Managing contaminated sediments: Do in-situ remedies ... · Active AC-based thin-layer capping...

Managing contaminated sediments:Do in-situ remedies really ”work”?

Joe Jersak

SAO Environmental Consulting AB

Skype-seminarium om åtgärder av förorenade sediment

23 April 2020

Before getting into remediesInvestigate site and document problem

• Characterize conditions

• Develop conceptual site model, CSM

• Conduct risk assessments

2Skype-seminarium om åtgärder av förorenade sediment, 23 April 2020

Before getting into remediesAddress contaminant source(s)

• Identify major ongoing sources

• Control source(s)

Even a perfectly selected, designed and implementedremedy does little to reduce long-term risks ifre-contamination occurs


Ex-situ versus in-situ remediesA fundamental difference

• Ex-situ remedies• Removes risks from aquatic environment

• In-situ remedies• Manages risks within aquatic environment

Many contaminated aquatic environments are

• Complicated

• Dynamic

• Not always predictable


In-situ sediment remediesOverview

• Övervakad naturlig självrening (ÖNS)• Isolationsövertäckning• Förstärkt ÖNS (FÖNS)• Aktiv kol-baserad tynnskiktstäckning• ’Klassisk’ in-situ behandling

Presentation terminology• Remedy = method = technique = type• Mixing Swedish and English


all different types ofcapping

Except ’classic’ in-situ treatment, all remedies• Recognized and accepted, to varying degrees

• Can significantly reduce risks in their own unique way• No sediment remedy can completely eliminate risks

• Developed and refined mainly for contaminatedmineral-based (minerogenic) sediments

• Potential for use at fiberbank sites, but its complicated• For details, see Åtgärdsportalen, ”Fibersediment”

Not focusing on sediment type in this presentation6Skype-seminarium om åtgärder av förorenade sediment, 23 April 2020

In-situ sediment remediesOverview

For each in-situ remedy, describe

• What it is

• What it does

• Timeframe for effectiveness

• Appropriate conditions for use

• Advantages and limitations

• International recognition and use


Most graphics (plus related source references) from Åtgärdsportalen, unless noted otherwise

ÖNSGeneral description

• Leaving contaminated sediments in-place

• Allows natural processes to eventually contain, destroy, and/or reduce contaminantbioavailability and/or toxicity to receptors

Monitoring critical, since we need to document thatthe natural processes are indeed occurring


Key: Gradual dilution in biologically active zone (BAZ) by new, cleaner sediments mixed in by benthic organisms

BAZ~10 cm

9

ÖNSGeneral description

Skype-seminarium om åtgärder av förorenade sediment, 23 April 2020

Long-term objective:

• Eventually reduce (not eliminate) risks to acceptable levels, and maintain over time

Rate of risk reduction to acceptable levels often veryslow, years to decades


ÖNSRemedial objective, including timeframes

ÖNSRemedial objective, including timeframes

concentration reductions

in sediments

concentration

reductions in fish tissue


ÖNSConditions most appropriate for use

Contaminants• Can manage various dissolved-phase, but not NAPLs (non aqueous-phase liquids)

• Best for non-bioaccumulative, degradeable contaminants

• Sediment concentrations relatively low, cover broad areas

• Concentrations in sediment, biota already moving towards recovery

Sediment• Bed relatively stable, resistant to re-suspension

Site• Low-energy and depositional

• Natural sedimentation rates at least ≈ 1 cm/yr (should be ”clean”)

