Gravity Septic Systems with Limited Soil Depth
These two example systems, Ford and Foxx, are designed for sites with limited soil (very shallow installations). Sites with shallow soil over a hard and impervious sub soil or over a shallow water table require special precautions explained with special notes on the plans. A building site with a typical shallow soil over a restrictive soil or a water table can be considered a “difficult” site.
Most clients and builders prefer a simple gravity type septic system over a pressurized drainfield, or any system design with a pre-treatment component. This is mostly because the cost for the initial construction now includes extra parts and the involvement of an electrician, as well as the expense of the ongoing maintenance. However, the depth and type of soil in the area where the drainfield is to be built will determine what type of system will be allowed by local health. This fact explains the importance of having the soil evaluation performed by a qualified expert.
The 2 or more test pits dug at the time of the soil and site evaluation will be used to determine what heroics, if any, may be required to meet the strict regulations of local health. Inspectors and designers are skilled in determining signs in a test pit that indicate seasonal water tables, even if the hole is dry at the time of the evaluation. Even with limited soil depth, a gravity system may still be permitted. These two examples show how these situations are detailed.