What is septic systemin construction?

Sizing comes from two inputs: the design wastewater flow (driven by building use and fixture counts, or bedrooms on residential work) and the percolation test, which measures how fast the soil absorbs water. The health authority or design engineer converts those into a required tank capacity in gallons and a drainfield area or lateral footage. Estimators should treat drainfield quantities as design dependent and avoid pricing them firm before the perc results and approved design exist.

On most projects the site utility or excavation contractor installs the tank, drainfield, and yard piping, often under a state or county installer license, while the plumber runs the building sewer to a point just outside the foundation. The exact handoff varies by contract, so the scope sheet should name the transition point, who sets the tank, and who supplies drainfield stone and fabric.

The tank is a buried watertight vessel where solids settle and begin to break down; it is counted as one each with a gallon capacity. The drainfield is the network of perforated laterals or a stone bed downstream of the tank where the liquid effluent soaks into the soil, measured in linear feet or square feet. The tank is a fairly fixed cost; the drainfield is the quantity that swings with soil conditions.