Groundwater vadose zone

If yes to 1.6.d, describe number, depth, and groundwater/vadose zone monitoring of wells. 

Lappala, E. and G. Thompson. Detection of Groundwater Contamination by Shallow Soil Gas Sampling in the Vadose Zone and Applications. In Management of Uncontrolled Hazardous Waste Sites Proceedings, Hazardous Materials Control Research Institute,Washington, D.C., 1984. 

Vadose zone Unsaturated zone of soil above the groundwater, extending from the bottom of the eapillary fringe all the way to the soil surfaee. 

As more sensitive analytical methods for pesticides are developed, greater care must be taken to avoid sample contamination and misidentification of residues. For example, in pesticide leaching or field dissipation studies, small amounts of surface soil coming in contact with soil core or soil pore water samples taken from further below the ground surface can sometimes lead to wildly inaccurate analytical results. This is probably the cause of isolated, high-level detections of pesticides in the lower part of the vadose zone or in groundwater in samples taken soon after application when other data (weather, soil permeability determinations and other pesticide or tracer analytical results) imply that such results are highly improbable. 

Pumping of the groundwater to lower the water table and enlarge the vadose zone, with simultaneous treatment of contaminated groundwater.10... 

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. 

May cause a lateral spread of dissolved or separate phase contaminant plume Contamination may be transferred from groundwater to die vadose zone Has limited applicability at sites with confined aquifers Low soil permeability or other heterogeneous conditions may reduce effectiveness... 

In some cases, such as areas of lower contaminant concentrations or in remote locations, contaminants stripped from the groundwater may be allowed to attenuate naturally in the vadose zone. 

Groundwater can be found in the traditional sense at the water table below which the soil pore spaces are essentially saturated and the water is free to move, and in the unsaturated zone (or vadose zone) above the water table. It is possible for water to migrate through both of these zones, transporting dissolved components (or contaminants). The interaction of the various forces involved will determine the direction and rate of migration. 

Above the water table, groundwater can also occur in perched aquifer conditions. In these instances, groundwater occurs in relatively permeable soil that is suspended over a relatively low permeability layer of limited lateral extent and thickness at some elevation above the water table. Perched groundwater occurrences are common within the vadose zone high-permeability zones overlie low-permeability zones of limited lateral extent in unconsolidated deposits. However, perched conditions can also occur within low-permeability units overlying zones of higher permeability in both unconsolidated and consolidated deposits. In the latter case, for example, a siltstone or clay stone overlies jointed and fractured bedrock such that groundwater presence reflects the inability of the water to drain at a rate that exceeds replenishment from above. 

Traditionally air sparging has been used as a groundwater remediation tool. Occasionally, however, it has been successfully used to remediate the vadose zone. In this application, the compressed air is injected through a well screen that is open to the VOC-contaminated area. The injection wells may be either vertical or horizontal (Figure 10.7). In this setting, the injected air is usually captured by a corresponding set of SVE wells (Figure 10.8). Properly spaced patterns of injection and recovery wells are necessary for efficient operation. 

Laney, D. F., 1988, Hydrocarbon Recovery as Remediation of Vadose Zone Soil/Gas Contamination In Proceedings of the National Water Well Association Second National Outdoor Conference on Aquifer Restoration, Groundwater Monitoring and Geophysical Methods, Vol. Ill, Las Vegas, NV, May, pp. 1147-1171. 

Marley, M. C. and Hoag, G. E., 1984, Induced Soil Venting for Recovery/Restoration of Gasoline Hydrocarbons in the Vadose Zone In Proceedings of the National Water Well Association and American Petroleum Institute Conference on Petroleum Hydrocarbons and Organic Chemicals in Groundwater Prevention, Detection and Restoration, November, pp. 473-503. 

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