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The Environmental Protection Agency (EPA) is promulgating revisions to its major New Source Review (NSR) applicability regulations to clarify when the requirement to obtain a major NSR permit applies to a source proposing to undertake a physical change or a change in the method of operation (i.e., a project) under the major NSR preconstruction permitting programs. Under these programs, an existing major stationary source proposing to undertake a project must determine whether that project will constitute a major modification subject to the major NSR preconstruction permitting requirements by following a two-step applicability test. The first step is to determine if the proposed project would result in a "significant emissions increase" of a regulated NSR pollutant (Step 1). If the proposed project is determined to result in such an increase, the second step is to determine if the project would also result in a "significant net emissions increase" of that pollutant from the source (Step 2). In this action, we are promulgating revisions to our major NSR applicability regulations to clarify that both increases and decreases in emissions resulting from a proposed project can be considered in Step 1 of the major NSR major modification applicability test. We refer to the consideration of emissions increases and decreases in Step 1 as project emissions accounting.