This article was downloaded by: [University of California, Riverside Libraries]On: 10 October 2014, At: 23:02Publisher: Taylor & FrancisInforma Ltd Registered in England and Wales Registered Number: 1072954 Registered office: MortimerHouse, 37-41 Mortimer Street, London W1T 3JH, UK

Journal of the Air & Waste Management AssociationPublication details, including instructions for authors and subscription information:http://www.tandfonline.com/loi/uawm18

Soil Remediation Techniques at UncontrolledHazardous Waste SitesRobin Anderson a , Richard E. Woodward b , Sunil I. Shah c , J. N. Hartley d , StephenC. James e & Ronald C. Sims fa U.S. Environmental Protection Agency , Washington , D.C. , USAb ENSR Consulting and Engineering , Houston , Texas , USAc Union Carbide Chemicals and Plastcis Company , South Charleston , West Virgina ,USAd Battelle Environmental Management Operation , Richland , Washington , USAe U. S. Environmental Protection Agency , Cincinnati , Ohio , USAf Utah State University , Logan , Utah , USAPublished online: 06 Mar 2012.

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 & WasteManagement 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

PLEASE SCROLL DOWN FOR ARTICLE

Taylor & Francis makes every effort to ensure the accuracy of all the information (the “Content”) containedin the publications on our platform. However, Taylor & Francis, our agents, and our licensors make norepresentations or warranties whatsoever as to the accuracy, completeness, or suitability for any purposeof the Content. Any opinions and views expressed in this publication are the opinions and views of theauthors, and are not the views of or endorsed by Taylor & Francis. The accuracy of the Content shouldnot be relied upon and should be independently verified with primary sources of information. Taylorand Francis shall not be liable for any losses, actions, claims, proceedings, demands, costs, expenses,damages, and other liabilities whatsoever or howsoever caused arising directly or indirectly in connectionwith, in relation to or arising out of the use of the Content.

This article may be used for research, teaching, and private study purposes. Any substantial or systematicreproduction, redistribution, reselling, loan, sub-licensing, systematic supply, or distribution in anyform to anyone is expressly forbidden. Terms & Conditions of access and use can be found at http://www.tandfonline.com/page/terms-and-conditions

Soil Remediation Techniques at UncontrolledHazardous Waste Sites

Critical Review Discussion Papers

The A&WMA Critical Review entitled "Soil Remediation Techniques at UncontrolledHazardous Waste Sites" was presented by Ronald C. Sims, Department of Civil andEnvironmental Engineering, Utah State University, Logan, Utah. Dr. Sims presentedhis review at the 83rd Air & Waste Management Association Annual Meeting, held inPittsburgh, Pennsylvania in June 1990. Prepared discussions presented during theCritical Review session are published here, along with some closing remarks by Dr.Sims. Ronald Harkov, Chairman of the Critical Review Subcommittee of the Publica-tions Committee, served as moderator of the 1990 A&WMA Critical Review session.

Prepared DiscussionRobin AndersonU.S. Environmental Protection AgencyWashington D.C.

I appreciate the opportunity to discuss Dr. Ronald Sims'critical review of soil remediation techniques of uncontrolledhazardous waste sites. Dr. Sims provides an excellent over-view of treatment alternatives for soil contamination andproposes a conceptual methodology for site assessment andremedy selection and evaluation. Current practices at Su-perfund sites are consistent to a large extent with Dr. Sims'proposal. The degree to which his proposal is implemented isdependent on the information available, the complexity ofthe site, and the state of science.

Remediating sites which pose current or potential futurerisks due to releases of hazardous substances and pollutantsor contaminants involve complex scientific and policy issues.Today I will discuss how these issues impact our remedyselection process through a discussion of the statutory andregulatory requirements and remedial process. I will end mytalk with a discussion of Dr. Sims' proposal as comparedwith the current Superfund practices. While Dr. Sims' re-view of the subject focused principally on a scientific evalua-tion of the processes involved, my discussion focuses on thepolicy framework in which decisions are made.

Statutory and Regulatory Background

The Comprehensive Environmental Response Compensa-tion, and Liability Act (CERCLA) of 1980 provided a statu-tory basis for addressing uncontrolled hazardous waste sites

Copyright 1990—Air & Waste Management Association

that pose a threat to human health and the environment.1

Congress revised CERCLA with the Superfund Amend-ments and Reauthorization Act (SARA) of 1986 adding newauthorities and responsibilities to the program.2 The SARAamendments, among other new requirements, provide gen-eral rules for remedy selection, describe requirements forclean-ups, and emphasize long-term effectiveness and per-manence.

