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NGI’s Strategic Institute Program 2003-2008 Final report, 30 September 2008 NGI report no. 20031020-4

Stability of contaminated sediments

2

Stability of contaminated sediments, NGI’s Strategic Institute Program 2003-2008, Final report.

Background

BackgroundThe Research Council of Norway (RCN) granted a five-year (2003-2008) Strategic Institute Programme (SIP) “Stability of Contaminated Sediments” to the Norwegian Geotechnical Institute (NGI).

The research program focused on advancing the state of knowledge on physical and chemical sediment stabil-ity, the understanding and prediction of contaminant transport, and the design of long-term containment methods.

OrganisationThe programme was coordinated by the Norwegian Geotechnical Institute under the overall supervision of Gijs D. Breedveld. Quality control and quality assurance was carried out by Knut H. Andersen, Technical Direc-tor, Kjell Karlsrud, Technical Director and Audun Hauge, Division Director Environmental Engineering. The research team consisted of Amy Oen, Anne Kibsgaard, Arne Pet-tersen, Espen Eek, Gerard Cornelissen, and Tore Kvalstad.

An Advisory Board has been formed to promote inter-action between researchers and stakeholders, as well as to adjust the research aims during the programme. The Board consisted of the following members:

Kristoffer Næs, Norwegian Institute of Water Research•Harald Solberg, Norwegian Pollution Control Authority•Torild Jørgensen, Oslo Port Authority•Inger Staubo, County Governor of Buskerud•Erle Grieg Astrup, Elkem•Trond Gulbrandsen, Statoil-Hydro •Guri Kirkhaug, Secora•Jørn Lindstad, Research Council of Norway•

Cooperation with universities and research organisations Contamination of sediments in rivers, harbour and the coastal zone is recognised as a problem with global dimensions. To find proper solutions cooperation between various scientific disciplines is required on an international level. The main research partners in this research programme were:

Norwegian Institute of Water Research, Norway•Department of Geosciences, University of Oslo, Norway•Norwegian Geological Survey, Norway•Institute for Marine Research, University of Quebec, •CanadaDepartment of Environmental Sciences (ITM), •Stockholm University, SwedenPatras University, Greece•Stanford University, USA•University of Maryland Baltimore County, USA•SedNet, EU•

This report presents the main results of the research pro-gram. A bibliography of the published papers is given in the last section of the report. Those who are interested in more detailed information are referred to these documents.

3Table of contents

Table of contents

4 Introduction

6 Contaminants and their behaviour

9 Field measurement

11 Improved risk assessment

12 Alternative remediation methods

15 Environmental benefit

17 Finding site-specific solutions

18 Bibliography

4


Introduction

Sediment challenges in NorwayIn Norway serious contamination of marine sediments has been found in fjords and coastal areas. The Ministry of the Environment has identified the abatement of these con-taminations as a top priority for the coming years.

As a result of the general depth of Norwegian fjord sys-tems, there is a limited need for maintenance dredging. Large-scale remediation will therefore be initiated based on environmental requirements only. Remediation and construction works will often exert extreme changes in physical/chemical conditions. These stresses might result in a deterioration of the present environmental status over a defined period of time.

To be able to assess the effectiveness of sediment reme-diation options, a proper understanding of the physical and chemical stability of the contaminants is required. This will allow a prediction of contaminant mobilisation and migration under various environmental stresses as well as support decisions on remediation priorities.

PolicyThe contamination of marine sediments in more than 120 areas has resulted in restrictions on the consumption of fish and fish products in fjords and harbours covering 1200 km2. At present all consumption of fish liver is dis-couraged for children and women in the fertile age. To prevent deterioration of the present situation, remedia-tion is predicted to cost NOK 8 billion. Improvement of today’s situation to a level that ensures no risk for the eco system is estimated to cost NOK 25 billion. The Norwe-gian Pollution Control Authority has identified 17 fjords as priority remediation areas, including harbour and dock-yards in the region. For each of these areas a regional remediation plan has to be developed. Remediation should be carried out within the coming 10 years.

Outline of researchThe main focus of the research program was on the integration of knowledge on the physical and chemical interactions in contaminated sediments, with the follow-ing objectives:1. Quantify the principal parameters determining the

physical and chemical stability of contaminants in the sediment matrix.

2. Determine the contaminant migration resulting from engineering operations in contaminated sediments, like dredging, backfilling and construction works.

3. Establish design criteria for containment methods with a long-term intrinsic stability and required safety.

4. Develop tools to evaluate effectiveness of remedia-tion methods.

5. Develop innovative methods for sediment remediation.

Research methodologyPhysical stabilityBoth physical and chemical characterisation of the sedi-mentary material are important to determine the stability of the contaminants. Dredged materials are usually softer than in-situ sediments. Classical geotechnical charac-terisation methods are not suitable for the determination of the properties of these sediments. This results in the use of large safety factors when the bearing capacity is evaluated. In this research programme physical stability has been studied using various methods to determine sedimentation and consolidations rates as well as very low shear strengths both under laboratory and field conditions.

Migration and transportHigh contaminant loads have resulted in increased levels of organic matter in near-shore sediments, resulting in anoxic conditions. The organic matter in the sediments effectively sorbs organic contaminants while the anoxic conditions stabilise heavy metals in sulphide complexes. At present there are few methods to predict the fraction of contaminants that can become available as a result of resuspension or other disturbances of the environ-mental conditions.

Introduction

Physicalstability

Contaminantmigration

Chemicalstability Containment

methods

Overview over the main areas of research in “Stability of Contaminated Sediments”.

