The International Information Center for Geotechnical Engineers

Soil Vapor Extrusion

Contaminant and Site Suitability

Types of Contamination for Which SVE is Suitable

Typical contaminants that soil vapor extraction is applicable for are volatile organic compounds.  Volatile organic compounds (VOCs) are compounds that have a low boiling point and a high vapor pressure.  This low boiling point causes the molecules within the compound to evaporate from the liquid and enter into the air.  According to the World Health Organization (WHO), volatile organic compounds are classified by the boiling point to which they volatilize to the atmosphere (USEPA 2012a).   These classifications are divided into three categories; very volatile organic compounds (VVOCs), volatile organic compounds (VOCs), and semi volatile organic compounds (SVOCs).  The more volatile the contaminant is, the better SVE is at removing that particular contaminant.  Table 1 provides the VOC classification with their respective boiling points. 

Figure 2

Table 1. VOC Classifications (USEPA, 2012a)

Figure 3

 

Table 2. VOCs Considered to be Amenable to SVE (USACE, 2002)

Contaminants with this type of classification include petroleum and chlorinated compounds.  Table 2 provides a list of constituents that are suitable for SVE remediation systems.  The sources of these contaminants are usually caused by leaking underground storage tanks (USTs), fueling sites, and dry cleaners.  Some of the contaminants that are present in petroleum are BTEX compounds; benzene, toluene, ethylbenzene, and xylenes, where a common constituent that is leaked or spilled from dry cleaning operations is tetrachloroethene or perchloroethylene.  The boiling points for these substances range from 80°C to 144°C, which makes them all volatile organic compounds (Table 3).

Figure 4

Table 3. Method Detection Limits and Boiling Points for Volatile Organics (USEPA, 1996)

 

 Site Suitability

When determining the appropriateness of SVE for a particular contamination site, the soil type, permeability, and the level of the groundwater table are necessary factors to consider.  These factors are important because this process is applicable when the soils are fine to medium sands, highly permeable to permit greater air flow for better vapor extraction, and only appropriate in unsaturated soils (Sharma and Reddy 2004).  These soil types typically have a permeability greater than 10-6 cm/s, which allows for the contaminated vapor to flow around the soil particles.  SVE is best suited when the groundwater table is greater than 10 feet below the ground surface because upwelling can occur within the wells which can prevent soil vapor flow from occurring (USEPA 2012b).  A pump may be necessary when trying to implement SVE in an area where the water table is higher or if upwelling occurs near the extraction wells in order to draw down the water table so that the vadose zone is increased.  If the groundwater is contaminated as well a dual phase extraction (DPE) remediation technique should be used in order to extract the contaminated water and vapor which will go through a separator before treatment (USEPA 2012c).

  

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