Laboratory of Environmental Engineering, Department of Civil Engineering and Computer Science Engineering, University of Rome Tor Vergata, Via del Politecnico 1, 00133 Rome, Italy.
Equilon Enterprises LLC doing business as Shell Oil Products US, Houston, TX, USA.
Water Res. 2024 Dec 1;267:122559. doi: 10.1016/j.watres.2024.122559. Epub 2024 Sep 30.
This paper presents a simplified approach for the soil gas gradient method for estimating natural source zone depletion (NSZD) rates of specific contaminants of concern (COCs) at sites contaminated by light non-aqueous phase liquids (LNAPL). Traditional approaches to quantify COC-specific NSZD rates often rely on numerical or analytical reaction-transport models that require detailed site-specific data. In contrast, the proposed method employs simple analytical solutions, making it more accessible to practitioners. Specifically, it requires only the maximum soil gas concentration, the effective diffusion coefficient, and the diffusive reaction length calculated from vertical soil gas concentration profiles. The simplified approach was validated against a reactive transport numerical model reported in the literature, showing consistent results within the same order of magnitude for BTEX NSZD rates at a gasoline spill site in South Carolina. Further validation using a larger dataset involved comparing NSZD rate estimates for benzene and total petroleum hydrocarbons (TPH) against those obtained using BioVapor, utilizing empirical soil gas data from the USEPA Petroleum Vapor Intrusion Database. Results demonstrated a strong correlation between NSZD rates and maximum soil gas concentrations, allowing the development of a rapid screening approach based only on the measured soil gas concentrations and literature values for diffusion coefficients and diffusive reaction lengths. This approach aligned well with previous modeling studies and was consistent with literature values for TPH NSZD rates. Overall, both the simplified and screening approaches offer practical, easy-to-use tools for evaluating temporal variability in natural attenuation rates, supporting baseline assessments and ongoing performance evaluations of remediation at LNAPL sites.
本文提出了一种简化的土壤气体梯度法，用于估算受轻质非水相液体（LNAPL）污染场地中特定关注污染物（COC）的天然源区消耗（NSZD）速率。传统的量化 COC 特定 NSZD 速率的方法通常依赖于需要详细现场特定数据的数值或分析反应-传输模型。相比之下，所提出的方法采用简单的分析解，使其更易于从业者使用。具体来说，它只需要从垂直土壤气体浓度剖面计算出最大土壤气体浓度、有效扩散系数和扩散反应长度。简化方法已通过文献中报道的反应传输数值模型进行了验证，在南卡罗来纳州的一个汽油泄漏场地的 BTEX NSZD 速率方面，结果具有相同数量级的一致性。进一步使用更大的数据集进行验证涉及将苯和总石油烃（TPH）的 NSZD 率估计值与使用 BioVapor 获得的估计值进行比较，后者利用了 USEPA 石油蒸气入侵数据库中的经验土壤气体数据。结果表明 NSZD 率与最大土壤气体浓度之间存在很强的相关性，允许仅基于测量的土壤气体浓度和文献中扩散系数和扩散反应长度的值来开发快速筛选方法。该方法与之前的建模研究一致，并且与 TPH NSZD 率的文献值一致。总体而言，简化和筛选方法都为评估自然衰减速率的时间变化提供了实用、易于使用的工具，支持对 LNAPL 场地的基线评估和正在进行的修复效果评估。
