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Home > Management Activities > Groundwater Monitoring

The primary objective of the groundwater monitoring network at Sellafield is to monitor the groundwater quality and the hydrogeological features and processes that control it. There are a number of key components of the site that influence the design of the network, including the site boundaries, sources of contamination, migration pathways and potential receptors, i.e. the River Calder, the River Ehen and the Irish Sea. The groundwater monitoring programme provides time series data which not only provide early warning of the movement of contaminants off-site but provide data to validate the codes modelling contaminant transport.

The groundwater monitoring regime was significantly revised in 2006 following the findings and recommendations of a 2005 review (050268_02 First Issue) by Westlakes Scientific Consulting. The Sellafield Ltd groundwater monitoring programme was changed to adopt an integrated approach across the whole of the Sellafield site, rather than being restricted to the Site perimeter. This resulted in the total number of boreholes included in the site monitoring programme being increased to more than 150, with many of these boreholes containing multi-level monitoring installations.    

The objectives of the groundwater monitoring programme are as follows:

1. To provide data to enable current impact on humans and non-human species from contaminants in groundwater to be determined.
2. Monitor changes in the groundwater quality between the points that groundwater enters the Sellafield site to the points it leaves the site.
   • Determine the nature, scale and location of activity and other contaminants in the groundwater entering the Sellafield site
   • Determine the nature, scale and location of activity and other contaminants in the groundwater leaving the Sellafield site and/or available to human and non-human species.
3. Provide details of the groundwater quality across the Sellafield site.
   • Determine the nature, scale and extent of contamination in the groundwater beneath the Sellafield site.
4. Facilitate planning and prioritisation of remedial action.
   • Provide data to assess the direction and rate of migration of contamination entering the groundwater from contaminated land and other sources.
   • Provide data (contaminant concentrations, groundwater flows and directions) with which to assess the impact of contaminants in groundwater on actual or potential receptors including the sea or adjacent water courses (River Ehen and river Calder).
   • Provide data to assess the rate of discharge to groundwater from contaminated land.
   • Provide data to assess the rate of generation of waste.
5. Provide information to improve the conceptual hydrogeological model of the Sellafield site.
   • Monitor groundwater heads and hydraulic gradients across the site and provide information with which to improve the groundwater conceptual model.
   • Provide data to contribute to any routine water balance calculations for the site.

In addition to the above objectives, the programme has also been expanded to 

6. Provide information to identify the role of colloids, particles and dissolved salts in the migration of contaminants within groundwater.

The sampling methodologies and the analytical limits of detection have also been changed following the reviews.  These changes have resulted in a number of boreholes now having detectable concentrations of radionuclides within the groundwater.   An example of this is from the analysis of Total Alpha in groundwater which had a reduction in the limit of detection from 200 Bq/m3 to 30 Bq/m3.  This reduction has resulted in a number of locations where activity has been detected between the old and current detection limits.  To further investigate the sources of the elevated Alpha activity changes have been made to the frequency of sampling and the analytical suite. 

Each year the schedule for groundwater monitoring is developed in conjunction with the Environment Agency.  Part of this process includes the review of the previous year data and the development of the programme in line with the monitoring objectives. This annual review is submitted to the Environment Agency at the end of September. (2009 Annual Report (13.5MB))

Future objectives for the groundwater monitoring at Sellafield are to:

• Provide data to support hydrogeological assessment on the Sellafield site;
• Undertake further investigation, including the provision of further groundwater monitoring locations within the Separation Area.