A quantitative measure of how much contaminant mass is moving through a defined plane of a groundwater plume per unit time, typically expressed in grams per day. The transect method calculates it by integrating contaminant concentration and groundwater flux across a line of wells perpendicular to flow.
Mass discharge captures plume strength in a way that point concentrations cannot. Two sites with identical peak concentrations can differ by orders of magnitude in the actual mass crossing a property boundary each year, and that difference drives remedy selection, receptor-risk modelling, and closure economics. The transect method places a row of monitoring wells across the plume, measures contaminant concentrations and hydraulic conductivity at each, computes mass flux per cell, and integrates across the transect.
Integral pump tests and passive flux meters are alternative methods that yield the same metric with different sources of uncertainty. Mass discharge is now built into ITRC guidance, U.S. EPA technical impracticability evaluations, and increasing numbers of state and provincial frameworks as the preferred basis for remedy performance metrics. For destruction-based remedies, comparing mass discharge across the source zone before and after treatment is the most defensible demonstration of source-zone reduction.
Also known as: mass discharge, mass flux transect, transect method, integral pump test.
DNAPL and LNAPL (Non-Aqueous Phase Liquids): treatment approach
Free-phase organic liquids that do not fully dissolve in water and act as long-term source zones for dissolved plumes — DNAPL (denser than water: TCE, PCE, creosote, coal tar) pools below the water table; LNAPL (lighter than water: gasoline, diesel, jet fuel) floats on it.
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.