5Introduction

Development of predictive tools for contaminant release is critical to quantify migration of contaminants, as well as risk assessment. Laboratory and field methods have been developed to quantify these processes.

ContainmentThe remediation of contaminated sediments has often been based on removal, triggered by maintenance dredging of harbours and major waterways. Dredging material has mainly been stored in controlled disposal sites. Capping has also been used as an in situ remediation approach. These methods have mainly been applied on an empirical basis and little is known about the critical factors in the containment solutions and the long-term stability. This program studied the long-term containment stability of different cover constructions as well as the natural consolidation conditions, both in lab and field. In addition the chemical interaction between capping material and sediment was studied, as well as the potential of innovative sorbent amendment methods.

Field studiesPilot study demonstration sites have been established at Oslo Harbour, Bispevika/Bjørvika (stability assessment, capping), and in Trondheim Harbour (sorbent amend-ment). The contaminant profile in the sediments from Oslo and Trondheim Harbour represents typical urban harbour sediments. The Oslo study site has been used to determine in-situ conditions concerning transport and migration as well as the effects of engineering operations and containment solutions. The Trondheim Harbour field pilot was aimed at in-situ testing of activated carbon amendment to chemically immobilize organic pollutants.

The top sediments in the inner part of the Oslofjord

provide a historic account of the industrial activities in the

region. The contaminated sediment layer can be clearly

observed in sediment cores by its black colour as com-

pared to the blue gray of clean marine clay. The thickness

varies from 0.5 to 4 m in the inner parts of the Oslo harbour.

Chemical analyses of the sediment material show a clear

transition in the chemicals applied in industry throughout

the industrialisation that started at the end of the 19th

century. The deepest and oldest part of the contaminated

sediment layer shows high levels of polycyclic aromatic

hydrocarbons (PAH) which can be related to a society

based on energy from coal burning and coal gasification

in the municipal gas plant of Oslo.

PAH levels decrease when electrification and energy

supply from hydropower dams take over. However,

polychlorinated biphenyls (PCB) are found in increasing

levels at this time as a result of their application in trans-

formers and electronic equipment. After the ban on the

use of PCB in 1980, PCB levels are observed to decrease in

more recent sediments. In the top layers of the sediment,

tributyltin (TBT) is clearly visible as a result of its extensive

use in antifouling paint for boats. Despite restrictions on

TBT use since 2003, reductions in sediment levels of this

compound cannot be observed yet.

Industrial history in Oslo harbour sediments

PAH16

De

pth

(c

m)

0

20

40

60

80

100

120

140

160

0 100000 200000

PCB 7

0 200 400

Concentration (µg/kg) Concentration (µg/kg)Concentration (µg/kg)

TBT

0 150 300

An archive of the industrial history of the Oslo region is stored in the fjord sedi-ments. The use of chemicals has changed with time as shown by concentration changes with depth in the sediment core.

6


An understanding of the physical and chemical stability is required to find solutions for contaminated sediments. This allows the prediction of potential contaminant mobilisation and migration and thus the environ-mental risks exerted by the sediments. Whereas natural processes act over years, remediation efforts often involve dredging, backfilling or other construction work that result in changes in physical and chemical process-es with a time span of hours or days.

Physical processesWhen suspended particles transported by rivers or urban-runoff enter the coastal zone, they will over time settle on the seafloor. The upper boundary of the sediments is often of a very soft and “fluffy” nature, rendering it diffi-cult to determine a clear boundary between suspended solids and loose sediment. Dredged materials are usually even softer than in-situ material.

Contaminants and their behaviour

Sedimentation Photolysis

Erosion

Evaporation

BioturbationDi�usionDegradation

Mass�owSorption

10

8

6

4

2

10

Time (min.)1000 1000010010

He

ight

(cm

)

1350%

630%

440%370%

350%245%

Contaminants

Disposal of dredged materials in the marine environment shows a rapid consolidation and decrease in water content.

Main processes determining contaminant mobility in the aquatic environment

7

Chemical processes SorptionIndustrial and urban contamination has resulted in increased levels of organic matter in coastal zone sedi-ments, yielding anoxic conditions. The organic matter in the sediments effectively sorbs organic contaminants while the anoxic conditions stabilise heavy metals in sulphide complexes. Therefore, only a small portion of the total contaminant load is available for remobilization to the ecosystem.

Sediment-water fluxAfter the reduction of contaminant releases from land-based sources, the contaminant concentration in the sediment pore water often exceeds that in the overlying water. This leads to a potential for mass transfer of the contaminants across the sediment-water surface into the overlying water. This process is driven by random move-ments of molecules through the stagnant water layer above the sediment (molecular diffusion) or by mixing of particles and flushing water through sediment voids by benthic organisms (bioturbation). The sediment-water flux can contribute significantly to the transfer of biologi-cally available dissolved contaminants to the water overlying contaminated sediments.

Contaminants

The release of organic contaminants from the sediment to the aqueous phase is typically characterised by a rapid release followed

by a period of much slower desorption. Strong correlations have been found between the rapidly released fractions and the con-

taminant bioaccumulation of benthic organisms.

Consecutive desorption studies using an infinite-sink sorbent material like Tenax can provide detailed information regarding the potential

release of contamination. However, such studies are time-consuming (~3 months). Thus “one-point” Tenax measurements have been sug-

gested where the amount desorbed after ~1 day is an estimate of the rapidly desorbing and thus biologically available fraction.

