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

Halogenated Alkanes

Three classes of halogenated alkanes are considered in this section: methanes, ethanes, and propanes. The 17 chemicals profiled are the halogenated alkanes commonly found at Superfund sites and do not represent the universe of DNAPL alkanes.

All the chemicals addressed are volatile (i.e., vapor pressure equal to or greater than 0.1 mm Hg (Lewis 2001). Many of these chemicals are less viscous than water, and their calculated log Koc values indicate they will be mobile in the subsurface. Their water solubilities fall in the range of 170 mg/L (1,1,2-trichlorotrifluoroethane) to 20,000 mg/L (methylene chloride), which in most cases are orders of magnitude above their risk-based health concentrations.

All of the profiled DNAPL alkane chemicals are anaerobically biodegradable to some extent in the presence of an appropriate microbial consortium, which may or may not be present at a specific site. Some of the ethanes and methanes are also aerobically biodegradable.

All of the alkanes have moderate (e-04 atm-m3/mol) to relatively high (e-01 atm-m3/mol) Henry's constants and can be expected to form vapor plumes that emanate from the source area and the dissolved-phase plume, making them likely candidates for vapor intrusion into buildings. In shallow aquifers, vapor plumes can be traced by soil gas survey.

None of the alkanes are expected to bioaccumulate to an appreciable extent (log Kow range of 1.3 to 2.64), and all have relatively short half lives in surface water (i.e., a dissolved phase of hours to days) (Cohen and Mercer 1993 and Lewis 2001).

For Further Information

DNAPL Site Evaluation Adobe PDF Logo
Cohen, R. and J. Mercer. EPA 600-R-93-022, 369 pp, 1993

Hawley's Condensed Chemical Dictionary, Fourteenth Edition
Lewis, R. John Wiley & Sons, Inc., 1,223 pp, 2001