Geomembranes employed to overlay the excavation for landfills must be seamed together at the site of the landfill. To ensure the integrity of the containment system of the landfill, these sheets or blankets must be carefully seamed. The methods in present, common use are extrusion fillet welding whereby the extrudate is placed over the edge of the seam; extrusion flat welding whereby the extrudate is placed between the two sheets to be joined; hot wedge seaming, a thermal fusion bonding, whereby an electrically heated wedge melts the sheets to be joined, after which a roller applies pressure to ensure the seal; hot air seaming whereby hot air between the sheets melt the surfaces to be joined; chemical fusion whereby a liquid chemical is applied between the two sheets to be joined; and chemical adhesive whereby a dissolved bonding agent (adherent) is applied between the two sheets to be joined. (Copyright (c) 1992 ISWA.)