Glossary: A

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Here are a bunch of new words, and new meanings for old words, depending
on what subject you are exploring. The terms included in this glossary are a
grouping from numerous on-site industry sources. We hope you find them useful.

A HorizonAlso referred to as Topsoil. Generally the most biologically productive layer of soil, the A horizon is dark, loose and crumbly with varying amounts of organic material mixed with minerals. <

AbsorptionThe process whereby one substance is physically taken into and included within another substance, as the absorption of water by soil. <

Absorption FieldAlso referred to as Drain field, Leachfield or Dispersal area. Part of the onsite wastewater treatment system= the area of ground and system of subsurface pipes or chambers into which partially treated wastewater from the septic tank or advanced treatment system is discharged for final treatment and dispersal into the soil environment. <

Accredited InspectorAn individual who has undergone adequate training and has experience to pass an exam for the inspection of OWTS as set forth by local, state, or national accreditation programs. To learn more about Accredited Inspectors, or find on in your area, check out our Septicguy.com, "Dig up an Onsite Pro" section. <

Acid A substance that releases hydrogen ions when dissolved in water. Most acids will dissolve the common metals and will react with a base to form a neutral salt and water. An acid has a pH value lower than 7.0, will turn litmus paper red and has a sour taste. <

AcidicSubstance that has a pH of less than 7 and a high concentration of hydrogen ions. Soils with high amounts of rainfall tend to be slightly acidic. <

Activated SludgeProduct that results when effluent is mixed with bacteria-laden sludge and then agitated and aerated to promote biological treatment. <

Activated Sludge ProcessA biological wastewater treatment process in which a mixture of wastewater and aerobically decomposed sludge is agitated and aerated, speeding the breakdown of organic matter in raw sewage. The sludge is separated from the wastewater and disposed of or returned to the system, as needed. <

Acute ToxicityAdverse health effects that appear within seconds, minutes or hours of a one-time exposure to a chemical substance. The result may be severe biological damage or even death. <

AdsorptionAttachment of a substance to the surface of a solid, such as soil particles or sediment. Many different pollutants can adsorb to soil particles. <

Advanced TreatmentAny treatment of sewage that goes beyond the pre-treatment or anaerobic treatment stage and includes the removal of nutrients such as phosphorus and nitrogen and a high percentage of suspended solids. Advanced waste treatment is more stringent than pre-treatment, requiring an 85 percent reduction in conventional pollutant concentration or a significant reduction in non-conventional pollutants. <

Aerated LagoonA shallow, artificial treatment pond to which oxygen is introduced (e.g., via a mechanical aerator) to speed up the natural process of biological decomposition of organic wastes. <

AerationA step in wastewater treatment in which a mixing or air injection device adds air to wastewater, for the purpose of providing bacteria with the oxygen required to break down organic material (pollutants). <

AerobicIn the presence of, or requiring, free oxygen, as in aerobic bacteria. <

Aerobic BacteriaMicroorganisms living, acting or occurring only in the presence of free oxygen. <

Aerobic DigestionThe breakdown of suspended and dissolved organic matter by microorganisms in the presence of oxygen. Usually associated with the digestion of wastewater sludge. <

Aerobic LagoonOxygen-containing lagoon, often equipped with mechanical aerators, in which wastewater is partially treated by the metabolic activities of bacteria and algae. Small lagoons may remain aerobic without mechanical aerators. <

Aerobic Treatment Unit (ATU)Device that provides aerobic decomposition of wastewater by bringing the wastewater into direct contact with air via mechanical means (e.g., using air pumps, air injectors, lift pumps and biological-contact surfaces such as pipes, gravel and fabric). ATUs are not stand-alone wastewater treatment systems, but provide treatment prior to wastewater disposal in a subsurface drainfield system or provide pre-treatment to other alternative methods of wastewater treatment. <

Aerobic ZoneIn a wastewater treatment system, the zone characterized by the presence of oxygen, both in dissolved form and in combination with other molecules. <

AlarmAn audible and,or visual device connected to a sensor that monitors a specific condition or operating parameter of a process or system. <

