We’re Digging Deep—Literally! Soil Testing for a Septic System in the rural raw land
Hey everyone! Today, we’re getting down to business—literally. We’re digging into the ground! We’re doing a soil test on a client site to figure out what kind of septic system we can use for the house. This place is way out in rural farmland, so there’s no connection to city sewage.
So… where does the poop go when we’re living out here? Great question! That’s what we’re figuring out. Since we don’t have access to a public sewer, we’ll need an on-site septic system—which means we’ll be treating our own wastewater right here on the property, and making sure it’s safe before it returns to the ground.
Let’s dive in and see what we discover!
A soil test helps us understand what kind of septic system the land can support. It’s basically a medical checkup for the earth—evaluating whether the soil can safely filter and absorb wastewater.
There are a few key things a soil test evaluates:
If the soil drains too fast, untreated wastewater could reach groundwater. If it drains too slowly, it can back up—gross. We need that Goldilocks zone of drainage: not too fast, not too slow.
On site with us are Cammy and Bryant from Good Neighbor Soil Evaluators. Cammy is a PhD soil scientist—so we’re in excellent hands.
They start with a walkaround, using a soil probe to take shallow samples across the site. These give a quick read on the topsoil texture and help them decide the best location to dig deeper.
They’re especially focused on clay content. The percentage of clay in the soil is the #1 deciding factor for whether we can install a conventional septic system or if we’ll need to explore other options.
Cammy and Bryant map out a potential location for the system. The ideal spot is:
Once the spot is picked, Bryant gets to work digging the test pit. He pulls out samples every 12 inches, documenting the changes in soil texture and color as he goes.
💸 Cost note: A professional soil test in Missouri costs around $500 per hole. Usually one is enough unless you have multiple candidate locations.
He’s digging 52 inches down to get well below the frost line, which in Missouri sits around 36 inches. That depth is necessary to avoid freezing issues for septic components—because nobody wants to deal with frozen pipes or a backyard “poopsicle.”
Why is Bryant digging a 52-inch deep hole? It’s all about protecting the septic system from freezing. In Missouri, the frost line sits around 36 inches deep. A conventional septic tank is typically buried right at that 36-inch mark, and the drain lines sit slightly shallower, in trenches about 30 inches deep. So, by digging down to 52 inches, we’re making sure there’s plenty of buffer—keeping everything safely below the frost line and preventing any winter freeze-ups. No frozen pipes, no backyard disasters.
While Bryant digs, Cammy is focused on analyzing the soil quality. She starts by wetting each soil sample and squeezing it in her hand to form a ribbon or string. The longer the ribbon before it breaks, the higher the clay content. It’s a hands-on method that soil scientists use in the field to estimate clay percentage quickly.
But that’s not all—Cammy also uses a Munsell soil color chart to match the soil’s color. By comparing the soil samples to this chart, she can identify things like the level of organic matter, oxidation, or even signs of drainage issues. Darker colors often mean more organic material, while gray or mottled tones can suggest poor drainage. She’s building a full soil profile layer by layer—kind of like reading the Earth’s diary.
Meanwhile, my dog Snowy is taste-testing the soil. Very committed to her work. Yummy, yummy.
Here’s a quick breakdown of what soil scientists care about:
Soil is made of three particle types:
Most soils are a mix, but the ratio determines drainage.
Dead plant and animal material that helps retain nutrients and water. This usually makes the soil look darker—black or rich brown.
This is how fast water drains through the soil. It’s not just about texture—compaction, layering, and moisture levels matter too. Some areas may require separate perc tests (percolation tests), which involve filling holes with water and timing how long it takes to drain.
Okay, let’s check our “soil muffins.”
To qualify for a conventional septic system, Missouri requires the clay content to be less than 34%.
Here’s what we found:
Oh no—our hopes are sinking just like our high-clay soil. Above 34% clay means we’re not eligible for a conventional system.
That leaves us with two options:
High clay content is super common in Missouri, so this isn’t a huge surprise. We’ll go over our next steps—and these alternative systems—in the next blog (and video!).
Thanks for digging in with us—see you soon!
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