Partially installed R-Tanks at the bottom of the Centre and Herron Stormwater Project in the Hill District.

“Underground storage” is one of the strategies we use to manage stormwater runoff in Pittsburgh. These storage systems are designed to hold stormwater back from the sewer system, which helps reduce street flooding, basement backups, and river pollution. They can be installed beneath rain gardens, playgrounds, pavement, or grassy areas. 

Stormwater is routed into the underground storage system through storm drains, soil, or domed grates. Pittsburgh has clay soil, so it is often difficult for stormwater to soak into the ground. Instead, most of our storage systems slowly release the stormwater into the sewer system after it rains. Depending on the location and soil, we sometimes wrap the storage system with impermeable liners, which prevent stormwater from traveling into the ground and toward nearby buildings.

Here are some types of underground storage: 

• Gravel Storage: These layers of small stones contain empty spaces, called voids, that allow water to flow through and fill up the space. It is ideal for urban environments because it can support the weight of paving and vehicles.
• R-Tanks: These modular plastic crates can be placed side-by-side and stacked to fit small or large spaces. Water can pass through the openings in the sides of the crate, then fill up the empty space inside. Different versions can support different weights.
• Pipe Storage: These large circular or arched pipes are made of plastic, metal, or concrete, and have capped ends to hold stormwater inside. The pipes are placed side-by-side underground, connected, and then surrounded by gravel.