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Common Issues with Old Landfills
Common issues with old landfills
Why are we interested in this?
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Long history of landfill activity
Quarries and sand pits mostly
These became a waste disposal opportunity
Have since had land use changes:
– Former industrial/outskirts/undeveloped land are now suburbs
– Also: changes in older metro areas – infill and land reclamation (e.g.
Swan River)
• Nature of waste has also changed: less burning + more ‘throwaway’ items,+
more packaging = increasing volume (bigger bins), less dense, more ‘toxic’
• Result: ‘old’ landfills with:
– Limited management to control emissions (soil cover only)
– Development close by
– Limited awareness of issues (in the past) - now much more.....
www.bgs.ac.uk
Common issues with old landfills
Common issues with old landfills
....so got old landfills with people (and environmental receptors) nearby
What are common issues?
• Gases and vapours*
• Groundwater contamination
• Soil contamination
• Ground stability
Use a Conceptual Site Model (CSM) to discuss these
issues:
Why do this?
• It’s easier….a means of showing what is going on in a
way that can be readily understood
*Acknowledgment:
• Wilson et al (2009)
• CIRIA C665
• NSW EPA
Common issues with old landfills
Issues: Ground gases Landfilling
and vapours
Biodegradation process...
Origin of gases and vapours in old landfills
Need moisture….
(bacteria generally
• Domestic (and other?) wastes Conditions for
degradation (?)
don’t flourish in dry
– Diverse constituents – inert and degradable materials
conditions)
– A living, biological and chemical degrading ‘ecosystem’ – reacting and
changing over time…
Carbon
AEROBIC
• ‘Bulk gases’ - methane, carbon dioxide
dioxide and
degradation
water
• ‘Trace gases’ - hydrogen sulfide, carbon monoxide, (hydrogen
cyanide,
ammonia)
• Depleted oxygen environment
Oxygen
consumedasphyxiation) and chronic risks
• Variable properties - acute risks
(explosion,
– not replenished
• Vapours – VOC’s -100’s – e.g. from household chemicals, hydrocarbons
– Variable occurrence
– Typically lower rates of generation…
Methane and
ANAEROBIC
carbon
– ….But health risks (chronic) atdegradation
much lower concentrations
dioxide
NSW EPACommon
(2012)issues with old landfills
Issues: Ground gases and vapours
Key factors* determine gas generation potential:
*(Wilson et al, 2009)
• Volume of degradable material
• Conditions in landfill (now and future), e.g.
– Moisture: high (20%)=high degradation, saturated=lower, dry=low+longer)
– pH (6.5-7.5 ideal), temperature, nutrient content
– Toxics: heavy metals affect micro-organism communities
• Nature of degradable material, e.g.
– Wood (logs, timber): slow degrading - lignin
**not newspaper!
– Food, paper** (cellulose), sawdust: all quicker
– Particle size/surface area, density
• Containment (capping – affects infiltration and moisture, liner – affects
leachate build up) = effect on gas generation – but only if they’re present
• Age – peak generation (ideal conditions) at 10-15 years (???) – but not if dry
• Result: gas generation potential varies due to key factors
Common issues with old landfills
Issues: Ground gases and vapours
Problem: gases (and vapours) can migrate through the ground:
Can get migration in
Migration
groundwater:
via:
Horizontal and vertical
migration in permeable
But gases
Advection:
need specific
build uppressure
of pressure
conditions
– FLOW
to
materials (e.g. services,
become dissolved in water and then released
sand, limestone)
Diffusion: HIGH concentration – LOW concentration
-more a risk for deep landfills
Buoyancy of gases/gas mixtures
Always migrates via the easiest route
Common issues with old landfills
Issues: Ground gases and vapours
A lot of variables - CSM is critical:
• Define the source (the key factors -including gas generation potential and
volume)
• Define receptors (humans, environment etc.)
• Define all the possible pathways between them
• Caution! Also consider other gas and vapour sources:
– Biogenic – peat, alluvial deposits, swamps, coal, hydrocarbon
degradation
– Thermogenic (deep, high temperature processes – cracking+fracking)
– Vapours – spills, leaks, AST, UST, servo’s…….etc.
Common issues with old landfills
Issues: Ground gases and vapours
…So how to address?
• NSW EPA (2012) has a structured approach
• Consistent with other published guidance (cross references it)
• Sequential process:
– Preliminary screening – screen out ‘no risk’ or go to Level 1
– Level 1: Risk analysis and assessment - screen out ‘very low risk’,
manage ‘low risk’ or go to Level 2
– Level 2: Risk classification and prioritisation - management measures for
‘lower’ risk sites or go to Level 3 for ‘higher risk’ sites
– Level 3: Risk analysis and assessment – specify protection measures
• Based on Conceptual Site Model
• ….use to screen out ‘no action’ sites – provides lines of evidence
• Prioritise limited resources where needed
Common issues with old landfills
Issues: Groundwater Impact
Landfill – has a potential for impact upon groundwater:
• Site specific – CSM is critical to understanding
• Source characterisation – e.g. nature of waste:
– ‘Inert’ and/or domestic only?
