Data centers; permit requirements, emission limits for certain engine-generator sets.

The document layout was changed from a single-column format to a multi-column format with increased line spacing and indentation, likely for printing or formatting purposes.

Added a 'Substitute' header and committee attribution to indicate the bill was amended by the House Committee on Agriculture, Chesapeake and Natural Resources.

Adjusted line breaks and spacing to fit the new substitute format, but no policy content was added, removed, or altered.

The bill title changed from 'data center carbon dioxide-emitting backup generators; air monitoring' to 'permit requirements for data centers; emission limits for certain engine-generator sets', indicating a shift in focus from operational rules to regulatory standards.

New definitions were added for critical terms including 'data center', 'diesel oxidation catalyst', 'diesel particulate filter', 'engine-generator set', 'selective catalytic reduction', 'Tier 4 equivalent', and 'gen-set' to clarify regulatory requirements.

Specific operational mandates regarding the maximum number of hours backup generators can run (500 hours), the requirement to use energy storage for two hours, and the notification process for nearby residents were removed.

A new requirement was added stating that for any data center permit application submitted on or after July 1, 2026, the Department cannot issue a permit unless the emission limits for engine-generator sets are equal to or less than those achieved by a Tier 4 equivalent unit.

Provisions requiring the Department to establish air quality monitoring sites near clusters of generators and to monitor cumulative health impacts on human populations were removed.