IN-SITU CHEMICAL OXIDATION AND REDUCTIONMargy Gentile

September 30, 2016

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Disclaimers and NoticesThe materials herein are intended to furnish viewers with a summary and overview of general information on matters that they may find to be of interest, and are provided solely for personal, non-commercial, and informational purposes. The materials and information contained herein are subject to continuous change and may not be current, correct, or error free, and should not be construed as professional advice or service. You should consult with an Arcadis or other professional familiar with your particular factual situation for advice concerning specific matters.

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About the Presenter

c 1 510 432 6251e margaret.gentile@arcadis.com

MARGARET GENTILE, PHD, PEAssociate Vice President, Principal EngineerIn-Situ Reactive Treatment Lead for Arcadis North America

16 years of experience in environmental engineering with a strong focus on in-situ remediation design, implementation, and optimization for organic and inorganic contaminants. She particularly enjoys providing technical expertise on microbial and geochemical aspects of treatment, remediation of metals, and tackling large, complex plumes.

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Learning ObjectivesAfter attending this session, participants should be able to:Explain the underlying chemistry of common oxidant and reductant systemsRecognize the benefits and limitations of chemical oxidant systemsIdentify when ISCO is an appropriate remedial alternativeIdentify potential safety hazards associated with chemical treatment

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Chemical Treatment

COC = Reductant

Reagent = Oxidant

Chemical Oxidation

Reagent = Reductant

COC = Oxidant

Chemical Reduction

In-Situ Chemical Oxidation (ISCO)

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In-Situ Chemical Oxidation (ISCO)

ISCOBasics

• Health and Safety• Reaction Mechanisms• Reagents• COC Applicability

• Bench and Pilot Testing• Full Scale Design• Byproducts

• Strike Zone• Source areas vs dilute plumes

Applicability

Implementation

© Arcadis 2016

In-Situ Chemical Oxidation (ISCO)

ISCOBasics

• Health and Safety• Reaction Mechanisms• Reagents• COC Applicability

• Bench and Pilot Testing• Full Scale Design• Byproducts

• Strike Zone• Source areas vs dilute plumes

Applicability

Implementation

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Chemical Treatment

Aggressive, fast acting reactionsSignificant non-target reactant losses

Requires large volumes and tightly spaced injection points

COC = Reductant

Reagent = Oxidant

Chemical Oxidation

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Health & Safety MomentRapid Heat and Gas Liberation

January 2010 Industry Presentation Photos – Fenton’s Oxidation

September 2010 News Headline

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Example H&S Analysis

Crew is loading 40% NaMnO4from 5-gallon jugs diluting it to working strength

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Health and Safety Guidance Documents for ISCO Project Planning

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Chemical OxidationThe transfer of electrons from contaminant (oxidizing it) to an electron acceptor (oxidant).

Contaminants = Reductants• Petroleum hydrocarbons, MTBE, TBA• PAHs• Chlorinated organics• Some explosives• Emerging contaminants

Reagents = Oxidants• Permanganate• Catalyzed hydrogen peroxide (CHP)• Ozone• Persulfate

11

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MnO4- + 2H2O + 3e- → MnO2(s) + 4OH-

Permanganates

O

O

OO

Mn

Oxidant Reduction Half-Reaction:• Reaction Mechanism: direct oxidation

• Delivery/Residence Time: • Strong oxidant with slower kinetics

favors distribution and longer residence time

No activation required COC Targets:Strong affinity for carbon-carbon double (pi) bond in chlorinated alkenesPhenolsNot effective for chlorinated methanes or ethanes, limited effectiveness for aromatics

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Catalyzed Hydrogen Peroxide (CHP, aka Fenton’s Reagent)