The National Oil and Hazardous Substances PollutionAct (NCP) provides the regulatory blueprint for implemen-tation of the statute. It regulates EPA, other federal agen-cies', state's, and private parties' responses to releases. TheNCP was revised this year (March 8,1990, FR 8666-8865) toincorporate changes in the program required by SARA andthe Clean Water Act and to reflect the process which hasevolved over the first ten years that the Superfund programhas been in existence.3

The NCP details the program goal, expectations, and aprocess for remedy selection at Superfund sites which directthe site evaluation and ultimately the selection of remedy.The NCP states that the Superfund program goal is to uti-lize:

" . . . remedial actions that protect human health andthe environment, that maintain protection over time,and that minimize untreated wastes."

The goal reflects CERCLA's increased emphasis on treat-ment when practicable to provide for a permanent and reli-able solution.

The NCP expectations discuss circumstances under whichtreatment, engineering and institutional controls are likelyto be appropriate. They aid in streamlining the Superfundprocess but are not a substitute for the site-specific analysisto determine the extent to which treatment can practicablybe used in a cost-effective manner.

It is expected that remedies will generally include a treat-ment alternative that significantly reduces toxicity and/ormobility of the contaminants posing a significant threat,wherever practicable, to reduce the need for long-term man-

1232 J. Air Waste Manage. Assoc.

Dow

nloa

ded

by [

Uni

vers

ity o

f C

alif

orni

a, R

iver

side

Lib

rari

es]

at 2

3:02

10

Oct

ober

201

4

agement. The principal threat is defined as liquids, highconcentrations of toxic compounds, and highly mobile mate-rials. High concentrations of toxic chemical are anticipatedto be those wastes which are two to three orders of magni-tude above levels that allow for unrestricted use and unlimit-ed exposure.

The NCP clarifies the use of engineering and institutionalcontrols. Engineering controls include containment technol-ogies such as capping and slurry walls to prevent the migra-tion of contaminants. Institutional controls include deedrestrictions to limit the future use of the site to preventexposure. Engineering controls will be considered for wastesthat pose a relatively low long-term threat or where treat-ment is impracticable. Institutional controls are expected tobe used frequently to mitigate short-term impacts and tosupplement engineering controls for long-term manage-ment. Institutional controls will not be used as a substitutefor treatment or engineering controls unless such measuresare impracticable.

The NCP, in the preamble and the regulation, states thatprotection of human health and the environment may beachieved through a range of alternatives. Innovative tech-nologies will be considered when those technologies offer thepotential for comparable or superior treatment, fewer ad-verse affects, or lower cost for similar performance. TheNCP further established a treatment guideline of 90 percentor greater reduction of the concentration or mobility of con-taminants of concern. Remediation goals will be set, takinginto consideration site-specific factors and Agency guide-lines and goals.

Remedial Process

The NCP provides a systematic process that factors in theprogram goal and expectations and allows consideration andbalancing of site-specific factors in remedy selection. Theprocess consists of a site characterization phase called theremedial investigation (RI) and a remedial alternative inves-tigation phase termed the feasibility study (FS).4 The RIand FS are generally performed in a simultaneous mannerdue to their interactive nature. The remedy is selected basedon the RI/FS and comments received from the public on theproposed plan. The final decision is documented in the Re-cord of Decision (ROD).

The purpose of the RI is to collect data necessary to ade-quately characterize the site to support the identificationand evaluation of remedial alternatives. The RI includesfield investigations, treatability studies, and a baseline riskassessment to identify the extent of the problems and tosupport the identification and analysis of alternatives.

The purpose of the FS is to ensure that appropriate reme-dies are developed and evaluated in such a manner that adecision may be made on the appropriate alternative. Thedevelopment and evaluation of alternatives are scaled forthe complexity of the site and the action under study.

The identification of a preferred alternative and final se-lection of remedy is determined from an analysis of the nineevaluation criteria identified in the NCP (40 CFR300.430(f)(l) (ii)

Threshold Criteria1. Overall protection of human health and the environ-

ment;2. Compliance with applicable or relevant and appropri-

ate 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;

Dr. Harkov, on left, and Dr. Sims

Modifying-Criteria8. State acceptance; and9. Community acceptance.

As noted above, the criteria are categorized into threegroups: threshold criteria, primary balancing criteria, andmodifying criteria. Remedial alternatives must satisfy thethreshold criteria of protection and compliance with ARARs(or justify a waiver) to be eligible for selection. Remedialalternatives are then compared with each other based ontheir relative performance with regards to the primary bal-ancing criteria. The long-term effectiveness and the degreeto which the toxicity, mobility or volume is reduced throughtreatment are two of the most crucial balancing criteria sincethey focus on treatment and permanence, principal themesof SARA. Finally, state and community acceptance of thealternatives are considered as the modifying criteria.

Evaluation of Dr. Sims' Review

Dr. Sims identified the critical issues and research needsconcerning soil remediation as establishing clean-up criteriaand improving our understanding of technologies and theircapability to meet these goals. Specific areas on which weneed to focus our research efforts include:

• Improved understanding of multi-contaminant fate andtransport to aid in the establishment of realistic clean-up criteria.

