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District presents sediment sampling results; early tests show mostly sandy material and potential for beneficial reuse
Summary
Consultants reported completion of a sediment-characterization program for Humboldt Bay: most cores were sandy, finer material was concentrated near the old wharf and eelgrass areas, and toxicity/chemistry results are due to agencies next week with a full suitability determination expected in July.
Consultants from Moffatt & Nichol told the Humboldt Bay Harbor District on Thursday they completed a 12-day vibracore sampling program to characterize dredged material and determine whether sediment would be suitable for placement in the marine environment or for beneficial reuse.
"We just completed this in March," said Shelley Angera, a marine ecotoxicologist with Moffatt & Nichol, who described the program: crews collected 20-foot vibracores, composited samples for chemistry, grain-size, toxicity and bioaccumulation testing, and shipped samples under chain-of-custody to multiple laboratories. The program collected a large number of chemistry samples to allow follow-up analysis if initial results indicate unexpected contamination.
Angera said much of the sampled material was predominantly sand—useful for beach nourishment and other beneficial uses—while finer, organic-rich material was concentrated in quieter water near the existing wharf and adjacent to eelgrass beds. She noted three sites where sampling was abandoned because cores could not be recovered or sampling in eelgrass was deferred to avoid disturbance.
"We hope to have the results of the whole testing program in July," Angera said. She added that the first toxicity test (a sensitive amphipod 10-day exposure) and initial chemistry data were expected within days of the meeting; those early results will be shared with resource agencies and will inform whether additional bioaccumulation testing is required.
If agencies determine the sediments are suitable, the determination will be incorporated into permits and will guide where and how dredged material can be placed, including beneficial reuse options such as nearshore placement or beach nourishment. Angera said the team and resource agencies will use toxicity and bioaccumulation results together to decide suitability.
Commissioners and members of the aquaculture community asked whether the sampling would identify issues of concern to hatcheries, including possible local pH effects related to large concrete elements. Angera and other technical staff said ocean acidification on a global scale is driven by atmospheric carbon but that project-specific, localized water-quality effects would be evaluated as part of the environmental and sediment-review process.
The sediment characterization results will be forwarded to regulatory agencies for a suitability determination; the district expects a full testing memo and agency determination in July.
