---identifier: "/us/cfr/t40/s411.31"source: "ecfr"legal_status: "authoritative_unofficial"title: "40 CFR § 411.31 - Specialized definitions."title_number: 40title_name: "Protection of Environment"section_number: "411.31"section_name: "Specialized definitions."chapter_name: "ENVIRONMENTAL PROTECTION AGENCY"subchapter_number: "N"subchapter_name: "EFFLUENT GUIDELINES AND STANDARDS"part_number: "411"part_name: "CEMENT MANUFACTURING POINT SOURCE CATEGORY"positive_law: falsecurrency: "2026-03-24"last_updated: "2026-03-24"format_version: "1.1.0"generator: "[email protected]"authority: "Secs. 301, 304 (b) and (c), 306 (b) and (c), and 307(c) of the Federal Water Pollution Control Act, as amended; 33 U.S.C. 1251, 1311, 1314 (b) and (c), 1316 (b) and (c), and 1317(c); 86 Stat. 816 Pub. L., 92-500; 91 Stat. 1567, Pub. L. 95-217."regulatory_source: "39 FR 6591, Feb. 20, 1974, unless otherwise noted."cfr_part: "411"---
Identifier
/us/cfr/t40/s411.31
Currency
2026-03-24
Positive Law
No
Updated
2026-03-24
Chapter
Environmental Protection Agency
Authority
Secs. 301, 304 (b) and (c), 306 (b) and (c), and 307(c) of the Federal Water Pollution Control Act, as amended; 33 U.S.C. 1251, 1311, 1314 (b) and (c), 1316 (b) and (c), and 1317(c); 86 Stat. 816 Pub... Secs. 301, 304 (b) and (c), 306 (b) and (c), and 307(c) of the Federal Water Pollution Control Act, as amended; 33 U.S.C. 1251, 1311, 1314 (b) and (c), 1316 (b) and (c), and 1317(c); 86 Stat. 816 Pub. L., 92-500; 91 Stat. 1567, Pub. L. 95-217.
# 411.31 Specialized definitions.For the purpose of this subpart:(a) Except as provided below, the general definitions, abbreviations and methods of analysis set forth in 40 CFR part 401 shall apply to this subpart.(b) The term *10 year, 24 hour rainfall event* shall mean a rainfall event with a probable recurrence interval of once in ten years as defined by the National Weather Service in Technical Paper No. 40, “Rainfall Frequency Atlas of the United States,” May 1961, and subsequent amendments, or equivalent regional or state rainfall probability information developed therefrom.