(a) By May 1, 1986, the permittees of all domestic sewage and industrial wastewater treatment facilities discharging into the Lake Houston watershed which utilize gaseous chlorination disinfection systems shall install dual-feed chlorination systems which are capable of automatically changing from one cylinder to another.(b) Chlorination disinfection systems shall be operated so that a minimum chlorine residual of 1.0 milligram per liter (mg/l) and a maximum chlorine residual of 4.0 mg/l measured on an instantaneous grab sample is not exceeded for discharges into the Lake Houston watershed.