Sec. 169. For purposes of this part - 
     (1) The term "major emitting facility" means any of the fol-
  lowing stationary sources of air pollutants which emit, or have
  the potential to emit, one hundred tons per year or more of any
  air pollutant  from the following types  of stationary sources:
  fossil-fuel  fired  steam  electric  plants of  more  than  two
  hundred and  fifty million British thermal units  per hour heat
  input, coal cleaning plants (thermal dryers), kraft pulp mills,
  Portland Cement  plants, primary zinc smelters,  iron and steel
  mill plants,  primary  aluminum ore  reduction plants,  primary
  copper  smelters, municipal  incinerators  capable of  charging
  more than fifty tons of refuse per day, hydrofluoric, sulfuric,
  and  nitric acid  plants,  petroleum  refineries, lime  plants,
  phosphate
  rock processing plants,  coke oven  batteries, sulfur  recovery
  plants,  carbon  black  plants (furnace  process)  primary lead
  smelters, fuel conversion  plants, sintering plants,  secondary
  metal production  facilities, chemical process  plants, fossil-
  fuel boilers of more than two hundred and fifty million British
  thermal  units  per  hour  heat input,  petroleum  storage  and
  transfer  facilities with  a  capacity exceeding  three hundred
  thousand barrels,  taconite  ore processing  facilities,  glass
  fiber processing plants,  charcoal production facilities.  Such
  term  also includes any other source with the potential to emit
  two hundred  and fifty tons per year or more of any air pollut-
  ant. This  term shall  not include  new or modified  facilities
  which are nonprofit health or education institutions which have
  been exempted by the State.
       (2)(A) The term "commenced"  as applied to construction of
     a major emitting facility  means that the owner or  operator
     has  obtained  all  necessary  preconstruction  approvals or
     permits required  by Federal, State, or  local air pollution
     emissions and air quality laws or regulations and either has
     (i) begun,  or  caused to  begin,  a continuous  program  of
     physical  on-site  construction  of  the  facility  or  (ii)
     entered into binding  agreements or contractual obligations,
     which cannot  be canceled  or  modified without  substantial
     loss to the  owner or  operator, to undertake  a program  of
     construction  of  the  facility  to be  completed  within  a
     reasonable time.
       (B)  The  term  "necessary  preconstruction  approvals  or
     permits" means  those permits  or approvals required  by the
     permitting authority  as a  precondition to  undertaking any
     activity under clauses  (i) or (ii)  of subparagraph (A)  of
     this paragraph.
       (C) The  term "construction" when used  in connection with
     any  source  or  facility,  includes  the  modification  (as
     defined in section 111(a)) of any source or facility.
       (3) The term "best  available control technology" means an
     emission limitation based on the maximum degree of reduction
     of  each  pollutant subject  to  regulation  under this  Act
     emitted  from  or  which  results from  any  major  emitting
     facility, which  the permitting authority, on a case-by-case
     basis,  taking  into   account  energy,  environmental,  and
     economic impacts  and other costs, determines  is achievable
     for   such  facility   through  application   of  production
     processes  and available  methods, systems,  and techniques,
     including  fuel  cleaning,  clean  fuels,  or  treatment  or
     innovative fuel combustion  techniques for  control of  each
     such  pollutant.  In no  event  shall  application of  "best
     available control  technology"  result in  emissions of  any
     pollutants which  will exceed  the emissions allowed  by any
     applicable standard  established pursuant to  section 111 or
     112 of this Act. Emissions  from any source utilizing  clean
     fuels,  or any  other means, to  comply with  this paragraph
     shall  not be  allowed to  increase above levels  that would
     have been required under
     this paragraph as it existed prior to enactment of the Clean
     Air Act Amendments of 1990.
       (4) The term "baseline concentration" means, with  respect
     to a pollutant, the ambient concentration levels which exist
     at the time of the first application for a permit in an area
     subject to this part, based on air quality data available in
     the Environmental Protection Agency or a State air pollution
     control  agency and  on such monitoring  data as  the permit
     applicant is required to submit. Such ambient  concentration
     levels shall  take into account all  projected emissions in,
     or  which  may affect,  such  area from  any  major emitting
     facility on which construction commenced prior to January 6,
     1975, but  which has not begun operation  by the date of the
     baseline air quality concentration  determination. Emissions
     of  sulfur  oxides and  particulate  matter  from any  major
     emitting  facility  on  which  construction  commenced after
     January 6, 1975, shall  not be included in the  baseline and
     shall be counted against  the maximum allowable increases in
     pollutant concentrations established under this part.
[42 U.S.C. 7479]