Glossary

Absorption Field: The area where treated wastewater is released into soil for final filtration. Also called a drainfield or leach field. In Tennessee, terrain determines far more about it than anywhere else in the Southeast.

ATU (Aerobic Treatment Unit): A system that introduces air so aerobic bacteria treat wastewater, producing cleaner effluent than a conventional tank. Often required where soil or terrain won't support a gravity system.

Baffle: A barrier inside the septic tank that controls flow between compartments and keeps solids from escaping toward the drainfield. A failed baffle often produces symptoms that look like drainfield failure.

Certificate of Verification: Documentation from the county confirming a septic system's status. In Blount County this is the standard document requested during a property transaction.

Conventional System: A standard gravity septic system — tank plus drainfield, no pumps or engineered treatment. The least expensive option, and what most West Tennessee properties can support.

Drip Dispersal: A distribution method that releases effluent slowly through small emitters across a wide area. Used where shallow soil over bedrock limits conventional trench depth, which is common in East Tennessee.

Effluent: The liquid that leaves the septic tank and flows to the drainfield after solids settle out. Its 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. It should be cleaned at every pump-out.

Karst: Limestone geology that dissolves over time, creating sinkholes, caves and underground channels. Middle Tennessee sits on a large karst region, which means contaminants can reach groundwater with far less filtration than normal soil provides.

LPP (Low-Pressure Pipe): A distribution method that pumps effluent through small-diameter pipes to spread it evenly. Used on sloped sites and where soil requires more uniform dosing — common on Tennessee's ridges and hillsides.

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

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 it will cost.

Replacement Area: Space set aside on a lot for an entirely new drainfield if the original fails. Tennessee requires this, which is why lot size matters as much as soil quality.

Riser: An extension bringing 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.

Rule 0400-48-01: The Tennessee Department of Environment and Conservation regulation governing subsurface sewage disposal systems. It sets the statewide framework that county environmental health offices administer.

SDS (Subsurface Sewage Disposal System): Tennessee's formal regulatory term for what most homeowners call a septic system — any wastewater system serving a single property rather than connecting to a municipal sewer.

Setback: The minimum required distance between a septic component and a well, property line, water body, or structure.

Site Evaluation: An assessment of soil, slope and site conditions determining what system a property can support. Required before a Tennessee septic permit is issued.

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

Soil Map Unit: The classification describing a property's soil type and its suitability for wastewater absorption. Tennessee's three regions produce dramatically different map units, which is why cost varies so widely across the state.

TDEC: The Tennessee Department of Environment and Conservation — the state agency setting septic rules. Many counties administer permitting through TDEC's Environmental Field Offices rather than a separate county health department.

Vertical Separation: The distance between the bottom of the drainfield and groundwater, rock, or an impervious layer. Shallow bedrock in East Tennessee is the most common reason this requirement forces an engineered system.