Options Appraisal Flashcards
What are the 4 primary types of remediation?
Physical
Biological
Chemical
Civil Engineering
Why are contaminants harder to remove from fine-grained soils?
Electrostatics mean that contaminants bond more readily to fine particles
What are the 3 most significant factors when choosing initial options?
Type of contaminant
Acceptable outcome
Location of treatment
How is a conceptual site model used in options appraisal?
Potential options are mapped onto the CSM with indications of how they will break pollutant linkges
How is a decision matrix constructed and used?
Create and explain decision criteria
Weight criteria based on their relative importance
Score each option based on its performance in the criteria
Sum the weighted scores and compare
What does it mean for an option to be sustainable?
It is environmentally, socially and economically sustainable
How can a conceptual site model be changed during options appraisal?
The CSM can be reduced if certain features of it are thought to be insignificant
What regulations affect the selection of options?
WHO safe levels of contaminants
SEPA safe levels
Regulations around handling of radioactive material
Protection status of the site and adjacent land
What should always be included in an options appraisal?
Managed Attenuation/ Doing Nothing
In what 2 ways can contaminants be inhaled?
As gaseous vapours
As disturbed fine dust
Why are gas exposures a risk for houses with basements?
The pressure difference in the basement can draw gases in
What are the conditions for aquifers being considered ‘receptors of note’?
They are already notably polluted
They are used for water abstraction
What should be included in the strategy of a potential option?
The means by which it will be carried out consistently
What is Bioaugmentation?
Moving microbes of proven efficacy on one site to another site with similar contaminants
Why is biostimulation preferred to bioaugmentation?
It is preferred to use microbes which are already present at a site over importing microbes
Why is enrichment a proof of natural attenuation?
C13 carbon reacts slower than C12 carbon, so an increase in the ratio of C13 to C12 shows that the carbon is reacting to more stable forms
How is verification structured?
In 2 stages: The plan, carried out before remediation, and the report, carried out after
Aside from proving the efficacy of a treatment, what can verification help with?
Identifying cost savings
Demonstrating the sustainability of the techniques
What must a successful verification include?
Lines of evidence to prove the treatment efficacy
A proof that the option objectives were met
How can you test the accuracy of verification techniques?
Comparing them to surrogate (artificially contaminated) soil
What must be considered at the end of a verification report?
Provisions for the potential of the land to be recontaminated, or for immobilised contaminants to become mobile again
Why is the format of a verification report important?
It must be easily understood by laymen with the remediation target clearly presented
What are the 4 categories of groundwater contaminant remediation?
Containment
Extraction
Injection
Reactive Barriers
Why are pumping treatments a poor choice in permeable, cohesionless soil?
Pumping will destabilise the soil leading to localised collapse
If permanent groundwater control or excavation is required in an area of unstable soil, what techniques can be employed to maintain stability?
Grouting
Sheet Piles
How does Air Sparging work?
Uncontaminated air is injected into the saturated zone to encourage the vaporisation of in-situ hydrocarbons which can be vented out
When should Air Sparging NOT be used?
Free product is present
Basements or sewers are in close proximity
The contaminated aquifer is confined
How does Soil Flushing affect the local groundwater?
The water table is raised near the injection well and lowered at the extraction well
In what type of soil is Soil Flushing suitable?
High permeability
Low clay and silt
How can removal of DNAPLs be expediated?
Enhancing the treatment with the injection of surfactants
What type of chemical additive can be used to remove metal contamination from soils?
Chelating agents form the metals into stable, soluble complexes
How are permeable reactive barriers designed to maximise treatment?
The barrier is more permeable than the surrounding aquifer material to encourage throughflow
When is in-situ chemical oxidation used?
To reduce contaminant mass and concentration
To encourage contaminant flux in pump-and-treat systems
To reduce clean-up times for MNA and other methods
What are the 4 most common oxidising agents?
Permanganate
Catalysed Hydrogen Peroxide
Ozone
Persulfate
How do MnO4- and H2O2 compare as oxidising agents?
Permanganate (MnO4-) persists longer and so is better for longer term or wider spread applications
What types of contaminants can be treated by oxidation?
Organic contaminants
What types of contaminants can be treated by bioremediation?
Organic contaminants
When is capping used?
To prevent contact with the contaminants
To reduce precipitation infiltration and associated mobilising of contaminants
When is stabilisation/solidification unsuitable?
When contaminants include anions like Chromium 6 or arsenic, mercury or a mix of varied waste such as metals and volatile organics
When contamination is at significant depth
What is the name for forming the soil into a glass-like substance?
Vitrification
What limits the scale of vitrification treatment?
Volume (max 1000 tons per melt)
Depth (only soil close to the surface)
Why is soil washing often used in combination with other technologies?
Soil washing separates coarse and fine grains, reducing the treatment volume but not directly providing treatment
How does soil vapour extraction affect soil biological activity?
Vaporising contaminants causes bio stimulation
Why is simultaneous extraction of water and vapour useful for treating LNAPL spills?
Removing water lowers the groundwater level, exposing more of the soil for vapour extraction
How can organics be desorbed from soils in-situ without decomposing them?
Heating the soil to temperatures between 100 and 400^C
When are electrokinetic treatments employed?
When the soil is too low-permeability for soil flushing or other similar mobilisation strategies
