Absorption: The process by which one substance is taken into and included within another substance, such as the absorption of water by soil or nutrients by plants.

Aerobic: Having molecular oxygen as a part of the environment, or growing or occurring only in the presence of molecular oxygen, as in aerobic organisms.

Aerobic Bacteria Generator (ABG): A device that inserts into a septic tank or waste impoundment that grows species of bacteria that can survive in the drain field and reduce biomat clogging.

Aerobic treatment unit (ATU): A mechanical onsite treatment unit that provides secondary wastewater treatment by mixing air (oxygen) and aerobic and facultative microbes with the wastewater. ATUs typically use a suspended growth treatment process (similar to activated sludge extended aeration) or a fixed film treatment process (similar to trickling filter).

Alternative onsite wastewater treatment system: An onsite treatment system that includes components different from those used in a conventional septic tank and drain field system. An alternative system is used to achieve acceptable treatment and dispersal/discharge of wastewater where conventional systems may not be capable of meeting established performance requirements to protect public health and water resources. (e.g., at sites where high ground water, low-permeability soils, shallow soils, or other conditions limit the infiltration and dispersal of wastewater or where additional treatment is needed to protect ground water or surface water quality). Components that might be used in alternative systems include sand filters, aerobic treatment units, disinfection devices, and alternative SWIS’s such as mounds, gravelless trenches, and pressure and drip distribution.

Anaerobic: Characterized by the absence of molecular oxygen, or growing in the absence of molecular oxygen (as in anaerobic bacteria).

Aquifer: A geologic formation that is capable of yielding a significant amount of water to a well or spring. All of he spaces and cracks, or pores, between particles of rock and other mineral are saturated with water. Water can move through the pores toward a spring or other discharge are, or pumping well

As-Built Construction Plans: Plans reflecting location and dimension of structures on a site instead of how they were originally planned.

Biodegradable: Capable of being decomposed by living organisms, especially by bacterial action

Biochemical oxygen demand (BOD): A commonly used gross measurement of the concentration of biodegradable organic impurities in wastewater. The amount of oxygen, expressed in milligrams per liter (mg/L), required by bacteria while stabilizing, digesting, or treating organic matter under aerobic conditions is determined by the availability of material in the wastewater to be used as biological food and the amount of oxygen used by the micro-organisms during oxidation.

Biomat: The layer of biological growth and inorganic residue that develops at the wastewater-soil interface and extends up to about 1 inch into the soil matrix. The biomat controls the rate at which pretreated wastewater moves through the infiltrative surface/zone for coarse- to medium-textured soils. This growth may not control fluxes through fine clay soils, which are more restrictive to wastewater flows than the biomat.

Blackwater: Liquid and solid human body waste and the carriage waters generated through toilet usage.

Breakout: Discharge or ponding of effluent on the ground surface

Cesspool: A lined pit with holes in the bottom and/or sidewalls into which raw sewage is discharged

Centralized wastewater treatment system: A wastewater collection and treatment system that consists of collection sewers and a centralized treatment facility.

Chemical oxygen demand (COD): A measure of oxygen use equivalent to the portion of organic matter that is susceptible to oxidation by a strong chemical oxidizing agent.

Class V injection well: A shallow well used to place a variety of fluids at shallow depths below the land surface, including a domestic onsite wastewater treatment system serving more than 20 people. USEPA permits these wells to inject wastes below the ground surface provided they meet certain requirements and do not endanger underground sources of drinking water.

Cluster system: A wastewater collection and treatment system under some form of common ownership and management that provides treatment and dispersal/discharge of wastewater from two or more homes or buildings but less than an entire community.

Coliform bacteria: A group of bacteria predominantly inhabiting the intestines of humans or other warm-blooded animals, but also occasionally found elsewhere. Used as an indicator of human fecal contamination.

Conventional onsite system: A wastewater treatment system consisting of a septic tank and subsurface wastewater infiltration system.

