40 CFR § 61.201 - Definitions.

---
identifier: "/us/cfr/t40/s61.201"
source: "ecfr"
legal_status: "authoritative_unofficial"
title: "40 CFR § 61.201 - Definitions."
title_number: 40
title_name: "Protection of Environment"
section_number: "61.201"
section_name: "Definitions."
chapter_name: "ENVIRONMENTAL PROTECTION AGENCY"
subchapter_number: "C"
subchapter_name: "AIR PROGRAMS"
part_number: "61"
part_name: "NATIONAL EMISSION STANDARDS FOR HAZARDOUS AIR POLLUTANTS"
positive_law: false
currency: "2026-04-05"
last_updated: "2026-04-05"
format_version: "1.1.0"
generator: "[email protected]"
authority: "42 U.S.C. 7401"
regulatory_source: "38 FR 8826, Apr. 6, 1973, unless otherwise noted."
cfr_part: "61"
---


# 61.201 Definitions.

As used in this subpart, all terms not defined here have the meaning given them in the Clean Air Act or subpart A of part 61. The following terms shall have the following specific meanings:

(a) *Inactive stack* means a stack to which no further routine additions of phosphogypsum will be made and which is no longer used for water management associated with the production of phosphogypsum. If a stack has not been used for either purpose for two years, it is presumed to be inactive.

(b) *Phosphogypsum* is the solid waste byproduct which results from the process of wet acid phosphorus production.

(c) *Phosphogypsum stacks* or *stacks* are piles of waste resulting from wet acid phosphorus production, including phosphate mines or other sites that are used for the disposal of phosphogypsum.