(a) “Sulfide” shall mean total sulfide as measured by the potassium ferricyanide titration method described in appendix A or the modified Monier-Williams method described in appendix B.

(b) “Hide” means any animal pelt or skin as received by a tannery as raw material to be processed.

(c) “Retan-wet finish” means the final processing steps performed on a tanned hide including, but not limited to, the following wet processes: retan, bleach, color, and fatliquor.

(d) “Hair pulp” means the removal of hair by chemical dissolution.

(e) “Hair save” means the physical or mechanical removal of hair which has not been chemically dissolved, and either selling the hair as a by-product or disposing of it as a solid waste.

(f) “Chrome tan” means the process of converting hide into leather using a form of chromium.

(g) “Vegetable tan” means the process of converting hides into leather using chemicals either derived from vegetable matter or synthesized to produce effects similar to those chemicals.

(h) “Raw material” means the hides received by the tannery except for facilities covered by subpart D and subpart I where “raw material” means the hide or split in the condition in which it is first placed into a wet process.

(i) “Monthly average” means the arithmetic average of eight (8) individual data points from effluent sampling and analysis during any calendar month.

(j) “Interference” means the discharge of sulfides in quantities which can result in human health hazards and/or risks to human life, and an inhibition or disruption of POTW as defined in 40 CFR 403.3(i).