U.S. EPA Contaminated Site Cleanup Information (CLU-IN)

U.S. Environmental Protection Agency
U.S. EPA Technology Innovation and Field Services Division

Dense Nonaqueous Phase Liquids (DNAPLs)

Chemistry and Behavior

Multi-Component Waste

Because mixtures are often made from different feedstocks, their composition is extremely variable. The materials considered mixtures for this DNAPL classification lack a predominant chemical component in association with lesser additives or contaminants. Instead they contain hundreds of individual chemicals that can have vastly different chemical properties and behaviors when considered separately.

All of the DNAPL mixtures are more viscous than water—some much more so—and they have a wide range of solubility, Koc, and Kow values. Common components, such as some polycyclic aromatic hydrocarbons with high Kow values, have a tendency to bioaccumulate.

When released to ground water or surface water, mixtures typically behave differently based on their constituents. Coal tars and creosotes sink when released to ground water or surface water. Heavy oils, represented by bunker C and marine fuels, can float, sink, or be neutrally buoyant, depending upon the components used to make them—which can be different every time a product batch is made. Once in the water the more soluble components move into a dissolved phase. Some heavy oils that are released to surface water may float initially but eventually sink after the lighter components have volatilized.

While some components of DNAPL mixtures are biodegradable, if they separate from the mass by dissolving or volatilizing, many are very recalcitrant to biodegradation. Large masses of coal tars have been found at gas manufacturing plants that have been closed for 50 to 100 years.

For Further Information

Adobe PDF LogoEvaluating Potential Exposures to Ecological Receptors Due to Transport of Hydrophobic Organic Contaminants in Subsurface Systems
Ford, R.G., M.C. Brooks, C.G. Enfield, and M. Kravitz.
EPA 600-R-10-015, 69 pp, 2014

Detailed discussion of enhanced transport mechanisms is the focus of this technical paper. It recommends several types of screening assessments to evaluate site conditions for the potential to enhance transport of HOCs—PCBs, dioxins, fuels (including the influence of MTBE), and creosote and tar DNAPL—as well as site artifacts that result from inadequate well installation and sampling procedures within a groundwater monitoring network. These assessments are incorporated into a suggested three-tiered decision analysis process that provides a summarized view of the upland contaminant-source characteristics that need evaluation to establish whether facilitated transport of HOCs might occur at a given site.