Estimating the rapidly dissolving fraction

Fra

ctio

n re

ma

inin

g (

%)

Time (h)

100

Rapiddesorption

80

60

40

20

0

Slow and very slowdesorption

Fra

ctio

n re

ma

inin

g (

%)

Time (days)

100

Rapiddesorption

80

60

40

20

10 20 30 40 500

Slow and very slowdesorption

Tenax polymer beads used to determine the available fraction.

Typical desorption curve of organic contaminants from field-aged contaminated sediment

Carbon-containing particle in Bergen harbour sediment

8


Biological processes

BioturbationSediment-dwelling organisms play an important role in the physical mixing of sediments at the sediment/water interface as a result of their burrow-digging activity. Their mixing of surface sediment can result in the reactivation of ancient contaminants and the increase of sediment- water contaminant transport. Bioturbation will limit the effect of natural restoration by diluting the new and cleaner sedi-ments with old and relatively highly contaminated sedi-ment within the bioturbation layer. This increases the time required for the natural recovery of the sediments. Biological uptakeOne of the main concerns with contamination of marine sediments is the uptake of contaminants in benthic organ-isms, potentially resulting in contaminant transport in the marine food chain. Uptake in benthic organisms has been shown to be strongly related to the soluble or available fraction of the contaminants. This means that analysis of the total contaminant level in sediments is of little rele-vance to the potential environmental risk posed by a sediment. The contaminant level in porewater has been shown to be a good indicator of the potential for bio-logical uptake in benthic organisms.

Sediment properties and especially the level of black carbon have a major influence on the biological uptake of organic contaminants.

Soot and char, often called “black carbon”, are found in every sediment containing anthropogenic pollution.

Black carbon causes 50-100 times stronger binding of organic •pollutants in sediment

This stronger binding leads to 50-100 times lower uptake from •sediments with black carbon

In the absence of black carbon, the concentration of organic pollutants

in organisms (lipids) will be approximately the same as the concentration

in the sediment (organic matter). The biota-to-sediment-accumulation-

factor (BSAF), the concentration in the organisms divided by the concen-

tration in the sediment, is close to 1 in the absence of black carbon in the

sediments.

However, in three Norwegian sediments we found biota-to-sediment-

accumulation-factors that were much lower than 1, around 0.01. That

means that organisms take up 100 times less pollutant than expected for

sediment without black carbon.

Strong binding to black carbon limits biological uptake

0.001

0.01

0.1

1

10

100

1000

10000

100000

1000000

10000000

Sorptioncoe�cient

BSAF Nereisworm

BSAF Hinia snail

Sediment, no BCOslo sedimentBergen sedimentTroms sediment

Sorption and BSAF for sediment without black carbon (BC), and for sediment with BC.

Example for the PAH phenanthrene.

Contaminants

Bioturbation is visible because oxygen is transported into anaerobic sediments, resulting

in the formation of brownish iron oxides.

9

Historically, direct discharges from industry and urbanised areas have been the main source of contaminants. However, stringent source control over the last decades has resulted in a strong reduction of point sources. This raises the question whether the contaminant levels ob-served in biota today are either caused by diffuse land sources or by the remobili sation of contaminants stored in the bottom sediments of the fjords. Innovative mea-surement methods have been employed in the field to answer this question.

Physical stabilityThe top layer of marine sediments is often made up of fine-grained, cohesive materials with a high water con-tent. As a result, they possess a low shear strength which might result in resuspension and remobilisation as a result of currents, wave action and boat traffic. The strength properties and the bearing capacity of sediments were investigated both under in-situ conditions and after dredging and disposal. To this end, laboratory measure-ments were compared with model experiments and in-situ field measurements using innovative approaches. Traditional geotechnical methods and rheometer mea-surements were compared using large block samples collected with a box corer. Good agreement was found between these measurements and in-situ penetration depth measurements. This method reduced the risk for physical disturbance associated with sampling, while allowing multiple observations and measurements over a short time-frame.

Release rateThe sediment-water flux is an important contaminant transport pathway. The reduction of this flux can be used as a measure for the efficiency of remediation of con-taminated sediments. A benthic flux chamber, measuring sediment-water flux of dissolved PAHs and PCBs directly in the field, was developed. The flux chamber encloses a small water volume above the sediment surface.

PAHs and PCBs diffusing from the sediment surface are collected in a semi-permeable membrane device (SPMD). After 4 weeks of exposure, the flux chamber is col-lected and the SPMD is analysed to quantify the flux. The flux chambers provide a very useful tool for the documen-tation of capping effectiveness.

Field measurement

Field measurement

Benthic Flux Chamber

Outline of the design and functioning of the infinite-sink benthic flux chamber.

Picture of the flux chamber placed on the seafloor.

In�nite sink:SPMD

Di�usive boundary layerinside chamber

Di�usive boundary layeroutside chamber

10


The thin POM (polyoxymethylene) passive sampler material.

Equilibration of PAHs to thin POM (17, 40, 60 µm) in the field (Oslofjord, 43 m depth).

0 20 40 60 80

100 120 140 160

0 10 20 30 40 50 60 Time (d)

Equi

libriu

m (

%)

POM 17 µm POM 40 µm POM 60 µm

Field measurement

Freely dissolved concentration Freely dissolved concentrations (free molecules in the water) are directly related to amounts of chemicals taken up in organisms. Scientists nowadays agree that freely dissolved concentrations are therefore a much better measure for risk than total contents.

