WASTE
DISPOSAL
Types of Waste
• Inert wastes - no chemical or biological hazards
• Special (hazardous) wastes e.g.
– ignitable, corrosive, reactive
– Carcinogenic or mutagenic (PCBs, medical waste,
radioactive waste, asbestos)
– heavy metals, azides, acids/alkalis
UK
USA
Denmark
Waste disposal routes
Landfill Incineration Recycled Composted
88
11
1
<1
70
30
<1
31
50
18
1
Landfill Sites
There are 4000 operational and
4000 closed landfill sites in the UK
Many old landfills are poorly
designed and major environmental
hazard. They are not designed for
50, 100 or 1000 years into the
future
Two types of landfill in the UK are
• leach and disperse (old sites)
• containment and treatment (new
sites)
What Happens in a Landfill Site?
Rain water dissolves &
reacts chemically &
biologically with waste
Leachate
Landfill Gas
Leachate
• toxins kill aquatic life
• eutrophication in rivers
• precipitates iron
• kills vegetation
• pathogens/bacteria
• non-hazardous materials
can decompose into
hazardous products
• serious groundwater
pollution
Landfill Gas
methane
Landfill Gas
Loscoe, Derbyshire - 1986
Landfill Gas
Loscoe, Derbyshire - 1986
Possible Routes by Which Landfill Gas Can Migrate from a Site
Desiccation cracks
in soil
Caves & natural
cavities
Gas
vents
Highly permeable strata
Tree roots
Underground
services e.g.
sewer pipes
Mine shafts
Highly permeable strata
Fissured & fractured
strata
Landfill Site Selection
Geology of Area
• Porosity & permeability of rock
• Resistance to weathering
Impermeable to contain
leachate & landfill gas
• Joints & fracture systems in rock
• Dip of rock strata (no dip or synform)
• Free from disturbance (tectonic/subsidence)
Hydrogeology of Area
• Rate of groundwater flow
• Gradient of groundwater flow
• Depth to water table
Reduce groundwater
contamination from leachate
• Fluctuations of groundwater
Topography of Area
• Existing hole or steep sided quarry
A site capable of retaining
waste
Groundwater
Water Table
Recharge
Saturated
zone
Groundwater
Hydraulic Gradient
• Pore spaces
• Joints/fractures
Aquifers
Pore spaces
unsaturated
Groundwater
Pore spaces
saturated
Impermeable rock
What rocks in the UK make good aquifers?
Sandstone
40% porosity
30% specific yield
High permeability
Clay
45% porosity
3% specific yield
Low permeability
Impacts of pumping water from aquifers
Impacts of pumping water from aquifers
Cone of
Depression
Hydraulic
Gradient
Drawdown
Impacts of pumping water from aquifers
Saline
wedge
Control – reduce/stop abstraction, change
pattern of abstraction ( winter not summer)
or move borehole
Monitoring – chemical testing
(boreholes/salinity testing)
Site Preparation
top layer is about one foot of
compacted soil to protect the entire
liner
from the
waste.
very system
tough fabric,
called
a geotextile
fabric, tolayer
protect
the pipes.
one-foot
of gravel
with pipes
running through it. The leachate
collects
inflexible,
these pipes
is pumped
strong,
veryand
thick
plastic,
outcalled
of the
landfill
andpolythene
filtered.
high
density
(HDPE) known as a geomembrane.
two feet of compacted clay
Modern Landfill Site
Each
evening,
large
trucks
roll over
When
an area
of the
landfill
is
the
landfill tofull,
crush
the
day's with
completely
it is
capped
rubbish
andsoil.
then
cover
it landfill
with 15cm
clay and
This
final
ofcover
soil sohelps
the waste
doesn't smell
or
keep rainwater
out of
attract
flies and
and reduces
rats.
the waste
the
amount of leachate that forms.
Site Management & Monitoring
• monitoring groundwater for chloride
& ammonia in plumes
• monitoring unsaturated zone for
gases
• venting of methane gas by boreholes
• porous pipes to transfer leachate
into sumps for collection & removal
Site Restoration
Uses
• Parkland
• Recreation
• Open spaces
• Greenbelt
• Low level industrial development
• Housing
Site Restoration
Trumps Farm is a former sand pit which was
used by Surrey County Council for the disposal
of household waste from the early 1980s until
its closure in 1998.
The overall objective of the works is to
reinstate the landfill to pasture and meadow, to
a landscape typical of the area and create a
variety of wildlife habitats.
Site Restoration
Problems
• Methane gas hazard – leakage through permeable rocks
• Ground instability on completion - subsidence
• Groundwater pollution
• Landfill site needs to remain accessible for over 25 years to
manage & monitor
Contamination of aquifers
Industry
• Chemical leaks
• Chemical spills
• Contamination from
chemical storage
Waste Disposal
• Leachates from
landfill sites
• Radioactive waste
Agriculture
• Nitrates
• Pesticides
Contamination of aquifers
borehole
Chloride content
(milligrams per
litre) of leachate
Monitoring
• chemical testing of water from boreholes, springs, extraction wells
• ground penetrating radar (remote sensing methods)
Most
expensive
• electrical resistivity analysis (oil pollutants = high resistivity)
• soil gas chemical monitoring (organic pollutants give off a vapour
such as methane)
Cheapest
Contamination of aquifers
1. Control
• clay liner
• synthetic liner
• leachate collection
total containment
Contamination of aquifers
Barrier to predicted depth
of pollution
10 – 20m max
2. Control
Pollution localised
• build barriers to plume
• trenches filled with concrete
• hammered piles injected with cement grout
Contamination of aquifers
3. Control
• pump pollutant to surface for treatment/disposal
Contamination of aquifers
factory
pollutant
Bioreactive filter
Impermeable wall to direct
groundwater
4. Control
• direct polluted groundwater into to bioreactive barrier
• bioreactive barrier use naturally occurring bacteria to breakdown
the pollutant
• oxygen & nitrates injected into barrier to encourage decay processes
Factors Affecting
Site Selection
Non-hazardous
Waste Disposal
Site Preparation
Landfill Sites
Problems after
site is restored
Site Management
& Monitoring
Problems of
Leachate
What happens in
a landfill site
Pollutants
Problems of
Landfill Gas
Hazardous Waste
What are hazardous waste materials?
What specific problems do they cause?
What factors need to be taken in to account with
hazardous waste disposal?
What are the options for their disposal?
(examples)
Possible Routes by Which Landfill Gas Can Migrate from a Site