Underground Infiltration Basins: Stormwater on a Tight Site

Every new commercial building adds roof and pavement, and rain that used to soak into the ground now runs off. Local stormwater rules generally require the site to manage that runoff, and on a tight lot, where there's little room for an open pond, the solution is often underground.

What an infiltration basin does. An underground infiltration basin collects runoff from the roof and parking areas and holds it in a chamber surrounded by stone, letting the water soak slowly into the soil instead of rushing off the property. It manages runoff without taking up the surface space an open basin would.

A real example. The standout challenge at our AutoZone project in Stroudsburg was stormwater. The site called for two large underground infiltration basins, fed by 36-inch and 48-inch pipe and surrounded by stone aggregate, on a small footprint. Because the basins depend on the ground to absorb water, we did considerable soil testing and amendment work to get proper drainage underneath.

Why the soil matters. An infiltration system is only as good as the soil beneath it. If water can't soak in at the rate the design assumes, the system won't perform as intended. That's why testing the soil early, and improving it where needed, is part of the work and not an afterthought.

Other tools for other sites. Not every site calls for the same approach. At The Estate at Schollhammer's Farms, a new 13-lot subdivision, our scope includes stormwater conveyance, a rain garden, and a detention basin. At the Luzerne County Flood Authority garage expansion, the work includes stormwater management and a bio-retention rain garden.

For owners and developers. Involve your site contractor early. Stormwater design affects how much of the lot is buildable, how deep the excavation goes, and what the schedule looks like. Bringing a site contractor into the conversation while plans are still taking shape helps surface issues like soils, access, and sequencing before they turn into change orders.

Related service: Site Work & Excavation