Equilibrium passive samplers have been adapted in this project for the measurement of freely dissolved concen-trations under field conditions. Passive samplers are no more than small sheets of polymer that are exposed in the field and reach equilibrium with the water phase in 2-6 weeks. The amounts of PAH, PCB or dioxin in the pas-sive sampler are then measured. These levels are directly related to the freely dissolved concentrations in the water through sampler-water distribution ratios that are constant for one compound in all environmental systems (soil, sediment, water).

Thin (< 60 µm) polyoxymethylene (POM) has been found to be a suitable passive sampler material for the follow-ing reasons:• Itcaneasilybecleanedduetoitssmoothsurface• Itreachesequilibriuminthefieldwithin2-6weeks• Itcanbeusedatallconcentrations• Itgivesatime-integratedvalueofthefreely

dissolved contaminant concentration.

Various POM thicknesses lead to various equilibrium times and various intervals of time integration. The thinnest POM (17 µm) reaches equilibrium in < 2 weeks under marine conditions (current < 2 cm/sec); 60 µm thin POM takes about 6 weeks to reach equilibrium.

11

Environmental risk assessment of contaminated sediments has traditionally been conducted by analyzing the total content of contaminants in sediments and comparing these levels to numerical sediment quality guidelines. For most compounds these guidelines are based on toxicity data from tests performed in the aqueous phase, which are subsequently converted to sediment criteria using a fixed sediment/water distribution coefficient (equilibrium partitioning). However, risk is often overestimated in this way. This is a result of the strong sorption capacity of many sediments due to the presence of soot and coal. The consequence is a low availability of contaminants for both uptake and degradation. This sorption capa-city has been shown to be site and sediment-specific.

Generally speaking it has been found that strong sorp-tion to soot and coal causes actual risks to be 10-30 times lower than estimated on the basis of traditional risk assessment with generic sediment-water distribution ratios. In order to improve risk assessments and estimate realistic levels of environmental, methods to quantify the available fraction have been developed.

A good expression of the activity of the contaminants can be achieved by the determination of the actual pore water concentration benthic organisms are exposed to. This way, water quality criteria can be used directly without the need of a conversion with ambi-guous sediment-water distribution coefficients.

Improved risk assessment

There is a large variation in the sediment’s ability to sorb hydrophobic organic contaminants and thus in the reduction of bioac-

cumulation. These differences can be explained by (i) the sorbent characteristics, especially the carbonaceous materials such as

black carbon (BC) and unburnt coal, and (ii) the sorbate characteristics,

especially the interaction of the contaminant with the sorbing phases.

In our studies we found that infinite-sink Tenax extraction as well as equilibrium POM

extraction can be successfully used to chemically evaluate the bioaccumulation

potential. Biota-to-sediment accumulation factors (BSAFs) calculated using rapidly

desorbing fractions as well as freely dissolved aqueous concentrations were in the

same order of magnitude as the measured BSAFs, in contrast to those based on

total sediment contents. The incorporation of black carbon (BC) contents in BSAF

modelling could explain the low bioavailability measured in organisms.

Limited bioavailability in harbour sediments

Risk assesment

Benzo[a]pyrene Sediment Porewater

Quality criteria 420 µg/kg 50 ng/l

Oslo harbour 1400 µg/kg 3.3 ng/l

Bergen harbour 6900 µg/kg 9.8 ng/l

Tromsø harbour 570 µg/kg 2.8 ng/l

In all three harbours the sediment quality cri-terium for BaP is exceeded by total sediment contents. However, the water quality standard is not exceeded by porewater concentrations.

12


Overview Natural recovery of contaminated fjords is possible by accumulation of clean sediments on the previously contaminated seafloor. However, sedimentation rates are often very low in Norwegian fjords. Natural recovery will therefore often take many decades after active sources have been terminated.

Sediments can be removed by various dredging methods. This might result in physical disturbance and remobilisation. In addition dredged material has to be stored or treated. Dredged material can be disposed either i) in the aquatic environment (“Contained Aquatic Disposal”; CAD), ii) near shore (“Confined disposal facili-ties; CDF), or iii) on land. These methods have mainly been applied on an empirical basis and little is known about the critical factors in the confinement solutions and the long-term stability.

From an environmental point of view other remediation methods than dredging might be preferable because of limited physical disturbance and potential reductions in remediation costs. Both capping with clean sediments and in-situ chemical stabilisation with activated carbon are identified as methods that can achieve significant environmental improvement in fjords.

Accelerated recovery Source control and source reduction are the most important remedial measures for the improvement of the environ mental quality of fjord systems. Stringent source control will allow natural recovery of the fjords by time. Although many point sources have been removed, diffuse pollution from human activity is still significant.

Relatively low pollution levels in newly formed sediment relative to the existing sediment will improve the environ-mental conditions on the seafloor. However, low sedimen-tation rates will cause the improvement to take several decades as a result of mixing of the sediment by benthic organisms. An increase in sedimentation rate can be achieved over large areas by locally supplying additional sediments. This method is called “thin-capping”, and can support and accelerate the natural recovery process by increasing the sedimentation rate from for instance 1 mm to a few cm per year.

To improve the effect of thin-capping, materials can be supplied that actively reduce the contaminant concen-trations in the water column by strong sorption. These materials need to be effective in small amounts and exert minimal negative effects on the benthic organisms. Activated carbon has been identified as a material with a high potential for this application.

Alternative remediation methods

Natural Recovery

Dredging

In situ treatment

Treatment

Disposal

Capping

Laboratory studies have shown that AC amendment can reduce

the porewater concentration considerably (factor of 10-100) and

thereby reduce the availability of the contaminants for uptake in

sediment-dwelling organisms. This method was applied in a pilot

study in Trondheim harbour (page 15).

