Many heavily contaminated sites contain free products within the soils and water table. Removal of this free product is essential in remediating contaminated sites, as free-phase contaminants represent the largest reservoir of pollutants, allowing contaminants to migrate and cause further pollution.
There are two types of free products:
Free-phase product recovery is often combined with other treatment processes, such as soil vapour extraction (SVE), dual-phase extraction, ex-situ treatments, and bioremediation. It is rarely undertaken alone, except in the least sensitive environmental settings. Depending on physical properties, free product can be recovered as a liquid or vapour, and recovery can be enhanced through methods such as steam injection or surfactant flushing.
Free product recovery is applicable to a wide range of chemicals. Common free product contaminants include:
Free-phase product recovery can be conducted as an ex-situ method from open excavation, using floating or sinking skimmers, or via in-situ remediation methods. This can involve excavating or installing wells or trenches to access the free product. Skimmer or top-loading total fluid pumps are used to collect LNAPL free product, or product-only for low-intensity recovery where time is not a critical factor. Bottom-loading total fluid pumps are applied for DNAPL recovery. Collected free product is filtered and stored onsite before being sent off-site for recycling at a licensed facility. Volatile free products (e.g., petrol or xylene) can be volatilised using air sparging and recovered as vapour through dual-phase or high-vacuum systems.
Free product recovery equipment typically includes:
VertaseFLI has designed and operated numerous free-phase product recovery systems for both open excavation recovery and in-situ systems. One such system was deployed to remove LNAPL free product from a disused aluminium casting foundry in preparation for the site’s redevelopment.
The free product recovery system involved drilling 32 abstraction and monitoring wells, and using pneumatic top-loading total fluid and product-only pumps to remove the free product. The abstracted free product was filtered through a tilted plate oil-water separator and stored onsite, ready for off-site recycling.
This system ran automatically, requiring periodic maintenance checks over a 68-week period. A total of 16,800 litres of free product was removed, the majority during the first 28 weeks of operation. Despite the duration of the remedial works, the compact design and in-situ remediation techniques used by VertaseFLI ensured that remediation did not impact the redevelopment schedule.
The Vertase team were always polite and professional, both on calls and on site. Our H&S team were very impressed by Vertase.
Jo McKay
Managing Consultant, Ramboll UK, DS Smith
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