Using Fenton's Reagent · Acknowledgernents 1 would like to thank Dr. Ken Reimer, the director of the Environmental Sciences Group and my thesis advisor, and Dr. Ron Weir, the Dean

Chemical Remediation of PCB Contaminated Soils

Using Fenton's Reagent

Jason P. Stow

A Thesis submitted

to the Department of Chernistry and Chemical Engineering

Royal Military College of Canada

Kingston, Ontario

In partiai filfilment of the requirements for

the degree

Master of Engineering

April 1997

6 Copyright by J.P. Stow 1997 This thesis may be used withio the department of National Defence but copyright for open publication remains the property of the author.

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Polychlorinated biphenyls (PCBs) are persistent organic contaminants that are prone to bioaccumulation and biomagnification; the effects of which are amplifieci in the arctic ecosystem. PCB contaminated soils in the Canadian Arctic present a difficult remediation problem. For the most part contamination is found in areas around abandoned and presentiy operating military installations at remote arctic sites. The diffidty of transportation to and fiom these sites, lack of existing infrastructure and a short work season (aaywhere Born one to three months) requires that any remediation strategy be relatively low tech and on-site. Current methods that are available for soil remediation include incineration and thermal desorption; the first involves transportatioo of materials to an approved incineration facility in the south, and the second involves the nansponation of heavy, expensive equipment to remote locations.

Fenton's reagent is a combination of hydrogen peroxide and ferrous iron that produces hydroxyl radicals that are capable of non-specific oxidation of organic compounds including PCBs. Laboratory experiments were carried out to deterrnine if

Fenton's reagent could degrade the PCB mixture Aroclor 1260 in weathered soils collected at an abandoned radar station in Saglek, Labrador. In addition to the laboratory experiments, scaled-up field experiments were conducted on-site at Saglek. Soi1 washing experiments were also perfomed in both the laboratory and at Saglek.

The laboratory experhents revealed an interesting anornaly, not previously reported, that impacts significantly on the application of standard analyticai procedures to

wet Fenton's-treated soils. Analysis of such samples that had not been completely dried led to unreliable results.

A process was developed, whereby soils were treated three consecutive times with doses of 22% (wt.%) H202 and 0.01 M ~ e ~ + . It was detennined that such a treatment in combination with soi1 washing was capable of reducing PCB concentrations in 80% of the overall soil rnass to below 50 ppm The results of the laboratory studies also suggest that higher levels of contamination could be successfully dealt with. Field work revealed that laboratoty processes could be successfùlly scaled up using relatively "low tech", inexpensive, equipment. The application of Fenton's reagent could result in significant cost savings, associated with site remediation.

Acknowledgernents

1 would like to thank Dr. Ken Reimer, the director of the Environmental Sciences Group and my thesis advisor, and Dr. Ron Weir, the Dean of Graduate Studies, whose collective efforts made it possible for me to undertake graduate work at RMC. Spetial

thanks goes to Dr. Ken Reimer for providing me with such an interesting and challenging project.

For her much appreciated guidance, I would like to thank Dr. Aliison Rutter who oversaw this research every step of the way. Thanks also goes to Dr. Stephen hm for his helpful advice, and tolerance (of my presence in the analytical lab). For assistance in

laboratory analysis 1 would like to acknowledge the efforts of the Environmental Sciences

Group halytical Lab staff, as well as the staff of the Queen's Analytical Services Unit. Finally, a large thanks goes out to the entire Environmental Sciences Group who working with has been both educational and a great pleasure.

The Saglek field work would not have been possible without the combined efforts of Jemifer Rogers, the field team leader; Doug Noonan and Sandra Englander who were responsible for the logistical success of the field expedition. On-site, the helpful efforts of Todd Adamsson and Dr. Allison Runer, especially in sieving al1 that soil, were greatly appreciated.

For the production of this thesis 1 would like to th& Dr. Allison Rutter, Dr. Ken Reimer, and Marjorie Pine for their helpful comrnents.

Finally I would like to acknowledge the North Waming System Office of the Department of National Defence, and the Department of Indian and Northem Affairs for their continued financial support of this work.

Table of Contents

ACKNOWLEDGEMENTS .......................... ... ........................................................................ U

TABLE OF CONTENTS .......... ..... .... ..................................................................................... III

LIST OF TABLES ........................... ., ................................................................................... VII

LIST OF FIGURES ................................................................................................................. IX

LIST OF PHOTOGRAPHS ..................... .., .....,.................... ............................................... iX

LIST OF MAPS ....................................................................................................................... iX

1 . INTRODUCTION ................................*.............,................................................................... 1

2 . BACKGROUM) ......................... .... ....................................................................................... 3

2.1 PCBS: GENEUL NFORMATION ..................................................................................... 3

2.2 ENVIRONMENTAL CONCERNS .............................................................................................. 4

2.3 REGULATION OF PCBS .................. ,., ................................................................................... 5

2.4 DETER,M INATION OF PCB CONCENTRAïïON ......................................................................... 5

2.5 REMED~A~QN OF PCB CONTAMINATED SOU ...................................................................... 7

2.5.1 Contaminant destntcrio~l teclinologies ...................................................................... 8

2.5.2 Ph-vsical separotiori t ech ologies ............................................................................. 10

2.5.3 Contaiiimenr ............................................................................................................ 17

2.6 D E S C ~ O N OF r n y SITE ............................................................................................. 13

2.7 FENTON'S REAGENT .......................................................................................................... 18

......................................................................... 2.7.1 PCB oxidation by hydroqf radicab 18

......................................................................................... 2.7.2 Basic Fentoti S c8ernirtt-y 19

.................................................................................. 2.7.3 Hydroxyf radical scavenging 2 0

7 7 2.7.4 Sources of iron caraiysrs in the Fenton reaction ................... ..,. ............................ .-

............................................................................. 2.7.5 LW enhanced Fenton S rreatmenr 24

27.6 Treatmettr of orgonic coritaminancs in soif using Fenzon S reagent .......................... -34

.......................................................................................................................... . 3 METHODS 27

3.1 GENERAL EXPERIMENTAL PROCEDURES ............................................................................. 27

3.1.1 Soif washing ........................................................................................................ 7 7

3.1.2 Fenron 's reagent ..................................................................................................... 28

................................................................................ 3.2 GENERAL A N A L ~ C A L PROCEDURES 2 9

3.2. I Analysis o/PCB concentraliori ................................................................................. 29

3.2.2 Loss on ignition ................................................................................................. 3 2

............................................................................................. 3.3 E V A ~ U A ~ O N OF RESULE 3 2

............................... 4. FENTON'S REAGENT EXPERIMENTS: LABORATORY SCALE 33

4.1 OVERV~EW OFRESEARCH .............................................................................................. 3 3

.......................................................................................... 4.2 ~ L T S AM) DISCUSSION - 3 4

4.2.1 Soil wmhing ........................................................................................................... 3 4

4.2.2 Fenton 's reugent ..................................................................................................... -35

............................................................ 4.3 CONCLUSIONS OF TKE LABORATORY EXPERIMENTS 49

................................................................................................... . 5 PCB MASS BALANCE 5 0

................................................................................................. 5.3 &SULTS AND DISCUSSION 5 1

.............................................. ............................ 5.3. f Removitig PCB escape path wa-vs ,... 51

................................................................................. 5.3.2 Additional Soxhlet extracrion 5 3

............................ ............................ 5.3.3 Cornplete drying of samples prior ro anatysis ,, 5 5

............................................................................... 5.3.4 Incomplere Soxlilet extractions 5 7

5.4 CONCLUSION OF THE PCB MASS BALANCE INVESrrGATION ................... .. ........................ 6 0

6 . SAGLEK CHJIMICAL REMEDIATION EXPERLMENTS .............................................. 61

................................................................................................................ 6.2 EXPE~UMENTAL 62

6.2.1 Soit source ............................................................................................................... 62

......................................................................................... 6.2.2 Soif washing experirnenrr 62

............................................................................................. 6.2.3 Merhods and marerials 63

............................................................................................... 6.2.4 EIecnic stirrer mixer 64

.............................................................................................. 6.2.5 Cerneut mber reacfor 64

................................................................................................. 6.2.6 Scale-up experimenr 67

................................................................................................... 6.2.7 In-situ experimenu 67

.......................................................................................... 6.2.8 Summary ofexperimenls 68

.......................................................................................................................... 6.3 RESLJL.TS 69

6.3.1 Soil washing ............................................................................................................. 69

........................................................................................................ 6.3.3 Stired reacror 6 9

........................................................................................................... 6.3.3 Cement mixer 72

6.3.4 Scale-up experimettt ................................................................................................. 73

v

............................................................................................... 6.4.2 Fenton S wperimenis 75

................................................ 6.4.3 Treatrne~it comparison: Type I vs . Type 2 vs . Type 3 77

.............................................................................. . 64.4 Cemenr mixer vs electric stirrer 78

.............................................................................. 6.4.5 Reductions may be exaggerared 8 0

.................................................................................................. 6.4.6 PCB mars balance 8 2

6.4.7 Organic conzenr of saniples as determined @ loss orr ignition atiaiysis ................... -84

6.4.8 Settling of soilpanicfes over time .......................................................................... 85

6.4.9 Tire scale-up experirnerit ......................................................................................... 8 6

6.4.10 In-situ Fenton 's experimenrs .............................................................................. 86

........................................ ......... 6.5 CONCLUSIONS OF THE SAGLEK FiEL.D EXPENMENTS ,, 8 7

................................... 7 . CONCtUSIONS AND RECOMMENDATIONS ...... .................O.. 88

7.1 DES~GN OF FUTURE SCALE-UP EU'ERIMENT ................................................................... 8 9

8 . REFERENCES .............. .......... .......................................................................................... 90

List of Tables

....................... . .................................. T ~ L E 4- 1 REsUtTS OF SOL WASHING EXPERIMENTS ON SG4 SOIL ,. 34

........................... TABLE 4.2 . S ~ M A R Y OF EXPEREMEN'TAL RESULTS FROM BATCH SG.4. 5/16 SIEVED SOL 35

TABLE 4.3 . SUMMARY OF EXPERlMENTAL RESULTS FROM BATCH SAGJO+. ~ H # I O (2MM) SIEVED S O L .. 38

TABLE 4.5 . RESULTS OF LONG TERM EXPERIMENT ......................... ..,. ....................................................... 44

TABLE 4.6 . REWLTS OF HARSH TREATMENT EXPERIMENTS ......................................................................... 47

TABLE 5- 1 . EXPERMENT SG- 1 (96-SG-84 SOL) ...................................................................................... 52

TABLE 5 4 . EXPEIUMENT SG4 (96-SG-8 1 son) ....................................................................................... 56

................................ . . TABLE 5.5 E X P ~ SG.7. COMPARISON OF DRY VS WET PCB SOIL EXTRACTION 56

TBLE 6- 1 . RESULTS OF WASHiNG EXPE3UMENT. 10 KG OF SMALL STONES WASHED 3 TiMES FOR 10 .MN WI?)I

....................................... 1 O L OF WATE R. (CONCENTRATIONS OF AROCLOR 1260 EXPRESSED IN PPM) 69

TABLE 6.2 . RESULTS OF FIELD EXPERIMENTS TREATiNG 6 KG OF HIGHLY CONT'AMINAED BATCH 1 SOIL IN THE

.................... ELEC~UC SI~RRER REACTO R. ( C O N C ~ T I O N S OF AROCLOR 1260 MPRE~~ED IN PPM) 71

TABLE 6.3 . RESULTS OF REPEATED DAILY SAMPUNG OF SET # I . SEQUENTIAL AND SET #2. 0% CONTROL . (CONCENTRATIONS OF AROCLOR 1260 EXPRESSED IN PPM) .............................................................. 71

TABLE 6.4 . RESULTS OF FIELD EXPERlMENTS TREATING 6 KG OF LESSER CONTAMINATED SOIL IN THE ELEClWC

S~IRRER REACTOR (CONCENTRATIONS OF AROCLOR 1 260 EXPRESSED M PPM) .................................. - 7 1

vii

TABLE 6-5. RESULE OF FELD EXPERMEN-E SET# 5 ' I R E A ~ G 10 KG OF HIGHLY CONTAMNATED SOIL IN THE

......................... CE!MENï MIXER REACTOR (CONCENTRATIONS OF AROCLOR 1260 EXPREssED iN PPM) 73

TABLE 6-6. REsULTS O f FIELD EXPERlMENTS SET## 6 TREATING IO KG OF HIGHLY CONTAMINATED SOIL IN THE

CEMENT ;MIXER REACTOR (CONCENTRATIONS OF AROCLOR 1260 EXPRESSED iN PPM) ......................... 73

TABLE 6-7. RESUL'IS OF TREATING 40 KG OF COARSE SEWD, BATCH 4 SOU., IN THE CENENT MIXER.

(CONCENTRATIONS OF AROCLOR 1260 EXPRESSED DIC PPM) .................................................... 7 4

T ~ L E 6-8, RE~ULT OF IN-SITU FENTON'S DBERIMENTS. (CONCENTRATIONS OF AROCLOR 1260 EXPRESSED iN

PPM) ..................... .,,. ................................................................................................................. 7 5

TABLE 6-9. THE DIFFERENCE BETWEEN CONCENTRATIONS IN DRY S O L AND O% CONlROL EXPERIMENTS.

(CONCENTRATIONS OF AROCLOR 1260 EXPREssED iN PPM) .............................................................. 83

TULE 6-1 O. RELATIONSHIP BElWEEN ORGANIC CONTENT AND REDUCTION OF PCBS (LOI- LOSS ON

IGNITION) (CONCENTRATIONS OF AROCLOR 1260 EXPRESSED EN PPM) .......................... ., ............ 84

viii

List of Figures

FIGURE 2.1 . TWO PCB MOLECULES XAMED ACCORDING TO W A C NOMENCLATURE .................................... 3

FIGURE 2.2 . SAMPLE CHROMATOGRAPH OF AN AROCWR 1260 PRODUCED BY GCECD ................................ 6

FIGURE 4.1 . PEAK /CHLORINE CONTENT RnA'llONSHrP AS D E T E R W D BY GC/MS AND TRANSFERRED TO

........................................................................................................................................ GCfECD 42

FIGURE^.^. ~NDMDUAL PEAK ANALYSIS FOR EXPERlMENT SG-6 ................................................................ 4

FIGURE 4.3 . WMDUAL PEAK ANALYSIS FOR EXPERIMENT SG.9 ........................ ... ............. . . . . . . . . . . . . 4 5

FIGURE 4 4 . INDIVIDUAL PEAK ANALYSIS FOR EXPERIMENTSG.~. nrrPLE T R E A N T ................................. 47

FIGURE 5- 1 . INDIVIDUAL PEAK ANALYSIS FOR EXPERIMENTS SG-7 AND SG.8 .............................................. 59

List of Photographs

PHOTOGRAPH 2.1 . ANTENNA HILL FROM THE AIR ...................................................................................... 17

............................................................................. PHOTOGRAPR 6- 1 . THE ELECTRIC ~ R R E R REACTOR 6 5

....................................................................................... PHOTOGRAPH 6.2 . THE CEMENT MIXER REACTOR 66

List of maps

Introduction

Contamination of soil by polychlorinated biphenyls (PCBs) is one of Canada's greatest environmentai concems. PCBs are environmentally persistent contarninants that bioaccumulate in food chahs and are suspected carcinogens(Safe et al. 1987). Presently there are sevenl ways of remediating PCB contarninated soils that have gained official and public approval. However, where contamination is found in remote locations such as Canada's north, inaccessibility causes the cost of such remedial technologies to increase dramatically .

PCB contaminated soils in the Canadian Arctic present a difficult remediation problern For the most part contamination is found in areas around abandoned and presently operating mil* installations at remote arctic sites. The difficulty of transportation to and from these sites, lack of existing iofrastnicture, and a short work season (anywhere from one to three months) requires that any remediation strategy be camed out on-site using easily transportable, relatively simple ("low tech"), equipment.

The current ovemding legislation concerning PCBs is the Canadian Environmental Protection Act (CEPA). CEPA has set out a 50 parts per million @pm) critenon for PCB contamination above which the contaminated matenal is regulated and must be treated in a prescribed marner. If the level of PCB contamination in materials is lowered below the 50 ppm limit, then the options available for responsible, cost effective disposal of the material increase substantially.

Fenton's reagent, a combination of hydrogen peroxide and iron salts, is a strong oxidizing agent that has been shown to oxidize a variety of organic contaminam (Wailing, 1976), including PCBs (Sedlak and Andren, 1991). Degradation of several organic contaminants in the soil medium has been achieved in laboratory s a l e experirnents. However it does not appear that Fenton's reagent has ever been applied, either on a laboratory or field scale, to soils that have been contaminated with PCBs for a long penod of time (weathered soils). A remedial process employing Fenton's reagent may be suitable for treatment of PCB contaminated soils at remote sites. Reagents are relatively inexpensive and non-toxic. Costly, elaborate, reaction vessels are not required.

The objective of this work was twofold: first to determine the effectiveness of Fenton's reagent in treating PCB contaminated soils in the laboratory and second, to develop a process for trial on a larger scale at a contaminated site in Saglek, Labrador. Experiments were carried out on soils that had been contaminated with PCBs for at least a decade. The primary goal of treatment with Fenton's reagent was to lower contamination levels below the CEPA criterion of 50 ppm. In addition to Fenton's reagent a soi1 washing process was developed to help reduce the total amount of PCB contaminated material. Considerable success was achieved and a cntical mass balance problem addressed.

This thesis will follow the following outline:

rn Background infomiaaon

Methods

rn Laboratory scale experiments

PCB mass balance

Field experiments

Conclusions and recommendations

In this thesis, the presentation of results is organised so that laboratory work and field work are treated separately. The order in which results are presented is not indicative of the chronologicd order in which they were discovered. The sequence in which these discoveries were made, however, are key to understanding this work. The chroaology of events is as follows: initial laboratory experirnents, Saglek field expenments, m a s balance investigation (laboratory), final laboratory experiments.

2. Background

The name polychiorinated biphenyl describes a group of chlorinated organic molecules that contain one or more chlorine atoms siaiated on a biphenyl ring. There are potentially 209 di fferent polychlorinated bip henyls (PCBs), known as PCB congeners, tw O

of which are displayed in Figure 2-1 with their appropriate International Union of Pure and App lied Chemistry (IUPAC) names (Safe et al. 1 987).

PCBs first came into widespread indusuid use during the late 1920s with their manufacture peaking at the end of the 1960s (Moore and Walker. 199 1). Because of their excellent dielectnc properties, heat capacity and chernical inertness, PCBs found widespread use in electrical eqtiprnent and heat exchangers, and as lubricants, plasticizers and f i e retardents (Safe et al. 1987). in North America, PCBs were manufactured under the trade name Aroclor by Monsanto Co. Different mixtures of PCBs were produced and

categorized according to the average chlorine content of the different congeners. For example, Aroclor 1254 was a commercial mixture of various PCB congeners containhg an average of 54% chlorine by weight (Safe et al. 1987).

