Glossary

Absorption Field: The area where treated wastewater from the septic tank is released into the soil for final filtration. Also called a drainfield or leach field. In Georgia this is the most expensive component to replace.

ATU (Aerobic Treatment Unit): A system that actively introduces air so aerobic bacteria treat the wastewater, producing cleaner effluent than a conventional tank. Common on Georgia's Piedmont clay, where slow-draining soil often can't support a conventional system.

Baffle: A barrier inside a septic tank that controls flow between compartments and keeps solids from escaping toward the drainfield. A failed baffle is a common cause of what looks like drainfield failure.

Cecil Series: The red clay soil that defines Georgia's Piedmont region, including metro Atlanta. It drains at roughly 60 to 120 minutes per inch — well below what a conventional gravity system needs, which is why engineered alternatives are so common around Atlanta.

Certified Soil Classifier: A professional licensed by the state to evaluate soil for septic suitability. Georgia requires a Level 3 soil report from one of these before a new-construction septic permit can be issued.

Chapter 511-3-1: The Georgia Department of Public Health rules governing on-site sewage management systems. It sets the statewide framework, though individual county boards of health may impose stricter local requirements.

County Board of Health: The local authority that actually issues septic permits, conducts inspections, and enforces compliance in Georgia. DPH writes the rules; your county board of health applies them. Georgia has 159 counties across 18 health districts.

Effluent: The liquid that leaves the septic tank and flows to the drainfield after solids have settled out. Effluent quality determines how much treatment the soil still has to do.

Effluent Filter: A removable filter at the tank outlet that catches solids before they reach the drainfield. Required on all Georgia residential tanks installed after February 20, 2000, and it should be cleaned at every pump-out.

Level 3 Soil Report: A comprehensive soil evaluation required before a new-construction septic permit in Georgia. It replaced the older percolation test. In the GNR Health District covering Gwinnett, Newton and Rockdale, it has been required for all permits including repairs since February 2022.

LPP (Low-Pressure Pipe): A distribution method that pumps effluent through small-diameter pipes to spread it evenly across the drainfield. Used on sloped sites and where soil conditions require more uniform dosing.

Mound System: An engineered system built above natural grade, creating a treatment zone where natural soil depth or a high water table won't allow a conventional in-ground drainfield.

NSF/ANSI Standard 40: The national performance standard aerobic treatment units are tested against. Class I effluent under this standard means CBOD5 of 25 mg/L and TSS of 30 mg/L — the quality level that lets Georgia permit a reduced vertical separation.

On-Site Sewage Management System: The formal regulatory term in Georgia for what most homeowners call a septic system — any wastewater treatment serving a single property rather than connecting to a municipal sewer.

Percolation Rate: How quickly water moves through soil, measured in minutes per inch. It is the single biggest factor in what type of system a property can support, and what that system will cost.

Performance Evaluation Report (Form 14.L): The county-issued document confirming a septic system's condition, commonly required by lenders during a Georgia property sale. It is the format title companies and all lender types accept.

Replacement Area: Space set aside on a lot for a completely new drainfield if the original fails. Georgia requires a 100 percent replacement area, which is why lot size matters so much on tight Piedmont properties.

Riser: An extension that brings a buried tank access lid up to ground level. Costs $200 to $400 and typically pays for itself within two pump-outs by eliminating the charge to dig out buried lids — especially worthwhile in Georgia's packed red clay.

Setback: The minimum required distance between a septic component and a well, property line, water body, or structure. In Georgia: 50 feet tank-to-well, 100 feet field-to-well, 10 feet tank-to-building, 25 feet field-to-water.

Sludge and Scum: The solids that settle to the bottom (sludge) or float to the top (scum) inside a septic tank. When these layers get thick enough to reach the outlet, solids escape to the drainfield — which is what pumping on schedule prevents.

Two-Compartment Tank: A septic tank divided into two chambers, which improves solids separation. Required with an effluent filter on all Georgia residential installations after February 20, 2000. A single-compartment tank usually indicates a pre-2000 system.

Vertical Separation: The distance between the bottom of the drainfield and groundwater, rock, or an impervious layer. Georgia requires 24 inches for conventional systems, reduced to 12 inches where ATU-quality effluent is used — a key reason ATUs can be permitted on tighter sites.