# Do dry wells work in clay soil?

> Do dry wells work in clay soil? Rarely in Plano. Houston Black clay soaks water in so slowly that a pit fills and stays full. What to use instead, with numbers.

URL: https://clayplanodrainagecompany.com/guide/do-dry-wells-work-in-clay/

A dry well only works if the ground around it can take water away. In Plano's clay, that takes days per pit. The arithmetic, the one place it differs, and the outlets that work instead.

Last Updated: November 11, 2026

The short answer

Rarely, in Plano. A dry well is a pit that stores water and lets it soak into the ground, and Houston Black clay takes in only about 0.03 inches an hour. A typical pit would take more than a week to empty, so it is still full when the next storm arrives. Piping water to the street works instead.

Key takeaways

- Houston Black is in hydrologic group D, the slowest-draining class of soil.
- A 3-foot-wide, 4-foot-deep pit holds about 210 gallons and would drain about 20 gallons a day in that clay.
- One heavy hour of rain on a 1,000-square-foot roof is about 1,100 gallons.
- Far west Plano's soil drains faster but sits shallow over chalk.
- Piped discharge to the street, or a pump where there's no fall, does the job a dry well can't.

## Thinking about a dry well for your yard?

A dry well sounds like the neat answer: bury a pit, pipe water into it, and let the ground take it away. It works where the ground can take water away. Plano’s clay can’t, at least not at any useful speed.

[Clay Plano Drainage Company](https://clayplanodrainagecompany.com/) plans drainage outlets across Plano and nearby cities. This guide shows why a soak-away pit struggles in this clay, with numbers you can check, and what to use instead.

## What a dry well does

A dry well is a buried pit or perforated tank, often filled with stone, that receives water from a downspout or drain line. It stores the water for a while and lets it soak out into the surrounding soil.

An infiltration trench works the same way, only stretched into a line. Both depend on one thing: how fast the soil around them takes in water.

## How slow Plano clay is

Houston Black, the clay under most of central, east and north Plano, passes water at about 0.21 micrometers a second when soaked. That’s about 0.03 inches an hour.

The USDA soil survey puts it in hydrologic group D, the class for soils with the slowest infiltration. Murphy, Parker, Wylie, central Allen and much of McKinney sit on the same soil.

### What a percolation test would show

A percolation test, or perc test, times how fast water drops in a soaked test hole. In fast soils the level falls in minutes. In clay rated at 0.03 inches an hour, the water level in a test hole barely moves through an afternoon.

On the first visit we probe the soil to see what the water is doing, which tells us early whether any soak-away design is worth considering.

## The dry well math

Numbers make the problem plain. Take a modest pit 3 feet across and 4 feet deep, and a storm with a 50% chance in any year, which drops 1.80 inches in an hour over central Plano by NOAA’s rainfall atlas.

| Quantity | Figure | How it’s worked out |
| --- | --- | --- |
| Water from one heavy hour on a 1,000 sq ft roof | About 1,100 gallons | 1,000 sq ft x 0.15 ft of rain = 150 cubic feet |
| What the empty pit can hold | About 210 gallons | A 3-foot circle, 4 feet deep = about 28 cubic feet |
| Soil the pit touches | About 45 square feet | Floor plus walls |
| What that soil takes in | About 20 gallons a day | 45 sq ft at 0.03 inches an hour |
| Time to empty a full pit | More than a week | 210 gallons at about 20 a day |

That’s a simplified figure at the soil’s mapped rate, and a real pit varies. The point holds either way: the pit overflows in the first minutes of the storm and is still holding water when the next one comes.

Richardson’s weather station, just south of Plano, records about 27 days a year with half an inch of rain or more in NOAA’s climate normals. In this clay, a dry well rarely gets the chance to empty between them.

## Far west Plano is the exception, partly

Around the Dallas Parkway and Arbor Hills, the soil is Eddy gravelly clay loam. It passes water at about 7.2 micrometers a second, roughly 34 times faster than Houston Black, so in its top layer a pit would empty in hours rather than days.

The catch is depth. Eddy and the nearby Stephen soils sit shallow over chalk, so a 4-foot pit can reach rock, and water stops at the rock instead of soaking down. A soak-away there still needs a backup outlet.

## Dry well or piped discharge?

The real choice in Plano is between storing water in the ground and moving it to the street. The city’s design manual has house lots drain to the street, which favors the second.

|  | Dry well | Piped discharge to the street |
| --- | --- | --- |
| Where the water goes | Into the soil around the pit | Out through an emitter, an existing line or a permitted curb outlet |
| In Houston Black clay | Fills and stays full for days | Empties as fast as the pipe allows |
| In a big storm | Overflows into the yard | Carries what it can; an overflow path handles the rest |
| Upkeep | Silt builds up in the pit over time | Clear the outlet and flush through cleanouts |
| Fits Plano’s lot rules | Only with an outlet of its own | Yes, it’s the outlet the rules expect |

The guide to [where yard drain water can go](https://clayplanodrainagecompany.com/guide/where-can-yard-drain-water-go/) compares every outlet a Plano lot can use, and [standing water in the yard](https://clayplanodrainagecompany.com/standing-water-in-yard/) covers how we find the cause when water already sits after storms.

