Abstracts

316 - Regional patterns and geochemical controls on shallow
groundwater chemistry in Southeastern Ontario
Laura M. Colgrove, Stewart M. Hamilton, & Fred J. Longstaffe
Department of Earth Sciences – University of Western Ontario, London, Ontario, Canada
This study reports regional chemistry for shallow groundwater from southeastern Ontario
and identifies the dominant geochemical processes responsible for its variability. The database
includes chemical analyses of groundwater from 264 wells located between the Frontenac
Arch and the Quebec border, which were sampled as part of the Ambient Groundwater
Geochemistry Program of the Ontario Geological Survey. Users of groundwater
in eastern Ontario experience unusually elevated levels of many chemical constituents,
including Na + , Cl - , I - , DOC, DIC and TDS. Whereas typical drinking water has TDS
ranging from 500-700 ppm, 39 Eastern Ontario samples can be classified as “brackish”,
ranging from 1000 – 10000 ppm, and 1 sample classified as saline at 10400 ppm. Spatial
variations in groundwater chemistry show a strong correlation with the occurrence of
Pleistocene (“Leda”) clays deposited by the Champlain Sea. Halogen ratios, water stable
isotope compositions and major-ion proportions suggest that the regional groundwater
flow system may be interacting with Champlain seawater still present in parts of the study
area. Infiltrating meteoric water is confined by thickening Champlain Sea clays, and its
chemistry evolves through ion exchange and mixing with Pleistocene water. Ion exchange
with these clays softens the water, creating potential health-related implications for drinking
water, including those associated with elevated concentrations of sodium and fluoride.
Elevated DIC, DOC and I - , along with the presence of HS - and CH 4
, are attributed to
anaerobic decomposition of organic matter associated with the Champlain Sea clays and
shale. The combined contributions of Champlain seawater and decomposition of associated
organic matter has produced the highest I - concentrations so far measured in Ontario,
which commonly exceed those of seawater by an order of magnitude.
119 - Challenges and Issues Related to the Water Supply from the
Brandon Channel Buried Valley Aquifer – Brandon, Manitoba
Jeffrey J. Bell
Friesen Drillers Ltd., Steinbach, Manitoba, Canada
The hydrogeology and recharge characteristics of buried valley aquifers on the Canadian
prairies are complex. The City of Brandon, in western Manitoba, relies on a water supply
from the Assiniboine River. A large buried deposit of sand and gravel was present within a
valley in the shale bedrock in Brandon. This deposit is called the Brandon Channel Aquifer.
The Brandon area was once a key restriction in the northerly drainage of the vast majority
of Central North America. This river system deposited a large amount of sediment. The
area was subsequently glaciated several times, during the Pleistocene. These glacial events
deposited related glacial deposits.
Two industrial plants utilize 30,000 m 3 /day of groundwater for process and cooling applications.
The aquifer is narrow in places and varies considerably in thickness and structure.
IAH-CNC 2015 WATERLOO CONFERENCE
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