• Identification of critical site characterization informa-tion needed to predict technology performance.

• Demonstration of innovative technologies (e.g., biodeg-radation) and technology train capabilities and under-standing of factors affecting performance.

• Identification of implementation issues (e.g., volatileemissions) and viability of engineering solutions.

Although we have come a long way in our understanding ofthe science and have broken new ground in melding thatscience with public policy, the scientific basis of our deci-sions is inexact. This is due to a combination of a lack ofscientific knowledge and the need to assume some risks inthe decision process so that we may expedite remediation tothe extent possible. We are often limited in our ability tofully characterize a site, as Dr. Sims proposes.

Dr. Sims' proposed methodology for characterizing sitesand evaluating remedies involves integrated data collectionactivities to support site characterization, risk assessment,remedy evaluation and selection, and performance monitor-ing. The proposal as outlined is that which is utilized in theSuperfund program. The Agency strives to maximize datacollection to support both the RI and the FS simultaneously.However, the Agency also recognizes the need to balance thedesire for definitive site characterization with the desire to

September 1990 Volume 40, No. 9 1233

Dow

nloa

ded

by [

Uni

vers

ity o

f C

alif

orni

a, R

iver

side

Lib

rari

es]

at 2

3:02

10

Oct

ober

201

4

implement protective remedies in an expeditious manner.The Agency will perform a site characterization sufficient tosupport the remedial response envisioned but which may notresult in an extended study of the site.

The Agency may limit data gathering and streamline theRI/FS particularly where site problems are straight forwardsuch as in situations involving a selected group of chemicalsor where remediations options are limited. A streamlinedapproach may also be appropriate in cases where an interimaction may be taken to eliminate or reduce the risk posedwhile additional studies progress to evaluate alternatives forthe final remedy.

The concept of "mass balance" is a key component in Dr.Sims' methodology. The idea presented is that we need athorough understanding of the fate and transport of con-taminants in order to ascertain the route of exposure and toselect the appropriate technology to remediate the site. Theextent to which mass balance is currently applied on a sitespecific basis is determined by nature of the constituents,the type of remediation appropriate for the site, and thelimitations in our scientific understanding.

The term "mass balance" connotes that we have a fairlycomplete knowledge of the fate of materials. In light of thefact that even well studied above-ground treatment process-es have not afforded the research community mass balanceclosure, it is highly unlikely that we will achieve this for mosttechnologies or complex sites in the near term. However, theconcept of mass balance is an ideal which we should strive to

achieve as we make decisions on a site specific basis to theextent that it is feasible. For example, we need to understandif volatilization or other treatment (e.g., biodegradation) isthe principal route of removal if we are to select and design aremediation process which will effectively remove the con-taminants.

Mass balance is expected to become increasingly achiev-able 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 Investigationsand Feasibility Studies under CERCLA (Interim Final)", Officeof Emergency and Remedial Response, EPA/540/G-89/004, Oct.1988. .

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

Prepared Discussion

Richard E. WoodwardENSR Consulting and EngineeringHouston, Texas

I commend Dr. Sims on compiling this summary of treat-ment technologies and his associated interpretations. Histreatment of this subject has elucidated deficiencies in thecurrently available technology, provided an effective con-ceptual framework for remediation and supplied some selec-tion criteria for remediation technologies. This is an impor-tant start for comparing remedial technologies for the unsat-urated zone and will be a useful reference for selectingremedial approaches and for developing treatment trains.

Physical, chemical and biological approaches to remedia-tion have been presented as individual techniques and ascomponents of a treatment train. Because of my training andexperience in biotechnology, I feel best qualified to addressthose technologies which deal with bioremediation alone oras part of a treatment train. Consequently my review will belimited to the bioremediation aspects of Dr. Sims presenta-tion.

Since this paper is the first strawman on the topic of theremediation of soil in the unsaturated zone, it tends to dis-cuss 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.

Regulatory Issues

Dr. Sims has provided a good review of the current regula-tory status affecting remediation in the unsaturated zoneand the historical perspective leading to its implementation.His presentation has stimulated several questions:

1. The relatively age-old question remains: "How clean isclean?" and continues to be an issue with both federaland state regulatory agencies.

2. Will the trend toward lower and lower decontaminationobjectives continue as our ability to detect contaminantsin the soil matrix continues to improve and our remedialoptions continue to expand?

3. Would you agree that the trend toward risk assessmentbased decontamination objectives will continue and per-haps expand?

4. Will remedial technology developments begin to driveregulators toward lower decontamination objectives?

Remediation Systems

Three remediation systems were discussed: in situ treat-ment, prepared bed and in vessel treatment. As the databaseexpands for these treatment systems, a "soil profile" shouldappear that will allow candidate soils to be evaluated againsteach treatment approach. A ranking system could then di-rect the remediator to the best technology. A matrix summa-rizing the:

• innate soil characteristics (bulk density, cation exchangecapacity, pH, macro, secondary and micro nutrient lev-els, pore size, permeability, etc.),

• contaminant characteristics (as outlined in the CriticalReview), and

• specific remediation treatment systems would provideuseful guidance in technology selection.

