The Arcata Wastewater Treatment Plant is one of the most important pieces of infrastructure at risk as the sea level rises, but it’s unlikely to be moved farther inland for at least another half century.
The treatment plant isn’t only at risk from rising sea levels potentially inundating it from the west, particularly during a storm surge, but also from rising groundwater and tectonic forces causing the land to sink, according to the 2018 City of Arcata Sea Level Rise Risk Assessment compiled by local sea level rise expert Alderon Laird. Laird has said to expect .9 feet of sea level rising by 2030, 1.9 feet by 2050 and 3.2 feet by 2070.
“The risk to wastewater infrastructure is ongoing,” the assessment states. “Based on existing conditions, exposure of wastewater infrastructure will become critical due to the combination of two feet of sea level rise and king tides that could result in three feet of sea level rise for several days a year.”
Man-made structures, such as dikes, are preventing Humboldt Bay from inundating the marsh and other low-lying areas, but those dikes get overtopped during storm surges. Building those dikes higher is complicated because of how land use is regulated along the coast, officials have said.
Arcata city officials said they are discussing moving the treatment plant to a different location in the future, but that’s too expensive to do right now.
“We have a plan for that,” said Mark Andre, Arcata’s director of environmental services, at a meeting on upgrades to the wastewater treatment facility at the Arcata Marsh Interpretive Center on Friday night. “But moving the treatment plant would cost three or four times what we’re talking about, and it would pretty much eliminate what we have, our wetland-based system, which is highly energy efficient.”
Instead, they’re making about $64 million in upgrades to the existing facility that will help it comply with state regulations and keep the city from being fined.
