Dry Well: Definition & Professional Guide
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A dry well is an underground stormwater infiltration structure that collects surface runoff from downspouts, sump pumps, or yard drains and allows it to percolate slowly into the surrounding soil. Dry wells are recognized by the EPA as a best management practice for managing residential stormwater at its source, reducing yard flooding, erosion, and the volume of runoff entering municipal storm systems.
Inlet Pipes, Gravel Bed, Geotextile & Soil Percolation Requirements
A dry well receives stormwater through one or more inlet pipes connected to downspouts, catch basins, or sump pump discharge lines. The water enters a buried chamber surrounded by clean gravel, typically number 57 stone, and wrapped in geotextile landscape fabric that prevents soil from migrating into the gravel void space. Water fills the chamber and gravel bed, then slowly seeps into the native soil through the bottom and sides of the excavation.
Soil percolation rate determines whether a dry well will function on a given property. Sandy and loamy soils drain quickly and support dry well installations well. Clay soils hold water and prevent adequate infiltration, causing the well to overflow rather than drain. A simple percolation test, performed by filling a test hole with water and timing the drawdown rate, reveals whether the soil can absorb water fast enough. If 12 inches of water takes more than 4 hours to drain, a dry well is the wrong solution for that location.
Dry wells handle stormwater only. Connecting laundry discharge, air conditioning condensate, or any gray water to a dry well violates health codes in most jurisdictions and risks groundwater contamination. The water source must be verified before the system is designed.
Plastic Chamber, Gravel Pit & Modular StormTech System Types
Plastic chamber dry wells use prefabricated structural chambers like the NDS Flo-Well that stack and connect to create a defined void volume. These chambers are lightweight, easy to install, and resist soil loading without collapsing.
Gravel pit dry wells consist of a lined excavation filled entirely with clean stone without a structural chamber. While functional, these have less storage capacity per cubic foot than chamber systems and are more prone to sediment clogging over time.
Modular chamber systems from manufacturers like StormTech use arch-shaped chambers that link together for larger capacity installations. These commercial-grade units handle higher volumes and are often required for new construction stormwater compliance.
Installation, Sizing & Sump Pump Discharge Connection Services
Dry well installation is part of Bonded Plumbworks’ outdoor and specialty plumbing services. Professional installation with properly routed inlet piping and a pre-treatment catch basin typically costs $1,500 to $4,000 depending on system capacity and excavation depth. Larger multi-well systems for properties with significant runoff can reach $8,000.
For homes with sump pump discharge that creates pooling or erosion in the yard, a dry well connected to the discharge line is often the most practical solution. Bonded Plumbworks’ technicians size dry well systems based on roof area, sump pump output volume, and verified soil percolation rate as part of sump pump and flood prevention work.
IRC Appendix C, EPA Class V Injection & Local Stormwater Ordinances
IRC Appendix C addresses stormwater disposal requirements for residential properties. The EPA classifies dry wells as Class V injection wells under the Underground Injection Control program, though most residential installations are authorized by rule without individual permits. Local stormwater management ordinances vary significantly and may require permits, setbacks from property lines and septic systems, or engineered drainage plans. In regions with high seasonal water tables, such as coastal or low-lying areas, the elevated groundwater frequently limits dry well effectiveness and may trigger additional regulatory review.
NDS Flo-Well & StormTech MC-3500 Infiltration Chamber Systems
NDS manufactures the Flo-Well residential dry well system, the most widely available chamber-based product at home improvement retailers, with a 50-gallon capacity per unit and daisy-chain capability for larger systems. StormTech, a division of ADS, produces the MC-3500 and SC-740 chamber series designed for higher-volume residential and commercial infiltration applications where engineered stormwater compliance is required.