One problem is that state permitting authorities, EPA regulators, and permitted sources all have interpreted the requirements for periodic monitoring differently. On several occasions, various EPA regions have objected to state or local draft permits because the periodic-monitoring provisions were insufficient. Periodic-monitoring requirements apply to Title V major sources for each emissions unit subject to requirements such as a federal or state regulation. The emission standard or regulatory requirement might include a sufficient-monitoring requirement. If it doesn't, the Title V permit will include periodic-monitoring conditions.
Periodic monitoring is required even when an add-on control device is used to meet requirements.
These considerations outline how to determine what is appropriate periodic monitoring. The rationale for the selected monitoring method should be clear and documented in the permit record. For most federally enforceable rules, the averaging period is clear, if not explicitly stated. In some cases, such as with construction permits, limits were placed on pollutants that aren't otherwise limited by state or federal regulations. In these cases, there also might be disagreement over the appropriate averaging period.