Soil and Water Science Department, University of Florida, Gainesville, Florida 32611, USA.
Environ Sci Technol. 2009 Dec 15;43(24):9374-9. doi: 10.1021/es902108z.
Dissolution of dense nonaqueous phase liquid (DNAPL) source zones can be accurately predicted based on appropriate characterization of the source zone architecture, which controls the rate of mass discharge or source strength function. However, the architecture changes temporally as the source zone mass is depleted by dissolution. To generalize comparisons between contaminated sites with different porewater velocities or contaminant solubilities, site age is defined in terms of the fraction of contaminant mass that has been eluted from the source zone by aqueous dissolution. Here changes in DNAPL architecture during dissolution of a source zone were measured by light transmission visualization in laboratory flow chambers. Architectures measured at ages corresponding to initial conditions, 20, 50, and 90% mass removal were used in an equilibrium streamtube (EST) model to accurately predict subsequent dissolution. It is shown both experimentally and theoretically that as DNAPL contaminated sites age, fractional reductions in contaminant discharge and mass converge to become equal, regardless of the initial architecture. This behavior is a consequence of convergence from log-normal to exponential behavior. Analysis of errors in dissolution predictions suggests that the age of many contaminated sites is likely sufficient that architecture and source strength function characterization may not be necessary as it can be assumed with reasonable accuracy that future dissolution will follow an exponential decay model.
基于对控制质量排放或源强函数的源区结构的适当描述，可以准确预测致密非水相液体（DNAPL）源区的溶解情况。然而，随着源区质量因溶解而耗尽，其结构会随时间发生变化。为了能够在具有不同水相速度或污染物溶解度的污染场地之间进行概括比较，根据污染物质量通过水相溶解从源区洗脱的分数来定义场地年龄。在实验室流动室中通过透光率可视化方法测量了源区溶解过程中 DNAPL 结构的变化。在平衡流管（EST）模型中使用在初始条件、20%、50%和 90%质量去除时测量的结构来准确预测后续的溶解情况。实验和理论都表明，随着 DNAPL 污染场地的老化，污染物排放和质量的分数减少趋于相等，与初始结构无关。这种行为是从对数正态到指数行为收敛的结果。对溶解预测误差的分析表明，许多污染场地的年龄可能足够大，因此可能不需要对结构和源强函数特征进行描述，因为可以合理准确地假设未来的溶解将遵循指数衰减模型。
