Soil-gas surveying techniques.

Delineation and remediation of subsurface contamination have become a major focus of environmental science during the past five years. Conventional technologies available for subsurface investigations always will be required to confirm and monitor subsurface contamination; however, quicker and less expensive techniques are useful for preliminary site evaluations. Soil-gas surveying is a technique that is applicable to a wide range of volatile organic compounds (VOCs) under a variety of geologic and hydrologic settings. The most common uses of soil-gas data include planning monitoring well networks and defining plume boundaries for remedial action. Preliminary screening techniques are effective in selecting locations for detailed sampling and analysis. Site investigators can use results from a preliminary soil-gas survey to drill monitoring wells at locations within the boundaries of a VOC volume. Soil-gas investigations also can be used to identify sources of VOCs and to distinguish between soil and groundwater contamination. Chemical analysis of soil gases has recently been used to monitor solvent and fuel leaks from underground storage tanks. In order to effectively design soil-gas surveys and interpret their results, the subsurface transport and fate of VOCs must be understood. These phenomena can have a profound impact on the presence and concentrations of VOCs more » in the soil atmosphere. Physical, chemical, and microbiological processes can be important in determining VOC concentrations in soil gas. « less