Figure 2-1. Two PCB molecules named according to IUPAC nomenclature.

2.2 Environmental concems

The same characteristics that made PCBs ideal for industrial application also made them resistant to chemical and biological degradation in the environment (Hooper et al.

1990). Furthermore PCBs have strong lipophilic properties which gives them a strong tendency to adsorb onto any organic matter (Hooper et al. 1990). Their resiçtance to degradation, coupled with their lipophilic nature make PCBs highly susceptible to bioaccumulation and biomagnification (Safe et al. 1987). Bioaccumulation describes how contaminants are found to collect in living organisms, and biomagnification descnbes bow contaminant levels increase in organisms at higher trophic levels in the food chah

The p r h m q concems with PCBs are the chronic effects that long-term exposure to low levels have on living organisms (Safe et al. 1 987). Certain PCB congeners have been

implicated as weak mutagenic and carcinogenic agents that eff+ect hepatic tissues (Parkinson and Safe, 1987). More noticeable, however, is the effect that PCBs have on reproduction. Defornation in tems was found to be a direct result of feeding on PCB contaminated fish, and PCBs are implicated in the diminished reproduction of seals and other fish eating mamrnals (Hansen 1987).

Because of the harsh conditions expenenced in the arctic and the nature of the organisms in those ecosystems, contaminant impacts can be greater than in the south (Barrie et al. 1992). Characteristics of Arctic ecosystems and their organisms, such as a food chain that relies on a very narrow base of primuy producers, and organisms with extended life spans and high concentrations of adipose (fatty) tissues, increase the risk of bioaccumulation of lipophilic contaminants (Barrie et al. 1992; Muir et al. in press). Furthermore, the diet of indigenous peoples of the oorth relies heavily on "country foods" consisting prirnarily of marine organisms and wildlife (Barrie et al. 1992). For this reason chemical contamination of the arctic environment and its biota could have a direct impact on northem populations and is a serious concern (Muir et al. in press).

2.3 Regulation of PCBs

The Canadian Environmental Protection Act (CEPA) was introduced in 1978 and initially banned any subsequent industrial use of PCBs. Since that time, CEPA has developed a set of regulations that govems the use, transport, storage and disposal of PCBs, PCB-containing rnaterials, and PCB solids. CEPA defines a PCB solid as any material containing PCBs in excess of 50 ppm and requires that such materials be treated in accordance with the regulations.

2.4 Detemination of PCB concentration

The m a l manner in which environmental contaminants are measured is on a parts per million (ppm) basis, which in solid substrates is equivalent to a mass ratio in units of pg/g. In North Arnenca, PCB concentrations are usually reported in reference to a certain

Aroclor mixture (for example 122 1, 1242, 1254, or 1260). The method of analysis is by

gas chrornatography with electron capture detection (GCECD) following Soxhlet extraction of the sample material. A detailed description of this procedure is included in Chapter 3.

Analysis by GC/ECD produces a chromatograph, displaying a pattern of peaks representative of the congener composition of the PCB mixture. The sample chromatograph displayed in Figure 2-2 is of an Aroclor 1260 standard. The concentration of a given s q l e is determined by comparing the peak area of the six most prominent peaks, to the peak area of the corresponding peaks in the standard chromatograph. In this way the PCB concentration of the sample is determined by averaging these six individuai results and is reported as compared to the Aroclor standard, in this case 1260. This method of determinhg PCB concentration in soils is based on the United States Environmental Protection Agency method 808 1, organochlorhe pesticides and PCB as Aroclors by gas chromatography capiliary coluinn technique, which outlines analytical techniques that are standard in the environmentai field.

Results of this research are intended to have practical application to the remediation of coataminated sites and therefore are aiso rneasured and reported according to these accepted methods.

Timi (min)

Figure 2-2. Sample chromatograph of an Aroclor 1260 produced by GCIECD

2.5 Remediation of PCB contaminated soils

The remediation of contamiaated soils cm be carried out in many ways. Any remedial technology is carried out either in-situ, without need for excavation of soi1 or ex-

situ which requires excavating the soil, treating it, and then back-fiiling appropriately. Ex- situ treatments can occur on site or involve transportation to a treatment facility off-site. The second major distinction between different remediation processes is whether the contaminant is actually destroyed sinqily removed from the soil and contained separately,

or immobilized and contained fkom exposure to the environment. A List of available remedial technologies is tabulated below. The treamients that are listed below could al1 be

used to treat PCB contaminated soils. However, very few bave been proven to be effective at a commercial sa le and even fewer have gained widespread public and regulatory acceptance.

2.5.1 Contaminant destruction technologies

2.S.l.l Incineration

Incineration is an ex-situ process whereby PCBs are destroyed at temperatures between 1 100-1300 ' C in a rotary kiln type combustion chamber. One of the dangers

associated with incineration is that incomplete combustion of the PCBs will result in the production of polychlorinated dibenzodioxins and polychlorinated dibenzofurans which are more toxic than PCBs (Erikson et aL, 1989). To avoid that production of these compounds, incinerators make use of combustion chambers such as rotary kilns. Currently there is only one licensed incinerator in operation in Canada at Swan Hills Alberta. hcinerators typically operate at destruction and removal efficiencies (DRE) of

99.999999% and release limits of 0.009 ng of dioxinhxn per cubic metre (Chiricosta, 1995). Drawbacks to incineration include the high cost of treatment, together with the cost of transportation of contaminated substrate to the facility from remote sites, and poor public perception.

2.5.1 -2 Chemical reduction

Chemical reduction technologies involve the replacement of chlorine atoms by

hydrogen through reduction reactions. The Eco-LogicTM company of Rockwood Ontario has developed a commercial ex-situ process that removes PCBs From soil via thermal desorption (see physical separation) and then reduces them in a hydrogen atmosphere at 850 ' C. DREs of 99.9999% have been achieved on PCB removed from spiked sediment

(Hassenbach, 1995). The mobile plant that is used to treat soils on-site requires several tractor trailers for transportation and consists of state of the art equipment. Mobilizing such equipment to remote northern sites may prove to be impractical and costly.

2.5.1.3 In-situ vitrification

In-situ vitrification is a process whereby electricity is used to melt soil giving rise to 1 600-2000 " C temperatures that volatilize and pyrolyze organic contaminants. Off gas

from the treatment is trapped by a gas collection hood that covers the site, and treated

pnor to emission. The process resuits in the formation of a solid monoiith resembling obsidian (volcanic glass) that has excellent resistance to weathering. In-situ vitrification has been successfuily used to treat 3500 tonnes of PCB contaminated soil at a site in the

U.S. (MSSIT, 1994). However, due to the enomous power requirements, in-situ vitrification would not be suitable for use at remote arctic sites.

2.5.1.4.1 Base catalyseci dechlorination (pilot scale)

Dechlorination of PCBs is achieved through reaction of polyethylene glycol and potassium hydroxide to create dkoxide which reacts with chlonne on the bipbenyl ring to form an ether (Amend and Ledemian, 1992) The treatment of soils generaliy requires the use of elevated temperatures, 150-350 O C. Full sale commercial units are not yet available for decontamination of soil though several pilot projects have been carried out successfully (ESG, 1996).

2.5.1.4.2 Photolysis (pilot seaie)

The photocatalytic degradation of PCBs can be achieved using Ti@ catalyst and UV radiation that results in complete mineralisation to C G and HCI. In order to successfully treat soils, reactors incorporate complete mixing and irradiation with natural and artificial UV radiation. Pilot seale treatment bas been successful at achieving 50% destruction of Aroclor 1248 in a contaminated sediment suspension in 6 bours of mixing (Zhang et al. 1993). Treatment relies on the ability for all elements of the mixture (soil particle, Ti02 catalyst, and W radiation) to be present at one the, an objective which is difficult to achieve.

2.5.1.4.3 Chernical oxidation (experimentai)

Fenton's reagent, a mixture of ferrous ion and hydrogen peroxide produces a hydroxyl radical which has the ability to oxidize virtually any organic contaminant including PCBs (Waiiing, 1974; Sedlak and Andren, 199 la). Experiments carried out in

soil contaminated with pentachlorophenol have been successfûl at achieving 98% contaminant degradation (Watts et al., 1993). The non-toxic reagents and relative simplicity with which Fenton's reagent could be applied to contaminated soil make it a possible candidate for application in remote sites.

2.5.1.4.4 Bioremediation

Extensive research has been coaducted on the use of micro-organisms to degrade PCBs. Researchers have had success at degrading PCBs in various media, with both naturally occurring indigenou micro-organisms and with geneticaily altered microorganisms (Dercova et al. 1995; Quensoo et al. 1990; Abmowicz, 1990). Difficulties with applying PCB degraders to contaminated soi1 media have prevented the transition to commercial viability, however, research is ongoing (ESG, 1997). A bioremediation treatment strategy could provide a viable solution for PCB contaminated soils in remote arctic locations.

2.5.2 Physical separation technologies

2.5.2.1 Thermal desomtion

Soils are heated in a non-oxidizing atmosphere to vaporize the PCBs yet avoid combustion that could lead to the creation of toxic dioxins and fiiram. Themial desorption is often camied out in rotary kih reactors. Vaponzed contaminants from the desorption chamber are condensed and contained or are destroyed in secondary treatment with the use of another technology such as incineration or chemicai reduction. Themial desorption is a proven technology and cornmercially available in the United States (VISITT, 1994) and Canada. The oniy aspect of thermal desorption that would limit use in remote northem locations is the high cost and contract nsk associated with the deployment of such equipment.

2.5.2.2 Soil washing

Soil washing reduces the amount of contaminated material by removing highly concentrated fine fiactions fkom the soil. In some cases, some of the actual contaminant can be removed fiom soi1 particles. Washing operations produce three waste streams;

coarse clean material; highly contaminated sludge; and wash water. PCBs are not prime candidates for soil washing due to their relative insolubility in water. Application to PCB contaminated soils is limited to soils consisting of sands and grave1 and having Little clay content as reductions cm only be achieved througb removal of the fines. Soil washing reduced sediment PCB concentration fiom 1.2 ppm to 0.21 ppm in 230 m3 of river sediment (Garbaciak et a[. 1995). Limitations due to fine soil particles and PCB insolubility nile out soil washing as a stand alone treatment, however some overail reduction in contaminated material could be achieved.

2.5.2.3 Solvent extraction

Soils are washed with a relatively non-toxic solvent that is able to dissolve PCBs, removing them fkom the soil matrix. Solvent, soil and aqueous phase are then separated and, if possible, contaminants are separated from solvent so that it can be recycled. Solvent extraction is reported to be commercialiy available in the U.S. with reported reductions of 98% in PCB concentration (VISITT, 1994). Sorne solvent remains in the soil which evennially evaporates. Solvent washing may be useful for individual items or small amounts of soil. However, remediation of large amounts of contaminated soil would be impractical in a remote location.

2.5.2.4 Emerimental se~aration technologies

2.5.2.4.1 Radio frequency ground heating

Radiofrequency 0 radiation heats soil to temperatures in excess of 300 ' C, vaporizing contaminants including PCBs in-situ, much iike thermal desorption techniques. Contaminants are collecteci by a vacuum system and condensed for further treatment by an appropriate destruction technology or containment. During a pilot study a 99.7% removal rate was achieved for Arocior 1242 contaminated smdy soil (Knikowski, 1993). Being an

in-situ process, radiofiequency ground heating could offer substantial swings over ex-situ

thermal desorption, however, power requirements would likely limit application in rernote locations.

2.5.3 Containment

2.5.3.1 Solidification and stabilization

Coataminated soi1 is rnixed with binders and additives and then allowed to cure in

the form of large concrete-like blocks. Contaminants are then considered to be suficiently immobilized and removed fmm the environment. However, tests on the blocks produced during field demonstrations performed in Vancouver, B.C. and the US. produced questionable results conceming long t em stability, particularly in t e m of freezelthaw resistance (DESRT reports, 1993; Amend and Lederman, 1992). The failure of solidified cells to pass weathering tests, especidy freezehhaw tests, in both field trials makes this stabilisation technology unsuitable for application at northem sites.

2.6 Descn'ption of study site

The North Warning System cuently mns a long range radar station at Saglek, Labrador, with the designation Lm-2. The site of the curent station is located on what used to be a rnilitary radar station that made up pan of the now d e h c t Pole-Vault iine built at the height of the Cold War. Pnor to construction of the oew site, structures remaining fkom the old station were dernolished, burned and then buried on site. The old site was the largest of the East Coast stations and consisted of a main station, two antenna sites, an airport and a beach landing area. When the old site was dernolished and the site cleaned up, approxirnately 100 m3 of PCB-contaminated matenal was removed fiom the site and transported to Goose Bay for destruction at an incineration facility.

Previous studies of the site conducted by the Environmental Sciences Group in 199 1, 1993 and 1996, revealed more than 1300 m3 of soil contaminated with PCBs in excess of the CEPA criterion. The main concentration of this contamination was located on what has become known as Antenna Hill, see Map 2-1 and Map 2-2.

Antenna Hill previously housed a set of large troposphenc antennae and some support structures that contained a variety of electrical equipment. The past location of the antennae and structures is indicated by large concrete pads which must have supponed them. It is in the vicinity of the largest of these concrete foundations that approximately 1200 m3 of the PCB contaminated soil (in excess of 50 ppm) is located. The concrete Wundation is clearly visible in a photograph of the hi% Photograph 2-1. Antenna Hill was chosen as the site for the scaled up field trials that were canied out during this research. In addition to "CEPA soils" there is also approximately 1 130 m3 of soil containing between 5 and 50 pprn PCBs and another 3270 m3 of soil containing between 1 and 5 pprn PCBs. Options for disposal of these lesser contaminated soils may include burial in an on- site engineered land fili. Should a portion of the "CEPA soils" have PCB concentrations reduced below that of the 50 pprn critenon, they could be treated in the same manner as the lesser contaminated soils at significantly reduced costs.

Geographically, Saglek is typical of contaminated sites in the north and a prime candidate for a mobile, on-site, "low tech" PCB remediation technology. The only ways to reach Saglek are by aircraft or by ship. In this respect Saglek is at an advantage over many arctic sites as the air sbip is paved and can support larger aircraft than most others, which only have grave1 airstrips suitable for Twin Ottess. Saglek is also relatively far

south compared to other sites, making sea lifts to the site a somewhat simple, but nevertheless expensive, task. At other locations, transportation of equipment to and from the sites is less reliable and expensive due to the greater distances and the presence of ice. The ideal treatment apparatus is one that cm be transported on a s m d aircraft, yet not so valuable that it could not be left over the winter at a remote arctic site.

Map 2-1 : Location of Saglek

Photograph 2-1. Antenna Hill kom the air

2.7 Fenton's reagent

After having reviewed aIi of the available technologies for PCB remediation, Fenton's reagent was considered to be the most kely candidate for a "low tech" on-site application at Saglek. The reagents that are used in Fenton's reagent are relatively inexpensive and non-toxic. Application to soils does not require elaborate reaction vessels, and reactions can take place at ambient pressure and temperature. The following section outlines how PCBs are oxidized by hydroql radicals, how Fenton's reagent produces hydroxyl radicals and how such treatment could be applied to PCB contaminated soils.

2.7.1 PCB oxidation by hydroxyl radicals

PCBs and other persistent organic contaminants are degraded by naturally occwring reactions in surface waters and the atmosphere (Zepp et al., 1992). The majority of this degradation takes place due to the oahiral occurrence of hydroxyl radicals. The hydroxyl radical is the second most powerfùl oxidizing agent next to fluorine and has the ability to oxidize Wtuaiiy any organic substance (Walling, 1975). Naturaiiy occming photolytic reactions are responsible for the creation of hydroqd radicals in the atmosphere and it is estimated that as much as 8300 tonnes of PCBs are destroyed every year because of them (Anderson and Hites, 1996).

Several studies have been perfonned on the oxidation of PCBs by the hydroxyl radical. In order to investigate the oxidation of PCBs in the atmosphere by hydroql radicals, Anderson and Hites (1996) studied the gas phase reaction. Hydroxylated polychlorinated biphenyls were identified as an intermediate product of the oxidation (Anderson and Hites, 1996). It appears that the OH radical attacks the PCB molecule at non-halogenated sites resulting in the addition of the hydroxyl group. This hydroxyl addition improves the reactivity of the molecule by promoting M e r attack by the slightly electrophilic OH radical. Follow*og the initiai attack, accelerated oxidation of the rnolecule can lead to ring cleavage and hydrodechiorination (Pignateilo, 1994). Because the oxidation of the PCB molecule is initiated with the hydroxyl addition at a non- halogenated site, it would be expected that reactivity would decrease with increases in the degree of chlorination (Piccinno, 1991). Relative reaction rates measured for individual

congeners found in Aroclor 1242 showed a decrease in reativity by a factor of 2 as the

nwnber of substituted chlorines increased ftom 2 to 5. Reaction rates were also found to Vary among rnembers of each homologue group indicating that stenc hindrance also played a role in reactivity (Sedlak and Andren, 199 1 a).

2.7.2 Basic Fenton's chemistry

Fenton's reagent was discovered in 1894 by H. J. H. Fenton (Walling, 1975). Fenton found that a combination of ferrous salts and hydrogen peroxide was able to rapidly oxidize mahc acid. Since then, the addition of ferrous salts to hydrogen peroxide has been found to promote the oxidation of a variety of organic substrates, including chlorinated organics. The procedure Fenton followed involved the slow addition of dilute hydrogen peroxide to a rapidly stimng solution of ferrous ion and organic substrate. The reaction mechanism which is proposed is surnmarized by the following (Waliing, 1975):

(1) ~ 2 0 2 + ~ e ~ + * HO-+ Hom + ~ e ~ ' kt = 76 (mol L'I)-' s-'

(2) HO + ~ e * + -+ ~ e ~ ' + HO- k2 = 3x10~ (mol L-')-' s-'

(4) Ri + ~ e ~ ' + ~ e - ' + + product

(5 ) 2Rj 0 -* product (dimer)

1 1 1 k3 = 10'-10~~ (mol L- )- S-

Once bydroxyl radicais are produced, some may react with an organic substrate. This reaction creates one of three different intermediates by hydrogen abstraction or a kineticaiiy equivalent addition. This mode1 assumes the creation of three different types of

radicals, Ri., R,*, Re. These then undergo either oxidation, dimerization or reduction.

In the case of oxidation, ~ e " is regenerated and a redox chah reactioa cm propagate.

