lecture 1 ghoshal

8/17/2019 Lecture 1 Ghoshal

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Management and remediation of

sites for extractive industries

Subhasis GhoshalDepartment of Civil Engineering

McGill University, Canada

Universidad ORT Uruguay, Montevideo , Apri l 4-8, 2016

Organizer: Prof. Lorena Betancour, Universidad ORT Uruguay

Introduction



Introduction

• Why do sites get contaminated?

• How do we assess contamination at a site?

• What alternatives are available to clean upcontaminated soil and ground water efficiently?

– technologies: scientific principles, designfundamentals, implementation issues

– management: choice of technology, legislation

• how clean is clean?

– technologically achievable limits vs risk to

receptors

Groundwater Contamination

• Aquifers: important source of water formunicipal, agricultural and industrial use.



“A 2004 EPA report estimated that it will take 30 to 35 years and cost

up to $250 billion to clean up the nation’s hazardous waste sites”

Over 10,000 contaminated sites in Canada alone.Cost of clean up in billions of dollars!

Need for sustainable cost-effective solutions



• Routine (accidental?) spills

Sources of Contamination

Underground Storage Tanks

Active efforts for site remediation in

the U.S. (and elsewhere) started only

in the early 1980’s…..

What started it?

1980 Superfund Law passed by

U.S. President Jimmy Carter



• What are pathways of

contaminant exposure?

• What should be clean-

up levels?

• What is to cleaned up:

soil, water, source

disposal zone?

Love Canal: An in-famous contaminated site

• 70-acre industrial landfill located in Niagara Falls, New York



Love Canal

• Originally a canal excavated in the 1890s for an unfinished

hydroelectric project

• 1942 – 1952: Hooker Chemicals and Plastics (Occidental

Chemical Corporation) disposed of 21,000 tons of hazardous

wastes in the canal – including solvents

• 1953: area was covered and the property developed, including

the construction of an elementary school

• Included in the deed transfer was a "warning" of the chemical

wastes buried on the property and a disclaimer absolvingHooker of any further liability

Love Canal

• Complaints of odors and

chemical residues began

in the 1960’s, increased in

the 1970’s, as heavy

rainfall caused the

groundwater to rise,

flooding area basements

Spring 1978



Pathways of Contaminant Exposure• Indoor Air - Vapor Intrusion: Volatile chemicals in contaminated soil

or groundwater can migrate through subsurface soils and into indoor

air spaces of overlying buildings

Love Canal• May 1978 - EPA concluded

from basement air sampling

that vapors are a serious

health threat

• August 1978 – President

Jimmy Carter declared the

Love Canal area a federal

emergency

• More than 900 families were

evacuated

Engelhaupt,

Environ. Sci. Technol. 2008, 42, 8179–8186



Love Canal

• 20,000-plus tons of chemicals buried at Love

Canal are there still today

• EPA deemed it too dangerous to try to remove

them

Engelhaupt, , Environ. Sci. Technol. 2008, 42, 8179–8186

Love Canal

• Site publicity directly spurred

passage of EPA’s Superfund law in

1980

• December 1995 - Occidental ordered

to pay $129 million settlement

• Residents returned to portions of the

site in late 1990’s

Engelhaupt,

Environ. Sci. Technol. 2008, 42, 8179–8186



Love Canal

• Epidemiological study into potential health effects ongoing

– Children born at Love Canal twice as likely as children in

other parts of the county to be born with a birth defect

– Negative reproductive effects for the exposed population

over multiple generations

– The draft also reported elevated rates of kidney, bladder,

and lung cancers at Love Canal

A Canadian Example…..



Oil Sands Mining in Alberta:

Contaminated Site Legacy in the Making?

Oil Sands: Site Contamination



Subsurface Contamination Issues Changing?



Contaminated Site

Management Process

The Contaminated Site Management &

Remediation Process

• Preliminary Assessment/Site Inspection

• Remedial Investigation/Feasibility Study

• Records of Decision – Remediation? Containment?

