A dry well is a buried infiltration structure - either a stone-filled pit or a plastic infiltration chamber - that accepts water from a downspout, French drain, or catch basin and lets it soak into the surrounding soil, used where there is no legal or practical gravity outlet to send that water to instead.
When you need it — and when you don't.
When you need this
- A property has no downhill neighbor, street, or drainage easement to daylight a French drain or downspout to, leaving infiltration as the only realistic option for getting rid of collected water.
- Downspouts are dumping concentrated roof water right at the foundation or across a walkway because there is nowhere to route them by gravity to a surface outlet.
- A French drain or yard swale collects water effectively but ends at a property line with no legal place to discharge it onto a neighbor's land or the street.
- A sump pump is discharging onto the surface in a spot that just re-floods the same low area, and a properly located dry well could accept that discharge and let it disperse into the soil instead.
- Local suitable soil conditions - reasonably free-draining sandy loam rather than tight clay - and an appropriate depth to seasonal high water table make infiltration a realistic option for the site.
When this is the wrong fix
- If test digging or a percolation check shows dense clay or silt close to the surface, water will not leave a dry well fast enough between storms and it will simply stay full, doing little more than a buried bathtub.
- If the seasonal high water table sits close to the bottom of where the dry well would need to go, the structure may end up sitting in groundwater for part of the year with no capacity left to accept new water when it is needed most.
- If the volume of water expected - a large roof area, a whole yard's worth of French drain flow - exceeds what the site's soil can realistically absorb, an oversized or additional dry well is not a fix; a legal gravity outlet or a different strategy is needed instead.
How it's done.
Sizing and siting a dry well properly starts with understanding the ground it sits in, and South Jersey's coastal-plain soil is inconsistent enough from one yard to the next that assumptions are risky. A test pit or percolation test at the proposed depth checks how quickly water actually drains through the native soil and, just as importantly, how far down the seasonal high water table sits, since a dry well needs clearance below its base to that water table to have any working capacity. Two general approaches are used: a stone-filled pit, which is simple and inexpensive but has less storage volume for its footprint, or a modular plastic infiltration chamber system, which creates a large open void wrapped in stone and fabric and stores considerably more water in the same excavated area. Either way, the pit is excavated to the sized depth and diameter, lined with non-woven geotextile fabric to keep surrounding soil out of the infiltration void, and either backfilled with clean stone or fitted with chambers before the fabric is folded over the top. Inlet pipe - solid PVC, since this stretch only conveys water rather than collecting it - runs from the downspout, French drain, catch basin, or sump discharge to the dry well, sloped continuously so nothing sits in the pipe between the source and the structure. The unit is set far enough from the foundation, property lines and any well or septic system to satisfy the general setbacks used in this trade, then covered with topsoil and reseeded so the finished yard shows no sign of what is underneath it.
Materials & standards
| Item | Typical practice |
|---|---|
| Structure type | Stone-filled pit, or modular plastic infiltration chamber system for greater storage |
| Stone | No. 57 clean washed stone surround where a stone-filled design is used |
| Filter fabric | Non-woven geotextile wrapping the entire infiltration void |
| Inlet pipe | Solid SDR-35 PVC from the water source, sloped continuously to the well |
| Siting check | Percolation/soak test and seasonal high water table check before final sizing |
| Setbacks | Distance maintained from foundations, property lines, wells and septic components per general trade practice |
| Cover | Topsoil and reseeding restore the surface once buried |
How the job runs.
- 01
Dig a test pit at the proposed location and depth to check soil drainage rate and how close the seasonal high water table sits.
- 02
Size the dry well based on the expected water volume - roof area, French drain flow, or sump discharge - and what the percolation test shows the soil can accept.
- 03
Choose stone-filled or chambered construction depending on the storage volume needed and the space available to excavate.
- 04
Excavate the pit and line it fully with non-woven geotextile fabric before placing stone or chambers inside.
- 05
Run solid PVC inlet pipe from the source to the dry well with continuous fall so water does not sit in the pipe.
- 06
Fold the fabric over the completed structure to seal out surrounding soil, then backfill above it.
- 07
Restore the surface with topsoil and seed, and confirm the inlet drains freely with a hose test before considering the job finished.
What moves the number.
Every site is priced individually after we have walked it, in writing, with the scope itemized. These are the variables that decide where a job lands.
| Factor | Effect on price |
|---|---|
| Soil percolation rate | Slow-draining soil requires a larger structure or additional dry wells to handle the same volume of water compared to freely draining sandy soil. |
| Depth to seasonal high water table | A shallow water table limits how deep the well can go, which can force a larger-footprint or chambered design to get enough capacity within the available depth. |
| Chamber versus stone construction | Modular chamber systems cost more per unit but hold significantly more water in the same excavated footprint, which can offset the added material cost by needing a smaller overall excavation. |
| Volume of water to manage | A dry well serving a large roof area or a whole-yard French drain system needs to be sized well beyond one serving a single downspout. |
| Distance from source to well | A longer inlet pipe run from the downspout, catch basin or French drain to a suitably located dry well adds trenching and pipe. |
| Number of dry wells needed | Some sites need more than one smaller dry well spread across the yard rather than one large structure, depending on soil consistency and available space. |
Questions we get, answered.
A daylight outlet simply releases collected water at the surface at a lower point on the property or into an approved storm system. A dry well is used specifically when no such lower point exists; instead of releasing water at the surface, it lets water soak into the ground gradually through a buried infiltration structure.
In tight clay or silty soil that does not drain well, a dry well fills up during a storm and stays full for days, providing little more benefit than an open pit. That is why a percolation test at the actual proposed depth matters before committing to this approach rather than a legal gravity outlet.
It can, provided the soil and water table conditions support infiltration and the well is sized for the volume a sump pump can move, which is often more concentrated and higher-volume than a slow-soaking French drain flow. Undersizing it for sump discharge is a common reason a dry well appears to fail.
General practice keeps dry wells a meaningful distance from foundations, property lines, and any well or septic components, both to avoid saturating soil near the foundation and to respect typical separation requirements used in this trade; exact required distances should be confirmed for the specific site.
{{ NEEDS REAL DATA: municipal stormwater/soil-disturbance permit requirements and fees for dry well/infiltration systems by township }}