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

Abstract

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 (ε_gⁱ) 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 S_oil-REV size closely follows a Gaussian distribution in 0.0mm-11.0mm. Simultaneously, the frequency of minimum A_OW-REV size is close to a Gaussian distribution in 2.0mm-9.0mm and appears a peak value in 13.0mm-14.0mm. 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 tend to Gaussian distributions in 0.0mm-6.0mm and 0.0mm-9.0mm, 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.

Keywords: Change; Gaussian distribution; Remediation; Representative elementary volume (REV); Surface active agent.