September 20, 2011

Get a rare glimpse of the McMillan Sand Filtration Site

This weekend we got a rare tour of the dormant McMillan Sand Filtration Site just north of Bloomingdale.

The site sits behind locked fences between North Capitol Street, Channing Street NW, 1st Street NW, and Michigan Avenue NW.  The filtration site opened in 1905 to purify river water supplied to a burgeoning capital.

The filtration plant contains 25 acres of underground sand filtration cells.  Water flows from the “castle” on McArthur Boulevard NW at the Georgetown Reservoir through an arrow-straight tunnel to the valve house on 4th Street at the McMillan Reservoir.

Diagram of the Washington City Tunnel, U.S. Army Corps of Engineers

The reservoir opened in 1902 and is actually a dammed stream valley.  Since the reservoir stores untreated river water, the water must be cleaned before it can be distributed to residents’ taps.  

At the turn of the 20th century, a debate ensued between proponents of chemical purification and slow sand filtration.  Slow sand filtration won the debate and Congress provided money to build the sand filtration cells.

McMillan Sand Filtration Site under construction. Source: U.S. Army Corps of Engineers

The process of slow sand filtration is pretty simple. Water fills a cell that contains 2 feet of sand at the bottom— it’s like an underground beach.

Sand Pit

The water percolates through the sand leaving contaminants behind in the sand. When the water reaches the floor under the sand, it exits the cell and is distributed into the city’s water pipes.

The sand itself required routine cleaning to remove the contiminants. Clean sand was stored in the concrete silos that stand in rows on the site.


Workers replenished the cells by dumping clean sand through the various access holes on the roof of each cell.


In fact, an early photo shows fresh sand dumped into a cell.

Source: U.S. Army Corps of Engineers

Regulator houses contained valves for regulating the flow of water through each cell.

Regulator House


The top of the filtration site was turned into a park, as envisioned by Sen. James McMillan (R – Michigan), famous for his ambitious McMillan Plan to beautify Washington.

Park lightFrederick Law Olmsted, Jr., designed the park grounds on top of the sand filtration cells. Since the park closed to public access during World War II, the park’s recreational features, including green lawns, park lamps, walkways, and staircases, sit decaying today.

In the 1980s, the U.S. Army Corps of Engineers build a rapid sand filter on the part of the reservoir west of 1st Street NW, thus obviating the need for the slow sand filters east of 1st Street. The western section today holds the active open-air reservoir and rapid sand filters that supply clean water to much of Washington.

That section, which is still an active reservoir and water treatment plant, is closed to the public.  What’s most unfortunate is that the western section contains the most notable feature of the reservoir park.

Shortly after Sen. McMillan’s death, Congress and donors in his home state of Michigan decided to honor the senator with an ornate fountain to adorn the park that bears his name.

Source: U.S. Army Corps of Engineers

The 1912 fountain, designed by Herbert Adams, contains a bronze sculpture of 3 nymphs on a pink granite base. In 1941 the fountain was dismantled, left in storage and mostly neglected until the top portion of the fountain was returned to Crispus Attucks Park in 1983. In 1992 the top section was moved to its current location, at the active reservoir site, locked away from public access.

One can still see the top portion of the fountain by glancing through the fence on 1st Street NW.

McMillan Fountain

The base of the fountain remains somewhere in Fort Washington National Park in Prince George’s County. Perhaps someday the District, the federal government, and neighbors can raise the funds to reunite and restore the fountain for public enjoyment.

Categories: History, McMillan Sand Filtration Site
Tags: , ,

2 Replies

  1. Great run down on the history of the site and pictures, both new and old.

    jbcarron - September 21, 2011 @ 12:33 pm
  2. Great job. I forwarded your article to a friend who is at Historian at the Corps of Engineers. I really enjoy DC history, this is a nice addition.

    A. J. Thomas - September 22, 2011 @ 5:17 pm

Leave a comment