Install dry wells

Overview

A dry well is an underground container filled with stone or gravel that collects runoff from a building’s rooftop, driveway, and other impervious surfaces, temporarily storing the water before slowly releasing it into the surrounding soil through a filter fabric. Dry wells can help reduce flood risk to individual buildings by slowing the discharge of water into the ground and promoting infiltration and groundwater recharge, filtering out pollutants in the process. Generally small and low-capacity, dry wells work well in areas where space is limited.

Dry wells are often placed near a building to prevent surface erosion, which can occur if runoff is left unchecked. Since dry wells rely on the surrounding soil to absorb the collected water, they are only a good option if there’s a permeable layer of soil within a reasonable depth (about four feet). When collecting runoff from a roof, a drain pipe conveys the runoff from the downspout and directs it to the dry well and away from the building’s foundation, where the water could cause damage. Dry wells may include heavy-duty polyolefin rubber barrels – essentially underground rain barrels – which can increase storage efficiency and decrease the footprint of the dry well; these storage devices range in size from 50 gallons to several hundred gallons. They can be designed to be visible or hidden from view – either covered with topsoil and sod (or other shallow-rooted plants), buried under a walkway, or built to aesthetically border a driveway.

Minimal routine maintenance is required for a dry well. Maintenance may include the following:

• Removing debris from roof gutters and the dry well. If there’s a significant amount of debris or there’s tree canopy hanging over the gutter, a debris filter may be needed for the gutter system to prevent clogging.
• Cleaning and repairing inlets and outlets of the dry well.
• Looking to make sure that water is infiltrating and the dry well has not become clogged. Excess debris on top of the dry well can be removed by hand. Clogged dry wells should be refurbished or replaced.
• Removing any weeds.

Next Steps

1. Contact your local government to learn more about your property’s flood history and Base Flood Elevation, and to determine what federal, state and local permitting, code or ordinance requirements you will need to follow, before any work starts. If you are not sure who to talk to, check out our “who to contact” page. Your community’s floodplain management administrator also may be able to provide guidance as you search for a qualified engineer and/or contractor, if required. 
2. Choose the best dry well for your needs.
3. Choose the location for your dry well. If necessary, hire a qualified engineering service to determine runoff characteristics to figure out and design the right size and location for your dry well. Design criteria, land use regulations, zoning ordinances, and permits may dictate the size and location of the dry well.
4. Once a proposed location has been chosen, check it for underground utilities, electrical wiring, and sprinkler systems.
5. Make sure all necessary permits are obtained. 
6. If necessary, hire a qualified contractor and/or plumber to install the underground water storage tanks.
7. Check with your local government to determine any specific requirements for the maintenance of the dry.

Special Considerations

• Be careful not to redirect water flow from your property onto another property. No adverse impact (NAI) floodplain management is an approach that ensures the action of any property owner, public or private, does not adversely impact the property and rights of others. NAI calls for any adverse impact caused by a project to be mitigated as part of the project. By following NAI principles, you can: prevent flooding from increasing or damaging others; see a reduction in flood losses over time; and avoid challenges and lawsuits over causing or aggravating a flood problem.
• Check out the financial assistance page to see what funding or financing opportunities might be available to you.