Land Remediation

We have a chemical and its attributes are as follows:

\-High water solubility

\-low Soprtion

\-High persistance

Is this chemical a risk to groundwater contamination and why?

It is a risk because a high water solubility means it can travel great distances in ground water, low sorption means it does not sorb to soil so it can enter the GW and high persistance means its in the enviro for a long time.

We have a chemical and its attributes are as follows:

\-Low water solubility

\-High Soprtion

\-low persistance

Is this chemical a risk to groundwater contamination and why?

No because it isnt soluble in water so it cant travel with groundwater far, high sorption means it binds to soil and low persistance means it degrades quickly

What site would be more likely to hold a contaminant from dispersing into the groundwater?

**Site 1:**

\-Fine clay

\-Low OM content

\-Few, small micropores

\-depth to groundwater is 80m

\-minimal rainfall

**Site 2:**

\-Course sandy material

\-moderate OM content

\-many, large macropores

\-depth to ground water is 2 m

\-moderate/high rainfall

Site 1 would be more likely because although it has a low OM content it still has a clayey material with a very deep groundwater system so it is unlikely that the contaminant will reach it.

A contaminant is strongly sorbed if it has a Koc of atleast?

a) 10

b) 100

c) 1000

d)10 000

d)10 000

A contaminant is highly mobile if its s and Koc are:

a) >850 and

a) >850 and

A contaminant is highly volatile if its H is:

a)

d) >10^-3

Is this contaminant more easily or less easily degradable based on these attributes and why?

\-soluble in water

\-relatively large

\-fewer functional groups

\-compound is more oxidized in a reduced environment

\-biologically created

\-more than 10 Carbon chains

More easily degraded, because although it has 2 characteristics making it less degradable (>10 C chains and relatively large) it has more characteristics making it easily degradable

T or F: Nonaqueous phase liquids can dissolve and easily mix with water

False

What are the two types of non-aqueous phase liquids and describe the difference?

LNAPL-lighter then water so sits on top

DNAPL-denser then water so sits underneath

1 kg of NAPL can contaminate how many mg/L of groundwater?

100 000 mg/L

What is the vadose zone?

The unsaturated zone above the watertable

What are 3 ways the that you can remediate LNAPLs?

\-Excavation

\-Trenches, Drains, wells

\-Soil vapor extraction

\-Air sparging

\-Bioremediation

\-Physical barriers

What are 3 ways the that you can remediate DNAPLs?

\-Excavation

\-Trenches, drains, wells

\-Bioremediation

\-Physical barriers

\-Methanogenesis

Why wouldnt air sparging and soil vapor extraction work to remediate DNAPLs?

Because these are remediation techniques that work above the watertable and DNAPLs occur below it.

What are the 2 key distribution coefficients for the partitioning of a contaminant?

Sorption coefficient (Kd)

Henrys Law Constant (Kh)

What does Kd measure?

Distribution of a contaminant between porous-medium particles and water

What are the 3 phases a contaminant can partition to?

\-As a vapor in the air

\-Dissolved in water

\-sorbed to a porous medium particles, clay, sediments

What is the equation for looking at a contaminant partitioning between solid and water?

**Cs/Cw=Kd**=(mg/kg soil)/(mg/L water)

What is the equation for looking at a contaminant partitioning between water and vapor?

**Cg/Cw=Kh**= (mol/m^3 air)/(mg/m^3 water)

What is the equation for looking at partitioning of a compound between a dilute aqueous solution and the gas phase?

**Kh= Pi/Cw**= atm/ (mol/m^3)

What is vapour pressure?

The pressure of the vapour of a compound at equilibrium with its pure condensed phase. (i.e. the relative affinity of a chemical for itself)

If a compound has a high solubility does it have a high or low vapour pressure?

Low

Henrys Law deals with dilute solutions, what law deals with solutions where the compounds concentration is high?

Raoult’s Law

If a compound is highly polar, what does this mean in terms of its solubility?

The compound is highly soluble

What has a higher water solubility, charged or uncharged compounds?

Charged

If an acid is introduced to an acidic pH is it charged or nuetral?

neutral

Explain what Cw^sat refers to

saturation solution of a chemical

C= the concentration

w= in water

sat= at saturation

What are 3 things that Cw^sat of a compound by?

\-polarity and charge, more polar=more soluble

\-molecular size and shape, higher molecular weight=lower solubility

\-functional groups, polar/charged functional groups=more solubility

Temperature impacts the solubility of a compound in a _____ fashion (exponential or logarithmic)

logarithmic

Explain the what the octanol-water partition coefficient is.

This is the relative concentration of a compound in two immiscible phases, n-octanol and water

Explain the difference between adsorption, absorbtion, desorption.

Adsorption- adhesion of liquid or gas molecules to a solids surface

Absorption- movement of liquid or gas molecules into the structure of a solid

Desorption- the removal of liquid or gas molecules from the interior or exterior of a solid

What are 3 factors effecting adsorption-desorption?

