Calvert Landfill Site history and operations
Calvert Landfill lies between the villages of Calvert and Edgcott in the Aylesbury Vale, some 10Km to the south of Buckingham. The installation covers an area of some 314 hectares.
- Clay extraction and brick making commenced at Calvert with records dating back to the early 1900’s.
- Clay extraction was undertaken in a series of pits. Pits 4, 5 and 6 are currently excavated with pits 7 and 8 untouched.
- Planning permission for clay extraction from most of Pit 6, and the restoration of the excavations by landfilling, was granted in 1955 as part of a wider permission also covering Pits 4 and 5.
- A further consent for the landfilling of the same area was granted in 1977.
- Planning permission for the continuation of clay extraction in Pits 6 to 8 (i.e. those parts of the site not covered by the previous planning permissions) and the restoration of the excavations by landfilling with ‘controlled waste’ was granted in 1987.
- The brickworks associated with the clay extraction on site closed in the 1980’s and by the 1990’s all of the buildings and chimneys were demolished.
- FCC Environment (Waste Recycling Group as they were previously known) took over ownership of the site and land filling activities in 2004.
- The approved restoration contours and slopes covering Pits 4, 5 and 6 were too shallow to be considered acceptable by modern standards therefore the restoration contours for Pits 4 and 5 were consequently modified and approved in 2008.
- Waste is predominantly household; circa 85% is delivered by rail.
- In addition, the site accepts road borne waste from the Cherwell Valley District in Oxfordshire, Buckinghamshire County Council and local trade waste.
- Several trains also arrive on site carrying spoil used for engineering purposes
- Site has the capacity to accept up to 10 trains per day but is currently accepting on average 4 per day.
- The site accepts approximately 65,000te of waste per month
- Operational hours are from 7.00am to 4.30pm Monday to Friday for road borne waste
- For train borne waste site is operational from 05:00 until 18:00. However, there may be occasions in which the site remains operational until 23:00.
- Each Saturday following a bank holiday site may be operational up to 16:00.
- Waste arising comprises; local industrial and commercial waste, household waste, transfer station waste, soils and other cover material.
- Site front line machinery includes a 55te compactor, D6 bulldozer, 360 Excavator, 963 tracked loading shovel, 3 Bell dump trucks and a tractor with various attachments.
- Up to 7 articulated modified dumpers service the trains, loaded with the aid of the crane system in the rail sidings for waste containers.
- For trains that contain spoil, a grab is used which then loads these dumpers with the material ready to transport onto site.
- The site employs 21 staff.
Gas Control and Utilisation
- The environmental gas control system is installed throughout the site.
- A network of vertical 225mm and 160mm diameter wells (approximately 650) are installed across the site and collected via 160mm to 355m pipe work laid across the surface.
- Wells are drilled through the emplaced waste to the base of the site to ensure gas is collected through all strata.
- The extracted methane gas generates up to 17MW of renewable electricity via 9 gas utilisation engines and ancillary equipment connected to gas flare compounds. This is the equivalent amount of electricity required to power around 17,000 homes.
- Leachate is generated when clean water passes through waste and becomes polluted.
- Leachate sits on the base of the landfill site within the engineered containment.
- Leachate is extracted from the site through a network of pumps installed in a series of wells and collected in nine 50m3 storage tanks.
- The site runs a Reverse Osmosis plant to treat leachate. The plant acts as a large filtration device, removing contamination from the liquid so that the residual water can be discharged to surface water.
- Approximately 165m3/day of leachate can be treated through the works. A similar amount is tankered off site and disposed of at a sewerage treatment facility.
Geology and Engineering Phasing
- The site is located in an area where glacial till overlies Oxford Clay, Kellaways Sand and Blisworth Limestone.
- The landfill phasing comprises 2 pits filled on a cellular basis which have been filled progressively from the North to the South of the Site
- Due to the revised pre settlement contours the site is currently being surcharged in accordance with a phasing plan. This is starting from the northern part of the site (pit 4) and will progress southwards (pit 5)
- This surcharging commenced in 2010 and is likely to continue until 2016
- Once completed pit 6 will be engineered and filled in a phased manner with tipping expected to continue for many years until the approved restoration contours have been achieved
- As each phase of the surcharging is completed, the areas will be progressively capped and restored.
- Additional leachate and gas extraction systems will be installed as required.