This document is intended to serve as guidance for air monitoring agencies that are considering requesting a waiver of one or more ambient air monitor siting criteria requirements. Additionally, this document clarifies the regulatory requirements that must be met for a waiver to be approved and provides examples and instructions on what information should be submitted with a waiver request. This document intends to promote consistency in how these waiver requests are developed by monitoring agencies and evaluated by EPA Region 4. It is meant only to provide clarification of existing requirements and does not create new requirements or supersede existing requirements.

Monitoring agencies should endeavor to ensure that siting criteria requirements are met, especially at long-term monitoring sites, and siting criteria waiver requests should be rare. To ensure that siting criteria requirements are met and reduce the need for waiver requests, monitoring agencies should conduct siting evaluations of all monitoring sites annually, and provide the results of these evaluations in their annual ambient air monitoring network plans.

As stated in 40 CFR Part 58, Appendix E, Section 10, new sites should generally be able to meet siting criteria and existing sites may be granted exceptions if provisions in the CFR can be met and it is adequately demonstrated that the need or purpose for monitoring is still relevant if siting criteria are not met.

• Region 4 Guidance on Ambient Air Monitor Siting Criteria Waivers (PDF)(5 pp, 611 K, September 26, 2018)