Why must geomembranes be used for anti-seepage in garbage dumps?

During the decomposition of garbage, a liquid containing many harmful elements is generated, which permeates the soil surface and pollutes groundwater. If groundwater is severely polluted, the consequences can be imagined. Geomembranes can effectively prevent harmful liquids from penetrating the soil layer, so landfill sites should use geomembranes for anti-seepage.