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Professor Buzzkill: Pittsburgh’s Fourth River

We love our Steelers, we love our pierogies, and we love our rivers. The aristocratic Allegheny has its yacht clubs and kayaks. The muddy, muscular Mon does all the hard work. And the Ohio is our gift to the midwest, forged by the combination of the other two rivers’ personalities.

But what about the fabled fourth river in Pittsburgh? Stand still for more than 10 minutes anywhere in the 412 and you’re bound to be approached by a yinzer, ready to regale you with Pittsburgh tales: the bomber in the Mon, the Green Man, and the famous fourth river. It’s underneath us, they say, and has been covered up by city streets. Strange, golem-esque creatures are down there. They live off blind river fish and have Myron Cope accents. The fourth river isn’t entirely underground, locals will tell you. While most rivers simply empty out into oceans or lakes, our beloved fourth provides its own majestic finale by shooting up powerfully to form the fountain at Point State Park.

I wish these weird tales were true, but they aren’t. The truth about the fourth river is even weirder. At least, that is, for all us who aren’t geologists. The river beneath downtown is an aquifer, which was formed during the last Ice Age (somewhere between 12,000 and 100,000 years ago), along with our other rivers and valleys. An aquifer is an underground layer of rock, sediment, sand, and gravel that is permeable enough to hold water (and to have water flow slowly through it).

The aquifer is constantly active, with water flowing into it from the Allegheny and the Mon as well as from its own supply. What’s more interesting, and weirder in a way, is that the aquifer is used for heating, cooling, and regulating the temperature in some of the major buildings downtown. Staying within a range of 50 to 54 degrees year-round, the aquifer water provides the perfect thermal baseline for these buildings. It only takes a little extra energy to boost the water’s temperature in the winter and almost no energy to use it as a coolant in the summer.

Wells were sunk all over the downtown area over the years, and the aquifer water was drawn whenever it was needed. Once mechanized heating and cooling systems became sophisticated in the early 20th century, aquifer water became an essential civic and commercial resource. Even hyper-modern PPG Place uses the fourth river as part of its heating and cooling system. Our region’s water companies even draw from the aquifer. And some of the fourth river’s water is combined with city water to create our beloved Point State Park Fountain.

It’s easy to visualize water from our above-ground rivers being used for commercial and industrial purposes. After all, drawing river-water has been common in human history. The key thing that makes the fourth river so useful, however, is that it is easier to transport its water, and it’s much cheaper to get it to the temperature needed for the purpose. Imagine having to pipe water from either of the big rivers, and then massage its temperature for all of downtown’s needs. Aquifer wells turned out to be more direct, efficient, and cost effective.

And by using the fourth river, early yinzers were only following what had been done for centuries — using the most readily available and replenish-able resource. Digging a well to the aquifer was smart. Hauling it from one of the rivers was dumb.

What’s weird about the existence of the aquifer is that it means that downtown seems to be resting on a sponge. Granted, it’s a pretty stiff sponge, but it’s still porous and soaked with water. But aquifers aren’t exactly the type of river or water source that we’re used to seeing, and the unseen is usually the source of myths. But legends about being able to kayak down it via our sewer system are not to be taken seriously. First of all, you can’t really get to the fourth river. It doesn’t exactly “flow” as rapidly as above-ground rivers. And your kayak would get stuck on the sediment. So aquifer really is a better term for our fourth river. Geologically speaking, of course.

But Pittsburghers don’t stand for fancy science-talk. We like giving things our own names, like “gum bands” and “dippy eggs.” So the only thing missing from our fourth river is a real Pittsburgh name.

Let’s call it Myron.