By PHIL LEBLANC, guest columnist

To better understand Brown County soils, you must look at the topography or the lay of the land.

Basically, we see long, narrow ridges, steep slopes and narrow stream bottoms. This is because only a small part (northeast corner) of Brown County was covered by the last glacier, which was about 12,000 years ago. That glacier left most of Indiana nearly flat.

The landscape that we see today in Brown County has been sculpted over the last 100,000 years or more. The tops of the hills are over bedrock 300 to 350 million years old. Water has eroded down through the siltstone, sandstone and shale bedrock to form our valleys.

Three major ridge systems extend across Brown County in a northeast-southwest direction. Three major streams with valleys about a quarter- to half-mile wide flow parallel to these ridges, in the southwest direction. These are Bean Blossom Creek, in the northern part of the county, the North Fork of Salt Creek in the central part of the county and the middle Fork of Salt Creek in the southern part.

Most of our soils have been formed or developed in place (over bedrock) for a long period of time. Much of our soil has been developed in a mantle of windblown sand, silt and clay-sized material deposited on top of and mixed with the weathered bedrock. Generally speaking, our deepest soils (over the bedrock) are located on the level to gently sloping ridge tops and become more shallow to bedrock on the eroded, steeper side slopes of the ridges. Valley soils are more complex because most of the soil material has been washed there from the valley slopes or deposited by the valley streams. High water tables are common and many of the valley soils are in floodplains.

Our soil is a living entity. It is still developing, changing and growing today. If we look closely at soil, you’ll find all kinds of living creatures, like earthworms, ants, other bugs, animals (like moles), tree and grass roots, and other organisms you can’t see like bacteria. All of these contribute to the mixing, breaking down soil particles into smaller sizes and building the soil. Even frost contributes to a soil’s development. As the moisture in the soil freezes, it expands and breaks rocks and soil particles apart. The smaller particles migrate down further into the soil and create layers. This is why soils typically have a higher percentage of larger particles (like sand) in their “lighter” upper portion and have “heavier” (more silt and clay-sized particles) in their lower portions. It is easier for water (moisture) to travel into and through a “lighter” soil than a “heavier” soil.

Our most common soil texture (mixtures of sand, silt and clay) in the county and on the ridge tops and side slopes is called “silt loam.” A “silt loam” soil type can have varying combinations of sand, silt and clay and still be called a “silt loam” soil. A soil can also have other characteristics depending on how it developed. All of these factors are considered by the soil scientist when he maps, classifies and names the soil. It is the soil and its characteristics that determine its suitability for use in a septic system.

What do soils have to do with a septic system?

The wastewater from the septic tank drains out of the tank into a drain field. A drain field is a series of finger-like lines with holes along its length that are buried in the soil that lets the wastewater enter into the soil. When the wastewater enters the soil, the soil has to have the “ability” to allow the wastewater to enter the soil as fast or faster than the wastewater is coming out of the septic tank and into the drain field. If not, the wastewater would flood the drain field and back up into the tank. A soil test is required before a septic system drain field site is approved to determine the soil’s ability to accept wastewater.

Once the wastewater has entered into the soil, a “factory like” process takes over. Organisms of all types break down the wastewater so that it can become a usable part of nature and the environment. The odor is taken away and the waste materials are digested by the soil bacteria so plants and organisms can utilize the nutrients and water to grow.

A drain field can have a long and successful life (usually about 25 years) — if it is taken care of. There must to be a delicate balance of moisture, air and bacteria in the soil for the system to work. If any of these are out of balance, the system slows down or can even stop.

When the soil system slows down or stops breaking down the waste, the soil can become clogged, and if the “out of balance” is allowed to continue, the septic system fails. The soil can no longer accept the wastewater, the drain field starts to flood, odor starts to occur and the wastewater backs up into the tank. You then have a septic system failure.

Some things that you can do to ensure your septic system’s long life are:

Make sure that you are using the system as it was designed — in other words, a two-bedroom home for a two-bedroom-designed septic system.

Don’t put materials down your drain like grease or oil, powered detergents, paints, pesticides, etc. Your septic tank and drain field work because of bacteria and they must be kept healthy.

Have the solids that accumulate in your septic tank pumped on a regular basis, usually every three to five years.

Keep vehicles off the drain field and don’t allow trees to grow on your drain field because their roots will grow into the drain field and clog the drains. Only allow grass to grow on the drain field.

For further reading, you can go online (nrcs.usda.gov) to view the Indiana Soil Survey of Brown County, or you can stop by the local soil and water conservation district office on Memorial Drive in Nashville to view a printed copy of our county soil survey. You can also read Purdue Extension Bulletin No. HENV-107W, “Operating and Maintaining an OnSite Sewage System,” for more information.

Phil LeBlanc of Brown County grew up in Ripley County and graduated from Purdue University with bachelor’s and master’s degrees in agronomy (soils option). Now retired, he has worked 40-plus years in soils-related jobs. He is a volunteer on the Brown County Regional Sewer District Board. He can be reached at [email protected].