In recent months, the Agency for Toxic Substances and Disease Registry (ATSDR) and the “minimal risk levels” (MRLs) established by ATSDR have played a direct role in EPA’s efforts to regulate stationary sources under the Clean Air Act. The ATSDR is an advisory agency created by CERCLA in 1980 to help EPA assess health hazards associated with Superfund Sites. ATSDR’s role was expanded by the 1984 RCRA Amendments to assess risks from hazardous substance releases at landfills and surface impoundments. In 1986 SARA further expanded ATSDR’s responsibilities under CERCLA to assess the health impacts of hazardous substance releases.
In response to its CERCLA mandate, ATSDR has developed MRLs which define the level of daily human exposure to a hazardous substance release that is likely to result in no appreciable risk of an adverse non-cancer health effect. MRLs are designed to be a screening tool and are not intended to identify levels that would trigger cleanup or other action. As a result, exposure to a hazardous substance above an MRL does not necessarily mean that adverse health effects will occur. Rather, MRLs “are set below levels that, based on current information, might cause adverse health effects in the people most sensitive to such substance-induced effect.”
In comparison to the MRLs developed under CERCLA, there are two sets of standards established by EPA under the federal Clean Air Act to address health impacts from air emissions. One of these is the National Ambient Air Quality Standards (“NAAQS”) which define the concentration of a criteria pollutant in ambient air deemed to be protective of human health. State implementation plans are designed to achieve compliance with NAAQS. Likewise, the air emissions from permitted stationary sources are analyzed to ensure consistency with NAAQS. NAAQS are developed through a rigorous process that solicits input from the scientific community and public at large, and are promulgated as rules which are invariably subject to legal challenge and judicial review.
EPA also establishes emission limitations under Section 112 of the Clean Air Act to control toxic air emissions. These standards limit the emissions of hazardous air pollutants from specified categories of stationary sources. EPA assesses the risk to public health and the environment that remains after implementation of these limitations and must promulgate new health based standards to mitigate those residual risks.
In recent months EPA has moved beyond the NAAQS and toxic air pollutant standards to rely upon the ATSDR and its MRLs in identifying the allowable, and ostensibly enforceable, concentration of pollutants in ambient air under the Clean Air Act.
In one case, EPA asked ATSDR to evaluate the ambient air quality surrounding a stationary source. ATSDR concluded that the monitored concentrations of manganese from that source exceeded the pollutant’s MRL. Based on this finding, US DOJ filed a civil complaint against the facility. One of the claims alleged that the monitored manganese concentrations presented an imminent and substantial endangerment to public health and that injunctive action was necessary under Section 303 of the Clean Air Act. The complaint requested a judicial order requiring installation of fence-line air monitors and implementation by the source of all measures necessary to prevent exceedance of the MRL for manganese at those monitors. In effect, EPA identified the MRL as the allowable concentration of manganese to be emitted under the Clean Air Act. The case has settled.
In other matters, EPA Region 5 utilized the information from an ATSDR health consultation to justify issuance of a Section 114 order under the Clean Air Act which required installation of fence-line PM10 monitors around a facility with outdoor storage piles where manganese emissions were also an issue. The company refused to install the monitors and EPA filed a civil complaint seeking to enforce the Section 114 order. EPA sought summary judgment, relying in part upon an ATSDR finding that manganese concentrations in the ambient air surrounding a nearby facility exceeded the MRL. The underlying ATSDR assessment also used PM10 Air Quality Guidelines (AQG) from the World Health Organization (WHO) to conclude that ambient PM10 concentrations might cause respiratory problems for sensitive individuals. Notably, the WHO AQG are more conservative than the NAAQS (the WHO AQG for PM10 is 50 μg/m3 as a 24-hour mean, whereas the NAAQS for PM10 is 150 μg/m3 averaged over that same time period). The case settled.
It’s worth noting that ATSDR has finalized approximately 150 inhalation based MRLs covering pollutants emitted by a broad range of industrial facilities. However, I think it is safe to assume that stationary sources do not view MRLs as imposing any additional Clean Air Act strictures on their operations since the MRLs are not listed as applicable requirements in air permits. Moreover, the Title I and V permitting programs do not require sources to perform dispersion modeling to ensure compliance with MRLs.
It remains to be seen whether EPA under the new administration will continue to reach out to ATSDR and utilize the MRLs in addressing air pollutant emissions, particularly where such limits have never been vetted through a rulemaking process. I wouldn’t bet on it.