on the lake front was prohibited, and the Tunnel Company responded by building a new disposal station on the Chicago River. Here, elevators lifted tunnel cars to the surface where they were dumped into self-propelled catamaran "dump scows" with a capacity of . The scows then took the debris out into the lake for dumping in deep water. George W. Jackson, the Tunnel's chief engineer, filed a patent on a scow fitting this description. Filling on the lakefront began again in 1913, with the construction of a tunnel extension to a new disposal station on the lake shore beyond what was then the south end of Grant Park. Here, twin elevators lifted the cars to the surface. Fill from this disposal station created the land under the Field Museum of Natural History and the Century of Progress Exposition (Now the site of Soldier Field and McCormick Place). In 1913, the tunnel system handled 51,685 carloads of excavation debris and 14,605 carloads of cinders and other refuse. Excavation debris and ash were billed per carload, so the tonnage is not available. A 1929 estimate put the average combined excavation and ash traffic at 75,000 carloads per year. Immense amounts of fill were hauled by tunnel to the lake during construction of Chicago's new main post office adjacent to Union Station in the early 1920s. Even though coal deliveries were made with trucks, it was still more efficient to remove ashes by tunnel. This basically left the company in the ash removal business for the last ten years of operation. Secondary businesses The tunnel company had a curious secondary business, namely air conditioning, which was accomplished by selling naturally cool tunnel air to theaters above the tunnels. The McVickers, Rialto and four other theaters owned by the same company used tunnel air. Tunnel air was also utilized in the winter, as heating this air required less energy than heating the often much colder outside air. They estimated that they used less than one-third the coal they would have used without the tunnel connection. The tunnel air was a constant year round. In 1933, the tunnel company sought financing from the Reconstruction Finance Corporation to diversify into district heating, using the tunnels to carry steam pipes from a central steam plant to various customers. At the time, an estimated ten percent of Chicago's loop businesses already used district heating services provided by the