Spill response, environmental site assessment and remediation

REDS Group were commissioned to handle an emergency oil spill in an industrial unit. They discovered a leak in a hydraulic oil supply pipe, which caused oil to flow into a nearby drainage balance pond.


REDS Group were initially commissioned on an emergency spill response to an industrial unit where oil had been observed in an adjacent drainage balance pond. Site staff had identified a leak from a hydraulic oil supply pipe and oil was then observed migrating to a surface water drainage chamber.

Following the completion of emergency spill response works, REDS were commissioned to undertake a full environmental assessment of the site, delineate the extent of oil impact, identify migration pathways, and then design and implement a long-term remedial strategy.

Project Works 

Preliminary Risk Assessment

 Detailed Phased Intrusive Site Investigation

 Remedial Strategy

Spill Response  

  • A Preliminary Risk Assessment was conducted to assess site sensitivity and identify at-risk receptors. The key receptor is a brook connected to a balance pond through an underground culvert, located approximately 200m from the site.
  • Response works included installing hydrocarbon booms and absorbents to prevent oil migration from the balance pond to a culvert and from the drainage discharge point to the nearby brook.
  • Monitoring points were set up in the surface water network, and communication was maintained with the Environment Agency on behalf of the site.
  • A short-term monitoring program was agreed upon with the Environment Agency during the balance pond oil recovery. On-site efforts were made to stop further leakage into the damaged surface water drain and prevent further offsite migration.
Balance Pond Absorbant
Case Study. Oil in bailer

Site Investigation & Risk Assessment 

  • A detailed phased intrusive site investigation was carried out to review underlying geology, oil impact, and migration pathways.
  • Boreholes were constructed for monitoring groundwater around the building. These were completed as monitoring wells to allow monitoring of groundwater.
  • Investigation revealed clay geology with granular material present, enabling migration to the surface drainage system.
  • Additional boreholes constructed inside the building confirmed oil migration towards the drainage trench.


  • REDS designed a remedial strategy based on the migration pathway from the site to the surface water drainage system.
  • A remedial cut-off trench was created to install between the building and the drain lines. The cut-off trench has permanent oil recovery infrastructure to allow for the removal of any residual oils migrating from under the building foundations.
  • The damaged drain line was excavated to allow the recovery of accumulated oils from the drain trench. As anticipated, oils had accumulated in the drain trench and were recovered via pumps and a vacuum tanker for offsite disposal.
  • Poorly sealed drain line and connection to the inspection chamber allowed oil migration directly into the chamber. Repairs were made to prevent future leakage. Contaminated material was removed and disposed of offsite.


All works were completed by REDS operatives and supervised by a REDS environmental consultant who carried out soil verification sampling from the base and side walls of the excavations.

Oil around pipe in trench
Works complete

Verification & Monitoring 

  • Post-remedial verification monitoring has demonstrated no further impact on the surface water drain, balance pond, or associated brook.
  • Small volumes of residual oil accumulated in the remedial cut-off trench immediately following the remedial work and was recovered using oil absorbents.
  • No further accumulation of oils has been recorded.


We concluded the remedial works have successfully recovered the vast majority of spilt oil and have broken any migration pathways from the site to the balance pond and associated brook. On this basis, 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
Initial response
Environmental site investigation
Design & implementation of remedial strategy
Verification & regulatory sign off

Date Posted: 21/07/2023