No person shall discharge or cause to be discharged to any treatment
works wastewaters containing substances subject to an applicable categorical
pretreatment standard promulgated by EPA in excess of the quantity
prescribed in such applicable pretreatment standards except as otherwise
provided in this section. Compliance with such applicable pretreatment
standards shall be within three years of the date the standard is
promulgated, provided, however, compliance with a categorical pretreatment
standard for new sources shall be required upon commencement of discharge
to the treatment works.