(a) Wastewater treatment systems other than oxidation ponds systems.(1) By January 1, 1993, all domestic wastewater discharges from wastewater treatment systems other than oxidation pond systems shall meet the following effluent limits:Attached Graphic(2) By January 1, 1993, all wastewater treatment systems other than oxidation pond systems shall employ filtration to supplement suspended solids removal.(3) Domestic wastewater discharged from wastewater treatment systems other than oxidation pond systems shall be disinfected prior to discharge in a manner to protect public health and aquatic life. Any appropriate process may be considered and approved on a case-by-case basis. If chlorine is utilized as the disinfectant, the effluent shall have a minimum concentration of 1 mg/liter chlorine after a 20 minute detention time. The maximum chlorine residual in any discharge shall in no event be greater than four mg/liter, or that necessary to protect aquatic life.(b) Oxidation pond systems. (1) All domestic wastewater from oxidation pond systems shall meet the following effluent limits:Attached Graphic(2) Unless otherwise specified in a permit, chemical disinfection is not required for oxidation pond systems when the total retention time in the wastewater treatment system (based upon design flow) is at least 21 days.