The occurrence of aerobic biodegradation in the vadose zone between a subsurface source and a building foundation can all-but eliminate the risks from methane and petroleum vapor intrusion (PVI). Understanding oxygen availability and the factors that affect it (e.g., building sizes and their distribution) are therefore critical. Uncovered ground surfaces allow oxygen access to the subsurface to actively biodegrade hydrocarbons (inclusive of methane). Buildings can reduce the net flux of oxygen into the subsurface and so reduce degradation rates. Here we determine when PVI and methane risk is negligible and/or extinguished; defined by when oxygen is present across the entire sub-slab region of existing or planned slab-on-ground buildings. We consider all building slab sizes, all depths to vapor sources and the effect of spacings between buildings on the availability of oxygen in the subsurface. The latter becomes critical where buildings are in close proximity or when increased building density is planned. Conservative assumptions enable simple, rapid and confident screening should sites and building designs comply to model assumptions. We do not model the aboveground “building” processes (e.g., air exchange), and assume the slab-on-ground seals the ground surface so that biodegradation of hydrocarbons is minimized under the built structure (i.e., the assessment remains conservative). Two graphs represent the entirety of the outcomes that allow simple screening of hydrocarbon vapors based only on the depth to the source of vapors below ground, the concentration of vapors within the source, the width of the slab-on-ground building, and the gap between buildings; all independent of soil type. Rectangular, square, and circular buildings are considered. Comparison with field sites and example applications are provided, along with a simple 8-step screening guide set in the context of existing guidance on PVI assessment.

中文翻译：

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扑灭地面平板建筑物的石油蒸气入侵和甲烷风险：简单指南

在地下源和建筑物基础之间的渗流区中发生好氧生物降解可以消除甲烷和石油蒸气入侵（PVI）的风险，但可以消除。因此，了解氧气的供应量和影响氧气供应量的因素（例如建筑物的大小及其分布）至关重要。裸露的地面允许氧气进入地下，从而有效地生物降解碳氢化合物（包括甲烷）。建筑物可以减少流入地下的氧气净流量，因此可以降低降解率。在这里，我们确定何时可以忽略和/或消除PVI和甲烷风险；定义为何时在现有或计划中的地上建筑的整个子楼板区域中都存在氧气。我们考虑了所有建筑板的尺寸，蒸气源的所有深度以及建筑物之间的间距对地下氧气供应的影响。在建筑物附近或计划增加建筑物密度的情况下，后者变得至关重要。如果场地和建筑设计符合模型假设，那么保守的假设可以进行简单，快速和自信的筛选。我们不对地上“建筑”过程（例如，空气交换）进行建模，而是假设地面平板密封地面，以便在建筑结构下将碳氢化合物的生物降解减至最小（即，评估仍是保守的）。两个图表代表了整个结果，可仅根据地下蒸汽源的深度，源内蒸汽的浓度，地上建筑物的宽度以及建筑物之间的间隙；全部与土壤类型无关。考虑矩形，正方形和圆形建筑物。提供了与现场站点的比较和示例应用程序，以及在现有的PVI评估指南中设置的简单的8步筛选指南。