An official website of the United States government.

Due to a lapse in appropriations, EPA websites will not be regularly updated. In the event of an environmental emergency imminently threatening the safety of human life or where necessary to protect certain property, the EPA website will be updated with appropriate information. Please note that all information on the EPA website may not be up to date, and transactions and inquiries submitted to the EPA website may not be processed or responded to until appropriations are enacted.

We've made some changes to If the information you are looking for is not here, you may be able to find it on the EPA Web Archive or the January 19, 2017 Web Snapshot.


CASTNET Independent Audit Program

An independent auditor visits each CASTNET site at least once every other year to perform a Field Systems Audit (FSA). Regulatory ozone monitoring sites are audited annually by an independent auditor or a local monitoring agency. Performance evaluation results are loaded into EPA's Air Quality System (AQS) database routinely.

The Quality Assurance Project Plan (QAPP) and Standard Operating Procedures for the independent audits are available below. The quarterly and annual audit reports are also provided below.

You may need a PDF reader to view some of the files on this page. See EPA’s About PDF page to learn more.