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Step 8: Ambient Monitoring Plan

​A facility must first complete and submit a risk assessment before requesting to pursue air monitoring. Once the risk assessment is approved the facility has 30 days to submit a toxic air contaminant monitoring plan to DEQ as part of the application for a Toxics Air Contaminant Permit Addendum (TACPA).

Note: If the results of the approved risk assessment for the facility indicate that risk levels exceed either an excess cancer risk of 200 in a million or a Hazard Index (HI) of 20, 12, or a Risk Determination Ratio (RDR) of 4[1], then the facility must not delay implementation of the approved Risk Reduction plan prior to obtaining monitoring results. If facility risk does not exceed those levels, then DEQ will issue a TACPA addressing only the monitoring requirements - i.e. compliance and reporting schedule for implementing the toxic air contaminant monitoring plan.

Monitoring must then be performed for at least 12 months and must have a minimum of 12 months of valid data with over 75% data completeness per quarter. Upon completion of the monitoring the facility must submit a risk assessment based on the monitoring data and other relevant data. For any TAC not monitored, the facility must use the modeled values in this revised risk assessment.

The TACPA will then be revised to include the updated risk assessment results, which may affect Source Risk Limits and related permit conditions.

[1] – OAR 340-245-0050(1)(c)(B)(i)(I) language is based on statutory requirements that any existing facility exceeding four times the Toxics Best Available Control Technology (TBACT) Risk Action Level (RAL) must not delay implementation of their Risk Reduction plan. For noncancer health effects this RAL is dependent on the composition of TACs a facility emits – the following conditions could exist: (i) all TACs have a TBACT RAL of 5; (ii) all TACs have a TBACT RAL of 3; or (iii) there are a mixture of TACs from (i) and (ii) where the TBACT RAL is a Risk Determination Ratio of 1. 

The monitoring plan must be submitted 30 days after approval of a facility's risk assessment as part of the Toxic Air Contaminant Permit Addendum (TACPA). The monitoring plan must at a minimum include the following:
  • Identification of all toxic air contaminants (TACs) that will be monitored
  • Description of:
    • All monitoring locations
    • Monitoring equipment and method for each TAC
    • Sampling methods and handling, including custody and storage requirements
    • Frequency and duration of sampling at each location
    • Analytical methods and analytical detection limits, and subsequent reporting limits, for each TAC
    • QA/QC measures
    • Security measures to protect equipment
  • Discussion of how to determine and account for the ambient concentration of each TAC being monitored that results from sources other than the facility
  • Meteorological monitoring equipment and siting
  • Data analysis and reporting requirements

​No. You may only request to conduct ambient air monitoring for Cleaner Air Oregon only after completion of an initial Level 3 or Level 4 risk assessment. This initial risk assessment requires a complete and approved emissions inventory.

Cleaner Air Oregon frequently asked questions for facilities 

The frequently asked questions (FAQs) on this page are provided to answer common questions about completing air toxics risk assessments for the Cleaner Air Oregon program, and ensure consistency across assessments. As the Cleaner Air Oregon process evolves, DEQ will update this page with common questions or unique scenarios. If there is a question you would like to see answered or have feedback on a response below, please contact us at

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