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Terms & Acronyms

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Term	Acronym	Vocabulary	Vocabulary Type	Definitions
1,1,1-Trichloroethane	1,1,1-TCA	RCRA Glossary of Terms	Glossary and Key Word List	Definition: Please see the ATSDR fact sheet for 1,1,1-TCA.
1,1-Dichloroethane	1,1-DCA	RCRA Glossary of Terms	Glossary and Key Word List	Definition: Please see the ATSDR fact sheet for 1,1-DCA.
1-(2-Pyridyl)piperazine	1,2-PP		Abbreviation and Acronym List
1,3,5-Trinitrobenzene	1,3,5-TNB		Abbreviation and Acronym List
One-Dimensional Model	1-D	Sediment Total Maximum Daily Loads (TMDLs) Glossary	Glossary and Key Word List	Definition: A mathematical model defined along one spatial coordinate of a natural water system. Typically 1-D models are used to describe the longitudinal variation of water quality constituents along the downstream direction of a stream or river. In writing the model, it is assumed that the cross-channel (lateral) and vertical variability is relatively homogenous and can, therefore, be averaged over those spatial coordinates.
Ten-to-The-Minus-Sixth	10 to -6	Pesticides Glossary	Glossary and Key Word List	Definition: Used in risk assessments to refer to the probability of risk. Literally means a chance of one in a million. Similarly, ten-to-the-minus-fifth means a probability of one in 100,000, and so on.
Tabloid	11" x 17"	Communications Stylebook Glossary	Glossary and Key Word List	Definition: a page half the size of a broadsheet, or twice the size of a sheet of standard paper.
One-Dimensional Monte Carlo Analysis	1-D MCA	EPA EV-Research-Research Resources-Analytical Methods & Protocols	Taxonomy	Definition: A method of simulating a distribution for an endpoint of concern as a function of probability distributions that characterize variability or uncertainty. [EPA Definitions of Terms Relevant to PRA and References for Further Reading at http://www.epa.gov/oswer/riskassessment/rags3adt/pdf/appendixe.pdf]
10-Day Lethal Concentration 50 Percent	10-Day LC, 10-day LC5	EPA EV-Regulatory Activities-Regulatory Quantities	Taxonomy	Definition: Applied to the sediment toxicity BAT effluent limitations and NSPS means the concentration (milligrams/kilogram dry sediment) of the base fluid in sediment that is lethal to 50 percent of the Leptocheirus plumulosus test organisms exposed to that concentration of the base fluids after ten days of constant exposure. [40 CFR 435.11 (CFR 2017)]
10-Day Lethal Concentration 50 Percent	10-Day LC, 10-day LC5	EPA EV-Regulatory Activities-Regulatory Quantities	Taxonomy	Definition: Applied to the sediment toxicity BAT effluent limitations and NSPS means the concentration (milligrams/kilogram dry sediment) of the base fluid in sediment that is lethal to 50 percent of the Leptocheirus plumulosus test organisms exposed to that concentration of the base fluids after ten days of constant exposure. [40 CFR 435.11 (CFR 2017)]
11-Aminodecanoic Acid	11-AA	EPA EV-Chemical Substances	Taxonomy	Definition: Chemical substance, CAS Number 2432-99-7.(2) [40 CFR 704.25 (CFR 2013)]
2,4,6-Trinitrotoluene	2,4,6-TNT		Abbreviation and Acronym List
2,4-Dichlorophenoxyacetic acid	2,4-D		Abbreviation and Acronym List
2,4-Dinitrophenylhydrazine	2,4-DNPH		Abbreviation and Acronym List
Two-Dimensional Model	2-D	Sediment Total Maximum Daily Loads (TMDLs) Glossary	Glossary and Key Word List	Definition: A mathematical model defined along two spatial coordinates where the water quality constituents are considered averaged over the third remaining spatial coordinate. Examples of 2-D models include descriptions of the variability of water quality properties along: (a) the length and width of a river that incorporates vertical averaging of depth, or (b) length and depth of a river that incorporates lateral averaging across the width of the waterbody.