Effectiveness of four dosages of activated carbon for reducing

freely dissolved porewater concentrations in Oslo sediment. CW: freely dissolved porewater concentration. PHE, PYR, BAP, BGP:

example PAHs with 3,4,5,6 rings, respectively.

Activated carbon amendment to stabilise contaminants

Remediation

0.01

0.1

1

10

100

0% AC 0.2% AC 0.5% AC 2% AC 4% AC

PHE

PYR

BAP

BGPCW

(n

g/L

)Alternative remediation methods

13

The capping of dredged sediments with thin layers of sand or

clay has been studied in the inner Oslo fjord. Sediment profile

imaging (SPI) has been used to document capping efficiency, in

cooperation with NIVA (Hans Nilsson). The in-situ shear strength of

the sediments could be determined at 70 m water depth based

on the observed penetration depth of the camera, its physical

geometry and submerged weight.

Sediment Profile Imaging

Capping Remediation by capping is achieved by placing a clean material as a barrier between the contaminated sediment and the overlying water. This barrier has the following functions:

Isolate the benthic fauna from the contaminated •sedimentIsolate the contaminated sediment from water •currents causing erosion of contaminated particles or advection in sandy sediments.Provide chemical isolation of the contaminated sedi-•ment by increasing the length of the diffusive path.Provide sorption capacity to reduce availability of •contaminants mixed into the cap. Such active caps can be thin compared to the layer influenced by bioturbation.

The advantage of capping over environmental dredging is that the contaminated sediment is minimally disturbed and that the method is usually less expensive (no need for dredging or disposal). Lab and field studies in this project have demonstrated that capping often provides sufficient protection against a sediment-water contami-nant flux.

Remediation

PAH

-

PCB

-

2 000

4 000

6 000

8 000

10 000

12 000No Cap

ng

m-2d

-1

ng

m-2d

-1CappedNo CapCapped

5

10

15

20

25

30

Measured flux of PAH and PCB from uncapped and capped sediment.

14


Granulated activated carbon was initially used at the Trondheim field site

to chemically stabilise contaminants. Contrary to the laboratory studies,

monitoring data showed little or no effect on the contaminants under field

conditions. Based on these results, powdered activated carbon was used

in a second round in April 2008. A 30 x 30 m field was covered in Trondheim

harbour by pumping out a slurry of activated carbon with 10%-salt water.

Three fields were established: i) 1:1 activated carbon: bentonite clay, to

facilitate placement and prevent erosion, ii) activated carbon only, iii)

activated carbon with 5 mm sand to prevent erosion. The placement was

shown to be successful; an even layer of activated carbon was spread

out on the seafloor, and this layer was not disturbed by 5 mm of sand.

Field site Trondheim harbour

Seafloor amended with AC only; and seafloor amended with AC and covered with 5 mm sand after 5 months in the field (the latter

picture taken after disturbing the sand layer to check the presence of AC). Core sampling has also shown that the AC is present under

the sand and has not been eroded away by sand cap placement.

Dredging and disposalThe physical disturbance created by the dredging of con-taminated sediments will result in large volumes of sludge with a high water content. Dredging is therefore a complex and often expensive remediation method. Resuspension and fall-back of contaminated sediment during dredg-ing can reduce the effectiveness of remediation. Proper management of this residual layer of contaminants can strongly improve the effect of the remedial measures. After dredging the sludge can be relocated in a subaqueous, near-shore or land-based disposal site. Both the surface area required for land disposal and the chemical changes induced in the sediments by dewatering and oxidation might pose a significant environmental challenge. Disposal on land or in the aqueous environment both require strin-gent measures to prevent remobilisation and transport of contaminants.

Confined disposal facility (CDF)Near-shore facilities to store dredged material are called confined disposal facilities (CDF). The advantage of this method is that sediment remediation can be combined with land reclamation creating valuable properties at the water front. To achieve this in an environmentally sound way, a CDF has to be designed to retain the suspended solids in the sludge while allowing consolidation and de-watering. The potential loss of contaminants to the sur-rounding environment should be strictly controlled. The

construction of the surface cover of a CDF is critical for the future use of the site. Stabilisation methods with e.g. cement can be applied to improve the physical strength of the CDF and to increase the value of the reclaimed land. This has been applied successfully as part of a pilot study in Trondheim harbour

Contained aqueous disposal (CAD)Often neither on-land disposal nor CDF construction are feasible for large volumes of dredged materials from extensive sanitation projects. The construction of a sub-aqueous disposal site can create sufficiently large capa city for disposal. The confined volume needed for the CAD can be obtained by excavating clean sediments at the seabed. Alternatively, a natural depression in the seafloor can be filled up with dredged material. A prerequisite for this disposal method is that the dredged material can be placed in the CAD with minimal contaminant release. This will ensure that the total effect of the remedial action will reduce the contaminant release. In order to prevent long-term release from the disposed dredged material a layer of clean material should be placed on the CAD (capping). Monitoring of a CAD requires field monitoring which can benefit substantially from the use of innovative measure-ment methods for both physical and chemical parameters developed in this research program.

Remediation

15

The basis for the evaluation of the environmental benefit from remedial action is the reduction in the release rate of contaminants from sediments at the site. Normally, a high observed release rate, implying a potential environ-mental risk, will trigger remedial action. During remedia-tion, handling of contaminated sediment can cause an initial increase in contaminant release.

After a successful sediment remediation the release of contaminants to the environment will decrease. To achieve a net positive environmental effect from remedi-ation, the increased release during the remediation must be outweighed by the reduced release after the reme-diation. This emphasizes the need for quantifying release rates both before remediation and during all stages of the process.

