soil remediation technologies - hasiera - … of natural resources in an european context ......

Subject 2.- EXPLOITATION OF NATURAL RESOURCES IN AN EUROPEAN CONTEXT

Module 2 B. SOIL RESOURCES, ATMOSPHERE AND BIOREMEDIATION

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SOIL REMEDIATION TECHNOLOGIES

LECTURER:

Iñaki Susaeta ElorriagaFUNDACION GAIKERParque Tecnológico de Zamudio. Edf 20248170 [email protected]

PROGRAMME:

1. Introduction ( 5 minutes)2. Selecting Soil remedial Actions (20 minutes)3. Classification of Soil Remediation Technologies (10 minutes)4. Treatability test for the implementation of a remediation technology

(10 minutes)5. Physico-Chemical Remediation Technologies (20 minutes)6. Permeable Reactive Barriers (PRB) as an alternative remedial option

(15 minutes)7. 1 Problem. Calculation of some remedial parameters (10 minutes)8. CD presentation “ Images form the deep” (15 minutes)

OBJECTIVES:

§ To learn about Soil remediation Technologies§ To study the basic processes of different technologies§ To evaluate treatability studies as a tool for a selection of a

remediation technology



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§ To introduce PRB as an alternative remedial option for the protectionof groundwater

INTRODUCTION:

Several billion EUROS are spent in the EU each year on the remediationof land affected by contamination. It is an important goal from allperspectives that this money is spent wisely and appropriately. A riskbased decision-making process for remediation is now the norm acrossmost EU member states.

There are two factors that impact on the cost-effectiveness ofremediation technologies. The first is the impact of waste legislationand regulation that, in certain nations, determines the fate ofcontaminated soil, and the potential for its treatment, disposal,recovery, recycling and reuse. The second is the designated land-use ofa remediated site; this has a profound effect on site values and hencethe options available for remediation.In general remedial options fall into one or more of the following broadcategories :

• Excavation and containment (Removal to landfill: the disposal ofmaterial to an engineered commercial void space; Deposition withinan on-site engineered cell, generally with a view to combining thedisposal of waste with the reclamation of land area from the voidspace; Engineered land-raising and land forming, where materialsare deposited on the land surface to make a hill or mound above thenatural surface level suitably contained.)

• Engineered systems (In situ Physical Containment: designed toprevent or limit the migration of contaminants left in place orconfined to a specific storage area, into the wider environment.Approaches include in-ground barriers, capping and cover systems;Hydraulic containment and pump-to-contain approaches.)

• Site rehabilitation measures are those used to bring back somemeasure of utility to a site whose contamination cannot be treated or



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contained for technical or economic reasons. Examples includegrowth of grass cover tolerant of contaminants, covering with soil orsoil substitute, liming and other cultivation measures.

• Treatment based approaches destroy, remove or detoxify thecontaminants contained in the polluted material (e.g. soil, groundwater etc). Using treatment technologies in contaminated landremediation is encouraged by agencies in many countries, becausethey are perceived as having added environmental value comparedwith other approaches to remediation such as excavation andremoval, containment or covering / revegetation. The "added"environmental value is associated with the destruction, removal ortransformation of contaminants into less toxic forms.

Treatment based approaches can be described as:

• Biological Processes (Bio): contingent on the use of living organisms• Chemical processes (Chem): destroy, fix or concentrate toxic

compounds by using one or more types of chemical reaction• Physical processes (Phys): separate contaminants from the soil

matrix by exploiting physical differences between the soil andcontaminant (e.g. volatility) or between contaminated anduncontaminated soil particles (e.g. density).

• Solidification and stabilisation (S/S): processes immobilisecontaminants through physical and chemical processes (Solidificationprocesses are those which convert materials into a consolidatedmass. Stabilisation processes are those in which the chemical form ofsubstances of interest is converted to a form which is less available).

• Thermal processes: exploit physical and chemical processesoccurring at elevated temperatures.

Ex situ approaches are applied to excavated soil and/or extractedgroundwater. In situ approaches use processes occurring inunexcavated soil, which remains relatively undisturbed. On sitetechniques are those that take place on the contaminated site. They maybe ex situ or in situ. Off site processes treat materials that have beenremoved from the excavated site (ex situ).SELECTING SOIL REMEDIAL ACTIONS:



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There is a number of factors that need to be considered in selecting aneffective remediation solution. These include considerations of coreobjectives such as risk management, technical practicability, feasibility,cost/benefit ratio and wider environmental, social and economicimpacts. In addition, it is also important to consider the manner inwhich a decision is reached. This should be a balanced and systematicprocess founded on the principles of transparency and inclusivedecision-making. Decisions about which risk management option(s) aremost appropriate for a particular site need to be considered in a holisticmanner. Key factors in decision making include:

• Driving forces to remediate and goals for the remediation objectives;• Risk management;• Sustainable development;• Stakeholders' views;• Cost effectiveness• Technical feasibility

Driving forces to remediate and goals for the remediation objectives:

Most remediation work has been initiated for one or more of thefollowing reasons:

• To protect human health and the environment. In most countries,legislation requires the remediation of land, which poses significantrisks to human health or other receptors in the environment such asgroundwater or surface water. The contamination could either befrom "historic" contamination or recent spillage of substances from aprocess or during transport. Groundwater protection has in manycountries become an important driver for remediation projects.

• To enable redevelopment. Remediation of formerly used land maytake place for strictly commercial reasons, or because economicinstruments have been put in place to support the regeneration of a



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particular area or region; and/or ( Brownfields redevelopmentconcept)

• To “repair problems. In some cases remediation work must beretrofitted to a newly developed site.

• To limit potential liabilities. Remediation can take place as aninvestment to increase the potential value of land. Owners mayperceive that a particular site could potentially have anenvironmental impact, which might leave them liable to third partyactions.

