The objective of this project is to complete a comprehensive, robust, scientific evaluation of the use of the FLUTe™ Activated Carbon Technology (FACT™) as a low-cost contaminant screening tool for fractured bedrock environments. The evaluation includes developing context and guidelines for interpreting the results in a dual porosity system in which groundwater flow and contaminant transport occur in the secondary porosity and contaminant storage (in solute and sorbed phases) occurs in the primary porosity. Another objective is to assess how varying primary porosity affects the results. This screening tool can then be used to improve the quality of site characterizations and conceptual site models (CSM) while reducing the cost of characterization. Improvement in the CSM translates into more efficient and effective remedies.
The FACT™ is a flexible borehole liner equipped with a reactive covering for nonaqueous phase liquid (NAPL) detection and a continuous 0.125-inch thick x 1.5-inch wide strip of activated carbon felt. The carbon felt is located on the inside of a hydrophobic cover. A diffusion barrier is located between the carbon felt and the liner to isolate the carbon from the liner. The liner is everted into the borehole using a pressure differential between water added to the inside of the liner and the hydraulic head in the borehole. The liner presses the carbon felt firmly against the borehole wall while sealing the entire borehole. The carbon felt strip sorbs organic solutes from the formation, both from the secondary porosity (fractures) and from the primary porosity. After sufficient equilibration time, the liner is recovered by inversion, preventing the carbon felt from contacting any other portion of the borehole wall during removal. Once removed from the hole, the carbon felt is sectioned at closely spaced intervals, placed in sample bottles with a solvent (e.g., methanol or pentane), and analyzed in a lab. The laboratory analysis measures mass of contaminant per unit mass of carbon felt. Modeling tools are being developed and evaluated by Danish Technological University researchers in collaboration with this team to understand how the mass on the carbon felt relates to contaminant concentrations in matrix porewater.
Benefits to the Department of Defense (DoD) from implementation of the FACT™ technology exist on two levels: (1) The application of high resolution site characterization (HRSC) methods to fractured bedrock sites provides more insight into contaminant distribution and controlling processes, resulting in more accurate CSMs, leading to better remedial decisions and more efficient and effective remedial designs; and (2) There is a great need for effective screening technologies for use in fractured rock HRSC to reduce investigation costs. The FACT™ is expected to identify the zones in fractured rock boreholes where contaminant levels are relatively high and low in a rapid and cost-effective manner. The use of more expensive techniques such as rock matrix sampling and analysis, packer testing, and completion of multi-level monitoring installations can then focus only on the pertinent sections of bedrock flow system, reducing the costs of evaluating full profiles over long vertical intervals and in locations that may not increase understanding of source areas or transport pathways.
Use of FLUTe™ liners is an inexpensive way to temporarily seal boreholes, preventing cross contamination and minimizing the confounding effects of evaluating a discontinuous flow system with continuous cross connected boreholes. In contrast to other means of sealing boreholes (e.g., grouting), the hole remains available for future use by simply removing the liner. If the liners are used, the incremental costs of gathering additional data such as transmissivity profiling are small. In combination, the NAPL/FACT™ provides detailed data on the presence or absence of NAPL as well as the qualitative distribution of contaminant mass within a borehole. Exploratory boreholes could be drilled using cheap and rapid drilling techniques and screened with the NAPL/FACT™. If no significant contamination is found, the hole can be properly abandoned with little or no additional investigative work. (Anticipated Project Completion - 2019)