1. (a) Baseline amount. For the purposes of this subchapter, the baseline amount must be calculated as the lower of the following:

   1. (1) total amount of baseline emissions; or
   2. (2) total annual emissions allowed under authorizations, including authorized emissions from maintenance, shutdown, and startup activities, applicable to the source in the baseline year. Emissions from pending authorizations with administratively complete applications as of December 31 of the baseline year may be included in the total annual emissions allowed under authorizations.

2. (b) Baseline emissions. For the purposes of this subchapter, the baseline emissions must be calculated from:

   1. (1) the baseline year; or

   2. (2) a historical period, if the major stationary source's or Section 185 Account's emissions are irregular, cyclical, or otherwise vary significantly from year to year. Any single 24-month consecutive period within a historical period preceding January 1 of the baseline year may be used to calculate an average baseline emissions amount in tons per year for the major stationary source as the historical period. If used, the historical period must be:

      1. (A) ten years for non-electric utility steam generating units; or
      2. (B) five years for electrical utility steam generating units.

3. (c) Historical period. If a major stationary source or Section 185 Account uses a historical period as defined in subsection (b)(2) of this section, the baseline amount will:

   1. (1) use adequate data for calculating the baseline emissions;
   2. (2) be adjusted downward to exclude any unauthorized emissions that occurred while the source was operating above an emissions limitation that was legally enforceable during the consecutive 24-month period; and
   3. (3) be adjusted downward to exclude any emissions during the consecutive 24-month period that would have exceeded an emissions limitation that was legally enforceable in effect by December 31 of the baseline year.
4. (d) Adjustments. The baseline amounts must be adjusted downward to exclude any emissions that exceeded an emissions limit that was legally enforceable in effect by December 31 of the baseline year.
5. (e) Emissions units. Baseline amounts must include all emissions units located at the major stationary source as of December 31 of the baseline year. When control or ownership of emission units changes during the baseline year, the emissions from those emission units will be attributed to the major stationary source with control or ownership of the emissions unit on December 31 of the baseline year.
6. (f) Calculations. A baseline amount, reported in units of tons per year, must be calculated separately for each pollutant, volatile organic compounds and/or nitrogen oxides, for which the source meets the major source applicability requirements of §101.701 of this title (relating to Applicability).
7. (g) Compliance schedule. The owner or operator of each major stationary source meeting the requirements of §101.701 of this title must submit to the executive director a report establishing its baseline amount on a form published by the executive director. The baseline amounts forms must be submitted by the emissions inventory due date as specified under §101.10 of this title (relating to Emissions Inventory Requirements) for the fee assessment year, or 120 days after the effective date of a finding of failure to attain, whichever is later.
8. (h) Review. Where the baseline amount does not align with information recorded in either the emissions inventory database or the air permitting data systems, the executive director may direct that the baseline amount be based on the lower of reported emissions under §101.10 of this title or total annual authorized emissions. After review, the baseline amount will be fixed and not be changed except as allowed under this subchapter.

Source Note:The provisions of this §101.705 adopted to be effective November 13, 2025, 50 TexReg 7293.