Contaminant: Any physical, chemical, biological, or radiological substance or matter in the water, in quantities considered to threaten health

Decentralized system: Onsite and/or cluster wastewater systems used to treat and disperse or discharge small volumes of wastewater, generally from dwellings and businesses that are located relatively close together. Decentralized systems in a particular management area or jurisdiction are managed by a common management entity.

Denitrification: The biochemical reduction of nitrate or nitrite to gaseous molecular nitrogen or anoxide of nitrogen.

Design Flow: The quantity of sewage, expressed in gallons per day (gpd), for which a sewage disposal has been designed

Digestion: The biological decomposition of organic matter in sludge, resulting in partial gasification, liquefaction, and mineralization.

Disinfection: The process of destroying pathogenic and other microorganisms in wastewater, typically through application of chlorine compounds, ultra-violet light, iodine, ozone, and the like.

Dissolved oxygen (DO): The oxygen dissolved in water, wastewater, or other liquid, usually expressed in milligrams per liter (mg/L), parts per million (ppm), or percent of saturation.

Drain field: Shallow, covered, excavation made in unsaturated soil into which pretreated wastewater is discharged through distribution piping for application onto soil infiltration surfaces through porous media or manufactured (gravelless) components placed in the excavations. The soil accepts, treats, and disperses wastewater as it percolates through the soil, ultimately discharging to groundwater.

Distribution Box:† A small, subsurface structure which receives septic tank effluent and distributes it in substantially equal portions to all segments of the soil absorption system.

Effluent: Sewage, water, or other liquid, partially or completely treated or in its natural state, flowing out of a septic tank, subsurface wastewater infiltration system, aerobic treatment unit, or other treatment system or system component.

Effluent filter (also called an effluent screen): A removable, cleanable device inserted into the outlet piping of the septic tank designed to trap excessive solids due to tank upsets that would otherwise be transported to the subsurface wastewater infiltration system or other downstream treatment components.

Environmental sensitivity: The relative susceptibility to adverse impacts of a water resource or other environments that may receive wastewater discharges.

Eutrophic: A term applied to water that has a concentration of nutrients optimal, or nearly so, for plant or animal growth. In general, nitrogen and phosphorus compounds contribute to eutrophic conditions in coastal and inland fresh waters, respectively.

Evapotranspiration: The combined loss of water from a given area and during a specified period of time by evaporation from the soil or water surface and by transpiration from plants.

Graywater: Wastewater drained from sinks, tubs, showers, dishwashers, clothes washers, and other non-toilet sources

Groundwater: Water that has seeped into the ground under the forces of gravity until it has reached a depth where water fills all of the openings (pores) in the soil and rock

Inlet Pipe: A distribution line that brings effluent into a system component

Microorganism: Any microscopic organism (includes bacteria, protozoa, and viruses)

Mineralization: The conversion of an element from an organic form to an inorganic state as a result of microbial decomposition.

Nitrate: Nitrate is a class of compounds called nutrients. Nutrients are needed by plants to survive and are often added to lawns and soil as fertilizer. Nitrate also occurs as a by-product from animal waste. Nitrate is a problem for water quality when levels get too high, Nitrate is the end product of the break-down of ammonia.

Nitrification: The biochemical oxidation of ammonium to nitrate.

Nitrogen Load: The amount of nitrogen added to a natural system usually expressed in units of milligrams per liter.

Nitrogen Sensitive Area: An area of land and/or natural resource area determined to be particularly responsive to nitrogen inputs.

Onsite wastewater treatment system (OWTS): A system relying on natural processes and/or mechanical components that is used to collect, treat, and disperse/discharge wastewater from single dwellings or buildings.

Operating permit: A renewable and revocable permit to operate and maintain an onsite or cluster treatment system in compliance with specific operational or performance requirements.

Organic soil: A soil that contains a high percentage(more than 15 to 20 percent) of organic matter throughout the soil column.

Pathogenic: Causing disease; commonly applied to microorganisms that cause infectious diseases.

Percolation: The downward flow of water through he pores or spaces of unsaturated rock or soil.

Percolation Rate: A measure of the permeability of soils reflected in minutes per inch

Permeability: The ability of a porous medium such as soil to transmit fluids or gases.

pH: A term used to describe the hydrogen ion activity of a system.

