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Contaminated land remediation by free product recovery and in-situ chemical oxidation

Client: Local developer
Location: Exeter
Contract period: 6 weeks

This housing development site was previously used as a railway terminal, resulting in significant hydrocarbon contamination of the groundwater. Telluric Land Remediation was appointed as specialist contaminated land remediation contractor to undertake in-situ chemical oxidation (ISCO).   

Thirty six injection points were installed across the affected area. However, during this initial phase of work, significant free product (LNAPL) was unexpectedly identified within a small area of the site. As the presence of free product could undermine the efficiency of the ISCO application, a sump was excavated in the area of concern to enable removal of the free product by vacuum tanker.  Approximately 26,000 litres of oil and grossly contaminated groundwater were removed and taken to a suitably licensed facility for disposal.

Following the free product removal exercise, each borehole was primed with a catalyst prior to the application of oxidant.  The oxidant (Fenton's reagent) was introduced by gravity, via a flowmeter to ensure the correct volume was dispensed to each individual location. Two full rounds of xidant application were undertaken in a three week period to ensure compliance with the remedial targets and to keep within the construction programme.

Groundwater was monitored and sampled before treatment began, between the two oxidant applications and after the final application.  Parameters monitored included soil gas concentrations, groundwater levels, VOC concentrations, conductivity, oxidation-reduction potential, dissolved oxygen and pH.  Groundwater samples were recovered and sent to an independent accredited laboratory to be analysed for TPH, benzene, toluene, ethylbenzene and xylene. 

 telluric bullet Our solution

  • Environment Agency liaison
  • Removal of LNAPL and grossly contaminated groundwater
  • Installation of 36 ISCO injection wells
  • Injection of chemical oxidant
  • Monitoring and sampling of groundwater
  • Compilation of validation report

Our solution resulted in rapid, cost effective, site remediation that discharged planning conditions and allowed redevelopment to progress without delay.

A pdf version of this groundwater remediation case study is available here