Pollution can affect both soil and groundwater. Contaminants can enter the soil and groundwater through settled air emissions, spills and direct discharges. Geologists and engineers use a variety of treatment methods to clean the pollutants from the soil and groundwater. These methods range from slow, passive methods to fast, active systems. Each remediation method has pros and cons depending on the type and severity of the pollution, the geology of the area and the project’s budget and timeframe.
Soil Removal and Groundwater Extraction
Properties that have localized pollution often respond well to simple soil and groundwater removal procedures. You can excavate contaminated soil with a backhoe, contain the soil in a roll off or drum and properly dispose at a landfill or soil treatment facility. You can remove localized groundwater impact using one or more recovery wells by pumping the contaminated water out of the subsurface and treating the water. These methods work for a variety of constituents but become cost-prohibitive if the impact is widespread.
Dual Phase Extraction and Air Sparging
Volatile and semi-volatile constituents respond well to dual phase extraction and air sparging methods. Dual phase extraction treats both soil and groundwater by using a high-powered vacuum pump to extract groundwater and soil vapors. Conversely, air sparge treats groundwater contamination by pumping air into subsurface layers below the water table, causing constituents to volatilize and travel upwards through the subsurface to the atmosphere. Air sparging may use vapor extraction wells in the unsaturated soil zone to help remove volatilized constituents from the upper soil.
Injectables
Some of the newer treatment methods include injecting cleaning agents into the subsurface that stimulate pollutant degradation in the groundwater and soil. These methods are proven for a variety of constituents and are favorable for busy locations that cannot have equipment sitting on the land surface for extended periods. Once you inject the material into the subsurface, you can perform periodic sampling to monitor the progress of the degradation.
Phytoremediation
Phytoremediation is gaining popularity as the use of trees and shrubs is proven to reduce the concentration of contaminants in the subsurface. This method uses plants to uptake soil and groundwater pollution through their root system, which remediates the area. Numerous plants are effective for a variety of pollutants; therefore, site cleanup is achievable with the correct plant species and plant spacing.
Natural Attenuation
Natural attenuation, or monitored natural attenuation, is a method of treatment where constituents naturally degrade in the subsurface due to the presence of microorganisms that feed on organic matter. Natural attenuation works well for organic constituents like gasoline that readily degrade. Continued monitoring is necessary to ensure proper remediation of the area. Natural attenuation is often used in conjunction with active remediation methods to complete the cleanup process.
References:
United States Environmental Protection Agency; Green Remediation: Best Management Practices for Excavation and Surface Restoration; 2008
United States Environmental Protection Agency; Pump-and-Treat Ground-Water Remediation; 1996
United States Environmental Protection Agency; Dual-Phase Extraction; 1994
United States Environmental Protection Agency; Air Sparging; 1994
In Situ Remediation at a Brownfield Site in Pennsylvania using Reinjectable Points; L. Donald Ochs and Baxter E. Duffy
Rensselaer Polytechnic Institute; Phytoremediation of Soil and Organic Compounds; Nathan Florio and Hayes Rembijas; 1997
American Society of Plant Biologists; Phytoremediation: Using plants to remove pollutants from the environment; Ilya Raskin, et al; 1997
University of Washington: Phytoremediation Research at the University of Washington
United States Environmental Protection Agency; Monitored Natural Attenuation of Petroleum Hydrocarbons; Daniel F. Pope and Jerry N. Jones; 1999
Tracy Barnhart - Over the last 16 years, I have worked for several environmental consulting firms as a Professional Geologist specializing in the ...
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