Land Remediation Part B

When contaminants are released, what are the 4 ways they may exist?

1) Mobile free product or nonaqueous phase liquid (NAPL)

2) Adsorbed phase

3) Dissolved phase

4) Vapour phase

The distribution of contaminants into the listed phases is governed by…

\-Attributes of the contaminant

\-Nature of the environment in which it occurs

What are NAPLS?

\-Non-aqueous phase liquids

\-organic liquid contaminants that do not dissolve in, or easily mix with water

What are the two type of NAPLS?

\-LNAPL: lighter than water (settles on top)

\-DNAPL: denser than water (settles on the bottom)

What type of NAPL is a continuous mass that can flow under a hydraulic gradient?

Mobile Phase NAPL (or free phase NAPL)

What type of NAPL gets trapped in the pore spaces between the soil particles and cannot be easily moved hydraulicly?

Residual Phase NAPL

What are the 7 remediation practices of an LNAPL

1) Excavation

2) Trenches, drains, and wells

3) Soil Vapour Extraction

4) Air Sparging

5) Enhanced oil recovery

6) Bioremediation

7) Physical barriers

A DNAPL can be broken down by methanogenesis but only in ____ conditions

anoxic conditions

What are 4 examples of DNAPLs

1) Creosote (timber preservative)

2) Coal tar

3) PCBs

4) Chlorinated solvents (TCE, PCE)

What are the 5 remediation practices of DNAPLs

1) Excavation

2) Trenches, drains, and wells

3) Enhanced oil recovery (water, steam, cosolvents, surfactants)

4) Bioremediation

5) Physical Barriers

What are the 3 phases contaminants in the environment reside in?

1) vapour

2) Dissolved in water

3) sorbed to porous medium particles, clay, sediments

What are the two key distribution coefficients of phase distribution?

Sorption Coefficient (Kd) and Henry’s constant (Kh)

What is the sorption coefficient?

the distribution of a contaminant between porous-medium particles and water (sorption). Calculated by Koc x foc

What is Henry’s Constant?

The distribution between gas and water phases (volatilization)

Describe Vapour Pressure (P0)

The pressure of the vapour of a compound at equilibrium with its pure condensed phase

Define Air-Water Partitioning

The tendency of a compound to escape from a dilute aqueous solution determined by interactions between the compound and water

A compound that has a high affinity for aqueous solution (high solubility) will have a ___ tendency to escape into an adjoining gas phase

Low

What are the two restrictions associated with volatilization?

1) it is only useful for estimating released of pure compounds

2) Does not consider soil-phase mass transfer resistance, so not appropriate when spilled contaminants have seeped into surface soils

What is the ability of a contaminant to dissolve in water called? What shorthand expression is used?

solubility. Kow

Polar compounds have a higher/lower water solubility than non-polar compounds

Higher

Charged molecules have increased/decreased water solubility relative to their uncharged counterparts

increased

The ionization of a compound is influenced by the ___ of the surrounding environment

pH

The water solubility of a compound is influenced by what 3 things?

1) Polarity and charge-more polar, more soluble

2) molecular size and shape-higher molecular weight, lower solubility

3) functional groups-polar functional groups or charged functional groups increase solubility

True or False: there is always a linear relationship between temperature and solubility

False

What does a high Kow signify in terms of level of solubility?

Low solubility

What does a low Kow signify in terms of level of solubility?

High solubility

What is the interaction of a solute ion or molecule with a solid?

Sorption

What are 3 things that sorption affects?

1) bioavailability

2) susceptibility to leaching

3) volatility

What is the adhesion of a molecules of a liquid or gaseous substance to the surface of a solid?

Adsorption

What is the movement of the molecules of a liquid or gaseous substance into the structure of a solid?

Absorption

What is the movement of molecules from a solid into a liquid or gaseous substance?

Desorption

Adsorption and desorption of organic molecules are controlled by the ____ properties of the molecule and the surface

Chemical

What are 7 chemical properties that affect adsorption and desorption?

