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Zook v. EPA: Does the EPA Have a Duty to Regulate Emissions From Animal Feeding Operations?

Updated: Jul 2, 2020

Cows in a barn (Photo by Edwin Remsberg).

This post should not be construed as legal advice.

Earlier in November, the U.S. Supreme Court denied a petition for a writ of certiorari in Zook v. Environmental Protection Agency. In Zook, plaintiffs brought a citizen suit against the Environmental Protection Agency (EPA) to compel EPA to regulate air emissions from animal feeding operations (AFOs) under the Clean Air Act (CAA). The U.S. District Court for the District of Columbia dismissed the suit and the court of appeals upheld this dismissal.

Clean Air Act

The CAA directs EPA to identify certain air pollutants and establish permissible levels that those pollutants can exist in the air. These pollutants are called criteria pollutants under the CAA and require the head of EPA to determine: 1) the emissions’ cause or contribution to air pollution which may reasonably be anticipated to impact human health or welfare; 2) if pollution comes from diverse or multiple stationary or mobile sources; and 3) whether the criteria was not established prior to Dec. 31, 1970.

Once EPA determines a pollutant is a criteria pollutant, it sets National Ambient Air Quality Standards (NAAQS) for that pollutant. The NAAQS will set permissible ambient air levels to protect human health and welfare. Since the CAA was enacted, EPA has only established six pollutants as criteria pollutants and set the subsequent NAAQS. Those six criteria pollutants are:

People walking past a barn (Photo by Edwin Remsberg).
  1. Ozone

  2. Particulate Matter

  3. Carbon Monoxide

  4. Nitrogen Oxides

  5. Sulfur Dioxide

  6. Lead

States develop plans to control emissions from these criteria pollutants.

The CAA also has a provision enabling EPA to regulate stationary sources by setting New Source Performance Standards (NSPS), focused on limiting emissions of a certain pollutant through best management practices. EPA is to reevaluate this list of NSPSs from time to time.

The final provision to briefly discuss is the CAA’s citizen suit provision, which is very limited. Citizens can bring suits against EPA for failure to perform a duty which is not discretionary, or for unreasonable delay to carry out a nondiscretionary duty. The citizens’ suit provision does not allow citizens to direct EPA to perform a discretionary duty.

Facts of Zook

Zook and other plaintiffs are all residents of Iowa who teach at, attended, or have children at a school which was the focus of a study that recommended to EPA to regulate air emissions from AFOs . EPA has declined to regulate certain emissions from AFOs as criteria pollutants and set NAAQS or regulate as stationary sources. EPA argues that this is a discretionary duty and the Zooks and other plaintiffs have not alleged a nondiscretionary duty to bring a CAA citizen suit action.

District Court’s Ruling

The district court finds that EPA’s duty to list pollutants as criteria pollutants and establish NAAQSs for those pollutants is nondiscretionary, but EPA must first make the policy determination to list that pollutant. The CAA leaves that determination to the EPA administrator’s sole judgment. Absent EPA making this determination, there is no nondiscretionary duty to set standards for those pollutants.

In the Zooks case, EPA has made no determination that air emissions from AFOs could be considered criteria pollutants. Because the Administrator has not made this determination there is no nondiscretionary duty to allow plaintiffs to bring a citizen suit to order for EPA to list those pollutants as criteria.

Looking at secondary sources, the CAA allows EPA the discretion to make the determination that a stationary source endangers human health or welfare. Once that determination is made then EPA has a nondiscretionary duty to list the sources and set NSPS standards.

Aerial image of a farm (Photo by Edwin Remsberg).

The court pointed out the plaintiffs could file a rulemaking petition seeking EPA to make the plaintiffs’ desired policy outcomes. If the EPA makes that determination, then the duty would become nondiscretionary. The court granted EPA’s motion to dismiss.

Appeal to the Court of Appeals

The Zooks and other plaintiffs appealed the district court’s decision to dismiss and the U.S. Court of Appeals for the DC Circuit affirmed the district court’s decision. The court of appeals agreed with the district court that the plaintiffs had not identified any nondiscretionary action that EPA failed to perform. The judgment to act on information is placed solely in the hands of the EPA and the court cannot substitute its own judgment for that of the EPA, according to prior court decisions. Finally, although scientific evidence could show that emissions from AFOs could impact human health that evidence did not give rise to a nondiscretionary duty to EPA to act. For these reasons, the district court was proper to dismiss the plaintiffs’ case.

U.S. Supreme Court

As stated earlier, the U.S. Supreme Court denied a petition for a writ of certiorari by the plaintiffs, which means they will not be hearing an appeal in this case. The decision of the court of appeals affirming the district court’s opinion dismissing the plaintiff’s case will stand.

What Does This Mean for You?

Many of you may operate AFOs (either dairies or poultry houses) in Maryland and currently EPA is taking no action to regulate air emissions from your AFOs. Until EPA decides to 1) list emissions from AFOs as criteria pollutants, 2 set NAAQSs for those pollutants or as stationary sources and 3) require adoption of NSPS standards, then the EPA cannot be forced to make this determination. The Zook case upholds the idea that listing these pollutants is within EPA’s discretion. Once EPA makes this determination, though, then the duty becomes nondiscretionary.

EPA has pushed in the past to determine the amount of emissions from AFOs. In 2005, EPA announced an amnesty program for AFO operators. The program was designed to gather data from participating AFOs on air emissions and exempt the participating farms from lawsuits for CAA violations. EPA’s goal was to gather data to establish methodology to regulate emissions from AFOs. To date, EPA has not acted on the data gathered from the participating farms.

EPA’s exemption from reporting air emissions of certain hazardous emissions has been challenged in federal court as well. This exemption was granted to requirements under Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA) and the Emergency Planning and Community-Right-to-Know Act (EPCRA). Both acts require reporting when a threshold quantity of certain substances is released into the environment (including through the air).

Bird's eye view of a farm (Photo by Edwin Remsberg).

In 2010, EPA asked the federal court to return the final determination to exempt AFOs from the reporting requirements so EPA could reconsider the exemption and announce a new policy by 2012. As of 2015, EPA had not announced any new policy and the original parties challenging the exemption repetitioned the court to force EPA to make a final determination. More on that here: Reporting Exemption for Animal Feeding Operations Challenged. To learn more about the exemption, see this webinar conducted by Shannon Ferrell, Oklahoma State University, earlier this year.

At this time, air emission issues from AFOs will continue to be a growing legal issue that isn’t going anywhere soon. Although the Zook decision upholds the principle that the EPA has discretion to act on when to regulate AFO emissions, EPA may one day decide to act on that discretion — which could potentially bring new regulations to AFO operators.


Zook v. Envtl. Protection Agency, 611 Fed. App’x 725 (D.C. Cir. 2015), cert. denied, 15-350 (Nov. 2, 2015).

Zook v. McCarthy, 52 F.Supp3d 69 (D. D.C. 2014).

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