When Guidance Falls Short: Defensible PFAS Data Beyond the Method

Ensuring Reliable Data
Oral Presentation

Prepared by N. DeStefano
Metiri Group, 2704 Heathersmith Court, Raleigh, NC, 27604, United States


Contact Information: [email protected]; 919-698-3670

ABSTRACT

PFAS monitoring is expanding into matrices where analytical methods provide a defined measurement procedure but limited end-to-end guidance on sampling design, preparation choices, reporting basis, and what constitutes sufficient QA/QC evidence for defensible decisions. In these situations, laboratories and data users are left to fill gaps that can drive inconsistent practices across projects and laboratories. The result is avoidable variability, friction during data review, and weakened public confidence when results differ or are interpreted outside the method’s intent.
This presentation describes a practical approach for maintaining defensibility when method guidance is incomplete. Rather than prescribing how to sample or analyze a specific material, we focus on repeatable decision points that can be applied across non-traditional matrices: define the decision the data must support, identify the highest-risk sources of variability, document assumptions and limitations in plain language, select fit-for-purpose QC evidence, and standardize reporting language so results are not over-interpreted under public scrutiny. We emphasize where commercial laboratories can strengthen trust through transparency and consistency, including clear qualifier language, reporting-limit context, and comparability constraints.
Plant tissue is used as a case study to illustrate how guidance gaps surface in practice (for example, moisture basis, representativeness, and heterogeneity) and how a structured documentation and QC approach can reduce disagreement and improve interpretability when the method alone does not answer every practical question.