Colorado petroleum release closure criteria

The Division of Oil and Public Safety (OPS) closes a petroleum release event by issuing a No Further Action (NFA) determination, and it has developed a four-tiered closure approach for doing so. Closure is based on the risk of exposure to any remaining contamination, so a closed release is not always a release with nothing left in the ground.

In a Phase I ESA

ASTM E1527-21 does not name closure criteria among its standard record sources. They are how to read a closed petroleum release event. OPS says its database indicates the closure criteria applied to each archived release, so the tier is a fact to look up, not to assume.

Five details matter when the tier is III or IV.

• They are fallbacks. OPS says Tier III or IV may be considered for a release that cannot achieve Tier I or II, and that corrective action plans are written to meet Tier I or II, not the later tiers.
• Removal comes first. Both tiers require contaminant removal to the maximum extent practicable, and post-remediation monitoring long enough to show that the dissolved-phase plume is stable or diminishing.
• Neighbors are told. Under Tier III the owner or operator should notify the owner of the impacted public roadway that contamination is, or is predicted to be, beneath it. Under Tier IV the notice goes to the owners of the impacted property. For a property beside a closed release, ask whether such a notice was sent.
• Tier IV limits the source property. The property where the release originated cannot have an active petroleum storage tank system. OPS says the Director may grant exceptions case by case for newer secondarily contained systems installed less than 10 years ago that have operated in compliance and have no reported releases.
• The letter is conditional. OPS says every NFA letter states that the release was closed on the information available at the time and on the existing exposure pathway conditions, and that a release may be reopened if exposure conditions change. A change of land use on or near the release is a reason to read the letter again.

OPS's guidance says it will map Tier III sites to a map on its website, to inform the public about petroleum contaminants left in place. The Tier IV section of the guidance repeats that sentence and still names Tier III, so the pages read do not settle whether Tier IV closures are on the map.

Where to look a site up

• The tier is recorded in the OPS database, which the guidance links at the portal OPS calls COSTIS-IA.
• Closed events are in the dataset Active and Closed OPS Petroleum Release Events in Colorado, linked from OPS's Maps page.
• The Remediation Section is at 303-318-8547 and cdle_remediation@state.co.us.

Getting the file

Ask for the NFA letter and the closure evaluation. OPS's Petroleum Data & File Request page links a Petroleum File & Data Request form for individual files from a facility, such as reports and letters.

Sources

Colorado Department of Labor and Employment, Division of Oil and Public Safety pages, read October 7, 2026, no modified date shown:

• Release Closure Criteria
• Release Response
• Corrective Action
• Maps
• Petroleum Data & File Request