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Role of Sodium in Hardpan Soil


Clay soil turns to a hardpan when introduced to excessive amounts of sodium. In one year a 4 person household will discharge the equivalent of 56 pounds of salt, which is made of sodium chloride.

Household cleaning and laundry products also contain sodium which makes its way to the drain field.

Discharge of water softener backwash into septic drain fields can also contribute to the problem.

Over time all of this combined will affect the soil's ability to absorb water.

Hardpan Soil

Hardpan is a distinct layer, usually found 4 to 48 inches below the surface, it reduces or halts drainage, and impairs root penetration.

Clay particles are smaller than 0.002 mm and are shaped like flakes or plates. This means that when these minute particles come in contact with sodium in wastewater, they stick together and create an impenetrable hardpan layer.

Comparison of Gravel, Coarse Sand, Silt, and Clay Particles

How Much Clay Is In Your Leach Field Soil?

A soil's texture is determined by the size of particles it contains. Sand, silt, and clay are derived from rock that has been broken down over thousands of years by climatic and environmental conditions.

The larger, mineral particles are Gravel. Leach beds are often filled with gravel, which provides good drainage.

Other materials in leach field soil are:


  1. Sand can range from very fine .05 - .10 mm, to very coarse 1.0 - 2.0 mm.

  2. Silt particles are 0.002 to 0.05 mm and, when dry, feel similar to flour.

  3. Clay particles are extremely fine — smaller than 0.002 mm. They feel sticky in your fingers when wet and clump together, you can't see an individual particle of clay with the naked eye, it takes a microscope.

The proportion of these three mineral particle sizes determines the soil texture.

Clay soil absorbs water slowly. The tiny clay particles interlock tightly, with minute air spaces, water can only penetrate as quickly as it can fill those spaces. Compaction of the surface by foot traffic, rainfall, overhead sprinkling or vehicle traffic smashes these particles closer together making a hardpan substance that water cannot penetrate.


The presence of a large proportion of clay in the composition of your leach field soil can lead to soil drainage problems, especially as a system ages.

What Kind of Soil Do You Have?

Clay Soil

Here’s a simple test you can do at home.

  1. Fill a glass jar with straight sides about two-thirds full of water

  2. Add enough soil from your yard, outside of your drain field, to almost fill the jar (dig down a little)

  3. Add a pinch of laundry detergent to help the soil components separate

  4. Tighten the cover on the jar and shake vigorously

  5. Set the jar in a place where it will be undisturbed for up to five days


As the particles making up the soil settle into layers, the larger sand particles will settle to the bottom, the next layer will be silt and the top layer will be clay.

The clay may stay suspended and cloud the water for several days, which is why the sample needs to sit undisturbed. Organic matter will float on or just below the water surface.

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