Application and assessment of grouted-in pressure transducers to determine long-term in situ hydrogeologic properties of argillaceous aquitards

Abstract Characterizing the in situ hydrogeologic properties of aquitards is difficult due to their low hydraulic conductivity ( K ) and slow response times. Consequently, numerical models often rely on laboratory determined values for geotechnical and hydrogeological parameters, which may be unreliable due to sample disturbance. This study shows that fully grouted, vibrating wire pressure transducers (VWPs) can be used to estimate the in situ compressibility ( α ), specific storage ( S S ), and in situ horizontal hydraulic conductivity ( K h ) of overconsolidated aquitards by analyzing pore pressure responses to barometric pressure fluctuations and post-installation recovery. While these methods have been used in shallow or short-term studies, their application in deeper, low- K formations with long-term monitoring remains limited. This study presents results from 34 VWPs installed across five boreholes at a single site (site 2) and compares them with previously published data from a similar site (site 1) in the Williston Basin (WB) where the methods were first developed and tested. The dataset provides a rare, high-resolution record of pore pressure behavior in glacial till and Cretaceous shale over monitoring periods of up to 16 years. The findings demonstrate the reproducibility of the methods across different lithologies and support their use in estimating representative hydraulic parameters for regional-scale models. This work adds to the growing body of research supporting in situ methods for aquitard characterization and highlights the value of long-term monitoring in improving the understanding of low- K systems in sedimentary basins.