• Remedial Design/Remedial Action

• Long-term Monitoring



• Conceptual Contamination scenario from site assessment

– Intensive site data requirements

Site Assessment

Remedial Investigations & Feasibility Studies(RI/FS)

• Conduct Field Investigations to characterize site

– Site physical characterization (surface features,geology, hydrogeology, population & land use,ecology)

– Sources of contamination

– Nature and extent of contamination

• Data analysis to establish contaminant fate andtransport – determine risk of exposure to receptors

• Treatability studies – determine remedial objectives



Remedial Investigations & Feasibility Studies

(RI/FS)

• Data analysis to establish contaminant fate andtransport – determine risk of exposure to receptors

– Pollutant levels in soil vapour phase? in

groundwater?

– Potential for contaminant migration?

• Treatability studies

– Determine remedial objectives− Feasibility of remediation systems

Resistivity



• Ground Penetrating Radar

− radio frequency waves

− Shallow contamination detected (buried objects, oil

phase, water table…)

Auger and Rotary Drilling



Direct-Push Rig for Cone Penetration Test

Equilibrium Partitioning

of Pollutants

(Chemical Thermodynamics)



• By understanding the potential of achemical to move from oneenvironmental compartment to another,we can evaluate the direction andmagnitude of contaminant transfer andtransformation

• Important for understanding contaminantmigration and feasible remediationalternatives


• Equilibrium partitioning varies greatlyfrom one contaminant to other and fromone environmental system to another

• Understanding of the theoreticalframework very important to developpredictive capability (modeling)

• Focus on two cases – petroleum liquids (mixture of non-ionicorganic compounds)

– arsenic (metal)




• Compound properties governing equilibriumphase transfer behaviour of nonionic organicchemicals:

– Vapour Pressure (Pure liquid/solid phase –air partitioning)

– Aqueous Solubility (Pure liquid/solid phase – water partitioning)

– Henry’s Law Constant (Air - waterpartitioning)

– Solvent-Water Partition Coefficient

– Sorption Coefficient (Soil-WaterPartitioning)




Vapour Pressure

• Vapour Pressure: the pressure of the vapour of a

compound at equilibrium with its pure condensed phase

(liquid or solid)

• If a compound exists in the pure solid or liquid phase, the

maximum concentration of a compound that can be

attained in the air phase is its vapour pressure

)(or)( ,, s P l P ioio

Vapour Pressure:

Pure Phase Organic Liquid – Air Partitioning

Initial State Equilibrium State

Benzene conc. in

air?

Pure Phase Liquid (say benzene)

air

- Molecule of benzene



Vapour Pressure

Range of

values

Environmental

Organic

Chemistry

Schwarzenbach,

R., Gschwend, P.,

Imboden, D.

Vapour Pressure

Effect of

temperature

significant

Environmental

Organic

Chemistry

Schwarzenbach,

R., Gschwend, P.,

Imboden, D.



Soil Vapor Extraction

Johnson et al., 1990, Groundwater, 28:413-429

• Aqueous solubility: the maximum conc. ofa chemical that can be attained in a water

phase

• Exact definition: abundance of the chemical per unitvolume in the aqueous phase when the solution is inequilibrium with the pure compound in its actualaggregation state (gas, liquid, solid)

Aqueous Solubility

or, at w

iat w C C



water

Pure Phase – Water Systems

(l)iat wC ,


Pure Phase Liquid of i

water

Pure Phase Solid of i

water

water

(s)iat

wC ,

Aqueous Solubility

Range of

values

Environmental

Organic

Chemistry

Schwarzenbach,

R., Gschwend, P.,

Imboden, D.



Aqueous Solubility

What happens

during dissolution?

ΔHs =ΔH1 +ΔH2 +ΔH3 +ΔH4

EnvironmentalOrganic

Chemistry

Schwarzenbach,

R., Gschwend, P.,

Imboden, D.

Aqueous Solubility

Effect of

temperature

Environmental

Organic

Chemistry

Schwarzenbach,

R., Gschwend, P.,

Imboden, D.



Pumping well

Storage

Tank

Leaked Oil Dissolved contaminants

Newell, C.J. and O’Connor, J.A. American Petroleum Institute, 1998

Chemical Potential

• Chemical Potential can be used to assess the tendency of a

compound i to be transferred from one system to another

or to be transferred within a system

• At constant T, P and composition, the Gibbs free energy

added to the system with each added increment of i is

referred to as the chemical potential µi of component i

• Chemical potential of i in each phase is equal atequilibrium



Chemical Potential

Environmental

OrganicChemistry

Schwarzenbach,

R., Gschwend, P.,

Imboden, D.

