Tom Tallis L6D
Explain how the geological problems associated with domestic waste disposal in
landfill sites might be overcome by good site selection and engineering practice.
The positioning of landfill sites is extremely important with the local geology in the area. The
location of the landfill site is crucial as problems such as groundwater contamination and
subsidence may arise if the planning is not well done. A landfill site is a licensed facility where
waste is deposited for permanent disposal.
Groundwater contamination is caused as a direct result of leachate passing through permeable
or porous rocks and entering through the water table to contaminate the groundwater sources.
Leachate is formed when the water percolates through the solid waste and it is highly toxic.
Groundwater contamination can be avoided if the rocks beneath the proposed landfill sites are
impermeable, such as granite. The landfill site should also avoid being anywhere near faults or
well jointed rocks such as limestone, as the leachate can easily percolate down the fault line or
through the joints breaking under stress to reach the water table and contaminate the water, it
should also be away from any aquifers. This is because aquifers are where most of our drinking
water comes from and if that becomes toxicated due to the leachate then the population
dependant on that aquifer for drinking water will be affected and it could cause severe illnesses.
The landfill site should be positioned a minimum distance of 1 kilometre from groundwater
sources to prevent contamination. All landfill sites should have impermeable liners, lined with
compacted clay or geo membranes. They prevent leachate from leaking into surrounding soils,
bentonite enhanced sand is also commonly used as a liner. The waste should be compacted to
reduce the permeability and volume. It should also be covered every night so that rain or surface
water cannot percolate through the waste. IT also prevent pests such as rats and seagulls from
carrying the rubbish and it prevents the bad smells from escaping the site. These are called
landfill caps.
Landfill sites can also have leachate management systems, these may be long pipes which
reach down to the base of the landfill and collect the leachate, it is then dispatched through pipes
so it can be re-circulated. There are also leachate drainage blankets at the base of the landfill and
wells to monitor and extract the leachate. Landfill gas management systems are installed to
prevent the build up of gases within the landfill and to prevent spreading of landfill gas through
the underlying strata. There are two ways landfill gas can be managed:
Passive management systems comprise of wells with perforated tops to allow the gas to vent into
the atmosphere
Active management systems involve the active extraction of the gas .The extracted gas can be
used to generate electricity.
The environment agency regulates waste management through a system of licences (PPC
Permits) they are responsible for ensuring that waste produced in the UK is correctly disposed of
in a way in which it has minimal impact on people and the environment.
Describe the potential uses of former landfill sites after waste disposal ceases, and
the problems associated with their development
A former landfill site will have closed to accepting rubbish and will have been restored.
Landfill sites are regularly monitored after they have been “restored” or covered up after
use, they are relatively safe. There is however, a risk of landfill gases escaping although
this will more than likely just cause plants and trees to die rather than cause danger to
humans due to explosions. When a landfill site is originally granted permission to act on,
the future land use is occasionally agreed as part of the planning application. If this is not
the case then the site could be restored for recreational uses such as golf courses or
football pitches or even grazing land for farming.
Due to the possible gas that may escape from the former landfill site, it is much
safer to use the site for recreational purposes rather than building houses on it. This is so
that any released gas will go straight into the atmosphere rather than building up in a
house. This has had a devastating impact on a town called Loscoe in Derby in 1970, no
one died but a small cottage was blown to pieces due to gas release from a nearby capped
landfill site. Methane and carbon dioxide built up in the lid of the capped landfill, the air
pressure dipped and the landfill site had no venting, meaning that the gas would take the
weakest line of resistance through the geology and into the nearby houses. A spark then
ignited with the gas and blew up the cottage.
This disaster caused the government to take much more care with used landfill sites,
they made sure that they vented out the excess gas and then burn off all the methane and
in certain cases, turn the gas into electricity using gas turbines supplying the national
grid.
The main hazards for building houses are the biodegradable materials which release
flammable and explosive gases as they decay, the geotechnical properties, which may be
unsuitable for building and construction purposes, and the presence in the soil of toxic
substances or the chemicals that attack building materials. This means that landfill sites
are unsuitable for hard forms of development unless remedial treatment is carried out
before construction.