Risk management:

A risk-based approach has been adopted for the management ofcontaminated land in many countries (CLARINET and NICOLE, 1998). Theassessment and management of land contamination risks involves threemain components:

• The source of contamination (e.g. metal polluted soils, a leaking oildrum);

• The receptor (i.e. the entity that could be adversely affected by thecontamination e.g. humans, groundwater, ecosystems etc.); and

• The pathway (the route by which a receptor could come into contactwith the contaminating substances).

A pollutant linkage (see Figure 1) exists only when all three elements arein place. The probability that a pollutant linkage exists needs to beassessed. Risk assessment involves the characterisation of such arelationship, which typically includes: delineation of the source,measurement and modelling of fate and transport processes along thepathway, and assessment of the potential effect on and behaviour of the



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receptor. A consideration of risk must also take into account of not onlythe existing situation but also the likelihood of any changes in therelationship into the future. From a risk management standpoint,remediation technologies are applied to the control of the source termand/or the management of contaminants along the pathway.

Figure 1: The pollutant linkage (including source, pathway and receptor)analysis needs to be addressed when considering the risk of acontaminated site. Remediation includes any action taken tobreak the linkage. (Adapted from BARDOS 2000)

Sustainable development:

The concept of sustainable development gained internationalgovernmental recognition at the United Nation’s Earth Summitconference in Rio de Janeiro in 1992. A number of definitions forsustainable development have been proposed in different countries,based on the original consept of: “Development that meets the needs ofthe present without compromising the ability of future generations tomeet their own needs" (BRUNDTLAND, 1987). Underpinning all of theseapproaches are three basic elements to sustainable development:economic growth, environmental protection and social progress.

At a strategic level, the remediation of contaminated sites supports thegoal of sustainable development by helping to conserve land as aresource, preventing the spread of pollution to air, soil and water, andreducing the pressure for development on Greenfield sites. However,

PathwaySource

ReceptorPathway



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remediation activities themselves have their own environmental, socialand economic impacts. On a project-by-project basis, the negativeimpacts of remediation should not exceed the benefits of the project. Atpresent there are no generally agreed means of carrying outsustainability appraisal for remediation projects. Although approachesto assessing the wider impacts of individual elements of sustainability(e.g. wider environmental effects) are under development in severalcountries, a truly integrated approach has yet to be found. There issome way to go before an international consensus can be reached in theway that agreement has emerged about the principles of riskassessment and risk management. This is hardly surprising given thecomplex interplay of economic, environmental and social factors thataffect and are affected by a remediation project.Remediation objectives typically relate to environmental and health risksand perhaps performance of geotechnical / construction measures.These may form part of a larger regeneration project with social andeconomic aims, such as attracting inward investment. What isrealisable, and the approaches that can be taken, will be subject tocertain site/project specific boundaries, for example the time andmoney available for the remediation works, the nature of thecontamination and ground conditions, the site location and many more.Hence the objectives that can be realised by remediation worksrepresent a compromise between desired environmental qualityobjectives and these site-specific boundaries. This compromise isreached by a decision making process involving several stakeholders.This decision making process is often protracted and costly. Itsconclusions can be said to represent the core of the remediation project.While achieving environmental quality objectives will normally underpinany project dealing with contaminated land, desired quality objectivesmay be driven by a combination of technical criteria and third partynon-technical perception of risk.

From a broader perspective remediation processes will achieve thesecore objectives, by:• Helping to conserve land as a resource• Preventing the spread of pollution to air and water



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• Reducing the pressure for development on green field sites

In a broader perspective, a number of questions must also beaddressed, such as:

• How justified is it to excavate ground materials and put themsomewhere else?

• How justified is it to burn huge amounts of fossil fuel to treat groundcontaining grams of hydrocarbon per kilogram?

• How justified is it to strip VOC to atmosphere?

The grand question is therefore, should the remedial regime also besustainable? If the undesirable impacts of these remediation processesexceed the desired benefits of the core objectives, the core objectivesmay need to be re-evaluated. If proper risk management procedureshave been followed, along with a thorough cost benefit analysis andstakeholder consultation, the risks of such a situation arising should beminimised, depending on the remediation approach selected. Differentremediation approaches will vary in their wider environmental impacts,and perhaps also their wider social and economic effects. For example,the acceptability to local residents of different processes can differ. It istherefore useful to consider the route taken to affect the remediation, aswell as the core objectives of the remediation project. Assuming anoverall "sustainability value" of the core objectives these "non-core"considerations help determine the remediation approach, which detractsleast from this overall value.The wider consequences of a particular remedial project are site-specificin their nature. Some may be temporary (e.g. lorry movements; trafficproblem, noise), other permanent (e.g. loss of soil function). Thesignificance of these consequences also depends on the location of thesite being remedied. The importance of "nuisance" issues (e.g. odours,dust, noise) associated with remedial options, may, for example be lessfor a remote site than for a a site in a city neighbourhood. The relativesignificance that attaches to any particular wider effect of remediationwill itself vary at a local, regional and / or national level, for example as



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a result of cultural differences, differences in population density, use ofresources etc.

Stakeholders' views:

The principal stakeholders in remediation are generally considered to bethe "problem owners" (usually the polluter or site owner), and also allthose with an interest in the land, its redevelopment, and theenvironmental, social and financial impacts of any necessary riskmanagement works. Depending on the size and prominence of the sitethese stakeholders will include several of the following:• Land owners• Problem holders• Regulatory authorities• Planning authorities• Site users, workers, visitors• Financial community (banks, founders, lenders, insurers)• Site neighbours (tenants, dwellers, visitors)• Campaigning organisations and local pressure groups• Consultants, contractors, and possibly researchers

Stakeholders will have their own perspective, priorities, concerns andambitions regarding a site. The most appropriate remedial actions willoffer a balance between meeting as many of their needs as possible, inparticular risk management and achieving sustainable development,without unfairly disadvantaging any individual stakeholder. It is worthnoting at this point that for some stakeholders, the end conditions ofthe site are likely to be significantly more important than the actualprocess used to arrive at that condition. Such actions are more likely tobe selected where the decision-making process is open, balanced, andsystematic. Given the range of stakeholder interests, agreement ofproject objectives and project constraints such as use of time, moneyand space, can be a time consuming and expensive process. Seekingconsensus between the different stakeholders of a decision is importantin helping to achieve sustainable development.



