Glossary of Terms

Definitions of Common Terminology

In many cases terms and definitions are often mistakenly or broadly used out of context. 

Below are common terms used in the septic and soils industry. For a full list of defined terms refer to the Soils Handbook of Tennessee.


  • Department: Tennessee Department of Environment and Conservation.

  • Drain (As Used On Soil Maps): (TDEC)

    • A "one-dot" drain starts and ends where the actual accumulation or collection of water is concentrated in an area (channel) that can be easily identified This type of drain usually has a maximum depth of  1 foot (12 inches). These drains may or may not have the potential to flood. The standard setback is 25 feet unless the soil consultant recommends a larger or smaller distance. Fifteen is the minimum setback to be recommended by a soil consultant.

    • A "two-dot" drain starts and ends where the actual accumulation or collection of water is concentrated in an area (channel) that is usually more than 1 foot (12 inches) deep. This drain is more visible and defined than a one dot drain. These drains may or may not have the potential to flood the surrounding area. The standard setback is 25 feet unless the soil consultant recommends a larger or smaller distance. Fifteen feet is the minimum setback to be recommended by a soil consultant. 

    • A "double-line" drain is usually big enough to be referred to as a creek, stream or river. These drains may flood the surrounding area and some may flood often. The minimum setback is 25 feet along drains of this size. The width of these drains may vary, but most are a minimum of 10 feet wide. 

  • Percolation Test: A method of determining the usability of an area for SSDS disposal by testing for the rate at which the undisturbed soil in a series of test holes of standard size will absorb water per unit of surface area. 

  • Soil Absorption Rate: The rate in minutes per inch (MPI), that clean water is absorbed by or drains through a soil during least favorable climatic conditions when soil are at or near field capacity. Estimated absorption rates are established in Appendix I of the Regulations to Govern Subsurface Sewage Systems for soil series and phases of soil series that have been recognized in Tennessee. For soil series that have been recognized but not listed in Appendix I, the Department shall establish the adsorption rate. Estimated soil adsorption rate for variants of soil series and miscellaneous land types may be proposed by an approved soil consultant; however, those rates will be evaluated by the Department. 

  • Soil Map : A record on a map showing soil series, drains, and other pertinent information for the use of SSDS systems. 

  • Soil Map Notes: A format used that organizes information on a soil map in a fashion that makes the necessary information easy to find and use. (TDEC)

  • Soil Observation: Each individual auger boring or put utilized, typically at the grid stakes or grid box center, by the Soil Scientist to see and identify soil characteristics at one location. (TDEC)

  • SSDS: Subsurface Sewage Disposal System; in the Soils Handbook of Tennessee this term includes all septic systems. (TDEC)