1234 J. Air Waste Manage. Assoc.

Dow

nloa

ded

by [

Uni

vers

ity o

f C

alif

orni

a, R

iver

side

Lib

rari

es]

at 2

3:02

10

Oct

ober

201

4

Conceptual Approach to Soil Remediation

The concepts of mass balance/materials balance need tobe put in the proper perspective in relation to remediationtechnology.

Mass balance is essential for validating the application ofa candidate technology for a given site, contaminant matrixand waste mixture. It is inappropriate and unrealistic toapply mass balance to field demonstrations, for the follow-ing reasons:1. Field systems are frequently poorly defined both in

terms of contaminant volume and specific chemical con-stituents; both are subject to sampling error and bias,

2. Field systems are open and subjected to the perturba-tions of the weather, such perturbations directly effectvolumes and may effect the rate of remediation indirect-ly,

3. Total accountability from a mass balance perspectivewill not eliminate the need for the frequent monitoringand analysis required of any field scale demonstration toassure compliance with ARARs and to verify ultimatedecontamination objectives,

4. Pursuit of mass balance in a field demonstration rapidlydrives the demonstration to the level of a research anddevelopment project, generally not justified from a costperspective.

Reaction Kinetics

Dr. Sims has provided an excellent summary and explana-tion 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 impliesthat mineralization of organic compounds is required foreffective bioremediation. Verification and monitoring of themodels by respirometry and/or the release of specific ions(Cl~, Br", So4

=, NO3~) supports this preoccupation withmineralization. Two problems exist with the use of mineral-ization to verify completion of the bioremediation process:

1. in most cases, listed constitutents comprise less than 2percent of the organic compounds present; 98 percent ofthe organic carbon at many sites is not listed or moni-tored by specific compound! As degradation progresses,nonlisted, larger molecular weight organics like kerogencan be degraded into smaller, listed organics. Likewiselisted organics can be removed from the listed by trans-formation without the production of carbon dioxide.

2. there is no precedent in the area of wastewater treat-ment of the use of mineralization to verify bioremedia-tion. Indeed, wastewater treatment is based on the con-cept of rapid transformation of organics into microor-ganism bodies and/or slimes which are then removed bythe clarifier. Only after the biomass is consolidated byclarification is mineralization a consideration. Biomassfrom a wastewater treatment plant is mineralized by avariety of processes including: extended aerobic diges-tion, composting, or anaerobic digestion.

Models

Models can provide effective prediction of the perfor-mance of remediation systems. Their real limitation lies intheir failure to deal with the heterogeneity of field condi-tions. Generally, the definition of field conditions are only asgood as the sampling program. Biased or limited samplingwill distort the data used to run a model and consequentlydistort the results of the model.

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

One approach to improving models is to model smallercomponents of the system. Models could be fine-tuned toreflect the three dimensional characteristics of the unsatu-rated soil zone. An improved vadose zone model would indi-vidually address the three sub-zones: upper belt, intermedi-ate belt and lower belt introduced earlier. Many of the threedimensional spatial models commonly used to model airtoxics could be directly applied to the spatial relationshipsin the soil systems.

Toxicity

Measurement of toxicity initially and during the remedia-tion of uncontrolled hazardous waste sites has been the focusof considerable misunderstanding by both the regulated andregulating community. Unlike toxicity measurements usedfor listing specific organic constituents or for risk assess-ment; the application of toxicity measurements to remedia-tion is not:

1. extrapolated to human health, and2. related to established toxicological values like exposure

limits (TLV, STEL, IDLH), dose response or measure-ments of acute or chronic toxicity.

The application of toxicity to remediation relates tochanges in toxicity and is therefore a measurement of rela-tive toxicity. Relative toxicity is a useful indicator of theoverall health of the microbial system. The toxicity bioassayis used directly to estimate the loading capacity of a soilsystem (Mathews and Bullich, 1985). When used in conjunc-tion with a standard chemical death curve of the indigenousmicroorganisms, relative toxicity can be used to estimate thetolerance of the microbes to toxicity during remediation.This toxicity limit is useful in regulating mixing and/or theintroduction of waste into an operating system without jeop-ardizing the viability of the biomass.

Treatability Studies

The purpose of the treatability study should be to validatethe chosen technology for application to a specific site. Inthis respect, mass balance determinations are completelyappropriate. A second and independent part of the treatabil-ity study involves optimization of the conditions required tostimulate bioremediation initially and to sustain activityduring treatment. Only after optimization of the treatmentconditions, can effective and realistic estimates of the reac-tion kinetics be made.

