7 research outputs found
Assessing Alternative Scenarios for the Cause of Underpressures in the Ordovician Sediments along the Eastern Flank of the Michigan Basin
Geoscientific investigations for a proposed deep geologic repository at the Bruce Site, located on the eastern flank of the Michigan Basin, have identified unique and significant underpressured conditions. Along with the measurement of environmental tracer profiles (e.g., helium), this study aims to explore, through a series of numerical simulations, the nature of long-term phenomena responsible for the generation and preservation of formation underpressures. Three families of inverse numerical experiments for underpressure formation were examined by means of one-dimensional hydromechanically coupled models through the vertical hydrostratigraphic column: (i) uncertainty in glaciation scenarios; (ii) uncertainty in initial heads prior to glaciation; and (iii) uncertainty in the degree of hydraulic connectivity between the more permeable Guelph Formation at the Bruce Site and the applied glacial loading, for a total of 20 scenarios, assuming fully saturated conditions. Underpressured initial heads for the paleohydrogeologic simulations lead to lower calibrated vertical hydraulic conductivities. The robustness and resilience of the groundwater system to external perturbations are greater for the state where underpressured conditions predate the onset of glaciation and are better able to preserve the present day helium tracer profile in 260 Ma exhumation analyses
Surface Roughness Impacts on Granular Media Filtration at Favorable Deposition Conditions: Experiments and Modeling
Column
tests were conducted to investigate media roughness impacts
on particle deposition in absence of an energy barrier (i.e., high
ionic strength). Media/collector surface roughness consistently influenced
colloid deposition in a nonlinear, nonmonotonic manner such that a
critical roughness size associated with minimum particle deposition
could be identified; this was confirmed using a convection-diffusion
model. The results demonstrate that media surface roughness size alone
is inadequate for predicting media roughness impacts on particle deposition;
rather, the relative size relationship between the particles and media/collectors
must also be considered. A model that quantitatively considers media
surface roughness was developed that described experimental outcomes
well and consistently with classic colloid filtration theory (CFT)
for smooth surfaces. Dimensionless-scaling factors <i>f</i><sub>roughness</sub> and <i>f</i><sub>PCIF</sub> were introduced
and used to develop a model describing particle deposition rate (<i>k</i><sub>d</sub>) and colloid attachment efficiency (α).
The model includes fitting parameters that reflect the impact of critical
system characteristics such as ionic strength, loading rate, hydrophobicity.
Excellent agreement was found not only between the modeled outcomes
for colloid attachment efficiency (α) and experimental results
from the column tests, but also with experimental outcomes reported
elsewhere. The model developed herein provides a framework for describing
media surface roughness impacts on colloid deposition