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NAPL

The term NAPL is an abbreviation for non-aqueous phase liquids. These substances are organic hydrocarbons in a liquid phase that are generally insoluble in water.

NAPL represents the "free product phase" of contamination—the actual liquid pollutant in the subsurface, not just dissolved traces in groundwater. When present in sufficient quantities, NAPL becomes mobile and slowly releases contaminants into surrounding soil and groundwater over extended periods.

1. LNAPL (Light Non-Aqueous Phase Liquid)

These liquids are lighter than water and float on the groundwater surface. LNAPLs accumulate in the fluctuation zone where the water table rises and falls seasonally, creating a contamination "smear" across this vertical interval. 
Common examples: Mineral oil hydrocarbons, petroleum products (gasoline, diesel, heating oil), monoaromatic compounds (BTEX)
Typical sources: Leaking fuel tanks, gas stations, industrial oil spills

2. DNAPL (Dense Non-Aqueous Phase Liquid)

These substances are heavier than water and sink through the groundwater until they reach an impermeable layer at the aquifer base. DNAPLs can pool in subsurface depressions, creating persistent contamination sources.

Common examples: Chlorinated solvents such as tetrachloroethylene and trichloroethylene, halogenated aromatic compounds
Typical sources: Dry cleaners, metal degreasing facilities, chemical manufacturing sites


Held, T., & Gerschütz, S. (2021). Management of contaminated sites of the petrochemical industry. Umweltbundesamt, Arcadis GmbH.

Hilberg, S. (2022). Umweltgeologie: Eine Einführung in Grundlagen und Praxis. Springer. https://doi.org/10.1007/978-3-662-65365-4