Abstracts

with a fibre optic cable. A new cable coupling technique using a flexible borehole liner was
tested and was shown to be highly effective for enhancing the seismic signal recorded with
the DAS. A comparison between two different cable structures, tight buffer and loose tube,
were also examined and it was determined that the different structures can strongly influence
the amplitude of the seismic signal. With good cable coupling, the DAS can provide
high-resolution VSPs to provide information on the bedrock aquifer matrix and optimal
cable structures can help maximize the signal to noise ratio of the profile.
297 - Depth-discrete contaminant mass composition and
concentration distribution emanating from an aged DNAPL source
zone in sedimentary rock
A. Buckley, J.R. Meyer, & B.L. Parker
G360 Centre for Applied Groundwater Research, School of Engineering, University of
Guelph, Guelph, Ontario, Canada
Prior to 1970 an estimated 72,700 L of dense non-aqueous phase liquids (DNAPLs)
were released into the subsurface at a site in south central Wisconsin. Investigations at
the site found that the DNAPL accumulated about 56 m bgs in a fractured sandstone
unit. Groundwater flow through the DNAPL source zone over three decades resulted in
a dissolved phase mixed organic contaminant plume extending about 3 km downgradient.
Evaluation of potential remedial options requires quantification of the mass and phase
distribution in and near the DNAPL source zone. In 2014, five holes were continuously
cored to between 55 and 63 m bgs in a transect downgradient of the source zone. The core
lithology and fractures were logged in detail and over 630 rock samples were taken (at least
1 per 30 cm) from the continuous cores for extraction and analysis of the contaminants
of concern. A comprehensive suite of geophysical and hydro-physical logs were collected
from each of the boreholes and all of the data was utilized to design high resolution multilevel
systems (MLSs) for each borehole. Hydraulic heads were measured and groundwater
samples for contaminant analyses were collected from the MLSs. The rock core contaminant
profiles provide a quantitative and high resolution view of the contaminant mass
and phase distribution in the rock matrix; commonly showing over an order of magnitude
change in concentration across less than 1 m of depth. The groundwater contaminant
profiles collected from the multilevel systems represent the contaminant distribution in the
fractures. Integration of the data sets provides a robust understanding of the two-dimensional
contaminant mass and phase distribution along a transect orthogonal to groundwater
flow to show the concentration distribution and mass composition relative to the
high permeability fractures and mass stored in the lower permeability matrix immediately
downgradient of the DNAPL source zone. Ultimately the variability in the contaminant
composition and concentration at different spatial scales across this transect will be compared
to geologic and hydrogeologic properties to provide additional insights into controls
on contaminant transport and fate in sedimentary rock.
IAH-CNC 2015 WATERLOO CONFERENCE
151