Field demonstration of multiphase removal of VOCs and NAPL during thermal treatment adjacent to open-water boundaries.

Thermal treatment is widely applied to VOC- and NAPL-impacted source zones, but field performance under hydraulically dynamic open-water boundary conditions remains poorly constrained, and field evidence linking boundary effects to contaminant removal remains limited. This study reports a field-demonstration thermal treatment system operated within a NAPL-impacted source zone located within meters of an open-water boundary, integrating thermal conduction heating, continuous multiphase extraction, and cryogenic condensation for phase-resolved mass quantification. Approximately 2.77 × 10 ³ kg of contaminant mass was quantified within the treatment train; most was recovered as condensed NAPL through the C3 system, with > 99% of extracted/managed mass retained before permitted discharge. Mass removal was front-loaded, with peak vapor-phase flux occurring during early heating when treatment-average monitored temperatures remained at approximately 70-80 °C, below treatment-wide attainment of the measured bulk-mixture boiling range. As heating progressed, vapor concentrations declined despite continued temperature increase, indicating depletion of mobile mass and transition toward diffusion/desorption-limited release. Spectral analyses identified no coherent semidiurnal tidal signature in the monitored temperature response, indicating that heating was not primarily controlled by tidal forcing during active extraction. Cumulative mass recovery relative to carbon footprint revealed late-stage diminishing returns, supporting carbon-informed, stage-dependent operation under dynamic boundary conditions.