September 1990 Volume 40, No. 9 1235

Dow

nloa

ded

by [

Uni

vers

ity o

f C

alif

orni

a, R

iver

side

Lib

rari

es]

at 2

3:02

10

Oct

ober

201

4

Approaches to Bioremediation

The science of microbial ecology and the related manipu-lation of the microenvironments to favor those populationseffective at degrading wastes has developed rapidly in thepast decade. During the bioremediation of mixed wastes,there are dramatic changes in the population diversity andenvironmental factors driving that diversity. The followingfour approaches to bioremediation listed by Dr. Sims can beused alone or in combination in various sequences to expe-dite remediation:

1. Enhanced biochemical mechanisms: stimulation of in-digenous microbial populations,Bioaugmentation: the addition of exogenous organisms,(Sayler and Blackburn, 1989),Cell free enzyme preparations, andVegetative uptake and assimilation.

2.

3.4.

The major aspects of microbial enhancement, bioaugmen-tation and vegetative assimilation were addressed in thereview. However the area of cell free extracts and enzymepreparations were overlooked. Cell free systems offer tre-mendous opportunities over living systems because they:

• are generally insensitive or much less sensitive to toxic-ity than living systems,

• do not require the life support systems (electron accep-tors, pH, nutrients, cometabolites, attachment surfaces,etc.) required by whole cells,

• are generally more mobile in percolating water and con-sequently subject to better redistribution than whole cellsystems.

Treatment systems employing cell free preparations offerexciting opportunities to direct hazardous waste metabo-lism, improve degradation kinetic and lower attainable de-contamination objectives by the following approaches:

• Pretreatment to reduce toxicity prior to more completetreatment with whole cells,

• Focused treatment of specific organics to avoid the pro-duction of toxic intermediates or end products (e.g.,TCE and other difficult-to-treat halogenated organics),

• Pretreatment to prime a contaminant for further bio-degradation via a preferred metabolic pathway (e.g., spe-cific ring cleavage).

Samples

The reliability of degradation experiments based on thedestruction of contaminants spiked into a soil sample ratherthan those adsorbed over time is controversial. Typically,spiked samples exhibit much faster degradation kineticsthan samples containing contaminants tightly sorbed to thesoil matrix over time. The use of spiked soils to estimatedegradation kinetics can therefore result in the over optimis-tic estimation of degradation rates.

Treatment Trains

Early treatment trains were designed with physical orchemical pretreatment prior to bioremediation. With recentadvances in biotechnology, biotreatment can be used priorto physical or chemical treatment to reduce volumes andconcentrate the constituents for the next process. Advancesin all three areas of technology justify a reassessment of theorder of cars in the treatment train and the development ofstrategies for establishing the optimum order. Mixed wastescomplicate the selection of treatment train components andmany questions remain to be answered. Should the order oftreatment be based on the most recalcitrant component ofthe waste mixture? Will today's regulatory climate increasethe number of cars in the treatment train?

Richard E. Woodward

Additional Comments

Additional agency databases that address bioremediationinclude the WERL database (Dostal, 1988) and QSAR data-base (Moore et al, 1990). Other databases relevant to reme-diation of uncontrolled hazardous wastes in the unsaturatedzone should be included in the critical review. These data-bases 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 clari-fied. Generally, anaerobic systems exhibit slow degradationkinetics, are sensitive to biomass volume and generate re-duced intermediates and end products that may producehigh relative toxicity values in aerobic bioassays. In anaero-bic systems, facultative organisms may provide more flexi-bility for utilizing oxidative and reductive metabolic path-ways for bioremediation than obligate anaerobes.

Conclusions

The critical review provided by Dr. Sims represents amilestone in the compilation and integration of technologiesavailable for remediation of hazardous wastes in the unsatu-rated soil zones. Because of the dynamic nature of remedia-tion technology, this topic should be addressed periodically.It is clear that the role of biotechnology will expand rapidlyas the pressure to destroy wastes, rather than store them,increases. Integration of biological, physical and chemicaltechnologies into treatment trains to reduce costs, expediteremediation and lower attainable decontamination objec-tives will continue to a major challenge for site remediatorsand regulators.

References

1. K. A. Dostal, "WERL Treatability Database," Risk ReductionEngin. Lab., USEAP, Cincinnati, OH, 1988

2. J. E. Mathews, A. A. Bullich, "A toxicity reduction test systemto assist predicting land treatability of hazardous wastes," inHazardous and Industrial Solid Waste Testing: Fourth Sympo-sium, STP-886, J. K. Petros, Jr. et al. Eds. American Society ofTesting and Materials, Philadelphia, PA, 1981, p. 176.

3. S. A. Moore, J. D. Pope, J. T. Barnett, Jr., L. A. Suarez, "Struc-ture-Activity Relationships and Estimation Techniques for Bio-degradation 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 AgriculturalWastewater, 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.