1) functional groups attached to the molecule

2) acidity or basicity of the functional groups

3) molecular size and shape

4) polarity and charge of the molecule

5) polarizability of the molecule

6) competing compounds for sorption

7) hydrophobicity

Name 4 characteristics of chemical adsorption (chemisorption) and an example of an isotherm

1) strong sorptive interaction

2) heat of adsorption >20 kcal mol

3) covalent or short-range electrostatic bonds

4) forms a mono-layer, is saturable

ex) Langmuir isotherm

Name 4 characteristics of physical adsorption and an example of an isotherm

1) Relatively weak sorptive interaction

2) heat of adsorption

What does a Langmuir isotherm describe?

a saturable adsorption phenomenon

What does a Freundlich Isotherm describe?

a non saturable adsorption phenomenon

What are 4 generalizations when it comes to estimating sorption behaviour?

1) cationic compounds are sorbed strongly

2) weak bases protonate at low pH and therefore are sorbed strongly

3) sorption of weak acids on negatively charged colloids is generally higher at low pH

4) the sorption of most uncharged, low-solubility compounds in surface soils is generally dominated by hydrophobic interactions with soil organic matter

Explain the Indirect method of determining the sorption of organic contaminants

Measures the solution concentration of the contaminant to estimate the amount sorbed

What is a downside to using an indirect method to determine the sorption of organic contaminants?

Where water moves quickly, it can overestimate the amount of compound in the solution

What is the flow-equilibrium method to the sorption of organic contaminants?

Set up a flow of contaminants in the solution through soil to simulate field conditions

What is a downside of using the flow-equilibrium method to determine the sorption of organic contaminants?

It is very time consuming

What is Kd?

It describes the liquid-solid phase partitioning of contaminants

What are 3 things Kd is affected by?

1) organic carbon content of the soil

2) ability of the contaminant to sorb to organic matter

3) Kow of the contaminant

To use Koc to calculate Kd, the contaminant must be ionic/nonionic…why?

nonionic because sorption of ionic contaminants is affected by soil pH

What are the 3 environmental compartments a contaminant can enter?

Water, atmosphere, solids

What is the measure of the tendency of a substance to free itself from its environmental compartment?

fugacity

A contaminant will move from a compartment of high/low fugacity to one of high/low fugacity

high, low

What 2 things does a contaminants fugacity depend on?

1) vapour pressure (Pa)

2) the concentration of the contaminant

What are the 3 properties of a contaminant that affect Kh (henry’s law constant)?

1) partial pressure

2) concentration of the aqueous solution

3) solubity

What are 2 ways contaminants move by in the environment?

1) advection-dissolved contaminant moves along with bulk liquid flow

2) hydrodynamic dispersion-process by which a contaminant plume spreads out during water movement

What law describes water movement?

Darcy’s Law

Do soil factors or contaminant factors affect the process of mechanical dispersion?

Soil factors

The process of what is the movement of a compound in response to a concentration gradient?

molecular diffusion

What is Soil Vapour Extraction (SVE)?

\-Vacuum extraction (VE); soil venting (SV)

\-an in-situ remediation technique used for VOCs and semi-VOCs in the unsaturated zone

What are the 7chacteristics that the airflow field that is developed by SVE is dependent on?

1) Level of applied vacuum

2) Available screen interval in the vadose zone

3) porosity

4) air permeability and its spatial variation

5) depth to groundwater

6) presence or absence of leakage from the ground surface

7) subsurface conduits

What contaminants does SVE target?

VOCs and other non strongly adsorbed contaminants

What are the 3 factors that affect efficiency of SVE?

1) Soil/site characteristics

\-porosity and permeability

\-moisture and organic matter content

\-temperature

2) contaminant characteristics/contaminant partitioning

\-vapour pressure and Henry’s law constant

\-solubility

\-sorption coefficent

3) low efficiency for low concentration of heavy VOCs and contaminants with low volatility (inorganics)

SVE is a likely candidate for a contaminant if it has what two characteristics?