\-functional groups of the molecule

\-acidity or basicity of functional groups

\-molecular size and shape

\-polarity or charge

\-polarizability of molecule

\-competing compounds for sorption

\-hydrophobicity

What is the main difference between how many layers of a molecule can attach to a solid for chemisorption and physical absorption?

Chemisorption- only 1 layer

Physical absorption- multiple layers

What does the equation x/m determine for sorption?

x/m=sorbate concentration in amount of contaminant sorbed per kg of dry soil

if Kd is not available what equation can help determine it?

Kd= Koc x foc

Koc- octanol water sorption coefficient

foc= fraction of organic matter in the soil

When using the equation Kd= Koc x foc to find Kd, what must teh contaminant be and why? (ionic/non-ionic)

Non-ionic, b/c sorption of ionic contaminants are impacted by pH of the soil

If Koc is not available, how can Koc be calculated by using Kow?

log Koc= 1(log Kow)- 0.21

What is fugacity?

a measure of tendency of a substance to escape by some chemical process from the phase in which it currently exists in

T or F: a contaminant will move from a contaminant of low fugacity to one of high fugacity?

False

What is the equation for fugacity in the atmosphere?

Za= 1/RT

R= ideal gas constant

T= absolute temperature K which is = degrees C + 273.15

What is the fugacity capacity for water equation?

Zw=1/Kh

Kh= henrys law constant

What is the equation for the fugacity capacity in soil?

Zs= KdxP/Kh

Kd= partition coefficient

P= density of sorbent

What is the equation for the fugacity capicity in biota?

Zb= BCFxP/Kh

BCF= bioconcentration factor (can be approximated by Kow)

P= density of the biota (=1g/cm^3 for microbes and inverts)

Kh=henrys law constant

What is the equation for determining the concentration of the contaminant in each compartment?

Ci=Zi x f

Ci= Concentration in the compartment

Zi= fugacity capicity of the compartment

f= fugacity

What is advection?

transport of contaminants by bulk movement of water

What is this equation called and what does it describe?

The Partial Differential Equation and it describes solute transport in the saturated zone

What is this equation called and what is it describing?

The advection-dispersion equation and it is describing the solute transport with first-order biodegredation in the saturated zone.

What does Darcys Law describe?

describes water movement

Explain what is meant by “solute transport by advection alone yields a sharp solute concentration front”

Behind advancing front, concentrtaion=intitial contam conc. at point of release

Immediately ahead of the front, solute conc= background conc.

What is hydrodynamic dispersion?

Process by which a contaminant plume spreads out during water movement

Hydrometric dispersion results from the combined effects of what two things?

mechanical dispersion and molecular diffusion

What are the 3 processes of mechanical dispersion?

Pore size, Tortuosity, friction in pore throat

What is molecular diffusion

movement of a compound in response to a concentration gradient and depends on teh diffusion coefficient for that molecule in the medium of interest (usually water)

Frick’s Second Law applies is systems where the dissolved contaminant concentrations are _______(changing/stable) with time

changing

in transport, what impacts the retardation of the rate of transport of the contaminant in soil?

Adsorption

Is t1/2 (half life) dependent or independent of concentration?

Independant

What do each component of this equation mean?

retardation, dispersion, advection, source/sink

What is SVE?

Installing a well into the contaminated zone that sucks out the air from the soil above the unsaturated zone

What can SVE be used on?

VOCs and semi VOCs

What characteristics of the site is required SVE this to work?

\-soil porosity

\-air permeability

\-depth to groundwater

\-presence/absence of leakage from ground surface

\-moisture and OM content

\-Temperature

To use SVE, we need a _____ vapour pressure and henrys law contstant, a ___ solubility and a ________ sorption coefficient

High, low, low

What are examples of contaminants with high vapour pressure and one with a high partial pressure?

benzene and TCE, BTEX

When using SVE, what can be done to increase the contaminants henrys law constant?

Adding in hot air (every 10 degrees C increase, increases KH by 1.6x

A contaminant is a likely candidate for SVE if vapour pressure and KH are:

a) >0.1 and >10^-6

b) >1 and >0.001

c) > 1 and > 10^-6

b) >1 and >0.001

Can a contaminant be removed by SVE if it is highly soluble?

No bc it will partition into the water

Name 3 advantages of SVE

\-causes minimum disturbance to the site

\-short treatment (6 mo-2 yrs)

\-very effective for VOCs in vadose zone

\-Not to expensive for treating large amounts of soil

\-can be installed quick

\-can be easily integrated with other remediation techniques

What are 3 limitations to SVE?

