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What is free product?

Free product, also known as free phase contamination, refers to concentrated contaminants that are not miscible with groundwater and therefore form a separate layer. There are two types of free product:

  • Light non-aqueous phase liquid (LNAPL). These contaminants are less dense than water and float on the surface. Examples include diesel, kerosene and lubricating oils.
  • Dense non-aqueous phase liquid (DNAPL). These contaminants are more dense than water and sink through groundwater until they reach an impermeable layer such as clay, or until they enter fissured bedrock. Examples include creosote and chlorinated solvents such as trichloroethene.

Removal of free product is important for remediation of any contaminated site as it forms a concentrated source of contamination that is likely to migrate causing further pollution. Once the free product has been effectively removed, it is usual practice to clean up the remaining soil bound and dissolved contamination by another method, for example in-situ chemical oxidation or in-situ bioremediation.

telluric bullet Recovery of free product

Where free phase oil is present on the groundwater, this can be efficiently removed by various means including pumping from abstraction boreholes or trenches. Product-only pumps are useful where large amounts of oil are present. These intrinsically safe, pneumatically operated pumps contain a hydrophobic filter which allows oil through but not water. Recovered oil is automatically pumped into an above ground bunded storage tank. 

Total fluids pumps can be top or bottom loading and will pump any liquids present including LNAPL, such as oils, and DNAPL, for example trichloroethene. The fluids are pumped to an above ground plant for processing. Separated and cleaned groundwater is disposed to foul sewer or soakaway and the oil is removed from site for recycling. LNAPL can also be recovered using dual phase extraction, which simultaneously removes dissolved phase and vapour phase hydrocarbon contamination.

telluric bullet Free product recovery equipment

As already mentioned, there are various ways of recovering free product and the choice of equipment will depend on site specific ground conditions, type and extent of contamination, budget and timescales. Some common items of equipment that we use for the recovery of free product include:

  • Floating skimmers – for removal of floating oil (LNAPL) from excavations or trenches.
  • Abstraction pumps, either top loading (LNAPL) or bottom loading (DNAPL). These can be product-only pumps or total fluid pumps.
  • Compressor station – for pneumatic pumps.
  • A dual phase extraction system.
  • Free product storage tank.
  • Oil-water separator.
  • Activated carbon adsorption vessel – for the removal of dissolved hydrocarbons from any abstracted groundwater.
  • Control systems to automate the remediation process.

 telluric bullet Free product recovery case studies

  1. Land Remediation Following Domestic Heating Oil Spill
  2. Contaminated Groundwater Remediation, London
  3. Contaminated Land Remediation by Dual Phase Extraction
  4. Contaminated Land Remediation on a Housing Development Site
  5. Remediation of Hydrocarbon Contaminated Groundwater
  6. Creosote Contaminated Soil and Groundwater Remediation

If you need any advice, Telluric will be happy to help you

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