You have a contaminated site which you need to clean up – what groundwater clean up options might you consider?
Remediation of brownfield sites often involves dealing with mobile contamination which has been derived from the contaminants present in soil entering the controlled waters – either through leakage/ingress into groundwater beneath or nearby surface waters. The approach to clean will depend upon the nature of the contaminants present in the groundwater however the techniques below illustrate the types of options available.
In Situ Biological Treatment for Ground Water, Surface Water, and Leachate
The main advantage of in situ treatment is that it allows ground water to be treated without being brought to the surface, resulting in significant cost savings. In situ treatment, however, generally requires longer time periods, and there is less certainty about the uniformity of treatment because of the variability in aquifer characteristics and because the efficacy of the process is more difficult to verify.
Bioremediation techniques are destruction techniques directed toward stimulating the microorganisms to grow and use the contaminants as a food and energy source by creating a favorable environment for the microorganisms. Generally, this means providing some combination of oxygen, nutrients, and moisture, and controlling the temperature and pH. Sometimes, microorganisms adapted for degradation of the specific contaminants are applied to enhance the process.
Biological processes are typically implemented at low cost. Contaminants are destroyed and little to no residual treatment is required. Some compounds, however, may be broken down into more toxic by-products during the bioremediation process (e.g., TCE to vinyl chloride). Where this occurs during in situ applications, these by-products may be mobilized in ground water if no control techniques are used and care is required to manage this potential impact.
Although not all organic compounds are amenable to biodegradation, bioremediation techniques have been successfully used to remediate ground water contaminated by petroleum hydrocarbons, solvents, pesticides, wood preservatives, and other organic chemicals. Bioremediation has no expected effect on inorganic contaminants.
In Situ Physical/Chemical Treatment for Ground Water, Surface Water, and Leachate
Physical/chemical treatment uses the physical properties of the contaminants or the contaminated medium to destroy (i.e., chemically convert), or separate the contamination. Passive treatment walls separate and destroy the contaminant from in situ ground water. Air sparging, directional wells, dual phase extraction, fluid/vapor extraction, and hot water or steam flushing/stripping are separation techniques.
Available in situ physical/chemical treatment technologies include air sparging, bioslurping, directional wells, dual phase extraction, thermal treatment, hydrofracturing, in-well air stripping, and passive/reactive treatment walls. Physical/chemical treatment is typically cost effective and can be completed in short time periods (in comparison with biological treatment). Equipment is readily available and is not engineering or energy-intensive.
Ex Situ Biological Physical/Chemical Treatment for Groundwater, Surface Water, and Leachate
The main difference between in situ and ex situ biological or physical/chemical treatment is that it requires pumping of groundwater, leading to increased costs and engineering for equipment, likely permitting, and material handling. The main advantage of ex situ treatment is that it generally requires shorter time periods and there is more certainty about the uniformity of treatment because of the ability to monitor and continuously mix the groundwater.
Containment Technologies for Ground Water, Surface Water, and Leachate
Containment measures are often performed to prevent, or significantly reduce, the migration of contaminants in soils or ground water. Containment is necessary whenever contaminated materials are to be buried or left in place at a site. In general, containment is performed when extensive subsurface contamination at a site precludes excavation and removal of wastes because of potential hazards and/or unrealistic cost.
The main advantage of containment methods is that they can prevent further migration of contaminant plumes, and allow for contaminant reduction at sites where the source is undetermined, inaccessible, or where long term remedial actions are being developed. Available containment technologies include physical/biological barriers e.g slurry walls.