Ground Conditions

The geo-environmental work during 2015 and 2016 was undertaken in support of ‘Soils Geology and Contaminated Land’ chapter for the Environmental Statement (ES) prepared in support of the former planning application for a mixed use development on the site. The outputs are made available within the data room provided, and include:

  • Phase 1 Contamination Risk Assessment (Dec 2015)
  • Baseline conditions ground investigation (fieldwork Apr /May 2016)
  • Phase 2 GI Interpretation and Land Contamination Risk Assessment (Aug 2016)

The Phase 2 report assessed the risks associated with the ground gases methane (CH4) and carbon dioxide (CO2). The report found the worst case ground gas concentrations and gas flows recorded in the monitoring installations that targeted the landfill located in the north-eastern corner of the site. It was concluded that Characteristic Situation 2 should be conservatively adopted for the general site (excluding the landfill) whilst the small landfill area was classified as Characteristic Situation 5. This means that mitigation measures would be required, for example in the form of a clean cover layer or installation of a passive venting system. Further assessment of ground gas risk should be undertaken at detailed design stage to appropriately characterise the separate development areas.

Account was also taken of the earlier window sample ground investigations undertaken by RPS (November 2015) on the southern and eastern site perimeters, and in relation to the historical spillage of diesel oil at the Larkfield Mill site. The RPS report is made available in the data room. It is understood that free phase product was continued to be removed from the historic Larkfield Mill spill site as part of a long term remediation programme until the recent demolition activities commenced.

In terms of geotechnical risk, the main concerns are likely to be associated with excessive settlement of structures in the Alluvium and Made Ground, particularly the landfilled area along the eastern boundary of the former Water and Effluent Plant Site. This may also influence the type of foundations that may be used during redevelopment of this site.

Exploratory borehole numbers and locations within the main plant area were constrained by the condition of the site at the time (2016), in particular the extent of the industrial buildings and associated hardstandings. Following the recent demolition of a significant proportion of the buildings and other structures associated with the main plant area, access has consequently improved. The opportunity for further intrusive ground investigations and interpretive reporting has therefore presented itself, and is taking place by Pell Frischmann during Q3 2018.

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