Experiments performed by Walliug and those which seem to obey the above

reaction mechanian are usually performed at low concentrations of hydrogen peroxide, less than 1% (wt. %), excess ~ e * + and in a rapidly stirred aqueous solution. These types of reactions have also been used to degrade several other organic contaminants such as N-

nitrosodimethylamine (Wink et al., 1994), toluene, benzoic acid, benzamide, nitrobenzene and chlorobenzene (Merz and Waters, 1949), 2-chlorobiphenyl and Aroclor 1242 (Sedlak and Andren, 1 99 1 a), chlorobenzene and chlorophenols (Sedlak and Andren, 199 1 b; Barbeni et ai., 1987) and anisole (Jefcoate et al., 1969).

2.7.3 Hydroxyl radical scavenging

Reaction 1, between hydrogen peroxide and ~ e ~ + , which produces hydroxyl radicals is relatively fast (kl=76 (mol ~ ' l )*l s"). Some of these radicals would immediately begin reacting with the organic substrate by reactions 3-6 which are mucb faster than

I I 1 reaction 1 (k3= 10'- 10" (mol L- )- s- ), and therefore dependent on the diffusion rate of the substrate. If the rate of degradation of the substrate is slow, there could be a rapid build up

of hydroxyl radicals in solution. Furthemore, if the amount of ~e~~ is not sufficient to convert ali of the H 2 q to hydroxyt radicals, an unreacted portion of hydrogen peroxide would also be present. A situation in which excess hydrogen peroxide and hydroxyl radicals are present can lead to negative scavenging reactions. Scavenging of hydroxyl radicals occurs in ali types of Fenton's reagent, however the negative effect of hydroxyl scavenging is amplified at elevated H202 concentrations.

These reactions that consume hydroxyl radicals, but do not lead to the oxidation of organic substnite, are known as hydroxyl scavenging reactions and are expressed by

equations 8- 1 1.

(8) HO. + Eh4 -* HzO + HOp kS = (1.2-4.5)~ 1 0' (mol L''Y' s" (Walling, 1976)

kg = 5.3~10~ (mol L-')" s-'

20

(10) HO* + H02- -* &O + 0 2 kta = 6x1 0' (mol L-')" s" (Stephan, Hoy and Bolton, 1996)

( l l )HOim+HO~-*H202+02 kl t=8x105(mol~- ' )~1~-1 (Stephan, Hoy and Bolton, 1996)

The "classical" Fenton's reaction is typically canied out by the slow addition of dilute hydrogen peroxide to a rapidly stimng solution of ~ e ~ + and substrate. Under these conditions, substrate is in the aqueous phase and readily available for oxidation by the hydroxyl radicals. Because the hydrogen peroxide is added slowly over tune and the

organic substrate is readily available for degradation, there should be no build up of either hydrogen peroxide or hydroxyl radical and there should always be an excess of ~ e ~ + to catalyse the reaction. Under these conditions hydroxyl radical scavenging is kept to a minimum. However, if the hydrogen peroxide is dumped into a mixture in a lump dose andior only a certain amount of ~ e ~ ' are available for reaction, conditions for hydroxyl radical scavenging are optimal. A similar situation occurs if only a d l amount of organic substrate is available for degradation.

Hydroxyl scavenging reactioos are inhibited by low pH. As the pH gets lower the

rate of hydroxyl radical scavenging decreases. However higher pH increases the concentrations of certain iron complexes; Fe(0H)' for example, is thought to be even more reactive than ~ e ~ + in the degradation of hydrogen peroxide (Sedlak and Andren, 199 la). Thus a balance between high and low pH creates the most ideal conditions for hydroxyl radical formation. The optirmm pH for PCB degradation was found to lie between 2.3 and 4.3 (Sedlak and Andren, 1991 a). It is also thought that by lowering the

pH the amount of iron available to react with H z a is increased (Walling, 1976). The degradation of pentachlorophenol (PCP) in silica sand and soi1 media was optimized at a pH of 2-3; this pH dependence was attributed to an increase in dissolved iron (Watts et al., IWO).

Classical Fenton's treatrnent may not be a practical way of treating certain contaminated media In order to adapt the Fenton's method to one that may be more suitable, conditions of the reaction are often changed resuiting in higher reagent concentrations and less than ideai mVang (Watts et al., 1993). Situations descnied above that lead to reactions 8-1 1 are generally inefficient in t e m of hydrogen peroxide

consurnption but often create the strongest oxidizing conditions (Spencer, Stanton and Watts, 1994).

2.7.4 Sources of iron catalysts in the Fenton reaction

in situations where the reaction starts off with a high concentration of hydrogen peroxide, al1 of the ~ e ~ + gets converted to ~ e ~ + in the starting moments of the reaction. Once al1 of the ~e'' is oxidized to ~ e ~ + , the later becomes the sole source of iron for the

Fenton reaction. The ~ e ) ' reacts with the hydrogen peroxide, and is reduced to ~ e ~ + . This fernous ion can then react with hydrogen peroxide to produce a hydroxyl radical (Pignatello, 1992).

Pignatello investigated the use of femic iron as opposed to feirous iron in the Fenton's reagent. ~ e ~ + was substituted for ~ e ~ + in an aqueous solution containing the chlorophenoxy herbicides, 2,4-dichlorophenoxyacetic acid and 2,4,5- trichlorophenoxyacetic acid. It was found that when ~ e ~ ' w a s the iron source, the reaction proceeded more slowly. The initial burst of activity that is apparent in ~ e ~ ' systems did not occur, but more complete degradation of the herbicide substrate was achieved as shown by CO2 and Cl' recovery. ïhat the ~ e ) + catalysed reaction was more complete than the ~ e ~ ' catalysed reaction, is probably due to a reductioa in OH. scavenging (Pignatello, 1992). The mechanisn by which ~ e ~ ' catalyzed degradation of H2@ may result in OH* production is as follows (Pignatello, 1994).

(1 2) 2 ~ e ~ + + H z a -+ 2 ~ e ~ ' + 02 + 2 w (several steps)

It cm be seen fiom the above reactions, that the ~ e ~ ' ion regulates the release of ~ e ~ ' and ultimately the production of the hydroxyl radical. The ~ e ~ ' system is apparently l e s efficient in terms of hydrogen peroxide consumption and hydroxyl radical production. However, the fact that it produces hydroxyl radicals at a reduced rate may reduce hydroxyl radical scavenging making the overall oxidation more efficient in systems with excess H202. The differences in efficiency between the two systems would change depending on the concentration of hydrogen peroxide. At low concentmtions where scavenging is

minimal, the ~ e " system is likeiy the moa efficient, whereas the advantages of using ~ e ~ ' may increase with greater concentrations of &O2.

Where the oxidation of contaminants by hydroxyl radicals is quite fast and dependent on the difision rate of the contaminant, it may be advantageous to make use of a systern in which hydroxyl radicais are produced at a slower rate. By slowing d o m the initial production of hydroqd radicals, the sorbed contaminants would have more hine to diffise into the aqueous solution; as a result scavenging of hydroqd radicals would be reduced as would hydrogen peroxide consumption.

In many soil systems there are naturally occtming iron minerals that may also have the ability to catalyse hydrogen peroxide degradation, resultuig in the production of hydroxy l radicals. During an in-situ bioremediation experirnent hy drogen peroxide was added to the soi1 in an atternpt to improve oxygenation. However nahirally occuning reduced iron in the soils, which were contaminated with methyl and ethyl tert-butyl ether, was able to catalyse a Fenton type reaction resuitiag in the oxidation of the contaminants (Yeh and Novak, 1995). Hydrogen peroxide was ais0 used to treat soi1 spiked with diesel fuel and it was found tbat naturally occurring iron in the soil was sufficient to catalyse the Fenton's reaction (Spencer et al., 1993).

When meauring the efficiency of a proposed remediation system, the overall reduction of coataminants must be cornpared to the consumption of reagents. In a study investigating the treatment of chlorinated organic contaminants in natural soils, the most efficient treatment method, in tems of hydrogen peroxide consumptiont was one in which

the n a t d l y occuning iron minerals were used to catalyse Fenton-like oxidation (Tyre et

al., 1991). Whereas reactions carried out using iron (II) amendments produce large contaminant reductions in relatively short periods of t h e , the mineral catalysed reaction was slow and consumed far less hydrogen peroxide per gram of contaminant oxidized. In a spiked silica sand system, goethite and excess hydrogen peroxide (7%) were used to treat pentachlorophenol (PCP). It was found that while PCP degradation was slow, it was Linear over a 24 hr period and that hydrogen peroxide consumption was very low. It was concluded that a system that made use of these iron minerals could provide an efficient means of treating contaminated soiis (Watts et ai., 1993). Solid elemental iron was also found to be effective in catalysing the Fenton reaction in the treatment of tetrachloroethy lene contaminated waste water fkom a dry cleaning operation (Takernura et

al., 1994). The reticulated iron used in the process had been fonned by dipping a urethane foam in a iron powder s l u q . The foam was then dned and sintered thereby pyrolysing the

urethane and leaving a highly porous iron solid. These experiments show that by slowing down the degradation of hydrogen peroxide, the amount of hydroxyl radicals that are wasted is reduced and that the overall amount of hydrogen peroxide used is also reduced.

2.7.5 UV en hanced Fenton's treatment

In the atmosphere, ultra-violet light promotes the degradation of hydrogen peroxide and the subsequent formation of hydroxyl radicals (Stephan, Hoy and Bolton, 1996).

By creating hydroxyl ions directly fkom HZ02 and from other intermediates of the Fenton reaction, W light can significantly increase the efficiency of a treatment. Degradation of Aroclor 1242 in an aqueous solution increased from 15% to 52% when a previously unlit H Z @ / F ~ ~ + reaction was irradiated with four 15-W fluorescent lights emitting between 300 and 400 m (Pignateilo and Chapa, 1994). hdiat ion with W light bas provea to be helpfid in aqueous systems where radiation is able to penetrate below the

surface. W enhanced degradation in a soil sluny, however, would be very dependant on mixing as the surface would be the only affected area.

2.7.6 Treatment of organic contamlnants in soi1 using Fenton's reagent

Several studies have been canied out on organic contaminants in sands and soils. The resuits of these experiments were very important in deteminhg the experimental design for this project.

A shidy by Spencer et al. (1994) investigated the effectiveness of a Fenton's treatment on diesel contaminated soils. In this study, a soil with 0.1 1% (wt. %) total organic content, was spiked to a concentration of 1000 mgkg of diesel fuel. A combination of five di fferent hydrogen peroxide concentrations (0.1 %, OS%, 1 .O%, 5 .O% and 10% ) and four di fferent volumes (1.8 U k g , 3.6 Lkg , 7.1 L/kg and 10.7 m g ) were used to treat 5.0 g portions of the spiked soil. No iron amendrnents were used as naturaily

occwing iron minerals were thought to be SuniCient to catalyse the Fenton reaction. Once the hydrogen peroxide was added to the vials, the pH was adjusted to pH 3.

Hydrogen peroxide concentration was monitored daily until it dropped below the detection limit at which point the reaction was considered complete. The greatest amount of degradation was detected in the sample treated with 5% H202 at 10.7 Lfkg. The most efficient treatment was one that used 0.1 % H2@ at 10.7 Llkg. The authors also

suggested that the process could be carried out in-situ or in an ex-situ mixing operation. The advantage of an ex-situ ngxing operation would be an increase in treatment rates. (Spencer et al., 1994)

In a study performed by Ravikumar and Girol(1994), a packed siiica sand column, 9 1 cm long and 4 cm in diameter, was spiked with 0.53 m o l of PCP and 1.10 m o l of TCE (tetrachloroethylene). The column was then flushed with a total of 1.68 mm01 of hydrogen peroxide, no iron and no pH amendment. This treatment resulted in 61% oxidation of PCP and 50% oxidatioa of TCE. Based on these results, the authors calculated that 5.2 mol of hydrogen peroxide was required to oxidize 1 mol of PCP. Similarly a 3.1 mole HzOz per mole TCE ratio was required. (Ravikumar and Girol, 1994)

Several shidies performed by Watts et al. (1991) have examined the oxidation of various contaminants spiked onto sa& and soils. One mch experiment considered the ability of a Fenton's type treatment to oxidize octachlorodibenzo-p-dioxin (OCDD) in surface soils. Four different kinds of soils and silica sand were spiked with 200 pg

OCDDkg (200 ppb) and treated with 0.10 mmole ~ e ~ + (FeS04) and 12% &O2. Soi1 was treated in lg portions with 3mL of reagents. It was found that the sluny pH was 2.5-3.5 after the addition of reagents so no pH adjustment was necessary. Reactions were ailowed to continue until completion, then the whole process was repeated three more times with fresh reagents. It was found that the degree of OCDD removal was inversely related to the organic carbon content of the soil. Soi1 with 2% organic carbon saw reductions of 96% while soil with an organic content of 6.1% only resulted in 75% contaminant reductions. In M e r studies investigating the effects of hydrogen peroxide concentration, 3.5% and 35% hydrogen peroxide were found to be equally as effective at degrading OCDD in a natural s o l However 35% hydrogen peroxide was more than twice as effective in silica sand. The negative effects of soi1 organic carbon was thought to be due to cornpetition for the hydroxyl radicals. (Watts et al., 1991)

A traditional Fenton's approach was used in an attempt to degrade PCP spiked

onto a silica sand matrix in a study by Watts et al. (1993). A portion of sand was

suspended in a rapidly stirred solution of FeS04 and hydrogen peroxide was slowly added to the mixture. Results showed that treatment in this way was only effective on dissolved PCP, and only to a certain extent, as a point was reached when the treatment had no M e r effect. However, sequential addition of hydrogen peroxide and FeS04 was used to degrade PCP in silica sand with far greater success. A mixture of 2.5 g of spiked silica sand, 250 mgkg PCP, was treated by the sequentiai addition of 12.5 mL of 7% H202 and 1 mL of 160 mg/L FeSOI. The pH was adjusted to 3 by the addition of 1M NaOH or 1 M HCI as needed, and then monitored over a 24 hr period. No agitation was used. The result was a 98% reduction in PCP. The use of high H202 concentration dong with iron (11) amendrnents results in high reactivity and accelerated treatment times. The disadvantage is that use of hydrogen peroxide is quite inefficient because of scavenging reactions described above. To test the use of naturally o c c h g minerals in the Fenton like treatment, the same treatment descnied above was carried out on a silica sand system to which goethite, a naturaily occuniag iron mineral, had been added. No other source of iron was present. The results of this experiment were Les ciramatic but encouraging nonetheless. A Iinear decline in PCP degradation was observed over a 24hr period resulting in a total reduction of 16%. At the same time the reduction in hydrogen peroxide concentration was minimal. This result suggests that an in-situ treatment could be used to economically treat PCP contaminated soils. (Watts et al., 1 993).

Cases in which chlorinated organic contaminants were successfully degraded in a sand or soil matrix provide treamient methods that may be effective in remediating PCB contaminated soils. From these studies, it is clear that a non-traditional approach to Fenton's reagent is needed to degrade chiorinated organic contaminants in soil. Watts et al. (1993) showed that low concentrations of hydrogen peroxide (10: 1 H202:PCP) added to a rapidly stirred soil sluny was not effective at degrading PCP on spiked sand. But a harsher treatment invo1ving high molar ratios of hydrogen peroxide to contaminant (1000: 1) were necessaty to create conditions under which oxidation could occur. It is possible that under such conditions treatment of PCB contaminated soil could be canied out either in-situ or ex-situ.

Experiments involving soil washing and Fenton's reagent followed the same

general procedures throughout the entire research penod. Procedures that were developed in the iab provided the basis for methods that were used in field scale-up experiments. The est part of this section outlines the general experimental procedures used in the laboratory and the field for both soil washing and Fenton's reagent experiments. AU of the analytical procedures that were used to evaluate experimental results are descriied in the second part of this chapter.

3.1 General experimental procedures

3.1.1 Soil washing

During laboratory scale soil washing experiments, approximately 700 g of contaminated soil were sieved through a senes of standard laboratory sieves of descending mesh size, 5/16" (-8 mm), %" (-6 mm), Sieve #5 (4 mm) and Sieve #10 (2 mm). Sieves were stacked one on top of the other such that the various soil fractions were separated aii

at once. Each fraction was then washed individually by flushing the sieve with water sprayed f'rom a d l hose. Sieves were fined into the bottom of a pail which was then placed over the top of a second pail such that water draining from the sieve was collected in the bottom of the second and splashing was weli contained. Each fiaction of the soil was then analysed for PCB concentration by gas chromatography with electron capture detection (GCECD).

To sirupl@ the sieving process a variation of this experiment was conducted using a single 2 mm, Sieve #IO. PCB analysis was carried out on the two resulting fractions.

During field experiments a cernent mixer and water were used to wash Stones that

had been produced by sieviag operations canied out in conjunction with Fenton's experiments. These field procedures will be discussed in Chapter 6.

3.1.2 Fenton's reagent

Soils were füst sieved through 5/16" sieves, and later 2rrnn #10 sieves, to remove coarse material. Soil that had been coliected in a 10 L pail was then thoroughly homogenized by vigorous shaking and stimng. Hornogenized soi1 was then divided into - 400 g portions, placed in plastic bags and refiigerated in order to preserve the sample for future use.

Experknents were perfomed on 15 g of soil contained in 125 mL Erlenmeyer flasks. Soil was weighed into the flasks and then reagents were added to a final volume of 25mL. Reagents used in these experiments were; 30% hydrogen peroxide, purchased from Fisher ScientificN; and FeSOd 7&0 purchased from AldrichN. Concentrations of

hydrogen peroxide were detemked by iodometric titrations with sodium thiosulphate. Flasks were then stoppered with rubber stoppers that had a single hole to prevent spiliage yet allowed the escape of evolved gases. Flasks were shaken on a bench top shaker for 3 hr, then set aside for analysis the next day. After having sat in the flask ovemight, about 16 hr, slumes were thoroughly mixai, and then immediately filtered to separate excess liquid. AU sediment was coiiected in a pre-weighed WhatmmTM 41 ashless filter (speed - fast, retention - coarse and gelatinous precipitates) and water was collected in another Erlenmeyer flask. Once al1 of the liquid had finished dnpping into the flask, the filter paper and soil underwent Soxhlet extraction and analysis by GCECD. Selected liquid fractions, the exmiction for which is descnied in the following section, were also analysed by GCJECD.

Experiments were conducted to test the effect of hydrogen peroxide concentration, pH, iron arnendrnents and the addition of NaCI on PCB oxidation. Al1 experiments were conducted in sets of six flasks. Each experiment incorporated at least one flask of a control sample which was treated with 25 mC of distilled water.

As experiments progressed, the experimental process changed slightly, however the basic process whereby samples were mixed with reagents, shaken and then filtered remained the same. Each evolution of the process will be descnied in the Results and Discussion sections of Chaptea four and five.

