Short for Dense Non Aqueous Phase Liquid. Generally considered the most difficult class of contaminants to remediate in groundwater. A DNAPL is a hydrophobic substance, like an oil, which is denser than water. As a result, it can sink to great depths, which makes recovery difficult. The only thing stopping a sinking DNAPL plume is the interstitial capillary forces present in grain pore spaces. Sometimes, methods intended to clean up a DNAPL plume can actually worsen the problem. One example is when the DNAPL comes to rest on perched layer of clay material, and drilling through it opens a new pathway for its movement.

Contrast LNAPL.