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Risk communication and risk perception issues need specialconsiderations. Arguments and decisions need to be communicated in abalanced form to all stakeholders. A diverse range of stakeholders mayneed to reach agreement before specific remedial objectives can be set,for example, site owner, regulators, planners, consultants, contractors,site neighbours and perhaps others. Unsurprisingly once these remedialobjectives are set it may be hard to renegotiate them.In most practical situations, the members of the decision making teamwho are finally responsible for the choices of technology are thelandowner, the funder, the regulator and the service provider. All otherstakeholders are in a position of influence but in most cases their inputdoes not control the decision. Landowners provide finance to executeprojects. Regulators ensure compliance with acceptable environmentalquality standards. Service providers apply their expertise to deliverresults for both parties.

Cost effectiveness:

Costs of remediation depend on many factors and may be broken downinto mobilisation, operation (per unit volume or area treated),demobilisation, monitoring and verification of performance. Althoughdata can only be tentative, comparisons of indicative equivalent costsmay be a useful exercise in the early stages of consideration of differentremediation options. A range of indicative unit price costs is providedfrom one Member State in Table 1 (NATHANAIL, 2000). However, it isessential that site-specific factors be considered when estimatingremediation costs for a particular site.

Remediation technology Indicative unit price

Engineering capping £15-£30/ m²

Excavation and disposal to landfill £50/m3

Bioremediation £35-£45/ tonne



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Vitrification £40/ tonne

Incineration (special wastes) £750 - £1,000+/ tonne

Dechlorination £100 - £300/ tonne

Soil vapour extraction £40-60/m3 vadose zone

Soil washing £30 - £35/ tonne

Enhanced Thermal Conduction £35-45/m3

Oxidation of cyanide £400/ tonne

Solvent extraction and incineration £400/ tonne

Thermal desorption (including excavation andpre treatment)

£35 – 150/ tonne

Table 1: Indicative Costs of Remediation, UK experience ( Adapted fromNathanail, 2000).

A significant amount of remediation takes place as a result of theredevelopment of brownfield sites, either as a private commercialventure or as part of a wider regeneration initiative often supported bypublic funds. Brownfields remediation is discussed as a specific topic inthe Final Report of CLARINET (www.clarinet.at). Typically brownfieldsregeneration aims at stimulating wider economic regeneration by theattraction of new industries or other commercial activities. However,regeneration projects can also be suitable for "softer" end uses, forexample "country parks" in areas where the commercial drivers forredevelopment are less.The future use of land, and the money available for developing this use,is powerful controlling influences on the nature of remediationtechnologies that can be used. There is a constant pressure for lowerremediation costs, both to improve the economics of brownfield re-usefor "hard applications" such as housing or commerce; and for "softer"uses such as non-food (energy crops) agriculture. There is growingpressure to develop more cost-effective remediation technologies. Costeffectiveness is not just a product of reducing remediation costs, but



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also of finding remediation approaches that provide an additionalenhancement to the value of the land. ( The ABC model for brownfieldredevelopment)There are two further factors that impact on the cost-effectiveness ofremediation technologies. The first is the impact of waste legislationand regulation that, in certain nations, determines the fate ofcontaminated soil, and the potential for its treatment, disposal,recovery, recycling and reuse. The second is the designated land-use ofa remediated site; this has a profound effect on site values and hencethe options available for remediation.

Technical feasibility:

Remedial approaches can be categorised in a way that makes it easier tocompare their suitability in general for particular problems, and theirfeasibility for more specific site circumstances.A suitable technology is one that meets the technical and environmentalcriteria for dealing with a particular remediation problem. However, it isalso possible that a proposed solution may appear suitable, but is stillnot considered feasible , because of concerns about:

• Previous performance of the technology in dealing with a particularrisk management problem (in the countries);

• Ability to offer validated performance information from previousprojects;

• Expertise of the purveyor;• Ability to verify the effectiveness of the solution when it is applied;• Confidence of stakeholders in the solution;• Cost; and• Acceptability of the solution to stakeholders who may have

expressed preferences for a favoured solution or have differentperceptions and expertise.

In general, concerns over feasibility tend to be greater for innovativeremedial approaches, even if these have long standing track records in



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other countries. However, it is often these innovative solutions that areseen to offer more in terms of reducing wider environmental impactsand furthering the cause of sustainable development.

CLASSIFICATION OF SOIL REMEDIATION TECHNOLOGIES

Soil remediation technologies can be categorised in three broad groupsaccording to the fundamental principles involved in the contaminantremoval or treatment process.

Group 1 Mass Transfer Technologies

This group includes technologies that remove contaminant mass fromthe soil matrix by physical or chemical means, and subsequently treat ordestroy them in other process step. Such removal may or may notinvolve a change in the phase of the contaminant (e.g. from liquid togaseous phase). Strictly speaking, because these technologies alwaysinvlove transfer mass from soil solids, a change in phase will alwaysoccur. This group includes technologies that can be applied either insitu or ex situ, such as soil vapour extraction, low temperature thermaldesorption and solvent extraction. In Fig 2 an scheme of a thermaldesorption unit is shown.

Figure 2: Thermal Desorption Unit. A Mass Transfer Technology



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Group 2 Transformation/Destruction technologies

This group includes technologies that transform the contaminant massinto products of different chemical compositions by various chemical orbiochemical means. The purpose of these technologies is to transformthe contaminant into harmless by-products or into a new form that iseasier to treat or dispose. Such technologies include bioremediation andthermal destruction. In Figure 3 a simplified biological process is shown.

