A Two-Dimensional Analytical Model for Volatile Organic Compounds (VOCs) Transport in Layered Landfill Composite Cover System With Gas Collection System

Layered cover structures are widely used as landfill environmental barriers to reduce the escape of odor gases. An innovative two-dimensional analytical model is developed to examine volatile organic compounds (VOCs) migration via a four-layered soil cover made up of a gas recovery layer, compacted clay liner (CCL) layer, geomembrane (GMB), and protective layer. The effects of source concentration distribution, LFG collection system, saturation degree, contaminant degradation rate, and GMB on cover system performance were evaluated. For a significantly more tightly clustered source concentration, 1D models tend to produce more conservative results in contrast to the 2D models based on the analysis of nonuniform contamination source distribution. Results show that increasing saturation degree (S_r) and degradation rate lead to lower steady-state surface flux. VOCs migration in the cover system is more sensitive to S_r variation in the CCL and gas recovery layer than that in the protective layer. The 2D results suggest that decreasing the half-life of the contaminant to 0.01 years when S_r1 = S_r2 = S_r4 = 0.5 can improve the cover system performance. An intact GMB layer and the gas collection flow rate of over 6 m³/s are required for the cover system to achieve a 70% LFG collection efficiency and satisfy the surface flux tolerance value. The proposed analytical model can be used for the preliminary design of the landfill cover system and verification of the complex numerical model.