Pollution: Any substance, natural or synthetic, that degrades water quality to such a degree that water is not suitable for a particular use.

Pretreatment system: Any technology or combination of technologies that precedes discharge to a subsurface wastewater infiltration system or other final treatment unit or process before final dissemination into the receiving environment.

Regulatory authority (RA): The level of government that establishes and enforces codes related to the permitting, design, placement, installation, operation, maintenance, monitoring, and performance of onsite wastewater treatment systems.

Residuals: The solids generated and retained during the treatment of domestic sewage in treatment system components, including sludge, scum, and pumpings from grease traps, septic tanks, aerobic treatment units, and other components of an onsite or cluster system.

Sand filter: A packed-bed filter of sand or other granular materials used to provide advanced secondary treatment of settled wastewater or septic tank effluent. Sand/media filters consist of a lined(e.g., impervious PVC liner on sand bedding)excavation or structure filled with uniform washed sand that is placed over an under drain system. The wastewater is dosed onto the surface of the sand through a distribution network and allowed to percolate through the sand to the under drain system, which collects the filter effluent for further  processing or discharge.

Septage: The liquid, solid, and semisolid material that results from wastewater pretreatment in aseptic tank, which must be pumped, hauled, treated, and disposed of properly (i.e., in accordance with40 CFR Part 503).

Septic tank: A buried, preferably watertight tank designed and constructed to receive and partially treat raw wastewater. The tank separates and retains settleable and floatable solids suspended in the raw wastewater. Settleable solids settle to the bottom to form a sludge layer. Grease and other light materials float to the top to form a scum layer. There moved solids are stored in the tank, where they undergo liquefaction in which organic solids are partially broken down into dissolved fatty acids and gases. Gases generated during liquefaction of the solids are normally vented through the building’s plumbing stack vent.

Settleable solids: Matter in wastewater that will not stay in suspension during a designated settling period.

Scum: A mass of light solids, such as hair, grease, oils, and soaps floating on the surface of the wastewater in a septic tank

Standard Septic System: A system used to treat and dispose of wastewater underground consisting of at least an anaerobic septic tank and a soil absorption system

Sludge: The heavy, slimy deposit found at the bottom of a septic tank

Soils Absorption System: A system of trenches, chambers, pits, or beds, together with effluent distribution lines and crushed rock stone, which is installed to receive effluent from a septic tank and transmit it to the subsurface environment.

Soil survey: The systematic examination, description, classification, and mapping of soils in an area.

Soil texture: The relative proportions of the various soil separates (e.g., silt, clay, sand) in a soil.

Subsoil: In general, that part of the soil below the depth of plowing.

Subsurface wastewater infiltration system(SWIS): An underground system for dispersing and further treating pretreated wastewater. The SWIS includes the distribution piping/units, any media installed around or below the distribution components, the biomat at the wastewater-soil interface, and the unsaturated soil below.

Surface Water: Bodies of water, snow, or ice on the surface of the earth (such as lakes, streams, ponds, wetlands etc.)

Topsoil: The layer of soil moved in agricultural cultivation.

Total Kjeldahl nitrogen (TKN): An analytical method for determining total organic nitrogen and ammonia.

Treatment system: Any technology or combination of technologies (treatment trains or unit processes)that discharges treated wastewater to surface waters, ground water, or the atmosphere.

Unsaturated flow: Movement of water in a soil that is not filled to capacity with water.

Wastewater: Water discharged through residential or commercial plumbing system that may contain human wastes, detergents, food products or other wastes. Also known as sewage.

Water quality standards: A set of enforceable requirements under the Clean Water Act that include classification of receiving waters in accordance with their federal or state designated use(s), use-based water quality criteria that establish measurable limits for specific pollutants, and antidegradation provisions to ensure that water  quality is maintained or improved.

Water Table: The top of an unconfined aquifer where water pressure is equal to atmospheric pressure. The water depth fluctuates with climate conditions on the land surface above, and follows a contour similar to the land surface topography.