• No to minimal groundwater upwelling


ÖNSRelative advantages and limitations

Advantages• Least invasive and disruptive

• Least complex, quickest to implement

• No infrastructure restrictions or shorline space requirements

• Not restricted by bottom debris

• Least costly, overall

Limitations• Contaminants remain in-place,

often for a long time

• Not appropriate for NAPL

• Disturbances can increase risks

• Monitoring costs can add up

• Not compatible with somewaterway uses

• Institutional controls required


ÖNSInternational recognition and use

• Recognized in numerous countries

• In guidance, internationally• Including in Sweden

• So far, ≈ 30 projects, most in USA• No projects in Sweden, yet

• Accepted by most authorities, worldwide


Isolation cappingGeneral description


• Placing clean material(s) overtop contaminated sediments

• Intended to reduce long-term risks in different ways

Isolation cappingRemedial objectives, including timeframes


Long-term risk reductions by• Physical isolation

• Chemical isolation

• Erosion protection

This in-situ remedycan come the closestto ”eliminating” risks

Isolation cappingRemedial objectives, including timeframes

• Initially meeting objectives is rapid

• Continuing to do so is the challenge

• Re-contamination is a complicating factor


Isolation cappingCapping materials, conventional vs active


Isolation cappingConventional versus active approaches

conventional


active

Isolation cappingImplementation (cap construction)

Insure control, geotechnical stability, minimal re-suspension and cap-sediment mixing


Isolation cappingConditions most appropriate for use

Contaminants• Can manage various

dissolved-phase and NAPLs

• Concentrations relatively high

Sediment• Adequate bearing strength, or

can gain during construction

• Submerged slopes of roughly1:3 or less

Site• Often relatively high-energy, erosive

• Could be groundwater upwelling

• Adequate post-cap water depths

Other• Suitable capping material available

• Long-term risk reduction outweighsshort-term disturbances


Isolation cappingRelative advantages and limitations

Advantages• Can be used for NAPLs

• Reduces risks quickly

• Not restricted by debris

• Little to no post-cap residuals

• Clean, possibly unique habitat

• Less complex, faster than removal

• Can often use common equipment

• Overall, less costly than removal

Limitations• Metals, most organics remain

• Could affect site hydrology, ecology

• May not be compatible with somewaterway uses

• Active capping required whensignificant groundwater and/or NAPL

• May not be preferred habitat

• Protected species may be present

• Institutional controls required


Isolation cappingInternational recognition and use

• First projects in USA (all conventional)

• Recognized in many countries• Including in Sweden

• In guidance, internationally• Including in Sweden


Isolation cappingInternational recognition and use

• Conventional• ≈ 120 pilot or full-scale projects

• Most in USA, some in other countries

• Norway (11), Sweden (6)

• Active• ≈ 40 pilot or full-scale projects

• Most AC or organoclay

• Great majority in USA, others in Norway

• Norway (5), Sweden (1)


Förstärkt ÖNS (FÖNS)General description

• Close relative of ÖNS

• Hybrid of ÖNS and isolation capping

• Placing a thin layer of conventional cappingmaterial to fast-forward the natural recoveryprocess of sedimentation (burial)

• Also called ”conventional thin-layer capping”


FÖNSRemedial objective, including timeframes

• Long-term remedial objective same as ÖNS• Reduce (not eliminate) risks to acceptable levels

• But meets objective a bit differently• Not by gradual dilution, like ÖNS

• Placed layer significantly reduces contaminantconcentrations by its instant-and-clean presence

• Key: Placed material cannot actively bind contaminants• So, cannot reduce dissolved concentrations in

porewaters, which is the most bioavailable form



Layer thickness needs to be approx. equal to BAZ depth to greatly minimize direct organism-contaminant contact

FÖNS AC thin-layer capping



• Rate of risk reduction much faster than ÖNS

• Like isolation capping• Objective can be met pretty quickly

• Continuing to meet the objective is the challenge

• Re-contamination is a complicating factor


FÖNSImplementation (thin-cap construction)

• FÖNS is capping, contrary to how some folks see it

• Like isolation capping, during placement• Control is important

• Minimizing re-suspension, mixing is important

• Unlike isolation capping• Cap load is less, geotechnical stability often less

critical


FÖNSConditions most appropriate for use

• ≈ same as for ÖNS - with one critical difference• Most appropriate where low rates of sedimentation

• Same as for isolation capping• Suitable capping material available

• Long-term risk reduction outweighs short-term disturbances


FÖNSRelative advantages and limitations

• Advantages over ÖNS or isolation capping• Reduces risks more significantly and faster than ÖNS