Two Dimensional	2D		Abbreviation and Acronym List
2,3,7,8-Tetrachlorodibenzo-p-dioxin Toxic Equivalency Quotient	2,3,7,8-TeCDD TEQ	EPA EV-Regulatory Activities-Regulatory Quantities	Taxonomy	Definition: A procedure that expresses the toxicity of PCDD, PCDF, and PCB in terms of the most toxic dioxin, as specified in applicable regulations, permits, or other requirements. [40 CFR 63.11426 (2023)]
2-Butoxyethanol	2-BE	EPA EV-Chemical Substances	Taxonomy	Definition: A clear colorless liquid that smells somewhat like ether. It is usually produced by a reaction of ethylene oxide with butyl alcohol, but it may also be made by the reaction of ethylene glycol with dibutyl sulfate. 2-Butoxyethanol is widely used as a solvent in protective surface coatings such as spray lacquers, quick-dry lacquers, enamels, varnishes, and latex paints. It is also used as an ingredient in paint thinners and strippers, varnish removers, agricultural chemicals, herbicides, silicon caulks, cutting oils, and hydraulic fluids. It has other uses in metal cleaners, fabric dyes and inks, industrial and household cleaners (as a degreaser), and dry-cleaning compounds. It is also used in liquid soaps and in cosmetics. CASRN 111-76-2 [Adapted from Agency for Toxic Substances amd Disease Registry TOXICOLOGICAL PROFILE FOR 2-BUTOXYETHANOL AND 2-BUTOXYETHANOL ACETATE at http://www.atsdr.cdc.gov/ToxProfiles/tp118.pdf]
Two-Dimensional Monte Carlo Analysis	2-D MCA	EPA EV-Research-Research Resources-Analytical Methods & Protocols	Taxonomy	Definition: An advanced modeling technique that uses two stages of random sampling, also called nested loops, to distinguish between variability and uncertainty in exposure and toxicity variables. The first stage, often called the inner loop, involves a complete 1-D MCA simulation of variability in risk. In the second stage, often called the outer loop, parameters of the probability distributions are red efined to reflect uncertainty. These loops are repeated many times resulting in multiple risk distributions, from which confidence intervals are calculated to represent uncertainty in the population distribution of risk. [EPA Definitions of Terms Relevant to PRA and References for Further Reading at http://www.epa.gov/oswer/riskassessment/rags3adt/pdf/appendixe.pdf]
2-Methoxyethanol	2-ME	EPA EV-Chemical Substances	Taxonomy	Definition: Molecular Formula is C3H8O2 and the Chemical Structure is CH3OCH2CH2OH. 2-Methoxyethanol is used primarily as a jet fuel de-icer. It is also used as a solvent for cellulose acetate; resins (particularly in the electronics industry); some alcohol soluble dyes; and in quick-drying varnishes, enamels, nail polishes, and wood stains. Small amounts are also used as perfume fixatives and in the manufacture of photographic film. CASRN 109-86-4 [EPA EPA 749-F-94-019a CHEMICAL SUMMARY FOR 2-METHOXYETHANOL prepared by OFFICE OF POLLUTION PREVENTION AND TOXICS U.S. ENVIRONMENTAL PROTECTION AGENCY August 1994 at http://www.epa.gov/chemfact/s_methox.txt]
Three-Dimensional Model	3-D	Sediment Total Maximum Daily Loads (TMDLs) Glossary	Glossary and Key Word List	Definition: Mathematical model defined along three spatial coordinates where the water quality constituents are considered to vary over all three spatial coordinates of length, width, and depth.
