Organic contaminants vadose zone

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. 

Soil vapor extraction (SVE) is a relatively new yet widely applied technology for the remediation of soils contaminated with volatile organic compounds (VOC) in the unsaturated zone above the water table (vadose zone). The process consists of generating an airstream through the contaminated soil subsurface in order to enhance the volatilization of organic contaminants and thus remove them from the soil matrix.913... 

Phase Distribution of Organic Contaminants in the Vadose Zone... 

Organic contaminants can be present in the vadose zone in four distinct phases (Figure 14.2) ... 

FIGURE 14.2 Phase distribution of organic contaminants in the vadose zone. The solid arrows in the three-and four-phase models represent the equilibria taken into consideration in the equations of Table 14.3. 

Multiphase extraction uses a vacuum system to remove various combinations of contaminated groundwater, separate-phase petroleum product, and vapors from the subsurface. The system lowers the water table around the well, exposing more of the formation. Contaminants in the newly exposed vadose zone are then accessible to vapor extraction. Once above ground, the extracted vapors or liquid-phase organics and groundwater are separated and treated. 

The primary focus of this chapter is to introduce approaches that limit (or prevent) migration of hydrocarbon and organic contaminants from the vadose zone into underlying water-bearing zones. The more conventional strategies, including a brief discussion of the process, relative cost, practical constraints, and limitations, are presented. Also presented are two typical soil vapor extraction case histories. 

Morrow, M. T. and VanDerpool, G., 1988, The Use of a High Efficiency Blower to Remove Volatile Chlorinated Organic Contaminants from the Vadose Zone — A Case Study In Proceedings of the National Water Well Association Second Outdoor Action Conference on Aquifer Restoration, Groundwater Monitoring and Geophysical Methods, Vol. Ill, Las Vegas, NV, pp. 1111-1135. 

Contaminants retained on colloid surfaces may be transported by flowing water through the vadose zone and reach the groundwater or be relocated on the land surface by runoff processes. Operationally defined as particles between 1 j,m and 1 nm in size, colloids in the subsurface may be of mineral, organic, or biological origin. 

The duration of the remediation is dependent on the soil type, water content, and the nature of the contaminants. The HRUBOUT process cannot remove metals from soils. Polychlorinated biphenyls (PCBs) cannot be totally removed. The in situ HRUBOUT process is designed for removing contaminants from the vadose zone, (i.e., the zone between the surface aud the water table). Low permeability lowers system effectiveness and raises remediation costs. Soils with variable permeabilities may cause uneven delivery of air to contaminants. VOC removal rates may be reduced by high organic content in the soil because soil orgauics have a high VOC-sorption capacity. 

Soil vapor extraction (SVE) (also called vacuum extraction, soil venting, or in situ vaporization) is used to remove volatile organic compounds (VOCs) and some semivolatile organic compounds (SVOCs) from contaminated soil. SVE systems apply a vacuum in an extraction well to remove soil vapors. This creates a negative pressure that causes the volatilization of some chemicals in the vadose zone of the soil. The technology has also been used to extract non-aqueous-phase liquid (NAPE). Contaminant volatilization is often enhanced through the use of air injection wells to supply unsaturated air into the vadose zone of the soil. 

Vacuum-vaporized well (German Unterdruck-Verdampfer-Brunnen abbreviation UVB) technology for in situ treatment of the capillary fringe, phreatic zone, and vadose zone contaminated with volatile organic compounds, including NAPLs, represents to us one of the most promising in situ bioremediation technologies (U.S. 

This is the proceedings from a USA/CIS conference organized by the American Institute of Hydrology. Topics include evaluation techniques lor hydrogeologic conditions and extent of ground water contamination, chemical late and transport In die vadose zone, flow modeling, and species migration. 

Dense nonaqueous phase liquids (DNAPLs) are the chlorinated organic compounds that have a density higher than water. Because of this unique property, DNAPLs will pass through the vadose zone and contaminate groundwater. Some reside in... 

Environmental Problems—This section describes N Reactor operational activities that affected the environment. The affected environs are groundwater contamination (radionuclides, volatile organics, polychlorinated biphenyls (PCB), metals, and other Inorganics) soil contamination (surface and vadose zone contamination from radionuclides and organic compounds) biota contamination (flora [vegetation] and fauna [animals] from radionuclide uptake by plants or Ingestion by animals) and evaluated radiation at the Columbia River (unshielded sediments In the 1301-N Liquid Waste Disposal Facility). 

---