Septic System Glossary

Aeration / Aerobic Treatment Unit (ATU)

The process of introducing oxygen into a septic tank to support aerobic bacteria. An ATU is an advanced system with an aerator (pump) that does this, treating wastewater to a much higher degree than a conventional system.

Aerobic Bacteria

Microorganisms that require oxygen to live and break down waste. They are highly efficient and are the primary agents of treatment in a drainfield or an ATU.

Anaerobic Bacteria

Microorganisms that live and break down waste in an oxygen-free environment. This is the primary type of bacteria in a conventional septic tank. They work much more slowly than aerobic bacteria.

Baffle / Sanitary Tee

A T-shaped pipe fitting on the inlet and outlet pipes of a septic tank. The inlet baffle directs wastewater downward, and the crucial outlet baffle prevents sludge and scum from escaping into the drainfield.

Biochemical Oxygen Demand (BOD)

A technical measure of the amount of oxygen required by bacteria to break down organic waste in water. A lower BOD indicates cleaner, less polluted water.

Biomat

A slimy layer of anaerobic bacteria and organic matter that forms in the soil of the drainfield. A thin biomat is normal and helps filter pathogens, but an overly thick biomat will clog the soil and cause system failure. Read More →

Blackwater

Wastewater from toilets that contains human waste. It must be treated by a septic system or sewer.

Distribution Box (D-Box)

A concrete or plastic box that receives effluent from the septic tank and uses multiple outlets to distribute it evenly among the various trenches of the drainfield.

Dosage Tank / Pump Tank

A second tank after the septic tank that collects effluent. When it fills to a certain level, a pump is activated to send a specific "dose" of effluent to the drainfield, ensuring even distribution. Often required for mound systems or large drainfields.

Drainfield (Leach Field, Absorption Field, Soil Absorption System)

A network of perforated pipes laid in underground trenches where effluent from the septic tank is slowly released and filtered by the soil. This is where the final stage of wastewater treatment occurs. Read More →

Effluent

The partially treated liquid wastewater that flows out of the septic tank and into the drainfield.

Effluent Filter

A removable filter on the outlet baffle of a septic tank that traps larger suspended solids, providing an extra layer of protection for the drainfield.

Fats, Oils, and Grease (FOG)

A major component of household wastewater that should never be poured down the drain. FOG cools and solidifies in pipes and is a primary contributor to the scum layer in the septic tank.

Graywater

Wastewater from sinks, showers, and laundry that does not contain human waste. Some regulations allow graywater to be used for irrigation with a separate system.

Groundwater

The water found underground in the cracks and spaces in soil, sand, and rock. A properly functioning septic system treats wastewater before it safely returns to the groundwater.

Influent

The raw, untreated wastewater that flows from the house *into* the septic tank.

Inspection Port

A vertical pipe, usually 4-6 inches in diameter, that provides access to the septic tank or drainfield for observation and monitoring without needing to dig.

Pathogens

Disease-causing microorganisms, such as harmful bacteria (like E. coli) and viruses, that are present in raw sewage. The primary goal of a septic system is to remove these pathogens.

Percolation Test (Perc Test)

A test performed to measure the rate at which water is absorbed by the soil. It is a critical step in determining if a property's soil is suitable for a drainfield.

Pumping

The process of using a vacuum truck to remove the accumulated sludge and scum layers from inside the septic tank. This is the most critical form of septic system maintenance. Read More →

Risers

Large-diameter concrete or plastic pipes that extend from the septic tank lid(s) to the ground surface. They provide easy access for inspection and pumping without needing to excavate.

Scum Layer

The top layer inside a septic tank, composed of lighter materials that float, such as fats, oils, and grease.

Septic Additive

A commercial product (chemical or biological) that is added to a septic system with the claim of improving its function. Most are deemed unnecessary or harmful by the EPA. Read More →

Septic Alarm

A system with a pump tank will have an alarm (a light and/or buzzer) to warn the homeowner if the water level in the pump tank is too high, indicating a pump failure or blockage. Read More →

Septic Pump

An electric pump located in a pump tank that moves effluent uphill or to a distant drainfield.

Septic Safe

A term used on products (like toilet paper or cleaners) to indicate they are designed not to harm a septic system. "Septic safe" toilet paper dissolves easily, while cleaners are biodegradable and non-corrosive.

Septic System

An onsite wastewater treatment system consisting of a septic tank and a drainfield.

Septic Tank

The primary treatment tank where solids separate from liquids and are broken down by anaerobic bacteria.

Setback

The legally required minimum distance between a septic system component (like the tank or drainfield) and other features like wells, buildings, property lines, or bodies of water.

Sludge Layer

The bottom layer inside a septic tank, composed of heavier solids that settle out of the wastewater.

