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Soil Washing

Advantages

There are several advantages associated with using soil washing as a remediation technique. As a volume reduction technique, soil washing is very cost effective when it can reduce the amount of soil that needs further treatment or disposal. Soil washing, when performed under ideal conditions, can lead to a volume reduction of approximately 90% of the originally contaminated soil (Sharma and Reddy 2004). Since soil washing is performed on-site, the large volume of soil that is not contaminated after washing can be reused as backfill at the site.    

Additionally, soil washing is performed on site in a closed system where the conditions, such as pH level and temperature, of the soil being treated can be controlled and closely monitored (Sharma and Reddy 2004).  This on-site system saves money and time and generally the process can be run at a very high rate of around 100 cubic yards per day (US EPA 1996). The process also can remove a range of contaminants, both organic and inorganic, from the soil at the same time. Soil washing also only requires a few permits in order for it to be used, making it a relatively easy method to employ (Sharma and Reddy 2004).

 


Disadvantages

There are also several disadvantages associated with using soil washing as a remediation technique. Soil washing requires a large area in order to set up the system (described in the following section). This could be an issue based upon the setting of the site. Soil washing is also predominantly effective with soils that are very coarse.  The higher the percentage of coarse grains the more successful soil washing will be at remediating a contaminated site.   This means that at very silty or clayey sites soil washing will not work very well as it will not reduce the volume of contaminated soils quickly as it would with a gravely soil. Further treatment of the soil through other more expensive treatment methods would then be necessary and the use of soil washing under these circumstances might not save any time or money. In general, soil washing is ineffective for soils containing more than 30 to 50% silt, clay or organic matter (Sharma and Reddy 2004, US EPA 1993).

 

Another disadvantage is that the used wastewater, which often contains chemical additives, may need specialized treatment which is generally difficult to do and expensive. At the end of the process there may also remain small volumes of contaminated sludge that require further treatment or disposal off site.  Air emissions from cleaning equipment are another factor that can also increase the cost of the operation while reducing its appeal. Finally, exposure of the public to contaminants is also a concern as all the contaminated soil is being excavated and handled ex situ (Sharma and Reddy 2004). All of these factors will need to be accounted for before deciding upon soil washing as a part of the remediation process of choice.

 

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