Three Dimensional	3D		Abbreviation and Acronym List
3-Bag Federal Test Procedure	3-Bag FTP	EPA EV-Research-Research Resources-Analytical Methods & Protocols	Taxonomy	Definition: Federal Test Procedure specified in part 86 of this chapter, with three sampling portions consisting of the cold-start transient (“Bag 1”), stabilized (“Bag 2”), and hot-start transient phases (“Bag 3”). [40 CFR 600.002 (CFR 2013)]
Multimedia, Multireceptor, Multipathway Risk Assessment	3MRA	EPA EV-Outcomes-Risk Assessments	Taxonomy	Definition: Multi-media, fate and transport, multi-receptor exposures, and multi-pathway exposure routes risk assessments
Four-Zero-One (a) Certification	(401) (a) Certification	National Pollutant Discharge Elimination System (NPDES) Glossary	Glossary and Key Word List	Definition: The requirement of Section 401(a) of the Clean Water Act that all federally issued permits be certified by the state in which the discharge occurs. The state certifies that the proposed permit will comply with state water quality standards and other state requirements.
Fourth Generation Language	4GL		Abbreviation and Acronym List
4-Bag Federal Test Procedure	4-Bag FTP	EPA EV-Research-Research Resources-Analytical Methods & Protocols	Taxonomy	Definition: 3-bag FTP, with the addition of a sampling portion for the hot-start stabilized phase (“Bag 4”). [40 CFR 600.002 (CFR 2013)]
4-Day Lethal Concentration 50 Percent	4-day LC, 4-Day LC5	EPA EV-Regulatory Activities-Regulatory Quantities	Taxonomy	Definition: Applied to the sediment toxicity BAT effluent limitations and NSPS means the concentration (milligrams/kilogram dry sediment) of the drilling fluid in sediment that is lethal to 50 percent of the Leptocheirus plumulosus test organisms exposed to that concentration of the drilling fluids after four days of constant exposure. [40 CFR 435.11 (CFR 2017)]
4-Day Lethal Concentration 50 Percent	4-day LC, 4-Day LC5	EPA EV-Regulatory Activities-Regulatory Quantities	Taxonomy	Definition: Applied to the sediment toxicity BAT effluent limitations and NSPS means the concentration (milligrams/kilogram dry sediment) of the drilling fluid in sediment that is lethal to 50 percent of the Leptocheirus plumulosus test organisms exposed to that concentration of the drilling fluids after four days of constant exposure. [40 CFR 435.11 (CFR 2017)]
96-Hour Lethal Concentration 50 Percent	96-hour LC, 96-hour LC5	EPA EV-Regulatory Activities-Regulatory Quantities	Taxonomy	Definition: Concentration (parts per million) or percent of the suspended particulate phase (SPP) from a sample that is lethal to 50 percent of the test organisms exposed to that concentration of the SPP after 96 hours of constant exposure. [40 CFR 435.11 (CFR 2017)][40 CFR 435.41 (CFR 2017)]
96-Hour Lethal Concentration 50 Percent	96-hour LC, 96-hour LC5	EPA EV-Regulatory Activities-Regulatory Quantities	Taxonomy	Definition: Concentration (parts per million) or percent of the suspended particulate phase (SPP) from a sample that is lethal to 50 percent of the test organisms exposed to that concentration of the SPP after 96 hours of constant exposure. [40 CFR 435.11 (CFR 2017)][40 CFR 435.41 (CFR 2017)]
Ninetieth Percentile	90th Percentile	EPA EV-Measurements-Numerical Characteristics	Taxonomy	Definition: Value that would divide an ordered set of increasing values so that at least 90 percent are less than or equal to the value and at least 10 percent are greater than or equal to the value. [40 CFR 72.2 (CFR 2013)]
Ninety-Fifth Percentile	95th Percentile	EPA EV-Measurements-Numerical Characteristics	Taxonomy	Definition: Value that would divide an ordered set of increasing values so that at least 95 percent of the set are less than or equal to the value and at least 5 percent are greater than or equal to the value. [40 CFR 72.2 (CFR 2013)]

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