1236 J. Air Waste Manage. Assoc.

Dow

nloa

ded

by [

Uni

vers

ity o

f C

alif

orni

a, R

iver

side

Lib

rari

es]

at 2

3:02

10

Oct

ober

201

4

Dow

nloa

ded

by [

Uni

vers

ity o

f C

alif

orni

a, R

iver

side

Lib

rari

es]

at 2

3:02

10

Oct

ober

201

4

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

Mtotal = Mgas + Mliquid + MS0U

where: Mgas = /(MH2O; Muquid; H) + Mevapomtion

Ms0n = /(MH2O; Muquid; Kd) + Mfree uquid

The expression used to determine the VOC distributionbetween liquid and gas is as follow:

Cgas = H*Cuquid @ equilibrium

where: Cgas = VOC concentration in gas phaseCuquid = VOC concentration in liquid phase

H = Henry's constant.

Henry's constant is an index of the partitioning of a chemicalbetween dissolved and gaseous phases. Correlations basedon Henry's Law constant can be used to give indications ofthe relative VOC recovery potential, but in a multicompon-ent system, it becomes a function of concentration of allspecies present in solution and therefore the relationshipbecomes much more complex.

H2OSeparator

VACUUM

ActivatedCarbon toreclamation

disposal

Figure 1. Typical Vacuum Gas Extraction System.

The relationship between the VOCs in the soil solid andliquid is based on adsorption equilibrium models. The sim-plest expression is:

Csoil = Kd*CH2O

where: Kd = the distribution in coefficient.This model is valid in many water-soil systems but not all. Itinherently assumes close to a static condition.

The relationship between the VOC in the soil solid and gasis based on simple evaporation at equilibrium.

Yi = Pi/PT

•»:*:-:->: GAS PHASE >»:->:

Figure 2. Predicting SGE performance.

where: Y,- = mole fraction of component iPT = total pressure of gas phasePi = partial pressure of component i.

This contribution is rarely calculated or reported in theliterature.

The distribution of VOC between two liquids should beexperimentally measured since present prediction tech-niques are poor for any polar compounds in water. Predic-tion of multi-component solubility in water or any othersolvent requires sophisticated computer algorithms.

As you can see from the above expressions, there are waysto theoretically determine a mass balance under equilibriumconditions. However, as with most other in situ soil treat-ment techniques, equilibrium conditions do not exist, mak-ing our ability to use the mass balance approach difficult tonearly impossible.

However, by following the general mass balance approachthat Dr. Sims suggests, better insight into the remediationprocess can be obtained even though an in situ mass balanceprobably cannot be determined. The soil processes andchemical mechanisms that can influence the performance ofany in situ remediation technique should be identified andevaluated. The mass balance approach is a good startingpoint as long as it is recognized that the equations used todetermine distribution of chemicals are for equilibrium con-ditions which rarely exist during remediation.

Overall Dr. Sims' paper is a useful introduction to a com-plex and growing field. It is apparent that a lot of thoughtand work went into preparation of this paper. I commend Dr.'Sims for his effort and hope that he will continue to pursuehis approach to soil remediation.

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

Prepared Discussion

Stephen C. JamesU. S. Environmental Protection AgencyCincinnati, Ohio

I would like to congratulate Dr. Ronald Sims on his fineeffort to discuss and present an important issue that defi-nitely has a variety of opinions from various technical ex-perts in the field. Dr. Sims chose the subject of soil remedia-tion, which is a very complex technical area worthy of anentire Journal issue. Dr. Sims did an excellent job of pre-senting an overview of soil remediation in a single article.

1238 J. Air Waste Manage. Assoc.

Dow

nloa

ded

by [

Uni

vers

ity o

f C

alif

orni

a, R

iver

side

Lib

rari

es]

at 2

3:02

10

Oct

ober

201

4

The Hazardous Waste Action Coalition, in their publica-tion entitled "The Hazardous Waste Practice: Technical &Legal Environment," correctly points out that the uncer-tainties in hazardous waste engineering are far greater thanthose assumed in conventional engineering projects. Thesolutions to many of the problems encountered in the clean-up of hazardous waste sites are not yet clearly defined. Ingeneral, there is a very limited data base on technologies thatmay be applicable to these problems. We do know that thesolution to many of the existing problems begins with con-trolling the source of the contamination. It is here that weturn our attention to soil remediation.

A historical view at the Superfund Records of Decision(RODs) for past years shows that control treatment reme-dies have steadily increased each year. From the years 1987to 1989, treatment options such as biodegradation, soilflushing, vacuum/vapor extraction, thermal desorption, soilwashing, and chemical treatment have increased in the per-centage of treatment technologies specified, while the per-centage of high temperature thermal and solidification/sta-bilization options have shown a decrease. These technologiesmay be applicable to the treatment of contaminated soils.Currently for the treatment of soils both excavation andtreatment and in situ options are available.

