Contaminated soil is traditionally cleaned up by excavating and transporting the soil off site. A tested, yet time-consuming method. When Shell asked Ejlskov to remediate oil-contaminated soil after an oil spill at a pipe valve system at the Shell oil refinery in Fredericia (FDO area), Ejlskov proposed a new approach.
By using in-situ Trap & Treat® BOS 200® technology, Ejlskov was able to perform 170 high pressure precision-drilled injections in a 350 m2 area which required no soil excavation or interruptions to Shell’s everyday operations. Ejlskov made a precise evaluation of the contamination at the site and came up with a plan that removed the contamination while saving Shell significantly on both time and money by maintaining a full production at their refinery.
Project objectives
An evaluation of the site by Ejlskov showed that there was approximately 1600 kg of oil contamination in the soil. Ejlskov proposed a plan that would clean the soil to safe levels below the standards set by the Danish Environment Authority after 3-5 years. The advantages of Ejlskov’s in-situ remediation with Trap & Treat® BOS 200® included:
- Environmentally friendly technology
- No permanent energy-consuming installations
- Removal of the contamination by degradation, not by dilution or simply transplanting the contamination
- No interruption to Shell’s production at the oil refinery
The objective was to prevent migration of the oil contaminant plume, and provide total remediation of the soil.
Site Characterization
Ejlskov carried out two surveys using MIP (Membrane Interface Probe) and soil sampling that delineated the extent of the contamination over 350 m2 and to depths of 10 m below ground level. The site presented challenges both in the subsurface, with a complex geology, and on the surface obstacles with oil refinery structures and utilities. A flexible drilling equipment and technical expertise enabled Ejlskov to optimise the remediation design with some unique approaches: a triangular injection grid pattern with vertical offset injection levels, high pressure top-down injection techniques, inclined injection holes, and adjustment of the lateral and vertical injection spacing in relation to the utilities.
Remediation technologies
Ejlskov proposed the in-situ injection of Trap & Treat® BOS 200®, a proven technology that is effective at remediating oil contaminated soils. It works by trapping the contaminants via carbon absorption, and by removing the contamination by biological degradation. These two mechanisms provide immediate contaminant mass-reduction and plume control. The product consists of an active carbon powder with calcium sulphate, nitrate, phosphate, and ammonia that is mixed a blend of microbes and water before being injected. Ejlskov included additional sulphate nutrients to the injected material to enhance the anaerobic microbial activity and accelerate the biological degradation of the oil contaminant.
Results
The initial 18 months of monitoring after the injection show that Ejlskov’s Trap & Treat® BOS 200® injection technology has already reduced the levels of total hydrocarbon in the groundwater to below the standard set by the Danish Environment Authority. Ejlskov is on track to handing over a fully-cleaned site to Shell within the time period promised.