The change of representative elementary volume of DNAPL influenced by surface active agents during long-term remediation period in heterogeneous porous media

Representative elementary volume (REV) is important to characterize dense nonaqueous phase liquids (DNAPLs) during surfactant-Enhanced aquifer remediation (SEAR) period. To investigate the REVs of DNAPL in remediation, a perchloroethylene (PCE) SEAR experiment is conducted in a two dimensional (2D) heterogeneous translucent porous media. Light transmission techniques are used to quantify PCE saturation (S-oil) and PCE-water interfacial area (A(OW)). Afterward, corresponding REVs are estimated using a criterion of relative gradient error (epsilon(i)(g) to reveal the change of REVs of DNAPL over the entire remediation period. Results from this work suggest the presence of surface active agents strongly affect the REVS of DNAPL. At the beginning of the SEAR experiment, the frequency of minimum Sa-REV size closely follows a Gaussian distribution in 0.0 mm-11.0 mm. Simultaneously, the frequency of minimum A(OW)-REV size is close to a Gaussian distribution in 2.0 mm-9.0 mm and appears a peak value in 13.0 mm-14.0 mm. As SEAR experiment proceeds, both the shapes of frequency and cumulative frequency of REV sizes are changed. At the end of SEAR experiment, the frequency of minimum S-oil-REV and minimum A(OW)-REV size Lend to Gaussian distributions in 0.0 mm-6.0 mm and 0.0 mm-9.0 mm, respectively, which suggest both minimum S-oil-REV size and minimum A(OW)-REV size show decreasing tendency. Continuous quantification of the REVs of DNAPL is realized in this study to reveal the change of REVs influenced by surface active agent. The finding has important significance on improving our understanding of the characteristics of DNAPL in SEAR process, simulating DNAPL remediation and designing appropriate remediation scheme with high-resolution. (C) 2013 Elsevier B.V. All rights reserved.