(The “silencers” at CalPortland, which provided the photo)
The Duwamish River loading dock where at least one version of the notorious “Hum” was traced in September has continued working to quiet the offloading equipment that’s blamed for it. Tonight we have an update from Pete Stoltz of CalPortland, who says the promised additional silencing equipment has been installed, and will get a real-world test when another ship arrives this weekend:

In late September, we learned that the machine we use to offload ships at our terminal could be the source of the “West Seattle Hum.” We learned more about “the hum.” After meeting with the co-chairs of the Highland Park Action Committee, and hearing the nature of their concern, we decided to take steps to reduce noise from the machine even though noise levels measured by the City of Seattle and contracted noise experts confirmed the operation technically complied with State and local noise requirements.

We suspended ship-offloading operations to disassemble and inspect noise control equipment on the machine. We replaced one of the two silencers on the machine, ordered fabrication of a second replacement silencer from the factory, and our crew used down time during weather delays to install insulation, noise blankets and plywood noise shields. Unfortunately, this effort reduced measured noise levels at the machine, but reports of “the hum” continued.

CalPortland is happy to report delivery and installation of the second silencer is complete as promised. The crew tested the machine by running it empty before and after they installed the second new silencer and report being encouraged by the results. Their observations are consistent with the advice of noise experts, who predict that installation of the second silencer will substantially reduce noise levels.

We will be paying close attention with our fingers crossed when we begin offloading the next ship scheduled to arrive this weekend. Offloading will likely continue through next week as the weather permits. This is the only ship scheduled for offloading this month. The next ship will arrive after the New Year.

Based on the advice of noise experts, we are confident installation of the second silencer will address our neighbors’ concerns. We will evaluate the situation during this offloading event and consider the need for additional noise control measures. We will use the time between ships in December and January to identify and implement additional actions as necessary and appropriate.