40 C.F.R. § 418.26
The pretreatment standards under section 307(c) of the Act for a source within the ammonia subcategory, which is a user of a publicly owned treatment works (and which would be a new source subject to section 306 of the Act, if it were to discharge pollutants to the navigable waters), shall be the standard set forth in 40 CFR part 128, except that, for the purpose of this section, 40 CFR 128.133 shall be amended to read as follows:
In addition to the prohibitions set forth in 40 CFR 128.131 , the pretreatment standard for incompatible pollutants introduced into a publicly owned treatment works shall be the standard of performance for new sources specified in 40 CFR 418.25 ; provided that, if the publicly owned treatment works which receives the pollutants is committed, in its NPDES permit, to remove a specified percentage of any incompatible pollutant, the pretreatment standard applicable to users of such treatment works shall be correspondingly reduced in stringency for that pollutant.
40 C.F.R. §418.26