## Facts

- EPA promulgated New Source Performance Standards (NSPS) for lime manufacturing and lime-hydrating units under Clean Air Act § 111, limiting particulate emissions and imposing opacity limits for certain sources.
- Section 111 required EPA to identify the “best system of emission reduction” that has been “adequately demonstrated” and to set standards achievable by new sources using that system.
- EPA gathered information by visiting 39 plants and conducting emissions tests at 6 plants.
- EPA relied primarily on fabric filters (baghouses) and used test results to set numerical particulate limits and opacity standards.
- The lime industry contained many plant types and operating conditions; EPA acknowledged variability in feedstock characteristics, kiln gas velocity, operating capacity, particle size distributions, and dust generation (including from coal combustion).
- The administrative record did not clearly establish that the 6 tested facilities were representative of the range of regulated sources; only 3 of the 6 could consistently meet the proposed limits.
- National Lime Association petitioned for review, asserting that the record did not support the limits’ achievability across the industry and that EPA’s explanation failed requirements of reasoned decisionmaking under the Clean Air Act and the Administrative Procedure Act.

## Issues

1. Whether EPA adequately supported, on the administrative record, that the NSPS particulate and opacity limits were achievable across the regulated category using an “adequately demonstrated” emission-control system under Clean Air Act § 111.
2. Whether EPA’s explanation satisfied reasoned decisionmaking by addressing known sources of variability and justifying extrapolation from limited test data to industry-wide numerical limits, including in light of the 1977 Clean Air Act amendments emphasizing continuous emission reduction.

## Decision

- The court found inadequate support in the administrative record for the promulgated NSPS, particularly on industry-wide achievability.
- The court granted the petition in part and remanded the standards to EPA for further consideration and record development.
- The court did not vacate the rule outright but held that, as justified on the existing record, EPA’s action lacked the required reasoned support.

## Legal Principles

- Under Clean Air Act § 111, EPA must demonstrate both that the chosen control system is “adequately demonstrated” and that the numerical standards are realistically achievable for the source category on a continuous basis.
- EPA may not justify industry-wide standards using limited, unrepresentative test data without a reasoned explanation connecting the data to the chosen limits and addressing material operational variability.
- Judicial deference to technical agency judgments depends on an adequately explained and supported administrative record; technical complexity does not excuse failure to analyze relevant factors.
- Reasoned decisionmaking requires EPA to confront obvious sources of performance variation and explain how it extrapolates from tested facilities and conditions to the broader regulated universe.

## Conclusion

The D.C. Circuit remanded EPA’s lime-plant NSPS because the agency did not adequately show, with representative evidence and a reasoned explanation, that the selected control approach and numerical limits were achievable across the industry under realistic, continuous operating conditions.


Nat'l Lime Ass'n v. EPA, 627 F.2d 416 (D.C. Cir. 1980)