Abreu Lilian D V, Johnson Paul C
Department of Civil and Environmental Engineering, Ira A. Fulton School of Engineering, Arizona State University, Tempe, Arizona 85287-5306, USA.
Environ Sci Technol. 2005 Jun 15;39(12):4550-61. doi: 10.1021/es049781k.
A three-dimensional numerical model of the soil vapor-to-indoor air pathway is developed and used as a tool to anticipate not-yet-measured relationships between the vapor attenuation coefficient, alpha (indoor air concentration/source vapor concentration), and vapor source-building lateral separation, vapor source depth, and building construction characteristics (depth of building foundation) for nondegrading chemicals. The numerical model allows for diffusive and advective transport, multicomponent systems and reactions, spatially distributed foundation cracks, and transient indoor and ambient pressure fluctuations. Simulations involving different lateral separations between the vapor source and building show decreasing alpha values with increasing lateral separation. For example, alpha is 2 orders of magnitude less when a 30 m x 30 m source located 8 m below ground surface is displaced from the edge of the building by 20 m. The decrease in alpha with increasing lateral separation is greater for shallower source depths. For example, alpha is approximately 5 orders of magnitude less when a 30 m x 30 m source located 3 m below ground surface is displaced from the edge of the building by 20 m. To help visualize the effects of changing vapor source-building separations, normalized vapor concentration contour plots for both horizontal and vertical cross sections are presented for a sequence of lateral separations ranging from the case in which the 30 m x 30 m source and 10 m x 10 m building footprint centers are collocated to shifting of the source positioning by 50 m. Simulations involving basement and slab-on-grade constructions produce similar trends. In addition, when buildings are overpressurized to create outflow to soil gas on the order of 1-3 L/min, emissions to indoor air are reduced by over 5 orders of magnitude relative to intrusion rates at zero building underpressurization. The results are specific to simulations involving homogeneous soil properties, nondegrading chemicals, steady source concentrations and building underpressurizations, and the geometries studied in this work.
建立了土壤蒸汽到室内空气路径的三维数值模型，并将其用作一种工具，以预测尚未测量的非降解化学品的蒸汽衰减系数α（室内空气浓度/源蒸汽浓度）与蒸汽源与建筑物的横向间距、蒸汽源深度和建筑物结构特征（建筑物基础深度）之间的关系。该数值模型考虑了扩散和对流传输、多组分系统和反应、空间分布的基础裂缝以及室内和环境压力的瞬态波动。涉及蒸汽源与建筑物之间不同横向间距的模拟表明，随着横向间距的增加，α值减小。例如，当一个位于地下8米处的30米×30米的源从建筑物边缘向外移动20米时，α值减小了2个数量级。对于较浅的源深度，α值随横向间距增加的减小幅度更大。例如，当一个位于地下3米处的30米×30米的源从建筑物边缘向外移动20米时，α值大约减小了5个数量级。为了帮助直观地显示蒸汽源与建筑物间距变化的影响，给出了一系列横向间距（从30米×30米的源和10米×10米的建筑物占地面积中心重合的情况到源位置偏移50米的情况）的水平和垂直横截面的归一化蒸汽浓度等值线图。涉及地下室和平地建筑的模拟产生了类似的趋势。此外，当建筑物处于过压状态以产生约1 - 3升/分钟的土壤气体流出时，相对于建筑物零负压下的侵入率，向室内空气的排放减少了5个以上数量级。这些结果特定于涉及均匀土壤性质、非降解化学品、稳定源浓度和建筑物负压以及本研究中所研究几何形状的模拟。