Contaminant flux before, during and after remedial action.

Remediation period

Co

nta

min

an

t tr

an

spo

rt

Recovery time

Time

Without remediation

A�er remediation

Environmental benefit

Benefit

The effectiveness of a remediation (RE) can be quantified using estimates or measurements of contaminant transport in the different

phases of the project as shown in the formula, where time (t) is the number of years after the remediation is completed.

In order to calculate the correct remediation efficiency (RE) it is important that the estimated or measured release of contaminants

during and after remediation comprises all relevant processes.

For projects to be successful from an environmental point of view, the overall contaminant release after remediation has to be

reduced compared to the initial situation. This means that RE must be greater than 0 within a reasonable time frame (5 to 20 years

after the end of the remediation, depending on the type of project). If RE < 0 at the time of evaluation, the remediation has caused

a net increase in release of contaminants, and no environmental benefit has been obtained.

Remediation effectiveness

16


A CDF was constructed for Hg and HCB contaminated

dredged material on contaminated near shore sediments in

the Gunneklevfjorden close to one of Norway’s largest indus-

trial areas, Herøya. The efficiency of the CDF was evaluated

by making a budget of estimated contaminant emission from

the disposal area before, during, and after construction and

filling of the CDF.

Laboratory tests and an analytical model were used to calcu-

late advective and diffusive transport of contaminants both

from the dredged material and from the original contami-

nated seabed sediment at the disposal site. The estimates of

contaminant transport predicted that transport of contami-

nants from the CDF would be orders of magnitude less than

the release from the contaminated sediments at the disposal

site prior to the realization of the CDF.

Monitoring of contaminant transport, after realization of the

CDF, has so far shown that the actual transport is much lower

than the conservative estimate presented in the budget of

contaminant transport. These results show that there can be a

large environmental and cost benefit from disposal of dredged

material in CDFs at previously contaminated sites.

This case study demonstrates how budgeting and accounting

of contaminant transport can be a powerful tool for impact

assessment and definition of realsitic goals before realisation

of a remediation project. It will also help in the interpretation

of monitoring data and the identification of the most critical

transport mechanisms during the different phases of the

project.

Remediation effectiveness of a confined disposal facility

Release during remediation Under natural conditions on the seafloor, diffusion of con-taminants and sediment redistribution by bioturbation and erosion are the main contaminant release process-es. During remediation the dominating release process will be highly dependent on the selected remediation method. Physical disturbance during dredging will result in significant resuspension, possibly inducing desorption of contaminants and increased aqueous concentra-tions. Particle-bound transport can also contribute to the spreading of contaminants from the site.

During disposal particle-bound transport is often signifi-cant. Also consolidation of the dredged material can result in the in release of contaminated pore water to the water column. The load (stress) exerted by the cap on the underlying sediments can induce additional pore water expulsion. The significance of this effect will depend on the water content of the sediments and the effective stress the capping layer exerts on the underly-ing sediments.

Process Natural condition

Dredging Disposal Capping

Diffusion high high high low

Bioturbation high low low low

Resuspension low high high low

Desorption low high high low

Consolidation low low high low

Release mechanisms related to various remedion strategies.

Model describing the shear stress at the edge of a capping layer.

17

Finding site-specific solutionsLarge variations in geographical conditions, contamina-tion history and present-day area use make it impossible to find one unique solution for contaminated sediments. Based on a proper understanding of the many processes involved in contaminant behaviour and environmental risk, methods can be selected to achieve the environ-mental objectives for restoration of impacted fjords, harbours and the coastal zone.

Historically the sediments have been a sink for the con-taminant input, from rivers, urban and industrial activity as well as atmospheric input. Significant reduction in industrial point sources has been achieved over the last decades. Detailed site investigation can answer the question whether the present sediments still form a sink or, in contrast, are a secondary source of contaminants to the fjord system. Diffuse sources related to our daily life, like run-off from traffic and urbanised areas, have been shown to be significant for the coastal zone. This contaminant input sets clear limits to the environmental objectives that can be achieved by sediment remedia-tion alone.

Significant environmental improvement of fjords and coastal zones can only be achieved if a set of remedial measures is implemented that covers all relevant sour-ces, on-land, near-shore as well as off-shore ones. This clearly indicates that sediment contamination is not an echo from the past but a mirror of our daily behaviour.

The city of Drammen is situated 40 km south-west of Oslo,

the capital of Norway. Industrial development in the region is

concentrated along the Drammen river, Norway’s third larg-

est. Discharge from historical industrial activity has resulted in

pol luted sediments in the Dram-

mensfjord, a typical Norwegian

fjord with restricted circulation

due to a shallow sill at the end

of the fjord and a brackish sur-

face layer from riverine input.

As a result of pollution of the

Drammensfjord, restrictions on

fishery and fish consumption are

imposed.

In order to find a realistic environ-

mental goal for the remediation of the Drammensfjord, a large

field study was launched by the local environmental authorities.

During one year a whole range of novel scientific monitoring

methods, along with standard marine sediment sampling, were

used to quantify active sources and identify the dominating

processes of pollution transport in the marine environment.

After compiling and assessing the huge amount of data from

the field study a surprising conclusion had to be drawn: “Sedi-

ment remediation will be useless unless local diffuse sources are

eliminated”. These sources include effluent from a shipyard and

run-off from urban and industrial areas. The data also allowed

the establishment of realistic environmental objectives for any

remediation activity in the region.

