Which soil type is generally considered UNSUITABLE?

• A. Loamy soil
• B. Sandy soil
• C. Clayey silt
• D. Organic soils

Answer: (D)

The key idea is understanding what makes a soil suitable for a septic drain field: it needs reliable drainage, adequate strength to support the system, and the ability to filter and treat effluent as it moves downward. Organic soils, such as peat or muck, are generally unsuitable because their high organic matter content and unstable structure lead to poor and unpredictable performance. They tend to be poorly drained, can have fluctuating water tables, and are often low in bearing strength, which means they won’t reliably support a drain field or allow consistent infiltration and treatment of effluent.

Loamy soils have a balanced mixture of sand, silt, and clay, giving good structure and moderate permeability that support both drainage and filtration. Sandy soils drain quickly and aerate well, which can be suitable when design and percolation rates are appropriate, though very sandy areas may require special considerations. Clayey silt provides slower, more controllable drainage with decent filtration and stability, which can also work well within proper design limits. Because of these properties, organic soils are the minority that are generally deemed unsuitable for standard septic systems.