Carus Chemical Company v. United States Environmental Protection Agency

United States Court of Appeals, District of Columbia Circuit
395 F.3d 434 (2005)

ELI5:

Rule of Law:

An agency's long-standing interpretation of its own regulation is entitled to substantial deference and will be upheld so long as it is textually permissible and not plainly erroneous or inconsistent with the regulation.

Facts:

For over 100 years, the Matthiessen & Hegeler Zinc Company operated a smelter and rolling mill on a site in La Salle, Illinois.
During its operation, the company produced two large slag piles, which are byproducts of the smelting process.
One six-acre slag pile is located adjacent to, and partly within, the Little Vermilion River.
Carus Chemical Company later acquired a portion of this property to operate its own manufacturing plant, and part of the slag pile is located on its land.
Environmental testing of the site by the Illinois EPA in 1991 and 1993 revealed the presence of hazardous substances, including cadmium, copper, lead, and zinc, in sediment, groundwater, and soil samples.
The EPA determined that these hazardous substances were being released from the slag piles into the Little Vermilion River, which is classified as a fishery.

Procedural Posture:

The Environmental Protection Agency (EPA) scored the Matthiessen & Hegeler site using its Hazard Ranking System (HRS) based on data from the Illinois EPA.
The site's score exceeded the 28.50 threshold, leading the EPA to propose adding the site to the National Priorities List (NPL).
During the public comment period, Carus Chemical Company submitted comments and technical documents opposing the proposed listing.
The EPA reviewed Carus's comments, found them unpersuasive, and published a final rule in the Federal Register adding the site to the NPL.
Carus Chemical Company petitioned the U.S. Court of Appeals for the D.C. Circuit for review of the EPA's final rule.

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Issue:

Does the Environmental Protection Agency act arbitrarily and capriciously by interpreting its Hazard Ranking System regulation (§ 2.4.1.1) to require using the highest toxicity factor for a hazardous substance, regardless of whether the corresponding route of exposure is likely for the specific environmental pathway being scored?

Opinions:

Majority - Ginsburg, Chief Judge.

No. The Environmental Protection Agency's interpretation of its regulation was reasonable, consistent with the regulation's plain text, and entitled to deference. The court held that HRS § 2.4.1.1 unambiguously requires the agency to 'use the highest assigned value, regardless of exposure route' when a substance has toxicity data for multiple exposure routes. The court rejected Carus's argument that it was nonsensical to use a toxicity value for inhalation when scoring a surface water pathway. The court found that this was not a mere 'litigation position,' as the EPA had consistently interpreted and applied the rule this way since its promulgation in 1990, explaining that migration pathways can lead to multiple exposure routes and that this method simplifies the ranking process. Because the agency's interpretation was textually supported and long-standing, it was owed substantial deference. The court also affirmed the agency's decision to list the site, finding that Carus's new data did not demonstrate that the original data was incorrect or that the site score was wrong.

Analysis:

This decision strongly reinforces the principle of judicial deference to an agency's interpretation of its own regulations, often called 'Auer deference.' It establishes that a court will not disturb an agency's consistent and textually plausible reading of a complex rule, even if that reading seems counter-intuitive or scientifically imperfect in a specific application. The case demonstrates the difficulty challengers face in overturning agency actions under the 'arbitrary and capricious' standard, especially in highly technical areas like environmental science. For future cases, this holding solidifies the EPA's authority in applying its Hazard Ranking System, making it difficult for property owners to challenge NPL listings by attacking the logic of the scoring methodology itself, as opposed to proving factual errors in the data used.

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