Groundwater contamination remediation comes in three different techniques: containment, treatment, and monitoring natural attenuation.
1) Containment: These include items such as liners, curtains, grout, sheet piling, and caps to prevent water from infiltrating from the contamination to the groundwater. This remediation is preventative and is designed not to remove a contaminant plume but to stop spreading. The contamination could also be excavated to remove the bulk of the material. The remediation could also involve lowering the groundwater table so that it does not come into contact with the contaminant. Even if the ground water has been contaminated, containment of the remaining material is important to prevent further spreading. Containment is important because any contaminant that is prevented from spread saves millions in remediation.
2) Treatment: There are many types of treatment options including:
a. Soil Vapor Extraction: The contamination in the unsaturated zone is vented to the atmosphere.
b. Surfactants: Chemicals are injected into the groundwater contamination to “wash” clean the aquifer. Surfactants are often used in conjunction with another type of remediation because in areas of high heterogeneities the surfactants might not be able to come into contact with the entire plume. Like soap in the washer, surfactants can only clean the areas of aquifer with which it comes into contact.
c. Permeable Reactive Barriers: A carbon filter constructed underground in front of the plume that filters out the contaminant from the groundwater.
d. Pump and Treat: This remediation technique is widely used but has many problems associated with it. The pumping of the aquifer can spread the plume by smearing the contamination into the unsaturated zone when the water table drops around the cone of depression. A cone of depression is the downward facing cone created when wells are pumped. A late 80s early 90s study of pump and treat remediation found that 90% of the time they failed to meet their expectations of cleanup.
Not only can contamination by brought to otherwise clean areas, it can also stick to particles and not be mobile enough to be pumped out of the aquifer. Treatment of the contamination happens at the surface after the plume has been pumped out of the ground. Treatment usually consists of UV radiation treatment, wet air oxidation, or ozonization.
3) Monitoring: Monitoring the natural attenuation of the plume means to wait and allow the contamination to naturally breakdown and dissipate to acceptable levels. This process is enhanced by bioremediation. Bioremediation involves micro-organisms that naturally use the contamination for a food source. These organisms or enzymes can occur naturally in the aquifer or can be injected into the ground. As the organisms break the contaminant down, the plume begins to dissipate and diffuse, lowering the concentration. This remediation technique is not suited for all contaminants as there are many contaminants that are unaffected by bioremediation. Monitoring the natural attenuation of the plume is cheap, however, and is often recommended as a first option to other costly, high risk operations.
These groundwater contamination remediation techniques are not independently the answer. The best solution to cleaning up a plume in an aquifer is to start with prevention. Intuitive prevention is the number one source of best management practices. A combination of prevention, monitoring, and treatment should be used to have the best chance at cleaning up even the worst contamination problems.