Soil vapor extraction application

Ideally, the site characterization study has defined the vertical and horizontal extent of the contamination. Contoured site maps showing the (three-dimensional) distribution of the contaminants allow identification of areas that require extensive restoration, or may be allowed to be monitored to closure under natural attenuation. Knowledge of how much contamination exists and its location is the important first step in the remediation process. Evaluation of these data will permit consideration of the various remediation remedies available. Where the contaminant is contained within the shallow (<6 m) unsaturated zone and is recalcitrant (not readily biodegradable), excavation for off-site treatment or disposal may be the most expeditious procedure. Alternatively, depending on the contaminant, a variety of in situ procedures, including bioremediation, air sparging, soil vapor extraction, and fixation, may be applicable. 

SPSH has several advantages. It is applicable to sites where contaminants are present as non-aqueous-phase liquids (NAPLs). The technology reduces volatile organic carbon (VOC) removal time to a few weeks for a typical site, whereas soil vapor extraction (SVE) alone requires years for remediation. This reduction in removal time can signrhcantly decrease costs over SVE (from 2 to 10 times). Excavation and ex situ soil treatment is typically much more expensive to implement than SPSH, especially at deep sites. 

Potential applications for this technology include the treatment of airstreams contaminated with volatile organic compounds (VOCs) from air stripping, soil vapor extraction, industrial air emissions, and for the cleaning of air in closed environments. PCO is best suited for waste streams with low concentrations of contaminants, and with low to medium flow rates. The AIR-11 process can operate consistently in conditions where flow rates and VOC concentrations are highly variable, even intermittent. 

This technology is applicable to the treatment of industrial wastewater and contaminated groundwater. The same technology can also be used to effectively destroy airborne contaminants in the off-gases from industrial processes, air strippers, or soil vapor extraction operations. 

The primary application of the PSVE technology will likely be to complement active soil vapor extraction efforts. PSVE could also be used on the edge of unsaturated zone contaminant plumes where concentrations of volatile contaminants are low or for enhancement of bioremediation activities. The primary advantages of PSVE application are low capital costs and minimal operating costs. One-way valves may also be incorporated so that the system only takes in or lets out air through wells. 

Many applications for this technology utilize wells that already exist from previous soil vapor extraction operations. In these cases, costs are further reduced because the need to drill additional wells is negated. 

In 1999, HRC was used with other treatment technologies at a brownfield site in Aurora, Colorado. An in situ air sparge/soil vapor extraction system was first used at the site to treat TCE contamination however, additional measures were needed to prevent the migration of PCE off-site. After an unsuccessful application of zero-valent iron injection, 240 lb of HRC were injected at five locations by direct-push methods. Total project costs were 110,000, which... 

During SIVE applications, traditional soil vapor extraction (SVE) is augmented by steam, which is injected into the subsurface. The steam vaporizes volatile and semivolatile contaminants and displaces liquids in soil pores. Both vapor and liquids are then pumped to the surface via extraction wells. 

A soil vapor extraction (SVE) system, which included the Terra Vac DVE technology, was used to clean up the Tyson s Dump Superfund site in Upper Merion Township, Pennsylvania. Total remediation costs at this site were 39.9 million to treat 30,000 yd of soil, or l,330/yd of soil treated. These costs included construction, operation, and maintenance expenses. The U.S. Environmental Protection Agency (EPA) notes that technology costs at this site may be high when compared to other SVE applications because of enhancements made to the system during operation (D18517V, p. 255). 

A DDC system was nsed to treat petrolenm hydrocarbons at Keesler Air Force Base in Biloxi, Mississippi. One DDC well and 1 soil vapor extraction (SVE) well were installed for the pilot stndy at the site, and 32 DDC weUs and 6 SVE wells were installed for the fnll-scale application. Total costs were 360,000, inclnding 100,000 for the pilot stndy (D22635H, p. 5). 

Decision-Support Software for Soil Vapor Extraction Technology Application Hyper-Ventilate... 

HELD APPLICATION SCENARIOS 26.6.1 Soil Vapor Extraction... 

The model was then used to simulate two field application scenarios, that is, soil vapor extraction and the pump and treat method. The model predictions seem to be reasonable based on what is expected under the conditions applied in the field. 

Flow Rate/Mode of Injection. Once the type of gas to be injected is determined, the flow rate and mode of injection must be determined. Loden (1992) reported that flow rates of 2 to 16.5 scfm are typical for field application. Nyer and Suthersan (1993) reported that when soil vapor extraction systems are used at a site, injection flow rates between 4 and 10 scfm are used. It has been reported that any flow rates beyond contaminant diffusion kinetics are a waste of effort (Roberts and Wilson, 1993 Reddy and Adams, 1999 Adams and Reddy, 1999). Additionally, Rutherford and Johnson (1996) found that oxygen transfer into ground-water may actually be impeded by an injection flow rate that is high because the air wUl act to push the groundwater away from the point of injection, decreasing interfacial transfer area and oxygen transfer. 

The approximate cost for shallow soil mixing/thermaUy enhanced vapor extraction technology range from 60 to 100/yd of soils treated. Costs and applications of this technology are site specific. This cost may be reduced given the desired level of testing and quality assurance/quality control measures required (D13379J, p. 28). 

Geokinetics International, Inc., has developed other applications for this technology as weU. It can be set up as an electrokinetic ring fence to recover ionic contamination from groundwater as it flows past the electrodes. It may also be used as a soil heating element in conjunction with soil vapor or groundwater extraction to remove organics from soil. 

Two-phase extraction uses a vacuum source to remove contaminated groundwater and soil vapor from the subsurface. The vacuum is applied to an extraction tube within a water well to increase groundwater removal rates and to volatilize and extract VOCs. According to the vendor, vacuum lift of water is not a limiting factor in the application of the technology. Since a mixed vapor/liquid column is extracted from the weU, the two-phase extraction technology allows a single piece of equipment (a vacuum source) to remove contaminants in both the liquid and vapor phases. 

Where thermal desorption is inadequate to remove an analyte from the surface, a laser beam can be directed, focused or unfocused, against a solid, and compounds on surfaces of solids can be vaporized and ionized at ambient pressure in air. In one application of laser-based IMS to environmental analyses, soils contaminated with petroleum products were assayed for PAHs. In this, a laser was used to irradiate soil, vaporizing PAHs into the gas phase. This provided a direct, fast, extraction-free method for soil analyses. 

In some cases, steam has been nsed as the flnid in soil flnshing applications. The steam is injected into the snb-sniface throngh a ring of injection wells configured to sunound all or part of the subsurface plume to be treated. Liquid and vapor are extracted from one or more wells located near the center of the well pattern while steam is injected into the permeable layers through screened portions of wells constracted around the plume. The steam directly heats contaminated permeable layers in the process zone to lower the viscosity and increase volatility of the contaminants. The contaminants are swept toward the extraction wells as ground water is displaced in advance of the injected steam front. 

The extraction flow rate is very important in order to control air and contaminant vapor migration. Simply stated, the extraction rates must be higher than the injection rates in order to prevent soil pressure buildup. Loden (1992) reported that the ratio of extraction to injection commonly used during field application are between 4 1 and 5 1. Johnson et al. (1990) reported that typical extraction rates are between 100 and 1,000 standard cubic feet per minute (scfm). 

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