Two related performance metrics for contaminant transport. Mass flux (g/m²/day) is the contaminant mass crossing a unit area of a vertical control plane in the aquifer per unit time. Mass discharge (g/day) is mass flux integrated over the full plume cross-section.
Mass flux and mass discharge characterize what a contaminant plume is actually doing rather than its peak concentration. They are calculated from a transect of wells across the plume, where each well contributes a concentration and a Darcy flux based on hydraulic conductivity and gradient. Integrating across the transect gives mass discharge in grams per day.
The metrics matter because peak concentration can stay high even as the source mass and threat to downgradient receptors decline. ITRC Mass Flux Guidance and EPA performance-monitoring frameworks increasingly tie remedial action objectives and closure decisions to mass-flux reduction targets rather than concentration-only criteria, particularly for source-zone treatments such as in-situ thermal and ISCO.
Also known as: mass flux, mass discharge, Md, Jm.
In-Situ Chemical Oxidation (ISCO): treatment approach
In-situ chemical oxidation: injection of a chemical oxidant — permanganate, persulfate, or Fenton's reagent — directly into contaminated soil or groundwater to destroy dissolved-phase organic contaminants without excavation.
The regulatory metric for thermal destruction performance, expressed as the percentage of a target contaminant destroyed across the system. Common permit thresholds range from 99.99 percent for general hazardous organics to 99.9999 percent (six nines) for PCBs, dioxins, and PFAS.
The duration that gas, vapor, or solids remain inside the heated zone of a thermal treatment unit; together with temperature and turbulence, one of the three governing parameters of complete contaminant destruction.
Liquid that has percolated through contaminated soil, waste, or stockpiles, dissolving and carrying contaminants downward to groundwater or to a collection system. The principal migration pathway for PFAS, dissolved metals, salts, and hydrocarbons from impacted sites.
Laboratory method that oxidizes PFAS precursors in a sample into measurable perfluoroalkyl acids, then quantifies the difference against a pre-oxidation baseline. Reveals the hidden precursor mass that targeted PFAS analysis alone misses.