• Reaction Mechanism: combination of H2O2and Fe(II) at low pH creates OH•

O

H

Unpaired electron

𝐹𝐹𝑒𝑒2+ + 𝐻𝐻2𝑂𝑂2→𝐹𝐹𝑒𝑒3+ + 𝑂𝑂𝐻𝐻− + 𝑂𝑂𝐻𝐻• 𝑂𝑂𝐻𝐻• + 𝐻𝐻2𝑂𝑂2 → 𝐻𝐻2𝑂𝑂 + 𝐻𝐻𝑂𝑂2•

𝐻𝐻𝑂𝑂2•↔𝑂𝑂2•− + 𝐻𝐻+

Wide range of COC Targets

• Delivery/Residence Time: Very fast kinetics of OH• limited

distribution, limited persistence• Can liberate gross quantities of gas and heat (oxygen, volatiles, carbon dioxide)

http://upload.wikimedia.org/wikipedia/commons/8/8d/OH_orb5.jpg

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Ozone

• Reaction Mechanism: direct and radical-based oxidation can be induced

O

O O

Radical-Based𝑂𝑂3+ 𝑂𝑂𝐻𝐻− →𝐻𝐻𝑂𝑂2• + 𝑂𝑂2•

𝑂𝑂3 + 𝑂𝑂𝐻𝐻− →𝑂𝑂3− + 𝑂𝑂𝐻𝐻•

Direct𝑂𝑂3 + 2𝐻𝐻+ + 2e- → 𝐻𝐻2𝑂𝑂 + 𝑂𝑂2

• Delivery/Residence Time: • Gaseous reagent delivered by

sparging• Relatively fast kinetics• Longer duration injections

needed

http://upload.wikimedia.org/wikipedia/commons/8/8c/Ozone-CRC-MW-3D-balls.png

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Activated Persulfate

• Reaction Mechanism: radical-based oxidation

• Delivery/Residence Time: • Must be activated (heat, base, iron,

ambient)• Kinetics can be engineered

control on distribution and residence time

• Activation can generate heat and gas

S2O82- + Activator → SO4-• + X

Wide range of COC Targets• Chlorinated solvents• Petroleum hydrocarbons (BTEX)• Fuel oxygenates (MTBE)• Phenols, pesticides• Emerging contaminants

OH• , HO2•, O2••••

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In-Situ Chemical Oxidation (ISCO)

ISCO Basics

• Health and Safety• Reaction Mechanisms• Reagents• COC Applicability

• Bench and Pilot Testing• Full Scale Design• Byproducts

• Strike Zone• Source areas vs dilute plumes

Applicability

Implementation

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The ISCO “strike zone”

Safety

Delivery

Contact

Access

Contact of oxidant and contaminant is critical to ISCO success.Delivery includes oxidant distribution and residence time.

Safe implementation is required.

Access to source mass can lead to costly inefficient ISCO

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Generalized Cross-SectionSilt/Clay

Sand

Conceptualizing ISCO Treatment

ISCO becomes inefficient and cost prohibitive with significant COC storage

As treated aquifer is flushed, residual mass from fine-grained clays/silts contributes to ongoing dissolved phase concentrations (storage)

ISCO accesses dissolved phase mass

Re-injection needed based on rebound and reagent residence time

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Case Study 1: ISCO in Presence of Potential NAPLA A`

MIP

-12

MIP

-18

MIP

-1

MIP

-4

8 CHP ISCO injections were conducted

Pre-treatability study MIP data suggests source mass present

TCE in GW 8/05TCE in GW 6/07

50M

W-2

5

Conductivity Log

ECD Response

PID Response

Iron and peroxide response observed

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Case Study 1: ISCO in Presence of Potential NAPL

TCE rebound observed after each injection

MCLs not achieved after 8 injections

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Case Study 2: ISCO for a Dilute Plume• ISCO supplemented source area

removal• Low concentrations of TCE (

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In-Situ Chemical Oxidation (ISCO)

ISCO Basics

• Health and Safety• Reaction Mechanisms• Reagents• COC Applicability

• Bench and Pilot Testing• Full Scale Design• Byproduct Management

• Strike Zone• Source areas vs dilute plumes

Applicability

Implementation

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Laboratory Treatability Testing