1) Vapour pressure >1.00 mmHg at 20C

2) Kh> 0.001 atm m3/mol (or Kh’ > 0.04)

High solubility contaminant = high/low removal efficiency by SVE

low

What are 6 advantages to SVE?

1) can be implemented with minimum disturbance to site operations

2) short treatment times (usually 6 months to 2 years)

3) very effective in removing the volatile contaminant mass present in the vadose zone

4) potential for treating large volumes of soil at acceptable costs

5) can be mobilized and installed very quickly

6) can be easily integrated with other technologies required for site clean up (air sparging, bioventing)

What are 8 limitations to SVE?

1) soils with a high moisture content require higher vacuums

2) soils with a high organic matter content or soils that are extremely dry have high sorption capacity of VOCs

3) not suitable for low permeability soils

4) can raise groundwater level due to applied vacuum pressure

5) will not remove heavy oils, metals, PCBs, dioxins

6) exhaust air may require treatment (using vapour phase granular activated carbon)

7) field pilot study necessary to establish feasibility

8) not effective in the standard zone

What is bioventing?

a natural in situ biodegradation stimulated by providing oxygen to sustain microbial degradation of the target compounds

What contaminants can be remediated by bioventing?

petroleum hydrocarbons, nonchlorinated solvents, some pesticides, wood preservatives, etc.

What are 6 advantages to bioventing?

1) uses readily available equipment; easy to install

2) creates minimal disturbances to site operations. Can be used to address inaccessible areas

3) requires short treatment times: 6 months to 2 years

4) is cost competitive

5) easily combinable with other technologies (air sparging, groundwater extraction)

6) may not require costly offgas treatment

What are 4 disadvantages to bioventing?

1) high constituent concentrations may initially be toxic to microorganisms

2) not applicable for certain site conditions (low soil permeabilities, high clay content, insufficient delineation of subsurface conditions)

3) cannot always achieve very low cleanup standards

4) permits generally required for nutrient injection wells

What 4 conditions make a site a good candidate for bioventing?

1) low oxygen in soil gas (

Define Air Apraging

\-An in-situ technique for VOCs and semi VOCs in the saturated zone below the water table

\-Atmospheric air is injected, under pressure, into saturated zones to volatilize contaminants and promote biodegradation

Name 2 limitations of air sparging

1) not suitable for soils high in silt and clay

2) low effectiveness under heterogenous geologic conditions, low permeability

What are permeable reactive barriers?

\-put in place by constructing a trench across flow path and filling with reactive medium

\-AKA treatment walls, passive treatment walls, permeable barriers

What are 5 advantages of PRBs

1) no need for expensive above-ground facilities for storage, treatment, transport, or disposal, other than monitoring wells

2) after the installation, the aboveground cannot be re-used

3) limited or no operational and maintenance costs

4) more effective than the simple migration control achieved by impermeable barriers

5) contaminants are not brought to the surface

What are 6 limitations to PRBs

1) lengthy treatment time

2) potential for losing reactivity of the media, requiring replacement of the reactive medium

3) potential for decrease in reactive media permeability due to biological clogging and/or chemical precipitation

4) potential for plume bypassing the PRB due to seasonal changes in flow regime

5) currently limited to shallow depths

6) longevity of PRB performance is unknown

What is pump and treat?

\-Involves removing contaminated groundwater from strategically placed wells

\-contaminants removed from pumped water by various treatment technologies

\-treated water is either re-injected into an aquifer or discharged into surface water body or into municipal sewage plants

What are 4 limitations to Pump and Treat?