Figure 3: Simplified scheme of the biological process (In Spanish)

Group 3 Stabilisation/Fixation technologies

This group includes technologies that incorporate the contaminants intoa solid matrix so that leaching into the environment is reduced to levelsbelow those required by regulatory agencies. The incorporation of thecontaminant into a monolithic structure can be accomplishes by physicalor chemical means or by a combination of both. Such technologiesinclude cement or lime stabilisation, vitrification and other macro ormicroencapsulation techniques. In figure 4 a cement stabilisationprocess is shown



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Figure 4: Cement Stabilisation process of Contaminated Sediments( NY/Nj Port Authority)

TREATABILITY TEST FOR THE IMPLEMENTATION OF A REMEDIATIONTECHNOLOGY

From a technical standpoint, a remedial plan generally consists of fourdistinct phases:

Phase I Technology screening and selectionPhase II Testing of selected technologiesPhase III Pilot/field studyPhase iV Technology implementation

The primary focus of this part of the lessons is on phases I and II.



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Phase I (Technology screening and selection):

The objective of this phase of the study is to identify, in a relative shorttime, potentially effective technologies as candidates for bench scaletesting. Target clean up values are generally the most important criteriafor choosing potential treatment technologies. Cleanup levels must beclearly defined before beginning the selection and evaluation process.The fist step in this phase I requires site and soil characterisation. Thesite hydrogeologic characteristic and soil properties must be determinedand the extent and level of contamination defined. The second stepinvolves information studies and data collection related to thecontaminant type, site characteristics, and various treatmenttechnologies. Information can be obtained from many remedialtechnology investigations already implemented at industrial scale ( Youcan find a lot of additional information in www.clu-in.org).In step 3, lab scale (test tube/shaker flask) testing may be conducted aspart of the information gathering effort. These test are relatively fastand inexpensive and can provide valuable guidance for technologyselection. Carefully planned and executed lab experiments can be part



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of the initial technology screening an evaluation. The may also beperformed to determine key parameters such as biodegradability ofcontaminants and sorption characteristics of the soil.Step 4 assesses the need for pre-treatment and or post treatment of soiland other pollutant streams. For instance soil pre-treatment may berequired to remove debris and other large particles and to minimise theeffects of soil clodding, which may have a profound effect on theremoval efficiencies of mass transfer processesOnce all pertinent information is gathered and evaluated a decision isreached concerning which technologies will be tested at bench scalelevel. This is accomplished in steps 5 and 6. If more than one process isselected, as may be necessary in many cases, a testing protocol must bedeveloped for each selected technology.

Phase II (Bench-scale testing):

The primary objective of bench-scale testing is to assess theeffectiveness of a given remedial technology and generate data that willallow estimation of pertinent design parameters.A bench scale-scale study should produce reliable information at a lowcost and in relatively short time.. The average duration for bench scaletesting of physicochemical technology (soil washing, solventextraction...) is approximately four months.

The bench scale protocol should be flexible and allow exploration ofnew directions, provided that experimental findings obtained during itsexecution support such a deviations. The bench scale protocol shouldprovide details and step by step instructions of the following:

§ Materials and supplies§ Construction and equipment needed§ Sample handling and preparation§ Preparation of required solutions§ Experimental QA/QC plan (duplicates, control..)§ Scheduling and execution of the experimental procedures§ Sampling programme



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§ Development of analytical methods and analytical QA/QC§ Evaluation of technology effectiveness§ Estimation of scale-up parameters.

In table 2 typical design parameters Evaluated in a treatability studylisted by technology group is shown

Mass Transfer/Destructiontechnologies

Stabilisation/fixation technologies

Residence time Dose of immobilisation agentsTurbulence degree (mixing) Dose of other additivesSoil : contaminant ratio Ratio of soil to immobilising

agentsPh control Curing timeTemperature Ph controlFlow TemperatureBed height LeachingConcentration of desorptionenhancers

Permeability

Chemical dosages Durability ( freeze-thawconditions)

Soil:solution ratioNumber of stages

Table 2: Typical design parameters Evaluated in a treatability studylisted by technology group

In fig 5 the effect of additive in the Cd stabilisation process within a soilis shown



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Figure 5: Cement Stabilisation. Effect of additive in the Cdstabilisation process within a soil

RETENTIÓN DE Cd

0,0

20,0

40,0

60,0

80,0

100,0

120,0

0 10 20 30 40 50

% additive

% r

eten

ción



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PHYSICO-CHEMICAL REMEDIATION TECHNOLOGIES

SOIL WASHING

Contaminants sorbed onto fine soil particles are separated from bulksoil in an aqueous-based system on the basis of particle size. The washwater may be augmented with a basic leaching agent, surfactant, pHadjustment, or chelating agent to help remove organics and heavymetals.



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Ex situ soil separation processes (often referred to as "soil washing"),mostly based on mineral processing techniques, are widely used inNorthern Europe and America for the treatment of contaminated soil.Soil washing is a water-based process for scrubbing soils ex situ toremove contaminants. The process removes contaminants from soils inone of the followingtwo ways:

• By dissolving or suspending them in the wash solution (which canbe sustained by chemical manipulation of pH for a period of time);or

• By concentrating them into a smaller volume of soil throughparticle size separation, gravity separation, and attritionscrubbing (similar to those techniques used in sand and graveloperations).

Soil washing systems incorporating most of the removal techniquesoffer the greatest promise for application to soils contaminated with awide variety of heavy metal, radionuclides, and organic contaminants.Commercialization of the process, however, is not yet extensive.The concept of reducing soil contamination through the use of particlesize separation is based on the finding that most organic and inorganiccontaminants tend to bind, either chemically or physically, to clay, silt,and organic soil particles. The silt and clay, in turn, are attached to sandand gravel particles by physical processes, primarily compaction andadhesion. Washing processes that separate the fine (small) clay and siltparticles from the coarser sand and gravel soil particles effectivelyseparate and concentrate the contaminants into a smaller volume of soilthat can be further treated or disposed of. Gravity separation is effectivefor removing high or low specific gravity particles such as heavy metal-containing compounds (lead, radium oxide, etc.). Attrition scrubbingremoves adherent contaminant films from coarser particles. However,attrition washing can increase the fines in soils processed. The clean,larger fraction can be returned to the site for continued use.

