This document is the TN 6.01 Retention/Detention System Maintenance HDPE. System accessories, cross sections with descriptions provided.

A retention/detention system is comprised of a series of pipes and fittings that form an underground storage area, which retains or detains storm water runoff from a given area. As sediment and debris settle out of the detained stormwater, buildup occurs that requires the system to be regularly inspected and cleaned in order for the system to perform as originally designed.

The following provides the available fittings and guidelines for inspection and maintenance of an HDPE underground storage system.

Concentric Reducers are fittings that transition between two pipes, either in line with one another or at perpendicular angles. The centerlines of the two pipes are at the same elevation. When a concentric reducer is used to connect the manifold pipe to the lateral pipes, most debris will be trapped in the manifold pipe.

Eccentric Reducers are fittings that transition between two pipes, either in line with one another or at perpendicular angles. The inverts of the two pipes are at the same elevations. When an eccentric reducer is used to connect the manifold pipe to the lateral pipes, most debris will follow the flow of the storm water into the lateral pipes.

Risers are needed for each retention/detention system strategically placed for maintenance and inspection of the system. These risers are typically 24” in diameter or larger and are placed on the manifold fittings.

Cleanout ports are usually 4-, 6-, or 8-in diameter pipe and are placed on the manifold fittings. They are used for entrance of a pipe from a vacuum truck or a water-jetting device.

Maintenance of a retention/detention system is outlined by frequency, pre-inspection and inspection/maintenance.