Under a former petrol filling station the soil and groundwater was found to be contaminated with petroleum hydrocarbons (primarily BTEX). This had been caused by leaks from the station’s underground storage tanks (USTs). The storage tanks have been removed and surrounding soils excavated, however residual contamination persisted in both the soil and groundwater within the source area and the downgradient plume. The regulatory cleanup target is a 50% reduction of the BTEX / HC C5-C10 concentrations in groundwater.

Design and Application

An integrated in-situ remedial solution has been designed by REGENESIS and put in place by specialist remediation contractor Valgo, consisting of 26 PersulfOx injections on a 2 x 2m grid in the source zone for fast and effective treatment of the most impacted soils and groundwater.

PersulfOx is a sodium persulfate based chemical oxidation agent in which a patented catalyst has already been premixed into the formulation. This allows for safe and simple fieldwork and avoids the delivery and handling of large amounts of hazardous activator chemicals onsite. The reduced fieldwork complexity and smaller application volumes also provide cost savings for the remediation project.

ORC Advanced was also applied in the source zone to achieve long term in situ bioremediation of the residual petroleum hydrocarbons. In addition, Valgo installed an ORC Advanced barrier in the downstream plume area, to prevent off-site migration of the contamination.

ORC Advanced provides up to 12 months controlled release of dissolved oxygen from a single injection. This accelerates the natural biological degradation of the residual dissolved phase contamination.


The PersulfOx treatment reduced the contaminant concentration in the ground- water of the source area by 64% for C5-C10 and 71% for BTEX. Coupled with the ORC Advanced application, the levels would be expected to continue to drop as enhanced aerobic biological attenuation addresses a proportion of the residual contaminant mass. Downgradient of the ORC Advanced plume barrier, the dissolved phase contamination was reduced to non-detect following application, as the contamination is biodegraded as it passes through the treatment zone.


  • PersulfOx contains a unique built-in catalyst to enhance the oxidative destruction of hydrocarbons in the subsurface. The patented catalyst is already mixed in the product, so the application is much safer and easier to apply compared to other ISCO products.
  • This is the first PersulfOx application in France
  • Appropriate treatment technologies were used across the site:
    • In the core area; ISCO was used firstly, in order to reduce the high concentrations, followed by ENA to address the residual dissolved phase contamination.
    • In the downgradient plume, where there were lower concentrations and a long-term barrier was required, ENA only, using ORC-Advanced was most applicable , successfully preventing dissolved contamination from egressing the site.