Complex mixture of contaminants in the soil (such as a mixture ofmetals, nonvolatile organics, and SVOCs) and heterogeneous



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contaminant compositions throughout the soil mixture make it difficultto formulate a single suitable washing solution that will consistently andreliably remove all of the different types of contaminants. for thesecases, sequential washing, using different wash formulations and/ordifferent soil to wash fluid ratios, may be required.Soil washing is generally considered a media transfer technology. Thecontaminated water generated from soil washing are treated with thetechnology(s) suitable for the contaminants.The duration of soil washing is typically short- to medium-term.

Factors that may limit the applicability and effectiveness of the processinclude:

• Complex waste mixtures (e.g., metals with organics) makeformulating washing fluid difficult.

• High humic content in soil may require pretreatment.• The aqueous stream will require treatment at demobilization.• Additional treatment steps may be required to address hazardous

levels of washing solvent remaining in the treated residuals.• It may be difficult to remove organics adsorbed onto clay-size

particles.

CHEMICAL EXTRACTION



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Chemical extraction does not destroy wastes but is a means ofseparating hazardous contaminants from soils, sludges, and sediments,thereby reducing the volume of the hazardous waste that must betreated. The technology uses an Extracting chemical and differs fromsoil washing, which generally uses water or water with wash-improvingadditives. Commercial-scale units are in operation. They vary in regardto the Chemical employed, type of equipment used, and mode ofoperation.Physical separation steps are often used before chemical extraction tograde the soil into coarse and fine fractions, with the assumption thatthe fines contain most of the contamination. Physical separation canalso enhance the kinetics of extraction by separating out particulateheavy metals, if these are present in the soil.

Acid Extraction

Acid can also be used as the extractant. Acid extraction useshydrochloric acid to extract heavy metal contaminants from soils. In thisprocess, soils are first screened to remove coarse solids. Hydrochloricacid is then introduced into the soil in the extraction unit. The residencetime in the unit varies depending on the soil type, contaminants, andcontaminant concentrations, but generally ranges between 10 and 40minutes. The soil-extractant mixture is continuously pumped out of themixing tank, and the soil and extractant are separated usinghydrocyclones.When extraction is complete, the solids are transferred to the rinsesystem. The soils are rinsed with water to remove entrained acid andmetals. The extraction solution and rinse waters are regenerated usingcomercially available precipitants, such as sodium hydroxide, lime, orother proprietary formulations, along with a flocculent that removes themetals and reforms the acid. The heavy metals are concentrated in aform potentially suitable for recovery. During the final step, the soils aredewatered and mixed with lime and fertilizer to neutralize any residualacid



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Solvent Extraction

Solvent extraction is a common form of chemical extraction usingorganic solvent as the extractant. It is commonly used in combinationwith other technologies, such as solidification/stabilization,incineration, or soil washing, depending upon site-specific conditions.Solvent extraction also can be used as a stand alone technology in someinstances. Organically bound metals can be extracted along with thetarget organic contaminants, thereby creating residuals with specialhandling requirements. Traces of solvent may remain within the treatedsoil matrix, so the toxicity of the solvent is an important consideration.The treated media are usually returned to the site after having met BestDemonstrated Available Technology (BDAT) and other standards.The duration of operations and maintenance for chemical extraction ismedium-term



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ESTABILIZATION TECHNOLOGIES

Contaminants are physically bound or enclosed within a stabilized mass(solidification), or chemical reactions are induced between thestabilizing agent and contaminants to reduce their mobility(stabilization).S/S contaminants are physically bound or enclosed within a stabilizedmass (solidification), or chemical reactions are induced between thestabilizing agent and contaminants to reduce their mobility(stabilization). Ex situ S/S, however, typically requires disposal of theresultant materials. Sometimes, material can be replaced on site.There are many innovations in the stabilization and solidificationtechnology. Most of the innovations are modifications of provenprocesses and are directed to encapsulation or immobilizing the harmfulconstituents and involve processing of the waste or contaminated soil.Nine distinct innovative processes or groups of processes include: (1)bituminization, (2) emulsified asphalt, (3) modified sulfur cement, (4)polyethylene extrusion, (5) pozzolan/Portland cement, (6) radioactive



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waste solidification, (7) sludge stabilization, (8)soluble phosphates, and(9) vitrification/molten glass.Typical ex situ S/S is a short- to medium-term technology.

Sulfur cement

Modified sulfur cement is a commercially-available thermoplasticmaterial. It is easily melted (127° to 149° C (260° to 300° F)) and thenmixed with the waste to form a homogenous molten slurry which isdischarged to suitable containers for cooling, storage, and disposal. Avariety of common mixing devices, such as, paddle mixers and pugmills, can be used. The relatively low temperatures used limit emissionsof sulfur dioxide and hydrogen sulfide to allowable threshold values.

Portland cement

Pozzolan/Portland cement process consists primarily of silicates frompozzolanic-based materials like fly ash, kiln dust, pumice, or blastfurnace slag and cement-based materials like Portland cement. Thesematerials chemically react with water to form a solid cementious matrixwhich improves the handling and physical characteristics of the waste.They also raise the pH of the water which may help precipatate andimmobilize some heavy metal contaminants. Pozzolanic and cement-based binding agents are typically appropriate for inorganiccontaminants. The effectiveness of this binding agent with organiccontaminants varies.

The target contaminant group for ex situ S/S is inorganics, includingradionuclides. Most S/S technologies have limited effectiveness againstorganics and pesticides, except vitrification which destroys most organiccontaminants




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• Environmental conditions may affect the long-termimmobilization of contaminants.

• Some processes result in a significant increase in volume (up todouble the original volume).

• Certain wastes are incompatible with different processes.Treatability studies are generally required.

• Organics are generally not immobilized.• Long-term effectiveness has not been demonstrated for many

contaminant/process combinations.

INCINERATION



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High temperatures, 870-1,200 °C (1,600- 2,200 °F), are used tocombust (in the presence of oxygen) organic constituents in hazardouswastes.

