Tangled web lies beneath

Pavement covers all sorts of items, from water and sewer pipes to utility lines and unusual artifacts.


WALLA WALLA - If you could peel back a typical city street, what would you find in the earth below?

Depending on the vintage of the street, you could expect to find water supply lines made of iron or even hollowed-out tree trunks wrapped with metal bands (no, those aren't in use today).

You'd find sewer pipes in materials ranging from plastic, ceramic or concrete to the more exotic Orangeburg, which gets its name from the city in New York where it was produced. Orangeburg is made of cellulose fibers bound with coal tar pitch and tends to soften as it ages.

Besides those vital underground channels for water and waste, city streets sit atop conduits for fiber optic cables, gas lines, old streetcar tracks and other artifacts.

How far below the streets this mishmash lies depends on location. Water supply and stormwater lines tend to run three to four feet below the surface, according to city public works employees. Sewer lines, which rely on gravity to make sure certain materials roll downhill, can run 20 feet or farther below the surface.

The city's early plumbing ran heavily toward hollowed tree trunks wrapped with metal. You can see an example of the pipe for yourself at City Hall near the top of the stairs leading up from the main entrance.

This style of piping was common and widespread in the 19th century, when water supply systems did not operate under the same pressures they do today.

These pipes were typically made from locally available trees by teams of two who would make their way from place to place boring out logs as a business.

As Walla Walla shifted away from an early water system centered on what is now Pioneer Park to its current system that pulls water from the Walla Walla Watershed to the treatment plant on the east end of town and into the city, a more modern pipe system has been installed.

But the system is showing its age, leaking an estimated one billion gallons of treated drinking water each year because of broken and leaking pipes.

As city crews work their way through the coming decades of repair and replacement of streets and the water and sewer systems below, the quirky diversity is likely to fade to a much more regular network.

Today's supply lines are made of ductile iron, a classification of the metal invented in the 1940s and notable for its flexibility and durability.

Public works employees say the lines in Walla Walla are at their largest - 36 inches in diameter - between the Walla Walla Watershed and the city water treatment plant and run from 24 inches down to 2 inches as they head downstream from the plant to area homes.

Sewer mains these days are made of PVC and run from 8 inches in diameter up to 36 inches, depending on how much sewage needs to flow through them on the way to the wastewater treatment plant.

Stormwater pipes can run even bigger, ranging from 8 inches up to 48 inches, according to city workers.

You might expect a 36- or 48-inch plastic pipe would need to be pretty thick to hold up, but because of the careful layering of earth and crushed gravel that the pipes lie in underground, the pipe can be quite thin, about 1/4 to 1/2 inch thick.

Perhaps ironically, this system for bringing water in and taking waste away is the primary mover behind the city's current infrastructure program, but just as you can't see the trouble from the surface, its solution will disappear into anonymity long before the last lines have been painted on the smooth asphalt above.

Alasdair Stewart can be reached at alasdairstewart@wwub.com or 526-8311.


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