In‐situ groundwater remediation is usually limited by the incomplete mixing of reactive species due to creeping flow characteristics and limited dispersion in porous media. In this study, we propose a novel approach to deliver chemicals through a multi‐screen well (MSW) to enhance the in‐situ remediation efficiency without extra energy or labor costs. The basic idea is to separate the injected solution into several plumes to enlarge the contact area between injected chemical compounds and ambient contaminants and enhance the mass exchange flux and reactive mixing. We perform laboratory experiments and numerical simulations of steady‐state instantaneous reactive transport in two‐dimensional porous media. We consider three separate screens in an MSW for the injection of treatment solutions and compare its plume distributions with a classical single‐screen well system. The experimental results confirm our conjecture and demonstrate the reliability of the numerical model. Furthermore, we derive an optimal injection interval of the MSW system by comparing analytical and numerical methods and demonstrate its capability to achieve effective transverse mixing and reaction enhancement. An interval that is smaller than the optimal injection interval leads to the exhaustion of contaminants between the injected plumes and the coalescence of the separate injected plumes at the downgradient portion along the travel distance, which reduces the effectiveness of the MSW system. We also investigate the sensitivity of the injected concentration, individual screen length, transverse dispersivity, and seepage rate on the determination of the optimal injection interval and provide suggestions about the design of an MSW system.

Periodic groundwater table fluctuations are found frequently in natural aquifers due to sea tides or seasonal recharge. However, their impact on the transport of volatile organic compounds in the vadose zone released from a groundwater contaminant source (i.e., vapor intrusion) has not been well known. A 2D numerical model was developed to explore vapor intrusion processes in the sandy vadose zone, subject to a fluctuating groundwater table with a range of fluctuation amplitudes and periods. A carcinogenic compound, Trichloroethylene (TCE), was chosen as the groundwater contaminant of interest in the current study and assumed to transport into the dwelling through a crack at the corner of the basement. Results showed that the resistant effect caused by high soil moisture contents in the thin capillary fringe is weakened by periodic groundwater table fluctuations, resulting in a higher concentration of gaseous TCE at the building foundation crack, in comparison with that under a static groundwater table. The increase of the gaseous TCE concentration was induced by the enhancement of diffusion and advection due to groundwater table fluctuations. Sensitivity analyses indicated that a higher amplitude and frequency of fluctuations lead to a higher TCE concentration at the crack under the dynamic equilibrium condition. Specifically, compared with the static groundwater table condition, the TCE concentration at the crack increased by one order of magnitude under the condition of groundwater table fluctuations with an amplitude of 0.2 m and a period of one day. The results obtained could provide insights into the importance of the amplitude and frequency of groundwater table fluctuations on vapor intrusion.

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