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Leachate generation from sanitary landfills is regularly expected in tropical regions whenever the municipal solid wastes (MSW) attain its field capacity. However, there seems to be no studies documenting the behavior of high moisture laden MSW in sanitary landfills constructed or proposed in arid areas. Therefore, in this study prediction of leachate quantities is conducted using the water balance method with reference to a semi-aerobic sanitary landfill that would be designed to dispose 1,130 tons of pre-compacted MSW per day (in 2035) having a high moisture content of 70 % by w/w from the Metro Colombo Region which has a mean annual rainfall of 2,500 mm (but the landfill to be sited in Aruwakkalu; an arid area having a mean annual rainfall of < 1,500 mm). This article also discusses the feasibility of leachate treatment (considering the expected quality) and other issues that would arise due to leachate generation. Leachate production occurs during the peak rainy seasons (October; 2nd inter-monsoonal period and November-December; north-east monsoonal period) only despite the fact that the incoming MSW has a high moisture content. Furthermore, the generated leachate is a methanogenic leachate with a low BOD5/COD (< 0.3). At higher leachate heads, leachate breakthrough time and the time of travel (TOT) for Cl- are lower, but seepage velocities and flow rates are higher for both leachate and Cl-. Breakthrough time and hydraulic conductivity show an inverse relationship considering groundwater contamination in Aruwakkalu having a silty-sand soil (33-93 % sand), but no proper relationship between breakthrough time and seepage velocity.