## When the lot has no fall

Dry wells come up most on lots that can’t drain to the street by gravity: a flat back yard, a lot below the street, or a low corner with nowhere downhill to go.

For those yards, a pump basin does what a dry well promises. It collects water in a sealed basin, and a pump lifts it through a buried discharge line to the curb or an approved outlet; see [yard sump drainage](https://clayplanodrainagecompany.com/sump-pump-drainage/).

- Our typical range for an outdoor pump basin with its discharge line is $1,500 to $4,000 per pump basin; the site visit and written estimate set yours.
- Where the low spot fills mid-storm, a [catch basin](https://clayplanodrainagecompany.com/catch-basins/) can feed the pump basin; the guide to [French drains or catch basins](https://clayplanodrainagecompany.com/guide/french-drain-vs-catch-basin/) explains when a basin fits.

## AC condensate and other small flows

An AC condensate line drips a slow, steady flow through the cooling season. A pit for it stays soggy for the same reason a storm pit does.

Better options for condensate:

- A short solid line to a pop-up emitter in open lawn
- A tie-in to an existing [downspout line](https://clayplanodrainagecompany.com/downspout-drainage/) that reaches the street side
- A planted bed well away from the slab, where the plants use the water

If a dry well is already in your yard and the ground around it stays soft, the fix is a solid line to a real outlet. [Drain repair and cleaning](https://clayplanodrainagecompany.com/drainage-repair/) covers reworking old systems, and the guide to [French drains in clay soil](https://clayplanodrainagecompany.com/guide/french-drains-in-clay-soil/) explains how collection drains are built for this ground.

To find the outlet that works for your lot, call [(469) 551-8518](tel:+14695518518) or send photos through the form below.

## Questions about this guide

### Can a dry well take my AC condensate line?

In Plano clay, a pit for condensate tends to stay wet and soft, because the clay can't absorb a steady trickle any faster than it absorbs rain. A short solid line from the drip to a pop-up emitter, a downspout line or a planted bed well away from the slab handles it without a pit.

### Would a bigger dry well work better in clay?

Only a little. A bigger pit stores more water, but the clay still takes it away at the same slow rate through the walls and floor, so it just stays full longer. Every storm adds to what's still in it from the last one.

### What about a dry well with an overflow pipe?

Then the overflow pipe is the real outlet, and it has to reach a legal place just like any drain. In Plano that means the street side of the lot. At that point, sending the water straight there in solid pipe is simpler and leaves nothing standing in the yard.

## Related service

- [Service**Yard sump pumps** An outdoor pump basin that collects yard water on a lot with no downhill path and pushes it through a buried line to the street or another approved outlet.](https://clayplanodrainagecompany.com/sump-pump-drainage/)

## More guides

- [Decision Guide**Where do you drain a French drain in Plano?** The outlet decides the design, so we choose it first. Every option a Plano yard has, what each one needs, and how to pick when the lot is flat.](https://clayplanodrainagecompany.com/guide/where-can-yard-drain-water-go/)
- [Learn**Do French drains work in clay soil?** Plano's clay moves water at a crawl, which changes where a trench goes, how much stone it holds and what keeps it from silting up. What works here, and why some clay drains quit.](https://clayplanodrainagecompany.com/guide/french-drains-in-clay-soil/)
- [Decision Guide**Do you need a French drain or a catch basin?** One works below ground and slowly, the other at the surface and fast. A simple timing test tells you which problem you have, and some yards need both on one line.](https://clayplanodrainagecompany.com/guide/french-drain-vs-catch-basin/)
- [Learn**Why is my yard wet when it hasn't rained?** A soggy patch in a dry week has a water source you can often find in an afternoon. The order to check things in, the meter test for hidden leaks, and when it really is a drainage problem.](https://clayplanodrainagecompany.com/guide/soggy-yard-no-rain/)
- [Learn**Is it a floodplain problem or a yard drainage problem?** A flooded back yard by a creek and a flooded back yard on a flat lot look alike from the patio. Where the water came from decides who can fix it, and what a yard drain can and can't do.](https://clayplanodrainagecompany.com/guide/floodplain-or-drainage-problem/)

## Get an estimate for your yard

Tell us where the water stands and when. We walk the yard and send a written estimate.