Light Nonaqueous Phase Liquids

Nonaqueous phase liquids (NAPLs) are hydrocarbons that exist as a separate, immiscible phase when in contact with water and/or air. Differences in the physical and chemical properties of water and NAPL result in the formation of a physical interface between the liquids which prevents the two fluids from mixing. Nonaqueous phase liquids are typically classified as either light nonaqueous phase liquids (LNAPLs) which have densities less than that of water, or dense nonaqueous phase liquids (DNAPLs) which have densities greater than that of water. A previous issue paper developed by the Robert S. Kerr Environmental Research Laboratory reviews processes and management issues pertaining to DNAPLs (Huling and Weaver, 1991). Light nonaqueous phase liquids affect groundwater quality at many sites across the country. The most common LNAPL-related groundwater contamination problems result from the release of petroleum products. These products are typically multicomponent organic mixtures composed of chemicals with varying degrees of water solubility. Some additives (e.g., methyl tertiary-butyl ether and alcohols) are highly soluble. Other components (e.g., benzene, toluene, ethylbenzene, and xylenes) are slightly soluble. Many components (e.g., n-dodecane and n-heptane) have relatively low water solubility under ideal conditions. Physical and chemical properties which affect transport and fate of selected LNAPL compounds and refined petroleum products are presented in Table 1. In general, LNAPLs represent potential long-term sources for continued groundwater contamination at many sites.