Dissolution of an Emplaced Source of DNAPL in a Natural Aquifer Setting

Abstract

Field-scale dissolution of a multicomponent DNAPL (dense nonaqueous-phase liquid) source intentionally emplaced below the water table is evaluated in a well-characterized natural aquifer setting. The block-shaped source contained 23 kg of a trichloromethane, trichloroethene, and perchloroethene mixture homogeneously distributed at 5% saturation of pore space. Dissolution was monitored for 3 yr via down-gradient samplers (1-m fence) and occasional intra-source sampling. Although intra-source equilibrium dissolution was shown and endorsed by supporting modeling and literature lab data, less than equilibrium concentrations were predominantly monitored in the 1-m fence. This was ascribed to significant by-passing of the source by groundwater flow due to its low permeability relative to the aquifer and associated dilution of concentrations emitted from the source. Heterogeneous source dissolution occurred despite the relative homogeneity of the source and aquifer and was ascribed to dissolution fingering, which has not been previously field-demonstrated. Bulk bypass of groundwater flow around the source zone caused slow dissolution rates, with 77% of the source remaining after 3 yr and a projected longevity of approximately 25 yr. Observed dissolution fingering would have significantly increased longevity as it increasingly caused intra-source bypass of remaining DNAPL. Our dissolution interpretations were endorsed by additional data collected after 6 yr during source remediation via permanganate oxidation.

Subsoil heterogeneities controlling porewater contaminant mass and microbial diversity at a site with a complex pollution history

“…Many field studies show that the concentrations in the subsoil can vary over few centimeters vertically, while horizontally the change takes place at decimeter scale (Feenstra, 2005). Thus, there is anisotropy in the spatial distribution of the NAPL concentrations, which is controlled by the geological anisotropy of the subsoil (Rivett and Feenstra, 2005).…”

Simulation of DNAPL infiltration and spreading behaviour in the saturated zone at varying flow velocities and alternating subsurface geometries

“…Although a lot of research has been done on the topic of DNAPL migration in the saturated zone with respect to small and large scale heterogeneities (Bradford et al 2003;Broholm et al 2005;Dekker and Abriola 2000;Fagerlund et al 2006a;Illangasekare et al 1995;Jawitz et al 2005; Kueper and Frind 1988;Page et al 2007; Rivett and Feenstra 2005;Saenton et al 2002;Bao et al 2004), dissolution processes (Zhu and Sykes 2000;Falta 2003;Falta et al 2005;Fure et al 2006;Rivett and Feenstra 2005;Li et al 2011;Bao et al 2004) and mass flux (Christ et al 2009;Fure et al 2006;Illangasekare et al 2006;Jellali et al 2003;Page et al 2007;Soga et al 2004), there has to the knowledge of the authors, not yet been a distinct focus on enhanced groundwater flow velocities (v w ). The effects of v w up to 1.0-1.5 m/day in combination with heterogeneities have already been investigated with numerical simulations by several research groups.…”

The influence of precipitate formation on the chemical oxidation of TCE DNAPL with potassium permanganate

“…The bulk of work examining rate-limited mass transfer has been conducted using onedimensional column experiments (e.g., [39,[42][43][44]30,15]), a limited number of two-dimensional experiments (e.g., [56,50,41]), and a few three-dimensional field trials (e.g., [49]). Due to the complexity of NAPL dissolution, conceptual models have generally not been derived to describe the mechanisms, and the core of research has progressed by developing empirical expressions that capture the general equilibrium/non-equilibrium dissolution behaviour for a particular system.…”