## 1 Introduction  
Since trichloroethylene (TCE) is one of the most ubiquitous and carcinogenic pollutants in contaminated groundwater [1], its migration from subsurface environments into the indoor air of overlying buildings is one of serious concern [2]. TCE is chemically stable and resistant to biodegradation in aquifers due to its low viscosity, high density, low solubility, relatively high volatility and strong affinity for subsurface materials [3], making it a persistent, long-term pollution source of contamination. TCE can penetrate below the water table as a dense, non-aqueous phase liquid (DNAPL), from which it may slowly dissolve over decades [4; 5], posing sustained threats to groundwater quality [6; 7; 8]. Consequently, remediation efforts often require extended timescales, sometimes spanning decades [1]. Various remediation strategies have been explored at a laboratory scale to remove TCE from contaminated soil and groundwater. Environmentally friendly approaches, such as in situ biodegradation and phytoremediation, driven by natural or solar processes, are considered ideal [9; 10; 11]. However, high concentrations of contaminants can inhibit microbial activity, and many bioremediation methods require significantly longer timeframes compared to chemical treatments [9; 10; 11]. Pump-and-treat technologies often fail to achieve complete contaminant removal and necessitate prolonged site management due to contaminant rebound and tailing effects [12; 13]. In contrast, chemical oxidation has gained widespread application for groundwater and aquifer remediation over the past several decades [14; 15; 16; 17]. This method can degrade a broad spectrum of organic pollutants via electron transfer or generation of reactive free radicals (mainly including \(\bullet\)OH, SO\({}_{4}\bullet\)-, O\({}_{2}\bullet\)-, and HO\({}_{2}\bullet\)), which have strong oxidizing properties [18; 19; 20; 21; 22]. Among the various oxidants, including [PERSON]'s reagent, ozone, potassium permanganate (KMnO\({}_{4}\)) and persulfate [23], KMnO\({}_{4}\) stands out for its strong oxidative potential, high efficiency, low cost, aqueous stability, broad applicability, and formation of nontoxic byproducts [3; 17; 24; 25; 26]. KMnO\({}_{4}\) has been widely used in drinking water and wastewater treatment for decades. By the late 20 th century, it has also become a popular choice for in situ chemical oxidation (ISCO) [27; 28], offering a rapid and cost-effective treatment strategy for zones of high residual contamination. A survey of ISCO applications reported that KMnO\({}_{4}\) was widely used in remediation projects [29]. It has proven effective in degrading a wide variety of organic compounds, including chlorinated solvents, chlororphene, triclosan and bromophenols, across a broad pH range [30; 31; 32; 33; 34]. Permanganate ions (MnO\({}_{4}\)\({}^{-}\)) are particularly suited for oxidizing organics contaminants that contain carbon-carbon double and single bonds, aldehyde, or hydroxyl functional groups, including chlorinated ethenes [30; 35]. Compared with [PERSON]'s reagent, KMnO\({}_{4}\) often demonstrates higher removal efficiency for some chlorinated solvents [36]. Its stability and durability allow MnO\({}_{4}\)\({}^{-}\) to remain reactive and mobile, facilitating contact with subsurface contaminants [37; 38]. KMnO\({}_{4}\) acts as a strong oxidant, rapidly degrading chlorinated solvents such as TCE and perchloroethylene (PCE) into MnO\({}_{2}\), CO\({}_{2}\), and Cl\({}^{-}\) as the primary reaction products [39; 40]:  
\[\text{C}_{2}\text{HCl}_{3}+2\text{MnO}_{4}\text{${}^{-}$}\to 2\text{MnO}_{2} \text{(s)}+2\text{CO}_{2}+3\text{Cl}^{-}+\text{H}^{+} \tag{1}\]  
The widely accepted mechanism for the oxidation of TCE by KMnO\({}_{4}\) involves an electrophilic attack on the carbon-carbon double bond, forming a cyclic hypomanganate diester intermediate [41]. For TCE, kinetic modeling indicates that the formation of the intermediate is the rate-limiting step in the overall reaction [42].