We investigated treatment techniques for the leachates derived from an abandoned waste disposal landfill facility known as Nan Ji Do in Seoul, Korea. To this end, the general characteristics of those leachates were carefully examined. The feasibility of leachate handling techniques was then examined through an application of both off- and on-site processes as a combination of direct treatment methods and/or pretreatment options. They include operation of such systems or methods as: (1) activated sludge process, (2) adsorption-flocculation methods, and (3) anaerobic digestion. When the fundamental factors associated with the operation of an activated sludge process were tested by a simulated system in the laboratory, those applications were found to be efficient at leachate addition of up to 1%. Application of adsorption/precipitation method was also tested as the pretreatment option for leachates by using both powdered activated carbon (PAC) as adsorbent and aluminum sulfate (alum) as flocculant. Results of this test indicated that the removal of chemical oxygen demand (COD) was optimized at PAC and alum contents of 100 to 300 mg/L, respectively. In addition, an anaerobic digester also examined the effect of leachate components on the rate of anaerobic digestion. According to our study, treatment and pretreatment options investigated were, in general, effective enough to reduce the rate of organic loading and the occurrences of hazardous incidents.