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Between 1993 - 1995, excavations were conducted at the site of the Dung Repository, or Stercorary, located along the South Ha-Ha wall. Originally built in 1787 across the South Lane from the Stable, the Dung Repository was a manifestation of Washington’s desire to adopt agricultural innovations to increase his crops – in this case, the use of composted dung and other organic materials for fertilizer.

Morley Williams, Mount Vernon's Director of Research and Restoration, excavated several trenches across the site in 1935, uncovering remnants of a brick footing along the eastern and western gable ends of the building and the densely packed cobblestone floor of the structure. Williams was unable to determine if the Repository had stood until 1799.

The 1993-95 excavations opened the entire building footprint, revealing these architectural remains within a 31 x 12-foot building. They also discovered a series of postholes and molds, representing two generations of posts, set along the façade of the building, south of the cobblestone floor. No corresponding postholes were found behind the South Ha-Ha wall to the north, suggesting that the north side of the building rested upon the Ha-Ha wall itself. The brick footings found along the gable ends appear to have supported posts along these short sides as well. They also were likely used to shore up the soil, as the floor of the building was laid nearly two-feet below the 18th-century grade. Artifacts recovered from the fill within the Repository date to as late as the 1820s, suggesting the building stood many years after George Washington's death.

A layer of dark, organic soil immediately above the cobblestones was thought to be the remains of composting manure. Soil scientists discovered grass phytoliths, or silica crystals.   Many species of plants have a distinctive phytolith appearance, similar to our fingerprints, and because these crystals preserve well, archaeologists use them to identify what vegetation was nearby.  These grass phytoliths found at the Dung Repository suggest that Mount Vernon horses were being allowed to graze, rather than being fed a diet solely of processed grains.

The excavation also uncovered four postholes for a later building that intruded the cobblestone floor of the Dung Repository. These postholes and the posts set within them were very large and spaced four feet apart, forming a square. The artifacts recovered within the postholes and postmolds suggest this small structure was built and demolished between about 1820 and 1850. We do not know what this building was, perhaps a small storage structure or earlier corn house.

As a result of the temporal and structural information obtained about the Repository for Dung from these excavations, and the artifacts recovered, and in conjunction with historical sources such as an 1808 drawing of a stercorary by agriculturalist Richard Peters, the Dung Repository was reconstructed on its original foundation in 2001. The reconstruction, incorporating the surviving masonry walls and cobblestone floor, today actually houses dung, providing an authentic effect to this corner of the Lane.