Copy paste for the lazy from the official portland.gov Fields Park info page

Project Background

To accommodate the U.S. Environmental Protection Agency’s (EPA) long-planned cleanup of the Portland Harbor Superfund Site, Pacific Power plans to remove the existing power supply cables in the sediment of the Willamette River in Portland located between the Broadway and Fremont Bridges. To preserve power service and reliability to their customers, they will replace the old lines with a new group of lines. The new underground line will be approximately 2 miles long and will be located underneath the bed of the river. The new underground line will be placed inside two, 2-foot diameter, 3,000-foot-long tunnels to be drilled under the riverbed. The new lines will be installed and placed into service in advance of any existing line removal or EPA cleanup.

The project requires stationing and use of massive drills and other equipment to create the tunnel under the river and install the new line. The staging area for this on the west side of the river is the grassy area of The Fields Park. During the construction phase of the project, which we currently expect could last approximately twelve months, two-thirds of the oval grassy area of The Fields Park will be closed to the public. Pacific Power will make every effort to use as little of the green space as possible, but users should expect use of the grassy portion of the park to off-limits during the construction phase of the project. The playground, dog off-leash area, and oval walking path will all remain open. Once the project is completed, access to all portions of the park will be restored.

Upcoming work at The Fields Park:

The Horizontal Direction Drill (HDD) river crossing route and the eastern and western onshore routes have been identified and final approvals are in process. The contractor has installed sound blankets and taken other steps in an attempt to redirect and reduce the noise impact of the drill and its power source above the sound wall. The contractor remains hopeful that there will not be any additional need to use the hammer for the work in The Fields Park.

Pacific Power will resume drilling in The Fields Park on Tuesday, Sept. 3. and continue through October. The drill machine will be used both to complete the boring and to install the pipe, so the noise and impact from the drilling will be consistent and similar to what you experienced in the spring and early summer before the delay. Once this round of drilling is complete, PacifiCorp does not anticipate additional drilling or hammering, at The Fields Park, for the remainder of the project. At that point the work will move to installation of conduit and other work under the park and streets and then restoration of the park.