Showing papers by "John A. Cherry published in 2015"

Hybrid Multilevel System for Monitoring Groundwater Flow and Agricultural Impacts in Fractured Sedimentary Bedrock

Abstract: Understanding agricultural contamination in bedrock aquifers is challenging due to complexity of fracture networks and limitations in data acquisition imposed by instrumentation and drilling costs. Engineered assemblages known as multilevel monitoring systems (MLSs) maximize data from each borehole by providing numerous, depth-discrete monitoring intervals for profiles of hydraulic head and hydrochemistry. This article describes a hybrid MLS that uses key components of the Waterloo MLS, with extra piezometers of sufficient diameter to accommodate removable transducers for continuous pressure monitoring, attached to the outside using custom clamps. Monitoring intervals are created with sand packs separated by bentonite seals, either via backfilling from surface or tremie placement. The hybrid MLS is best suited for use in rotary drilled boreholes 12 to 15 cm diameter, smaller holes have insufficient space for the MLS and added piezometer(s) while larger holes have excessive backfill material and purge requirements. Variations were installed to 60 m depth in sandstone in Prince Edward Island, and to 150 m in dolostone in southwestern Ontario. Transducers in the external piezometers provided temporal head data under ambient and stressed conditions in key intervals, and manual measurements in all ports provided detailed vertical hydraulic snapshots. Combined with hydrochemistry profiles from groundwater sampling, the hybrid MLS provided detailed composite datasets for interpreting flow and transport in these bedrock aquifers. The hybrid MLS offers promise as a versatile low-cost option for groundwater studies in agricultural areas providing improved insights on groundwater flow systems and vertical distribution of nitrate and other contaminants, allowing more informed management decisions.