Removal of releases of petroleum hydrocarbons and chlorinated hydrocarbons from soil and groundwater has been a nationwide effort since the mid-1980s. Successes have been rare. Mechanical removal systems have been found to require an inordinate amount of time. Bioremediation has used existing, added, or altered microorganisms to metabolize or biodegrade hydrocarbons. Problems with delivering the microorganisms directly to the hydrocarbon and specific site factors have combined to thwart or slow bioremediation.
Phytoremediation uses plants to biodegrade shallow soil contamination in the rhizosphere. Trees are used to extract groundwater from aquifers and simulate a pumping system for contaminated groundwater plume control. Simultaneously, the trees create a rhizosphere biodegradation zone and extract hydrocarbons through uptake in the transpiration stream. Phytoremediation is proposed for environmental cleanup of historical contamination as a method that will occur in place, at a reasonable cost, and require little maintenance.
The initiative of one major oilfield service company at a Louisiana site is described. The effort commenced in June 1995 with the planting of 92 hybrid poplar trees for the purposes of (1) controlling groundwater movement, (2) uptaking constituents from soil and groundwater, and (3) enhancing bioremediation of soil and groundwater in the rhizosphere. Results to date are reported.
Hydrocarbons in soil and groundwater have been the subject of thousands of laboratory experiments in search of removal and destruction techniques or technologies. To control the parameters that require analysis and monitoring, these experiments usually focus on one or a few specific hydrocarbons and use a consistent soil and water matrix. These ideal conditions are not duplicated in an actual site containing soil that is horizontally and vertically heterogeneous. If the site also has point sources of hydrocarbons, the range of concentrations can be orders of magnitude in both soil and groundwater.
One step up from laboratory pilot tests are bench tests that analyze the remediation techniques and new technologies on representative samples drawn from the actual site. The mere process of soil removal from the site can change the compaction of the sample. Combined with the greater surface area exposed to air or water in the laboratory column, the bench tests frequently produce more optimistic remediation time periods and greater destruction or removal efficiencies.
Aromatic hydrocarbons and chlorinated aliphatic compounds are some of the most common groundwater contaminants. Many aromatics are the more soluble components of gasoline, such as benzene, ethylbenzene, toluene, and xylene. Together with diesel components, they constitute the compounds normally found from leaking underground storage tanks and connecting fuel service lines or from overfills and spills.
The chlorinated hydrocarbon compounds were commonly used as degreasing solvents for truck and automobile repair and for pipe cleaning. P. 717
