Administrative deference – in essence, that courts resolve close questions in favor of “expert” agencies – is a cornerstone of environmental practice and we’ve blogged frequently on this issue. Courts question agencies, however, when their decisions do not square with cited evidence. For regulatory challenges, courts also confine their review to the administrative record and agencies cannot interject new evidence during a judicial appeal of a regulation.

In one of the most recent examples of this and a great reminder to environmental practitioners and legal departments of both utilities and manufacturers, the D.C. Circuit Court of Appeals vacated an Environmental Protection Agency (EPA) regulatory decision adding the West Vermont Drinking Water Contamination Site to the Superfund National Priorities List (NPL) earlier this month. The two potentially responsible parties for the site petitioned for review of this designation, arguing that the EPA’s decision was arbitrary and capricious because it failed to consider and address evidence contradicting the EPA’s decision. Inclusion of the site on the NPL means it would be considered high priority for remedial action.

The vacature is rare enough to warrant explanation. The site includes two aquifers that the EPA treated as a single hydrologic unit for purposes of quantifying risk and placing the site on the NPL. The record included evidence of a confining layer of clay or till separating the two aquifers, which suggests the aquifers were not a single hydrologic unit. There was no indication that the EPA considered or addressed this contrary evidence. Had the aquifers been treated separately, the site would not have reached the threshold risk required for inclusion on the NPL.

Notably, the court explained that while the EPA is not required to address every fact or opinion included in comments to a rulemaking, it must respond to comments that would result in a change to the rule if true. The EPA presented some evidence at the judicial appeal stage that did address petitioners’ adverse comments, but the court held that the EPA’s evidence was just too late to support its NPL listing.