In 2005, Alexandria's Archaeological Protection Code requirement forced Diamond Properties to halt its construction to allow for an archaeological excavation of the Colross site. The excavation occurred between March and June 2005, as mandated by the city of Alexandria. Diamond Properties paid R. Christopher Goodwin & Associates Inc., a cultural resource management firm, approximately $100,000 to explore the site for historical artifacts and to ensure all burial plots had been removed. While only a few artifacts were recovered, historians said the dig offered a clearer view of early 19th-century life at Colross. Discoveries included an underground domed brick cistern that served as a water purification system and evidence that slaves lived in outbuildings on the Colross estate. Archaeologists also discovered the mansion's original basement floor, which was laid in a herringbone bond. Evidence of the estate's exterior walls, the foundations of the smokehouse, stables, and a burial vault were also unearthed. In the northwestern portion of the property, what is thought to have been the foundation of a rectangular burial vault was found. No burial remains were discovered. All interments were presumably removed in the early 20th century. Thomson Francis Mason was originally interred at the Colross graveyard in 1838, as were two of his daughters. Subsequent residents had their remains reinterred at Christ Church Episcopal Cemetery in Alexandria. According to the Alexandria Economic Development Partnership, the delay in construction caused 79 condominium buyers to abandon their purchases. The Colross estate was the location for several significant events involving the Mason family. Sarah Elizabeth Mason (1819–1907), a daughter of Thomson Francis Mason and his wife Elizabeth Clapham Price, married St. George Tucker Campbell at Colross on November 17, 1841. Virginia Mason (1830–1919), another daughter of Thomson and Elizabeth married William Hathorn Stewart Davidge at Colross on February 1, 1853. Colross was also the venue for the funeral of Mrs. Virginia King, wife of Dr. Benjamin King, on December 31, 1850. King was a sister of Mrs. Judge Mason. According to local tradition, two small Mason children, William and Ann, were playing in the estate's yard when a storm arrived. William took shelter in the estate's chicken coop but the wind toppled the structure, killing him. Soon after William's death, his sister Ann drowned in a bathtub at Colross. Both children were interred in the estate's burial vault in the garden. Successive residents at Colross, including members of the Smoot family, claimed the estate was haunted by the deceased Mason children; they reported hearing children "giggling, singing, and talking", and witnessed apparitions of children in pre-Civil War attire.