Leachate recirculation using permeable blankets in engineered landfills

Subsurface leachate recirculation or liquid injection methods for municipal solid waste (MSW) landfills are horizontal trenches, vertical wells, and permeable blankets. In this study, results of field-scale testing and numerical modeling of a recently developed subsurface leachate recirculation system called permeable blankets have been presented. In the field, at a MSW landfill located in Michigan, the travel of injected leachate in a 60-m-wide by 9-m-long by 0.15-m-deep blanket made up of crushed recycled glass was measured using an automated sensing system consisting of sensors embedded in the blanket. Leachate injection rates used in the field and simulated in this study ranged from 1.1 to 3.6 m(3)/h per meter length of the injection pipe embedded in the permeable blanket. HYDRUS-2D was used to simulate the travel and pressure head of injected leachate in permeable blankets. The influence of the following parameters on the hydraulic performance of permeable blankets was evaluated: (1) hydraulic properties of permeable blanket and waste; (2) geometry of permeable blanket; (3) settlement of permeable blanket; (4) leachate dosing frequency; and (5) initial degrees of saturation of permeable blanket and waste. The key findings of the study are: (1) the rate and maximum distance of travel of injected leachate are a strong function of the relative hydraulic properties of the permeable blanket and underlying waste and the rate and frequency of leachate injection; and (2) the maximum pressure head in the blanket due to liquid injection does not exceed the injection pressure. The field data and the numerical modeling results indicated that permeable blankets can be designed to inject liquids or recirculate leachate in MSW landfills. Long-term performance of such blankets needs to be evaluated.