Fugacity of compound i

Ideal gas

Pure organic

liquid

Non-ideal

liquid

solution

Environmental Organic Chemistry

Schwarzenbach, R., Gschwend, P., Imboden, D.



Fugacity

• Fleeing tendency of a compound

• Relative fleeing tendencies used forcalculation of equilibrium partitioning

oi j

i j

i j

i j f x f ,••= γ Fugacity of a compound i in phase j =

Concentration of compound

Activity coefficient= f (comfort of compound

i in phase j)

Reference phase

fugacity

Organic Liquid Mixture (Oil) – Water

Partitioning

iw

ioil f f =

Fugacity of a compound i is equal in all phases when equilibrium is attained, e.g. for

an air phase – water phase system


c1A ?

Phase 2 contains mixture of A ( ), B ( )

Phase1

(water)

Phase2

(oil)

c1B ?



Organic Liquid Mixture (Oil) – Water Partitioning


c1A ?

Phase 2 contains mixture of A ( ), B ( )

Phase1

(water)

Phase2

(oil)

Aw

Aw

Aw

Ao

Ao

Ao

A A

f x f x

f f

....

12

γ γ =

=Compound partitioned

Phase into which it is partitioned

o: oil

w: water

c1B ?

Partition coefficient for

Oil-Water System

Aow

Aw

Aw

Aoo

Aoo f x f x

,, .... γ γ =

Aoo

Aow

Ao

Aw

wo

Ao

f

f

x

x

,

,

phasewaterinAof Conc. phaseoilinAof Conc.tCoefficienPartiton

γ

γ =

==


c1A ?Phase1

(water)c1

B ?



Air-Water Partitioning

• Equilibrium partitioning of chemicals between the gas

phase and an aqueous phase

• Henry’s Law Constant, K H (air-water distribution constant)

phaseaqueousincompoundof abundance

phasegasincompoundof abundance

i

i K H =

essdimensionl'

⋅=mol

L

L

mol

C

C K

w

a H

Solvent-Water Partitioning• Octanol-water partition constant K ow

– Octanol is a surrogate for natural organic phases (soils, sediments,

suspended particles)


phaseorganicincompoundof abundance

i

i K ow =

essdimensionl

⋅=mol

L

L

mol

C

C K

w

org

ow



Soil-Water Partitioning

• Why is this important?

1. Reason for contamination of the soil phase

2. Controls the rate at which contaminants move

in soil and in subsurface systems (retardation)

3. Affects other pathways (i.e., volatilization,

oxidation processes, biodegradation, etc.) –

availability reduced

4. Must be understood and quantified to carry

out effective remediation

Soil-Water Partitioning• Governing variables:

– Properties of sorbent (solid)

• hydrophobicity, specific surface area, presence of

surface charges (clays)

– Properties of sorbate (contaminant)

• hydrophobicity (K ow

), Ionic charge

– Properties of fluid medium (water, air)



Properties of Soils• Composition highly variable

• Example: silt loam soil

Properties of Soils

• Soil Organic Matter

1. Humic materials (humus): dark brown,

yellowish polymers formed by microbial

reactions - molecular weights 10,000 or higher

• fulvic acid (soluble & extractable in base and acids)

• humic acid (soluble & extractable in base only)

• humin or kerogen (not extractable in base)

2. Non-humic materials: unaltered proteins,cellulose, etc. - biochemicals from living

organisms



• Humic acids: Hydrophobic fraction of soils

Properties of Soils

• Linear sorption coefficient K d – Partitioning in to organic matter or mineral

surface

– Infinite number of homogeneous sorption sites


solidssoiloncompoundof abundance

i

id K =

⋅=

mol

L

kg

mol

C

C K w

sd

Solid - Aqueous Phase Partitioning



Linear-Isotherm

Schwarzenbach et al.

• Linear correlations between log (K om or K oc) & Log K ow

Solid - Aqueous Phase

Partitioning

omoc

ococw

ococd

omomw

omomd

f f

K f C

f C K

K f C

f C K

5.0

.=.

.=.

