The Remediation of Chemical Groundwater Contamination at Harwell

The Remediation of Chemical Groundwater Contamination at Harwell3.2 Groundwater Plant Operations 2008The groundwater containment plant at the SSA was decommissioned in April 2002, withthe agreement of the EA. This followed the successful completion of the SSA landremediation project.The original hydraulic containment plant at the WSA became fully operational in 1994. Theneed for a replacement plant was identified several years ago because the original planthad reached the end of its design life, and predictions, based on extrapolation of themonitoring data for the original plant, indicated that a containment plant could be neededuntil around 2025.The replacement plant, referred to as Harwell Groundwater Containment Plant (HGCP),has been operating very successfully since June 2007.HGCP uses granular activated carbon (GAC) to remove the contaminants from thegroundwater. GAC is used in domestic water filters, as well as many other applications. Itis very effective at removing organic chemicals from water, and is robust and costeffective.The original groundwater plant at the WSA used GAC to effect water treatment, but inconjunction with a process called air stripping. However, contaminant concentrations in thegroundwater at the WSA have been successfully reduced to a level where liquid phaseGAC treatment alone is viable. This has simplified the design, operation and regulation ofHGCP, resulting in significant cost and environmental benefits. As an example, the airstripping system on the original plant required the operation of a 27 kW heater, and this isnot needed in HGCP.The liquid phase GAC filters themselves are an improvement over those used on theoriginal plant, which were fixed vessels. Removal of the spent GAC filter medium fromthese filters required personnel to enter the vessels. Although these operations werealways managed safely, the opportunity to eliminate industrial hazards such as confinedspace working and working at height was taken with HGCP.When the GAC used on HGCP requires replacement, the entire filter unit is transported ona special lorry to a regeneration plant. Here the GAC is removed without the need forpersonnel to enter the vessel. The GAC is then treated to remove and destroy thecontaminants. The regenerated GAC is returned to the vessel and the vessel deliveredback to the plant at Harwell. No interruption to the operation of HGCP is needed duringthis process, in contrast to the GAC change operation on the old plant, which required ashutdown of up to five days.Overall, the replacement plant offers the following improvements over the original plant:• Industrial safety hazards eliminated (no routine confined space working or working atheight);• Lower energy consumption (the electricity used by HGCP is around 30% of that usedby the original plant);• Minimal waste generation (the GAC is regenerated rather than being sent to landfill);• Ease and flexibility of operation (flows can be precisely specified for each borehole,and the plant can be monitored and operated remotely via a laptop PC).LSG Groundwater Report 7 March 2009