Term	Definitions	Acronym	
Aerobic Treatment Unit
 	A mechanical wastewater treatment unit that provides secondary wastewater treatment for a single home, a cluster of homes, or a commercial establishment by mixing air (oxygen) and aerobic and facultative microbes with the wastewater. ATUs typically use a suspended growth process (such as activated sludge-extended aeration and batch reactors), a fixed-film process (similar to a trickling filter), or a combination of the two treatment processes. 	ATU 	
Alternative Septic System
 	A wastewater treatment system that includes components different from those typically used in a conventional septic tank and subsurface wastewater infiltration system (SWIS). An alternative system is used to achieve acceptable treatment and dispersal of wastewater where conventional systems either might not be capable of protecting public health and water quality or are inappropriate for properties with shallow soils over ground water or bedrock or soils with low permeability. Examples of components that can be used in alternative systems are sand filters, aerobic treatment units, disinfection devices, and alternative subsurface infiltration designs such as mounds, gravelless trenches, and pressure and drip distribution. 		
Centralized Wastewater Treatment System
 	A managed system consisting of collection sewers and a single treatment plant used to collect and treat wastewater from an entire service area. Traditionally, such a system has been called a publicly owned treatment works (POTW) as defined at 40 CFR 122.2. 		
Cesspool
 	A drywell that receives untreated sanitary waste containing human excreta, which sometimes has an open bottom and/or perforated sides (40 CFR 144.3). Cesspools with the capacity to serve 20 or more persons per day were banned in federal regulations promulgated on December 7, 1999. The construction of new cesspools was immediately banned, and existing large-capacity cesspools must be replaced with sewer connections or onsite wastewater treatment systems by 2005. 		
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 that collects wastewater from two or more dwellings or buildings and conveys it to a treatment and dispersal system located on a suitable site near the dwellings or buildings. 		
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. 		
Construction Permit
 	A permit issued by the designated local regulatory authority that allows the installation of a wastewater treatment system in accordance with approved plans and applicable codes. 		
Conventional Septic System
 	A wastewater treatment system consisting of a septic tank and a typical trench or bed subsurface wastewater infiltration system. 		
Decentralized System
 	An onsite or clustered system used to collect, treat, and disperse or reclaim wastewater from a small community or service area. 		
Dispersal System
 	A system that receives pretreated wastewater and releases it into the air, into surface or ground water, or onto or under the land surface. A subsurface wastewater infiltration system is an example of a dispersal system. 		
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. 		
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
 	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. 		
Effluent Screen
 			
Engineered Design
 	An onsite or clustered wastewater system that is designed and certified by a licensed/certified designer to meet specific performance criteria for a particular wastewater on a particular site. 		
Environmental Sensitivity
 	The relative susceptibility to adverse impacts of a water resource or other receiving environment from dispersal of wastewater or its constituents. The impacts may be low, acute (immediate and significantly disruptive), or chronic (long-term, with gradual but serious disruptions). 		
Graywater
 	Wastewater drained from sinks, tubs, showers, dishwashers, clothes washers, and other non-toilet sources. 		
Large-Capacity Septic System
 	An onsite method of partially treating and disposing of sanitary wastewater having the capacity to serve 20 or more persons per day subject to EPA's Underground Injection Control regulations. 		
Management Entity
 	An entity similar to a responsible management entity, but managing a limited set of management activities (e.g., homeowners' association, contracted provider of management services). 		
Management Model
 	A 13-element program designed to protect and sustain public health and water quality through the use of appropriate policies and administrative procedures that define and integrate the roles and responsibilities of the regulatory authority, system owner, service providers, and management entity, when present, to ensure that onsite and clustered wastewater treatment systems are appropriately managed throughout their life cycle. The program elements include public education and participation; planning; performance; training and certification/licensing; site evaluation; design; construction; operation and maintenance; residuals management; compliance inspections/monitoring; corrective actions; recordkeeping, inventory, and reporting; and financial assistance and funding. Management services should be provided by properly trained and certified personnel and tracked through a comprehensive management information system. 		
Management Services
 	Planning, design, permitting, inspection, construction/installation, operation, maintenance, monitoring, enforcement, and other services required to ensure that the wastewater treatment performance requirements established by the regulatory authority are achieved. Management services should be provided by properly trained personnel and tracked by means of a comprehensive management information system. 		
National Pollutant Discharge Elimination System
 	A national program under Section 402 of the Clean Water Act for regulation of discharges of pollutants from point sources to waters of the United States. Discharges are illegal unless authorized by an NPDES permit. 	NPDES 	
Nonconventional Onsite Treatment System
 	System using technologies or combinations of technologies that are used where conventional septic systems cannot meet established performance or prescriptive requirements because of limiting site conditions. Also referred to as alternative septic systems. 		