≈

=

=

K oc = soil organic carbon distribution coefficient

K om = soil organic matter distribution coefficient

Log Koc or Log Kom= a* Log Kow + b



Solid - Aqueous Phase

Partitioning• Kom is invariant of soil type

Schwarzenbach et al.

Properties of Soils

• Soil Organic Matter usually measured as organic carbon



Sorption Isotherms

Freundlich Model1/K n

s f wC C =

Kf = Freundlich sorption coefficient

1/n = Freundlich exponent (measure of non-linearity)

Linearized version: log log K 1/ log s f w

C n C = +

Case 1 (n < 1)

Cw

C

s

Case 2 (n = 1)

Cw

C

s

Case 3 (n > 1)

Cw

C

s

Case 1 (n > 1) Case 2 (n = 1) Case 3 (n < 1)

Solid-Aqueous Phase Partitioning

• Irreversible sorption or Hysteresis

• Sequestration and Contaminant agingphenomena

– continuous diffusion and retention ofcompound molecules in remote andinaccessible regions within soil matrix

– The longer a contaminant is in contact with soilorganic matter, the more resistant it is toaqueous extraction




• Real-world example of contaminant “aging”

Nash and Woolson (1967) Science 157, 924-927

Solid-Aqueous Phase Partitioning• Implications of contaminant aging

– Clean-up of persistent contaminants difficult, if not impossible

– What are available options for remediation and future land use?

– Reduced mobility in subsurface

– Reduced bioavailability

– Risk assessment

– Establishing meaningful regulations for clean-up




• Irreversible sorption or Hysteresis

• Sequestration and Contaminant agingphenomena

– continuous diffusion and retention ofcompound molecules in remote andinaccessible regions within soil matrix

– The longer a contaminant is in contact with soilorganic matter, the more resistant it is toaqueous extraction

Equilibrium States for

Metal Pollutants



Inorganic Contaminants

• Metals: only 30 or so used industrially – Heavy metals: metals with densities > 5.0 g/cm3


Chromium (Cr)

• Cr(VI) used to control

corrosion at a natural gas

plant

• 12,000 ppb vs 50 ppb

• Water source for 18

million people




• Speciation of metals affects watersolubility, transport, toxicity,

bioavailability, and treatment

• Metals may be present as

– anions (AsO43-, CrO4

2- )

– cations (Pb2+ , Hg2+ )

– complexes (CdCl3

+)

• Solubility determined by precipitation-

dissolution, redox, acid-base chemistry

Inorganic Contaminants• Partitioning of metals in soils



Chemical reactions determining

equilibrium speciation1. Acid – Base reactions

– Speciation represented by log C vs. pH

relationships

– Dissociation constants, Ka

2. Precipitation reactions

– Solubility product, Ksp

– Precipitates can be transported in groundwater

as particulates (colloids)

Chemical reactions determiningequilibrium speciation

3. Complexation reactions

– Complex: an ion that forms by combining

simpler cations, anions, and sometimes

molecules

– Facilitated transport – certain complexes are

soluble

4. Redox reactions

– Electrode potential controls speciation



Complexation Reactions

• Complex:

Metal Cation + Ligand (anion or organic molecule)

• Complexation facilitates the transport of toxic metals at near

neutral pH

• Without complexation, metals are most soluble/mobile in

their free ion form which only occurs at low pH

• Calculation of the distribution of metals among various

complexes involves the solution of a series of mass law

equations and knowledge of the total metal ionconcentration in the solution

Complexation Reactions• Examples of metal complexes:

Cr 3+ + OH- Cr(OH)2+

Mn2+ + Cl- MnCl+

Fe2+ + CO32- FeCO3

Al3+ + 3OH- Al(OH)3



Complexation Reactions

• General form of complexation reaction and the stabilityconstant

• Large values of β are associated with the stronger or more

stable complexes

[ ][ ] [ ]h H l L M

hl Lh H l MLhH lL M =↔++ β

Metal Ligand Hydrogen ion

Complexation Reactions• Speciation is controlled by pH

• Log C-pH diagram



Redox Reactions

• Oxidation-Reduction Reactions: – chemical reactions where participating elements

change their valence state through gain or loss ofelectrons

• Reduction: electron gain, loss of positive valence

Fe2+ + 2e- Feo

• Oxidation: electron loss, gain of positive valence

Fe2+ Fe3+ + e-

• Mediated by microorganisms (catalysts)

