A New Depth-Discrete Multilevel Monitoring Approach for Fractured Rock

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Abstract

A new approach for monitoring in fractured rock was demonstrated in a contaminated (trichloroethylene and metolachlor) dolostone aquifer used for municipal water supply. The system consists of two related technologies: a continuous packer for temporary borehole seals (Flexible Liner Underground Technologies Ltd. [FLUTe] blank liner) and a depth-discrete multilevel monitoring system (MLS) (the Water FLUTe) for temporary or permanent monitoring. The continuous borehole liner consists of a urethane-coated nylon fabric tube custom sized to each hole. The FLUTe MLS consists of the same liner material with many depth-discrete intervals for monitoring hydraulic head and/or ground water quality. The FLUTe blank liner seals the entire borehole, prior to FLUTe multilevel installation, to prevent vertical cross connection while allowing borehole logging and testing. The FLUTe multilevel system also seals the entire borehole with the exception of each monitoring interval where the formation water has direct hydraulic connection to the pumping system via a thin permeable mesh sandwiched between the liner and the formation. The blank sealing liners and the multilevel systems were used in five boreholes ranging in diameter between 9.6 and 14.5 cm in the dolostone aquifer to depths of 150 m. The systems were custom designed for each borehole and included between 12 and 15 monitoring intervals. The application demonstrated the ease of installation and removability and facilitated obtaining large data sets with minimal labor. The system offers unique and versatile design features not possible with other bedrock monitoring devices and has been used at many bedrock contamination sites across North America.

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