AlgaeSimple photosynthetic plants lacking stems, roots and leaves. Found in aquatic and damp terrestrial environments, algae range in size from microscopic, unicellular phytoplankton to multicellular seaweeds that are meters in length. <

Algal BloomPopulation explosion of certain types of algae in surface waters. Algal blooms are usually caused by an increase in nutrients (e.g., nitrates and phosphates) brought about by fertilizer run-off, improperly treated wastewater entering surface waters or other causes. Algal blooms can deplete the oxygen in water, causing the death of fish and other aquatic life. <

AlkaliA substance that has a pH value greater than 7.0; the opposite of an acid. Alkali substances create a bitter taste and slippery feel when dissolved in water and will turn red litmus paper blue. Alkalis may include the soluble hydroxide, carbonate and bicarbonate salts of calcium, magnesium, potassium and sodium. <

AlkalineSubstance that has a pH of greater than 7. <

AlluvialRelating to sediments of gravel, sand, silt, clay or other particulate rock material deposited by flowing water, usually in the beds of rivers and streams, on a flood plain, on a delta or at the base of a mountain. <

Alternating Bed SystemsAlso referred to as alternating drainfield. An absorption system designed with a backup absorption field for use while the primary absorption field rests. Wastewater is directed to one field or the other via a manually operated diverter valve located in the line from the septic tank. Septic systems that have failed might be retro fitted with a backup absorption field, allowing the primary field to rest and recover through biological activity. <

Alternative SewerWastewater treatment system that may be used when 1. hookups to conventional sewers are not available and are too expensive to build, and 2. site conditions (soil characteristics, lot sizes) make individual onsite wastewater treatment alternatives inappropriate or expensive. Depending on site conditions, alternative sewers may use gravity, electrical power, vacuum suction or pipe pressure to transport wastes for final treatment--which may take place at a centralized sewage treatment plant, large community leachfield or lagoon. <

Alternative SystemAn alternative to a conventional septic system. Alternative systems may be used if advanced treatment is desired (to reduce nutrient levels or pathogens) or if a particular site cannot accommodate a conventional technology (e.g., as a result of slope of ground, high groundwater, fast percolation soils, slow percolation soils, and proximity to a waterway or waterbody). Some alternative systems are designed to take the place of traditional septic tanks (e.g., media filters or ATUs); others provide an additional treatment step between the septic tank and the final treatment and dispersal area Alternative systems can also greatly reduce the need for large dispersal areas. <

Alternative ToiletAlternative to a conventional toilet. Includes: composting toilets, waterless toilets designed to compost wastes deposited into the receptacle via the action of microorganisms, low-flow toilets and ultra low-flow toilets that use 1.6 gallons or less of water per flush, incinerating toilets, toilets in which wastes are deposited directly into a receptacle with a combustion chamber for incineration (fueled by electricity, gas or oil) and chemical. <

Ammonia-Nitrogen (NH3-N) LoadAn indicator of the quality of treated wastewater and a component of biochemical oxygen demand. <

AmoebaA usually microscopic single-celled protozoan that is widely found in fresh and salt water. Some types of amoebas cause diseases such as amoebic dysentery. <

AnaerobicGrowing in the absence of oxygen, as in anaerobic bacteria in a septic tank. <

Anaerobic BacteriaMicroorganisms living, acting or occurring in the absence of free oxygen. Decomposition of wastes in a septic tank takes places via anaerobic bacteria. <

Anaerobic DigestionThe bacterial decomposition and treatment of sewage in the absence of free oxygen, such as takes place in a septic tank. <

Anaerobic LagoonConstructed pond-like body of water or basin designed to receive, hold and treat wastewater for a predetermined period of time in the absence of oxygen. Anaerobic lagoons are most often used to treat animal wastes from dairies and pig farms, commercial or industrial wastes or as the first treatment step in systems using two or more lagoons in a series. Anaerobic lagoons are designed to hold and treat wastewater from 20 to 50 days, are relatively deep (e.g., 8-15 feet) and work much like septic tanks. Solids separate and settle into layers, the top scum layer keeping out air to create anaerobic conditions and the bottom sludge layer eventually accumulating and requiring periodic removal. Also as with a septic tank, wastewater from an anaerobic lagoon always requires further treatment (e.g., in a series of lagoons). Anaerobic lagoons are often covered with a floating cover whereas methane gases can be collected and recycled as a fuel source. <