Redox Reactions• Quantifying oxidation potential

• Half reaction

Ox + ne- = Red

Mass law expression: [ ]

[ ]

Red

Oxn

K e−

=

[ ]

[ ]

1/

Red

Ox

n

ne

K

−

=

Electron

activity



Redox Reactions

• Quantifying oxidation potential

– Positive values of pe, E H : oxidizing conditions

– Negative values of pe, E H : reducing conditions

• Example: metals in sulfur systems

Possible species: SO42-, H2S, HS-, S2-

Complexes: metals sulfates or metal sulfides

Oxidizing conditions: SO42-

dominates, metals soluble

Reducing conditions: H2S, HS-, S2- dominate, metals insoluble

Redox Reactions• EH-pH diagram



Metal Contaminants

• Reaction processes affecting transport ofmetals

– Precipitation / dissolution (low pH)

– Complexation: binding with ligands affects

solubility and sorption

– Redox conditions: determine predominance of

soluble or insoluble species

– Sorption / Ion exchange:

• Negative charges on clays, metal oxides, andhumus

• Metal ions may have greater affinity for sites



Geogenic

Anthropogeni

c

Biogenic

Arsenicdynamics in

soil and

aquatic

ecosystems

Mahimairaja et al, 2005

Wang and Zhao, 2009



Arsenic Sources

What do we know about As fate in the

environment?• As(V) is less mobile, less toxic and more sportive

than As (III)

• Natural oxidation of As(III) to As (V) by oxygenis slow

• Chemical oxidation involves the use of strongoxidizers like chlorine, ozone, iron chloride,hydrogen peroxide/Fe2+, permanganate andmanganese oxides, which may lead to secondaryenvironmental problems.

• Microorganism can transform As(III) to As (V)and other species

• As(V) binds to iron surfaces (eg. iron oxide, ZVI)



As(III) and As(V)-NZVI

reactions

Ramos et al, 2009; Weilie. Y et al,2010 & 2012;

• Experiments pH 8-

11

• Eh: -198 to 158

Transport of Dissolved

Contaminants



• Dissolved Contaminants

• inorganic or organic ions and/or

molecules dissolved in groundwater

– The term dissolved contaminant thus

excludes an oil phase or sorbed-phase

contaminants but includes molecules thatdissolve from those phases into water

Transport of Dissolved Contaminants in

Groundwater

Contaminant Transport• Contaminant Transport Mechanisms

(dissolved contaminants)

- Advection

- Diffusion

- Mechanical Dispersion

• Contaminant Transport Influenced by

- Sorption

- Reactions (chemical or biological)

Hydrodynamic

dispersion



• Advection – Movement of contaminants along with flowing

groundwater from the source point/area, according

to the average linear velocity

– Plug flow

Mechanisms of Contaminant Transport

• Dissolved Contaminants

• inorganic or organic ions and/or

molecules dissolved in groundwater

– The term dissolved contaminant thus

excludes an oil phase (NAPL) butincludes molecules that dissolve from it

into water

Transport of Dissolved Contaminants inGroundwater



• Diffusion• Process whereby molecules move under the influence of their kinetic

activity in the direction of the concentration gradient

• Molecular-scale process

Mechanisms of Contaminant Transport

Diffusion

Diffusion Process:

• Molecular-scale process

• causes spreading (mixing) due to theconcentration gradients and random motion

• no bulk movement (fluid velocity) needed for

diffusive transport• continues till concentration gradients becomenon-existent (system has reached equilibrium)



One drop of red ink

Diffusion

• Fick’s First Law of Diffusion:

Mass flux is proportional to the

concentration gradient

(for fluid medium)

Fx = Mass flux [M/L2

/T]Dd= Diffusion coefficient [L2/T]

= Concentration gradient [M/L3/L]

dx

dC D F d x −=

dx

dC

Dispersion: Tendency of solute to spread out fromthe path that it would be expected to follow

Dispersion is caused by heterogeneities in the medium thatcreate variations in flow velocities and flow paths

• in individual pore channels molecules travel at differentvelocities at different points in the channel due to dragexerted on the fluid by the roughness of the surface

