A dry well is an infiltration bet, not a guaranteed outlet.

O’Fallon Quality Drainage treats dry wells as a last-resort infiltration idea on slowly permeable soils. Read Web Soil Survey, the clay-soil note, and French drain installation before you ask for a review.

When infiltration is the discharge, not a pipe

A dry well stores water and waits for soil to take it

A dry well stores water and waits for soil to take it. That only works if the soil actually takes it between storms. On many St. Charles plats, storms arrive faster than clay drains. A well that stays full is a buried cistern with nowhere to go.

Treat the dry well as a proposed storage-and-release system, not as a hole that makes water disappear. Identify the contributing leaders or surface area, the available storage, the observed soil behavior, and the emergency path when storage is full. If any of those pieces is unknown, the outlet decision is still open.

Soil percolation and clay limits in St. Charles County

Do not advertise a perk rate you have not measured

Do not advertise a perk rate you have not measured. A provider can run a simple infiltration test in the proposed location. If the hole still holds water the next day, infiltration is not the outlet. Write that result in the file instead of hoping.

The Web Soil Survey is useful context, but it is not a substitute for conditions at the proposed chamber location. Fill, compaction, shallow water, and a nearby foundation can differ across one yard. Record the test location and recent weather, because a single wet-day observation should not be presented as a universal soil conclusion.

Sizing volume to roof or yard contribution

Overflow is not optional

When the well is full, water will come out somewhere. Design that somewhere on purpose.

Roof laterals dump quickly. A well sized for a pretty photograph but not for roof area will surcharge. Ask for the storage volume and the contributing area in the same sentence.

Separate roof contribution from slow lawn seepage before discussing chamber size. A roof leader arrives in bursts; an uphill grade issue may arrive over a longer period. The proposal should identify which source is entering the well, what is intentionally excluded, and whether the design depends on an overflow for a larger storm.

Overflow protection when the well saturates

An overflow pipe to a legal daylight or a high-ground pop-up keeps the well from geysering at the foundation

An overflow pipe to a legal daylight or a high-ground pop-up keeps the well from geysering at the foundation. A well without overflow is an unfinished thought.

The overflow is not a backup detail to hide at the end of a drawing. It is the path water will use during the event that tests the system. Show its elevation, its outlet location, and whether water can move there without crossing a walk, a neighboring parcel, or an unapproved public connection.

Setbacks from foundations and property lines

Putting a well against the same wall you are trying to dry can feed the backfill

Putting a well against the same wall you are trying to dry can feed the backfill. Keep infiltration away from basements, septic fields, and neighbors. If there is no room, choose a pipe outlet instead.

A site visit should locate walls, property edges, known utilities, septic components where present, and the proposed overflow before a chamber is selected. Do not use a generic setback number from another jurisdiction as a design answer. Confirm the current local requirements and let the available site geometry decide whether infiltration is suitable.

Maintenance of a buried infiltration chamber

Silt from downspouts fills chambers

Silt from downspouts fills chambers. A debris trap upstream is cheaper than digging the well twice. If nobody can find the lid, nobody will maintain it.

Keep access visible on the as-built sketch and state who is expected to inspect it. After a heavy rain, check whether water stands at the inlet, whether the overflow operated, and whether sediment is accumulating upstream. Maintenance planning is especially important when a roof line carries leaves, granules, or mulch toward the system.

When a dry well should be rejected for a daylight outlet

If perk is poor, if the lot already sits in a bowl, or if the only space is next to the foundation, reject the well

If perk is poor, if the lot already sits in a bowl, or if the only space is next to the foundation, reject the well. A French drain or downspout lateral to a real release is more honest. National cost bands for French drains do not make a dry well cheaper; they are a different product.

Rejecting a dry well is a useful result, not a failure to sell a component. A visible surface route, a solid lateral to a legal release, grading, or a different collection method may be easier to inspect and maintain. Compare the water path rather than choosing an underground chamber because it appears less visible.

The first heavy-rain review should be planned before excavation. If the well is intended to receive roof water, inspect the leader connection, inlet, access point, overflow, and finished release in that order. If any part of the route cannot be observed or safely maintained, record that limitation. A concealed system is not automatically a durable system.

The decision record should end with a plain conclusion: infiltration supported by measured conditions, infiltration still unconfirmed, or infiltration rejected in favor of a visible release. That conclusion is more useful than a generic dry-well label because it tells the next provider why the selected outlet was chosen.

Retain the observation date and test location with that conclusion. Soil and weather context make the result more useful than an unsourced claim that a dry well will work everywhere on the property.

City stormwater context is on the O’Fallon Engineering page and in the permit note. Do not use a dry well to dodge a legal discharge question.