Section 3.10: Site Plans and Technical Data - Rick Neufeld Comments

Northern Gateway Pipelines Inc.
Section 3.10: Site Plans and Technical Data
Table of Contents
2.5.1 Single-beam and Multi-beam Bathymetric Surveys
The single-beam and multi-beam bathymetric results reveal an irregular and steeply-sloping surface
descending from the shoreline to great depth at the bottom of the channel. The slopes of the near-shore
seabed vary across the site. In certain areas there are steep vertical rock faces near the shoreline grading to
seabed slopes in the order of 1V:2H and steeper. The near-shore slopes in the northern portion of the site
tend to be steeper than in the southern portion of the site. These slopes extend to depths of 100 to 160
metres and can have localized steep to near-vertical faces. Below these depths the seabed becomes
relatively flat near depths of 190 metres. The surveys measured depths as great as 190 metres, with the
deepest part of the channel being in the order of 220 metres as confirmed on the nautical charts for
Douglas Channel. The bathymetry suggests that the proposed VLCC class vessels will be able to berth
relatively close to shore with minimal dredging requirements.
2.5.2 Sidescan Sonar Surveys
The sidescan sonar data indicate that the seabed can be characterized as steep slopes covered by a
relatively thin layer of fine-grained sediments with outcrops of exposed bedrock. The sidescan images
also reveal numerous debris flow features at the base of the steep slopes which may be related to historic
or recent debris flow events from onshore streams / gullies. The bedrock surfaces show linear features
that may be remnants of glacial erosion, or possible geological lineaments.
2.5.3 Seismic Reflection Surveys
The seismic reflection surveys were designed to provide imagery of the upper layers of seabed sediments
from the surface to the bedrock below. The results confirm that the seabed areas are characterized by
relatively thin layers of fine-grained sediment draped over the more steeply dipping seabed slopes. Most
of the near-shore areas appear to have only thin or non-existent sediments. Where overburden sediments
do exist, their thicknesses are highly variable and range in thickness from approximately 1 to 5 metres.
However, the southern portion of the site may have near-shore sediment layers as thick as 10 metres due
to the slopes being less steep. Also, in the northern portion of the site there are some near shore sediment
zones, in proximity to runoff streams and gullies, which are interpreted to have localized sediment
thicknesses up to 8 to 10 metres. These fine-grained sediment layers gradually become thicker towards
the bottom of the channel as the side slopes decrease with depth.
Since the seismic reflection signal was able to penetrate through the sediment to an acoustically hard
layer, it suggests there are only minimal amounts of organic material or biogenic gas within the sediment.
The hard layer has been interpreted as bedrock; however, it may be possible that in certain areas it is
made up of coarse sediment.
2.6 Geotechnical Studies
2.6.1 Marine Geotechnical Investigations
A marine geotechnical investigation will be conducted during the detailed design phase of the project. It
is anticipated this investigation will include the drilling of underwater boreholes and the testing of core
samples to determine the strength characteristics of the bedrock and establish appropriate foundation
design parameters for the marine structures. In addition to the marine investigation, bore holes will also
be drilled along the foreshore as part of the detailed uplands geotechnical investigation in order to
establish the foundation requirements for onshore structures, such as trestle abutments and mooring
points.
January 20, 2010 FINAL - Rev. 0 Page 2-17