• difference in pore sizes along the flow paths - differentvelocities in different pore channels

• variable path lengths, branching and tortuosity of pores

Mechanical Dispersion



Mechanical Dispersion

• Mechanical dispersion: caused by any combination of the

following…

• Turbulence of fluid

• Fluid shear

• Porous medium

• Boundary effects

1-D Models

x

C v

C D

t

C x x

∂

∂−

∂

∂= )(

2

2

∂

∂

Rate of

change of

concentration

with time at

any x

Dispersion Advection



Analytical Solutions to Mass Transport

Equation

1-D Models

t xv

x D x x

∂

∂=

∂

∂−

∂

∂ CCC2

2

Instantaneous source in 1-D:

( ) ( )

−−=

t D

t v x

t D

M

x

x

x4

exp4

tx,C2

π

where M = injected mass per unit cross-sectional area

Initial concentration C(x,0) = 0

Boundary conditions:

C(0,t)=Co, 0<t≤t0; C(0,t)=0, t> t0

C(∞,t)=0, t≥0

Contaminant Transport• Pulse or Instantaneous Source

Advection only

Advection +

dispersion



Continuous Supply of Contaminants

Constant vel

water Co

Contaminant

reservoir

t=t1 t=t3t=t2

Packed

Porous media

(sand)

1-D Contaminant Transport

C vs. x plot

Continuous Supply – No Sorption

Constant v

Advection

0 1.00.5

C/Co

X ( m )

Constant vCo

Contam

reservoir

Advection &

Dispersion



Advection only

Contaminant Transport

• Continuous Source

Advection +

dispersion

Sorption Effects

• R = retardation factor

sorption

sorptionno

d

b

v

v

K n R =

+=

ρ

1


t x R

v

x R

D x x

∂

∂=

∂

∂−

∂

∂ CCC2

2



sorption

0 1.00.5

C/Co

X ( m )

Co

1-D Contaminant Transport

C vs. x plot

Contaminant

reservoir

no sorption

Contaminant TransportContinuous Supply (with sorption)

Co

Constant v Constant v

t = t1 t = t1

t = t1 t = t2

Groundwater flow

Without sorption

t = t0 t = t1 t = t2

t = t0

With sorption

Contaminant TransportInstantaneous Supply



• Plume Spreading: Separation of contaminants in aplume

– Gasoline spill (BTEX and MTBE)


source

xylenes

benzene

MTBE

1) Rate of release (solubility)

2) Sorption

3) Biodegradation

• Natural Gradient Field Tests

– Tracers injected into shallow sand and

gravel unconfined aquifers

– Purpose: to assess the validity of

assumptions made in modeling

contaminant transport

Case Studies

1. Canadian Forces Base Borden, Ontario

2. Otis Air Base, Cape Cod, Massachusetts




• Canadian Forces Base Borden

– 12 m3 of chloride injected

into aquifer

– 5000 observation points

monitored over 2 years

– Data analyzed to determine

advection and dispersion


• Canadian Forces Base

Borden

• Results

– Dispersivities vary

with scale




• Cape Cod, Mass.

– 7.6 m3 of tracer solution injected into

aquifer

– Bromide used as conservative tracer

– Lithium, molybdate, and fluoride used as

reactive tracers

– 9840 sampling points monitored over 3

years

– Data analyzed to describe movement

and behavior of plume in saturated zone


Contaminant Transport• Cape Cod, Mass.



Interphase-Mass Transfer

Rates of chemical transfer from

one phase to another

Oil-Water Mass Transfer

Interface

Water

Distance

Oil



Film Theory: Oil-Water

Given that

wowoil t

t wwoil

t ot

K C

C

k k K K

C K

C K J

W oil ow

wo

1

*

1

1

where

/

,/

,

//

/

+=

−∗=

=

Oil-side Boundary Layer Mass

Transfer Limitation

Interface

Water

Distance

Oil

C w,eq



Water-Side Boundary Layer Mass

Transfer LimitationInterface

Water

Distance

Oil

C w,eq

)()(2

2

t eqt x x C C V

A K

x

C v

C D

t

C −−

∂

∂−

∂

∂=

∂

∂

Rate of

change ofDispersion Advection Mass transfer

lecture 1 ghoshal

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