What are DNAPL and LNAPL?

gasoline
Posted: July 24, 2017
Category: Groundwater
Tags: disposal, dnapl, gasoline, lnapl, pollutants

Non-aqueous Phase Liquids are hazardous organic liquids such as dry cleaning chemicals, fuel oil and gasoline that do not dissolve in water.  They are always associated with human activity, cause severe environmental and health hazards, and are difficult to remove from the water supply once it has been compromised.  DNAPL & LNAPL are the two major categories of these pollutants.

DNAPL

DNAPL or “Dense Non-Aqueous Phase Liquid” is denser than water and does not dissolve in water.  When DNAPL is spilled it infiltrates the ground, contaminates the groundwater and then sinks below the water table, only stopping when it reaches impermeable bedrock. Since they can be so far below ground surface, they are difficult to find when investigating sites for contamination.

Examples of DNAPLs:

  • Chlorinated solvents
  • Coal tar, creosote, PCB’s
  • Extra heavy crude oil

LNAPL

LNAPL or “Light Non-Aqueous Phase Liquid” is lighter than water and non-soluble in water.  For LNAPL is less dense the water, when it is spilled it infiltrates the ground but remains on top of the water table.

Examples of LNAPLs:

  • Gasoline
  • Benzene
  • Toluene
  • Xylene and other hydrocarbons

lnapl and dnapl

It is almost impossible to remove all of the NAPLs once they are released into the ground and an aquifer contaminated with these substances can remain for tens or hundreds of years. It will probably never become drinking water quality again.  These pollutants can often also move quite rapidly through the ground determined by the porosity of the ground and the chemical viscosity of the spill.

Many different treatment techniques have been developed to deal with these contaminants and new methods are still being developed.  Pump and treat, where contaminated ground water is removed, treated and then reintroduced to the aquifer is quite common in dealing with LNAPL, but with DNAPL it can be much less efficient.  A monitoring oil well skimmer can be employed to remove LNAPL from the surface of the well and also often DNAPL from the bottom of the well.

Randle Reef in Hamilton Harbour is an extreme example of this type of contamination.  It is so severe that remediation is not even being attempted, but rather a 6.3 hectare containment facility is currently being constructed in the middle of the harbour into which the surrounding polluted sediment will be placed and sealed.

hoil-bag

To determine the presence of these liquids, Heron Instruments manufactures the perfect tool.  Our H.0IL interface meter will indicate the presence of any NAPL as well as the depth of the contaminant level, whether LNAPL or DNAPL.  We also have the Sm.0IL, available in a 20m length, for use in shallow wells or tanks.  A visual and audible signal will be given at the top of the layer and at each interface.  Both these meters are CSA Class 0 Certified Intrinsically Safe and boast a Kynar jacketed, high tensile steel core tape able to withstand hydrocarbons, solvents and other harsh contaminants.

 

 

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