Department of Civil Engineering, University of Colorado at Boulder, Boulder, CO, 80309, ¹303-492-6754 and ²303-492-6644
Various technologies are currently being investigated to remediate aquifers contaminated with organic chemicals that are in the from of non-aqueous phase liquids (NAPLs). After a spill, NAPLs remain entrapped in the soil for long periods of time, thus acting as a source of contamination. The possible use of surfactants as a way of enhancing dissolution and thus depleting the source is under study. In our ongoing research we have demonstrated the importance of heterogeneity in the transport and entrapment distribution of NAPLs in aquifers. We have identified two modes of entrapment, namely microscale entrapment at the pore scale and macro-scale entrapment that is produced by the larger heterogeneities of the aquifer. We have investigated the effects of relative permeability and dimensionality on the dissolution of these chemicals, both under micro- and macroscale entrapment. This paper presents the results from a study where we have investigated the process of enhance dissolution under macro- and microscale entrapment. These results will be used to develop and validate models that can be used to design and evaluate field remediation schemes that use surfactants.
A series of two-dimensional experiments were conducted to investigate the dissolution of non-aqueous phase liquids (NAPLs). Experiments were conducted for NAPLs at both residual saturations and under macroscale entrapment conditions. Aqueous phase samples were collected downgradient of the source, and the dissolved NAPL concentrations were measured by gas chromatography. The breakthrough curves were analyzed to determine the overall mass transfer coefficients. The mass transfer coefficients were used to investigate the effects of entrapment saturations and the dimensionality of flow on enhanced dissolution. The experimental design, results and data analysis are presented. Conclusions on the use of these results for the design of large pilot-scale, enhanced-dissolution experiments to study scale effects are presented.
ground water, NAPL, dissolution, surfactants, heterogeneities
This paper is from the Proceedings of the 10th Annual Conference on Hazardous Waste Research 1995, published in hard copy and on the Web by the Great Plains/Rocky Mountain Hazardous Substance Research Center.