remediation projects under CERCLA under the Resource Conservation and Recovery Act Dense nonaqueous phase liquids (DNAPLs), have low solubility and are with viscosity markedly lower and density higher than water-asphalt, heavy oils, lubricants and also chlorinated solvents-penetrate the full depth of the aquifer and accumulate on its bottom. "DNAPL movement follows the slope of the impermeable strata underlying the aquifer and can move in the opposite direction to the groundwater gradient." Groundwater remediation technologies have been developed that can address DNAPL in some settings. Excavation is not always practicable due to the depths of the DNAPL, the dispersed nature of the residual DNAPL, mobility caused during excavation, and complexities with near-by structures. Technologies that are emerging for treatment include the following in situ chemical oxidation (ISCO) potassium permanganate hydrogen peroxide (with or without an iron catalyst) ozone sparging persulfate in situ enhanced reductive dechlorination in situ surfactant flushing air sparging heating Most DNAPLs remain denser than water after they are released into the environment (e.g. spilled trichloroethene does not become lighter than water, it will remain denser than water). However, when the DNAPL is a more complex mixture, the density of the mixture can change over time as the mixture interacts with the natural environment. As an example, a mixture of trichloroethene and cutting oil may be released and originally be denser than water—a DNAPL. As the mixture of trichloroethene and oil is leached by groundwater, the trichloroethene may preferentially leach out of the oil and the mixture may become less dense than water and become buoyant (e.g. the liquid may become an LNAPL). Similarly changes can be seen at some coal gasification plants or manufactured gas plants where the tar mixtures can be denser than water, be neutrally buoyant or be less dense than water and the densities can change with time. See also NAPL LNAPLs (light non-aqueous phase liquids) - water immiscible liquids that are lighter than water. External links USEPA's web page on DNAPL: http://cluin.org/contaminantfocus/default.focus/sec/Dense_Nonaqueous_Phase_Liquids_(DNAPLs)/cat/Overview/ Interstate Technology & Regulatory Council (ITRC) page on DNAPL: http://www.itrcweb.org/guidancedocument.asp?TID=8 ITRC Integrated DNAPL Site Strategy technical/regulatory guidance: http://www.itrcweb.org/documents/IntegratedDNAPLStrategy_IDSSDoc/IDSS-1.pdf References Organochlorides Hydrogeology