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Defining TCE Plume Source Areas Using the Membrane Interface Probe (MIP)

A variety of traditional characterization methods, such as soil gas surveys, soil and groundwater sampling, and fixed laboratory analysis, is commonly used to define the magnitude and extent of soil and groundwater contamination in volatile organic compound source areas. One significant limitation of these methods is that they require multi-media sample collection to define the full unsaturated and saturated vertical profile in any given location. In addition, attaining higher resolution by increasing sample frequency increases costs substantially. A relatively new technology, the Membrane Interface Probe (MIP), was used to define trichloroethene plume source areas at F.E. Warren Air Force Base in Cheyenne, Wyoming, and at a confidential security products manufacturer in Tennessee. The MIP offered significant advantages over traditional drilling and direct-push methods and yielded data critical to a fuller understanding of subsurface conditions. The near-continuous MIP profile minimized the number of soil and groundwater samples required to fully delineate the extent of the plume-head source areas. In addition, the MIP is also able to collect data in the vadose and saturated zones, providing detailed vertical contaminant profiling information and geologic conditions based on soil conductivity that aided in the development of the site conceptual model. The MIP was not without its disadvantages; principal among these the relatively high detection limit (approximately 100 ppb in soil and groundwater), making the method useful for source characterization but limited for delineating lower levels of contamination. The data obtained from the MIP are considered screening-level data and need to be supplemented with analytical soil or groundwater data to fully support risk or remediation decisions. In summary, the vertical profiling obtained using the MIP aided in the interpretation of the complex relationship between the presence of gross contamination in soil and groundwater and the geologic conditions controlling contaminant distribution.