California Code, Health and Safety Code - HSC § 39666

(a) Following a noticed public hearing, the state board shall adopt airborne toxic control measures to reduce emissions of toxic air contaminants from nonvehicular sources.

(b) For toxic air contaminants for which the state board has determined, pursuant to Section 39662, that there is a threshold exposure level below which no significant adverse health effects are anticipated, the airborne toxic control measure shall be designed, in consideration of the factors specified in subdivision (b) of Section 39665, to reduce emissions sufficiently so that the source will not result in, or contribute to, ambient levels at or in excess of the level which may cause or contribute to adverse health effects as that level is estimated pursuant to subdivision (c) of Section 39660.

(c) For toxic air contaminants for which the state board has not specified a threshold exposure level pursuant to Section 39662, the airborne toxic control measure shall be designed, in consideration of the factors specified in subdivision (b) of Section 39665, to reduce emissions to the lowest level achievable through application of best available control technology or a more effective control method, unless the state board or a district board determines, based on an assessment of risk, that an alternative level of emission reduction is adequate or necessary to prevent an endangerment of public health.

(d) Not later than 120 days after the adoption or implementation by the state board of an airborne toxic control measure pursuant to this section or Section 39658, the districts shall implement and enforce the airborne toxic control measure or shall propose regulations enacting airborne toxic control measures on nonvehicular sources within their jurisdiction which meet the requirements of subdivisions (b), (c), and (e), except that a district may, at its option, and after considering the factors specified in subdivision (b) of Section 39665, adopt and enforce equally effective or more stringent airborne toxic control measures than the airborne toxic control measures adopted by the state board. A district shall adopt rules and regulations implementing airborne toxic control measures on nonvehicular sources within its jurisdiction in conformance with subdivisions (b), (c), and (e), not later than six months following the adoption of airborne toxic control measures by the state board.

(e) District new source review rules and regulations shall require new or modified sources to control emissions of toxic air contaminants consistent with subdivisions (b), (c), and (d) and Article 2.5 (commencing with Section 39656).

(f) Where an airborne toxic control measure requires the use of a specified method or methods to reduce, avoid, or eliminate the emissions of a toxic air contaminant, a source may submit to the district an alternative method or methods that will achieve an equal or greater amount of reduction in emissions of, and risk associated with, that toxic air contaminant. The district shall approve the proposed alternative method or methods if the operator of the source demonstrates that the method is, or the methods are, enforceable, that equal or greater amounts of reduction in emissions and risk will be achieved, and that the reductions will be achieved within the time period required by the applicable airborne toxic control measure. The district shall revoke approval of the alternative method or methods if the source fails to adequately implement the approved alternative method or methods or if subsequent monitoring demonstrates that the alternative method or methods do not reduce emissions and risk as required. The district shall notify the state board of any action it proposes to take pursuant to this subdivision. This subdivision is operative only to the extent it is consistent with the federal act.