What is it?
A dry well is a subsurface stormwater facility consisting of either a structural chamber or an excavated vault that is only used to collect and temporarily store stormwater runoff from rooftops. The dry well inflow is connected by an exposed pipe alongside a building that runs down into the ground. The sides and top of the dry well are completely lined with filter fabric to avoid fines clogging the system. The rate of infiltration from the subsurface layers is an important component, since these layers provide outflow from the system.
When is it used?
A dry well may be used to comply with groundwater recharge design and performance requirements. Also, it may also be used to reduce the volume of clean roof runoff.
What are some key general considerations?
- The dry well is only intended for small storm events, and all excess water must be designed to flow around the structure.
- Subsurface layers must be sufficiently checked and maintained to ensure minimum permeability rates.