Jas Garrett
JUNEAU, Alaska (KINY) – The Alaska Department of Transportation and Public Facilities (DOT&PF) last week engaged a contractor to conduct a geophysical site survey for the Juneau-Douglas North Transverse Project and Environmental Liaison (PEL) study. Fieldwork was conducted from February 13th to February 17th.
Geophysical data collection to be conducted at alternative sites at Sunny Point West and East, Vanderbilt and Twin Lakes will be evaluated for feasibility and environmental impact. Greg Lockwood, project manager for the Alaska Department of Transportation’s South Coast Region, explained how a PEL study works.
“The benefit of a PEL is that you can link the environmental process with the planning process. This saves time in the long run when going into the NEPA process about duplicative work, duplicate planning work, and project alternatives that you are doing during this PEL.” There is environmental work to do,” he said. “This is a relatively new process as we work on federal highway projects. It has been developed only recently to accelerate projects and coordinate with the public, government agencies and stakeholders. It is one of the tools that has been
PEL is scheduled to be completed in early summer. Lockwood added that this data will help DOT estimate the approximate cost of the project.
Geoscience Manager Keri Nutter said the preliminary geophysical study is non-invasive and a subsurface evaluation.
“They make use of seismic refraction and electrical resistivity. They use a sledgehammer with a steel plate to make soundings, and cables to create geophones placed in a row at regular intervals. “We can put it on the ground and from its soundings we can gather information for a timed return based on a variety of information: the layers of soil and rock beneath the surface,” she said.
The seismic method of hitting a metal plate with a sledgehammer allows geotechnical engineers to determine earthquake velocities. For electrical resistivity, electrodes are placed in the ground using cables with low voltage direct current connected to them. This allows geotechnical engineers to measure how well the ground conducts electricity.
David Barrick and Chloe Jungwirth both worked for DOWL and were contracted to conduct geophysical field surveys. Barrick lives in Montana and travels around the country conducting geophysical research. Jungwirth graduated from the South Dakota School of Mines last year and moved to Anchorage for work. She enjoys being outside, she said.
“Our goal with this project is to figure out the depth of the bedrock, because if you want to build a bridge, the deeper the bedrock, the more expensive the bridge will be,” Barrick said.
The challenge Barrick and Jungwirth faced last week was working around the tide and moving thousands of pounds of equipment through dense forest.
“The geology in Alaska is much more complex than in the lower 48. That’s why we have these mountain ranges and everything like that. This is Alaska, we have to be tougher here.” said Varrick.
Barrick added that another challenge with seismic data is the movement of water through nearby traffic and creating noise.
A special area permit to conduct fieldwork within the Mendenhall Slough State Game Refuge was issued by the Alaska Department of Fish and Game on January 30, and is in collaboration with federal agencies such as the U.S. Army Corps of Engineers and the National Marine Fisheries Service. Discussions have also been completed.
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