A geomembrane liner for a containment system including liner panels and connected by a seam at overlapped edges, with the top panel having a conductive lower surface which is non-conductive across the seam. Heat welding of the seams is accomplished by a welder having a heating unit with a projection which interrupts the conductive lower surface of the top panel before forming the seam. Such seams may be used separately or selectively with a lined containment system having a plurality of liner panels covering at least a portion of the containment system bottom. The liner panels have a conductive lower surface and overlap with adjacent panels, and conductive members underlie adjacent panels and contact the conductive lower surface of both adjacent panels to provide an electrical connection between the conductive lower surfaces of the adjacent panels.