Abstracts

within the Quadra aquifer generally follows surface water drainage basin with discharge
to rivers, whereas flow in underlying Mapleguard and bedrock aquifers is directed towards
the Strait of Georgia without significant hydraulic connection with rivers. Hydrogeological
insights gained through this study shows that the complexity of this aquifer system can
make groundwater management challenging and that each system component should be
carefully understood to ensure sustainable management.
312 - Hydrogeochemical Assessment of a Regional Geochemical
Anomaly, Niagara Peninsula
Caitlin McEwan & Greg Slater
School of Geography and Earth Sciences, McMaster University, Hamilton, Ontario, Canada
Stewart Hamilton
Ontario Geological Survey, Ministry of Northern Development and Mines, Sudbury,
Ontario, Canada
A geochemical anomaly in the Niagara Peninsula affecting water quality to the point of
non-potability was first identified by the Ontario Geological Survey in 2010 by the Ambient
Groundwater Geochemistry study. Interpretation of data collected during that field season
shows two anomalous geochemical zones that are distinct with respect to the groundwater
chemistry of the same geologic units elsewhere in Southern Ontario. Elsewhere, bedrock
groundwater geochemistry in these Paleozoic strata is reasonably consistent within formations
and reflects the lithological and mineralogical composition of the host rock. The first
zone exists in the western Niagara Peninsula, and is characterized by Ca-Mg-SO 4
2-
-HCO 3
rich waters and has high pCO 2
and bacterial counts. This geochemical zone spans several
geological formations including Devonian carbonates, Silurian evaporates and Silurian carbonates
along a north-south trend, and in some cases cross-formational flow is indicated.
The potentiometric surface was plotted to assess groundwater flow using the static water levels
of wells, GPS elevations and locations, well stick-up and well depth following the protocol
of the Ambient Groundwater Geochemistry Program. The assessment of hydraulic heads
along a north-south transect crossing the Niagara Escarpment and the buried Onondaga Escarpment
in both shows groundwater to flow northward and southward from each bedrock
topographic high. Several new monitoring wells installed in the local Silurian carbonate/
evaporite contact aquifer through collaborative efforts of the Ontario Geological Survey and
the Niagara Peninsula Conservation Authority will provide hydrogeological ‘golden spikes’
for the determination of regional flow direction. Ongoing work seeks to identify sources
of these geochemical anomalies with additional sampling to increase the density of sample
points. The collection of ∂ 34 S, ∂ 13 C, ∂ 18 O, and ∂D isotopic samples at each site during ongoing
sampling will aid interpretation of the geochemical processes occurring in this anomalous
geochemical zone. Previous work has suggested several possibilities for the source of
the anomalous geochemical zones including the presence of corroded abandoned gas well
casings as a mechanism for groundwater transport from depth and groundwater transport in
karst aquifers. Identification of the sources of these water quality problems will be a first step
in identifying safe and reliable groundwater supplies for local residents and providing data to
make informed decisions by other stakeholders on long term water supplies in the region.
170 IAH-CNC 2015 WATERLOO CONFERENCE