<descriptor thcode="2"><thesaurus thcode="2" name="USGS Thesaurus" scope="Topics and methods of scientific study carried out by USGS, with product types, scientific disciplines, geologic time, and types of institutional structure and activities.  Broad and shallow, used to help people find scientific information." creator="U.S. Geological Survey" rights="Public domain" edition="2.0" date="2020-01-09" codetype="number" prefix="topic" uri="https://www2.usgs.gov/science/USGSThesaurus" tblname="term" nonpref="nonpref" relterm="relterm" root_code="1" contact="pschweitzer"><category><term thcode="25" code="29" name="distinct labels" parent="26" scope="Preferred labels (descriptor texts) are distinct within the thesaurus. A concept can be specified either by its unique identifier (code) or by the text of its descriptor."/><term thcode="25" code="16" name="hierarchical" parent="11" scope="Substantive broader-narrower relationships exist among the terms."/><term thcode="25" code="13" name="transitive" parent="12" scope="Narrower terms have an &quot;is a&quot; relationship with their broader terms, and generally can be described as part-of, type-of, or instance-of the broader term."/><term thcode="25" code="21" name="disciplines" parent="2" scope="Broad categories of human inquiry or activity, such as scientific disciplines."/><term thcode="25" code="20" name="methods" parent="2" scope="Actions taken to obtain or analyze information"/><term thcode="25" code="19" name="organizational functions" parent="2" scope="Things that organizations do, typically including various types of programs, projects, and services."/><term thcode="25" code="7" name="temporal" parent="2" scope="Terms indicate periods of time, such as chronostratigraphic units, named historical periods or intervals surrounding known historical events, or seasons."/><term thcode="25" code="5" name="theme" parent="2" scope="Terms indicate domains of human concern, such as scientific discipline, societal problems, or characteristics of earth, space, oceans, and living things."/><term thcode="25" code="29" name="distinct labels" parent="26" scope="Preferred labels (descriptor texts) are distinct within the thesaurus. A concept can be specified either by its unique identifier (code) or by the text of its descriptor."/><term thcode="25" code="16" name="hierarchical" parent="11" scope="Substantive broader-narrower relationships exist among the terms."/><term thcode="25" code="13" name="transitive" parent="12" scope="Narrower terms have an &quot;is a&quot; relationship with their broader terms, and generally can be described as part-of, type-of, or instance-of the broader term."/><term thcode="25" code="21" name="disciplines" parent="2" scope="Broad categories of human inquiry or activity, such as scientific disciplines."/><term thcode="25" code="20" name="methods" parent="2" scope="Actions taken to obtain or analyze information"/><term thcode="25" code="19" name="organizational functions" parent="2" scope="Things that organizations do, typically including various types of programs, projects, and services."/><term thcode="25" code="7" name="temporal" parent="2" scope="Terms indicate periods of time, such as chronostratigraphic units, named historical periods or intervals surrounding known historical events, or seasons."/><term thcode="25" code="5" name="theme" parent="2" scope="Terms indicate domains of human concern, such as scientific discipline, societal problems, or characteristics of earth, space, oceans, and living things."/></category><altlabel><altlabel>USGSThesaurus</altlabel><altlabel>USGSThesaurus</altlabel></altlabel></thesaurus><term thcode="2" code="1723" name="industrial pollution" parent="769" scope="Introduction of harmful substances into the environment by manufacturing, power generation, mining, or material processing."/><uf><usefor name="PCBs"/><usefor name="oil spills"><usewith><term thcode="2" code="1804" name="petroleum" parent="1005" scope="Naturally occurring hydrocarbons, typically fluid or gas, often of economic use.  Includes oil, natural gas, and asphaltic compounds found in tar sands and oil shales."/></usewith></usefor><usefor name="polychlorinated biphenyls"/></uf><bt><term thcode="2" code="769" name="contamination and pollution" parent="1174" scope="Introduction of harmful substances into the environment by human action or natural processes."/><term thcode="2" code="1174" name="topics" parent="1" scope="Themes, subjects, and concerns for which USGS information resources are relevant."/><term thcode="2" code="1" name="Categories" scope="Thematic terms for categorizing information resources.  This thesaurus is intended to support finding and understanding scientific information."/></bt><nt><term thcode="2" code="1724" name="mine drainage" parent="1723" scope="Introduction of harmful substances into the environment from mines and tailings."/><term thcode="2" code="2270" name="produced water" parent="1723" scope="Water produced during generation and development of energy resources, particularly hydrocarbons, as well as related fluids injected into reservoirs for energy development and associated waste disposal."/></nt><rt><term thcode="2" code="2274" name="PFAS" parent="769" scope="Per- and polyfluoroalkyl substances (PFAS) are a group of man-made chemical compounds that are an emerging contaminant."/><term thcode="2" code="1725" name="abandoned mines and quarries" parent="548" scope="Mines and quarries that have been abandoned and may expose harmful chemicals to the environment."/><term thcode="2" code="2273" name="coal ash" parent="2271" scope="Solid waste material remaining from the burning of coal."/><term thcode="2" code="2272" name="slag" parent="2271" scope="Solid waste material produced by the industrial processing of ore materials."/><term thcode="2" code="2271" name="solid industrial waste material" parent="1199" scope="Waste solid materials produced by industrial processing of earth materials, not simply material extracted in the search for ores."/></rt></descriptor>