Anaerobic Waste TreatmentDecomposition of wastes through the action of microorganisms in the absence of oxygen. Septic tanks provide anaerobic waste treatment, as do anaerobic lagoons. <

Anaerobic ZoneIn a wastewater treatment system, the zone characterized by the absence of oxygen, whether in dissolved form or in combination with other molecules. <

AnoxiaThe absence of dissolved oxygen. Anoxia in lakes. <

Anoxic ProcessAlso referred to as anoxic denitrification. A process that occurs only at very low levels of free oxygen or in the absence of free oxygen. Also refers to the process by which nitrate-nitrogen is converted biologically to nitrogen gas in the absence of oxygen. <

Anoxic ZoneIn a wastewater treatment system, the zone in which there is no dissolved oxygen but where oxygen is present combined with other molecules. <

AntibiosisIn general, the creation of metabolic byproducts that are toxic to other organisms. For example, during the decomposition process, bacterial reactions produce substances that are toxic to most pathogens. <

Application AreaSometimes referred to as the "wetted perimeter," it is the actual surface area which wastewater comes into contact with before entering the surrounding soil. When a septic system is functioning normally, this application area forms a biological layer (the biomat) that helps decompose the wastewater before it moves through the soil. <

Approved PlanThe plan for the design of a septic system, developed by a licensed septic designer

AquiferAn underground geological formation or group of formations containing usable amounts of groundwater that can supply wells and springs. Aquifers are more protected from contaminants than surface waters, but may still be tainted by fecal coliform from improperly functioning OWTS. Half of all Americans get drinking water from aquifers. Of these, roughly a third have their own wells, while the remainder use municipal water systems that draw on underground sources. <

Areal RateThe rate of loading (addition of a substance) per square meter of surface area. <

As-Built PlanThe plan that depicts a OWTS (including dimensions, distances from dwellings, roads, surface water, wells) as it was built by a installing contractor. A copy of this plan should be on file with the local board of health and,or building permit office. It supplies the background information required by an Inspector to evaluate the design/siting of the system and subsequent performance. <

At Grade SystemAn OWTS dispersal system with specific design parameters that has the infiltrative surface located at, or close to, the original grade, (e.g. mounds or bottomless sand or peat filters). <

Attached Growth ProcessesAlso referred to as Fixed Film Processes. Wastewater treatment processes in which the microorganisms and bacteria treating the wastes are attached to some inert media (e.g., rock, designed ceramic or plastic). This method of wastewater treatment can be used for BOD removal, nitrification and denitrification. Examples of wastewater treatments that utilize attached growth processes include trickling filters and attached growth units. <

Attached Growth UnitsAn alternative design for aerobic treatment of wastewater. Attached growth units consist of a surface made of material that bacteria can attach to. This surface is exposed alternately to wastewater and to air, done either by rotating the surface in and out of the wastewater or by dosing the wastewater onto the surface. Pretreatment is required. The air needed for the process is either naturally present or is supplied mechanically. Trickling Filters are an example. <

Available Water CapacityThe capacity of soils to hold water available for use by most plants. Defined as the difference between the amount of soil water at field capacity (i.e., the amount of water that remains in soil after gravitational water has drained away) and the amount at the wilting point. <

Average Daily FlowThe average amount of wastewater that enters an OWTS over a 24 hour period, measured in gallons. A household average daily flow is calculated by multiplying the number of bedrooms by (120 - 150) gallons per day, (gpd). Actual number is determined by your local permitting authority. <

Content assembled from numerous sources including, septic-info.com, National Small Flows Clearinghouse, Ken Keri - Operating Training Manual, USEPA and Septic Guy.