Microbially mediated sulfate reduction is a ubiquitous process in many subsurface systems. Isotopic fractionation is characteristic of this anaerobic process, since sulfate-reducing bacteria (SRB) favor the reduction of the lighter sulfate isotopologue (S³²O₄²⁻) over the heavier isotopologue (S³⁴O₄²⁻). Detection of isotopic shifts has been utilized as a proxy for the onset of sulfate reduction in subsurface systems such as oil reservoirs and aquifers undergoing heavy metal and radionuclide bioremediation. Reactive transport modeling (RTM) of kinetic sulfur isotope fractionation has been applied to field and laboratory studies. We developed a benchmark problem set for the simulation of kinetic sulfur isotope fractionation during microbially mediated sulfate reduction. The benchmark problem set is comprised of three problem levels and is based on a large-scale laboratory column experimental study of organic carbon amended sulfate reduction in soils from a uranium-contaminated aquifer. Pertinent processes impacting sulfur isotopic composition such as microbial sulfate reduction and iron-sulfide reactions are included in the problem set. This benchmark also explores the different mathematical formulations in the representation of kinetic sulfur isotope fractionation as employed in the different RTMs. Participating RTM codes are the following: CrunchTope, TOUGHREACT, PHREEQC, and PHT3D. Across all problem levels, simulation results from all RTMs demonstrate reasonable agreement.

在许多地下系统中，微生物介导的硫酸盐还原是一个普遍存在的过程。同位素分馏是该厌氧过程的特征，因为硫酸盐还原细菌（SRB）较重同位素同位素（S ³⁴ O ₄ ^2-）有利于减少较轻的硫酸盐同位素（S ³² O ₄ ^2-）。）。同位素转移的检测已被用作替代地下系统中硫酸盐还原的开始，地下系统例如是经过重金属和放射性核素生物修复的油藏和含水层。动力学硫同位素分馏的反应运输模型（RTM）已应用于现场和实验室研究。我们开发了一个基准问题集，用于模拟微生物介导的硫酸盐还原过程中动力学硫同位素分馏。基准问题集包括三个问题级别，该问题集基于对铀污染的含水层中土壤中有机碳修正的硫酸盐还原作用进行的大规模实验室柱实验研究。问题集包括影响硫同位素组成的相关过程，例如微生物硫酸盐的还原和硫化铁的反应。该基准还探索了不同RTM中采用的动力学硫同位素分馏表示形式的不同数学公式。参与的RTM代码如下：CrunchTope，TOUGHREACT，PHREEQC和PHT3D。在所有问题级别上，所有RTM的仿真结果均显示出合理的一致性。