Remediation of residual hydrocarbon contamination

REDS Group were commissioned to complete remediation of residual hydrocarbon contamination at a former industrial site, prior to the surrender of an existing lease and future redevelopment.


All works were required to be completed and validated in under six months, requiring a highly aggressive and focused remedial strategy.

The site was located in an area of high environmental sensitivity, adjacent to a tidal river and designated SSSI. The underlying geology was variable and complex, the former operational areas were spilt over two distinct zones and the site had suffered a significant fuel leak in the past.

Project Works 

Baseline Monitoring

Intrusive Site Investigation

Detailed Quantitive Risk Assessment (DQRA)

Remedial Strategy

  • We completed a detailed groundwater monitoring exercise & additional intrusive site investigation to assess underlying groundwater quality and contamination within the soil and groundwater
  • Down-hole pressure transducers (‘divers’) were used to examine potential tidal influences on underlying groundwater
  • We established the full extent of contaminant distribution in underlying groundwater




  • Confirmed that groundwater was directly influenced by tides based on our monitoring data
  • Completed MNA assessment to review active natural processes
  • Carried out a Detailed Quantitative Risk Assessment (DQRA) to establish site-specific remedial targets for the site and inform the final remedial strategy

Comparison of dissolved hydrocarbon concentration (red) vs dissolved oxygen concentration (green) suggesting natural attenuation processes were active under the site.
Dissolved hydrocarbon concentration

Dissolved hydrocarbon concentration

Dissolved oxygen concentration

Dissolved oxygen concentration

Groundwater and High Tide Correlation

Direct correlation observed between groundwater elevations and tide

Step 2: Excavation of soils
  • We designed an aggressive remedial strategy for the site based on targeted contaminant source removal as a key component
  • Conducted excavation of hydrocarbon impacted shallow soils in three areas of the site
  • Removed free phase hydrocarbon impact and targeted key residual contamination sources through excavation
  • All soils disposed of offsite at a soil treatment facility
  • Installed temporary remedial infrastructure in the excavations to support in-situ treatment efforts
In-situ Remedial Treatment
  • Our team then utilised in-situ treatment of groundwater using a combination of In-Situ Chemical Oxidation (ISCO) and Oxygen Release Compound (ORC)
  • We used an in-house chemical mixing system for preparing ISCO reagents
  • Pumped ISCO reagents into the underlying aquifer via remedial sumps to reduce residual contaminant mass through oxidation and desorption
  • Abstracted impacted groundwater and desorbed hydrocarbons from wells across the site after the initial in-situ treatment
  • Conducted final in-situ remedial treatment using ORC to enhance natural degradation of residual hydrocarbons in the groundwater over an extended period
Step 5: Mixing tanks
Verification & Monitoring 
  • Post-remedial verification monitoring was completed during a series of return visits to the site
  • Groundwater samples were collected using low-flow sampling techniques and key groundwater parameters were reviewed to confirm natural attenuation processes had been enhanced and were active

  • Dissolved hydrocarbon concentrations reduced rapidly following our remedial works, with none of the hydrocarbon concentrations recorded in groundwater found to exceed the site-specific remedial target levels for the site


We concluded the site did not pose a potential risk to identified receptors and was suitable for ongoing commercial use.

All works completed in-house by REDS Environmental Consultancy Team
Project Review & Verification Monitoring
Additional site characterisation
Design & implementation of remedial strategy
Verification & sign off

Date Posted: 27/07/2023