Verify activation/oxidation chemistry if novel contaminant or questionable site geochemistry

Assess treatment efficacy

Establish oxidant and activator dosing

Screen secondary effects – VOCs and metals

Role of Pre-Design Testing Bench Testing

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Case Study 3: TPH-DRO Persulfate Treatability DataBench Testing

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Field Injection Testing

Define delivery hydraulics- injection flow rate, mobile porosity, achievable ROI

Confirm treatment efficacy observed in lab

Fine-tune dosing requirements at large sites

Evaluate in-situ oxidant consumption, and persistence, and extent/rate of rebound

Evaluate secondary effects observed in lab

Role of Pre-Design Testing Pilot Testing

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Dose Response/Residence Time Monitoring

Reagent Monitoring ParameterPermanganate MnO4- (field test), VisualOzone DOCHP T, pH, SCPersulfate S2O82- (field test), SC

Pilot Testing

• Confirm injection hydraulics• Confirm reagent distribution• Evaluate reagent reactivity

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Arcadis Innovation- Persulfate Field Test Kits

• Comparison to commercially available kits:

• Uses less harmful chemicals- avoids DOT/IATA regulations• One kit for both high & low range S2O82- concentrations• No dilutions• Lower cost per sample

• Arcadis Treatability Laboratory developed an alternative to commercial field test kits using the iodometric titration-based analytical method*

*Based on literature by Kolthoff and Carr (1953)

Pilot Testing

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Case Study• Site contaminated with chlorinated

solvents• 1,1,1–trichloroethane

• Perchloroethene

• Trichloroethene

• Lab study completed –• Top performer was high concentration

sodium persulfate activated with ferrous sulfate heptahydrate and citric acid

• Field injection – 4 wells

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Observation

What caused this?

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How Did It Happen?

Design• 5 mol iron :1 mol citric acid

Improper formulation: oxidant/activator ratio

Final ratio was 5 mol Fe2+ : 7.0 mol Citrate

NOMENCLATURE!• 1 mol Fe2+ is not the same as 1 mol

FeSO4*7H2O!!!!!

• MW ratio = 278/55.9 = Factor of 5.0Field decision

• Minimization of waste

• 50 lb / 35 lb = factor of 1.4

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Full Scale Design Layouts

TCE Treatment

AreaExcavated to

13 ft

Reagent distribution throughout target treatment area

Inject and drift with persistent reagent

Design

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Byproduct Management- Halogenated Byproducts

Halogenated byproducts

THMsChlorinated

ethanes

Halide radicals

+Organics

Halide ions +

SO4•¯ or OH•

Byproducts

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By-Product Formation – Activated Persulfate Example

0.0

1.0

2.0

3.0

4.0

5.0

6.0

7.0

8.0

0

500

1,000

1,500

2,000

2,500

Baseline-1 T1 - 1 week T2 - 3 weeks T3 - 5 weeks

pH

Conc

entr

atio

n (u

g/L)

Acetone Chloromethane Ethylbenzene Methylene Chloride

1,2,4-Trimethylbenzene Xylenes pH

15 g/L Na2S2O8500 mg/L Fe (5:1 molar ratio Fe:citrate)

Byproducts

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Broader View of Field Results

1

10

100

1,000

10,000

-50 0 50 100 150 200 250

Conc

entr

atio

n (µ

g/L)

Days After Injection

• Results from three field test sites• #1 SP near peat• #2 SP in silty sand• #3 SP with chelated iron in

mostly silt

• Chloromethane and methylene chloride are most frequently detected under various activation strategies

• Attenuation typically seen with 6 months of applicationChloromethane

Methylene chloride

Byproducts

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Byproduct Management- Metals Byproducts

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678910111213

0

1

10

100

1,000

10,000

Jul-06 Aug-10 Sep-14

pH (s

.u.)

