DNAPL Behavior in Fractured Rock – Transport Facilitated by Pickering Emulsions

Laboratory experiments demonstrate that finely divided solid materials (bentonite, iron oxide, magnesium oxide and manganese oxide) can form stable o/w emulsions for NAPLs such as PCBs, TCE, and diesel fuel. These emulsions, referred to as Pickering emulsions, are stabilized by finely divided solid materials that coat the NAPL-water interface; they do not require the presence of a surfactant to form or to be stabilized. In addition to the presence of finely divided solids, Pickering emulsions require energy to initially emulsify the NAPL. It is proposed that drilling through NAPL source zones in fractured bedrock may provide both the energy and the finely divided solids to form and stabilize Pickering emulsions. Pickering emulsions can represent a form of facilitated NAPL transport in fractured bedrock in that the emulsion droplets have the potential to migrate through large aperture fractures. Evidence of such behavior would include (i) measured aqueous phase concentrations greater than the solubility of the NAPL, (ii) the presence of aqueous phase contamination beyond where advective-dispersive transport subject to sorption can account for it, and (iii) short-term concentration spikes immediately following drilling activities. Pickering emulsions have been visually observed exiting bedrock fractures at a site in the north-eastern U.S. in the vicinity of a fault plane within a DNAPL source zone where extensive drilling had taken place.