High temperatures, 870 to 1,200 °C (1,400 to 2,200 °F), are used tovolatilize and combust (in the presence of oxygen) halogenated andother refractory organics in hazardous wastes. Often auxiliary fuels areemployed to initiate and sustain combustion. The destruction andremoval efficiency (DRE) for properly operated incinerators exceeds the99.99% requirement for hazardous waste and can be operated to meetthe 99.9999% requirement for PCBs and dioxins. Off gases andcombustion residuals generally require treatment.

Circulating Bed Combustor (CBC)

Circulating bed combustor (CBC) uses high velocity air to entraincirculating solids and create a highly turbulent combustion zone thatdestroys toxic hydrocarbons. The CBC operates at lower temperaturesthan conventional incinerators (1,450 to 1,600 °F). The CBC's highturbulence produces a uniform temperature around the combustionchamber and hot cyclone. The CBC also completely mixes the wastematerial during combustion.

Infrared Combustion

The infrared combustion technology is a mobile thermal processingsystem that uses electrically-powered silicon carbide rods to heatorganic wastes to combustion temperatures. Waste is fed into theprimary chamber and exposed to infrared radiant heat (up to 1,850 °F)provided by silicon carbide rods above the conveyor belt. A blowerdelivers air to selected locations along the belt to control the oxidation rate of the wastefeed.

Rotary Kilns

Commercial incinerator designs are rotary kilns, equipped with anafterburner, a quench, and an air pollution control system. The rotary



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kiln is a refractory-lined, slightly-inclined, rotating cylinder that servesas a combustion chamber and operates at temperatures up to 980 °F(1,800 °F).Incinerator off-gas requires treatment by an air pollution-controlsystem to remove particulates and neutralize and remove acid gases(HCl, NOx, and SOx). Baghouses, venturi scrubbers, and wet electrostaticprecipitators remove particulates; packed-bed scrubbers and spraydriers remove acid gases.Incineration, primarily off-site, has been selected or used as theremedial action at more than 150 Superfund sites. Incineration issubject to a series of technology-specific regulations, including thefollowing federal requirements: CAA (air emissions), TSCA (PCBtreatment and disposal), RCRA (hazardous waste generation, treatment,storage, and disposal), NPDES (discharge to surface waters), and NCA(noise).The duration of incineration technology ranges from short- to long-term

Incineration is used to remediate soils contaminated with explosives andhazardous wastes, particularly chlorinated hydrocarbons, PCBs, anddioxins.


• Only one off-site incinerator is permitted to burn PCBs anddioxins.

• There are specific feed size and materials handling requirementsthat can impact applicability or cost at specific sites.

• Heavy metals can produce a bottom ash that requiresstabilization.

• Volatile heavy metals, including lead, cadmium, mercury, andarsenic, leave the combustion unit with the flue gases and requirethe installation of gas cleaning systems for removal.

• Metals can react with other elements in the feed stream, such aschlorine or sulfur, forming more volatile and toxic compoundsthan the original species. Such compounds are likely to be short-



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lived reaction intermediates that can be destroyed in a causticquench.

• Sodium and potassium form low melting point ashes that canattack the brick lining and form a sticky particulate that fouls gasducts

PERMEABLE REACTIVE BARRIERS (PRB) AS AN ALTERNATIVE REMEDIALOPTION

The extraction and treatment of contaminated ground water athazardous waste sites continues to be an extremely costly endeavor, theeffectiveness of which is often dubious at best. Permeable reaction wallsare an emerging technology for the treatment of contaminatedgroundwater. Successful treatment of contaminated groundwater usingthis technique requires that the contaminant be rendered innocuous orimmobile during transport through the in-situ treatment zone. Theextent of treatment, and the success of the permeable barrier system



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depends on the nature of the contaminant, the selection of the reactivematerial, the physical design of the treatment system, and natural siteconditions. Instead of trying to remove the contaminated water from thesubsurface for above-ground treatment, the emplacement of apermeable reactive geochemical barrier which intercepts thecontaminated plume and transforms the contaminant to a non-toxicform is attractive for a number of reasons. First, the in situ approachrequires no above ground treatment facilities and the space can bereturned to its original use. Second, there is no need for expensiveabove-ground treatment, storage, transport or disposal. Third, there islittle or no operation and maintenance costs.

A Permeable Reactive Barrier is an engineered treatment zone of reactivematerial(s) that is placed in the subsurface in order to remediatecontaminated fluids as they flow through it. A PRB has a negligibleoverall effect on bulk fluid flow rates in the subsurface strata, which istypically achieved by construction of a permeable reactive zone, or byconstruction of a permeable reactive ‘cell’ bounded by low permeabilitybarriers that direct the contaminant towards the zone or reactive media”

A PRB is built by digging a long, narrow trench in the path of thepolluted groundwater. Thetrench is filled with a reactive material thatcan clean up the harmful chemicals. Iron, lime-stone,and carbon arecommon types of reactive materials that can be used. The reactivematerials may be mixed with sand to make it easier for water to flowthrough the wall, rather than around it. At some sites, the wall is part ofa funnel that directs the polluted groundwater to the reactive part of thewall. The filled trench or funnel is covered with soil, so it usually cannotbe seen above ground.

The material used to fill the trench depends on the types of harmfulchemicals in the groundwa-ter.

Different materials clean up pollution through different methods by:

• Trapping or sorbing chemicals on their surface. For example, carbon hasa surface that



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chemicals sorb to as groundwater passes through.• Precipitating chemicals that are dissolved in water. This means thechemicals settle out of the groundwater as solid materials, which gettrapped in the wall. For example, limestone can cause dissolved metals toprecipitate.• Changing the chemicals into harmless ones. For example, iron canchange some types of solvents into harmless chemicals.• Encouraging tiny bugs or microbes in the soil to eat the chemicals. Forexample, nutrients and oxygen in a PRB help the microbes grow and eatmore chemicals. When microbes com-pletely digest the chemicals, they canchange them into water and harmless gases such as carbon dioxide.

The most common of the permeable barrier walls is the Iron TreatmentWall. It is made up of zero-valent iron or iron-bearing minerals thatreduce chlorinated contaminants such as perchloroethylene (PCE). Asthe iron is oxidized, a chlorine atom is removed from the compoundusing electrons supplied by the oxidation of iron. The chlorinatedcompounds are reduced to nontoxic by-products.

