Waste and Landfill
How is a modern Landfill made?
Modern landfills are made up of a series of
“cells”.
To build a new cell, the base of the quarry is
levelled with soil to create a platform. The
platform at the Wollert landfill slopes to one
end along the cell. The other end of the cell is
filled against the rock wall of the quarry to
form a steep ramp. This helps contaminated
water drain from the cell and be collected.
What’s a Landfill?
A landfill is a carefully constructed space on
the ground to store waste, as it gradually
breaks down into chemically inactive material.
Landfills can be built in valleys, quarries or on
top of the land to form hills. In Victoria most
large landfills are in quarries. While waste
such as household garbage breaks down it
needs to be kept separate from the outside
environment by barriers. Barriers on the base,
sides and top of the landfill are built of clay
and sometimes plastic. While the landfill is
filled the garbage is covered every day with
clean soil. These actions make landfill a safe
place to bury household garbage.
Banyule City Council and other councils in the
northern metropolitan region of Melbourne are
using a Wollert basalt quarry to bury
household garbage.
Once the platform base is ready a clay layer
one metre thick is placed on the bottom and
up the ramp. The clay is moistened and
compacted by special machinery, so that water
cannot move through it easily. It would take
over 25 years for any contaminated water or
leachate to move down through the clay liner.
To make the landfill even safer, a layer of
plastic two millimetres thick is placed on top
of the clay. It would take over 1000 years for
any leachate to move through the plastic liner.
A thick protective underlay called a geo-textile
is placed on top of the plastic liner to protect
it from being punctured and then a layer of
rocks the size of those used on railway lines is
placed to help drain the leachate away. The
leachate is collected in four large pipes inside
the rock layer that stretch from one end of the
cell to the other. The rock layer is covered
with another geo-textile to filter out silt in the
leachate and keep the rock clean.
What happens to your garbage
at a Landfill?
A description of the Hanson Landfill Services
landfill at Wollert north of Epping, Victoria.
The entry and exit point at any large landfill is
the weighbridge. All garbage trucks must stop
and be weighed before going to the active cell
to tip a load of garbage. Customers are
charged according to the weight of the garbage
and the weighbridge records the registration
number, customer and weight. The
weighbridge also checks to make sure that the
trucks are not tipping the wrong type of waste.
A large landfill like Wollert will have 1000
tonnes of waste delivered by 150 trucks each
day. This is the amount of waste generated
from homes, workplaces and the construction
and demolition activities of a community of
half a million people.
The garbage truck is driven to the “tipping
face” where the garbage is tipped from the
truck on to the ground. A bulldozer then
pushes the waste into the face in a pile that is
two metres deep. While this is going on, a
large and very heavy landfill compactor
compresses the waste pile so it takes up the
least amount of space possible. A dump truck
tips a load of soil on top of the compacted
waste where it is spread by the bulldozer to a
300mm thick covering layer. The tipping face
moves along the landfill cell in two metres
thick “lifts” until it is full.
Once the cell is full tipping activity moves to
the next cell. If you could view a cross section
of the cell you would see layer upon layer of
waste interspersed with bands of soil.
Covering the waste this way prevents odour
and lightweight waste from becoming litter. At
Wollert each cell is 100m wide and 350m long
and holds on average 700,000 cubic metres of
waste. It takes about two years to fill one cell
at the rate of one Olympic sized swimming
pool every two days. The tipping face is two
metres high and 50 metres long and occupies
only a very small part of the cell each day.
Waste and Landfill
2
How is a Cell capped?
When a cell is filled to the final level a ‘cap’ is
placed on the top to stop rainwater from
soaking into the waste. The final surface at
Wollert will be formed as a small hill so that
rainwater runs off the cap. To stop the
rainwater soaking into the waste a layer of
clay 0.5 metres thick similar to the base of the
landfill is built on top of the waste. The clay is
covered with another 0.7 metres of soil. The
final cap is planted with local native trees,
bushes and grasses so that it will look like any
other hill in the area.
The Wollert landfill has started a three and a
half year research project with Melbourne
University to develop an alternative final cap
that has no clay layer in it. Instead, a thicker
layer of soil is put down and special plants
pump the rainwater out of the soil naturally
through their roots and leaves.
The rainwater that runs off the final cap is
channelled to a sedimentation pond before
discharging into the Darebin Creek. The water
will be tested for leachate contamination to
make sure it doesn’t pollute the creek.
What is Leachate?
When it rains, rainwater trickles down through
the cell layers dissolving some of the waste
(about five per cent) releasing different types
of chemicals, most commonly salts and
ammonia, on its way. The resulting liquid is
called leachate. By the time the leachate
reaches the bottom of the landfill it is very
black and smells. The leachate is collected
and reinjected back into the waste. The
reinjected leachate filters down through the
waste and is absorbed by the dry waste and
helps it to break down quicker.
To make sure the leachate is not leaking out
of the landfill there are 18 monitoring bores
around the edge of the waste. These are tested
twice a year for any leakage. The ponds
around the landfill cells are also tested.
How does Landfill make methane
and carbon dioxide?
