The main objective of this study was to evaluate and optimize the chemical oxidation process to be implemented at a power plant in Penghu County, Taiwan through laboratory and pilot-scale experiments were used to evaluate and optimize the chemical oxidation process at a power plant in Penghu County, Taiwan. Prior to pilot test, bench-scale tests were performed in the laboratory and analytical results indicated that persulfate oxidation achieved 90% removal of fuel oil while Fenton-like oxidation achieved only 41% removal of fuel oil within three days of testing period. Persulfate oxidation coupled with Fenton-like reaction was then used in a pilot test to treat the contaminated soil onsite. The Fenton-like reaction served the first stage of oxidation which formed hydroxyl radicals to break down fuel oil. The excess heat and ferrous ions resulted from such oxidation process would then activate persulfate oxidation which, in turn, produced sulfate radicals for continual brake-down of fuel oil. Result of soil pilot test indicated that the concentration of fuel oil was reduced to below the regulated standard in less than a week. Because the treated soil was originated from the local basaltic basement rock, it is rich in heavy metals, by nature. As such, the heavy metals as nickel and chromium were detected in leachate collected from the treatment cells, at concentrations exceeding the Taiwan Contaminant Control Standard and would have posed secondary contamination to the ambient environment if in-situ soil persulfate oxidation was implemented. Therefore, the result of this case study provides an alert that implementation of in-situ persulfate oxidation for soil and groundwater treatment could pose a threat of secondary contamination of heavy metals to the ambient environment.