Health & Saf. Code, § 40925

(a) On or before December 31, 1994, and at least once every three years thereafter, every district shall review and revise its attainment plan to correct for deficiencies in meeting the interim measures of progress incorporated into the plan pursuant to Section 40914, and to incorporate new data or projections into the plan, including, but not limited to, the quantity of emission reductions expected from the control measures adopted in the preceding three-year period and the dates that those emission reductions will be achieved, and the rates of population-related, industry-related, and vehicle-related emissions growth actually experienced in the district and projected for the future. This data shall be compared to the rate of emission reductions and growth projected in the previous triennial plan revision. Upon adoption of each triennial plan revision at a public hearing, the district board shall submit the revision to the state board.

(b) A district may modify the emission reduction strategy or alternative measure of progress for subsequent years based on this assessment if the district demonstrates to the state board, and the state board finds, that the modified strategy is at least as effective in improving air quality as the strategy which is being replaced.

(c) Each district which cannot demonstrate attainment by December 31, 1999, shall prepare and submit a comprehensive update of its plan to the state board not later than December 31, 1997, unless the state board determines, by not later than February 1, 1997, that a comprehensive plan update is unnecessary. The revised plan shall include an interim air quality improvement goal or an equivalent emission reduction strategy, subject to review and approval by the state board, to be achieved in the subsequent five-year period.