Soil Type

The composition of the soil (e.g., sand, loam, clay) which determines its ability to absorb and treat effluent. Sandy and loamy soils are ideal for drainfields, while heavy clay soils have poor permeability and may require an alternative system design.

Surface Discharge

The release of treated effluent directly onto the ground surface or into a waterway. This is only permissible with highly advanced treatment systems (like some ATUs) and requires a specific permit.

Tank Lid

The heavy concrete or plastic cover on top of the septic tank that provides access for pumping and inspection.

Total Suspended Solids (TSS)

A measure of the solid particles remaining in wastewater after primary treatment. Lower TSS is a key indicator of effective treatment.

Vent Pipe

A pipe, usually extending through the roof of the house, that allows gases from the plumbing and septic system to safely escape, preventing odors from entering the home.

Wastewater

All water that has been used in a home, including water from toilets, sinks, showers, and laundry, which requires treatment.

Water Table

The level below which the ground is saturated with water. A high water table can interfere with drainfield function and is a major consideration in system design.

Cesspool / Seepage Pit

An older, outdated type of system consisting of a single pit with perforated walls that acts as both a holding tank and a drainfield. They provide very little treatment and are no longer permitted for new construction in most areas.

Chamber System

A type of drainfield that uses large, open-bottomed plastic chambers instead of traditional gravel-filled trenches to create a void for effluent distribution.

Conventional System / Gravel Trench System

The most common type of septic system, consisting of a septic tank followed by a drainfield made of gravel-filled trenches.

Evapotranspiration System

A specialized system used in arid climates with a lined drainfield that disposes of effluent through evaporation from the soil surface and transpiration from plants, rather than absorption into the soil.

Gravity-Fed System

A standard septic system where effluent flows from the house to the tank and to the drainfield using only the force of gravity, without the need for a pump.

Mound System

An engineered drainfield constructed in a raised bed of sand above the natural ground surface. Used for properties with poor soil, shallow bedrock, or a high water table.

Pressure Distribution System

A system that uses a pump to force effluent under pressure through small-diameter pipes in the drainfield, ensuring perfectly even distribution over the entire area.

Sand Filter System

An advanced system where effluent from the septic tank is filtered through a bed of sand before being discharged to the drainfield, providing an extra level of treatment.

Subsurface Drip System

A type of drainfield that uses a network of flexible tubing with small emitters (like a garden soaker hose) to slowly and evenly drip effluent into the soil over a large area.

As-Built (Drawing/Plan)

A diagram created after a septic system is installed, showing the exact location and dimensions of all components. Usually on file with the local health department.

Code / Building Code

The set of rules and regulations established by a local or state authority that govern the design, installation, and maintenance of septic systems.

Compliance Certificate

A document issued by a licensed inspector or health department certifying that a septic system has passed an inspection and meets all relevant codes, often required during a real estate transaction.

Installer / Operator

A licensed professional who is certified to design, install, inspect, and maintain septic systems.

Maintenance Contract

A service agreement with a septic professional for regular inspections and maintenance, often required for advanced systems like ATUs.

Permit / Permitting

The official approval required from a local health or building department before a septic system can be installed or repaired.

Regulations / Local Health Department

The specific rules governing septic systems in your area, enforced by the town, city, or county health department.

Service Record

A log of all maintenance performed on a septic system, including dates of inspections and pumpings. Essential for proper management and for real estate transactions.

Site Plan

A map of a property showing the location of buildings, wells, property lines, and the proposed or existing septic system.

Variance

An official exception granted by a regulatory authority that allows a septic system to be installed in a way that deviates from the standard code, usually due to challenging site conditions.

Backflow / Sewage Backup

The worst-case scenario for a homeowner, where wastewater from a failed septic system flows backward through the plumbing and into the house.

Clog

A blockage in any part of the system, from the main house drain to the drainfield pipes, often caused by flushing improper items or by root intrusion.

Flooding (of Drainfield)

A condition where the drainfield becomes saturated with water, often indicated by spongy ground or standing water on the surface. This means the system is no longer treating wastewater.

Hydraulic Overload

A state where the system receives more water than the drainfield can absorb, leading to saturation and failure.

Remediation

The process of fixing or reversing a failing septic system. This can range from simple clog removal to more advanced techniques like drainfield aeration or, in worst-case scenarios, full system replacement.

Root Intrusion

The process of tree or shrub roots growing into septic pipes, causing cracks and severe blockages.

Soil Saturation

The condition where the soil in the drainfield is completely filled with water, preventing it from absorbing more effluent and halting the aerobic treatment process.

System Failure

The point at which a septic system can no longer effectively treat and dispose of wastewater, posing a health hazard and requiring major repair or replacement. Read More →