Considerable research during the past several years has focused on thedegradation of chlorinated solvents, such as TCE and PCE, by reactionsat the surfaces of Fe(0). Although met with initial skepticism, thedegradation process is now widely accepted as abiotic reductivedehalogenation, involving corrosion of the Fe(0) by the chlorinatedhydrocarbon.Iron corrosion processes in aqueous systems have been studiedextensively. Until recently, the fate of corrosion processes in diluteaqueous concentrations of chlorinated solvents acting as the oxidizingagents have not been investigated. The net reductive dechlorinationreaction promoted by Fe(0) (Equation 3) may be viewed as the sum ofanodic and cathodic reactions occurring at the iron metal surface(Equations 1 and 2, respectively), resulting in hydrocarbon products ifthe dechlorination proceeds to completion.

Fe 0→ Fe 2+ + 2e - Anodic Reaction (1)RCl + 2e - + H +→ RH + Cl - Cathodic Reaction (2)



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Fe 0 + RCl + H +→ Fe 2+ + RH + Cl - Net Reaction (3)

Under aerobic conditions, dissolved oxygen is usually the preferredelectron acceptor and can compete with the chlorinated hydrocarbon asthe favored oxidant (Equation 4). Indeed, chlorinated hydrocarbons suchas PCE and carbon tetrachloride have oxidizing potentials very similar tothat of O 2 . When sufficient oxygen is present, the Fe 2+ generated inEquation 4 further oxidizes to Fe 3+ (Equation 5) and can precipitate asferric hydroxide or (oxy)hydroxides (Equation 6) at the elevated pHtypical of corroding Fe systems. Corrosion of the iron can generate largeamounts of iron oxides and (oxy)hydroxide precipitates that can exertsignificant additional chemical and physical effects within the reactivesystem. The rapid consumption of dissolved oxygen at the entrance toan iron system (column or barrier) has been shown to result in theseprecipitates that might impact a system’s hydraulic performance at itsupgradient interface.

2Fe 0 + O 2 + 2H 2 O → 2Fe 2+ + 4OH - (4)4Fe 2+ + 4H + + O 2 → 4Fe 3+ + 2H 2 O (5)Fe 3+ + 3OH -→ Fe(OH)3(s) (6)Fe 0 + 2H 2 O → Fe 2+ + H 2 + 2OH - (7)Fe 2+ + 2OH -→ Fe(OH)2(s) (8)

Anaerobic corrosion of iron by water (Equation 7) proceeds slowly. Bothreactions 4 and 7 result in an increased pH in weakly buffered systems,yielding ferric (oxy)hydroxides in aerobic systems (Equation 6) andferrous (oxy)hydroxides in anaerobic systems (Equation8). The aqueouscorrosion of iron is mediated by the layer of oxides, hydroxides andoxyhydroxides that are present at the iron-water interface. Theformation of these precipitates might further occlude the iron surface



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and affect its reduction-oxidation properties. However, this passivecoating appears to be converted to magnetite, which is non-passivating,and seems to allow sufficient contaminant degradation rates that can besustained over years of operation in the ground.

REFERENCES AND BIBLIOGRAPHY:

http://www.clarinet.at/library/WG7_Final_Report.pdf

CANADIAN COUNCIL OF MINISTERS OF THE ENVIRONMENT (1994). SubsurfaceAssessment Handbook for Contaminated Sites.

CANADIAN PETROLEUM PRODUCTS INSTITUTE (1991). Manual of PetroleumContaminated Soil Treatment Technologies. CPPI Report No. 91-9.

MALROZ ENGINEERING INC. (1994). Evaluation of Remediation Options for PetroleumContaminated Site.

MALROZ ENGINEERING INC. (1996). Site Investigation and Remediation ofContaminated Sites. Course notes.

U.S. ENVIRONMENTAL PROTECTION AGENCY (1994). Innovative TreatmentTechnologies. Annual Status Report. Sixth Edition.

U.S. ENVIRONMENTAL PROTECTION AGENCY (1993). Remediation TechnologiesScreening Matrix and Reference Guide. Version I.



35

U.S. ENVIRONMENTAL PROTECTION AGENCY (1994). Superfund Innovative TechnologyEvaluation Program, Technologies Profiles. Seventh Edition.

BARDOS, R. P.; BOYLE, C. & JOHNSON, S. (2001): Remediation Treatment Solutions forRedevelopment, Presented at Remediation Treatment Solutions for Redevelopment,Presented at: Brownfield Sites and Development 2001 – Meeting the Challenges, TheRoyal Society, London, 24 May 2001

BARDOS, R. P.: MARIOTTI, C.; MAROT, F.; NORTCLIFF, S.; SULLIVAN, T. & LEWIS, A.(2001): Review of Decision Support Tools and their use in Europe. Report of CLARINETWorking Group 2. In preparation, will be available from www.clarinet.at

BARDOS, R. P.; MARTIN, I. D. & KEARNEY, T. (1999): Framework for EvaluatingRemediation Technologies. Presented at: IBC's 10th Conference. Contaminated Land. July5th, Royal Marsden NHS Trust, London. Pub. IBC Technical Services Ltd, Gilmoora House,57-61 Mortimer Street, London, W1N 7TD

BARDOS, R. P.; MORGAN, P. & SWANNELL, R. P. J. (2000): Application of In SituRemediation Technologies – 1. Contextual Framework. Land Contamination andReclamation 8 (4) 1-22

BRUNDTLAND, G. H. (1987): Our Common Future. World Commission on Environmentand Development.

CLARINET / NICOLE (1998): CLARINET / NICOLE Joint Statement: Better DecisionMaking Now. October 1998. Available from http://www.nicole.org

CRUMBLING, D. (2000): “Improving the cost-Effectiveness of Hazardous Waste SiteCharacterisation and Monitoring,” US EPA Technology Innovation Office, Washington,D.C.

http://clu-in.org/tiopersp/default.htm

ELLEFSEN, V.; WESTBY, T. & ANDERSEN, L. (2001): Sustainability: The EnvironmentalElement – Case Study 1. Presentation at The CLARINET Final Conference in Vienna, June21-22 Proceedings; Umweltbundesamt, Austria, 2001.

