Petri Benjamin G, Fučík Radek, Illangasekare Tissa H, Smits Kathleen M, Christ John A, Sakaki Toshihiro, Sauck Carolyn C
Faculty of Nuclear Sciences and Physical Engineering, Czech Technical University in Prague, Prague, Czech Republic.
Department of Civil and Environmental Engineering, Colorado School of Mines, 1500 Illinois St, Golden, CO 80401.
Ground Water. 2015 Sep-Oct;53(5):685-98. doi: 10.1111/gwat.12284. Epub 2014 Dec 23.
The generation of vapor-phase contaminant plumes within the vadose zone is of interest for contaminated site management. Therefore, it is important to understand vapor sources such as non-aqueous-phase liquids (NAPLs) and processes that govern their volatilization. The distribution of NAPL, gas, and water phases within a source zone is expected to influence the rate of volatilization. However, the effect of this distribution morphology on volatilization has not been thoroughly quantified. Because field quantification of NAPL volatilization is often infeasible, a controlled laboratory experiment was conducted in a two-dimensional tank (28 cm × 15.5 cm × 2.5 cm) with water-wet sandy media and an emplaced trichloroethylene (TCE) source. The source was emplaced in two configurations to represent morphologies encountered in field settings: (1) NAPL pools directly exposed to the air phase and (2) NAPLs trapped in water-saturated zones that were occluded from the air phase. Airflow was passed through the tank and effluent concentrations of TCE were quantified. Models were used to analyze results, which indicated that mass transfer from directly exposed NAPL was fast and controlled by advective-dispersive-diffusive transport in the gas phase. However, sources occluded by pore water showed strong rate limitations and slower effective mass transfer. This difference is explained by diffusional resistance within the aqueous phase. Results demonstrate that vapor generation rates from a NAPL source will be influenced by the soil water content distribution within the source. The implications of the NAPL morphology on volatilization in the context of a dynamic water table or climate are discussed.
包气带内气相污染物羽流的生成对于污染场地管理具有重要意义。因此，了解诸如非水相液体（NAPL）等蒸汽源以及控制其挥发的过程至关重要。源区内NAPL、气相和水相的分布预计会影响挥发速率。然而，这种分布形态对挥发的影响尚未得到充分量化。由于现场量化NAPL挥发通常不可行，因此在一个二维水箱（28厘米×15.5厘米×2.5厘米）中进行了一项受控实验室实验，该水箱装有水湿砂质介质和一个注入的三氯乙烯（TCE）源。源以两种配置放置，以代表现场环境中遇到的形态：（1）NAPL池直接暴露于空气相；（2）NAPL被困在与空气相隔绝的水饱和区。让气流通过水箱，并对TCE的流出浓度进行量化。使用模型分析结果，结果表明，直接暴露的NAPL的传质速度很快，并且受气相中的平流 - 扩散 - 弥散传输控制。然而，被孔隙水阻隔的源显示出强烈的速率限制和较慢的有效传质。这种差异可以用水相中的扩散阻力来解释。结果表明，NAPL源的蒸汽生成速率将受到源区内土壤水分含量分布的影响。文中讨论了在动态地下水位或气候背景下NAPL形态对挥发的影响。
