Gravity System

Septic Installations

Septic Tank Installation in Statesville, Mooresville and Surrounding Counties

 Conventional Gravity System 


Septic tank installation is one of the many services offered by Lentz Wastewater Management.As the name implies, gravity drain fields work by letting gravity drain the effluent from the septic tank into a series of trenches.  This means that a gravity drain field area must be below the draining level of the septic tank.  If this is not the case then another type of system must be used.  Lentz Wastewater Management has been a certified septic installer since 2000.



1.  Septic Tank

2.  Drainfield

3.  Soil

4.  Repair area


A septic tank is a watertight container and about 9 feet long and 5 feet tall. It is buried in the ground just outside the home. The tank is generally precast from reinforced concrete.  Tanks are also made from plastic and fiberglass.  A tank size is determined by the number of bedrooms in a home.  The most common tank size used in North Carolina in the past several years is 1000-gallon liquid capacity.  Today, the design of the tank includes two chambers each equipped with a manhole cover for tank access. 

Wastewater from the home flows into the septic tank., including shower, bathtub, and washing machine.  As the wastewater flows into the tank, the heavy solid materials settle to the bottom of the tank (forming a sludge layer), and the lighter greases, fats and oils float to the top (forming a scum layer). The septic tank’s primary purpose is to retain the solids.  A properly working septic tank is full of wastewater. For every gallon of water that enters the tank from the home, a gallon of water is pushed out of the tank through the outlet baffle and enters the drainfield. Solids remain in the septic tank and gradually build up over time. If not removed by regular pumping, solids can overflow out of the tank and into the drainfield where they clog the soil and cause the septic system to fail. The outlet baffle (or a sanitary tee at the outlet end) prevents sludge and scum from flowing out with the liquids and entering the drainfield.  Septic systems installed since 1999,include an effluent filter in the septic tank. These are installed in place of the sanitary tee at the outlet end of the septic tank.


 The drainfield delivers the liquid sewage(effluent) to the soil.  The real treatment of the wastewater happens in the soil underneath the drainfield. Liquid sewage (effluent) flows out of the tank as a cloudy liquid that still contains many disease-causing germs and pollutants. In a conventional gravity system, the drainfield is made up of a network of perforated pipes laid in gravel filled trenches (2-3 feet wide) or beds (up to 10 feet wide) in the soil. Wastewater trickles out of the pipes, through the gravel layer, and into the soil for final treatment. The size and type of drainfield depends on the estimated daily wastewater flow from the home and soil conditions. Every new drainfield is required to have a designated replacement area. It must be maintained as a reserve in case the existing drainfield ever needs to be replaced.   


  • Gravel System- A gravelled system uses gravel/crushed stone in the drainfield trenches to create void space to store the effluent and release it slowly.  This type of conventional septic system functions using drainage. During construction, a ditch 1 to 3 feet below ground level is constructed. The length is determined by the anticipated flow of effulent(wastewater) into the system from the home or business, as well as the soil’s ability to absorb water.  Gravel is placed in the bottom of the ditch. A perforated pipe (pipe with holes)  is placed in the ditch.  Gravel is poured over and around a perforated plastic pipe.  The pipe is then topped with a covering to keep the soil from sifting through the gravel. Finally, a layer of soil is placed on top. The waste from the septic tank is then slowly diffused into the soil away from the home or business over time.  While some treatment of waste occurs in the septic tanks as bacteria within the tank operate on the waste, most of the treatment occurs as wastewater  from the tank enters the drainfield and is filtered through the gravel and the soil below. Over time, bacteria and other organisms, in the soil, consume material in the wastewater. These organisms multiply and form a layer called a biomat that sits on the soil layer. When sufficient oxygen is available, worms and other parasites feed on the bacteria as well as the material in the wastewater. When the drainfield is in balance, these organisms keep the biomat from becoming so thick that it won’t allow passage of wastewater to the soil below.


The soil below the drainfield provides treatment and disposal of the wastewater. After water passes into the soil, most of it percolates through the soil, eventually entering the groundwater. Local groundwater is the source of drinking water for the majority of people in rural areas, such as ours. A small amount of wastewater is taken up by plants through their roots, or it may evaporate from the soil. Most of the wastewater filters through the soil in small open spaces, called soil pores. Chemical and biological processes in the soil treat the wastewater before it reaches groundwater, or a restrictive layer, such as hardpan or bedrock. These processes work best where the soil is somewhat dry, absorbent, with plenty of oxygen for at least 3 feet below the drainfield.