(a) All sewage treatment facilities discharging into Segment 1428 of the Colorado River Basin and its tributaries, or Segment 1427, Onion Creek, and its tributaries, shall install dual-feed chlorination systems which are capable of automatically changing from one cylinder to another at the time they are constructed or by June 1, 1990.(b) Chlorination disinfection systems shall be operated so that a minimum chlorine residual of 1.0 milligrams per liter and a maximum chlorine residual of 4.0 milligrams per liter, measured on an instantaneous grab sample, are met for all discharges into Segment 1428, the Colorado River Basin, and its tributaries, or Segment 1427, Onion Creek, and its tributaries.(c) The commission may consider alternative disinfection methods on a case-by-case basis.