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Unlocking the Mysteries of Pittsburgh's 4th River

Pittsburgh’s underground aquifer may not resemble its above-ground siblings, but it still does plenty for the city.

photo by dave dicello


Our mythical “Fourth River” isn’t a fast-flowing body of water but something much cooler: It’s an aquifer, 50 feet of rock and sand on top of bedrock through which water flows. Formed many thousands of years ago by the coming and going of glaciers, the aquifer continues to fuel life as we know it. It's so important, we wanted to break it down:

Ice, water, rock, sand

  • Formative forces for the aquifer: Glaciers melted, water carved into the earth and deposited rock and sand that formed the rivers and riverbanks of our landscape.

80 trillion

  • The number of gallons of groundwater in Pennsylvania

6 million

  • Pennsylvanians who get part of their drinking water directly from groundwater

798,000 YEARS AGO

  • The time when glacial changes began to carve Pennsylvania’s landscape

50 to 54 degrees

  • The temperature of Pittsburgh’s groundwater


  • The number of gallons per minute a well could draw from Pittsburgh’s aquifer

North Side, South Side, Point

  • The areas built on top of the aquifer

Crop irrigation

  • The biggest use of groundwater, such as the water found in the aquifer, in the U.S.

9 million

  • The number of gallons of water downtown wells drew from the aquifer in 1950, when use was at its peak



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