Organic waste is broken down by the action of
bacteria that are some of the most ancient
living organisms on earth. These bacteria can
only live where there is no air. As the bacteria
break down the organic waste landfill gas and
heat are produced. The inside of a landfill can
be as hot a 60o centigrade. Over time about
25% of the waste in the landfill breaks down
into landfill gas. Landfill gas is made up of
methane and carbon dioxide and it escapes
through the cell layers to the surface. The
methane in landfill gas is 25 times more potent
in its greenhouse effect than carbon dioxide.
Landfill gas is combustible and will be collected
and used as fuel to generate electricity. The first
generators will be in place in 2006. Wollert will
in time generate enough electricity to power
700 nearby homes. To prevent the methane gas
contributing to the greenhouse effect before the
electricity generators are built it will be
collected and burnt in a flare. Landfill gas also
has an unpleasant smell, which another good
reason to collect it and burn it.
How is the environment protected?
All landfills have to be approved by the
Environment Protection Authority (EPA) and
operate under an EPA Licence. The Licence is
for discharge of waste onto land and it has
many detailed management requirements to
protect the environment. Every year landfill
operators must report landfill activities
including the results of all monitoring to the
EPA. An EPA appointed environmental auditor
reports on any harm or detriment the landfill
is having on the environment. The
environmental auditor also reports on the
construction of each cell to ensure that it is
constructed properly.
A very important part of the Licence is the
Environmental Improvement Plan (EIP). The
EIP sets down in greater detail how all the
various impacts of the landfill will be
managed and monitored. This includes things
like vermin, dust, and litter as well as leachate
and landfill gas. The Wollert landfill has
developed a special Environmental
Management System that documents all EIP
monitoring and reporting.
Waste and Landfill
3
Wollert Landfill statistics
Number of years of operational life The
landfill has a volume of about 700,000 cubic
metres per three hectare Cell. The quarry is
capable of accommodating over 50 of these
Cells. Depending on the annual waste intake
each cell lasts one to two years, so the
minimum life of the landfill is 50 years.
Total landfill area The area of the quarry that
is licensed to take waste is 350 hectares,
though not all of this will be used to allow for
an adequate buffer. The total area of the
quarry is 500 hectares and it also has
considerable buffers. Not all land set aside for
Bluestone extraction will be landfilled.
Landfill buffer zones The buffer exclusion
zone is 100 metres to the north and east and
200 metres to the west. The buffer to the
south will depend on future land use but will
be a minimum of 100 metres to Bridge Inn Rd.
This adds up to at least 100 hectares out of
the 350 hectares Licensed to take waste.
Fence line There is over eight kilometres of
fence line around the licensed landfill area.
Current landfill area has a fence line of 3.8
kilometres.
How long does it take to clean the fence of
litter The external fences are cleared every
day. Inside the site there are number of litter
fences including tall nets which are used on
the top of the landfill batters, and low “goal
post” litter nets that are used close to the
working face.
Litres of leachate generated per year Between
four million and eight million litres per year
depending on the weather. The leachate is all
recirculated back through the waste so there is
a proportion that is reabsorbed into the waste.
Staff There is one Site Operations Manager
and one Compliance Officer. Two people share
the work in the weighbridge. There are five
operations contractors and up to 12
construction contractors and supervisors (who
are on site when a new cell is being built or
capped). There are five members of the litter
cleaning crew. In Head Office there are a
Divisional Manager and Project Manager plus
accounting and management support. Overall
there are 16 people directly involved in the
landfill full time and this can increase to 28
when construction is going on.
Bird and animal life The site supports a wide
variety of wild water birds including Swans,
Ducks, Teal, Herons, Coots, Geese, Ibis, and
Peregrine Falcons. The majority of these live in
the water bodies or trees around the site. Only
a few of these species feed on the landfill.
Animals include kangaroos and wallabies,
wombats, and other native animals and a few
feral animals such as foxes and rabbits. Cattle
are agisted on the undisturbed land. There is
also a significant colony of the Growling Grass
Frogs and these are monitored and sustained.
Rehabilitation The quarry has a legal
requirement to restore the void by making the
edges safe by sloping and removing all plant
and equipment and revegetating the site. The
landfill operation will be responsible for the
restoration for the quarry and will create a
low hill planted with native plants indigenous
to the area. The long-term use of the bulk of
the site will be for passive recreation and
nature reserve. Areas along Epping Road and
Bridge Inn Road will be developed for
commercial uses.
Urban encroachment Urban encroachment is
emerging from the south along Epping Road.
The current planning boundary between Rural
and Urban areas is at Harvest Home Road
three kilometres south of the landfill. The
quarry has land 800 metres south of Bridge
Inn Road along Bindts Road, which will be a
permanent buffer. There is probably in excess
of 20 years of land development before the
planning boundary needs to be changed and
more than 40 years before it reaches the
southern boundary of the quarry land. There
will be limited development around the
Wollert crossroads. Expectation is that the
landfill will be protected from urban
encroachment for the entirety of its
operational life.
ACKNOWLEDGEMENTS
Sam Bateman Project Manager, Hanson
Landfill Services