Contaminated Land Planning Support at Whorral Bank Morpeth

DBS Environmental Phase 2 Ground Investigations

Contaminated Land Planning Support at Whorral Bank Morpeth, Dransfield Properties Limited

DBS was involved in the appraisal and remediation of a brownfield site at Whorral Bank in Morpeth on behalf of Dransfield Properties Limited (Dransfield) and Tolent Construction Limited (Tolent).

  • Client: Dransfield Properties Limited
  • Date: February 9, 2015

Summary

The site had been used for mining in the   late 1800, with two shafts present on site, and in later years had been used as a yard by Northumberland County Council for the storage of road salt.

The site was identified   as the location for a new vets and equine centre and work commenced in late

2011 to clear the site for development.   Thompsons of Prudhoe were appointed by Tolent to undertake site clearance and preparatory earthworks, and they were subsequently appointed to undertake site remediation. Tolent were the ‘Principal Contractor’ in accordance with the Construction (Design and Management) Regulations 2007

DBS were employed to undertake a phased risk assessment of the site in order to identify any contamination constraints associated with site redevelopment as a result of its former use.

The scope of DBS’ work was undertaken in full compliance with the requirements of Planning Policy Statement (PPS) 23; Annex 2 – Development on Land Affected by Contamination.

Site appraisal commenced with a Phase 1B Desk Study in order to fully understand the site history, confirm its regulatory status and to establish an initial Conceptual Model.

As part of the desk study process existing intrusive information and site chemistry data available for the site was re-interpreted. This allowed for the development of a robust Conceptual Model which identified data gaps to be filled by additional investigation, this enabled a highly targeted investigation to be scoped which saved time and resources in the site characterisation phase. The additional investigation work was designed to obtain soils and controlled waters data to aid further risk assessment work.   The work was also designed to install long term groundwater and gas monitoring wells and a programme of ground gas monitoring was undertaken in accordance with the requirements of CIRIA C665 guidance.

On completion of the work, the resulting data was used to further develop and refine the Conceptual Model to identify significant pollutant linkages that required mitigating during site remediation. All of the work was taken forward in the form of a Remediation Action Plan (RAP) report, this report provided one concise document including desk study work, data re-interpretation, intrusive work, initial and revised conceptual models and resulted in an Options Appraisal and remediation strategy. The options appraisal identified suitable remediation methods required to break significant pollutant linkages.

Constraints identified within the site related primarily to localised areas of contaminated made ground from leaching of the salt stockpile onto surrounding land, made ground from the mine, and widespread chloride contamination within the shallow soils of the site due to the former stockpile.

DBS developed a robust conceptual model for the scheme that identified that whilst chloride contamination was widespread across the site, there were no linking pathways for this material to impact receptors, other than new buildings and infrastructure to be built as part of site development. DBS entered into detailed negotiations with the Environment Agency on the conceptual model findings and after furnishing the agency with additional risk assessment the agency agreed to the discharging of the planning

conditions, without the developer having to undertake onerous site wide remediation and/or long term hydrogeological monitoring and DQRA of the underlying aquifer.

The new development was designed to mitigate risks from aggressive ground from chloride, and gas membranes were installed within building foundations to mitigate risk from ground gas.

Remediation work at the site comprised the exposure of the mine shaft caps to check their integrity, removal of contamination hotspots from the mine, and reworking of mine spoil (mudstone) across the site to create a development platform.

Throughout the project DBS worked closely with the regulators to ensure fluid and open progress through the various stages of site characterisation and risk assessment, obtaining contaminated land planning condition discharge from the local planning authority and Environment   Agency within very tight project timescales.

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