Remediation Approaches Flashcards
Remediation Approaches
- Covering systems
- In-situ air-sparging
- In-situ chemical treatment
- In-situ bio-remediation
- Slurry walls
- Permeable reactive barriers
- Pump & Treat Technology
Covering systems
- Prevent physical contact and exposure to waste
- Sufficient cap may be enough thickness of soil to prevent humans or animals from digging into waste materials
- Reduce or remove precipitation infiltration
- Reduces or prevents transport of contaminants to ground by infiltrating water.
In-situ air-sparging
- In-situ air sparging approach converts the groundwater contaminants from a dissolved phase to a vapour phase that then rises to the surface.
- Effective at targeting volatile organic compounds e.g. petroleum products
- Leads to the production of gas and vapour which if left just stays on-site or contributes to the atmosphere
- The remediation technologies are generally combined with a system of vapour extraction.
In-situ chemical treatment
- Can target contaminants in the unsaturared soil, in the groundwater or both.
- Chemical treatment involves the addition of chemicals to soil and or groundwater to oxidise or reduce the contaminants
- The chemical reaction can degrade contaminants, reduce toxicity, change solubility, or increase their susceptibility to other forms of remediation.
- Introducing the chemical reagents is often through injection wells, as a liquid solution.
Ex-situ chemical treatment
- Allows for extremely effective remediation because the chemicals can be mechanically mixed in but this involves the excavation of soil and neglects groundwater contamination.
In-situ bio-remediation
- The process of enhancing biodegradation
- Biodegradation is the natural breakdown of pollutants in the soil by microorganisms through aerobic or anaerobic respiration.
- In-situ bioremediation has many variants, each with a different method of introducing the oxygen or other reagents :
Bioventing is the injection of air flow into the unsaturated zone (soil above after table) through an injection well
Biosparging is into the ground water
Slurry walls
- Can be keyed into ‘floor’ or hanging
- Materials:
Soil-bentonite, lower K and less expensive
Cement-bentonite, greater shear strength and lower compressiblity. Used on slopes where strength is important and areas where apppropriate soils for SB are not available.
Additives include: - Fly ash to increase carbon for absorption
- Liners or sheet pile within wall to decrease K
Potential Failure:
Construction
- Improperly mixed backfill
- Sloughing or spalling of soils into trench
- Inadequate bottom excavation for wall key
Post-construction:
- Wall properties changed by freeze-thaw cycles
- Wet-dry cycles due to water table fluctuations
- Degradation due to contact with chemicals
Permeable reactive barriers
- A solution mostly used by civil engineers for groundwater contamination
- Physical barriers set into saturated and unsaturated ground
- Permeable materials allow groundwater to continue to flow through but introduces a filtration or reaction system
- Can be adapted to target different contaminants e.g. organic contaminants, heavy metals
- Barriers are prone to become less effective over time but can often easily be replaced.
Purpose of a landfill daily cover
Reduce moisture entering waste Most moisture enters waste during filling Control litter Reduce odours Limit access to rodents and birds Reduce fire risk Provide vehicle access to active face Improve aesthetics
Alternative liner materail
- Soil liner
Also called compacted clay liner (CCL)
- Flexible membrane liner (FML)
Also called geomembrane
- Geosynthetic clay liner (GCL)
- Composite liners
Advantages and disadvantages of soil liner
Advantages: - Clay can attenuate pollutants - Thickness provides redundancy, resistance to penetration - Long-lived, self-healing Inexpensive if locally available
Disadvantages:
- Construction is difficult – requires heavy equipment
- Thickness reduces volume for waste
- Subject to freeze/thaw and desiccation cracking
- Low tensile and shear strength – may shear or crack due to settlement
- May be degraded by chemicals
- Expensive if not available locally
Advantages and disadvantages of geomembrane liners
Advantages:
- Easily installed – needs only - light equipment
- Very low leakage rates if free of holes
- Has high tensile and shear strength, flexibility - accommodates settlement
- Thin – leaves volume for waste
Disadvantages:
- Slopes on geomembranes may be unstable
- High leakage if punctured or poorly seamed
- Some chemicals may be incompatible, permeable
- Thin – subject to puncturing
- No sorptive capacity
- Unknown lifetime
Advantages and disadvantages of geosynthetic liners
Manufactured composite of bentonite and geotextile
Advantages:
- Easily installed
- Self sealing
- Some sorptive capacity
- Low leakage rates
Disadvantages:
- Thin – easily punctured
Advantages and disadvantages of composite liners
Advantages:
- Low leakage rates
- Low contaminant mass flux
- Provides sorptive capacity
- Acceptable loss of waste storage space
- Acceptable ground-water protection
Disadvantages:
- Difficult to construct
- Expensive
What are composite liners and why use them?
Composite liner = two or more materials
Usually clay and geomembrane
Combines desirable properties of two materials
Geomembrane
Hydraulic properties - decreases leakage
Physical properties - Thin, can be torn or punctured. May crack under stress or strain
Endurance properties - Subject to ageing, not self-healing, chemical resistant
Clay
Hydraulic properties - delays travel time
Physical properties - Thick, cannot be torn or punctured. May crack under stress or strain
Endurance properties - Does not age, self-healing. May be affected by chemicals
