We’re digging a lot of new drainage in preparation for our house extension, including some new dry wells in the lawn. But will they work in our clay soil?

Dry wells are good for draining stormwater, but they work better in dry and grainy soils than in clay. To check your clay soil will drain, dig a 4-foot deep hole and do a percolation test with 5 gallons of water. If it drains slowly or not at all, then your clay soil isn’t suitable for a dry well.

Let’s dive down into the subject of dry wells in clay soil in more detail, discover how well they work in such conditions – and also answer your other pressing questions on digging and using dry wells in the yard…

Will My Dry Well Work in Clay?

Dry wells work by collecting unwanted water (such as excess rainfall) and then percolating it into the earth. The more porous the well, the more effective it will be at draining away the water. Because clay is such a dense type of soil, it really isn’t the best at percolating water.

If your yard has clay soil but you think you could use a dry well, don’t give up on the idea immediately. You could dig a hole and carry out a “perc test”, which will tell you if the soil is capable of draining away the water.

Using something like a soil auger, dig a test hole of about four feet deep. If this immediately fills with water then your water table is too high for a dry well to manage.  

Stage 2 (provided it hasn’t immediately filled with water) is to pour about 5 gallons of water into the test hole. Note the time it takes to drain away. If it drains slowly or even not at all, then your clay soil really isn’t up to the job.

Does Water Drain Well Through Clay?

You know why potters use clay to make their wares? Precisely. Clay is well-known for not being porous. Good if you need a new coffee mug, not so good if your yard has drainage problems.

Dry wells can be a great way of managing stormwater drainage, but they do work better in dry and grainy soils than in dense clay. However, if your well is deep enough, it may punch past the clay layer and into a more porous soil. Perhaps.

How Effective Are Dry Wells Generally?

Dry wells, in the right type of soil, can be really effective. They prevent rainwater runoff from entering streams and rivers, preventing contamination or flooding. In larger-scale use, they can return water to aquifers, which plays a part in drought prevention. So yes, they can be extremely effective.

In a domestic yard, they’re used to get rid of unwanted water, preventing your garden from becoming saturated. As they can cost around $3,000 to install (and this is one of those jobs that really should be left to the professionals), they may not always be the householder’s first solution for drainage issues.   

How Long Do Dry Wells Last?

A properly built and well-maintained (sorry…) dry well can last up to 30 years. We’ll look at maintenance in a moment; however, as a minimum, inspect it once a quarter and check it after heavy rainfall or a storm. 

Why Do Dry Wells Fail?

Dry wells fail if they become blocked. This can be prevented by checking them for leaves and sediment build-up. If the well fills with dead leaves or dirt, the water won’t be able to soak through its walls as effectively.

Because it’s harder to clean the well itself than the area around it, the best way to prevent clogging is to keep leaves out of the excess water. Cleaning your gutters and sweeping the yard regularly will prevent leaves from being gathered up by the water. 

A dry well can also collapse (although this is a rare occurrence). If the well starts to show signs of collapsing and it’s getting towards the end of its life, it can be simpler to fill it in and start again with a new one.

Are Dry Wells Legal?

Like many construction items, the law around dry wells varies from state to state. We’d always recommend checking with your local authority before getting someone in to dig a deep hole in your yard!

The reason why some districts don’t like dry wells is because of the risk of contamination. Yes, draining stormwater into the earth to join the groundwater is a good thing in many ways. However, if that runoff water has picked up any contaminants along the way, these will be introduced deep into the groundwater, and end up spread over a wide area.

Because so many areas need a permit before you sink a well, please check it out before you begin.

Are Dry Wells Expensive?

As we mentioned earlier, always get the professionals in to dig a deep hole in your property! Because of this, it’s not a cheap project. A dry well could cost you anything between about $1,600 and getting on for $5,000, with a typical job costing around $3,000.

You can save money on materials, as a traditional well made from loose stone will be cheaper than one made from concrete, or a ready-made plastic basin.

