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On the Potomac, Egg-Shaped Towers Will Be a High-Water Mark

Judging by photographs of many digester installations in Europe and the United States, it is doubtful that Corbusier would have found them all that appealing. They've been disguised by all sorts of cheap sheathings, so that the odd, rather heavyweight elegance of the basic form rarely comes through.

In Washington, things happily took a different course. Knowing that it had to face review boards such as the Commission of Fine Arts and the National Capital Planning Commission, WASA wisely brought an engineering-architecture team on board in the early planning stages -- BBS Engineers of Columbus, Ohio, and Sorg Architects of Washington.

Not surprisingly, with so many overseers, the design went through several variations. But as sometimes happens, the last one is in most ways the best.

From the beginning, Suman Sorg, with principal responsibility for exterior design, decided to link the eight digesters with bridges at the top, to make worker access more convenient and to bring aesthetic unity to the ensemble. Ditto for the four storage silos, arranged in a separate grouping close by the eggs.

But disagreements arose over the shape and detailing of the bridges and the "caps" at the tops of both digesters and silos. Some designers wanted bridges supported by steel archways ornamented with a sequence of circular forms in steel. Others wanted a slimmer, trimmer, more "industrial" look. And at one point, the eggs were sheathed in a patterned metal, sort of like water towers needlessly decorated in the 1970s age of Super Graphics.

Fortunately, the simplest view prevailed. With their elemental yet elegant steel trusses, the bridges and caps will look right at home. The dipping profiles of the trusses complement the curved form and the ribbed anodized aluminum cladding of the digesters. At the same time, they add a contrasting note of lightness. This is what Sorg humorously refers to as the "slimming effect."

"I wanted a delicate lacy effect to counteract the heavy industrial character of these structures," Sorg says. "More like the effect a necklace or a garland would have on an otherwise not so slender lady."

From most parts of Washington itself, this major addition to the skyline will be invisible, or very nearly so. But because of those prominent views from the south, the change gradually will work its way into the city's consciousness of itself, and into how the city is perceived by the outside world.

It is a change for the better. For all its beauty, monumental Washington sometimes does not quite seem to be a real contemporary city. Huge sewage digesters that stand tall by the Potomac, on the other hand, highlight the importance of sustainable urban infrastructure in a most fundamental way.

Besides, they'll be beautiful, in their way -- and almost magical, maybe, at night.

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