MOSS LANDING >> Highway 1 re-opened late Sunday afternoon near the Vistra storage plant, where a battery fire broke out Thursday.

CalTrans urged travelers in the area to be alert for emergency responders still on the scene at the incident command center near the Moss Landing Energy Storage Facility. The California Highway Patrol would also “continue to have an active presence in the area,” according to a press release.

Officials reported Saturday afternoon that they are “cautiously optimistic” that the worst has passed.

About 80% of the plant, and the lithium batteries it housed, were consumed in the fire, said Joel Mendoza, chief of the North Monterey County Fire Department, at Saturday’s press conference. The plant, located across from Moss Landing Harbor on the site of a former PG&E power plant, holds tens of thousands of lithium batteries. Such battery fires are notoriously difficult to extinguish, can burn at high temperatures.

Highway 1 had closed in both directions between Highway 183 and Struve Road, officials said, to make sure emergency vehicles had clear access to the site in case it flared up again.

Federal officials are monitoring the air quality in addition to Vistra’s roaming air quality monitoring efforts, said Olivia Trombadore, onsite coordinator for the U.S. Environmental Protection Agency. The agency set up nine air quality monitors the first night after the fire broke out to check for hydrogen fluoride and particulates, two contaminants that can pose health risks, in and around the fire site and evacuation area. Their models indicated that hydrogen fluoride, an acidic gas that is hazardous to inhale, would have been consumed in a fire of the size that occurred, she said.

“We have not seen any levels of these two contaminants that would pose a threat to the public,” she said.

Richard Stedman, the air pollution control officer for the Monterey Bay Air Resources District, said that despite news reports of unhealthy air quality, the real-time air monitoring stations have recorded data mostly in the “good” to “moderate” range. As of Monday morning, the stations in Monterey, Salinas, King City, Watsonville and Santa Cruz were reporting good air quality, while Hollister, Felton and Boulder Creek were reporting moderate air quality. This data can be viewed at MBARD.org/current-air-quality-forecast-1ac8512.

Stedman attributed the moderate air quality levels to the increase in residents firing up their wood-burning stoves as a result of the cold weather throughout California and said this does not warrant an air quality advisory at this time.

“Some people are looking and seeing localized impacts here, but indeed that’s happening throughout the state because of the cold weather,” he said. “Also, the cold weather actually keeps the pollutants closer to the ground, especially if we have an inversion or a marine layer. We didn’t have that when the fire first started, but a marine layer’s coming in now, and that has a tendency to trap pollutants, but we have had good dispersion throughout this incident.”

Marni Flagg, assistant director of the County of Monterey Environmental Health, said her department is working with the EPA and state partners to manage and analyze data and get a report out to the public.

“Those reports and information will categorize that there has been non-detect of HF, and the other particles that are in the air are not harmful,” she said.

A majority of residents living near the Vistra storage plant in Moss Landing returned home Friday night, officials said, just hours after an evacuation order was lifted.

The conflagration raises questions about the safety of a technology — battery storage — that is considered important for supporting California’s expanded use of solar and wind energy in the long term. In the past years, the state has been increasingly reliant on huge battery storage plants to capture electricity during the daytime and release it on the grid at night to reduce the risk of blackouts during hot summer months, when demand is high.

County Supervisor Glenn Church and state Assemblywoman Dawn Addis called on Vistra to provide greater safety assurances to the public when it comes to its roughly $1 billion battery storage facility.

“We need to make sure that when we say to a community, ‘We are working on climate solutions,’ we are not saying ‘We are doing that, but it’s on the back of your health and safety,” Addis said, calling for a full investigation of the fire.

“We will put the best technology and the best human minds to work to make sure that we can get the highest probability it won’t happen again,” said Vistra Senior Director of Community Affairs Brad Watson.

The fire was reported Thursday afternoon, when alarming plumes of black smoke billowed from one of the world’s largest battery storage plants. The event closed Highway 1 and evacuate residents in Northern Monterey County, from areas of Moss Landing south of Elkhorn Slough, north of Molera Road and Monterey Dunes Way, and west of Castroville Boulevard and Elkhorn Road to the ocean.

Fire crews did not engage with the fire, which was contained to the site, but let it burn out on its own. The flames continued to flare through Thursday and smoldered into Friday. Evacuation orders were lifted at about 6 p.m. Friday night, with officials advising returning residents to stay indoors, limit outdoor exposure and turn off their ventilation systems.

A county hotline at 831-769-8700 has also been established for residents to call officials with any questions about the air quality and best practices for keeping safe, Pasculli said. Current air quality can be checked at https://www.mbard.org/current-air-quality-forecast-1ac8512

Bay Area News Group staff writers Paul Rogers and Molly Gibbs, along with the Monterey Herald’s David Kellogg and Santa Cruz Sentinel’s Nick Sestanovich contributed to this report.