Scaled up versions of the laboratoiy experiments were carried out during field experiments at Saglek. Experimental procedures were altered slightiy to accomodate the

larger volumes of mils and different reactors that were employed during these experiments. Field procedures will be discussed in Chapter 6.

3.2 Geneml analytical procedures

3.2.1 Analysis of PCB concentration

Al1 PCB analyses, with the exception of field test kit analyses, were conducted at the Environmental Sciences Group halytical Laboratory, located at the Royal Military College in Kingston, Ontario.

3.2.1 - 1 Lisuid extraction

Liquids were poured into 250 mL separatory funnels and spiked with a decachlorobiphenyl (DCBP) surrogate standard. PCBs were then extracted with 25 mL of dichloromethane by thorough shalo'ng. The two phases were then allowed to separate and the solvent fraction was filtered into a round bottom flask through a filter packed with sodium sulphate. This process was repeated two more times and the extracts combined. The extract was concentrated by roto-evaporation and analysed by GC/ECD as described below in sections 3.2.1.3 and 3.2.1.4.

3 -2.1.2 Soi l extraction

From each sample an accurately weighed sub-sample (-2 g) was taken for analysis of moisture content. Moisture content was detemined by dryrng a pre-weighed sampie at 1 1 O ' C ovemight. The accurately weighed sample (10 g - 15 g) to which DCBP, sodium

sulfate (40 g) and Ottawa sand (20 g) were added, was Soxhlet extracted for 4 hours at 4- 6 cycles per hour using 250 mL of dichloromethane.

3.2.1.3 Extract menaration

The extracts produced by soi1 and Liquid extraction were concentrated by roto- evaporation to approximately 1 mL then 5 mL of hexane was added and again the volume was again reduced to 1 mL. This was repeated mice more, resulting in 1 mL of hexane solvent, which was then applied to a Florisil column for cleanup. The column was thoroughly rinsed with hexane and the eluant containing the PCBs was diluted to 10.0 rnL. A GC viai (2 mL) was then filied and submined for analysis by GCECD or gas chromatography with a mass selective detector (GC/MS) as required.

Each sample was analysed using an HP 5890 Series 1I Plus gas chrornatograph equipped with a 6 3 ~ i electron capture detector (GCECD), a S P B ~ - 1 fused silica capillaiy column (30 m, 0.25 mm ID x 0.25 pm film thickness) md the HPChem station software. The chrornatographic conditions were as follows: Sample volume - 2 pL , splitless injection, initial temperature - 100°C for 2 min; ramp - 10°Umin to 150°C,

S°C/min to 300°C; final time 5 min. C h e r gas used was helium at a flow rate of 1 mUmin. Nitrogen was used as a makeup gas for the ECD.

Each sample was analysed using an HP 5890 Series II Plus gas chromatograph equipped with an HP 5972 mass selective detector, a P T E ~ ~ - 5 fused silica capillary column (30 III, 0.25 mm ID x 0.25 p m film thickness) and the HPchem station software. The chrornatographic conditions were as foliows: Sample volume 1 IL, Splitiess injetion, Initial temperature - 70°C for 5 min; ramp lZOUm*n to 130 O C , SOUxn.in to 260°C, final time 27 min. The carier gas used was high purity helium with a column flow rate of 1 mUmin. The mass selective detector was used in the scan mode.

3.2.1 -6 Polvchlorinated biphenvl (PCB) field analysis

Field analyses of polychlorinated biphenyls (PCBs) were performed with MiIlipore ~ n v u o ~ a r d ~ PCB Test Kits. These utilize the enqme-linked immunoabsorbent assay

(ELISA) technique which is based on antibodies that are specifically designed to bind to PCB molecules. These antibodies are bonded onto the inside of polystyrene test tubes. The sample is added, aloog with excess enzyme-conjugate, which competes with PCB molecules in the sample for the available binding sites on the antibodies. The higher the concentration of PCBs in the sample, the l e s conjugate will be bound to the antibody. After incubation, the test tubes are washed thoroughly with water, leaving only the bound conjugate and bound PCB molecules in the tube. Enzyme substrate and chromogen are then added, which react with the bound conjugate - but not the bound PCB - to forxn a blue solution. Afier a timed interval for colour development, a reagent is added to stop the reaction, tuming the solution yellow. The colour intensity of the product is directly proportional to bound enzyme-substrate, and inversely proportional to the PCB concentration in the original sample in the test tube. Aroclor 1260 standards of 10, 5, 3, 1 and 0.5 ppm were used for calibration, rather than the Aroclor 1248 standards supplied by the manufacturer. These were prepared by serial dilutions of a 200 pprn standard supplied by Supelco. Quantification was performed using a MilliporeTM differential spectrophotometer.

The immunoassay was carried out accordiog to the manufacturer's instructions with a few minor modifications. A sub-sample was spread out on absorbent paper towels and allowed to air dry ovemight. Then a 5 g portion was weighed to + 0.1 g and extracted

with 5 mL methanol; in some cases more methanol was added until a liquid phase was present (for highly contaminated soils only 0.5 g of sample was used). The soil-methanol mixture was filtered and an aliquot of the emact used for subsequent analysis. Aliquots of 25 pL were used and the colour intensity recorded on a portable MiUporeTU differential spectrophotometer. When more than 5 mL of methanol was used, an appropriate dilution

factor was applied.

3.2.2 Loss on ignition

The loss on ignition test is designed to provide an estimate of soil organic matter content.

A representative soil sample was first dried ovemight. The following day approximately 2 g of sample were placed in a pre-weighed oven dried beaker. The sarnple was then oven dried at 105 ' C over a 24 hr penod. Once cooled, the beaker and dried

soil were accurately weighed. The sample and beaker were tben placed in a muffle h a c e at 420 ' C for 1.5 hours. The sample was then removed fkom the fumace cooled and

accurately weighed again. The % loss on ignition was recorded as the weight % lost due to combustion in the mume fimace.

3.3 Evaluation of results

The performance of each experiment was evaluated as a percent reduction. This was calculated as a fùnction of the difference in concentrations between 0% control experiments and the experiments being evaluated. In some cases such as the PCB mass balance investigation, percent reductions were expressed in ternis of the diy soil concentration. Control experirnents were performed along with every experiment, with few exceptions, and involved treatment of soils without active ingredient. Water was the only liquid added to these samples which in every other way were treated the same as active experiments. The prefix, 0% refers to the absence of hydrogen peroxide. The calcuIation used to determine % reduction is:

% reduction = (PCBl O%control - iPCB1 treatmentA) x 100% [PCB] O%control

4. Fenton's Reagent Experiments: Laboratory Scale

4.1 Ovewiew of research

In the s p ~ g of 1996, a senes of laboratory experiments were conducted to investigate methods of PCB contaminated soil remediation. M e r an extensive review of commerciaüy available and experimental technologies, it was decided that a chernical treatment involving Fenton's reagent had the greatest possibility for success at Saglek. The aim of these experiments was ta determine the best way in which to apply Fenton's reagent to the contaminated soils. Success was measured as percent reduction in the PCB concentration of the soils. The methods that were discovered to work the best in the initial lab experiments were chosen for scaled up field experiments at Sagiek-

As weii as Fenton's experiments, several soil washing experiments were canied out. The goal was for the resulting separated fraction to contain contamination levels under the 50pprn CEPA criterion, thereby avoiding costly treatment. By removing a certain fraction of the soil the overall m a s of matenal to treat according to CEPA standards would be significantly reduced. Soi1 washing was also attempted on a iarger scale at Saglek.

Upon returning fiom the field, m e r experiments were undertaken to refine the experimental method. The primary goal of these experùnents was to resolve problems with a PCB mass balance. These experiments and the resolution of the mass balance problem are dealt with in Chapter 5.

Once experimental and analyticai procedures had been improved, previous treatment methods were re-evaluated and a different, harsher treatment approach was implemented.

4.2 Results and discussion

4.2.1 Soil washinq

Two soil wasbing experiments were canied out on soil (labelled as SG-4) that was collected in Saglek dunng the !995 field season. Unsieved, non homogenized SG-4 soil was contaminated with over 500ppm Aroclor 1260. The purpose of these experiments was to reduce the amount of material that had PCB concentrations in excess of 50pprn. Due to a reduced surface area relative to mass, larger constituents in the soi1 do not contain as great a concentration of PCBs as do the finer fractions. By removing larger particles fkom the soil and washing off the fines, the volume of material that is contaminated in excess of 50 ppm, is reduced. The results of the soi1 washing experiments are contained in Table 4-1.

Table 4-1. Results of soil washing experiments on Sç-4 soi1 1 Soi1 Washing

Experiment 1

The weighted average concentration of the PCBs in the coarse materials removed in experiment 1 was 42 ppm, and the weight of the material removed represented 46 % of the total overall mass. In the second experiment, only the 2mm sieve was used and the and

washing of al1 of the material took place at once in the one sieve. In the second expenment, 37% of the total mss of the soi1 was removed by the sieve and the washed

Experiment 2

minimum particle size (mm) total

> 8 m m >6 mm, 4 mm

>4 min, <6 mm

>2 mm, <4 mm

total

mass of matenal (g),

% of total mass

. 693 g 191 g, 28%

27 g, 4%

40 g, 6%

55 g, 8%

757 g

I

PCB] (ppm)

5 ,

28

69

160

material was 90% iower in PCB concentration thm that of the matenal that passed through the sieve.

The amount of water that was used to wash the second batch of soil was 5L. Tbough the PCB concentration of the coarse material was not reduced below CEPA Ievels, the 90% reduction in PCB concentration indicates that soils containhg less than

500ppm PCBs could be effectively separated and washed. Even if a conservative estimate of the total removable mass of matenal is set at 30%, the possible cost savings that could

be achieved through such a process are significant. Soil washing could therefore be incorporated into a remediai treatment strategy as a primary step and, water used in the wash recycled to the chemical treatrnent process.

4.2.2 Fenton's reagent

The results of the first round of experiments are shown in Table 4-2. The soi1 used for these experiments was of the same type (SG-4) used for the soi1 washing experiments, though not the same soil. The soil was first well mixed in a large bag and then sieved through a 5/16" sieve. Once it had been sieved, the soil was thoroughly mixed again and then placed in clean plastic bags for M e r use. The sieved soil was sarnpled and analysed and found to have a dry PCB concentration of 7 1 ûppm.

Table 4-2. Summary of experimental results hom batch SC-4,5116 sieved soE 1 I i

The bench top shaker shook samples in a side to side motion such that contents of the flasks were washed around ia a swirling type motion. Soil slumies appeared to be perfectly mixed while the shaker was in motion, but as soon as power was cut to the

treatment 0% control

result @pm PCB) 510k94

apparent %reduction

machine settling of larger soil pam'cles was hunediate. The soils of control experiments had a dark chocolate brown colour.

In the three kinds of experiments summarized in Table 4-2, a final solution of 1 0% hydrogen peroxide was used to give soil slunies a H2@:PCB molar ratio of 2300: 1, (assuming hexachlorobiphenyl). Experiments to which hydrogen peroxide was added began to bubble upon addition of the liquid reagents to the soil. When shaking commenced, a thin layer of foam appeared on the surface of the sliil~y. Towards the end of the three hours of shaking, this foam layer was thinner, but stili evident. The colour of the slurry had become noticeably lighter, and seemed to take on a siightly yeliowish tinge. Suspended in the sluny were flecks of shiny rnaterial thought to be mica.

Concentrated hydrochloric acid was added drop wise to adjust the pH of slurries in the second type of treatment once al1 of the other reagents had been added. For these experiments, the pH of slurries was measured using pH paper. Acidimg the slunies had the visual effect of intensifjing bubbling and colour changes. Shiny particles were also evident in these experiments.

A solution of FeSW 7H20 had been prepared at a concentration of 0.02M. Equal portions of iron solution and 20% hydrogen peroxide solution were added to the soil, mixed, and acidified by the drop wise addition of HCl. The use of ~ e " caused the sluiry to bubble more intensely than when no iron was used. When the shaking was complete, the sluny had an obvious yellowlorange tinge to it. As seen in the treatments without iron, the darkness of the soil was reduced and shiny flecks were present in the sluny.

The bubbling of slunies upon addition of hydrogen peroxide was a positive sign that hydrogen peroxide was being degraded in some manner. The gas that was being produced may have been oxygen being evolved by previously mentioned hydroxyl scavenging reactions, and could have included COz being given off by the oxidation of organic materials in the soil. The slurries of the control experiments maintained a dark brown colour throughout the fidl three hours of shaking and subsequent ovemight standing period. The dark colour of the soil could be a function of soil organic content, in which case the lighter colour of the treated soils may be attributed to the oxidation of organic matter. The appearance of the shiny particles Ui the soil also indicates a change in the treated samples that was not apparent in the control samples. Somehow, whatever had masked the shiny particles in the control samples had been removed by the treatment with

hydrogen peroxide. This may have also been a consequence of the oxidation of organic mater.

As indicated by the intensifiai appearance of their reactions, the reductions in

PCBs brought on by the treatment at pH 3 and with iron amendments was greater than for

treatment with straight hydrogen peroxide.

Addition of ~ e ~ + amendments did not appear to irnprove overail reduction in PCB concentration relative to experiments where the pH was altered to 3. After comparing results for each type of experiment, it appeared that each had achieved the sarne 29% apparent reduction in PCB concentration relative to the control. Though the reaction with ~e '+ may have proceeded faster as indicated by the intense bubbling, the extent of degradation was evidentiy not enhanced. This rnay have been a fûnction of increased hydroxyl radical scavenging. Hydrogen peroxide degradation catalysed by nahirally occurring iron would have been responsible for hydroxyl production in the soils that did

not receive iron amendments. As previously descnbed, natural iron catalysed reactions have been shown to result in as high a degree of degradation as ~e* ' catalysed reactions (Pignatello(l993); Watts et aL(1993)).

The maximum apparent reduction in PCB concentration achieved by this process was 29%. It was considered that this limitation could be due to the slow rate of desorption of PCBs into the aqueous phase. It was thought that changing the properties of the

by adding a surfactant or additional salt could promote the desorption process.

The second round of experiments treated a l e s contaminated (SAGJO+) soil that had also been coiiected at Saglek, sieved through a mesh #10 (2mm) sieve and homogenized. The soil had been sieved through a finer sieve in an attempt to irnprove the homogeneity of the soil. The concentration of PCB in the dry soil was 380+90 ppm

Experiments tested the effects of using a less concentrated, 6% hydrogen peroxide solution, and the use of an NaCl additive. The results of the experiments perfonned on SAG-50+ soil are presented in table 4-3.

Table 4-3. Summary of experimental resdts from batch SAG50+, mesh#lO (2mm) sieved soil.

The experiments that used only 6% hydrogen peroxide displayed ali of the same

qualitative characteristics of the £ira set of experiments. The pH of al1 of the experiments on SAG 50+ soil was altered to pH 3 using HCI. In the previous set of experiments it had been shown that treatment at pH 3 significantiy irnproved the performance of the treatment. This may have been due to increased solubility of iron and organic substrate as well as increased formation of iron complexes. Lowering the pH also decreases hydroxyl radical scavenging (Sedak and Andren, 199 1 a; Watts et al., 1990).


When NaCl was added to the slurry, apparent reductions in PCB concentration of alrnost 50% were achieved. It was thought that by increasing the ionic strength of the

that PCBs may have been more easily desorbed fiom the soil.

These p r e b a r y resdts provided the basis for the experiments that were canied out during field trials at Saglek. Experiments that used 6% hydrogea peroxide, pH 3, and

NaCl would be the focus of scaled up field work. The work conducted at Saglek and the

scale-up procedures are descnbed in Chapter 6.

result @pm PCB) 3 10275

An ioteresting result of the experiments descnbed above -especially those descnbed in Table 4-2 - was the apparent loss of PCBs in the control experirnent. This problem with

PCB mass balance was the focus of a series of experiments that was undertaken upon retuming fiom Saglek. The investigation of PCB mass balance is the subject of Chapter 5.

apparent % reduction

During an investigation of PCB m a s balance (Chapter 5), it was discovered that

the standard Soxhlet extraction was not effective on wet sarnples generated in Fenton's experiments, a previously unreported phenornena. Once the experimental process had been changed, to analysing only samples thoroughly dried pnor to analysis, complete

extraction was achieved. Experiments which had previously been canied out were repeated. Further changes to the experimental method involved conducting experiments in

four sets of five sample flasks, for a total of 20 flash per experiment. The experiments that used 6% hydrogen peroxide and combinations of HCl, FeS04 and NaCl were repeated

and their success re-evaluated. The resuits of al1 of these experiments are displayed in Table 4-4.

Table 44. Result of experiments using 6% H 2 0 r and analysis of dried samples. Experiment #

SG-6

*n = 5 for each value

treatment 1 * resdt apparent 1

SG-5

diy soi1

O%, control

6% H2G, pH3

dry soi1

O%, control

6% H202, 10% NaCl, pH3

6% H2@, 0.0 1 M ~ e ~ + , 10% NaCl, D H ~

1 10+4

1 17k4

1 17I4

-6%

-6%

101+3

99k3

9 5 I 3

9612

2% 6%

4%

Resuits fkom experirnents SG-5 to SG-9 reveal that the treatment of contaminated soils with 6% hydrogen peroxide and different combinations of HC1 FeS04, and NaCl is not as effective as it may have seemed in previous experiments. The minor differences m soil concentration that appear between different experiment sets, generally fàll within the experimental uncertainty for control experiments and treated experiments. A t-test was canied out to determine whether a significant difference existed between sets of control data and respective experimental data (=s, 1982). None of the differences calculated

by the t-test indicated a significant change had occurred in PCB concentrations, p>0.5. Therefore it was concluded that none of the treatments with 6% hydrogen peroxide had a significant effect on PCB concentration. These resuits provide M e r confirmation that

previous apparent reductions in PCB concentrations were due to an analfical anomaly which is described in Chapter 5.

4.2.2.4 Whv treatments were ineffective

Observations of the experiments in progress indicated that treatment with 6% hydrogen peroxide had some effect on the soil slurries. Vigorous bubbling, changes in colour and the appearance of shiny particles in the soil ali indicated reactivity.

Even though there was no noticeable reduction in PCB concentration, there may shill have been oxidation of organic materials in the soil. The total organic content of SG- 8 1 soil, determined by a loss on ignition method, was 1.2 %. if the hydroxyl radical has the ability to oxidize organic material indiscriminately, then all of the soil organic matter would compete for hydroxyl radicals equally. In a soi1 containing lOûppm PCB and 1.2% (12000 ppm) organic material, for every lppm of PCB oxidized the soil would lose 120 ppm of total organic material. While hydroxyl radicals may attack organic matenal indiscriminately, that material first bas to become available for oxidation. The rate of oxidation steps in the Fenton's reaction are dependent on diffusion into the aqueous phase. The relative extent of oxidation that would be expenenced by different organic materials would depend on their relative rates of desorption. A change in colour due to oxiàation of organic matenal could have occurred without any significant change in PCB concentration. Any oxidizing treatment designed to remove PCBs fkom a soi1 sluny would have to eliminate almost all soil organic matter in order to be effective. The efficiency of a Fenton's treatment will therefore decrease as a function of soil organic content.

