『Abstract
The remediation of non-aqueous phase liquid (NAPL) contaminated
sites is impeded due to subsurface complexities, including wettability.
Wettability quantifies which of two immiscible fluids preferentially
coats a solid. At most contaminated sites water-wetting conditions
are typically assumed despite mounting evidence that this is not
always the case. In this study, wettability was examined for two
NAPL samples of contrasting origin: a fresh and a field sample.
Wettability was assessed through (i) cyclical, ‘cumulative elapsed
contact time’ intrinsic contact angle measurements, (ii) interface
jar tests, and (iii) cyclical, pseudo-static capillary pressure-saturation
curves. The work as a whole demonstrated that while the fresh
diesel sample was consistently water-wet, the field diesel sample
exhibited repeatable cycles of wettability reversal between water
drainage and imbibition. And while wettability hysteresis increased
with contact tome for the field diesel, the occurrence of wettability
reversal at each change of saturation direction was independent
of contact time. Such behavior is not easily assessed by standard
wettability indices. Moreover, it contrasts with the permanent
wettability alteration observed for complex organics (e.g., coal
tar) observed in most studies. It is hypothesized that the cyclical
wettability reversal is related to cyclical changes in intermediate
pore wettability due to sorption of surface active compounds (causing
NAPL-wetting imbibition) and rupturing of the soil grain water
film (causing water-wet drainage). The wettability differences
between the two NAPLs may be due to additives (i.e., a surfactant)
in the original formulation and/or byproducts from subsurface
weathering. These results support better characterization of site-specific
wettability, improved model development and more realistic site
conceptual models for improved remediation efforts.
Keywords: Wettability; NAPL; Remediation; Retention functions』
1. Introduction
2. Materials and methods
2.1. Materials
2.2. Weathering
2.3. Interfacial analysis
2.4. Interfacial tension and contact angle
2.5. Capillary pressure-saturation experiments
3. Results and discussion
3.1. Weathering analysis of diesels
3.2. Interfacial analysis
3.3. Interfacial tension and contact angle
3.4. Capillary pressure-saturation main curves
3.5. Capillary pressure-saturation scanning curves
4. Conclusions
Acknowledgments
References