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C#06,9cra l Tecknus Inc Page 6 In Situ Remediation Feasibility Study Project No 507 2 September 20,2002 1 3 2.2 Concerns & Limitations ' A number of factors keep vapor extraction from being a promising technology at the site • Shallow depth to groundwater Thin vadose zones are problematic to vapor extraction due to the tendency of the air to short circuit to the ground surface The shallow depth to groundwater would also create a problem with groundwater mounding • Low permeability of vadose zone soils The vadose zone materials at the site are primarily composed of clays, which have low permeability Low permeability soils create problems for vapor extraction systems by limiting the radial influence of the extraction wells and make this option very ineffective A blower with high vacuum ' potential must be used which increases energy consumption 01� 3.3 Aar Sparging ' 3 3.1 Technology Review Air sparging is the process of infecting air into the aquifer to volatilize contaminants from ' the groundwater These contaminants are captured in the vadose zone and removed with the use of a vapor extraction recovery system The addition of air into the aquifer also aids in increasing the rate of natural degradation by supplying oxygen to an otherwise anaerobic environment 3 3.2 Concerns & Limitations The same factors that limit vapor extraction from being effective at the site also limit the use of air sparging They are summarized as follows • Shallow depth to groundwater A thin vadose zone makes capturing the vertically migrating vapors more difficult and increases the possibility that short-circuiting of the vapors could occur This would lead to releasing uncontrolled emissions to the ' atmosphere Low permeability of vadose materials The soil is a low permeable clay rich material, which inhibits airflow through the subsurface • Low permeability of aquifer materials The aquifer materials at the site are primarily composed of clays and silts, which have low permeability Low permeability soils create problems for sparging systems because the injected air does not easily or freely move through the aquifer ate_ 3.4 In-Situ Chemical Oxidation 3.4.1 Technology Review Advanced oxidation processes (AOPs) are processes that create and use a highly reactive radical that effectively oxidize MTBE and other organic compounds by chemical reaction The most prominently used radical is the hydroxyl radical, designated as OH The OH ion will capture a hydrogen atom from a molecule of contaminant, which then causes the contaminant molecule to become unstable and breakdown further The end products of this