The Southern California Fires of 2007 occurred throughout seven counties and burned more than 350,000 acres in inhabited and open space areas. The fires consumed more than 2200 residential and commercial structures, as well some 2000 vehicles. The destruction left in the wake of the fires had the potential to result in wide-spread public exposure to toxic materials. Experiences from fires of a similar nature indicate that many hazardous substances may be found in burned residential areas, including metals, pesticides and herbicides, polycyclic aromatic hydrocarbons (PAHs), asbestos, and polychlorinated biphenyls (PCBs). Because of the widespread destruction affecting multiple population centers, the California Environmental Protection Agency (CalEPA) made the determination that the burn ash and debris posed an immediate threat to public health and safety according to the Federal Environmental Management Agency (FEMA) Disaster Assistance Policy 9523.13. As part of that determination, Geosyntec Consultants, in conjunction with scientists from CalEPA and the US Environmental Protection Agency (US EPA), designed a comprehensive sampling and analysis plan to determine the nature and concentration of contaminants of concern in the ash and debris.
Using a statistically-based sampling plan, debris samples were collected from 70 different burn sites in two affected counties. The samples were analyzed for the presence of constituents which may pose a risk to human health, including California Title 22 metals and PAHs.
Results indicated that the ash contained significant levels of heavy metals, including arsenic (mean range 7.31–14.0 mg/kg), cadmium (mean range 2.64–23.0 mg/kg), copper (mean range 3835–4383 mg/kg), and lead (mean range 404–1493 mg/kg), even after household hazardous waste was removed from the sampling area. Concentrations of these metals were significantly above California background levels and exceeded the health-based standards set forth in the US EPA Preliminary Remediation Guidelines (PRGs) and the California Human Health Screening Levels (CHHSLs).
Based on the results of this study, CalEPA undertook a massive clean-up effort in the affected jurisdictions. This was the second time such an analysis has been undertaken in the aftermath of massive wildfires in California, and represents, to our knowledge, the first comprehensive characterization of the public health risk from fire ash and debris. The results of this study underscore the importance of emergency recovery efforts and may provide information on which to base decisions for future firestorm events.