**2. Remediation techniques**

The comprehensive objective of any soil remediation approach is to create a final solution that is protective of human health and the environment. The remediation strategies should incorporate reduction of metal bioavailability and the reduction should be demonstrated for a long term, only if the reduction of heavy metal is equated to reduced risk [14].

A successful process of remediation includes the following steps: 1) Technology pre-screening and treatability study scoping; 2) Remedial investigation of the contaminated site; 3) Feasibility study of pre-screened remediation technology; 4) Determination of best remediation method; 5) Design and implementation of remediation practices; 6) Evaluation and monitoring of remediation process; 7) Depletion in concentration and/or removal of toxic metal [15].

Various remediation techniques applied to soil can be employed via *ex-situ* or *in-situ* methodologies. Although the *ex-situ* methodology of soil remediation is less expensive, fast, and easier to apply, it generates a significant amount of waste product that must be treated before storing or releasing it in the landfill sites. While *in-situ* remediation methodology involves low land disturbance, applicable to a broad range of inorganic pollutants, lesser in cost, and reduced risk of spreading contamination. Broadly various remediation techniques known for improving the quality of contaminated soil are studied under three categories of their application:


#### **2.1 Physical remediation techniques**

The remediation techniques that are applied through physical amendments to the soil are incorporated under this category. The physical techniques of remediation include the capping of contaminated sediments, washing, and excavation of soil.

#### *2.1.1 Capping*

It is a non-intrusive and cost-effective method for remediating contaminated sediment. The technique is utilized to decrease the solubility, mobility and transfer

#### *Conventional and Contemporary Techniques for Removal of Heavy Metals from Soil DOI: http://dx.doi.org/10.5772/intechopen.98569*

rate of heavy metals in the sediment [16]. It is usually applied in sub-aqueous conditions. Sandy material and apatite are usually tiered in specific proportions, which are placed on the contaminated sediment like a cap. The cap is usually composed of a, (i) stabilizing base layer which supports the added weight of cap; (ii) an isolation base layer, it isolates the contaminants from the sediment; (iii) a filter layer for hydraulic protection for the base layer; (iv) an armor layer, it inhibits erosion for the protection of filter and base layer. Capping can be performed in two ways, Passively (inactive) or Reactively (active). The former methodology includes a cap composed of clean and neutral material which provides a physical barrier between the environment and contaminated sediment. However, passive methods have been observed to cause leaks of toxic metals. The latter methodology includes the cap with reactive material which can reduce the mobility, toxicity, and bioavailability of contaminants in sediments. This technique is not appropriate for shallow water or marshes or water bodies with large water flows as the capping material can be washed away [17]. Below is a graphical representation of the capping methodology (**Figure 3**) [18].
