Civil Construction 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 effluent 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 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 Civil Construction drainfields provide 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 in Keaau, Hawaii 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.