Current treatment technologies have come from the de-velopment of a new technology or the adaptation of an exist-ing technology to the hazardous waste field. In either case,supporting systems (such as material handling, delivery sys-tems, etc.) need to be closely integrated with the selectedtreatment system. Because of the volumes of contaminated,soil to be treated, high throughput/low-cost systems are re-quired. Technologies with special requirements, such as ex-tensive feed preparation, may not be economically feasible.

The development of new technologies follows a processusing 1) initial concept development; 2) research and devel-opment, including bench/laboratory testing; 3) pilot testing;4) field demonstration; and commercialization. During eachof these stages, important questions concerning the intend-ed use of the technology (including waste matrix, contami-nant levels, desired treatment effectiveness, etc.) need to beaddressed. This is, in essence, the application of data qualityobjectives to the process of treatment technology develop-ment. Through a process of research and testing* commer-cialization and use of the treatment technology will be real-ized.

Dr. Sims presented an excellent overview of a very broadsubject area. He also conducted an excellent review of theexisting literature. In the critical review, Dr. Sims presents

several issues/concepts. Two of these, chemical mass balanceand treatability studies, are of interest. As most are aware,the various contaminants and the level of these contami-nants present in contaminated soils at a hazardous waste sitewill vary widely. This is one reason why the treatment ofthese contaminated soils may involve treatment trains toeventually remediate the site. In estimating a mass balanceor in conducting treatability studies, one is collecting datafrom very controlled laboratory experiments using actualwaste from the hazardous waste site. Because of the aboveand other numerous reasons, field demonstrations and/oractual use of technologies during site remediation do notoperate under the ideal conditions that can be controlled inthe laboratory. Many times I have observed or been involvedin field demonstrations or ongoing remediations at Super-fund sites. During this field work, problems that could nothave been anticipated by laboratory experiments or studiesalways have occurred. Primary among these are changingfeed characteristics (contaminants, contaminant levels, soilproperties, etc.) which can result in changing the feed prepa-ration process, operating parameters of the technology, andcontrol of emissions/residues from the. technology. To date,we have not been able to complete a mass balance on any ofthe technologies which we are evaluating under the Super-fund Innovative Technology Evaluation Program. However,demonstrations of the technologies in the field under actualconditions have provided the Environmental ProtectionAgency (EPA) and the technology developer with invaluableinformation on the performance of their technology andwhere problem areas with the operation of their technology/process exist.

Treatability studies are an important aspect of technologydevelopment and evaluation. They indicate that the waste isor is not applicable to the proposed treatment technologyand can provide information of the optimal level of treat-ment effectiveness that the technology can achieve. It isimportant to recognize that treatability studies can be veryexpensive and should be carefully tailored to obtain therequired information. Appropriately designed treatabilitystudies coupled with field demonstrations of technologiescan provide a valuable evaluation of a treatment technology.

Stephen C. James is Chief, SITE Demonstration & Evalua-tion Branch, U. S. Environmental Protection Agency, Cincin-nati.OH 45288.

Closing Remarks

Ronald C. SimsUtah State UniversityLogan, Utah

I take this opportunity to sincerely thank the Air and WasteManagement Association for having invited me to presentthe eighteenth Critical Review, "Soil Remediation Tech-niques at Uncontrolled Hazardous Wastes Sites," June 27,1990.1 also thank the individuals who participated in a paneldiscussion with me and who provided insight and comment

Copyright 1990—Air & Waste Management Association

concerning the Critical Review. These individuals are JamesHartley of Battelle Northwest Laboratories, Sunil Shah ofUnion Carbide Corporation, Robin Anderson of U.S. EPA-OERS, Richard Woodward of ENSR Consulting and Engi-neering, and Steven James of U.S. EPA-ORD. Approachesand methods for determining and evaluating remediationtechniques that I presented were evaluated by each panelist,and their comments reflect their professional backgroundsand present functions in the private and federal governmentsectors as well as their extensive experience in the area ofhazardous waste site remediation.

The panelists were unified in their assessment that soilremediation at uncontrolled hazardous waste sites is a com-plex issue, both from a regulatory standpoint and from atechnical perspective. There was a consensus that contami-nated soil, at many sites, represents the source of contamina-tion of groundwater, air, and surface water, and that there is

September 1990 Volume 40, No. 9 1239

Dow

nloa

ded

by [

Uni

vers

ity o

f C

alif

orni

a, R

iver

side

Lib

rari

es]

at 2

3:02

10

Oct

ober

201

4

a limited data base of technologies that may be applicable tohazardous waste contaminated soil.

Two issues that were commented on consistently by thepanelists, and that were addressed in the Critical Review,included the concepts of: (1) mass balance, and (2) treatabil-ity studies. Interpretations of these concepts by the panel-ists varied and indicated both the advantages as well as theproblems involved with using familiar scientific and engi-neering terminology.

