Site contamination at ground or groundwater level is immensely difficult to remediate. Light non-aqueous phase liquid (LNAPL), a toxic mixture of petroleum hydrocarbon liquids and water, will infiltrate through soil and only stop when it encounters a barrier that can store the yield. However, it may move laterally as a continuous, free-phase layer, which can make clean-up almost impossible.
In Cardiff, South Wales, an oil terminal suffered a major tank failure that resulted in about 20,000 L of petroleum hydrocarbons gushing into the groundwater beneath the site. Remediation expert RemedX, an RSK company, was tasked with containing the contaminated plume and preventing it from entering controlled waters near the site.
To deliver optimal solutions for the client, the team ascertained the level of contamination and created a remediation strategy before carrying out a tidal assessment and a pilot study. Using the data, the team designed an LNAPL skimming system to operate 24/7, installed 28 wells close to the failed tank for groundwater monitoring and began remediation testing and skimming.
Specialist teams stored recovered petroleum in double-bunded product tanks in a secure location. The LNAPL recovery rate dropped from about 108 L per month immediately after the spill to an average of 7 L per month less than two years later. Consequently, the team switched off the skimming system and installed passive skimmers to continue shrinking the plume. Since the system has been operational, 650 L of LNAPL has been recovered. The project is ongoing.