4.2.2-5 Individual D& analvsis

Although no overall change in total Aroclor concentration was detected in soils treated with 6% H2Q, the results were exarnined to determine whether the treatment had afTected individual congeners.

From chromatograp hs generated by GC/MS, a relationshi p couid be deterrnined between major peak and chlorine content. Of eight major peaks in the Aroclor 1260 spectrum, 2 were identified as being pentachiorobiphenyls, 3 hexachlorobiphenyls and 3 heptachlorobipheny 1s. Because anaiysis by GClMS and by GC/ECD produce chromatographs with identical peak patterns, the correlation between peak and chlorine content could be trmsferred fi-om one to the other. These relationships are explained in Figure 4-1.

# OF CI ATOMS PER PCB

Time (min)

Figure 4- 1. Peak /chlorine content relationship as determined by GCMS and transferred to GCECD.

Each of the eight peaks identifïed in Figure 4-1 was identified according to chlorine content and numbered. From left to nght they are pental, penta2, hexal, hexa2, hexa3, heptal, hepta2, hepta3, and may be referred to as individual congener peaks. A

concentration associated with each peak was calculated by cornparhg sample peak areas

with those of a 10 ppm Aroclor 1260 standard.

The goal of individual peak analysis was to determine whether a certain treatment had a noticeable effect on individual congeners and how the effect on each congener relited to chlorine content. In order to do this, individuai peak concentrations were graphed such that dry soil results were normalized to a value of 1, the result being a straight, horizontal line for the dry soil data. Data for treated soils in the given experirnent

were then plotted on the same graph. A slope was assigned to each set of data by drawing a linear bea fit line through plotted points and a cornparison was made based on these slopes. If a given set of data displayed a positive slope, the indication was that higher chlorinated PCB congeners were more abundant in the sample relative to lesser chlorinated congeners and vice versa. No attempt bas been made to treat these resuits in a statistically rigorous manner. The intention of this analysis was to identiw possible trends in the results, that could promote further understanding of the Fenton's process.

The results of the individual peak analysis for experirnent SG-6 are shown in graphical form in Figure 4-2. The slopes of the linear best fit lines seen on the graph show how some congeners were affected differently by their respective treatments. The slope of the linear best fit line fitted to the 0% data is relatively horizontal compared to those of the data representing soils treated with various reagents. The slope of the 6% H202/ pH 3 treated soil is slightly positive, indicating that if any oxidation did start to occur, pentachlorobiphenyls were degraded more readily than heptachlorophenols. The slope of the data representing the 6% H~o~/F~ ' ' /~H 3 treated soil has an even greater slope than that of the 6% HzOz/ pH 3 treated soil. A greater slope indicates that even more of the pentachlorobiphenyls may have been degraded relative to heptachlorobiphenyls and that the oxidative process had been allowed to progress M e r . The results of this analysis indicate that treatment with hydrogen peroxide and iron may be the rnost likely combination for successfiil oxidation of PCBs.

Figure4-2. Individual peak analysis for experiment SG-6.

4.2.2.6 Harsh treatments

4.2.2.6.1 Long term treatment

0%

A 6%, pH3

X 6d/a,pH3.Fe

U m a r (0%) - Umar (Pl&, pH3) - Linear (6%. pH3, - I Fe) Unear (dry sol)

Two experiments were perfomed that tested the effectiveness of treating soils with highly concentrated hydrogen peroxide. The first used 25mL of 30% hydrogen peroxide to treat 15g of soi1 over a 96 hotu penod without any shaking. There was no adjustment to the pH nor was there any addition of ïron amendments. Bubbling wmmenced upon addition of the hydrogen peroxide to the soil and a thin foarn layer fomed on the surface of the liquid. Bubbling continued for the whole 96hr of treatment, but after 24hr had slowed considerably and continued to slow until only a few bubbles were present when the

soi1 was decanted into a filter.

Table 4-5. Results of long term experiment

Experiment SG-9 - 30% H2G -96hr. no shaking:

treatment

dry soi1

0% control

30%. 96 hr

remit

(ppm PCB) 109+7

108k7

10414


1% 5%

Expriment SE9

congener designatlon

C3

Figure 4-3. Individual peak analysis for experiment SG-9.

+ dry soi1

Oo/oconîrol

A 6%

1 30"/, in-situ

L i n e a r (6%) - tinear (3W in-

- Linear (dry mil) - Linear (O%/&contm 1)

As was the case for the previous experiments, results from experiment SG-9 (Table 4-5) show that treatment with 30% hydrogen peroxide was not effective at reducing the overall PCB concentration. Results of a t-test showed that differences between the control data and the long terni treated data were insignificant, p>0.5.

f i e i y 3 fi al a = QI QI z .c C a ! g 3 r al L al

Individuai peak analyses were, however, perfoxmed on the chromatographs for experiment SG-9. The individual peak analysis is included in Figure 4-3, and displays linear best fit lines for the 0% control data, 6% H Z a treamient data and the long term 30% Hz@/ 96 hr data.

The dope of the 0% control line was quite similar to that given for the 0% control in experiment SG-6. The dope of the 0% controls is consistentiy Iess than the dopes given for treated samples in both experiments, suggesting that treatments with 6% hy drogen peroxide had some effect on the relative congener concentration in the soil. As expected, the best fit lhe for the 30% data bad a steeper slope than that for the 6% hydrogen peroxide line, which was in tum less steep than the 60/dpH3/Fe iine resulting fiom expetiment SG-6.

Upon examination of the individual peak analysis results, for each expriment, it appeared that the bea combination for optimal PCB oxidation would be a treatment incorporating high H2@ concentrations and ~e'+.

4.2.2.6.2 Triple treatment

Due to the inability of treatment with 6% hydrogen peroxide to produce any signifiant reductions in overall PCB concentration, it was decided that a far more harsh treatment would be required. Experiments performed by Watts et ni. (1991) successfully oxidized octachlorodibemo-p-diogn (OCDD) in soil using 4 successive treatments with O.lmM FeS04 and 12% Hz02 and a soil to reagent ratio of 1:3. In soil spiked with 200 ppb OCDD that had 2% organic content, 96% removal was achieved (Watts et al., 1 99 1 ).

A harsh process was therefore carried out whereby soil was treated three tirnes with fiesh 22% hydrogen peroxide, and 0.0 1 M ~ e ~ ' which were mixed in the flask. Flash were swirled by hand penodically throughout the reaction. Towards the end of each treatment, slunies were left for a few minutes to settle, then liquid, including some suspended solids, were decanted into a filter. By the t h e aU three treatments were complete and al1 of the liquids had been decanted, fine soil materiai lined the inside of the filter.

Following the first addition of reagents, the reaction commenced to bubble vigorously. The rate of bubbling increased slowly over the first five minutes at which point it reached a peak. The temperature in these experiments was monitored and rose steadily with the rate of bubbling. At the peak of the first reaction the temperature of the slunies reached from 70-75 ' C. M e r bubbling had slowed coosiderably and the temperature began to fail, the slurry was allowed to settle and the liquid was decanted. The thne it took for the whole iteration, from addition of the reagents to the decanting of the liquid, was about 30 minutes. The soil became noticeably lighter in colour and took on a yellow- orange colour. Shiny particles that had been noticed in earlier experiments, were also evident in these experiments.

During the second treatrnent, temperatures rose fkom 80-87 ' C and during the third some slurries reached 90 ' C. The increased maximum temperature on the second and third

treatments was presumably due to reagents that had not been consumed in the previous treatment. Remlts of these experiments are included in Table 4-6. Experiments SG-8 and 9 were perfomed on 96-SG-81 soil that had passed through a 2mm sieve and been thoroughiy homogenized

Table 4-6. Results of harsh treatment erperiments

Triple treahnent of soi1 sarnples resulted in a 66% reduction of PCBs in 90% of the soi1 that was treated. In the fine mterial that was coiiected in the filter paper, the concentration of PCBs was 340 ppm. PCBs were concentrated in the fractions of the soil

that were easily camied out of the flask by the decanting action. The easily suspended materials would have been the very fine soil particles and the less dense organic matenals. Both of these fiactions hold the greatest proportion of PCBs due to the large surface area of the fine materials, and the enhanced adsorption to organic matends that is inherent with iipophilic compounds such as PCBs. The mass of decanted material represented 10% of

the total m a s of the sample that was treated. The overall degradation of PCB was calculated by combining resuits fiom both the treated soil and decanted fines and found to be 17%.

- triple treatment

3x (22% H202 + - 0.01 M ~ e ~ + )

Experiment SG-8, triple treatment

A triple treatment

triple treatment -treated soi1

-decanted fines

combined results

- Linear (triple treaiment) - 'Linear (dry soii)

1- Linear (triple ûealment(ff nes))

90%

10%

100%

Figure 4-4. Individual peak analysis for experiment SG-8, triple treatrnent.

22k4

340k49

5524

66%

17%

As well as the harsh triple treatment, experiment SG-8 included a 6%/Fe2'

treatment for which an individual peak analysis appears on the graph in Figure 4-4. The slope of the best fit line for the 6%/Fe2' is sirnilar to those for 6% hydrogen peroxide

treatments of experiment SG-6 and 6% treatment in SG-9. The slope of the long term treatment line in experiment SG-9 is greater than ail of the 6% treatments and the slope for the triple treatment of experiment SG-8 is the highest of ail. This general trend supports the theory that the oxidation of pentachlorobiphenyls by hydroxyl radicals is more rapid than hexa and heptac hlorobip heny 1s.

Treatment with 30% hydrogen peroxide over a 96 hr penod was not effective at reducing PCB concentrations in 96-SG-8 1 soil. Due to the success of the triple treatment

experiment, it was suspected that the long tenn treatment with 30% hydrogen peroxide would be able to produce similar reductions in PCB concentration. However, no iron was added to the long term experiments, leaving natural iron sources to be the sole catalyst for the Fenton's reaction. The triple treatment received fresh ~ e ~ + with every addition of new hydrogen peroxide. The differences in reactivity could be seen immediately in the vigorous fkothing and nsing temperatures of the triple treatment sarnples and the minor bubbling and stagnant temperatures of the long tem treatment. The resuits of these experiments iodicates that ~ e " is necessary for effective treatment of contaminated soils. It also appears that a harsh treatment that continualIy regenerates itself with fiesh ~ e ~ + and H202 is required to achieve any significant reductions in PCB concentration.

A harsh triple treatment process could be scaled up and used to significantly reduce the amount of material contaminated with over 50 ppm PCBs by a combination of chernical oxidation and concentration/separation. Results from experiment SG-8 reveal that the m a s of soil contaminated with between 50 and 145 ppm PCBs could be reduced by up to 90% by treatment with a harsh triple treatment process. With M e r refinements, the capabilities of such a process could be substantiaily improved. A large sa le process

incorporating soil washing and chemicai oltidation, is proposed at the conclusion of this report.

4.3 Conclusions of the laboratory experfments

1. By sievuig the soil and washing the coarse soil particles with water it is possible to reduce PCB concentrations in 30% of the overall soil mass to below 50 ppm in Saglek soils contaminated with up to 400 ppm PCBs. Soi1 sieving and washing of coarse particles is a worthwhile pre-treatrnent process to include in any fûture remediation processes.

2. Treatment of Saglek soils with 6% hydrogen peroxide, and any combination of FeSOs, NaCl, andor HCI is not effective in reducing the concentration of PCBs. Signifiant reductions in PCB concentration due to oxidation were ody achieved by the treatment of soils with three successive additions of 22% hydrogen peroxide and 0.01 M FeS04. The ~e"' ion was show to be essential to the oxidation of PCBs in Saglek soil. Treatment with 30% hydrogen peroxide and no FeS04 did not generate my significant reductions in PCB concentration.

3. Up to 90% of soi1 contaminated with between 50 and 145 ppm PCBs could be treated to below 50 ppm PCBs with a harsh triple treatment process. With M e r

refinements, it is anticipated that the efficiency of such a process could be substaotially improved.

4. A remediation process that incorporates soi1 washing as a pre-treatment step followed by a triple treatment type process could be successful at attaining <50 ppm target concentrations in a large portion of contaminated soil located at Saglek.

5. PCB Mass Balance

Following the preliminary Fenton's experiments and initial anaiysis of the field results, it was discovered that substantial quantities of PCBs that should have been present in the 0% control experiments were unaccounted for. Dry soil that had been shipped from Saglek, sieved and homogenized, was found to contain 30% more PCBs than those of the 0% control experiments perfomed on SG-4 soil, and 20% in the case of SAG-50+ soil. As

soils in control experiments had only been treated with water there was no reason to believe that PCBs could have been degraded. Because of these results, a set of experiments was undertaken that would determine the reason for these discrepancies and appropriate corrective measures.

Experiments were initiaily conducted to eliminate possible avenues of PCB los. These pathways could have been one of the following: loss to the atmosphere via vaporisation; loss to the liquid fiaction previously not analysed; adsorption onto the mbber stoppers and other components of the apparatus, or some combination thereof.

5.2 Experimental

Soi1 for these experiments came fiom 5/16" sieved 96-SG-84 and 96-SG-81 soi1 that had been sieved on site in Saglek and brought to Kingston in 1996. Several kilogram of this soil was sieved through a mesh #IO (2 mm) sieve and thoroughly homogenized in a 10 L pail. Homogenisation was achieved by shaking the capped pail fidl of sieved soil for several minutes. Soi1 was then placed into WhirlpW bags in -650 g batches and set aside for experimentation.

As in previous experiments, shaking took place on the bencb top shaker in Erlemeyer flasks with 15 g of soil and 25 mL of liquid. Experiments were camied out in sets of 20 samples fiasks (maximum single nui capacity of the PCB analytical lab). The set of 20 was split into 4 sets of 5 individual flasks, such that in every experiment 5 flasks represented 0% controls and 5 were dry soils with the exception of experiment SG- 1. The remaining 2 sets of five were given different combinations of reagents, HCl, NaCl, Hz02 and FeS04.

Due to the presence of the wet filter paper in the analysed sample, determination of

the exact sample mass was difficult. in order to accurately measure the amount of soi1 that was in the final analysed sample, a mass balance on the soil was performed on each experiment. The initial amount of soil that went into each pre-weighed flask was accurately weighed. Foiiowing treatment and decanting of the soi1 into the filter, the dirty

flask was dried over night in an oven and weighed again the next rnoming to detemine the mass of remaining soil. The mass of dry soil remaining in the fiask and the mass of soil taken for wet/dry analysis were then subtracted from the dry weight of the original soi1

m a s to determine the dry mass of the actual analysed sample. Any PCBs that had dissolved in the water or had passed through the Nter on very fine soil particles were detected by analysis of the iiquid. The mass of PCB detected in the liquid sample was then added to the mass of PCBs in the soil and included in the overall calculation of

concentration.

5.3 Results and discussion

5.3.1 Rernoving PCB escape pathways

Rubber had been reported to adsorb PCBs quite readily, whereas it has been shown that aluminum is not PCB adsorbent (Bedard et al., 1986). Accordingly, aluminum foi1 was wrapped around the base of mbber stoppers in order to prevent contact with the soil sluny .

PCBs have been reported to volatilize during bioremediation experiments leading to fdse conclusions of PCB biodegradation (Chiarenzelii et al., 1996; Vrana et al., 1996). Though it seemed uniikely that PCBs could have been escaping the reaction vesse1 due to evaporation, an activated carbon filter was placed in the gas exchange hole of the mbber stopper. The fiiters, commonly used for attnospheric samphg, were collected and analysed for PCBs following experimentation.

In addition to preventing PCB adsorption and evaporation, an attempt was made to

reduce the amount of moisture in samples prior to extraction. This was achieved by rnixing sampies with approximately 40 g of extra sodium sulphate before extraction in the

Soxhlet apparatus. Special care was taken to thoroughly pulverize the sample and filter paper and mix them with the Ottawa sand and sodium sulphate.

The resdts of experiment SG-1, in which three separate experiments were conducted in sets of six, are presented in Table 5-1

Table 5-1. Ex~eriment SGl(96-SG84 soi11

This first experiment displayed a 53% ciifference between dry soi1 and 0% control experiments. The treatment with 6% hydrogen peroxide and the treatment with only HCI, to adjust the pH, produced identical results, a 65% and 64% apparent reduction in overall PCB concentration. Relative to the 0% control, these represeat 23% and 30% reductions respectively, but when subjected to a t-test, these differences were not statisticaily signifiant, pX0.5. The results do suggest however that a change in the pH of the soil sluny was able to decrease the apparent PCB concentration. This observation suggests

that some other mechanian, other than PCB loss to the air (or other medium), was resulting in apparent reductiom in PCB concentration.

-aluminum coated stoppers

-double NaS04 -activated carbon filters

The 0% control and the 0% pH 3 experiments appeared identical up until the moment of filtering. When samples were filtered, the water collected fkom the 0% control sample contained fine suspended soil particles. The water collected fkom the 0% pH 3 sarnples was quite clear. The same clarification of filtrate was displayed in the 6% H202 treated samples. Upon analysis of the liquid fraction from each experiment it was found that the 0% control water samples contained 96k 18 pg of PCB, approximately 20% of the total PCB mass detected in the entire control sample. The other two experiments that bad

clear filtrates, 0% pH 3 and 6% H& both had 0.5t0.1 pg of PCB in their filtrates, insignifiant in the overall mass balance calculations.

The PCBs that were being detected in the filtrate of the 0% control were there as a function of the fine particles that were penetrating the filter paper which retains particles larger thm the minimum pore size of 20-25 microns. The addition of HCI and hydrogen

treatment

dry soi1 0% control O%, pH 3 6%

result (ppm PCB) 60 26+4 20k3 19k2


53

64 , 65

peroxide had a coagulating effect on the finer particles of the treated experiments inhibiting solids from passing through the filter. However even when the mass of PCB detected in

the filtrate was combined in the overall concentration calcdation, the result was stiii 53% Iower than that of the dry soil.

PCB levels detected in the carbon filters were very low. AU of the carbon filters had to be combined before any PCBs were even detected. The amount of PCB extracted from ail 18 filters was l e s than 50 ppb. It is possible that some liquid may have even splashed up into one or more of the filters and that none of the PCB detected in the filters was due to volatilisation. The amount of PCBs lost due to evaporation was deemed insignificant relative to the overail mass balance. This was also verified by performing control experiments in sealed flasks and observing similar apparent reductions in PCB concentration.

Since the rubber stoppers had been covered with aliiminum foil, adsorption of PCB onto the rubber was prevented. Since it was possible that a small fraction of PCBs could have been lost to the rubber in previous expenments, the aluminum foil was used on subsequent experiments.

