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D.C.'s Stonehenge: The History of the McMillan Sand Filtration Site

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Some describe the silos at  the McMillan sand filtration site as D.C.'s Stonehenge.
Jonathan Wilson/WAMU
Some describe the silos at  the McMillan sand filtration site as D.C.'s Stonehenge.

This is the first part of a two-part story on the McMillan Sand Filter Project. To find out more about the controversy surrounding new development at the McMillan site, read Part 2.

Sitting west of North Capitol Street, near Children's National Medical Center, is the sand filtration site next to McMillan Reservoir — a piece of land that has sat fenced in and unused for decades. With momentum building once again for new development there, the fascinating history of the property is once again coming to light.

In some ways, the McMillan site, with that collection of imposing concrete silos, has become D.C.'s version of Stonehenge, visually unmistakable and mysterious at the same time.

Taking the long view on water filtration

One person who's spent some time trying to remove that shroud of mystery is Emily Eig, an architectural historian who's part of Envision McMillan, a partnership between the mayor's office and the private sector that's putting forth a plan to redevelop the site.

Eig, who meets me on the corner of 1st and Channing Streets, says the story of the sand filtration site starts in the early 20th century, when Congress decided the District needed to expand its water system.

"The issue was whether it would be a chemical filtering system or a slow sand filtering system," Eig says. "A slow sand filtering system requires more space, and takes more time. And Congress at the time decided the sand was a safer system, even though chemicals at the time were extremely popular."

The bulk of the system is underground, comprised of large rectangular concrete cells.

"These cells — they're like caverns, a barrel-vaulted system, actually, that the sand sits within — each is one acre. Each acre has a completed cell," Eig says.

And though the filtration site required more space, and worked more slowly than a chemical system, sand filtration operates on a simple principle.

"Water comes through a pipe, and goes into sand, and then the particles and the bad things in the water attach and go to the bottom, and the clean water goes to the top and is then pumped out," Eig says.

A beautiful, mysterious aesthetic

When you walk down Channing Street towards North Capitol, the steep grassy manmade hill on the south side of the rectangular site is on the left, and seems to guard the edge. But the slope isn't there to keep people out, it's there because the site sits on a gradual incline.

"What this is, is a superstructure that's been built on top of the ground — on the earth — and then been covered with a layer, sort of like a green roof," Eig says.

Eig says from the beginning, architects and engineers on the project worked hard to ensure that the site would add to the beauty of the city instead of detracting from it.

The eminent landscape architect Frederick Law Olmstead, Jr. was brought into help. Eig says Olmstead introduced the idea of a tree-lined walking path around the rim of the site.

"People were encouraged to walk along the edge, and you could look across it. It was an ingenious way of blending or sort of disguising the industrial use that was going on there."

But the public was prohibited from walking across the site, and there was good reason to stay on the edge.

"There were 2,000 manhole covers on the site, and one-third of them were open at any particular moment," Eig says.

In the 1940s, with the country on a war footing, the federal government fenced off the property to protect it from enemy sabotage.

And in 1985, the Army Corps of Engineers shut down the site altogether after completing a new filtration system next to the McMillan reservoir, and offered the old sand filtration property to the District.

"When the federal government sold the property to District of Columbia in 1987, it was sold for $9.3 million with the intention for the District to develop it," Eig says.  "We know that because in fact, it was offered to the District for free — if they didn't develop."

So the District paid the money, but now it's been nearly two and a half decades, and the only thing that's really developed here is a sort of mystique.

"For many years, nothing was happening here. Nobody was walking here unless they were trespassing - and it seemed very mysterious," Eig says.

DC Water outlines their plan for the McMillan site.

Redevelopment on the horizon?

The city has put forward several plans to redevelop the site over the past few decades, but a lack of community support, financial backing, or both, doomed the efforts.

"The city has expectations for the site, and the neighborhood has expectations for the site, and those are not quite aligned," Eig explains. "So getting them aligned has been a complicated process. And there are people who value this as a very romantic, spiritual site now, which is very interesting, because it was an industrial site."

Which brings us back to the success of the first engineers and architects to work on the project, the people who wanted to achieve the perfect marriage between an industrial site and a space the public could enjoy.

Eig says that, ironically, their success in achieving that balance maybe what's made finding the right future for the McMillan Sand Filtration site so tricky.

"It is not a site where you can just take down the fence on the outside and turn it into a park," she says, "Because you'd fall down through the manhole covers, if it didn't collapse underneath of you."

And so, more than a century after it was built, the McMillan site stands as yet another monument to an age old lesson: there's no such thing as a perfect marriage.

Next week, Jonathan will have more details on the latest plan for redeveloping the McMillan Sand Filtration site, along with some input from those who oppose the plan.

[Music: "One Hour With You" by Donald Novis from Sentimental Memories]


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