Copyright ©1997-2012 Barr Limited
All items of plant on site are refuelled from a bunded diesel tank. The bund provides secondary containment for the main tank in the event of rupture or damage to associated pipework. The gravity-fed fuel nozzle is also stored over the bund when not in use to catch spills.
All vehicles leaving site are directed through a wheel wash to reduce the amount of carry-over on to public roads. The wheel wash consists of a long water-filled trench with a ridged bottom to aid displacement of dirt. Exceptionally dirty vehicles are also power-washed. Build-up of dirt in the wheel wash is cleared away and the water replaced on a regular basis.
Prior to filling, the cell base is lined with a 2mm layer of high-density polyethylene (HDPE) to prevent leachate from entering the sub-strata and any groundwater beneath the cell. After filling has been completed, the cell is capped with a layer of clay and again lined with HDPE; restoration material (e.g. soil) is then placed over the top of the liner as the final cap. Capping provides a seal within which drainage systems can remove leachate and landfill gas without emission to the environment. The photograph shows an aerial view of a completed cell at Garlaff; the exposed HDPE liner is visible around the flanks of the cell and capping soil has been deposited on top.
All landfill gas generated within the cell voids passes through an extensive pipe network to an on-site electricity generation compound, where it is used to drive a series of four gas-powered internal combustion engines. These engines are used to generate electricity up to a maximum capacity of 4MW. Any gas surplus to requirements is atomised in the flare system. Electricity generation from landfill gas is an example of a system that not only mitigates an environmental issue (i.e. prevents release of the gas to the atmosphere) but also results in a positive environmental impact (in this case, the generation of electricity from a more sustainable source than, for example, from fossil fuels).
Leachate collected from within landfill cells must be treated prior to discharge to the aquatic environment. The leachate is stored in a holding lagoon and is aerated as a form of pre-treatment. Small amounts of leachate are then added to a second lagoon (sequencing batch reactor (SBR)) containing micro-organisms which break the leachate down, thus reducing the concentrations of eco-toxic constituents such as ammonia and lowering its biological oxygen demand. Molasses and an iron supplement are also added to the SBR to provide nutrition for the micro-organisms. The temperature in the SBR is also kept relatively constant through the use of a heat exchanger and oxygen levels are maintained by active aeration. Discharge of treated leachate occurs through the site’s surface water drainage system.
In addition to treated leachate, all surface water drainage on-site is collected in a network of channels and directed into a series of reed beds and settlement ponds. Reed beds provide physical filtration of suspended soilds (e.g. silt from earthworks) and also reduce the eco-toxicity of leachate. The ponds provide further removal of solids through gravitational settlement; flocculation agents such as alum can be added to improve the rate of settlement. Reed beds and settlement ponds have to be cleaned out at least once per year to maintain their effectiveness.
A chemical odour suppressant is pumped from a tank through spray nozzles located around the site to reduce the level of odour from sources such as the leachate treatment plant and the active cell. This is a highly effective method of dealing with odour within close range of the sprays.
These consist of a variety of equipment including absorbent sheets, pillows, granules, seals and booms. They are used to prevent spills of potentially ecotoxic chemicals (e.g. oil, leachate) from migrating into water bodies or causing land contamination. The absorbent materials are oleophilic and hydrophobic, so that substances such as oils and fuels are selectively absorbed and water is repelled.
These are utilised to prevent the spread of wind-blown litter, both within the site and across the site perimeter. They are erected around the active cell and the site boundary and are effective in reducing the time and effort required for manual retrieval of litter. However, they must be securely erected as they are susceptible to wind damage and litter must be removed on a regular basis to maintain their effectiveness.
Copyright ©1997-2012 Barr Limited