© 2010 19 th World Congress of Soil Science, Soil Solutions for a Changing World 1 – 6 August 2010, Brisbane, Australia. Published on DVD. 49 Measurement of gas transport parameters for final cover soil at Maharagama landfill in Sri Lanka Praneeth Wickramarachchi A , Kaushalya Ranasinghe B , Udeni P. Nawagamuwa B , Ken Kawamoto A , Shoichiro Hamamoto A , Per Moldrup C and Toshiko Komatsu A A Faculty of Civil and Environmental Engineering, Saitama University, Saitama, Japan, Email praneeth1977@yahoo.co.uk B Dept. of Civil Engineering, University of Moratuwa, Katubedda, Sri Lanka, Email udeni@civil,.mrt.ac.lk C Dept. of Biotechnology Chemistry and Environmental Engineering, Aalborg University, Aalborg, Denmark, Email pm@bio.aau.dk Abstract To make a proper evaluation and better understanding of gas component movement inside a landfill site, and investigation of the different parameters related to gas flow is important. In this study, air permeability (k a ) and gas diffusivity (D p /D o ; where D o is the gas diffusion coefficient in free air) were measured as a function of soil air content (ε) in final cover soil at Maharagama landfill in Sri Lanka. The k a and D p were measured at different gravimetric water content in some samples and another set of samples were treated under different pF conditions (pF= log (-ϕ) where ϕ is the soil water matric potential in cm H 2 O). Results showed that greater variation of k a with ε in both experimental conditions. The k a rapidly increased with ε at relatively higher gravimetric water condition and then less variation near field water content and finally at drier condition the ka increased again with ε significantly. D p /D o exhibited exponential variation with ε. Based on measured data, predictive models for D p and k a were tested and pore connectivity parameter (α) and water blockage parameter (X) were calculated accordingly. Key Words Air permeability, gas diffusion coefficient, predictive models, pore connectivity, water blockage Introduction Gas generation and transport phenomenon are very important to understand in landfills to improve environmental aspects, landfill gas recovery or air supply for a better aeration inside the site. Moreover, when landfill gas is released into the atmosphere or migrates beyond landfill boundaries, it threatens the environment as well (Kallel et al., 2004). In recent years, landfills have been identified in greenhouse warming scenarios as significant sources of atmospheric methane (CH 4 ). In addition, it is well known that toxic gases such as hydrogen sulphide (H 2 S) and volatile organic chemicals (VOC) are emitted from the landfill sites (Song et al., 2007). All these gases are emitted to the environment through the final cover soil layer, therefore better understanding of transport, fate and emission of gases through such a final cover layer plays vital role as mentioned in many studies (Moon et al., 2008; Kallel et al., 2004). Moreover, open dumpsites are being gradually replaced by sanitary landfills where negative impacts to the environment are less compared to open dump site in developing countries (Chiemchaisri et al., 2007). The gas exchange through the final cover soils is controlled by advective and diffusive gas transport. Air permeability governs the advective gas transport induced by soil-air pressure gradient, while gas diffusion coefficient is governed by soil-gas concentration gradient. Generally, landfill final cover soils are highly compacted to prevent precipitation infiltration. Weeks et al. (1992) have reported bulk density ( b ) ranging from 1.57- 1.74 (g cm -3 ) for differently-textured landfill cover soils. Further in this study, the field investigation showed that the in situ bulk density reached 1.90 (g cm -3 ). Soil compaction has a major impact on gas transport characteristics. Hamamoto et al. (2009) showed that soil compaction simultaneously caused reduced water blockage effects and reduction of larger-pore spaces. It is a widely accepted fact that the soil physical and chemical properties of soil and soil texture are also vital for gas transport phenomena. Therefore selection of construction material for final cover soils is needed to be considered in engineering applications. In this study, the main objective was to measure the gas transport parameters and to test with some acceptable models in landfill final cover soil at Maharagama in Sri Lanka where municipal solid wastes were dumped and final soil cover was applied. Methods Materials and Method A waste landfill site located at Maharagama in Sri Lanka was selected as a sampling site in this study. The