Remediation of groundwater pollution by in situ reactive zone: A review

Establishing an in situ reactive zone (IRZ) is an effective groundwater pollution remediation method that has been utilized extensively in actual contaminated sites. However, some controversial factors and technical bottlenecks hinder the establishment of an IRZ. For instance, we need to decide whether, under high pressure and high flow velocity, the colloidal remediation agent should be injected into the aquifer to increase or reduce its migration ability. Additionally, methods need to be developed to monitor the diffusion range of colloidal remediation agents in the process of IRZ construction in real time and optimize the layout of injection wells. To clarify these uncertainties and resolve bottlenecks, this review first summarizes the development and design of IRZ technology to remedy contaminated groundwaters. Then, the types of colloidal remediation agents commonly used in IRZ technology are outlined, and the main mechanism of degrading pollutants is thoroughly analyzed. Additionally, the main mechanism of transport of colloidal remediation agents in aquifers is generalized. Finally, current knowledge gaps and future research prospects are identified and proposed. This review significantly improves our understanding of IRZ technology and provides valuable insights to researchers in this field.