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

Aerobic: Having molecular oxygen as a part of theenvironment, or growing or occurring only in thepresence of molecular oxygen, as in “aerobicorganisms.”

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 mechanicalonsite treatment unit that provides secondarywastewater treatment by mixing air (oxygen) andaerobic and facultative microbes with the wastewa-ter. ATUs typically use a suspended growth treat-ment process (similar to activated sludge extendedaeration) or a fixed film treatment process (similarto trickling filter).

Alternative onsite wastewater treatment system: An onsite treatment system that includes compo-nents different from those used in a conventionalseptic tank and drain field system. An alternativesystem is used to achieve acceptable treatment anddispersal/discharge of wastewater where conven-tional systems may not be capable of meetingestablished performance requirements to protectpublic health and water resources. (e.g., at siteswhere high ground water, low-permeability soils,shallow soils, or other conditions limit the infiltra-tion and dispersal of wastewater or where additional treatment is needed to protect ground wateror surface water quality). Components that might beused in alternative systems include sand filters,aerobic treatment units, disinfection devices, andalternative SWISs such as mounds, gravellesstrenches, and pressure and drip distribution.

Anaerobic: Characterized by the absence ofmolecular oxygen, or growing in the absence ofmolecular 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 commonlyused gross measurement of the concentration ofbiodegradable organic impurities in wastewater.The amount of oxygen, expressed in milligrams perliter (mg/L), required by bacteria while stabilizing,digesting, or treating organic matter under aerobicconditions is determined by the availability ofmaterial in the wastewater to be used as biologicalfood and the amount of oxygen used by the micro-organisms during oxidation.

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

Blackwater: Liquid and solid human body wasteand the carriage waters generated through toiletusage.

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: Awastewater collection and treatment system thatconsists of collection sewers and a centralizedtreatment facility.

Chemical oxygen demand (COD): A measure ofoxygen use equivalent to the portion of organicmatter that is susceptible to oxidation by a strongchemical oxidizing agent.

Class V injection well: A shallow well used toplace a variety of fluids at shallow depths below theland surface, including a domestic onsite wastewatertreatment system serving more than 20 people.USEPA permits these wells to inject wastes belowthe ground surface provided they meet certainrequirements and do not endanger undergroundsources of drinking water.

Cluster system: A wastewater collection andtreatment system under some form of commonownership and management that provides treatmentand dispersal/discharge of wastewater from two ormore homes or buildings but less than an entirecommunity.

Coliform bacteria: A group of bacteria predomi-nantly inhabiting the intestines of humans or otherwarm-blooded animals, but also occasionally foundelsewhere. Used as an indicator of human fecalcontamination.

Conventional onsite system: A wastewater treat-ment system consisting of a septic tank and subsur-face 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 clusterwastewater systems used to treat and disperse ordischarge small volumes of wastewater, generallyfrom dwellings and businesses that are locatedrelatively close together. Decentralized systems in aparticular management area or jurisdiction aremanaged by a common management entity.

Denitrification: The biochemical reduction ofnitrate 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 organicmatter in sludge, resulting in partial gasification,liquefaction, and mineralization.

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

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

Drain field: Shallow, covered, excavation made inunsaturated soil into which pretreated wastewater isdischarged through distribution piping for applica-tion onto soil infiltration surfaces through porousmedia or manufactured (gravelless) componentsplaced in the excavations. The soil accepts, treats,and disperses wastewater as it percolates throughthe 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, partiallyor completely treated or in its natural state, flowingout of a septic tank, subsurface wastewater infiltra-tion system, aerobic treatment unit, or othertreatment system or system component.

Effluent filter (also called an effluent screen): Aremovable, cleanable device inserted into the outletpiping of the septic tank designed to trap excessivesolids due to tank upsets that would otherwise betransported to the subsurface wastewater infiltrationsystem or other downstream treatment components.

Environmental sensitivity: The relative suscepti-bility to adverse impacts of a water resource orother environments that may receive wastewaterdischarges.

Eutrophic: A term applied to water that has aconcentration of nutrients optimal, or nearly so, forplant or animal growth. In general, nitrogen andphosphorus compounds contribute to eutrophicconditions in coastal and inland fresh waters,respectively.

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

Graywater: Wastewater drained from sinks, tubs,showers, dishwashers, clothes washers, and othernon-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 elementfrom an organic form to an inorganic state as aresult 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 ofammonium 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): Asystem relying on natural processes and/or me-chanical components that is used to collect, treat,and disperse/discharge wastewater from singledwellings or buildings.

Operating permit: A renewable and revocablepermit to operate and maintain an onsite or clustertreatment system in compliance with specificoperational or performance requirements.

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

Pathogenic: Causing disease; commonly applied tomicroorganisms 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 suchas soil to transmit fluids or gases.

pH: A term used to describe the hydrogen ionactivity 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 combina-tion of technologies that precedes discharge to asubsurface wastewater infiltration system or otherfinal treatment unit or process before final dissemi-nation into the receiving environment.

Regulatory authority (RA): The level of govern-ment that establishes and enforces codes related tothe permitting, design, placement, installation,operation, maintenance, monitoring, and perfor-mance of onsite wastewater treatment systems.

Residuals: The solids generated and retainedduring the treatment of domestic sewage in treat-ment system components, including sludge, scum,and pumpings from grease traps, septic tanks,aerobic treatment units, and other components of anonsite or cluster system.

Sand filter: A packed-bed filter of sand or othergranular materials used to provide advancedsecondary treatment of settled wastewater or septictank effluent. Sand/media filters consist of a lined(e.g., impervious PVC liner on sand bedding)excavation or structure filled with uniform washedsand that is placed over an underdrain system. Thewastewater is dosed onto the surface of the sandthrough a distribution network and allowed topercolate through the sand to the underdrainsystem, which collects the filter effluent for furtherprocessing or discharge.

Septage: The liquid, solid, and semisolid materialthat 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 tankdesigned and constructed to receive and partiallytreat raw wastewater. The tank separates and retainssettleable and floatable solids suspended in the rawwastewater. Settleable solids settle to the bottom toform a sludge layer. Grease and other light materi-als float to the top to form a scum layer. Theremoved solids are stored in the tank, where theyundergo liquefaction in which organic solids arepartially broken down into dissolved fatty acidsand gases. Gases generated during liquefaction ofthe solids are normally vented through thebuilding’s plumbing stack vent.

Settleable solids: Matter in wastewater that will notstay in suspension during a designated settlingperiod.

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, descrip-tion, classification, and mapping of soils in an area.

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

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

Subsurface wastewater infiltration system(SWIS): An underground system for dispersing andfurther treating pretreated wastewater. The SWISincludes the distribution piping/units, any mediainstalled around or below the distribution compo-nents, 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 agriculturalcultivation.

Total Kjeldahl nitrogen (TKN): An analyticalmethod for determining total organic nitrogen andammonia.

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

Unsaturated flow: Movement of water in a soil thatis 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 enforceablerequirements under the Clean Water Act thatinclude classification of receiving waters inaccordance with their federal or state designateduse(s), use-based water quality criteria that estab-lish measurable limits for specific pollutants, andantidegradation provisions to ensure that waterquality 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.