NAPL-VAPOR PHASE INTERPHASE MASS TRANSFER PROCESSES

汽相传输过程对化学反应具有根本的重要性。 挥发性有机化学品（VOCs）的迁移和持久性 地下环境 这些过程控制有机物的释放， 蒸汽进入大气，有机蒸汽溶解进入地下水， 以及地下室、下水道和地下设施中烟雾的积累， 这可能会造成最直接和最广泛的健康风险， 挥发性有机化合物溢出。 气相传输过程也是基本的， 土壤-气体采样方法的发展和解释， 有效的土壤通风补救策略。 本研究将重点 关于汽相输运的以下两个方面， （a）自然界中以多组分扩散为主的运输 土壤和（B）在强制条件下截留的有机液体的挥发， 空气平流 重点将放在实验室的整合 和建模研究。 子项目0017旨在调查 天然土壤中气相扩散的控制机制。 扩散 行为的两个模型挥发性有机化合物，苯和三氯乙烯，将 探讨了 将进行实验以测量气相 渗透率，克努森扩散系数和曲折因子， 一系列的土壤水分，体积密度，和颗粒大小的条件。 在 此外，还研究了气相吸附对有机蒸气扩散的影响 将对类似土壤和实验条件下的速率进行研究。 利用有机-土壤复合物作为减少有机污染的一种手段 还将评估蒸气迁移率。 多组分扩散 模拟器，其中包括几个扩散机制和气相 吸附，将被开发，以评估这些相对重要性 流程. 将进行稳态和瞬态柱实验 以验证建模方法。 在子项目0006中，实验将 进行检查的VOC的传质速率从不混溶 稳态和瞬态下有机液相到气相 条件 一些有机化合物和土壤基质将 研究了 相关性包括流速、 有机相、土壤含水量和土壤结构将得到发展 用于气相传质。 多相流和输运模型， 在目前的NIEHS资助下开发的，将用于探索 速率限制的质量传递对土壤通风效果的影响 技术.

Vapor-phase transport processes are of fundamental importance to the migration and persistence of volatile organic chemicals (VOCs) in subsurface environments. Such processes control the release of organic vapors into the atmosphere, dissolution of organic vapors into groundwater, and accumulation of fumes in basements, sewers, and underground utilities, which may pose the most immediate and widespread health risks following a VOC spill. Vapor-phase transport processes are also fundamental to the development and interpretation of soil-gas sampling methods and the design of effective soil venting remediation strategies. This research will focus on the following two aspects of vapor-phase transport which are not well understood; (a) multicomponent diffusion-dominated transport in natural soils and (b) the volatilization of entrapped organic liquids under forced- air advection. Emphasis will be placed upon the integration of laboratory and modeling studies. Subproject 0017 is designed to investigate the mechanisms governing vapor-phase diffusion in natural soils. The diffusive behavior of two model VOCs, benzene and trichloroethylene, will be explored. Experiments will be conducted to measure vapor-phase permeabilities, Knudsen diffusion coefficients, and tortuosity factors for a range of soil moisture, bulk density, and particle size conditions. In addition, the effect of vapor-phase sorption on organic vapor diffusion rates will be investigated for similar soils and experimental conditions. The utility of organo-soil complexes as a means of attenuating organic vapor mobility will also be evaluated. A multicomponent diffusion simulator, which incorporates several diffusion mechanisms and vapor-phase sorption, will be developed to assess the relative importance of these processes. Steady-state and transient column experiments will be performed to validate the modeling approach. In subproject 0006, experiments will be conducted to examine the rate of mass transfer of VOCs from the immiscible organic liquid phase to the vapor phase under steady-state and transient conditions. A number of organic compounds and soil matrices will be investigated. Correlations incorporating flow rate, composition of the organic phase, soil moisture content and soil structure will be developed for vapor-phase mass transfer. A multiphase flow and transport model, developed under current NIEHS funding, will be used to explore the implications of rate-limited mass transfer on the efficacy of soil venting technologies.