Four-year review of a hydrogeological risk assessment for an active landfill

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Courtesy of ESI Ltd - Environment Specialists

Client: Waste Management Industry

Location: Cambridgeshire, UK

Services: Hydrogeological Risk Assessment, compilation and assessment of monitoring data

Issues: Potential risk to groundwater, trigger level compliance

Summary: ESI undertook the 4-yearly Hydrogeological Risk Assessment review for the site. Data were reviewed and appropriate changes to the leachate levels and concentrations in the risk assessment model were made. The results of the additional modelling continued to support the original HRA conclusions and showed that there was no additional impact to controlled waters as a result of the changes. 

In order to comply with the PPC permit issued for a large, active landfill located in Cambridgeshire the client was required to submit to the Agency a four-year review of the Hydrogeological Risk Assessment for the site.  ESI was asked to complete this assessment to determine whether the conceptual model that underpinned the original study was still applicable and to assess the potential impacts of the landfill on the Lower Greensand major aquifer.

The landfill is located in a former Chalk and clay quarry within a cement works and provides on-site disposal for the majority of the waste produced by the cement making process, principally cement kiln dust (CKD).  The excavation into the Chalk major aquifer has partially penetrated the underlying Gault clay which confines the Lower Greensand at depth.  Pumped leachate is recirculated by spraying onto the landfill surface to control levels.

The scope of work included the compilation and assessment of hydrogeological and hydrochemical monitoring data with regards to trends and comparison with the trigger levels set by the permit.  The original HRA conceptual model was found to remain appropriate to the site while leachate levels are managed, with the Lower Greensand aquifer representing the potential environmental receptor.  However, recent data showed that actual leachate levels and concentrations have exceeded those originally modelled and that plans to cap the landfill in the near future would reduce the modelled recharge.  To demonstrate that there will be no additional impact to any environmental receptors, an updated version of the risk assessment model was constructed in a site specific spreadsheet model based on ESI’s commercial software package Risk Assessment Model (ESl Ltd, 2000). 

The results obtained from this risk assessment continue to support the original HRA conclusions, demonstrating that that the site is likely to comply with the Groundwater Regulations 1998 and has containment and leachate control consistent with the performance required by the Landfill (England and Wales) Regulations 2002 and subsequent amendments.  Close communication with the client was maintained throughout the project, which greatly facilitated the smooth production of outputs.

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