Drought-prone Wilmington needed a storage reservoir, so scenic Mill Stream Valley was dammed, destroying a colonial mill (1732 datestone) that T. Coleman du Pont had restored and enlarged (c. 1908). Local soils proved inadequate for an earthen dam, so 105,000 cubic yards of concrete were used instead. Poured in 1930 by contractors from Long Island, the structure was 135 feet high, 90 feet thick at the base, and 900 feet long. A hopper-bottom railroad car delivered cement from Hercules Cement Company. The material was pumped 2,000 feet from the railroad siding to a concrete mixer, from which conveyor belts carried it up the hillside to the dam. The structure is V-shaped to take best advantage of underlying rock layers. The reservoir was not needed until 1941, but water consumption has increased enormously since then, making it critical today.