5.3.2 Additional Soxhlet extraction

From expehent SG-1, it was deemed that the apparent reductions in PCB concentration could have been a result of an aualytical anomaly. One possibility was that

PCBs were not being fully extracted during the Soxhlet extraction. In order to detemine whether or not PCBs were being left behind following extraction, the sarnples in experiment SG-2 underwent a second 4 hr Soxhlet extraction. The 3 treatments chosen for experiment SG-2 were a 0% control, 0% H202/0.01 M ~ e ~ ' and a 6% &02/pH 3. Results of experiment SG-2 are displayed in Table 5-2.

Table 5-2. Ex~eriment S G 2 (96-SG81 soi11 -alurninum coafed i t o p doubk N a m -second Saxhiet extraction (4hr)

a ~ a t m a t '

diy soi1 0% controt 0%. 0.01M Fe2+ 6%. pH3

spparen t %reducUon (dry)

57 60

7 1 -

resdt (PPm PCB) 1"extnctlon 2- extraction o v e W 95 36 34 23

< 1 5 4 4

95f 12 41f6 3 8 I 6 2712

Part of the overall PCB concentration cdculation for experiment SG-2 was the combination of results arising from a second 4 hr Soxhlet extraction using fresh soivent, with the initial result. The second extraction was only done on four of the sarnples, one sample representing each type of treatment, dry soil and 0% control included. The amount of PCB extracted in the second extraction was calculated as a percentage of the total and factored into the finai PCB concentration of each individual red t . The second 4 hr of extraction was able to extract additional PCBs fiom each type of sarnpie. The percentage of total PCBs extracted in the additional extraction period was less than 1% of the total for the dry soil sample. The amount of PCB detected after a second extraction of the 0% control and the two treated samples was 13%, 10% and 14% of the total found in each respectively. Clearly a significant amount of PCB remained in the wet samples following the standard Soxhlet extraction. Whereas the amount of remaining PCB detected in the dry samples was within the extraction eficiency predicted by the decachlorobiphenyl (DCBP) surrogate standard, that of the treated samples was not. The extraction efficiency of the DCBP standard was clearly not representative of efficiencies for PCB extraction in the treated samples.

The amount of PCB left behind in the sample, afier a standard extraction, remained in question. Was the second extraction enough to coilect al1 of the remaining PCBs? To investigate the answer to this question, samples first undenvent a standard extraction followed by an overnight extraction with fiesh solvent. The two active treatments that were chosen for this experiment were 6% H2@/0.01 M ~ e ~ + / pH 3 and a treatment with straight 10% NaCl only. The results of these experirnents are in table 5-3.

The additional overnight extraction resulted in a vast improvement in extraction efficiencies. Whereas experirnents SG-1 and 2 could not account for between 50 and 60% of the PCBs in the 0% control samples, 0% control saniples of experiment SG-3 were only missing 33%. The amount of PCB recovered fiom the additional overnight extraction was 33% of the 0% control total PCB concentration, 22% of the 6%/ ~ e ~ ' / pH3 total concentratioa, and 20% of the 10% NaCl total concentration. Clearly the additional 4hr of

Table 5-3. Experiment S G 3 (96-SG81 soil)

-duminumcoatcd stoppcrs double N a m -second extracSon (overnight)

treatment '

dry soi1 O"rb conuol 6%. 0.01M FC". pH 3 10% NaCl

apparent % reduction (dry)

3 3 60 59

mtrlt ( P P ~ PCB) lu ertracîîon 2" extraction w e d

44 30 3 1

2 1 8 8

96k4 65I6 38i4 39f 5

extraction tirne did not recover ail of the PCBs in experiment SG-2, and it was Iikely that some PCBs still remained in samples following ovemight extraction in experiment SG-3.

Experiment SG-3 shows that treatment of soils with just NaCl resuited in the same apparent reductions in PCB concentration as treatment with 6% ~ 2 0 t / ~ e ~ + / p ~ 3. This time, when a t-test was perfomed on the data, a signifïcant difference was found between the control and the two respective treatments, p<0.01 for both treatments. It was suspected that the acid added to the 0% H&/pH 3 treatment in experiment SG-2 reduced the efficiency of extraction, however the t-test did not detect a significant difference relative to the control results. The addition of NaCl altered the soil slurry in some way such that the apparent concentration of PCBs was reduced relative to the control. It is Iikely that the addition of HCI had the same effect. This phenornena is discussed in more detail uoder "incomplete Soxhlet extraction".

5.3.3 Complete drying of samples prior to analysis

The 0% control samples contained significantly more moisture when submitted for analysis than did the dry untreated soil samples, -30% compared to -5%. Therefore, samples analysed for experiment SG-4 were filtered and then dned completely before analysis. The danger in doing this was that additional PCBs could be lost to evaporation, the primary reason why standard analytical techniques avoid such a step. However, studies that had monitored PCB volatilisation during bioremediation studies only reported significant loss in the lower chlorinated congeners, 4 chlorines and less (Chiarenzelli et al.., 1996). Aroclor 1260 contains primary congeners with an average of 6 chlorines, so evaporation would be unlikely. Furthemore, no significant losses due to evaporation were detected during the SG-1 experiment, therefore, drymg of soils was not expected to result in furiher PCB loss. The results of Experiment SG-4 are show in Table 5-4.

Table 5-4. Experiment SG4 (96-SG81 soil) 1 -samples dned ovemight treatment r esult % reduction

By eliminating al1 of the moisture from the treated samples, complete exmiction of

PCBs was achieved using the standard Soxblet extraction process.

drv soi1 0% control 6%, pH3,10% NaCl

The effect of àyng samples was tested in an experiment that directly compared 0% control samples that had been dried to those that had not been dried. Two sets of dry samples were also analysed One set was taken directly from the bulk source of soii, the other was partitioned into samples and allowed to dry for an ovemight period. The results of these analyses are in Table 5-5.

(ppm PCB) 101+3 9913 9513

It is believed that the presence of excess water prohibits contact between the dichloromethane @CM) used for extraction and aii of the soil particles. DCM and water are non-miscible. hesumably the flow of DCM through the thimble during extraction drives the water into localized globules enveloping whole portions of the soii sample. Soi1 that ended up encapsulated by water would not have corne in contact with DCM and as a result PCBs would not have been extracted f'rom the sample, nor would they have been included in the overall calculation of concentration.

(dry)

2- 5

Table 5-5. Experiment SG7, cornparison of dry vs. wet PCB soil extraction

- 2 sample sets ûried - 2 sample sets

analysed wet

treatment dry soi1 (dried)

dry soi1

0% control (dried)

O%control(wet)

result (ppm PCB) 1 17+3 121k4

1 1 7+3

44k5

% reduction (dry)

63%

5.3.4 lncomplete Soxhlet extractions

In experiments SG-1 through 3 samples that received one of HCl, FeS04, or NaCl displayed apparent reductions in PCB concentration, without the presence of hydrogen peroxide. The only explanation for these apparent reductions is that the change in soil propeaies brought about by the addition of the various reagents rendered Soxhlet extractions even more inefficient than they were for the 0% control experiments. In al1 of these experiments, sluny filtrates were relatively clear compared to the 0% connol experiment filtrates. The coagulation of fine suspended particles is a common effect caused by raising the ionic strength of an emulsion (Shaw, 1992). The same clarification

effect that was apparent in previously treated filtrates using hydrogen peroxide was also apparent in the samples that only received one of the three amendments. A possible

explanation for reduced extraction efficiencies is that soil-DCM interaction was reduced by the effect of the various reagents. The same coagulating effect that caused finer soil

particles to remain in the filter would have reduced the overall soil surface area, reducing DCM contact with the fine soil particles. It was shown in analysis of the filtrate form 0% control samples that fine soil particles hold a signifiant amount of PCBs. If these fine particles were trapped in tightly bound micelles, the PCBs contained within would not be available for extraction.

M e r having dried and thea analysed samples fiom experiment SG-4, it appeared that no signifiant reductions in PCB concentration occurred due to treatment with acidified hydrogen peroxide and iron or with acidified hydrogen peroxide and NaCl. Reductions in PCB concentration that had been reported in early experiments may have only been a function of inefficient extractions and not oxidation.

Experiment SG-8a treated two sets of soil in the same way with 6% hydrogen peroxide and 0.01 M FeS04. One set was dried overnight following filtering, the other was analysed immediately after filtering while it was still wet. The results of experiment SG-8a are included in Table 5-6.

Table 5-6. Experiment SG8 results (96-SG-81 soii)

Results of experiment SG-8a show that treatment with 6% hydrogen peroxide and 0.0 1 M FeS04 did not result in a reduction of PCB concentration. Resuits also show how when samples are analysed wet, a false reduction in PCB concentration is achieved.

treatmen t drv soi1

iiried overnight

-wet anahsis

Individual peak analysis comparing &ta fiom experiments in which sarnples were analysed wet and dry are included in Figure 5-1. Experiments SG-7 and SG-8 were carried out in sets of 2 x 5 sarnple batches - one batch of 5 was anaiysed wet, the other dry. The procedure for individual peak anaiysis that produces graphs such as those displayed in figure 5-1 was discussed in detail in the previous chapter. Graphs in Figure 5- 1 display negative slopes when samples were analysed wet and positive slopes when samples were analysed m. Both the 0% control, of experiment SG-7, and the 6% H*O~/F~Z+, of experiment SG-8, wet analysed results show a negative tinear best fit line for the individual peak data. The data for the dried 0% control data produced a linear best fit with a siightly positive slope, and the dry andysed 6% H ~ Q / F ~ ~ + data produced a positive slope similar to those discussed in the results of the previous chapter.

remit (ppm PCB) 66k2

, 6%, 0.01 M ~e '+

6%. 0.01 M ~ e "

% reduction (dry)

69k4

22&4

-5%

67%

Experiment SG-7

Experiment SG-8,6% treatment

dry sail rn 070

A 0% (wet) I

L h e a r (0%) - Lhear (0% (we!)) 1 - LHiear (dry soit) '

Figure 5-1. Individual peak analysis for experiments S G 7 and SG8.

The barrier to desorption of PCBs into the DCM provided by the presence of water in the soi1 made extraction of the PCBs incomplete. For this reason slight differences in ease of extraction between different congeners became apparent as can be seen in the individual peak analysis plots of the wet analysed sarnples. However, when sarnples are extracted dry, no such barrier to desorption fiom the soil rnatrix exists and vimialIy all of the PCBs are extracted in the right proportion, as seen in the dry analyseci, 0% control data. Individual peak anaiysis for soils treated with 6% &02/l?e2+, wet aoalysed, show complete suppression of the positive slope seen in the dry anaiysed sarnples. The positive siope is an indication that some oxidation of lesser chlorinated congeners may have occurred as a result of treatment with Fenton's reagent.

5.4 Conclusion of the PCB mass balance investigation

The treatment of soils with any combination, one or aii, of HCl, NaCl, FeS04, a d o r Hz@, in an aqueous soil slurry causes the coagulation of fine soil particles. This alteration to the soi! slurry strongly inhibits the abiiity of the standard Soxhlet extraction to extract aU of the PCBs fiom a wet sample. For this reason ai l samples must be thoroughly dned prior to extraction. This phenornena appears to be previously unreported in the literature and suggests that results obtained by others may be, in fact, exaggerated.

6. Saglek Chemical Remediation Experiments

6.1 Introduction

Antenna Hill is the name given for a hill at the long range radar station at Saglek. The h i U housed two large tropospheric antemae and various buildings that contained a variety of eleciricai equipment. When the structures on the hi11 were tom dom, much of the debris was bumed and buried on the site. These past activities have led to the contamination of the hili with a substantial amount of PCBs. Extensive contaminant delineation performed by the Environmental Sciences Group bas revealed that there are approximately 1200 m3 of soil contaminated with Aroclor 1260 in excess of 50 ppm on Antenna Hili. The majority of this contamination is in the vicinity of the main concrete foundation.

In the summer of 1996 experiments were performed on Antenna Hill to investigate the viability of a Fenton's treatment for the remediation of the contaminated soil. The strategy was to use methods that had been developed in the lab previous to the field work. The methods that had showed the most promise at that time in the lab were scaled up and used to treat several hundred kilogram of contaminated soil in 32 separate experiments.

One type of experiment used 6% hydrogen peroxide only, another 6% hydrogen peroxide and NaCl and the 1 s t used a sequential treamient of 6% hydrogen peroxide followed by treatment with NaCl. Al1 experiments involved alteration of slurry pH to 3.

Experiments were canied out in two different types of reactors; one made use of an irnpeller type stimng mechanism, the other a cernent mixer. As well as different mixing actions, soils with varying degrees of contamination were also used. Sets of experiments were perfomed in batches such that each batch used a single source of contaminated soil. Each set consisted of each of the 3 previously mentioned experiments, and a control experiment, referred to as a 0% control, as only water was used to f o m the slurry.

The importance of lessons leamed duriug the initial field trials could have important repercussions for any fithire work to be carried out at Saglek

6.2.1 Soil source

Soil was coilected for all experiments fiom two general areas. The soil with the highest concentration of PCBs (1500-2000 ppm) was collected from an area to the north eaa of the large concrete foundation in the vicinity of ESG tag #1070. This highly contaminated soil was split up into three different batches, 1, 2, and 4. The other soil was coiiected from an area of lesser contamination (-100 ppm) on the south side of the concrete foundation near tag #1089, and made up Batch 3. Soil was dug up manuaiiy using shovels and sieved once through a 5/16" sieve onto a plastic sheet. This coarse sieved material was then sieved again through a mesh #10 sieve (2 mm) onto a separate sheet of plastic. Soil was sieved through both sieves manually and was found to be very labour intensive. At any larger scale, soil would have to be sieved mechanicaiiy. Pnor to starting a batch of experiments, an appropnate amount of fine sieved soil was set aside in a large plastic container and thoroughly mixed. M e r having homogenized the soil through sieving and mking, several soil samples were taken fiom different areas of the container. Some samples were analysed using PCB test kits on site to ensure appropnate PCB concentrations were obtained, the procedure for penorming field malysis for PCBs is presented in Chapter 3. Soil was weighed out into a pail which was suspended fiom a spring loaded scale; weights were accurate to within 0.3 kg.

6.2.2 Soil washing experiments

A soil washing experiment was conducted on some of the stones that were collected during sieving operations to determine whether or not they could be

decontaminated sirnply by rinsing off fine particles with water. This was done by placing 10 kg of stones with 10 L of water in a cernent mixer and mùMg for 10 minutes, then decanting the water and repeating the process 2 more times with fkesh water. Samples of the stones were taken before and after the soi1 washing process was cornplete and these were subsequently anaiysed by GUECD.

6.2.3 Met hods and materials

Al1 experiments were performed in sets of four, with the exceptions of the scaled up cernent mixer, soil washing and in-situ experiments. Each set of four experiments was perforrned on a homogenized batch of soil and consisted of a 0% control experiment, in which only water was added to the soil and mixed for three hours, and three different treatments. These three methods had been previously developed in a laboratoiy and were briefly discussed in the introduction.

- Type 1 experiment- 3 hr, 6% Hz@, pH3 ,1.25 L: 1 kg (1iquid:soil ratio)

-Type 2 experiment- 3 hr, 6% HZ02, NaCI, pH3, 1.25 L: 1 kg: 100 g (liquid:soil:salt ratio)

- Type 3 experiment- sequential treatment 1.25 L: 1 kg: 100 g (liqui&soil:salt ratio)

-3 hr, 6% H202, pH 3

-3 hr, addition of NaCl to slurry

When discussing the three different Ends of experiment they will be referred to by Type 1,2 01-3.

Chemical reagents had to be packaged in a way that was cornpliant with the air transport regulations, therefore dilution and packaging in 1 L bottles was essential. The hydrogen peroxide that was used for these experiments had been diluted to 15% in the laboratory prior to shipping it to Saglek. This hydrogen peroxide was made fiom a 30% H202 solution that had been purchased from Fisher ScientificTM. Transport of chernicals in the future, where possible, should be can-ied out by swnmer sea lift to avoid this effort. For experiments using the electric stining motor and 6 kg of soil, hydrogen peroxide and 2

M HC1 was measured out in a graduated jug and cylinder respectively, and then added to a 20 L polyethylene pail. For experiments using salt, the sait was weighed on an appropriate scale and added to the rapidly stirred soil slurry. The pH of the slurry was measured using pH paper once ail the ingredients had been added and the mixture was stimng. Foliowing 3 hr of stining, pails were set aside to allow for settling of the soil particles.

Experirnents performed using the cernent mixer involved treating 10 kg of soil Ui

12.5 L of liquid and were carried out in the same way as for the elecûic stimng motor. When the cernent mixer was being used samples were taken immediately after the 3 h o u mixing period to aliow for rinsing of the mixer and commencement of the next experiment.

SampIes were taken fiom both the cernent mixer and the pails while aIl of the reagents were stili in the respective reactor. Care was taken to withdraw a representative sample from the reactor using a plastic scoop. To accomplish this, portions of the sample were taken randody fiom various positions in the reactor. Samples were placed in sterile, clearly labelleci WhirlpakTM sample bags and refrigerated at 4' C until analysis had been performed. Al1 analysis of PCBs was camied out by GCECD.

6.2.4 Electric stirrer mixer

Two types of e n g apparatus were used to perform the Fenton's experiments at Antenna Hill. In one type of experiment, 6 kg of soil were treated in a 20 L polyethylene pail. The sluny was stirred using an electric stimng motor mounted on a wooden frame that was constructed on site and powered by a gasoline powered generator. The stirrer is displayed in Photograph 6- 1. The impeiier shaft entered the pail through a hole cut in the lid, so that none of the contents could spili out, and the impeller was positioaed so that it rested just above the bottom of the pail. The inipeller itself was a three blade bras propeller with an 8cm diameter. In this type of reactor, aII of the iiquid ingredients were added first. Once the liquid ingredients had been added, and the impelIer was placed in position, the motor was started. Once the liquids were being stirred the soil was slowly added to the mixture. The ingredients were added in this order to ensure immediate and complete suspension of al1 the soi1 particles.

6.2.5 Cernent mixer reactor

The second type of mixer that was used was a portable cernent mixer displayed in Photograph 6-2. The mixer was of steel constmction and was powered by % hp electric motor. On the inside of the mixer there were three steel mixing blades. In the cernent mixer 10 kg of soi1 was treated at a tune as opposed to 6 kg in the pails. Unlike the

procedure used for the stirring mixer, soi1 was added to the cernent mixer fïrst followed by

the liquids and then the mixer was started. Due to the tumbling nature of the mixer, the . order in which ingredients were added did not affect mixing efficiency.

