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Mixed science as Moss Landing MOS‑300 battery cleanup proceeds; supervisors request more monitoring
Summary
Federal and state agencies reported steady battery‑removal progress at Mos Landing's MOS‑300 site while DTSC's draft screening did not identify expected chronic human‑health risk from sampled soils; independent researchers reported a thin, patchy fallout layer of battery metals in Elkhorn Slough and early biota sampling showing nickel/cobalt signatures, prompting the board to ask staff to seek independent, ongoing biological monitoring funded by the responsible company.
Monterey County supervisors spent a large portion of their March 17 meeting on the MOS‑300 battery fire cleanup at Moss Landing, hearing divergent scientific findings and significant community concern before asking staff to pursue additional independent monitoring.
Federal and state operations: U.S. EPA, which leads on‑site battery removal, reported crews have deenergized and removed the bulk of accessible intact battery modules and expect continued demolition and debris characterization through mid‑ to late‑2026. County emergency management emphasized continued coordination with state and federal partners to protect public safety.
Draft assessments and agency view: Monterey County Environmental Health and the California Department of Toxic Substances Control (DTSC) summarized multi‑phase environmental sampling (soil, surface water, sediment, pore water) and a draft Preliminary Environmental Assessment (PEA) equivalent prepared by Vistra's consultant. DTSC toxicologist Dr. Wei Ying Jiang said the draft risk assessment, using conservative exposure assumptions (child residential receptor), concluded that chronic risks from the sampled soil and surface water are not expected under the scenarios modeled. DTSC emphasized the draft status and noted the assessment does not replace acute exposure analyses for the time of the fire.
"We evaluated the sampling data collected by the consultants and concur with the conclusion that human health risks are not expected from chronic exposure to the sampled soil and surface water," DTSC said in its presentation, stressing the conservatism of its exposure assumptions.
Independent research and community concerns: Researchers from the Ember consortium (Elkhorn Slough Reserve Foundation, Moss Landing Marine Labs, Monterey Bay Aquarium research partners) reported a different picture on near‑term ash deposition. Using handheld XRF and targeted early sampling days after the fire, Ember researchers said they detected a thin, highly concentrated, patchy fallout layer of battery metals (nickel, cobalt, manganese) on marsh surfaces that dissipated rapidly after rainfall and tidal action. Ember argued sampling approaches that core deeper soil months later can dilute or miss such thin surface layers.
"Battery metals were deposited in adjacent Elkhorn Slough wetlands as a thin patchy fallout layer that dispersed within weeks," said Ember researcher Dr. Kirsten Wson, urging thorough, multi‑date biota sampling to detect slow or uneven bioaccumulation.
Ember also presented early biota results showing correlated nickel/cobalt concentrations in mollusks and crustaceans at some sites; the researchers cautioned that bioaccumulation can take months or years to reveal ecological impacts and said many species, sites and dates are needed before drawing conclusions.
Community groups, including Never Again Moss Landing, criticized the cleanup plan and agency sampling and demanded expanded testing for dioxins/furans and long‑term health tracking. Never Again Moss Landing representative Ed Mitchell said regulators' methods had been inadequate during the early fire period and urged a broader, independent review and more comprehensive sampling.
Board response and requests: The board heard repeated requests to reconcile the agency and Ember findings. Supervisors asked staff to pursue two near‑term steps: (1) a written technical response from state agencies addressing Ember's methodological concerns and (2) a plan to seek independent, long‑term biological monitoring of Elkhorn Slough, with the county requesting Vistra fund a neutral third party (local research institutions were suggested for oversight). Staff agreed to research options and return with recommendations.
Why this matters: The MOS‑300 fire is the state's largest battery facility fire to date in scope and raised new questions about how best to detect and characterize combustion‑derived particle deposition on sensitive wetlands. The scientific disagreement centers on sampling timing and methods: early, high‑resolution surface screening versus later laboratory cores and broader screening levels. Both approaches provide different information; the board sought synthesis and additional independent monitoring.
What's next: DTSC and county health agencies continue interagency review of the draft PEA‑equivalent; EPA will proceed with phase‑2 demolition and waste characterization of heavily burned building sections. The board requested staff pursue a written technical response to Ember's critiques and return with options for independent biological monitoring paid by Vistra.