MARTIN, I. & BARDOS, P. (1996): A Review of Full Scale Treatment Technologies for theRemediation of Contaminated Soil. Report for the Royal Commission on EnvironmentalPollution. EPP Publications, 52 Kings Road, Richmond, Surrey TW10 6EP. E-mail:[email protected]

NATHANAIL, C. P. (2000:): Cost of remediation. Environment Business, May 2000.

NATHANAIL, J.; BARDOS, R. P. & NATHANAIL, P. (2001): Contaminated LandManagement: Ready Reference. EPP Publications and Land Quality Press in associationwith r3 Environmental Technology Limited and Land Quality Management Ltd at theUniversity of Nottingham. EPP Publications, 52 Kings Road, Richmond, Surrey TW106EP. [email protected]



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OKX, J. (2001): Sustainability: Integrated Assessment – Case Study 3. Presentation atThe CLARINET Final Conference in Vienna, June 21-22, Proceedings;Umweltbundesamt, Austria, 2001

U. S. EPA (1999): United States Environmental Protection Agency, (1998): Roadmap toUnderstanding Innovative Technology Options for Brownfields Investigation andCleanup, Second Edition. EPA 542-B-99-009, OSWER 5102G.

U.S. EPA (1998): NATO CCMS’ Pilot Studies. EPA/542/RE-98/002.

U.S. EPA (2000): NATO CCMS; Evaluation of Demonstrated and Emerging Technologiesfor the Treatment and Clean Up of Contaminated Land and Groundwater. Pilot Studyreport 1985-2000. 2000 Update.

VIK, E. A. & BARDOS, P. (2001): Summary of CLARINET’s key findings on RiskManagement Solutions and Decision Support in Europe. Current State of the Art inEurope. Presentation at CLARINET's Final Conference on Sustainable Management ofContaminated Land, Vienna, Austria, 21-22 June, Proceedings; Umweltbundesamt,Austria, 2001

GOROSTIZA, I.; SUSAETA, I.; BILBAO, V.; DÍAZ, A. I.; SAN VICENTE, A. I.; and SALAS,O.(1998). Biological removal of wood preservative (PCP) wastes in soil. Autochthonousmicroflora and effect of compost addition. In: Proceedings of The Sixth InternationalFZK/TNO Conference on Contaminated Soil - ConSoil’98, Edinburg, UK, pp. 1149-1150, Thomas Telford, London.

SALAS, O.; SAGARDUY, M.; SAN VICENTE, A.I.;DIAZ,A.I.; DE LA QUINTANA,E.; andSUSAETA,I.(1998).Recovery of HCH (Hexachlorocyclohexne) contaminated soils usingsolvent extraction Technologies.. In: Proceedings of The Sixth International FZK/TNOConference on Contaminated Soil - ConSoil’98, Edinburg, UK, pp. 1151-1152, ThomasTelford, London.

ACILU, M, BERGANZA, J. Y SUSAETA I (1999) " Supercritical fluid extraction:Revalorization od agrofood by-products and other environmental applications" InGlobal Symposium on Recycling waste treatment and clean technology" Vol III. 1895-1902.

SALAS O, GASCON, J.A, SUSAETA, I.,(1998) " Treatability estudies on solvent extractiontechnologies:Bench scale evaluation. 5 th International HCH and Pesticides Forum. 153-158

SALAS O , GASCON, J.A, SUSAETA, I.,(2000) " Solvent Extraction ofHexachlorocyclohexane (HCH) and Heavy metals contaminated soils in the BasqueCountry " In Case Studies in the Remediation of Chlorinated and RecalcitrantCompounds " 293-300



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J.A. GASCÓN, V. MARINA, O. SALAS, I. SUSAETA, I. (2000)" Two-phase solventextraction of Polychlorinated Biphenyls (PCB) and heavy metals (Cd, Cu) fromcontaminated soils” Land Contamination and Reclamation 8 (4) 281-286

GARAY I., ACILU M., SUSAETA, I. (2000)" PCB Separation from transformer oils.Theoretical approach. Cleaning up of transformer solid elements by SCCO2".Proceedings of the 7 th Meeting on Supercritical fluids” Volume 2, 853-858

DIAZ A.I.,ZURUTUZA A.,ETXEBARRIA,A., SUSAETA I. And GOROSTIZA I. (2001) “Assessment of biodegradation as an additional treatment mechanism in a TESVEsystem. Proceedings of the First European Bioremediation Conference. 13-16.

ZALLO, M.; SUSAETA, I.; BARGOS, Tx.; and GOROSTIZA, I. (1996). “Evaluation of theperformance of two commercial starters on the bioremediation of soils contaminatedwith mineral oil and HCH (Hexachlorocyclohexane)”. Biotechnology Letters 18: 339-342.

GARAY, M. ACILU, AND I. SUSAETA (2002) Removal of PCBs from transformers (oils andsolid parts) by Supercritical Fluid Extraction (SFE) I. Paper 2H-18, in: A.R. Gavaskar andA.S.C. Chen (Eds.), Remediation of Chlorinated and Recalcitrant Compounds—2002.Proceedings of the Third International Conference on Remediation of Chlorinated andRecalcitrant Compounds (Monterey, CA; May 2002). ISBN 1-57477-132-9, publishedby Battelle Press, Columbus, OH,

BURMEIER, H., “Evaluation of Demonstrated and Emerging Technologies for theTreatment of Contaminated Land and Groundwater – Phase III, Special Session onTreatment Walls and Reactive Barriers”, North Atlantic Treaty Organization’s Committeeon the Challenges of Modern Society (NATO/CCMS), EPA 542-R-98-003, Report #229,p. 3, May 1998.

soil remediation technologies - hasiera - … of natural resources in an european context ......

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