The Essential Plumbing Resource For Homeowners

Why Do You Need A Perc Test And What Happens If You Fail?

If you're installing a new septic system, you'll typically need to perform a percolation (perc) test on your property. This test evaluates the condition of your soil for a critical part of your septic system: the leach field. The leach field is the final stage in your waste disposal pathway, and the drain tiles in the field allow effluent to disperse into the surrounding soil.

Perc tests are nearly always required before you can begin installing your new leach field. This process can sometimes be nerve-wracking if you're installing on a new property since it can influence your septic design or even prevent you from installing a septic system. Understanding how these tests work, their purpose, and what you can do if you fail is an essential part of preparing for your leach field installation.

How Do Perc Tests Work?

While they might sound a bit complicated, percolation tests are surprisingly simple, although the details can vary between code jurisdictions. In general, a soil engineer will need to dig one or more holes on your property. These holes can be deep, so they usually require excavation equipment. The hole depth may depend on local soil conditions and substrate qualities.

Once the hole is in place, the soil engineer or inspector will fill the hole with water and measure the drainage rate. Inspectors are looking for water to drain away at an acceptable rate, proving that the soil can effectively drain effluent from a septic system without causing a backup. If the ground doesn't meet minimum code requirements, it may prevent you from installing a septic system.

What If You Fail Your Perc Test?

If you pass your site perc test, you can continue with your leach field installation as usual. However, a failure can be a substantial setback. In these cases, you may need to consider alternative locations on the property to install your field. Each site will require its own perc test, so you should be prepared to make adjustments and dig more holes for the inspector.

In the unlikely event that you cannot find a suitable site, you will need to consider alternative options before beginning your leach field installation. Alternative options, such as sand filters and aerobic treatment systems, may be viable if your property lacks the correct soil conditions. You will still need a suitable site for the leach field, but these pre-treatments can reduce your soil requirements.

While perc tests can be frustrating, they're essential to correctly siting your septic system components. Choosing an area with viable soil not only allows you to meet local code requirements, but also ensures your septic system will function reliably and hygienically for many years into the future.