Vapor extraction wells

The vacuum extraction process involves using vapor extraction wells alone or in combination with air injection wells. Vacuum blowers are used to create the movement of air through the soil. The air flow strips the VOCs from the soil and carries them to the surface. Figure 18.14 shows the flow diagram for such a process. During extraction, water may also be extracted along with vapor. The mixture should be sent to a liquid-vapor separator. The separation process results in both liquid and vapor residuals that require further treatment. Carbon adsorption is used to treat the vapor and water streams, leaving clean water and air for release, and spent GAC for reuse or disposal. Air emissions from the system are typically controlled by adsorption of the volatiles onto activated carbon, by thermal destruction, or by condensation. 

During SVE, contaminated soil vapors are extracted by inducing a vacuum at one or more extraction points that are typically constructed as vertical vapor extraction wells. Horizontal extraction wells or trenches have also been employed as extraction points. In general, SVE is applied at depths... 

These factors affect the number of vapor extraction wells, vacuum level required, type of off-gas treatment, and length of time required for treatment.34... 

Remediation commenced with the interception of the recoverable gasoline. One 4-in.-diameter vapor extraction well and three 2-in. vapor monitor wells were installed. Each well was constructed with 4 ft of well screen placed and filter packed across the unsaturated portion of the shale. The annulus of the wells was sealed to the surface with bentonite and cement grout according to local standards. The monitor wells were located in a triangular pattern around the vapor extraction well at distances of 5.3, 10.6, and 25.4 ft. 

Vapor-flow sensor and vapor-sampling ports located near the vapor extraction well heads. 

Analytical Results for Soil Vapor for Vapor Extraction Well VEW-1... 

FIGURE 10.19 Graphs of vapor analytical results at vapor extraction well. 

In all, 11 vertical soil vapor extraction wells and 9 vertical air sparge wells were installed in the treatment area. Sand chimneys (boreholes filled with coarse sand) were also installed to facilitate vertical air circulation. Mechanical remediation equipment and systems control installed for remediation were mosdy automated with minimal operator control required. 

In 1995, PF was used with enhanced dual-phase extraction in a full-scale application at a site in central New Jersey. As a result of manufacturing activities at the site, groundwater had become contaminated with TCE. Twenty vapor extraction wells and a 500-ft /min vapor system were used to treat 1.5 acres to a depth of 30 ft. According to ARS Technologies, total costs were 1.1 million (D22628I, p. 1). 

An example of S.A.V.E. system costs comes from a remediation project conducted in Silver Springs, Nevada, between 1994 and 1995. Installation of the S.A.V.E. system at the site, including eight monitoring and soil vapor extraction wells, cost 35,000. A S.A.V.E. 11 unit was purchased for 72,000, and its direct operating costs over 10,182 hours of operation were 29,000. 

The remediation site must be capable of supporting drilling operations where vapor extraction wells are required. Microorganisms used for bioremediation are not effective in toxic soil conditions. Also, because the rate of bioremediation is much slower than vapor extraction, the system must operate for a period of time after volatile contaminants have been removed by vapor... 

After initial installation of the system (wells, manifold, and treatment system), system operation, monitoring, and maintenance are routine. The most difficult part of this technology is the proper selection of well screening intervals. If the vapor extraction well is not properly screened, air will enter the well from regions of the soil that do not contain the contaminant, leaving regions that do contain the contaminant bypassed by the airflow. 

Yamazaki-Nishida, S., Read, H., Nagano, J., Jaiosh, T., Eddy, C., Cervera-March, S., and Anderson, M., 1994, Gas phase photocatalytic degradation on Ti02 pellets of volatile chlorinated compounds from a soil vapor extraction well, J. of Soil Contam., 3(4) 363-378. 

Read, H. W., Fu, X., Clark, L. A., Anderson, M. A., Jarosch, T., 1996, Tield Trials of a TiOj Pellet-Based Photocatalytic Reactor for Off-Gas Treatment at a Soil Vapor Extraction Well , Journal of Soil Contamination, Vol. 5, No. 2, pp. 187-202. 

A network of 107 electrodes covering two-thirds of an acre was established. To treat beneath a warehouse, 85 of those electrodes were constructed directly through the floor of the building. Electrically conductive from 11-21 ft bg, the electrodes actively heated the depth interval from 5-24 ft bg. Once subsurface temperatures reach boiling, steam laden wifli chlorinated solvents was collected by a network of 37 soil vapor extraction wells screened to 5 ft bg. 

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