StacksVerified U.S. regulatory reference

40 CFR Part 63, Table 1

Verified against eCFR.gov as of June 20, 2026View official text on eCFR.gov
Operating time (% of year)Equivalent continuous process monitoring frequency time in use
MonthlyQuarterly | Semiannually
0 to <25Quarterly | Annually | Annually.
25 to <50Quarterly | Semiannually | Annually.
50 to <75Bimonthly | Three times | Semiannually.
75 to 100Monthly | Quarterly | Semiannually.

[89 FR 43234, May 16, 2024]