A subsoil structure for disposing of methane beneath the ground, comprising: (i) a subsoil biofilter layer which receives methane, the biofilter layer containing biofilter material for converting the methane to carbon dioxide and water, and comprising a first horizontal array of prefabricated units each of which has an apertured upper wall, an apertured lower wall and apertured side walls (4, 5, 6, 7); the walls of each prefabricated unit of the first horizontal array defining an interior which contains biofilter material; wherein the side walls of each prefabricated unit of the first horizontal array have upwardly extending portions which resist compression and prevent crushing of the biofilter material; and the apertured walls of each prefabricated unit of the first horizontal array are pervious to gas to permit gas to pass into and out of the biofilter layer; (ii) a subsoil ventilation layer above the biofilter layer, defining a ventilation space into which the carbon dioxide from the biofilter layer passes and is diluted with air, the ventilation layer comprising a second horizontal array of prefabricated units each of which has an apertured upper wall, an apertured lower wall and apertured side walls (4, 5, 6, 7); wherein the side walls of each prefabricated unit of the second horizontal array have upwardly extending portions which resist compression; the walls of each prefabricated unit of the second horizontal array defining an interior which is part of the ventilation space; and the apertured walls of each prefabricated unit of the second horizontal array are pervious to gas to permit gas to pass into the ventilation space from the biofilter layer; and (iii) a first vent communicating with the ventilation space so that the diluted carbon dioxide is vented to the atmosphere. (i) a subsoil biofilter layer which receives methane, the biofilter layer containing biofilter material for converting the methane to carbon dioxide and water, and comprising a first horizontal array of prefabricated units each of which has an apertured upper wall, an apertured lower wall and apertured side walls (4, 5, 6, 7); the walls of each prefabricated unit of the first horizontal array defining an interior which contains biofilter material; wherein the side walls of each prefabricated unit of the first horizontal array have upwardly extending portions which resist compression and prevent crushing of the biofilter material; and the apertured walls of each prefabricated unit of the first horizontal array are pervious to gas to permit gas to pass into and out of the biofilter layer; (ii) a subsoil ventilation layer above the biofilter layer, defining a ventilation space into which the carbon dioxide from the biofilter layer passes and is diluted with air, the ventilation layer comprising a second horizontal array of prefabricated units each of which has an apertured upper wall, an apertured lower wall and apertured side walls (4, 5, 6, 7); wherein the side walls of each prefabricated unit of the second horizontal array have upwardly extending portions which resist compression; the walls of each prefabricated unit of the second horizontal array defining an interior which is part of the ventilation space; and the apertured walls of each prefabricated unit of the second horizontal array are pervious to gas to permit gas to pass into the ventilation space from the biofilter layer; and (iii) a first vent communicating with the ventilation space so that the diluted carbon dioxide is vented to the atmosphere.