\-Soil with higher moisture content requires higher vaccums

\-Doesnt work great on soils with high OM or soils taht are extremely dry

\-Not suitable for soils with low permability

\-Can raise ground water level due to pressure

\-Will not remove heavy oils, metals, PCBs, dioxins

\-Exhaust air may require treatment

\-Concentrations reduction above 90% hard to do

\-Not effective in saturated zone

What is bioventing?

Natural biodegradation stimulated by providing oxygen to sustain microbial degredation of the target compounds

Bioventing can lead to degradation of contaminants in what compartments?

sorbed to solids, volatilized in the gas compartment of the soil

What are 3 contaminants that can be degraded by bioventing?

petroleum hydrocarbons, non-chlorinated solvents, pesticides,, wood preservatives etc.

What are the 3 characteristics of the site/soil that would make it a good candidate for bioventing?

\-Low oxygen levels (

What is air sparging?

injecting air into the saturated zone to volatilize contaminants and promote biodegradation

What remediation method is used to take out the contaminants that are volatilized into the Vadose zone after air sparging?

SVE

What type of contaminants can be remediated by Air Sparging?

VOCs and semi VOCs below the water table

Air Sparging works for contaminants that are in what compartments?

Bound to solids (soils), dissolved in the groundwater or below the groundwater.

What are limitations to air sparging?

\-not suitable for soils with high silt/clay content

\-low effectiveness under low permeability

What is biosparging?

Adding oxygen/nutrients into the saturated zone to biodegrade the contaminates in teh saturated zone

Permeable Reactive Barriers

Installing a reactive medium across the flow path of a contaminant

What are the 2 configurations for permeable reactive barriers, what is most common and which directs the contaminant towards the barrier?

Continuous permeable wall (most common), funnel-and-gate (directs contaminant towards barrier b/c it acts as a funnel)

What are 3 reactive barrier material for inorganics?

\-activitaed alumina

\-activated carbon

\-ferric oxides and oxyhydroxides

\-Magnetite

\-Peat, humate, lignite, coal

\-Phosphates

\-Zeolite

\-Biota

\-Limestone

many others

What is a reactive barrier material for organics?

\-Ferrous minerals

\-Zeolite/activated carbon/clay

What are 3 advantages to PRBs?

\-No need for expensive above ground facilities (storage, treatment etc)

\-After installation, above ground can be used

\-Limited operation and maintenance costs involved

\-Contaminants arent brought to surface so no potential for contamination across compartments

What are 3 limitations of PRBs?

\-Lengthy treament time

\-lose reactivity overtime do to clogging

\-potential for plume to pass the barrier

\-limited to shallow depths

\-longevity of PRB is unknown

What is pump and treat?

Pumping out contaminated water, treating the water and either pumping it back into the ground or into other water bodies/sewage

What are 3 limitations of pump and treat?

\-effectiveness depends on geology of the aquifer and the type of contaminant

\-takes decades-centuries and tends to fail at removing all contaminated water

\-very costly

\-doesnt removed sorbed particles or NAPLs

What is in situ chemical oxidation?

use of chemicals called oxidants that help change harmful contaminants in the soil or groundwater into less toxic ones

What are the 4 major oxidants used in chemical oxidation?

permanganate, persulfate, hydrogen peroxide and ozone

What are 3 types of contaminants taht can be treated with chemical oxidation?

fuels, solvents and pesticides

Following chemical oxidation what other methods are used to clean up the smaller amounts of contaminants left behind?

pump and treat, monitored natural attenuation

What are 3 examples that will cause chemical oxidation to take longer to work at a site?

\-contaminated site is large

\-contaminants are trapped in hard to reach areas (clay)

\-soil does not allow oxidant to spread quickly

\-groundwater flow is slow

\-oxidant doesnt last long underground

What is soil washing?

Extracting the soil from teh site, putting it through a “washing” treatment and putting it back on site

What is excavation?

Digging the contaminated soil for above ground treatment or safe disposal

Why is excavated soil covered until it can be disposed of or treated?

so no soil and contaminants become airborne or wash away in teh rain

What are 2 reasons that excavation would be used on a contaminated site?

to save money and its fast if the contaminants are likely to cause a problem they can be removed right away

What are the 3 thermal processes?

Thermal desorption, incineration and vitrification

What is thermal desoprtion?

Elevated temps to get rapid physical and chemical loss of a contaminant through combustion, volitalization or pyrolysis

what contaminants can thermal desorption be used for?

VOCs like BTEX, Chlorinated VOCs, lower molecular weight PAHs

What is produced after soil is thermally desorped?

a soil like residue

What are 3 advantages to soil desorption?

\-Completely remediates soil

\-reliable and cost-effective

\-can be done on many soil types

\-Hydrocarbons are not released into atmosphere

\-Allows for the reuse of the remediated soil

What are 3 limitations to soil thermal desorption?

\-Not as effective on clay rich soils (less heat transmission)

\-high energy cost if material is wet

\-destroys biological component

\-possibility of incomplete combustion leading to harmful substances