can be very expensive and should be carefully tailored to obtain the required information. Appropriately designed treatability studies coupled with field demonstrations of technologies can provide a valuable evaluation of a treatment technology.

Closing Remarks

concerning the Critical Review. These individuals are James Hartley of Battelle Northwest Laboratories, Sunil Shah of Union Carbide Corporation, Robin Anderson of U.S. EPAOERS, Richard Woodward of ENSR Consulting and Engineering, and Steven James of U.S. EPA-ORD. Approaches and methods for determining and evaluating remediation techniques that I presented were evaluated by each panelist, and their comments reflect their professional backgrounds and present functions in the private and federal government sectors as well as their extensive experience in the area of hazardous waste site remediation. The panelists were unified in their assessment that soil remediation at uncontrolled hazardous waste sites is a complex issue, both from a regulatory standpoint and from a technical perspective. There was a consensus that contaminated soil, at many sites, represents the source of contamination of groundwater, air, and surface water, and that there is

Ronald C. Sims Utah State University Logan, Utah

I take this opportunity to sincerely thank the Air and Waste Management Association for having invited me to present the eighteenth Critical Review, "Soil Remediation Techniques at Uncontrolled Hazardous Wastes Sites," June 27, 1990.1 also thank the individuals who participated in a panel discussion with me and who provided insight and comment Copyright 1990—Air & Waste Management Association

September 1990

Volume 40, No. 9

Stephen C. James is Chief, SITE Demonstration & Evaluation Branch, U. S. Environmental Protection Agency, Cincinnati.OH 45288.

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a limited data base of technologies that may be applicable to hazardous waste contaminated soil. Two issues that were commented on consistently by the panelists, and that were addressed in the Critical Review, included the concepts of: (1) mass balance, and (2) treatability studies. Interpretations of these concepts by the panelists varied and indicated both the advantages as well as the problems involved with using familiar scientific and engineering terminology. The Critical Review paper stated that "The concept of a chemical mass balance is familiar to professionals trained in the physical or life sciences or in engineering," and was proposed as a conceptual framework for remediation technique evaluation, selection, and monitoring. Several panelists and many readers, I suspect, interpreted mass balance in a strict quantitative sense and assumed that the goal was to obtain 100 percent mass balance in field applications of technologies. However, also stated in the Critical Review paper was the following: "In contrast to obtaining quantitative accuracy regarding the amount of contaminants initially present at an uncontrolled site, the chemical mass balance provides a rational and fundamental basis for asking specific questions and obtaining specific information that is necessary for determining fate and behavior, for evaluating and selecting treatment options, and for monitoring treatment effectiveness at both laboratory scale and at field scale." I would like to emphasize that the mass balance "approach" combined with a knowledge of soil processes provides a framework for asking relevant questions with regard to technology development and application, e.g., which specific chemicals need to be treated in which phase(es)- gas, liquid, nori aqueous phase liquid (NAPL), and/or solid. Robin Anderson's comment that " . . .the concept of mass balance is an ideal which we should strive to achieve as we make decisions on a site specific basis..." succinctly places the use of mass balance in the appropriate context. Also, a mass balance approach does not necessarily imply that a laboratory or field system needs to be at equilibrium in order to use the mass balance to make decisions concerning fate and behavior or concerning remediation technology selection. The mass balance analysis approach can be used to indicate the "tendency" for a chemical(s) to move from one phase to another, e.g., chemicals with high vapor pressures that are found associated with NAPL can be expected to move into the soil air phase (interphase transfer potential). Selection of a treatment technology can then be based on "frustrating" the attempt of the system to attain equilibrium in order to remove the contaminant from the site, e.g., application of vacuum extraction to remove the NAPL so that equilibrium between NAPL and soil gas phase cannot occur, or removing volatile chemicals in the air phase to cause the continual displacement of chemicals from the water phase so that an equilibrium between air and water phases does not occur. These examples illustrate use of a mass balance in the context of the questions: Where is the contamination and where is the contamination going? When

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this information is obtained, it is then often possible to select a site-specific and chemical-specific treatment technology that efficiently addresses the problem of source control. With regard to treatability studies, due to the lack of a mass balance approach and a lack of well defined goals, many treatability studies are not effective in providing valuable information that can be applied to site remediation. Perhaps because treatability studies have been used inappropriately, they have become suspect with regard to their value in evaluating and selecting remedial technologies. The value of treatability studies should perhaps be related to the efficiency with which the studies lead to successful screening of technologies and effectiveness with regard to field scale monitoring. Stephen James pointed out, appropriately, that treatability studies should be carefully tailored to obtain the required information, and that they are an important aspect of technology development and evaluation. Historically, the "careful tailoring" has not been generally practiced often because of a lack of understanding of soil processes and the lack of an "approach" to formulating the problem (problem assessment as discussed in the Critical Review). An effective way to ensure that treatability studies are neither efficient nor effective is to provide insufficient funds for conducting at least a preliminary mass balance. Concerning costs associated with conducting treatability studies, they can be expensive, as Stephen James points out, and also elaborate. Another framework for evaluating costs would be to compare the cost of treatability studies with the cost of design, technology implementation, and monitoring for a number of sites. My observation is that there does not presently exist a method or procedure for evaluating the usefulness of treatability studies, over the range of costs from inexpensive to expensive (intensive), in terms of application to successful site cleanups. Also, as with the use of the terminology "mass balance," "treatability study" has most often been interpreted to be a laboratory-scale activity. However, as discussed in the Critical Review, treatability studies can be conducted at fieldscale dimensions. The critical elements that determine the time, cost, and energy invested in treatability studies concern questions and issues and approaches that are generated as results of treatability studies, which can assist in designing, implementing, and monitoring field scale application of a chosen technology. Finally, I conclude with an observation on the usefulness of treatability studies versus the usefulness of experience gained in conducting field demonstrations of technologies under actual conditions will. I suggest that an iterative process involving both treatability studies and field applications/demonstrations of technologies represents an optimum utilization of thie strengths of both approaches. Treatability studies can be utilized to guide selection of technologies for field-scale evaluation, and results from field-scale evaluations can be used to "tailor" treatability studies to answer questions concerning mechanisms that are operating to limit or enhance a particular technology.

J. Air Waste Manage. Assoc.