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Cognition is carrying out remediation works at Hinkley A station as part of the site wide decomissioning works.
Hinkley Point A, the first power station to be built at Hinkley Point was constructed in the 1950’s and is now in the process of being decommissioned. The site is located on the north Somerset coast, approximately 13 km northwest of Bridgwater and adjacent to Bridgwater Bay. During the decommissioning process a number of detailed site investigations have been undertaken to highlight ‘areas of potential concern’ which are then further assessed and remediated if necessary.
Cognition, working in partnership with Golder Associates, was contracted to design and implement and a remediation strategy to address an area of diesel contamination associated with the former diesel generator building on the site.
As well as presenting a risk to the wider environment, there is concern that the dewatering to be undertaken during the construction of the new C station might influence the migration of contamination towards Bridgwater Bay.
A two phase remediation strategy was developed which involved removing the primary source of contamination, free product (otherwise referred to as non-aqueous phase liquids - NAPL), from shallow soil and groundwater beneath the former diesel generator building, followed by pumping and treating deeper groundwater from an array of wells drilled down gradient of the contamination source.
To address the primary contamination, Cognition demolished the slab and broke out obstructions prior to excavating a groundwater extraction trench backfilled with clean stone. Groundwater was pumped from large diameter extraction wells installed in the trench to a water treatment plant comprising of an oil water separator, sand filter, crossflow filter, granular activated carbon vessels and buffer/storage tanks. Phase 1 of the works has recently been completed and monitoring has demonstrated that free product has successfully been removed.
Contaminated soil from the source area was bioremediated on site using cultured indigenous bacteria to reduce the levels of contamination and minimise disposal costs. A perimeter odour/dust control system was installed around the treatment area to minimise impact beyond the working area.
For phase 2 of the remediation works, Cognition installed pneumatic pumps in an array of fourteen wells drilled between 11m and 18m to the north of the source area. The groundwater will be pumped continuously for 2 weeks with water passing through the water treatment plant to ensure any hydrocarbon contamination is removed.
Cognition also installed a NAPL fabric extraction system on a well within the extraction trench to assist in the removal of the diesel. This innovative system targets free product by drawing it from groundwater wells using a continuous loop of oleophilic/hydrophobic fabric which is capable of adsorbing the product with a 99% recovery-efficiency. Oil adsorbed to the fabric is extracted at the surface, draining to a tank for off-site disposal. There are a number of key advantages of the NAPL fabric extraction system over conventional groundwater remediation techniques; the system only targets hydrocarbons so a water treatment plant is not required. The system occupies a small footprint and can be installed below ground and therefore run on busy operational sites. It also uses very little power, and can be combined with a solar panel or small wind turbine to make the system