Rapid prediction of long-term rates of contaminant desorption from soils and sediments

A method using heated and;superheated (subcritical); water is described:for rapid prediction of long-term-desorption rates from contaminated geosorben ts.:Rates of contaminant release are measured at temperatures between 75 an d 150 degreesC using a dynamic water desorption technique. The subcritical desorption rate data are then modeled to calculate apparent activation ener gies and these activation energies are used to predict desorption behaviors at any desired ambient temperature,,Predictions of long-term release rates based on this methodology were found to correlate well with experimental 2 5 degreesC desorption data measured over periods of up to 640 days,even tho ugh the 25 degreesC desorption rates were observed to vary by up to 2 order s of magnitude for different geosorbent-types and initial solid phase conta inment loading levels. Desorption profiles measured under elevated temperat ure ana pressure conditions closely-matched those at 25 degreesC and ambien t. pressure but the time scales associated with the high-; temperature meas urements were up to 3 orders of magnitude lower; The subcritical water tech nique rapidly estimates rates of desorption-resistant contaminant release a s well as those for more labile substances. The practical implications of t he methodology :are significant because desorption observed under field:con ditions and ambient temperatures typically proceeds over periods of months or years, while the high temperature experiments used for prediction of Suc h field desorption phenomena can be completed within periods of only hours or days.