Will it be necessary to dredge or cap the marine sediments in

the area, after sufficient source control? In contrast to many

Norwegian fjords, where low sedimentation rates prevail, natural

recovery could well be a feasible solution in the Drammens-

fjord. This alternative will be the focus of an intense monitoring

program the coming years. The aerial photo clearly shows

sediments from one of the two major rivers entering the Dram-

mensfjord. Is this material of such quality and deposited in such

amounts that it can act as a natural “cap”?

Remedial action plan Drammen

Urban run-o� Riverine inputAtmospheric deposition

Groundwater

Fjord system

Sediment

Solutions

Sources of contamination in fjord systems.

18


Bibliography

2008 Barthe, M., Pelletier, E., Breedveld, G.D. and Cornelissen, G. (2008) Passive samplers versus surfactant extraction for the evaluation of PAH availability in sediments with variable degree of contamination. Chemosphere, 71, 1486-1493.Brändli, R., Bergsli, A., Ghosh, U., Hartnik, T., Breedveld, G.D. and Cornelissen, G. (2008) Quantification of activated carbon contents in soils and sediments using chemo- thermal and wet oxidation methods. Environ. Sci. Technol. submitted.Brändli, R., Breedveld, G.D. and Cornelissen, G. (2008) Tributyltin sorption to marine sedimentary black carbon and to amended activated carbon. Environ. Toxicol. Chem. 27, in press.Cornelissen, G., Pettersen, A., Broman, D., Mayer, P. and Breedveld, G.D. (2008) Equilibrium passive samplers to determine freely dissolved native PAH concentrations in field and laboratory. Environ. Toxicol. Chem. 27, 499- 508.Cornelissen, G., Pettersen, A., Eek, E., Nesse, E., Helland, A. and Breedveld, G.D. (2008) The contribution of urban runoff to organic contaminant levels in harbour sediments near two Norwegian cities. Marine Pollution Bulletin, 56, 565-573.Cornelissen, G., Arp, H.P.H., Pettersen, A., Hauge, A. and Breedveld, G.D. (2008) Assessing PAH and PCB emissions from the relocation of harbour sediments using an equilibrium passive sampler. Chemosphere, submitted.Eek, E., Cornelissen, G., Kibsgaard, A. and Breedveld, G.D. (2008) Diffusion of PAH and PCB from contaminated sediments with and without mineral capping; measurement and modelling. Chemo- sphere, 71,1629-1638.

2007 Breedveld, G.D., Pelletier, E., St.-Louis, R. and Cornelissen, G. (2007) Sorption characteristics of Polycyclic Aromatic Hydrocarbons in aluminum smelter residues. Environ. Sci. Technol. 41, 2542-2547.Eek, E., Godøy, O., Aagaard, P. and Breedveld, G.D. (2007) Experimental determination of efficiency of capping materials during consolidation of metal- contaminated dredged material. Chemosphere, 69, 719-728.

Hammes, K., Schmidt, M.W.I., Smernik, R.J., Currie, L.A., Ball, W.P., Nguyen, T.H., Louchouarn, P., Houel, S., Gustafsson, Ö., Elmquist, M., Cornelissen, G. et al. (2007) Comparison of quantification methods to measure fire-derived (black/elemental) carbon in soils and sediments using reference materials from soil, water, sediment and the atmosphere. Global Biogeochemical Cycles, 21, doi:10.1029/ 2006GB002914.Kalaitzidis, S., Christanis, K., Cornelissen, G. and Gustafsson, Ö. (2007) Tracing dispersed coaly-derived particles in modern sediments: an environmental application of organic petrography. Global NEST Journal, 2007, 9, 137-143.Siavalas, G., Kalaitzidis, S., Cornelissen, G., Chatzia - postolou, A. and Christanis, K. (2007) Influence of lignite mining and utilization on organic matter budget in the Alfeios River plain, Peoloponnese (S Greece). Energy and Fuels, 21, 2698-2709.

2006 Cornelissen, G., Næs, K., Oen, A.M.P., Breedveld, G.D. and Ruus, A. (2006) Bioaccumulation of native PAHs from sediment by a polychaete and a gastropod: Freely dissolved concentrations and activated carbon amendment. Environ. Toxicol. Chem. 25, 2349–2355.Cornelissen, G., Breedveld, G.D., Kalaitzidis, S., Christanis, K., Kibsgaard, A. and Oen, A.M.P. (2006) Strong sorption of native PAHs to pyrogenic and unburned carbonaceous geosorbents in sediments. Environ. Sci. Technol. 40, 1197-1203.Eek, E., Pettersen, A., Hauge, A., Breedveld, G.D., Solberg, A., Heines, S.U., Solberg, K. and Lie, S.O. (2006) Disposal of contaminated dredged material in a local confined disposal facility, budgeting and accounting of contaminant transport. Journal of ASTM international, 3 (7), 13 p.Holme, J.K., Docter, L., Eek, E., Jensen, T.G., Løken, T. and Breedveld, G.D. (2006). Material behavior of dredged contaminated sediments from simple laboratory tests and oedometer tests. Journal of ASTM international, 3 (7), 10p.Koelmans, A.A., Jonker, M.T.O., Cornelissen, G., Bucheli, T.D., Van Noort, P.C.M. and Gustafsson, Ö. (2006) Critical review: Black carbon: The reverse of its dark side. Chemosphere, 63, 365-377.Oen, A.M.P., Cornelissen, G. and Breedveld, G.D. (2006) Relation between PAH and black carbon contents in size fractions of Norwegian harbor sediments. Environ. Pollut. 141, 370-380.