The Critical Review paper stated that "The concept of achemical mass balance is familiar to professionals trained inthe physical or life sciences or in engineering," and wasproposed as a conceptual framework for remediation tech-nique evaluation, selection, and monitoring. Several panel-ists and many readers, I suspect, interpreted mass balance ina strict quantitative sense and assumed that the goal was toobtain 100 percent mass balance in field applications oftechnologies. However, also stated in the Critical Reviewpaper was the following: "In contrast to obtaining quantita-tive accuracy regarding the amount of contaminants initiallypresent at an uncontrolled site, the chemical mass balanceprovides a rational and fundamental basis for asking specificquestions and obtaining specific information that is neces-sary for determining fate and behavior, for evaluating andselecting treatment options, and for monitoring treatmenteffectiveness at both laboratory scale and at field scale." Iwould like to emphasize that the mass balance "approach"combined with a knowledge of soil processes provides aframework for asking relevant questions with regard to tech-nology development and application, e.g., which specificchemicals need to be treated in which phase(es)- gas, liquid,nori aqueous phase liquid (NAPL), and/or solid. Robin An-derson's comment that " . . .the concept of mass balance isan ideal which we should strive to achieve as we make deci-sions on a site specific basis. . ." succinctly places the use ofmass balance in the appropriate context.

Also, a mass balance approach does not necessarily implythat a laboratory or field system needs to be at equilibriumin order to use the mass balance to make decisions concern-ing fate and behavior or concerning remediation technologyselection. The mass balance analysis approach can be used toindicate the "tendency" for a chemical(s) to move from onephase to another, e.g., chemicals with high vapor pressuresthat are found associated with NAPL can be expected tomove 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 equilibri-um in order to remove the contaminant from the site, e.g.,application of vacuum extraction to remove the NAPL sothat equilibrium between NAPL and soil gas phase cannotoccur, or removing volatile chemicals in the air phase tocause the continual displacement of chemicals from the wa-ter phase so that an equilibrium between air and waterphases does not occur. These examples illustrate use of amass balance in the context of the questions: Where is thecontamination and where is the contamination going? When

this information is obtained, it is then often possible to selecta site-specific and chemical-specific treatment technologythat efficiently addresses the problem of source control.

With regard to treatability studies, due to the lack of amass balance approach and a lack of well defined goals,many treatability studies are not effective in providing valu-able information that can be applied to site remediation.Perhaps because treatability studies have been used inap-propriately, they have become suspect with regard to theirvalue in evaluating and selecting remedial technologies. Thevalue of treatability studies should perhaps be related to theefficiency with which the studies lead to successful screeningof technologies and effectiveness with regard to field scalemonitoring. Stephen James pointed out, appropriately, thattreatability studies should be carefully tailored to obtain therequired information, and that they are an important aspectof technology development and evaluation. Historically, the"careful tailoring" has not been generally practiced oftenbecause of a lack of understanding of soil processes and thelack of an "approach" to formulating the problem (problemassessment as discussed in the Critical Review).

An effective way to ensure that treatability studies areneither efficient nor effective is to provide insufficient fundsfor conducting at least a preliminary mass balance. Concern-ing costs associated with conducting treatability studies,they can be expensive, as Stephen James points out, and alsoelaborate. Another framework for evaluating costs would beto compare the cost of treatability studies with the cost ofdesign, technology implementation, and monitoring for anumber of sites. My observation is that there does not pres-ently exist a method or procedure for evaluating the useful-ness of treatability studies, over the range of costs frominexpensive to expensive (intensive), in terms of applicationto successful site cleanups.

Also, as with the use of the terminology "mass balance,""treatability study" has most often been interpreted to be alaboratory-scale activity. However, as discussed in the Criti-cal Review, treatability studies can be conducted at field-scale dimensions. The critical elements that determine thetime, cost, and energy invested in treatability studies con-cern questions and issues and approaches that are generatedas results of treatability studies, which can assist in design-ing, implementing, and monitoring field scale application ofa chosen technology.

Finally, I conclude with an observation on the usefulnessof treatability studies versus the usefulness of experiencegained in conducting field demonstrations of technologiesunder actual conditions will. I suggest that an iterative pro-cess involving both treatability studies and field applica-tions/demonstrations of technologies represents an opti-mum utilization of thie strengths of both approaches. Treat-ability studies can be utilized to guide selection oftechnologies for field-scale evaluation, and results fromfield-scale evaluations can be used to "tailor" treatabilitystudies to answer questions concerning mechanisms that areoperating to limit or enhance a particular technology.

1240 J. Air Waste Manage. Assoc.

Dow

nloa

ded

by [

Uni

vers

ity o

f C

alif

orni

a, R

iver

side

Lib

rari

es]

at 2

3:02

10

Oct

ober

201

4