Formatted Title
The DNAPL “1 Percent Rule”: Is It Still Relevant?
Background/Objectives
The United States Environmental Protection Agency first published the so-called “1 percent rule” for dense non-aqueous phase liquid (DNAPL) in 1992. According to this “rule”, groundwater concentrations of DNAPL-related chemicals above 1 percent of pure-phase solubility or effective solubility indicate a potential for DNAPL presence at a site. Over time, this guideline that was intended to help practitioners determine whether DNAPL characterization is warranted at a site has been misused as well as challenged. For example, the ITRC 2015 Integrated DNAPL Site Characterization and Tools Selection (ISC-1) Guidance said the “1 percent rule” is viewed as unreliable. Over 30 years later, this “rule” is still being followed by practitioners and referenced by regulators. The objective of this paper is to assess whether the “1 percent rule” should still be applied.
Approach/Activities
We will review the historical development of the “1 percent rule” and its adaptation within the remediation industry and assess the applicability of this “rule” based on literature and ERM experience at multiple DNAPL sites across the US and Western Europe.
Results/Lessons Learned
We will present our recommendations for whether to follow the “1 percent rule” in practice and how the use of alternative methodologies/approaches to DNAPL site characterization can assist in validating or deviating from this “rule”. The lessons learned include how such an assessment will support developing more sustainable remediation strategies.