Soil vapor extraction design

A U.S. EPA study (41) showed that soil vapor extraction (SVE) is an effective treatment for removing volatile contaminants from the vadose zone. Sandy soils are more effectively treated than clay or soils with higher organic content because higher air flows are possible in sand and clays—organic soils tend to adsorb or retain more contaminants. Removal of volatiles is rapid in the initial phase of treatment and thereafter decreases rapidly thereafter-an important consideration in the design of air emissions control over the life of the project. 

A pilot soil vapor extraction test was performed to determine whether this method would be effective to mitigate the concern. Such a test provided information used to design a full-scale recovery and vapor treatment system. With air permeabilities on the order of 1 to 3 D and TPH vapor concentration on the order of 330 ppm (weight), the pilot test supported SVE as a viable remediation approach. 

CONCEPTUAL DESIGN SOIL VAPOR EXTRACTION (SVE) SYSTEM... 

Conceptual Design for the Soil Vapor Extraction System... 

VESTRIP is a system designed for the in situ treatment of soils contaminated with volatile organic compounds (VOCs) benzene, toluene, ethylbenzene, and xylenes (BTEX) and other contaminants that are amenable to soil vapor extraction (SVE). The vendor, Ejector Systems, Inc. (ESI) has combined the key components of SVE systems with an air stripper to form a product that performs the functions of both. The name, VESTRIP, is a contraction of VES (vapor extraction system) and air stripping. 

Spartech is a mobile system designed for the removal of volatile contaminants from aquifers. It is a patented air sparging system that works by bubbling air through an aquifer and is essentially an in situ method of air stripping. The volatilized contaminants may be recovered by using a soil vapor extraction (SVE) system or similar device. 

NEPCCO SoilPurge soil vapor extraction systems are noncontacting, oil-free, explosion-proof vacuum systems designed to remove volatile organic compounds (VOCs) from soil in situ. According to the vendor, benzene, toluene, ethylbenzene, and xylenes (BTEX), chlorinated solvents and other hydrocarbons can be treated with SoilPurge systems. The technology can also remove radon from soil. 

Paragon has designed a system that combines soil vapor extraction (SVE) and oxidation tech-niqnes to remediate petrolenm-contaminated soils. The technology uses an SVE unit to volatihze petroleum hydrocarbons. The off-gases from this unit can then be treated using either a thermal or a catalytic oxidation method. The technology is no longer commercially available. 

Corrective action can be a combination of passive and aggressive actions designed to reduce constituent concentrations to levels considered protective of human health and the environment. These can include natural attenuation, soil vapor extraction, source removal, etc. In each case, the type of corrective action is selected to meet the remediation goals (i.e., RBSLs or SSTLs) developed under the appropriate tier for the site. This allows the project to focus only on those areas or media posing a threat to human health or the environment. 

This book assesses soil vapor extraction (SVE) technology and summarizes an expert workshop on SVE sponsored by EPA. This summary identifies current SVE technologies as welt as additional research needed In such areas as site characterization, pilot systems, full-scale system design and operation, attainment of cleanup criteria, and closure monitoring. 

One category of the vadose zone treatment technologies which has been apphed in relatively numerous instances is soil vapor extraction (SVE) (with or without the introduction of air) (Hutzler et ai, 1989 Johnson et ai, 1990, 1994). The most effective apphcations of SVE employ careful control of apphed vacumn through designed extraction points about which are arrayed air introduction points to ensure airflow through the most contaminated zones. Figure 6a shows a typical SVE process diagram (NRC, 1994). Success with SVE methods has been more difficult to achieve where toxic nonvolatile compoimds are present in the source, or where permeabihty of the subsurface limits the zone influence of gas flow. 

A major advantage of air sparging is that it requires only simple materials to constmct a field system. No special equipment needs to be designed and all equipment used is easily obtained. Equipment required for the air injection system and soil vapor extraction system is summarized in this section. 

The determination of explosives in soils has been mostly commonly associated with the detection of unexploded ordnance such as land mines (both anti-personnel and anti-tank). Chambers et al. [70] designed sampling subsystems for soil/vapor sampling. A probe was used to extract and concentrate vapors of explosives in the pore volume of soil in the vicinity of land mines with sub-part-per-biUion detection limits for TNT and related explosive munitions compounds [70]. As an... 

The two-phase vacuum extraction (TPVE) technology allows for the in situ remediation of soils and groundwater contaminated with volatile organic compounds (VOCs). Two-phase vacuum extraction is similar to conventional vapor extraction in the equipment required, with the exception that it is designed to actively remove contaminated groundwater from the extraction well along with the vapor-phase contamination. 

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