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

\-Slow: takes decades to centuries to remove contaminated water yet it often fails

\-Very costly

\-Does not always work: some contaminants are adsorbed and cannot be easily removed (desorbed), NAPLs cannot be removed

What is In situ chemical oxidation

\-use of oxidants to help change harmful contaminants in soil or groundwater into less toxic ones

\-The four major oxidants used are permanganate, persulfate, hydrogen peroxide and ozone

\-used to treat contaminants like fuels, solvents and pesticides

\-Other cleanup methods like pump and treat or monitored natural attenuation are often used to clean up the smaller amounts of contaminants left behind

In situ chemical oxidation will take longer if: (5)

1) if the source area is large

2) contaminants are trapped in hard to reach areas like fractures or clay

3) the soil or rock does not allow the oxidant to spread quickly and evenly

4) groundwater flow is slow

5) the oxidant does not last long underground

What are the 3 components of a dewatering stage in soil washing?

\-centrifugation

\-hot air drying

\-piles

Explain excavation

the digging of contaminated soil for above ground treatment or safe disposal in a landfill

What are the 3 thermal processes? Which uses the lowest temperature? Which uses the highest?

\-thermal desorption (lowest temperature)

\-incineration

\-vitrification (highest temperature)

What contaminants is thermal desorption used for?

BTEX, chlorinated VOCs, lower molecular weight PAHs. Mercury is removed but needs to be recovered

In thermal desorption, what happens at temperatures

What kind of residue does thermal desorption leave?

Soil-like residue

What are 7 advantages of thermal desorption?

\-provides for complete remediation of soils and destruction of hydrocarbons

\-provides a reliable and cost-effective option to landfill disposal

\-the equipment can process a wide variety of soil types

\-hydrocarbons are not released into the atmosphere

\-the exact level of concentration of contaminants of interest is defined immediately following treatment

\-allows for the re-use of the remediated soil in a variety of ways

\-removal and destruction of hydrocarbon contamination eliminated future liability and potential environmental problems

What are 5 limitations to thermal desorption?

\-material handling problems associated with clay-rich soils

\-energy cost of treating soils with high moisture content

\-destruction of the biological component of the soil

\-the possibility of incomplete combustion leading to emissions of products of incomplete combustion

What temperature is contaminated soil heated to during incineration?

880-1200C

What type of treatment residue does incineration leave?

slag or ash like

What are 4 limitations to incineration?

1) results in the destruction of soil texture

2) removed all natural humic components

3) Residues may have high metal components

4) exhaust gases need to be treated

5) costs heavily dependent on water content of media

What temperatures does vitrification use?

>1000C

What is produced from vitrification?

\-solid glassy mass

\-inorganic contaminants are incorporated into the glass

\-organic contaminants are destroyed (incinerated)

what is stabilization?

\-fixation or chemical fixation

\-uses chemical reagents to transform contaminants to immobile form

What are 3 limitations for stabilization?

1) it neither removes the contaminants from soils nor degrades them

2) may or may not change or improve physical characteristics

3) may be used as a pretreatment before disposal in a landfill

What are the 4 mechanisms of stabilization

1) encapsulation: physical entrapment in pore spaces

2) absorption and adsorption: electrochemical bonding between contaminants and agents in solid

3) precipitation: from aqueous form

4) detoxification: reduction

How do you implement ex situ stabilization?

Excavation → mixing of reagent with soil → curing → backfilling or landfilling of treated soil

How do you implement in situ implementation?

injection or mixing of agents into subsurface soil to immobilize contaminants

What contaminants does stabilization affect?

metals, radionucleotides, non-VOCs and SVOCs

What are 5 advantages of stabilization?

1) low cost due to use of widely available and relatively inexpensive additives and reagents

2) applicable to a wide variety of contaminants

3) applicable to different types of soils

4) uses readily available equipment and is simple

5) high throughout rates compared to other technologies

Name 5 disadvantages of stabilization

1) contaminants are not destroyed or removed

2) volume of treated soil may be increased significantly with addition of reagents

3) emissions of VOCs and particulates may occur during mixing procedures, requiring extensive emission controls

4) reagent delivery to subsurface and achieving uniform mixing for in situ treatment may be difficult

5) long-term efficiency of the process may be uncertain

What is solidification?

A treatment that encapsulates the contaminant in a solid monolithic mass of high structural integrity

What is the most used remediation technique?

Containment