Photograph 6-1. The electric stirrer reactor

65

Photograph 6-2. The cernent mixer reactor

6.2.6 Scale-up experiment

In order to test the effects of increasing the amount of soi1 while decreasing the amount of liquids, an experiment was performed on 40 kg of Batch 4 coarsely sieved soil. The soil was rnixed in a cernent mixer at fïrst for three hours with oniy water. This was sampled after three hours, at which time 3 samples were taken h m the mixer. The next phase of the treatment involved adding 10 L of 15% &O2 to the existing 20 L of water. After another 3 hr of mixing two more samples were taken fiom the mixer. Finally, 2 kg of NaCl was added to the m i m e , which was mixed for another 3 hr, and sampled three more times.

The final experiment investigated the viability of an in-situ treatment system. Three 1 m2 square plots of soi1 were staked out at various locations on Antenna hill. One plot (Plot 1)was located in the vicinity of tag RRMC70, the second (Plot 2) between sample tag# 1052 and the east side of the main concrete foundation, and a third (Plot 3) to the south east of the main concrete foundation. Two samples were taken fiom each the no& and south side of al1 three plots. Pottions of the samples were taken from ai i over the sampling area and mixed together in a Whirlpakm sample bag, thus providing a "composite sample" of untreated soil. Following initial sampling, plots 1 and 2 were watered with 6 L of 15% HzO2, Plot 3 received 6 L of water. The following day

composite sarnples were taken again from the north and south halves of each plot.

6.2.8 Summary of experiments

*EIectric stirring motor

Batch #1 soi1 (2050 ppm Aroclor 1260)- 2 sets (Set #1 and Set #2)

Batch #2 soil (1 24 ppm Aroclor 1260)- 2 sets (Set #3 and Set #4)

*Cement mixer

Batch #3a soi1 (1780 ppm Aroclor 1260)- 1 set (Set #5)

Batch #3b soil (1780 ppm Aroclor 1260)- 1 set (Set #6)

Scaled up cernent mirer

Batch #4 soil (375 ppm Aroclor 1260)

Soil washing

Batch #l , small Stones

ln-situ experiment

3 different plots of undisturbed soil

* note- Each set of experiments consisted of one 0% control experiment plus three different treatments, Type 1 (6% Hz%), Type 2 (6% H202, NaCl), Type 3 (sequential).

6.3 Results

6.3.1 Soil washing

Soil washing experiments were carried out on two 10 kg portions of andl stones that were produced during sieving of highly PCB contaminated Batch 1 soil. The unwashed stones had a dirty appearance from being covered with h e r soil particles. After just one wash, the stones were visibly cleaner. AU of the fine silt materials appeared to be suspended in the water which was poured into a separate container. The stones were washed a total of three times. A sample of the stones was taken before and after the soil washing was performed and submitted for analysis. The results of the soil washing experiment are displayed in table 6- 1.

Table 6-1. Results of washing experiment, 10 kg of mail stones washed 3 times for

I I I I 1 % reduction 1 I

10 min with 10 L of water. (concentrations of hoclor 1260 expressed in ppm)

treatment

6.3.2 Stirred reactor

unwashed

washed

Control experiments conducted with the use of the electric stinïng motor and the polyethylene pails displayed a good vortex while stimng. The colour remained a dark brown throughout the reaction and settling was quite rapid once the stimng propeller was removed fiom the sluiry. When the sediment was sampled, there was a layer approximately 1 cm thick of very fine silt on top of tbe sediment. The sample was taken by scooping out portions of the soil that included material fkom al l layers and positions of the pail.

expt #l results

The Type 1 experiments using 6% hydrogen peroxide and pH 3 displayed some foaming during mixing. The stirring motion of the propeller also formed a vortex in these

1250

393

expt #2 results

1100

389

average apparent

1170 391 67

experiments, hcwever the colour of the mixture was a bit lighter than that of the control. Once the mixing had ceased and the impeller was removed fiom the sluny, the mixture continued to foarn and a thick layer formed on the surface of the iiquid. Evident in this

foam was a large amount of fine soil particles. When a sample was coliected Rom the Type 1 experiments, the suspended particles had not fùlly settled to the bottom of the pail due to the continued generation of gas. Sarnples were coilected in the same way as the control samples were, however, the layer of fine silt that was found on the top of the control sediments was not apparent on the sediments of the Type 1 experiments; nor was it apparent in the Type 2 or 3 experhents. Another interesting characteristic of both the sediment and the particles suspended in the foam was the presence of reflective particles thought to have been mica. These reflective particles were not apparent in the control experiment. The same shiny particles had been observed in Fenton's treated soils in the laboratory .

The addition of NaCl to the treatment in Type 2 experiments appeared to increase the rate of bubbling in the mixture and increased the thickness of the foam once the stimng was complete. The Type 3 experiments, which saw the addition of NaCl to a Type 1 experiment which was then stirred for another 3 hr, displayed sirnilar foaming characteristics to the Type 2 experiments.

As the experiments had been sampled pnor to full settling of the soil particles, two experiments were set aside for sampluig over several days. A 0% control experiment and a Type 3 sequential experiment were both sampled three more t h e s on days 2, 3, and 4. Over this three day period the sequential experiment did continue to settle and the silt layer on the samples was more apparent though not as thick as on the control. Nor was the

tiquid any clearer or the foam on the surface of the mixture duninished to any signifiant degree.

The results of experiments that used the electric stimng motor are displayed in Tables 6-2 and 6-4. Table 6-3 shows results for experiments performed on highly contaminated soil, and included in the table are results of loss on ignition tests that determined organic content of the sample. The soil used for these experiments had an initial (dry) concentration of 2OSOf 28 ppm Aroclor 1260 and a loss on ignition of 1 3%. Two sets of identical experiments were perfonned on this soil and appear as Set #1 and Set #2 results. Table 6-2 shows the results of consecutive daily sampling of the sequential and 0% control experiments that had been set aside fkom experiment Set #1 and #2 respectively .

Table 6-2. Results of field experiments treating 6 kg of highiy contaminated Batch L soi1 in the electric stirrer reactor. (concentrations of Aroclor 1260 expressed in ppm)

6% H24, pH 3 6% Hz&, NaCI, pH3

Seauential

Table 6-4 shows the results of two identical sets of experiments, that made use of


Table 6-3. Results of repeated daiiy sampling of Set #1, sequential and Set #2,0% control. (concentrations of Aroclor 1260 expressed in ppm)

the electnc stimng type reactor, perforrned on lesser contaminated soil. Batch 2 soi1 used

1 150

1240

1060

Set #2,0% control Set # 1, seauential

for these experiments had an initial dry concentration of lMf 26 ppb Aroclor 1260. These

Set #2 results

1420

loss on ignition

1.1%

treatment

0% cootrol

resuits are listed as Set #3 and Set #4 results in Table 6-4.

average

1460

Set #l results

2400

0.7%

0.9%

0.6%

day 1

1420

1060

1110

1390

770

average

19OOk625

975k140

Table 6-4. Results of field experiments treating 6 kg of lesser contaminated soil in the electric stirrer reactor. (concentrations of Aroclor 1260 expressed in ppm)


49%

trea tmen t

0% controt

6%H~@,pH3 6% E&Oz,NaCl, pH3

Sequeutid

1130

1320

918

day 4

2280

934

day 2

2570

796

23

10

37

day 3

1310

1110

Set#3resuits

34

35

59

39

S e t M r e d t s

88

33 48

24

average

61 34 54

32


44

11

48

6.3.3 Cernent mixer

Unlike the experiments that used the electric stimng motor reactor, the cernent mixer reactor was able to treat 10 kg of soil with 12.5 L of liquid The control experiment was the first time the mixer had been tested in the d n g of this type of soil slurry and the mixing action appeared to be quite effective. During the initial minutes of the 3 hr mixing penod, some of the soil did stick to the bottom of the mixing chamber. However, &er several rotations none of the soil was sticking to the mixer. Following the 3 hr mWng penod a brkf settiing period was all that was required for the Liquid to become relatively clear, though settling was obviously not complete. Like the stirring motor control experiments, the cernent mixer control experiments also had a significant layer of fine silt, though to a lesser degree. Due to the short t h e fhme it was necessary that the cernent mixer be used constantly. Consequently samples had to be taken alrnost immediately after M n g . Therefore very Little settling was able to occur, except in the case of the control which senled more quickly.

The Type 2 experiments in the cernent mixer proceeded in a manner similar to those of the electnk stirrer. The mixture bubbled and took on a slightly üghter shade than the control. Unlike the stimng experiments, however, the mixture also gained a slightly msty colour and oxidation of the iron walls of the mixer was evident. Following the mixing, and prior to the sampling, the mixture started to accumulate foam on top of the liquid which, as was previousiy observed, suspended some of the b e r soil particles. Addition of NaCl in both the Type 2 and Type 3 experiments had the same effect that it bad on the stimed experiments i.e. the mixture appeared to bubble more vigorously and the foam that was formed following mixing was slightly thicker. The presence of reflective particlesin the sediments and foam of these experiments was also observed.

The cernent mixer experiments were conducted on Batch 3 soil having an initial (dry) concentration of 1780 ppm and a loss on ignition of 1.7%. Two sets of experiments were carried out using separately homogenized portions of the Batch 3 soil. The results of experiment Set #5 and Set #6 are displayed in Tables 6-5 and 6-6 respectively.

Table 6-5. Results of field experiments Set# 5 treating 10 kg of highly contaminated soil in the cernent mixer reactor. (concentrations of Arocior 1260 expressed in ppm)

treatment

0% control

6 % H2G, pH 3 6% Hz&, NaCl, pH3

Sequential

6.3.4 Scale-up experiment

Table 6-6. Results of field experiments Set# 6 treating 10 kg of highly contaminated soi1 in the cernent mixer reactor. (concentrations of Arocior 1260 expressed in ppm)

The cernent mixer reactor was used for an experiment that treated 40 kg of a coarse sieved, Batch 4 soil. The control samples were obtained from this experiment by mixing the soil with 20 L of water for 3 hr and then sampling. Because the üquid to soil ratio was reduced substantially fiom previous cernent mixer experiments, the slurry was quite thick, however, particles did seem to be weli suspended as no material was sticking to the walls of the reactor. Mer the initial 3 hr mixing penod, 10 L of 15% Hz& was added to the slurry and the mixer was started up again and rnixing continued for another 3 hr. The appearance of the mixture was vev similar to that of the correspondhg 10 kg

experiment with the exception of the thickness. For the final 3 hr of the experiment, 2 kg of NaCl was added to the mixture to simulate a sequential experiment; predictably, the

mixture's bubbling was slightly intensified. Batch 4 soi1 that was treated in this experiment had an initial dry concentration of 375k33 ppm Aroclor 1260. The results for this expenment are shown in Table 6-7.

Set #S results

1160

1 O00

1460

95 1


loss on ignition

0.3%

0.5%

0.8%

0.5%

Set #6 results 934

apparent % reductioa

13

O

18


Table 6-7. Results of beating 40 kg of coarse sieved, Batch 4 soü, in the cernent mixer. (concentrations of A

40 kg coarse sieved , Batch 4 soil

odor 1260 expressed in ppm)

samg le description

control 0% Sample #1 Sample

#2 Sample

#3 5% H24, pH3 Sample #l

Sample #2

6.3.5 In-situ experiments

results 180 160 126 average 155+27

207 198 average 202

sequential Sarnple#I

Sample #2

Sample #3

In order to cany out in-situ experiments, three plots were staked out on different one meter squares of Antenna Hill. These areas were relatively flat so that liquid poured onto the surface would not flow out of the staked area. Once the "composite sarnples" were taken fkom either end of the plot, water or hydrogen peroxide was poured evenly

over the staked area. Some bubbling of hydrogen peroxide was evident, though the iiquid was quickly absorbed by the soil. The foliowing day when sampling occurred again, there were no visible differences between the control plot and the treated plots. Results of the in-situ experiments are displayed in Table 6-8.

152 147 143 average 147+ 5

Table 6-8. Result of in-situ Fento II's experiments. (concentrations of Aroclor 1260 expressed in ppm)

I I i 1 I 1

I 1 unbeated ( loss on 1 treated (24 hr) 1 loss on 1 Plot #3,0% con1101 North half

1 Plot #2,6L 15% H202 North half 1 401 I 1 399 I l

South haif Plot #1,6L Z 5% &O2 North half

South half

1 South half 1 41 9 1 1 495 1

result 62

6.4 Discussion

12 1

265 414

6.4.1 Soil washing experiment

ignition

Prior to the field experiments at Saglek, it was determined that the volume of contamioated soil in excess of CEPA regulations could be significantly reduced by

separating coarse material from fine matenal and then washing the coarse. M e r sieving several kilograms of soil through a #10 (2 mm) mesh sieve, 46% of the overall mass bad been removed. Laboratory results showed that the removed coarse matenal had a PCB concentration 90% lower han that of the non-sieved source soil. Soil washing experiments in Saglek used the cernent mixer and water to wash 10 kg of fine stones. The PCB concentration in dirty stones was reduced by -70% and the reduction relative to the soil was -80%. In large scale operation a soil washing step could be incorporated that would reduce the amount of CEPA matenals by 30% or more. Such a reduction in material would represent substantial cost savings to any remediation plans. A small amount of water could be used repeatedly and treated with Fenton's reagent when it is no longer

1.1% 1.3%

needed.

6.4.2 Fenton's experiments

result 56

Examination of the results of the electric stirrer experiments seem to indicate that al1 three types of treatment were able to reduce the concentration of PCBs to some degree.

ignition

117 222 366

1 .O% 1.2%

Not only do the results teii us that some oxidation occuned but the observations made during the treatment aiso indicate reactivity in the mixtures.

The fim indication that the reaction was occurring was the generation of bubbles upon mking the reagents. This indicated that degradation of hydrogen peroxide was talang place. That hydroxyl radicals were being produced and oxidation taking place was indicated by the change in colour of the soil and the exposure of shiny particles. The darker colour of the sediment in the 0% control experiment was likely due to higher residual soil organic content. The oxidizing action of the hydroxyl radicals in the Type 1, 2 and 3 experiments could have caused the loss of some organic material and iightened the colour of the sediments. The Ioss on ignition data supports the idea that some organic material was oxidized. The shiny flecks that were found suspended in the f o m and sediments of the treated samples may also be an indication of oxidation of soil matenals. These shiny particles were not apparent in the control samples. It is Likely that whatever was coating these particles had been oxidized by hydroxyl radicals produced by the

Fenton's reagent.

The sequential treatment appears to have been the most effective followed by the Type 1 experiment, 6%/pH 3, and the least effective experiment, the Type 2 experiment that used 6% H202 and NaCl at a pH of 3 as shown in Tables 6.2, 6.3 and 6.5. This pattern of relative success is repeated in ail but the Set #3 experiments. Even in this experiment, however, we see that the Type 2 experiment is not nearly as effective as the Type 1 and Type 3 experiments (Table 6.4). The Set #3 data are pecuiiar in that the 0% control has a very low result of 34 ppm compared to the 88 ppm result of the Set #4 0% control. However the Type 1, 2 and 3 results obtained from the Set #3 experiments are quite comparable to those of Set #4. Results suggest that the process was successfid in lowering the PCB concentration below the CEPA level of 50 ppm

The results of the cernent mixer experiments also show some degree of contaminant reduction, with the exception of the Type 2 experiment in Set #S. These results also show the same pattern of relative effectiveness between Type 1 and Type 3 experiments. Unfominately, the results fiom the Type 2 experiments show mixeci results. The Set #5 result is 301 ppm greater thm the control and the Set #6 result indicated the greatest reduction of aü tbree types of treatment in the set. The lack of consistency in these two results is likely due to problems with the sampling method.

6.4.3 Treatment cornparison: Type 1 vs. Type 2 vs. Type 3

It is apparent fiom the results that the Type 2 treatment was not as effective as the Type 1 and 3 treatments. Initially it was thought that the NaCl wouid help to desorb PCBs corn the soil maûUr making them more amenable to oxidation by hydroxyl radicals. This was confirmed by several experiments that were carried out in the laboratory pnor to the field season. However, since retuming from the field it was discovered that by analysing samples while they were still wet, as was done in the lab prior to the field season, PCB extraction was incomplete. Experiments investigating extraction efficiencies for samples that had been treated in a variety of ways, and then analysed both wet and dry, revealed that results obtained from wet samples were unreliable. It was discovered that various treatments had different effects on the efficiency of the Soxhlet extraction beiog used to

extract the PCBs. In sumrnary, the relative effect of each treatment on the extraction cm be descnied as:

most efficient-------- least efficient

Therefore, what initially appeared to be an improvernent in treatment efficiency,

caused by the addition of NaCl, turned out to be false. In fact the addition of NaCL to the treatment process has a detrimentai effect on treatment efficiencies. Chlonde ion concentration in the sluny m y have contributed to hydroxyl scavenging by the following reaction

(14)HOW+ Cl- + HOCI- + W+ Ci + H20

k14 = 2x 10'' (mol L-')''s-' (Pignatelio, 1992)

At elevated concentrations of Cl-, given that the rate constant k14 is as high as it is, the majotity of hydroxyl radical would be consumed by reaction (14). If this were so, slight reductions in PCB concentration would be possible but not nearly as efficient as treatment without chlonde ion. Indeed, slight reductions were observed, and judging by the colour change in the soil oxidation of some organic material did occur, assuming that

tbe darker colour of the control was due to the presence of organic matter. That the Type 2 experiments seemed to bubble more rapidiy than the Type 1 experiments could be

atûibuted to an increased rate of hydroxyl radical scavenging, and hydrogen peroxide consumption.

Type 3 experitnents also showed a decrease in PCB concentration, however it was even greater than that of the Type 1 experiments. Since the first three hours of treatment in the Type 3 experiments was identical to a Type 1 experimenf a reduction of PCB concentration of at least the same magnitude wodd be expected. This is confinned by the data. That the Type 3 experiments often outperforrned the Type 1 experiments may be due to M e r PCB oxidation in the second three hours of mixing though based on Type 2 experirnental results it would have definitely been inhibiteci by the presence of chlonde ion. Accentuated bubbling and foam formation at the end of the experiment is evidence of Type 2 behaviour.

Though increased reductions in PCB concentrations were achieved using the Type 3 experiments, the Type 1 experiments were clearly the most effective at degrading PCBs. That m e r reductions could be achieved over an additional 3 hours of treatment with salt indicates that M e r treatment with 6% H2& couid be even more effective.

6.4.4 Cernent mixer vs. electric stirrer

The results fiom the cernent mixer experiments indicate that as a reactor it was not as effective as the electric stirrer. Comparing the results of experiments perfomed on highly contaminated soi1 fiom the electric stirrer and the cernent mixer, it would appear that the electric stirrer out perfomed the cernent mixer by a factor of 2 or 3 to 1. For Type 1 and 3 treatments respectively, the electric stirrer posted average reductions in PCB concentrations of 22% and 37%, where as the same results for the cernent mixer showed reductions averaging ooly 10% and 15%.

