The new ASTM standard provides a framework for closing petroleum UST release sites. Its most distinguishing and controversial feature is its treatment of LNAPL migration status—rather than the presence of LNAPL—as the key closure criterion, using stable footprints, low transmissivity, and declining groundwater concentrations as evidence of stability.
The document contains several helpful elements. The illustrations help convey the document’s message. The checklists are the most immediately functional component, covering conceptual site model adequacy, closure criteria, controls, and non-technical barriers. Though lacking prioritization, the checklists provide adaptable templates. I expect some states will adopt them with modifications. Appendix X2’s diagnostic gauge plots are practical; the section is a must-read portion of the document.
Strengths include recognizing natural plume stabilization, integrating sustainability, and offering multiple closure pathways. Weaknesses include process complexity, assumptions of universal regulatory flexibility, and inadequate guidance on uncertainty.
A critical oversight was dismissing contaminant mass estimations as too difficult. Without knowing whether 50,000 or 5 gallons of LNAPL remain, long-term risk assessment becomes speculation—especially problematic given the guidance’s own acknowledgment that “accurate prediction of LNAPL depletion is not possible with today’s science.”
Overall, this standard represents progress toward science-based closure, best achieved by experienced practitioners in mature programs that are willing to move beyond prescriptive standards while fully acknowledging site-specific applicability. The ASTM team has provided a timely and helpful standard.