How Much Water Can a Dry Well Hold?

Of course, this depends on the size of your well, as a deeper well can hold more water. In general, contractors aim to build wells that hold around 50 gallons of water.

Remember, however, that the dry well is there to suit your own yard’s needs. If you don’t get much rainfall, you don’t need a very deep well.

Can a Dry Well Cause a Sinkhole?

Yes, a poorly built or maintained dry well can cause a sinkhole, which is why we keep going on about hiring an expert to build yours. The well needs to have a good strong barrier and be packed well, otherwise, it could lead to the earth around it sinking.

What is a Gray Water Dry Well?

This is a great way to reuse wastewater. Gray water is the relatively clean waste from your laundry, dishwasher, shower, and tub. By diverting this into the dry well, the water goes back into the earth, creating a virtuous circle.

However, this is a contentious issue, as it could still be seen as introducing new chemicals into the earth. You’d need to find out what the rules are for your state or district, and if they support gray water drainage, you’d need to check the ingredients of your household products.

Where Should a Dry Well Be Placed?

Dig the well at least 10 feet away from your home, so it’s not soaking into the foundations. It needs to be in a place where the water tends to pool in order to be at its most effective. 

Close to the downspout is good (remembering the distance from your home). Work with any slopes in the garden, so gravity helps the water head towards the well.

Watch out for any utility lines. If you’re not sure what’s deep underground in your yard (and that’s fair enough!), contact your local planning unit. You may need a permit, anyway, and this would form part of the checks.

How Big a Dry Well Do I Need?

As we mentioned earlier, this really depends on the amount of excess water you need to get rid of, and also, whether you’re getting rid of your household gray water. Ideally, it will take away all the water from a full-on rainstorm without overflowing. The better draining the soil, the quicker the water will drain.

The French Drain Man takes you through everything you need to take into account when sizing a dry well.

What Does a Dry Well Look Like?

A dry well is basically a deep hole that’s either filled with a porous material like gravel, or left empty. Its sides are made from a permeable material that allows the water to drain away.

Here’s another great short film that shows you exactly what a typical dry well looks like.

What’s The Difference Between a Dry Well & a French Drain?

A French drain is different from a dry well. At its simplest, a French drain is a ditch filled with gravel and with pipes inside it. These carry water away from your house and collect it in a single point. 

The dry well also collects water; however, it soaks it back into the earth rather than leading it to a single endpoint.

How Fast Should a Dry Well Drain?

There’s no hard and fast rule about how quickly water should drain away from a dry well. When you’re carrying out the perc test, you’ll need to keep an eye on how fast the water is soaking away, and use your judgment as to whether it’s quick enough.

In general, if it drops an inch in three minutes, you’re onto a winner. If there’s still water in the hole the next day, you probably don’t have the right type of soil, and adding good dariange and materials won’t really help you.

Does a Dry Well Need To Be Pumped?

If your well stops draining and starts overflowing, you may need to have it pumped. This is to prevent it from backing up and flooding further, and to get to the root of the problem.

Dry wells are one of those things that are great when they’re working, and a complete pain when they’re not, as they’re notoriously hard to fix.

How Do You Maintain a Dry Well?

As we mentioned earlier, keep checking your dry well. Schedule visual inspections every three months or so, and always check it out after heavy rainfall. You could also book in an engineer to check it out from time to time.

The biggest problem is the well becoming blocked, so think about how you can prevent leaves and other debris from becoming washed into the well. Think about how the cover works, and try to prevent your yard from being clogged up with leaves, as they are the biggest culprits.

Final Words

Good news! It turns out our clay soil is not so dense that water won’t drain through it – so after our successful perc test we can go ahead and dig a couple of dry wells in the backyard.

Our lawn has always been left saturated by pools of water after a storm, so it will be great to get some proper drainage in there.

It’s not cheap to get them fitted but it’s a great long-term investment in the value of our property. 🙂