A device and method for increasing the area available for passing contaminated stormwater through a granular media. The device comprises of one or more hollow elements that are made of degradable material and are of predetermined size and shape. The increased area available for flow is obtained by introducing a first media into predetermined areas of the device, introducing a second media into predetermined areas that are adjacent to areas containing the first media, and allowing the elements to degrade to bring about contact between the first and second media.