| decompose | To separate into component parts or cause to decay. |
| dense non-aqueous phase liquid (DNAPL) | One of a group of organic substances that are relatively insoluble in water and more dense than water. DNAPLs tend to sink vertically through sand and gravel aquifers to the underlying layer. |
| depleted uranium | After uranium ore is processed to remove most of the fissile isotope (235U), the residual material is referred to as depleted uranium. It is primarily used for purposes requiring high-density material, and is used in weapons fabrication. |
| desiccated | To dry up thoroughly. |
| desorption | The act of removing an absorbed or adsorbed substance. |
| diffusion | The process where molecules in liquid or gas move under the influence of kinetic energy along the direction of their concentration gradient. Diffusion is a special case of dispersion. |
| dioxins | Any of a family of compounds known chemically as dibenzo-p-dioxins. They are chemicals formed during combustion. They are extremely toxic. |
| dispersion | Mechanical mixing of a dissolved chemical as it flows through a solution. Dispersion causes chemicals to spread away from the straight-line pathway into a wider path. Temperature, pressure, and chemical forces in the aquifer drive the process. Diffusion is a special case of dispersion. |
| disposal | The final placement of toxic or other wastes. Disposal may be accomplished through the use of approved secure landfills, surface impoundment, land farming, deep well injection, ocean dumping. |
| DOE | The Department of Energy. |
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