Stoichiometncaiiy, experiments performed in each reactor were exactly the same, therefore the difference in performance had to be due to Merences in reactor structure and or rnixing action. The inside of the cernent mixer was made of steel. It was evident that the steel uoderwent some oxidation noted from the presence of a mst colour in the slurry and rust on the inside of the mixer foiiowing experiments. It is possible that

reactions between the steel and the reagents inhibited the oxidation of PCBs by scavenging hydroxyl radicals or interfering in some other way. Iron however has been proven to promote the creation of hydroltyl radicals in many f o m , (Watts et al., 1993) and (Takemura et al., 1994), therefore a positive effect, if any, would be expected fiom using a steel reaction vessel. It is possible is that the polyethylene pail adsorbed some of the PCBs thereby increasing the apparent loss due to oxidation. PCB adsorption to polyethylene has been recorded and is known to account for concentration reductions of PCBs in aqueous solutions (E3edard et al., 1986). However, any loss of PCBs due to adsorption onto the walls of the polyethylene pails would have also occurred in the control experiments and therefore would not have accounted for a reduction in concentration relative to the control.

Since the difference in treatrnent efficiencies cannot be explained in terms of the structure of the different reactors, the difference must lie in the effectveness of the mixing action. Though the tumbling action of the cernent mixer appeared to keep the soil particles weil suspended, the action was not as violent as that of the electric stirrer. In the

pail with the propeller tuming, the soil sluny was whipped into a vortex with no apparent settling in the comers at the bottom of the bucket. This was tested by dragging a stirrhg rod through the s l q and feeling for undue resistance in the comers of the pail. Cnide as this method may be, it was effective in determinhg if aay build up had occurred. A

difference in mixing mechanisms could account for increased contacting between substrate and reagents, thereby accelerating rates of desorption and oxidation in the stimng reactor. This may have contributed to the apparent greater effectiveness of the stirred reactor over the cernent mixer, in reducing PCB concentrations.

When sampling the control experiments in the cernent mixer, PCB nch silt which had had a chance to settle in the stirred reactor pails, was stiIl suspended to a large degree in the cernent mixer. Because of the lack of settling, the amount of silt was not as great in the 0% control samples fiom the cernent mixer as was for the 0% control samples fkom the stirred reactor. AU of the treated samples were very low in silt content because it was suspended in the liquid and foam and not available for samphg in the bottom of either reactor. The distribution of silt caused the concentration of the 0% control fkom the

cernent mixer to be lower relative to treated samples than that of the stirred reactor, causing the apparent reduction in PCB concentration to appear greater for the stirred reactor than for the cernent mixer. Suspended particles as a function of perceived

oxidation of PCBs is discussed in greater detail below. Whether the electric stirrer was actually more efficient than the cernent mixer, or vice versa, is difficult to assess.

6.4.5 Reductions may be exaggerated

Under strictly controiled conditions, s i d a . experiments to those discussed here were carried out in the laboratory foilowing the 1996 field season during which the Saglek field experiments were camied out. Repeated and proven results have shown that treatment of Saglek soil fkom Antenna Hill, contaminateci with approximately lOOppm Aroclor 1260, with 6% H202 at a pH of 3, is not effective at significantly reducing concentrations of PCBs. However, the above results suggest that reductions in PCB concentrations were achieved under these conditions at Saglek during the summer of 1996.

Apparent reductions in PCB concentrations, that may have been misiakenly attributed to chernical oxidation, could be amibuted to several factors. One reason the concentration of PCBs in treated soil could have been lower than that of the untreated soil is due to suspension of PCB nch particles. Fine soil particles that were suspended in the foam and liquid of treated experiments may have been higher in PCB concentration than the sediment that was taken as a sample. Because dned samples had been anaiysed using correct standard procedures, exaggerated reductions could not have been due to anaiytical error.

In control experiments, however, these particles were able to settle to the bottom of pails and, to a lesser extent in the cernent mixer, prior to sampling. Fine particles on the surface of sediments was evident in a layer of silt that coated the sediments of O% control experiments. Because of the large collective surface area of these fine particles they would contain a higher concentration of PCBs than the larger particles that had settled quickly to the bottorn of the reactors. The absence of this silt fraction of the sediment in treated samples probably accounts for a large portion of the concentration reductions seen in the results.

Proof tbat the presence of silt in the control samples, and its absence of it in the treated samples, was responsible for false reductions of PCB concentrations m y lie in the

relatively d l reductions of the cernent reactor experiments. Because the cernent mixer

was in constant demand, the slunies did not get very much tirne to settle. Consequently,

the cernent mixer 0% control experiment sample wodd have contained less silt than that of the stirred reactor 0% control experiment, d g it more comparable to the treated (vimially siltless) treated samples. The differential in silt content for the stirred reactor was greater than that of the cernent mixer leading to greater degrees of contaminant reduction in the stirred reactor.

However, suspension of silt in ali 3 Types of experiments appeared to be equal by visual observation, if not greater in Type 2 and 3 experiments. Yet a signifiant

concentration gradient was observed among the three types of treatment. If the

assumption is made that al1 of the observed reduction in the Type 2 experiments was due to suspended silt, then some other factor must have been responsible for a portion of the PCB loss in the Type 1 and 3 experiments. The reduction due to silt suspension would account for at most 1/3 of the overall PCB reduction in the Type 1 and 3 experiments based on the above assumption. What must be called into question is the validity of the results themselves. Are these results reliable and could they be repeated again and again? In the case of the highly contaminated stirred reactor experiments, the resuits are fairy consistent. With the exception of the 0% control results in Sets #3 and #4 of the lesser contaminated stirred reactor results, results were also fâirly consistent. The fact that the same pattern of relative concentration is maintained in each set of experiments cannot be overlooked, and indicates a degree of consistency that cannot be attributed to chance alone.

Further proof that the Type 3 treatment resulted in oxidation of PCBs lies in the results of the experiments that were sampled on 4 consecutive days. Sampling each experiment four times aiiowed for a t-test to be performed on the two sets of data. The difference between the average concentration of the 0% control and the treated samples was 49%. Though standard deviations of the two averages were quite hi&. T-test results proved that the two data sets were significantly different, p<0.01.

It must therefore be concluded that the treatment of soils by methods Type 1 and 3 did result in partial oxidation of Aroclor 1260 in contaminated soils from Antenna W. The percentage of PCBs that were degraded is difficult to quanti@, but may lie between 5% and 20%.

Why success was achieved during field experiments and not in the laboratory may be attnbuted to several factors. The mixing mechanisms used in the field were different than the shaking used in the lab, and may have been more effective. The soil though very similar in appearance had different concentrations of PCBs and may have been different in other ways compared to the soil that was used in the lab, resulting in more effective treatment. The most ükely explanation for why reductions in concentration were seen in the field experiments and not in the lab experiments is the amount of t h e the samples were stored in WhirlpW sample bags before analysis. Wheo the samples were collected, they were placed in sample bags while still saturated with liquid. In the case of the samples treated with hydrogen peroxide, there would have been some unreacted hydrogen peroxide left in the bags. Therefore oxidation could have taken place inside the sample bags long after the samples were taken. Sample bags were observed to inflate with gas resulting fiom the degradation of hydrogen peroxide. As samples were not analysed for up to four months after they were taken, there was plenty of tirne for the remaining hydrogen peroxide to be consumed. Dwing laboratory experiments, sarnples were dned and

analysed in the day following treatment and would not have this extra opportunity to react.

6.4.6 PCB mass balance

Consider now, the difference in concentrations between 0% control samples and

the dry soil fiom which they came in the field experiments. Chapter 5 discussed PCB mass balance in ternis of the PCB escape pathways and analytical procedure. Results of the laboratory investigation revealed that Soxhlet extractions should be canied on ciried samples in order to achieve accurate results. Therefore, field samples were analysed on a dry basis, yet, with every batch of soil, the concentration of Aroclor 1260 decreased significantly between the dry untreated soil and the control experiments. These differences are tabulated in Table 5-9. The rather large discrepancy between the dry soil and control samples is disturbing and must be addressed. As a control experiment was performed with each set of experirnents, results could be accurately interpreted relative to the controls and independent of the dry soil.

Table 6-9. The dîerence between concentrations in dry soi1 and 0% control

A control experiment was performed with every experiment set such that the only component of the treatment that was rnissing was the active reagents. Those ingredients for the Saglek experiments were NaCl and hydrogen peroxide. ûtherwise the control soils were treated in the exact same way as the experiments. The samples were prepared in the same way, mixed with the same volume of iiquid, (scale-up experiment is an exception) for the same length of time, then sampled and analysed, in the same way. The control in these experiments was not supposed to have any effect on the PCB concentration, and should have contained the same amount of PCB as the dry soil. Therefore the question must be

asked, Where did the PCBs go?

experiments. (concentrations of Aroclor 1260 expressed in ppm)

Laboratory experiments discussed in Chapter 5 showed that PCBs were not escaping to the atmosphere; nor were they being dissolved in the liquid fraction. Therefore it is unlikely that they would have done so during field experiments.

Sarnple source

d q sieved soi1

0% coatroI % difference

The only explanation for the apparent reduction of PCBs in the control experiments, lies in the events leading up to the sampling of experiments. Treatment of the soil, independent of active reagents, resulted in a large fkation of PCB cootaining material to be omitted ftom samples.

The fiaction of sediment matenal that would have contained the highest concentration of PCB would have also been the finest, based solely on surface area. The other surfaces that would have contained high concentrations of PCB would have been organic rnatter, based on the lipophilic nature of PCBs. These materials would have also been the first to be suspended upon disturbance caused by sampling. The action of scooping up sediment, and then drawing it out of the vesse1 through the supernatant liquid, caused particles which were easily displaced to be swept away fiom the scoop. During laboratoty experiments fine particles that were decanted fiom harsh triple treatrnents,

Batch 1

2050 1460

29

Batch 2

124

61

5 1

Batch 3

1780

1060 41

Batch 4

375

155

59

discussed in Chapter 4, displayed concentrations an order of magnitude greater than the coarser material left in the flask.

Considering suspension alone, it would be logical to think that the cernent mixer control samples would have demonstrated the largest apparent PCB loss relative to the

stirrer. From the results, this would appear to be tnie. [f the 0% control of the lesser contaminated stirred reactor experiments is taken to be 89, then the % difference between control and dry soil for the Batch 3 soil is only 30%, Batch 1 soil 29%. The percent difference of the Batch 2 and 4 soils used in the cernent mixer were 41% and 59% respectively. Thus it would appear that the suspension of fine particles was responsible for an apparent loss of PCBs.

6.4.7 Organic content of samples as determined by loss on ignition analysis

Loss on ignition tests were performed on several samples taken during field experiments to examine the relationship between organic content and apparent reductions in PCB concentration. The organic carbon content was determined for the Set #1 samples of the stirred reactor, the Set #5 samples of the cernent mixer and the samples taken fiom Plot # 1 of the in-situ experiments. The concentrations, and organic content of respective samples is displayed in table 6-10.

Table 6-10. Relationship between organic content and reduction of PCBs (LOI- Loss on ignition) (concentrations of Aroclor 1260 expressed in ppm)

1 1 stirred reactor 1 cernent mirer 1 1 in- situ 1

1 seauential 1 1060 1 0.6 1 95 1 1 0.5 1 1 366 1 1.2 1 6%,NaCI 11240 10.9

The dry soil PCB concentration for the stirred reactor was 2050 t 28 ppm with an organic content of 1.8%. The cernent mixer dry soil had 1780 ppm PCB and 1.7% organic content. The above table shows a strong correlation between organic content and the

1460 1 0.8 treated 222 1 1.0

concentration of PCBs in the various samples. Results for the stirred reactor show how the PCB concentration was directly related to the amount of organic material in the sample. That trends in PCB concentration mirror those seen in organic content results provides support for arguments of suspended organic matenal.

It was stated in previous sections that apparent reductions in PCB concentration, and PCB rnass balance discrepancies, were due to the suspension of organic material. This is supported by the difference in organic content detected in the dry untreated soi1 and the 0% control samples. The organic content of the treated samples, however, follows the same trend relative to treatment type as overall PCB concentration. ûrganic content was highest in the Type 2 treated samples and lower in the Type 1 and Type 3 treated samples. Hydroxyl radicals are suspected to attack organic materials indiscriminately. Thus, it would be expected that reductions due to oxidatioa would be similar in both PCBs and total organic matter. This appears to be the case, and supports the idea that oxidation did

occur as a result of treatment with Fenton's reagent.

6.4.8 Settling of soi1 particles over time

To test the effects of settling in the stirred reactor sedimeots. two pails were set aside and sarnpled on 4 successive days. The results of this experiment are included in

Table 6-3. It was suspected that by allowing the mixtures more time to settle, finer rnatenals previously unavailable for sampling could get collected and increase the PCB concentration of the sample. This did not happen in the sequential experiment and results did not display any change in overall PCB concentration with respect to settling time. The average concentration of the four samples was 975+ 140 ppm Aroclor 1260.

Sampies taken from the control experiment on the four consecutive days were rather inconsistent. From one day to the next the concentration of the samples that were obtained varied by up to 1 100 ppm Aroclor 1260. The inconsistency in resuits showed no relation to the amount of settling time, but revealed sensitivity in the sampling procedures. A slight unintentional change in the way the sample was coiiected on &y 2 and 4 resulted in the inclusion of highly contaminated matenal in the sample (fines and organic matenal discussed previously in this chapter).

That sample concentrations in excess of those for dry Batch 1 soil were obtained Rom the Set #2 0% control experiment supports the theory that PCBs were not Iost during the control experiments. It is clear from this data that when samples where disnirbed in even the slightest way, PCB rich material was not included in the sarnple. Taking samples from soil slurries proved to be inconsistent and resulted in samples that were not representative of the overall composition of the scil. Future experiments should adopt a practice whereby samples are dried and properly homogenized pnor to sampling.

6.4.9 The scale-up experiment

ui this experiment an attempt was made at treating coarsely sieved soil, in greater quantities with l e s reagents. The results show that no signifiant reductions in PCB concentration were achieved. An indication of this resuit may be that larger liquid volumes are necessary in order to have interaction between oxidizing species and the PCBs. The results of this experiment reinforce the problems associated with sampling. The variation between sarnples and between sets of samples shows how difficult it is to take consistent, representative samples from soil slumies.

6.4.1 0 In-situ Fenton's experiments

It may appear that a slight reduction in PCB concentration was expenenced in Plot # 1 of the in-situ experiment, 12% and 16% for the south and north half respectively. Plot #2, expenenced no net change in concentration and neither did Plot #3, the control plot. Reaiisticaliy, none of these plots underwent any detectable change in PCB concentration. The plots that were staked out were treated as they were discovered. No homogenization of the surface soil took place. Instead a "composite sample", which included a combination of surface soils fiom d l over each half of the plot (north and south), was taken in an attempt to obtain the mean PCB concentration of the area.

The resuits show a ciifference in concentration fiom one haK of a plot to the other. Where Plot #2 seems to be relatively uniform, Plots #1 and #3 have almost 50% differences between concentrations of the aorth and south side samples. The difference

between the two sides is duplicated in both the untreated and treated samples, giving some ment to the "composite sample" method of mean concentration measurement. What the results fiom north and south sides of the plots also shows is inconsistency in contamination levels over a giveo area of surface soil.

In order to detect a small reduction in overall PCB concentration due to an in-situ treatment, experirnents must be camïed out on homogenized plots of soil and multiple composite samples must be taken and averaged to determine overall concentrations. The in-situ experiment perfomed at Saglek was designed to detect large reductions in PCB concentrations (>25%). The results show no indication of such a reduction and therefore it should be concluded that the in-situ treatment was ineffective.

6.5 Conclusions of the Saglek field experiments

1. Soi1 washing experiments were effective in reducing PCB concentrations in fine Stones by approximately 70%. A combination of these field results and laboratory results suggest that soil washing could reduce the amount of PCB material by 30% or more in

soils contaminated with up to 400 ppm PCBs.

2. Sampling fiom soil slmies does not provide consistent results nor does it

provide samples representative of the overall slurry composition and should be avoided in fiiture experiments.

3. Though treatment of PCB contaminated Saglek soil with 6% hydrogen peroxide was not effective in laboratory experiments it appears to have resulted in some reductions in PCB concentration during scaled up field experiments. Fenton's reagent can be scaled up for use in larger sa le treatment processes with the use of inexpensive, relatively "low- tech" equipment.

7. Conclusions and Recommendations

1. An investigation into the PCB rnass balance associated with Fenton's experiments revealed that PCB extraction by the Soxhlet method was ineffective on wet soils. It was found that samples needed to be completely dned prior to extraction. Therefore, aU samples from Fenton's experiments must be anaiysed dry in future experiments.

2. During field experiments, difficulty was encountered when removing samples directly from soil slurries. Resuits revealed that samples taken in this fashion may not have been representative of the entire soil mas. In the future slurries should be completely dried and then homogenized prior to sampling. This wiii ensure consistent representative samples are taken every t h e .

3. Dunng laboratory experiments it was discovered that the mass of soil contaminated with between 50 and 145 ppm PCBs could be reduced by up to 90% by treatment with a harsh triple treatment process. With M e r refinements, the capabilities of such a process could be substantially improved. Future experiments shodd be cmied out to optimize such a process.

4. Soi1 washing experiments canied out in the laboratory and during field experiments showed that the overall m a s of PCB matenals having up to 400 pprn PCBs could be reduced by 30% or more by sieving and washing of coarse matenal. Such a treatment could recycle water such that only a mal1 amount of water is ever contaminated. Contaminated water could then be treated with Fenton's reagent. Such a process shodd be incorporated into an overall remediation process as a pre-chernical treatment step.

5. Results of scaied up field experiments indicate that treatment of PCB contaminated soils with Fenton's reagent cm be achieved using relatively inexpensive, "low tech" equipment. The same scale-up equipment that was used durhg these field trials could be used for fûture field work involving harsher treatments to achieve reductions in volumes of "CEPA soils".

7.1 Design of future scale-up experiment

A fùhire scaied up field experiment shouid incorporate sieving of soil, washing of coarse materiais, and treatment of fine materials with a triple treatment/decanring process found to be successful in laboratory experiments. Overall m a s reductions of PCB contaminated soils of >go% could be achieved based on reported results.

1000 kg soü, [PCB] = 50-150ppm

700 kg sieved soü

Harsh triple treatment

70 kg fine material [PCB] >> 50 ppm 630 kg soil

[PCB] c 50 ppm

SoiI washing

300 kg of washed stones [PCB] < 50 ppm

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Documents

Using Fenton's Reagent · Acknowledgernents 1 would like to thank Dr. Ken Reimer, the director of the Environmental Sciences Group and my thesis advisor, and Dr. Ron Weir, the Dean