• Initial disturbances lower than for isolation capping

• Limitations compared to ÖNS or isolation capping• Initially more disruptive than ÖNS

• Not recommended when NAPL and/or significantgroundwater upwelling


FÖNSInternational recognition and use

• Recognized in the USA

• In newer American guidance

• Roughly 10 projects, nearly all in USA• Difficult to track number, for multiple reasons

• One project in Sweden (Lake Turingen)

• Recognition and acceptance is growing (in USA)• Project number behind ÖNS

• Project number far behind isolation capping


Active AC-based thin-layer cappingGeneral description

• Relies on two things• AC, which strongly binds dissolved contaminants,

reduces bioavailable porewater concentrations

• The natural bioturbation processes of macroinvertebrate organisms in the BAZ

Also considered a type of ”in-situ treatment”


Active AC-based thin-layer cappingRemedial objectives, including timeframes

Long-term objectives areto reduce (not eliminate) contaminant

• Exposure

• Uptake

• Mobility



FÖNSAC thin-layer

capping

layer thickness,usually cm-scale



• Risk reduction not as rapid as FÖNS or isolation capping, but still pretty fast• Can meet objectives much faster than ÖNS

• Like FÖNS and isolation capping• Continuing to meet objectives is the challenge• Re-contamination can be a significant factor, but…..


Active AC-based thin-layer cappingImplementation (thin-layer placement)

• AC particles are very small and low-density

• Very difficult to place as-is, need help with that

• Although layers of AC-bearing material are verythin, this is still constructing/placing a cap

• Control is the most critical placement concern


Active AC-based thin-layer cappingConditions most appropriate for use

• Still somewhat unclear

• In principle, should be most of the same conditions also appropriate for ÖNS and FÖNS


Active AC-based thin-layer cappingRelative advantages and limitations

Advantages• Relies on a well-established sorbent

• Significantly accelerates reductionin bioavailability

• Lower-impact, may be used in sensitive environments

• Not restricted by bottom debris

• Can be used around unstable in-water structures

• Long-term benefits often outweighshort-term disturbances

• Can treat new (post-remedy) contaminant inputs

Limitations• Many of the same for ÖNS

• Concerns related to negative biological effects from AC on macroinvertebrates


Active AC-based thin-layer cappingInternational recognition and use

• Concept of managing contaminated sediments with AC (not just thin-layer) recognized, internationally• Including in Sweden

• ≈ 12 AC thin-layer projects, most pilot-scale• USA (9), Norway (2), The Netherlands (1), Sweden (0)

• Recognition and acceptance is growing rapidly, not just in USA, but also in Scandinavia and elsewhere• Lots of interest from Swedish academics

• Concerns related to AC effects on macroinvertebratesremain a sticking point – especially in Scandinavia


’Classic’ in-situ treatmentGeneral description

• Rapidly incorporating treatment agents into contaminated sediments by mechanical meansto create or enhance one or more treatment processes

• Called the original - or ‘classic’ - in-situtreatment method because it came along first (before thin-layer AC)


’Classic’ in-situ treatmentGeneral remedial approach

• Treatment agentsoxidizing chemicals, nutrients, oxygen, microbes, cement, surfactants, AC, etc.


• Treatment processes Chemical, biological, immobilization, sequestration

’Classic’ in-situ treatmentImplementation (mixing-in agents)


’Classic’ in-situ treatmentStatus, recognition, and use

• Remedy originally developed for contaminated soils – so, why not try sediments?

