Abstract: Embodiments of the present invention provide underground bioretention systems that capture and treat surface water runoff. Such underground bioretention systems have a chamber formed by a chamber floor, a chamber ceiling, and at least one chamber wall; an access opening in the chamber ceiling fitted with an access opening cover; an influent opening in the chamber ceiling or the at least one chamber wall; an effluent opening positioned in the chamber floor or the at least one chamber wall beneath the influent opening; a filtration media positioned in the chamber beneath the influent opening; and an underdrain system positioned in proximity with the chamber floor. Also in such bioretention systems, the chamber floor, the chamber ceiling, and the at least one chamber wall are comprised of a material and a design adapted to form the chamber in a manner that withstands pressure applied thereon by subterranean and ground surface materials.