Bibliography

Publications in scientific journals

19

Oen, A.M.P., Breedveld, G.D., Kalaitzidis, S., Christanis, K. and Cornelissen, G. (2006) How quality and quantity of organic matter affect PAH desorption from Norwegian harbor sediments. Environ. Toxicol. Chem. 25, 1258-1267.Oen, A.M.P., Schaanning, M., Ruus, A., Källqvist, T., Cornelissen, G. and Breedveld, G.D. (2006) Predicting low biota to sediment accumulation factors of PAHs by using infinite-sink and equilibrium extraction methods as well as bc-inclusive modeling. Chemosphere, 64,1412-1420.

2005 Cornelissen, G., Gustafsson, Ö., Bucheli, T.D., Jonker, M.T.O., Koelmans, A.A. and van Noort, P.C.M. (2005) Critical review: Extensive sorption of HOCs to black carbon, coal and kerogen: mechanisms and conse- quences for sorption, bioaccumulation and biodegradation. Environ. Sci. Technol. 39, 6881-6895.Bortone, G., Arevalo, E., Deibel, I., Detzner, H.D., de Propris, L., Elskens, F., Giordano, A., Hakstege, P., Hamer, K., Harmsen, J., Hauge, A., Palumbo, L. and van Veen, J. (2004) Sediment and dredged material treatment. Synthesis of the SedNet work package 4 outcomes. Journal of Soils and Sediments, 4, 225-232.Heise, S., Apitz, S.E., Babut, M., Bergmann, H., den Besten, P., Ellen, G.J., Joziasse, J., Katsiri, A., Maass, V., Oen, A., Slob, A. and White, S. (2004) Sediment risk management and communication. Synthesis of the SedNet work package 5 outcomes. Journal of Soils and Sediments, 4, 233-235.den Besten, P.J., de Deckere, E., Babut, M.P., Power, B., DelValls, T.A., Zago,C., Oen, A.M.P. and Heise, S. (2003) Biological effects-based sediment quality in ecological risk assessment for European waters. Journal of Soils and Sediments, 3, 144-162.

Book chapters

Bortone, G., Arevalo, E., Deibel, I., Detzner, H.D., de Propris, L., Elskens, F., Giordano, A., Hakstege, P., Hamer, K., Harmsen, J., Hauge, A., Palumbo, L. and van Veen, J. (2007) Sediment management of nations in Europe. In: Bartone, G., Palumbo L. (Eds.) Sustainable management of sediment resources (SED NET). Vol 2. Sediment and dredged material treat ment. Elsevier, ISBN 978-0-444-51963-4.Heise, S., Apitz, S.E., Babut, M., Bergmann, H., den Besten, P., Ellen, G.J., Joziasse, J., Katsiri, A., Maass, V., Oen, A., Slob, A. and White, S. (2007) Sustainable management of sediment resources (SEDNET). Vol 3. Sediment risk management and communication. Elsevier, ISBN 978-0-444-51965-8.Parsons, J., Segarra, M.J.B., Cornelissen, G., Gustafsson, Ö., Grotenhuis, T., Harms, H., Janssen, C.R., Kukkonen, J., van Noort, P., Ortega Calvo, J.J. and Solaun Etxeberria, O. (2007) Characterisation of contaminants in sediments – effects of bioavailability on impact. In: Barcelo, D., Petrovic, M. (Eds.), Sustainable management of sediment resources (SEDNET). Vol 1. Sediment quality and impact assessment of pollutants, chapter 2, 35-60. Elsevier, ISBN: 978-0-444-51962-7.

PhD theses

Eek, E. (2008) Mechanisms of contaminant transport and the effect of containment of contaminated sediments. PhD thesis, Department of Geosciences, University of Oslo.Oen, A.M.P. (2006) Sequestration and bioavailability of native polycyclic aromatic hydrocarbons in harbour sediments. PhD thesis, Department of Biology, University of Oslo.

Bibliography

Contact: Gijs D. Breedveld, [email protected] Hauge, [email protected]

Key personnel:Gerard Cornelissen, Espen Eek, Anne Kibsgaard, Tore Kvalstad, Amy Oen, Arne Pettersen

Contributors: The Research Council of Norway, Norwegian Geotechnical Institute, Norwegian Institute of Water Research, Norwegian Pollution Control Authority, Oslo Port Authority - Norway, County Governor of Buskerud - Norway, Elkem, Statoil-Hydro, Secora - Norway, Department of Geo-sciences, University of Oslo - Norway, Norwegian Geological Survey, Institute for Marine Research Quebec - Canada, Department of Environmental Sciences (ITM), Stockholm University - Sweden, Patras University - Greece, Stanford University - USA, University of Maryland - USA, SedNet - EU

Main office:PO Box 3930 Ullevaal StadionNO-0806 Oslo, Norway

Street address: Sognsveien 72, NO-0855 OsloT: (+47) 22 02 30 00, F: (+47) 22 23 04 48 [email protected]

www.ngi.no

NGI (Norwegian Geotechnical Institute) is a leading international centre for research and consulting in the geosciences.

NGI develops optimum solutions for society, and offers expertise on the behaviour of soil, rock and snow and their interaction with the natural and built environment.

NGI works within the oil, gas and energy, building and construction, transportation, natural hazards and environment sectors.

NGI is a private foundation with office and laboratory in Oslo, branch office in Trondheim and daughter company in Houston, Texas, USA. NGI was awarded Centre of Excellence status in 2002 and leads the International Centre for Geohazards (ICG).

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