(a) Subject to the provisions of paragraph (b) of this section the following standards of performance establish the quantity or quality of pollutants or pollutant properties, controlled by this section, which may be discharged by a new source subject to the provisions of this subpart:

(b) Any overflow from facilities designed, constructed and operated to treat to the applicable limitations the precipitation and runoff resulting from a 10-year, 24-hour precipitation event shall not be subject to the limitations of this section.