Abstracts

Flow and Transport in Fractured Rock
Wednesday, October 28, 15:20 – 17:00
Chair: Kent Novakowski
Room: Schubert
300 - Hydrogeology and sequence stratigraphy correlations
used to inform a regional scale groundwater flow model for
sedimentary rock
J.R. Meyer & B.L. Parker
G360 Centre for Applied Groundwater Research, School of Engineering, University of
Guelph, Guelph, Ontario, Canada
E. Arnaud
School of Environmental Sciences, University of Guelph, Guelph, Ontario, Canada
A.C. Runkel
Minnesota Geological Survey, St. Paul, Minnesota, USA
L. Weaver, S.G. Shikaze & D.G. Abbey
Matrix Solutions Inc., Breslau, Ontario, Canada
Hydrogeologic units (HGUs) represent our understanding of the 3-D distribution of hydraulic
conductivity contrasts; and therefore, accurate delineation of these units is foundational
to conceptual and numerical models of groundwater flow. In standard practice,
existing lithostratigraphic units are often assumed to be HGUs and are used to guide the
length and position of well screens used to collect hydraulic data. This study describes a
unique approach to HGU delineation that relies on depth discrete and detailed (i.e., high
resolution) profiles of vertical gradient to delineate HGUs for a numerical model needed to
support decision making for a contaminated sedimentary rock site in southern Wisconsin.
Seven hydraulic head profiles obtained from high resolution multilevel systems (average of
3.4 monitoring zones per 10 m) monitoring to depths between 90 and 146 m were used to
determine the three-dimensional distribution, magnitude, and direction of vertical gradients.
When examined along 2 cross sections, each spanning 4 km, these vertical gradient
profiles indicated 11 laterally extensive contrasts in the vertical component of hydraulic
conductivity (K v
); the boundaries of which did not coincide with lithostratigraphic units.
Further investigations revealed that the K v
contrasts were strongly associated with regionally
extensive sequence stratigraphic units (maximum flooding intervals and unconformities)
and this relationship was used to delineate 3-D HGUs for the site scale (16 km 2 ).
Development of the 3-D numerical groundwater flow model required expanding the study
area to 300 km 2 in order to incorporate physically based boundary conditions. There were
over 400 additional boreholes in the model domain, but the data sets for most only included
lithostratigraphic picks. Therefore, the association between the high resolution vertical
gradients and sequence stratigraphic units developed on site were used to create guidelines
regarding the position of the HGUs relative to lithostratigraphic units and HGUs
were picked for the additional boreholes. All HGU picks were then examined along > 30
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