ESI Consulting Ltd

Hydrogeological risk assessment review


Courtesy of ESI Consulting Ltd

Client: Waste Management Industry

Location: UK

Services: Hydrogeological risk assessment (HRA) review.

Issues: Potential risk to groundwater, leachate levels and maintenance of hydraulic containment, regulatory compliance.

Summary: ESI undertook the hydrogeological risk assessment review this hydraulically contained site. The hydrogeological risk assessment review showed the conceptual model remained valid and also highlighted the need for prompt implementation of the new leachate management plan. It was concluded that the site remained compliant with the Groundwater Regulations (1998) and Landfill (England and Wales) Regulations (2002).

ESI were commissioned by the client to review the hydrogeological risk assessment (HRA) for the site which had been prepared for the PPC Permit application in October 2003. The client needed to submit the review to the Environment Agency in July 2008.

The review covered:

  • Determining if the Improvement Conditions included in the PPC permit had been implemented as required and if they affect the acceptability of the existing HRA.
  • Confirming that the requisite surveillance at the site had been carried out as required. In doing so there was also a need to compare the observed data to the assumptions used in the HRA model and existing baseline monitoring data.
  • Assessing whether the conceptual hydrogeological model included in the original HRA was still appropriate.
  • Confirming that the risk assessment methodology, the approach and the use of mathematical modelling in the HRA was still appropriate.
  • Review of properties used in the model (e.g. source term) to ensure their continued applicability.
  • Conclude whether the site was and would remain in compliance with the Landfill and Groundwater Regulations.

The review concluded that the conceptual model was still valid. The only change was to allow for a reduction in the total waste mass deposited. The review of monitoring data showed that the there were no changes to the external environment, as groundwater levels and quality had not changed significantly. No impact of leachate on the wider environment was identified.

The Permit for the site had been issued on the basis that the cells/phases at the site would be operated in the long term under hydraulic containment. The review recognised the need for prompt implementation of the new leachate management plan which was being prepared to ensure leachate levels were managed to maintain hydraulic containment.

This review showed that, in some cells/phases, whilst some leachate levels were still above the specified limits in most cases they were actually already reduced below adjacent groundwater levels.

The analytical data reviewed indicated that the leachate strength had increased from that modelled in the original HRA.  Although this would result in increased concentrations of modelled species reaching the receptor, scaling calculations were undertaken which showed that this would not result in an environmental impact. At the time of the review it was found that the site was compliant with the Groundwater Regulations (1998) and Landfill (England and Wales) Regulations (2002).

ESI is recognised as a UK centre of excellence for groundwater modelling, and is contracted by both public and private organisations to carry out similar work.

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