Moss Landing Air: How are air results evaluated?
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We calculate whether an air result is hazardous by comparing how much is in the air (the concentration) with how long you may have contacted it.
- Exposure to fire events like Moss Landing are short-term, acute exposures.
- Long-term exposure (months to years) are considered chronic exposures.
Acute and chronic exposures each have their own threshold (called a “screening level”) for what is considered potentially hazardous.
So, if you were exposed to a contaminant for a short period of time, the concentration of the contaminant would have to be higher for it to potentially have a health impact than the same concentration over a longer period.
Further, each contaminant has a different toxicity. This means the screening levels for each are different.
- We take these differences into consideration when we are evaluating your data.
- When no screening level exists, experts assess and use the most health protective value.
Lastly, safety margins are built into creating these screening levels. The levels are conservative and are based on protecting the most sensitive community members. This means that, if there was data showing a level had been exceeded, it does not mean all could expect health effects.
What happens if data shows increased levels of contaminants in the air and how does EPA respond?
There are two types of air quality data collected by the extensive air monitoring and air sampling network at the site perimeters and in the community. The first is continuous real-time air monitoring, which looks for particulate matter (PM)2.5, PM10, and hydrogen fluoride. This data is available in real-time and informs EPA’s work immediately. The second is air sampling, which consists of samples that are sent to a lab for analysis for heavy metals and asbestos fibers. EPA usually gets sampling data within a few days to one week after they are collected. The air monitoring data and the air sampling data are collected at the same locations, so that they can be compared to each other.
The continuous, real-time air monitoring data is checked by Vistra’s contractor and by EPA for elevated readings. If sustained elevated readings are detected, the site team reviews wind data and site activities then checks for any possible source of the elevated reading. Elevated dust readings can (and often do) result from non-site-related factors, such as elevated dust readings from increased traffic on public roads and from fog. The site team uses multiple points of data to rule out anomalies from non-site-related factors. Site work could cause a measurable increase in dust levels - if so, additional wetting may be needed for dust control or a change might be needed to the work approach and work may pause while changes are made. Since air monitoring results are available in real time, these changes can be made in the moment.
Vistra provides air sampling data to the County of Monterey as Vistra receives and processes the data reports. Vistra also compares the data to screening levels established for the community. An exceedance of a screening level does not necessarily mean that there is a human health impact. The screening levels are set very low and serve as an early warning and help inform dust mitigation strategy and site activities to prevent potential future exceedances. If an exceedance is found, the corresponding air monitoring data is checked for any trends, elevated readings, or patterns. The wind data and site activity for that day is also reviewed. Based on that information, a stop work order or a change to the dust mitigation or other work approaches may be required.
If a threat to human health is detected, such as a fire or thermal runaway event, all battery work will be stopped and EPA will ensure the County of Monterey Department of Emergency Management (DEM), Environmental Health Bureau, and North County Fire Protection District are immediately notified. County DEM is responsible for public notification, and EPA will provide real time air monitoring data to inform decision making. Additional air monitoring equipment may be deployed as needed according to Vistra’s site-specific Emergency Response Plan. The Emergency Response Plan was developed after the January 2025 fire as a requirement of the cleanup agreement (ASAOC).