• But it was recognized early-on that there are multiple and major limitations when trying to apply the remedy to submerged sediments


’Classic’ in-situ treatmentStatus, recognition, and use

• Consensus is that limitations are basically too great –technically and/or economically

• ‘Classic’ in-situ sediment treatment is not accepted as a viable in-situ remedy for contaminated sediments

• ONE really good thing came from all this work• Active AC-based thin-layer capping evolved from AC’s use

initially in the context of ‘classic’ in-situ treatment

But now there is the SPEARS project in Sweden (Tuffo)

• Stina Jansson, Umeå universitet, project leader• www.ecospears.com


Multiple project phases to considerRemedy selection, design, implementation

All must be executed site-specifically and correctly

• Don’t expect a remedy to magically ”work” if• Not the right one to meet objectives in the first place• Not site-appropriate, even if designed and

implemented correctly• A site-appropriate remedy is not designed correctly,

even if implemented according to the design• A site-appropriate remedy is also designed correctly,

but not implemented correctly

A good job on one phase cannot make up for a bad job on others


Remedy selection – in generalSome critical points to remember

• No remedy is better or worse than another

• Our collection of ex-situ and in-situ remedies aresimply different, unique tools in the toolbox

• No single ex-situ or in-situ remedy is a one-size-fits-all that is appropriate for all sites

• There should not be a pre-conceived notion (withno technical justification) that a particularremedy is, or should be, best for a given site


Remedy selectionNot a perfect science

• Selection is a site-specific process that must consider and juggle many different (and oftenconflicting) technical, economic, and other factors

• The selection process can vary greatly

systematice.g. multicriteriadecision analysis,

MCDA

not-sosystematic

e.g. experience and”gut instincts”, totally

cost-driven


Remedy selectionProcess-of-elimination plays an important role

FÖNS?

ÖNS?

AC thin-layercap?

remove?

isolationcap?exposure/

risk

erosionpotential

contaminantconcentrations

• Deciding BETWEEN circles simpler than WITHIN circles

• Also consider future land uplift, sea-level changes


Remedy combinationsBecoming common practice, worldwide

• In-sequence combinations• Manages risks more cost-effectively

• For example, dredge + cap

• ÖNS a finishing step to all remedies

• In-parallel combinations• Larger, complicated sites have broader range of

conditions requiring different remedies• For example, in a river, dredge or isolation cap in-

water sources upstream, ÖNS downstream


Remedy combinationsIn-parallel, example of erosion as driver

Onondaga Lakeproject

Syracuse,New York

USA

fromNYDEC

website,modified

~ 500 m



dredge


Syracuse,New York

USA

fromNYDEC

website,modified

~ 500 m



dredge


Syracuse,New York

USA

fromNYDEC

website,modified

~ 500 m



dredge


Syracuse,New York

USA

fromNYDEC

website,modified

~ 500 m



FÖNS

dredge


Syracuse,New York

USA

fromNYDEC

website,modified

~ 500 m



FÖNS

ÖNS

dredge


Syracuse,New York

USA

fromNYDEC

website,modified

~ 500 m


Remedy monitoringWhat, when, why

What → Construction monitoring Performance monitoring

When → During implementation After implementation

Why →To confirm implemented

as designedTo document performing

as intended long-term

ÖNS the whole point

FÖNS relatively less critical critical

AC thin-layercapping

critical critical

isolation capping

critical, including shortlyafter

critical


Remedy monitoringA few more words

• Performance monitoring can also tell you whenthe remedy is not working as intended, and where repairs or changes are needed

• Also monitor for possible re-contamination

• Performance monitoring should also apply to ex-situ remedies as well


Remedy monitoringTools & techniques


Remedy costsQuantitative

Remedy, ex-situ or in-situ Approx. unit cost, cost range

Removal-based, i.e. dredging 800 – 2 100 SEK/m3 (Pär’s presentation)

Isolation capping, conventional 135 – 500 SEK/m2

Isolation capping, active should be within above range

FÖNS should be near low end of above range

AC thin-layer capping 80 – 400 SEK/m2

ÖNS < 2 SEK/m2/year’’

• ”Should be” for different reasons

• Big ranges per remedy for lots of reasons

• Difficult to get clear, up-to-date information

• Comparing costs is often apples vs pears (units)


Remedy costsRelative

Most sediment remediation professionals agreeon relative remedy costs

ÖNS

conventionalisolationcapping

dredging-based

remedies<< <


There’s no such thing as bad weather – only bad clothing.


Thanks for yourattention ☺


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