Onsite Service Provider
 	A person who provides onsite system services. Providers include (but are not limited to) designers, engineers, soil scientists, site evaluators, installers, contractors, operators, managers, maintenance service providers, pumpers, and others who provide services to system owners or other service providers. 		
Onsite Wastewater Treatment System
 	A system relying on natural processes and/or mechanical components to collect, treat, and disperse or reclaim wastewater from a single dwelling or building. 	OWTS 	
Operating Permit
 	A renewable and revocable permit to operate and maintain an onsite or clustered treatment system in compliance with specific operational or performance criteria stipulated by the regulatory authority. 		
Package Plant
 	Term commonly used to describe an aerobic treatment unit serving multiple dwellings or an educational, health care, or other large facility. 		
Pathogenic
 	Causing disease; commonly applied to microorganisms that cause infectious diseases. 		
Percolation
 	The flow or trickling of a liquid downward through a contact or filtering medium. 		
Performance-Based Management Program
 	A program designed to preserve and protect public health and water quality by seeking to ensure sustained achievement of specific, measurable performance criteria based on site and risk assessments. 		
Performance Criteria
 	Any criteria established by the regulatory authority to ensure future compliance with the public health and water quality goals of the community, the state or tribe, and the federal government. Performance criteria can be expressed as numeric limits (e.g., pollutant concentrations, mass loads, wet weather flow, and structural strength) or narrative descriptions of desired conditions or requirements (e.g., no visible scum, sludge, sheen, odors, cracks, or leaks). 		
Permeability
 	The ability of a porous medium such as soil to transmit fluids or gases. 		
Permitting Authority
 	The state, tribal, or local unit of government with the statutory or delegated authority to issue permits to build and operate onsite wastewater systems. 		
Prescription-Based Management Program
 	A program designed to preserve and protect public health and water quality by specifying pre-engineered system designs for specific sets of site conditions such that systems that are sited, designed, and constructed properly are deemed to meet public health and water quality standards. 		
Prescriptive Requirements
 	Specifications for design, installation, and other procedures and practices for onsite or clustered wastewater systems on sites that meet stipulated criteria. Proposed deviations from the stipulated criteria, specifications, procedures, or practices require formal approval from the regulatory authority. 		
Pretreatment System
 	Any technology or combination of technologies that precedes discharge to a subsurface septic system or other final treatment unit or process before final dissemination into the receiving environment. 		
Regulatory Authority
 	The unit of government that establishes and enforces codes related to the permitting, design, placement, installation, operation, maintenance, monitoring, and performance of onsite and clustered wastewater systems. 	RA 	
Residuals
 	The solids generated or retained during the treatment of wastewater. They include trash, rags, grit, sediment, sludge, biosolids, septage, scum, and grease, as well as those portions of treatment systems that have served their useful life and require disposal, such as the sand or peat from a filter. Because of the different characteristics of residuals, management requirements can differ as stipulated by the appropriate federal regulations. 		
Responsible Management Entity
 	A legal entity responsible for providing various management services with the requisite managerial, financial, and technical capacity to ensure the long-term, cost-effective management of decentralized onsite or clustered wastewater treatment facilities in accordance with applicable regulations and performance criteria. 	RME 	
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. 		
Septage
 	The liquid and solid materials pumped from a septic tank during cleaning operations. 		
Septic Tank
 	A buried, watertight tank designed and constructed to receive and partially treat raw wastewater. The tank separates and retains settleable and floatable solids suspended in the wastewater and discharges the settled wastewater for further treatment and dispersal to the environment. 		
Source Water Assessment
 	A study and report required by the Source Water Assessment Program (SWAP) of the Safe Drinking Water Act addressing the capability of a given public water system to protect water quality. The assessment includes delineation of the source water area, identification of potential sources of contamination in the delineated area, determination of susceptibility to those sources, and public notice of the completed assessment. 		
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. 		
Underground Injection Well
 	A constructed system designed to place waste fluids above, into, or below aquifers classified as underground sources of drinking water. As regulated under the Underground Injection Control (UIC) program of the Safe Drinking Water Act (40 CFR Parts 144 and 146), injection wells are grouped into five classes. Class V includes shallow systems such as cesspools and subsurface wastewater infiltration systems. Subsurface wastewater infiltration systems with the capacity to serve 20 or more people per day, or similar systems receiving non-sanitary wastes, are subject to federal regulation. Class V motor vehicle waste injection wells and large-capacity cesspools are specifically prohibited under the UIC regulations. 		
Water Quality Criteria
 	A set of enforceable requirements under the Clean Water Act that establish measurable limits for specific pollutants based on the designated use(s) of the receiving water body. Water quality criteria can be expressed as numeric limits (e.g., pollutant concentrations or mass loads) or narrative descriptions of desired conditions (e.g., no visible scum, sludge, sheens, or odors). 		
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 anti-degradation provisions to ensure that water quality is maintained or improved.