Free moving objects are what most people will think of when they picture soil pollution. These can range from anything from a drinks can to military bullets, depending on the surrounding area and what the land was previously used for.
Free objects are arguably the easiest to tackle. Through classification and density separation, these items can be extracted for disposal or destruction (in the case of munitions) or reuse.
Contamination can be burnt or smeared on to soil following a fire, through excavation or when the water table fluctuates. Burning items can form liquid decomposition and cause leaching into groundwater or affect the long-term composition from the toxic ash residue.
Contamination that is smeared onto the material can be more difficult to ‘free up’ and requires further treatment in addition to density separation. Attrition cells or Counter Flow Classification Units (CFCU) are key technologies used to ensure ultrafine lightweights are separated from the soil.
Insoluble contaminants are less dangerous than their soluble counterparts as they are not mobile. That being said, some insoluble elements can become soluble under certain conditions. Soluble contamination is not visible to the naked eye but if left untreated, can do serious damage.
Soluble pollutants in the form of heavy metals such as zinc, mercury, nickel, as well as others, can contaminate groundwater and some can lead to illness in humans and animals. Not all heavy metals must be removed, however when levels are above regulations, they shouldn’t be ignored. The risk these contaminants present will largely depend on the soil environment and factors, such as acidity and the geology of the soil. For example, mercury is most toxic in its alkylated forms which are soluble in water and a soil of granular and free-flowing nature will allow for quicker leaching of the contaminant into natural water streams.
In addition, soil near the surface is most likely to be more contaminated initially but exposure to natural remediation mechanisms such as UV, water and oxygen usually mean that soil slightly below the surface is the most contaminated.
Soluble contaminants can be removed through soil washing techniques. This allows contamination to be isolated in the wash water and approved disposal methods to be applied. The safest and most effective techniques also employ advanced water treatment methods, to ensure that stubborn contaminants are removed.
There are many other ways to categorise soil contamination but the three discussed above are three of the most common. Although complex to tackle, with the right expertise and equipment, these three groups can be removed and treated for the land to be made safe again. Every contaminant found in soils (whether free object, smeared contamination, a soluble contaminant or other) has different requirements and different dangers. This means that an individual approach is always best. Governments, land owners and communities alike must consider contaminated soils as a priority, a problem that no longer should be avoided.
You might also be interested in our recent blog on the Aftermath of the UK Grenfell Tower disaster.
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 Wisconsin Department of Natural Resources, Smear Zone Contamination, https://dnr.wi.gov/files/PDF/pubs/rr/RR712.pdf [online] Accessed 30/04/2019
 Soil Care Network, Waste burning and toxic soil formation in urban areas, https://www.soilcarenetwork.com/single-post/2017/10/18/Waste-burning-and-toxic-soil-formation-in-urban-areas [online] Accessed 29/04/2019
 L. A. Smith, J. L. Means, A. Chen et al., Remedial Options for Metals-Contaminated Sites, Lewis Publishers, Boca Raton, Fla, USA, 1995.