– Industrial? (i.e. more ‘exotic’ waste types) – more toxic/mobile?
– Leachate?
• Pathways:
– Geological setting (strata type, permeability/preferential pathways)
– Groundwater depth, flow direction – migration likely?
– Containment? (unlikely for ‘old’ landfills)…but what is capping like?
– Development: present? more or less pathways from this?
• Receptors:
– Groundwater (again) – vulnerable to impact?
– Up gradient groundwater quality – other influences?
– Highest beneficial use? gw dep. ecosystem, surface water, bore uses etc.)
Common issues with old landfills
Issues: Groundwater Impact
So site specific….but some common characteristics for ‘old’ municipal landfills
exist:
• Impact?......depends on degradation processes taking place:
– If ‘dry’ or aerobic – limited effects (if any)
– If anaerobic degradation + water present = possible impact
• However for ‘old’ landfill......
– Early anaerobic
– ‘high
strength’
leachate - already
•Ammoniacal
nitrogen - (worst?)
dominant stage
(also look
for chloride,
TOC)
happened
•pH weak acidic to alkaline, higher COD, BOD, TDS (from breakdown process)
– (soluble degradable organics, acidic, very high ammonium, metals)
• Later heavy
stages:
•Limited
metals (except iron, manganese).
– Lower overall concentrations of substances
•Low level pesticides (recalcitrant)
– .....but can still be significant
•Low level organics (Higher organics concentrations indicate other source types in waste
mass).
•Change with distance (often short) - decrease - may become difficult to distinguish from
background influences
Common issues with old landfills
Capping
Issues: ‘soil’ contamination
‘Old’ landfills:
• Municipal waste - wide range of materials present:
– It’s a Source of contamination…but different to other ‘soil’ contamination
Waste
– Got metals, organics etc - but
is chemical analysis meaningful?
– …can also have finer soil/fill material – sometimes alot
– …Sharps (glass, porcelain, metal etc….even syringes)
– …Asbestos
• …so what’s the risk? - Conceptual Site Model important (again):
• What Receptors are present? – human? environmental?
• Have we got credible pathways present?
– Ingestion
– Inhalation
– Dermal (or other ‘physical’) contact
• Most common issue concerning these relates to capping integrity
Common issues with old landfills
Issues: ‘soil’ contamination
Capping integrity issues – ‘old’ landfills
• Engineered capping? (rare)
• Cover soil only – (sand?)
• Common issues:
– Variable cap thickness/presence
– Soil mixing
• Soil mixing processes:
– Human activity
– Biological processes (bioturbation)
• Earthworms (top 400mm)
• Burrowing animals (rats, mice rabbits….other – top 500mm?)
• Root disturbance 200mm+
– Other processes - physical properties, moisture…can all cause mixing
• Result: waste materials exposed at surface
• Not just a nuisance issue…asbestos is a common problem
• Also issues with illegal dumping or (maybe) cover soil was already contaminated?
Common issues with old landfills
Issues: Ground Stability
Is this an issue for ‘old’ landfills? – it can be
• Can get surface settlement effects
• Also slope movement/instability
• Common issues we see:
– Uneven surfaces/playing fields etc
– Damaged/fractured services
– Surface water ponding
– Tension cracks
• If landfill is ‘developed’ then add:
– Possible structural damage
– Reduced serviceability/lifespan
• These add maintenance liabilities…
• …but also introducing new pathways
• Again, conceptual site model is important to understand the risks
Common issues with old landfills
Common issues with old landfills - Summary
Landfills are ‘special’:
• A living, biological and chemical degrading ecosystem – reacting and
changing over time
• They have a range of common issues:
– Ground gases and vapours
– Groundwater impact (and surface water)
– ‘Soil’ contamination / exposure to waste
– Ground stability (settlement and slope stability)
• Contamination can be both on-site and migrate off-site (source site)
• Can continue to pose environmental hazard for many decades
However:
• ‘Old’ landfills…lower risk (probably)
• …Some may be very low/negligible risk
• Site specific…Conceptual Site Model is critical - use this to
assess…..screen and prioritise
Common issues with old landfills
•
Wilson et al (2009) Ground Gas Handbook
•
NSW EPA (2012) Guidelines for the Assessment and Management of Sites Impacted
by Hazardous Ground Gases
•
CIRIA C665 (2007) Assessing risks posed by hazardous ground gases to buildings
•
BS 8576 (2013) Guidance on investigations for ground gas – Permanent gases and
Volatile Organic Compounds (VOCs)
www.ghd.com
Common issues with old landfills