PFAS Investigation & Modeling Review
Contrary to many organic contaminants, per- and polyfluoroalkyl substances (PFAS) demonstrate unique physicochemical characteristics, complex multi-phase interactions, and remarkable persistence, making both their investigation and modeling particularly challenging and highly assumption-dependent. AA GeoEnvironmental provides, third party review of PFAS site investigation reports, conceptual models, data summaries, and fate-and-transport models.
Historical PFAS releases are largely undocumented. Thus, the investigation infers source location, release mechanisms, and mass distribution from limited data rather than direct observation. PFAS partition differently from conventional organic contaminants in soil, water, and air–water interfaces. Functional groups, chain length, and environmental media conditions affect their mobility and retention. PFAS concentrations vary greatly with depth and over short distances due to soil stratigraphy, hydraulic gradients, and preferential pathways. Investigation data often reveals only a fraction of subsurface conditions.
PFAS modeling uses mathematical and numerical frameworks to represent transport and retention processes inferred from investigation data. Modeling is inherently interpretive and depends on conceptual assumptions. PFAS models are tools to test hypotheses, not to replace site investigations.
Some of the mechanisms commonly evaluated include:
- Single- vs dual-porosity flow representation.
- Equilibrium vs rate-limited sorption/desorption.
- Unsaturated zone mass storage and release.
- Preferential flow and layered media effects.
- Multi-species PFAS behavior and precursor impacts.
- Sensitivity and uncertainty analysis.
PFAS modeling presents challenges that do not exist for most contaminants. AA GeoEnvironmental’s PFAS investigation and modeling reviews focus on:
Conceptual model defensibility
- Are PFAS mechanisms correctly represented?
- Are vadose zone and sorption processes oversimplified?
- Are preferential pathways ignored?
Model structure & assumption
- Are flow and transport models appropriate for PFAS?
- Are parameters defensible and literature-consistent?
- Are boundary conditions and source terms realistic?
Sensitivity & uncertainty evaluation
- Which assumptions actually control results?
- Are conclusions robust or assumption-driven?
- Have various probable scenarios been thoroughly assessed?
Interpretation & communication
- Do conclusions match the model results?
- Are assumptions and limitations clearly stated?
- Is the model reproducible, transparent, and documented?
For complex contaminants such as PFAS, independent review is often most valuable where technical work informs significant decisions.
What this Service Is
- Review of PFAS investigation and modeling reports.
- Clarification of uncertainty for internal, financial, or strategic decisions.
- Objective review of PFAS data summaries and interpretations.
- Review of whether PFAS mechanisms are accurately represented and modeling approaches are fit for intended purpose.
What this Service Is Not
- Field sampling or site investigation activities.
- Regulatory advocacy and compliance determinations or approvals.
- Certification, validation, or endorsement of conclusions.
- Remedial design, technology selection, risk management, or legal strategy
AA GeoEnvironmental does not serve as the geologist or engineer of record. Clients hold sole responsibility for decision-making and compliance to regulatory requirements.