Diluted bitumen (dilbit) spilled to rivers has the potential to sink and become trapped in coarse bed sediments. Hyporheic flow through the river bed can then lead to the dissolution of hydrocarbons from this trapped oil, and subsequent risks to water quality and aquatic life. It is important to understand the concentrations of dissolved hydrocarbons in water, relative to aqueous solubility, that may result from mass transfer under these conditions, particularly under conditions where coarse sediments lead to faster hyporheic flow that could promote rate-limited mass transfer conditions. In this study, the dissolution of dilbit (Cold Lake Blend) trapped in gravel was measured using one-dimensional columns at flow rates representative of fast hyporheic flow. Dissolved concentrations in the column effluent were found to be less than 20% of effective solubility (equilibrium) concentrations and decreased with increasing flow rate, indicative of rate-limited conditions. These results show that risks posed by the contamination of gravel-bedded rivers by trapped dilbit may be lower, but persist for a longer period of time, than those estimated assuming dissolution at concentrations near solubility limits.

中文翻译：

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困在砾石中的稀释沥青传质的室内研究

稀释的沥青（莳萝）溢出到河流中，有可能下沉并陷入粗糙的底泥中。然后，流经河床的渗流会导致碳氢化合物从这种被困油中溶解出来，进而对水质和水生生物造成危险。重要的是要了解在这些条件下，尤其是在粗大的沉积物导致较快的流变流动而可能促进速率受限的传质条件的条件下，传质可能导致水中溶解的烃相对于水溶解度的浓度。在这项研究中，使用一维色谱柱以代表快速低流速的流速测量一维（冷湖混合液）在砾石中的溶出度。发现色谱柱流出物中的溶解浓度小于有效溶解度（平衡）浓度的20％，并且随着流速的增加而降低，这表明存在速率受限的条件。这些结果表明，与假定溶解度接近溶解度极限时所估计的风险相比，被困的迪比特污染砾石床河流所带来的风险可能更低，但持续时间更长。