Measurement of groundwater and contaminant fluxes using a combined system of fractured rock passive flux meter and multiport sampler

Groundwater and contaminant movement in fractured rock aquifers is highly variable and its dependence on fracture aperture, orientation and network interconnectivity is not well understood. This poses a challenge on the measurement of groundwater and contaminant fluxes, especially using open-hole techniques, which significantly alter natural flow conditions by connecting different fractures along an open borehole or a well. The Fractured Rock Passive Flux Meter (FRPFM) is a closed-hole device for measuring water and contaminant fluxes at individual fractures. Here we present an improved FRPFM that is combined with the G³⁶⁰ MultiPort System (G³⁶⁰MPS), and perform laboratory tests to measure water and contaminant fluxes at inclined and perpendicular fractures of different apertures. Results showed that water and contaminant fluxes were measured with relative errors of ±25 % and ± 14 %, respectively. The results also showed that the selection of appropriate Activated Carbon Felt can improve the accuracy of water flux measurements, and the fraction of tracer remaining on the felt in each experiment exhibited the expected breakthrough curve behaviour. Water flux was measured correctly up to 50 % of tracer loss, but beyond this point, the measurements became less accurate as tracer displacement rate declined.