A 12-15 m3 gasoline spill was discovered in 2003 at a main Shell retail petrol station on the outskirts of Copenhagen. Since the spill, Shell had worked in close cooperation with the local municipality to prevent the contamination from spreading to the drinking water aquifer, and a range of remedial efforts had been implemented but without reaching satisfactory results. In April 2012 a pilot test to assess the effectiveness of Trap & Treat® BOS 200® was conducted in conjunction with a full scale Remedial Design Characterization (RDC) event. The positive results from these actions allowed Ejlskov to refine the conceptual site model and to sign with Shell a performance-based remediation full scale contract.
The solution
A full-scale Trap & Treat® BOS 200® in-situ treatment was provided by Ejlskov, effectively putting an end to the risk of further contamination spread and, in accordance to the agreed performance and timeframe strategy, bringing the site into alignment with environmental requirements set by the local authorities. In addition, Shell could benefit from the lower level of interruptions this technology caused to everyday operations at the station as this was clearly stated by the client as a major business objective.
Services provided by Ejlskov
Full-scale application of Trap & Treat® BOS 200® in-situ remediation on a performance-based contract, including:
- Remedial design characterization (RDC)
- Injection planning, on-site implementation and management
- Groundwater monitoring programming
Remediation process and results
During the pilot test, initiated April 2012, approximately 4,000 kg BOS 200® mix was injected across an approximate 100 m2 area. As part of the full-scale RDC, 27 MIP points, approx. 300 soil samples and 50 GW samples were collected. The comprehensive analytical and qualitative data from these samples along with the results obtained from prior pilot test, enabled Ejlskov to draw up a precise and efficient remedial injection plan for the finalization of a full-scale site cleanup.
Remediation works were performed under two separate phases between October 2014 and May 2015 while the station maintained mostly active. A period of 10-12 weeks was used by the client to refurbish the entire site building and dispenser area. In the same period Ejlskov performed injection works within the dispenser islands area and in between the underground storage
tanks. For this work a total of 287 injection points (all carefully pre-cleared via vacuum excavation) were performed on a 2.3 m triangular spacing grid targeting depths between 5 and 15 m bgl (or to bedrock).
In total, approximately 72,000 kg of BOS 200® and 1,200 liters of facultative bacteria were injected in the subsurface. At completion of the task, after surface refurbishment works, the retail station was delivered back to the client in brand new conditions, and the environmental end targets set for the site could eventually be fulfilled:
- Achievement of Danish EPA’s requirements regarding <1 ug/l benzene in the primary limestone aquifer.
- No re-occurring LNAPL in any of the monitoring wells.
- Fullfillment of risk-based clean-up criteria of <500 ug/l (on average) in the boulder clay formation located above primary limestone aquifer.