DESCRIPTION OF TIME-VARYING DESORPTION-KINETICS - RELEASE OF NAPHTHALENE FROM CONTAMINATED SOILS

Release rates of naphthalene from suspensions of freshly contaminted ( days to weeks) and aged (approximately 30 years) soil samples were obt ained using a gas purge method. A continuously increasing resistance t o desorption was observed with increasing purge time. Initial desorpti on rates were similar to those estimated using available empirical rel ationships, but subsequent desorption rates were lower by more than 1 order of magnitude. A model incorporating a continuum of compartments with a gamma (GAMMA) distribution of rate coefficients was postulated to describe the experimental data. An analytical equation with two adj ustable parameters was obtained for the mass fraction desorbed. Releas e profiles with this ''GAMMA model'' were able to describe the experim ental release profiles for long term desorption experiments. An implic ation of the gamma model is that increased incubation time will allow organic compounds to be sorbed to compartments or regions in the sorbe nt that exhibit slow adsorption/desorption kinetics. This has importan t implications for the fate and remediation of sites that have been co ntaminated with hydrophobic organic compounds for extended time period s.