---
kind: "section"
citation: "40 C.F.R. § 63.1965"
title: "40"
number: "63.1965"
heading: "What is a deviation?"
url: "https://uscodex.org/cfr/40/63.1965"
---

# §63.1965. What is a deviation?


A deviation is defined in [§ 63.1990](/cfr/40/63.1990.md). For the purposes of the landfill monitoring and SSM plan requirements, deviations include the items in [paragraphs (a) through (c)](#a..c) of this section.

- (a) A deviation occurs when the control device operating parameter boundaries described in [§ 63.1983(c)(1)](/cfr/40/63.1983.md?p=c-1) are exceeded.
- (b) A deviation occurs when 1 hour or more of the hours during the 3-hour block averaging period does not constitute a valid hour of data. A valid hour of data must have measured values for at least three 15-minute monitoring periods within the hour.
- (c) Before September 28, 2021, a deviation occurs when a SSM plan is not developed or maintained on site and when an affected source fails to meet any emission limitation, (including any operating limit), or work practice requirement in this subpart during SSM, regardless of whether or not such failure is permitted by this subpart.

## Notes

### Source

Source: 85 FR 17261, Mar. 26, 2020, unless otherwise noted.

### Authority

Authority: 42 U.S.C. 7401 et seq.

### Source

Source: 57 FR 61992, Dec. 29, 1992, unless otherwise noted.