Met

als

(ug/

L)

Case Study 5: Metals Generation and Attenuation

Metals mobility limited to treatment area

3-MW-13

~50 ft from nearest IP

678910111213

0

1

10

100

1,000

10,000

Jul-06 Aug-10 Sep-14pH

(s.u

.)

Met

als

(ug/

L) AsCr (T)

VdMo

Cr(VI)

pH

3-MW-15/15R

3-MW-13 GW

3-MW-15/15R

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Case Study 5: Metals Generation and Attenuation

Metals are slowly attenuating within treatment area

Byproducts

In-Situ Chemical Reduction (ISCR)

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Chemical Reduction

The transfer of electrons from reagent (reductant) to a contaminant (oxidant).

Reagents = Reductants• ZVI• Reduced iron minerals• Ferrous iron• Sulfides• Sulfur oxyanions (e.g., dithionite)

COC = OxidantsChlorinated compoundsRedox sensitive metals

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Zero Valent Iron- ChemistryTarget COCs• Chlorinated ethenes, ethanes,

methanes, propanes*• NDMA• Cr(VI)*also treated by zero valent zinc

FormsZVI- macroscalenZVI- nanoscaleeZVI- emulsified in organic, e.g. EVO

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Zero Valent Iron- PlacementInjection

WellsPermeable Reactive Barriers and In-Situ Stabilization

• Not generally recommended for ZVI

• Agglomeration of nZVI can limit distribution via injection wells

• Effective applications of ZVI

• Direct push with eZVIrelatively more successful

Direct Push

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Reduced Iron Minerals

• Naturally occurring minerals may support MNA• Formation from carbon injections and biological activity may support long term

abiotic reduction Reagent dosing strategies not as well developed for this approach as for in-situ biological reduction

Reductants = reduced iron minerals• mackaniwite• pyrite• magnetite• Green runs

COC = OxidantsChlorinated compounds

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Learning ObjectivesAfter attending this session, participants should be able to:Explain the underlying chemistry of common oxidant and reductant systemsRecognize the benefits and limitations of chemical oxidant systemsIdentify when ISCO is an appropriate remedial alternativeIdentify potential safety hazards associated with chemical treatment

© Arcadis 2016

Arcadis.Improving quality of life.

In-Situ Chemical oxidation and reductionDisclaimers and NoticesAbout the PresenterLearning ObjectivesChemical TreatmentIn-Situ Chemical Oxidation (ISCO)In-Situ Chemical Oxidation (ISCO)In-Situ Chemical Oxidation (ISCO)Chemical TreatmentHealth & Safety Moment�Rapid Heat and Gas LiberationExample H&S AnalysisHealth and Safety Guidance Documents for ISCO Project PlanningChemical OxidationPermanganatesCatalyzed Hydrogen Peroxide (CHP, aka Fenton’s Reagent)OzoneActivated PersulfateIn-Situ Chemical Oxidation (ISCO)The ISCO “strike zone”Conceptualizing ISCO TreatmentCase Study 1: ISCO in Presence of Potential NAPLCase Study 1: ISCO in Presence of Potential NAPLCase Study 2: ISCO for a Dilute PlumeIn-Situ Chemical Oxidation (ISCO)Role of Pre-Design Testing�Case Study 3: TPH-DRO Persulfate Treatability DataRole of Pre-Design Testing�Dose Response/Residence Time MonitoringArcadis Innovation- Persulfate Field Test KitsCase StudyObservationHow Did It Happen?Full Scale Design LayoutsByproduct Management- Halogenated ByproductsBy-Product Formation – Activated Persulfate ExampleBroader View of Field ResultsByproduct Management- MetalsCase Study 5: Metals Generation and AttenuationCase Study 5: Metals Generation and �AttenuationIn-Situ Chemical Reduction (ISCR)Chemical ReductionZero Valent Iron- ChemistryZero Valent Iron- PlacementReduced Iron MineralsLearning ObjectivesSlide Number 46