Ruins of the McMillan Sand Filtration Site – Washington, D.C. - Atlas Obscura
✨ Online experience gift cards are here! Buy Now »

Ruins of the McMillan Sand Filtration Site

An Industrial Revolution-era public work that purified water using nothing but sand. 


Typhoid epidemics regularly swept across Washington at the turn of the century as the population increased and industrial pollution worsened. A chief culprit was the city water supply. The unfiltered Washington Aqueduct carried a stream laced with bacteria and a notorious amount of Potomac mud, described by a Washington Post reporter as a “Seal-brown mixture of water and real estate.”

Shortly after the new city reservoir was completed at Howard University, Congress authorized funds for an adjacent filtration site to address the public health situation. The facility relied entirely on sand to clean the water; at the time, this method scaled better and was more cost effective than using chemicals.

“Raw water” came in from the reservoir next door and slowly percolated through the sand in 25 vaulted underground cells before making its way out into District taps. The 4-foot lining of sand actually did a remarkable job at removing bacteria and sediment from the water.

According to a historic preservation report, the sand was brought in from Laurel, Maryland on the B&O Railroad and “went through an extensive preparation process to meet specifications for cleanliness, removing all traces of clay and other undesirable particles.”

Enormous quantities of fresh sand were stored aboveground in parallel rows of stubby concrete silos. Engineers could shovel it out when necessary and drop it down into the cells through 2,100 manholes that are visible in satellite imagery.

Improvements like the Washington Aqueduct and the McMillan Sand Filtration Site came to D.C. as part of the City Beautiful reform movement. Its backers aimed to benefit society by taking on the squalid urban conditions of the Industrial Revolution.

At the time there was a different, more positive image of Washington’s water supply as a Public Work, and not merely a piece of infrastructure. As such, the nation’s foremost landscape architect was called in to devise a plan to pretty up the filtration site.

Frederick Law Olmsted Jr. designed a public park at the adjacent reservoir on the west side of 1st ST NW that became an important community gathering place for northeast District residents. For a time, it was a popular destination for picnics, outdoor activities, or a quiet stroll away from the bustle of city life. Unfortunately, the park was fenced off for security reasons during World War II and never reopened.

This park, is often referenced incorrectly as existing within the sand filtration site. In reality, Olmsted created a pathway that surrounded and overlooked the sand filtration site, rather than allowing public access on the plain, based on Olmsted’s recognition of the dangerous condition created by the 2,100 manholes across the plains, many of which would be open at any given time. (Records indicate that between three and four acres of manholes would be open at any given time to provide light and air to workers that were cleaning the sand in the filter beds below.) Olmsted was so concerned about this condition that he thought it was, “perhaps inexpedient to admit the public to use the plain even upon a fenced path.”

Olmsted’s plantings and perimeter pathway around the sand filtration site were designed to complement the “interesting and remarkable” appearance of the sand storage towers, the walls of which he covered in ivy. 

D.C. city government purchased the McMillan Sand Filtration Site after it closed in 1986, but the land has been abandoned and largely untended. It is a fantastic opportunity for preservation and a redevelopment project similar to New York’s High Line

Today all 25 acres sit behind a chain-link fence. The 20 massive cisterns have fallen into neglect, and in some cases have suffered collapse. There is a neighborhood movement to restore the underground and make it a public space, but its future is uncertain since the city has considered many other development plans for the site.

Know Before You Go

The sand filters are closed to the public and those who have gained access did so with the understanding that they were trespassing on private property. If a person were to gain access to the site they should remain vigilant. Dangers of falling through rotting/rusting manhole covers or into large pits are only a few risks that a person would be taking. Occasionally the property has been opened to the public for limited tours but not with any regularity.