Virtual Seminar - Dr. Jessica Meyer: 'How vulnerable is your aquifer?'
K-State Geology Seminar Series Presents
'How vulnerable is your aquifer?'
by Dr. Jessica Meyer, Assistant Professor of Earth and Environmental Sciences & affiliated faculty in IIHR Hydroscience & Engineering at the University of Iowa
Thursday, 06 April 2023 | 4:00-5:00 PM
Title: How vulnerable is your aquifer?
Abstract: Aquitards are conceptualized as parts of the subsurface that protect underlying aquifers from contaminants. Consequently, quantitative characterization of aquitards and assessment of their integrity is fundamental to management of groundwater resources. Integrity assessments for bedrock aquitards traditionally focus on lithology and associated hydraulic conductivity. In this study, we integrate a diverse set of data to evaluate the integrity of 7 aquitards within a sedimentary rock aquifer system to attenuating migration of dissolved and dense non-aqueous phase liquid (DNAPL) organic contaminants. Here, an aquitard is defined in a novel way as an interval of rock that produces a distinct increase in the vertical component of hydraulic gradient in a high-resolution (3 zones/10 m) head profile. Once delineated, the study area aquitards were put into a sequence stratigraphic context using cores and natural gamma logs and their lateral continuity was assessed. A 3-D numerical groundwater flow model was constructed and calibrated with emphasis on matching the observed high-resolution head profiles in order to provide robust estimates of bulk vertical hydraulic conductivity (Kv). Evaluation of the contaminant distribution from detailed sampling of continuous cores and groundwater sampling of high-resolution multilevel wells characterized the vertical extent of contaminant migration. For example, the aquitard with the highest integrity was a 6 m thick maximum flooding interval composed of very-fine to fine grained sandstone with the lowest model calibrated bulk Kv, high degree of anisotropy, and demonstrated integrity with respect to DNAPL. Regionally, this sandstone unit is not usually conceptualized as an aquitard because of its high lateral transmissivity. In addition, a contact between two units with poorly connected fracture networks had the second highest integrity rating based on the large measured vertical gradient, a dramatic shift from high dissolved phase contaminant concentrations to non-detects, and resistance to DNAPL penetration. These data demonstrated how poor fracture network connectivity can limit vertical groundwater and DNAPL phase flow, a concept that has been suggested in the literature but not shown with field data. This study highlights the importance of data-based assessment of aquitard integrity. Particularly given increased use of the subsurface for waste disposal activities and the reliance on aquitards to protect our groundwater not just from surface contamination but threats from below as well.
Bio: Jessica Meyer is an Assistant Professor in the Earth and Environmental Sciences Department and affiliated faculty in IIHR Hydroscience & Engineering at the University of Iowa. Her research focuses on field-based characterization of groundwater flow systems in heterogeneous geologic settings with emphasis on understanding the relationship between the hydraulic and geologic structure of the subsurface. Meyer’s current projects include developing new techniques for delineating aquitards in fractured, sedimentary rock; evaluating flow system controls on the natural attenuation of organic contaminants in fractured sandstones; and characterizing solute exchanges between groundwater and surface water bodies.
Modality: VIRTUAL (via Zoom)
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https://ksu.zoom.us/j/95830801645?pwd=eGgxM1JjZU44YVczTjliTGJxeE8zZz09
Meeting ID: 958 3080 1645
Passcode: 564494
Thursday, April 6, 2023 at 4:00pm to 5:00pm
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