The ornamental design for a supportmolding for an underground water storage or attenuation structure, as shown and described.
FIG. 1 is a perspective view of the support molding for an underground water storage or attenuation structure;
FIG. 2 is a view of the top of the support molding for an underground water storage or attenuation structure;
FIG. 3 is a view of the side of the support molding for an underground water storage or attenuation structure where the other sides would look identical; and,
FIG. 4 is a view of the bottom of the support molding for an underground water storage or attenuation structure.