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Geo-Environmental Investigation and Flood Risk Assessment at a Complex and Sensitive City Centre Site

Flood risk Site assessments Geotechnical Support

The client approached EPS for support in submitting a planning proposal for a city centre site comprising a large mixed use development. EPS was tasked to carry out Phase I & II site assessments and a flood risk assessment in order to evaluate the present contamination status at the site and also to undertake a detailed examination of the sub-surface ground conditions to aid in geotechnical design for the scheme.

  • The proposals for the development included an undercroft car park within a commercial area which included a bowling alley, a cinema complex and associated retail units. A variety of accommodation was also proposed on the site comprising student flats, apartments and affordable housing.
  • The initial desk study phase also identified several current and historical Potential Areas Of Concern which would require further investigation, including fuel tanks at a waste merchant’s depot, a former petrol filling station and an off-site historic hospital. The site was located within an area of relatively high environmental sensitivity on account of the underlying sands and gravels and Chalk being classed as secondary and principal aquifers respectively and with shallow groundwater assumed to be draining to the River Great Stour which passes along the northern boundary and whose floodplain extends onto the site.
  • In order to more accurately evaluate ground conditions for geotechnical design and establish environmental liabilities, the intrusive investigation was designed with the proposed redevelopment in mind whilst accommodating for the practicalities and needs of the existing users on the active parts of the site. A total of 28 boreholes were drilled to depths of up to 20m and the data acquired founded the basis for foundation design and recommendations for safeguarding future users of the site.
  • No physical evidence of contamination of soils or groundwater was encountered during the ground investigation although subsequent laboratory data did confirm that an agreed thickness of clean top soil cover would be required for soft landscaping and garden areas. A gas monitoring program also confirmed that only basic gas protection measures would be prescribed, despite some relatively high gas levels within peaty horizons towards the river.
  • EPS’ site investigation report and flood risk assessment will be submitted as part of the planning proposal for this scheme to support the discharge of any relevant conditions that might be placed upon the development. The results of the geotechnical investigation will aid the design of the most cost effective foundations for the scheme.