Dry Well

A dry well is a subsurface stormwater facility consisting of either a structural chamber or stone filled excavation that is used to collect and temporarily store stormwater runoff from rooftops. The dry well inflow is connected by roof leaders. The sides and top of the dry well are completely lined with filter fabric to avoid fines clogging the system.

Dry well detail.
Image Credit: Montgomery County, Maryland, 2018

Considerations:

• Dry wells are only intended for small storm events, and all excess stormwater must be designed to bypass the structure.
• Designers must ensure that soil conditions are suitable for infiltration.

Cost: Dry wells can be less expensive than other BMPs. However, under the new rules, dry wells may only be used to satisfy groundwater recharge requirements. If the project must meet water quality and water quantity standards, a BMP with the capacity to provide multiple benefits should be considered.

Maintenance: Regular maintenance activities include inspections for clogging and structural damage and sediment and debris removal. Roof drains should be checked and cleared regularly to prevent upstream clogging and to ensure that water reaches the system.