A Multidisciplinary Study of Controls on
Ground-Water Flow in a Karst Aquifer in the Ordovician Beekmantown
Group, Berks County, PA
Wolfinger,
Seth, Ward, Kristen, Holland, Jeremy, Nase, Andrew,
Ferguson, Lisa, Zellner, Greg, Friehauf, Kurt, Tindall, Sarah, and
Schultz, Lane, 2004, A
Multidisciplinary
Study
of
Controls on
Ground-Water Flow in a Karst Aquifer in the Ordovician Beekmantown
Group, Berks County, PA [abs]: Geological Society of
America
Northeastern Section (39th Annual) and Southeastern Section (53rd
Annual) Joint Meeting (March 25-27, 2004) Geological Society of America
Abstracts with Programs, vol. 36, no. 2, p. 128.
A
multidisciplinary approach has been employed that includes detailed
fracture mapping, water table monitoring, ground-water chemistry and
lithogeochemistry to study factors that affect cave formation and
ground-water flow through Ordovician carbonates proximal to an
aggregate quarry in Ontelaunee Township, Berks County, Pennsylvania.
Bedding in the quarry is oriented S38W-60NW and sedimentary structures
demonstrate the rocks in the pit are not isoclinally folded. Clay- and
boulder-filled dissolution conduits up to 5m wide exist parallel to
bedding and are exposed in the south wall of the quarry; dissolution
features are also prominent within a 10m wide, S80E-68SW fracture zone
near the southwestern corner. Dissolution is apparent in
bedding-parallel carbonate veins, whereas veins perpendicular to
bedding are less weathered.
Ten synchronized pressure transducers with data loggers installed in a
1-km2 monitoring well field continuously recorded water table
fluctuations and temperature during a storm event. By identifying water
table responses to storms, together with rock fracture characteristics
mapped in the quarry, prediction of dissolution channel formation in
the aquifer may be possible.
Ground-water temperature in each well remained unchanged during the
storm, with values ranging from 18ºC (temperature of adjacent
streams) to 12ºC. The 12ºC end member may represent
longer-term resident ground water and wells with intermediate
temperatures reflect mixing of infiltrating surface waters and cold
resident ground water.
Pressure transducer data suggest different sections of the well field
respond to storm-induced perturbations in one of three distinct
patterns. (1) Wells characterized by a symmetrical fluctuation
coincident with the rise and fall of the regional ground-water table
are interpreted to represent zones in the aquifer with unrestricted
flow. (2) Wells with a rapid initial water level increase followed by a
gradual return to base levels are interpreted to indicate more
restricted flow. (3) Wells characterized by an initial spike
superimposed on pattern (1) may have experienced initial channel
blockage, e.g. clay subsidence, followed by a clearing of blockage
allowing water levels to return rapidly to regional water table levels.
