An oilfield service company has been operating a site in Knowsley, Liverpool, UK for more than 20 years. The site was first developed during WWII as a Royal Ordnance Factory, and since that time has been used almost continually for the manufacture of specialty chemicals (including organic chemicals, organotin compounds, and lead-based compounds) by various companies.

Historical use and disposal practices have resulted in significant subsurface impacts including the presence of free-phase hydrocarbons (LNAPL) and mobile organotins within a complex geological and hydrogeological setting. Despite a number of efforts over the years to characterize and address site contaminants, issues remained and required clarification to resolve the regulatory roadblock that was preventing successful closure of the on-site remediation.

This case study presents the results of the recent successful efforts to develop a robust and defensible conceptual site model, highlighting the key lessons learned in terms of data assessment, integration and visualization. Two important areas of focus include:

  • Engaging with the regulators on a pragmatic, risk-based approach to managing LNAPL remediation. This included developing a remedial strategy focused on understanding whether there are actual risks rather than the mere presence of LNAPL.

  • Understanding the relationship and interaction of tributyl-tin (TBT) with LNAPL, where the LNAPL was acting as a preferential solvent, and enhancing the mobility of the TBT. As such, the risks presented and any subsequent remedial solution could not be considered as two separate problems and an integrated strategy was developed.

The use of risk-based approaches, robust conceptual models and a detailed understanding of contaminant distribution are critical to the development of long term sustainable solutions to remediate contaminated sites.

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