Xylene is exempted from the requirement of a tolerance when used as an aquatic herbicide applied to irrigation conveyance systems in accordance with the following conditions:

(a) It is to be used only in programs of the Bureau of Reclamation, U.S. Department of Interior, and cooperating water user organizations.

(b) It is to be applied as an emulsion at an initial concentration not to exceed 750 parts per million.

(c) It is not to be applied when there is any likelihood that the irrigation water will be used as a source of raw water for a potable water system or where return flows of such treated irrigation water into receiving rivers and streams would contain residues of xylene in excess of 10 parts per million.

(d) Xylene to be used as an aquatic herbicide shall meet the requirement limiting the presence of a polynuclear aromatic hydrocarbons as listed in 21 CFR 172.250.