Water, wastewater, or other liquid flowing into a reservoir, basin, or treatment plant. Information Collection Request (ICR): A description of information to be gathered in connection with rules, proposed rules, surveys, and guidance documents that contain information-gathering requirements. The ICR describes what information is needed, why it is needed, how it will be collected, and how much collecting it will cost. The ICR is submitted by the EPA to the Office of Management and Budget (OMB) for approval. Information File: In the Superfund program, a file that contains accurate, up-to-date documents on a Superfund site. The file is usually located in a public building (school, library, or city hall) convenient for local residents. Inhalable Particles: All dust capable of entering the human respiratory tract. Initial Compliance Period (Water): The first full three-year compliance period which begins at least 18 months after promulgation. Injection Well: A well into which fluids are injected for purposes such as waste disposal, improving the recovery of crude oil, or solution mining. Injection Zone: A geological formation receiving fluids through a well. Innovative Technologies: New or inventive methods to treat effectively hazardous waste and reduce risks to human health and the environment. Innovative Treatment Technologies: Technologies whose routine use is inhibited by lack of data on performance and cost. (See: Established treatment technologies.) Inoculum: 1. Bacteria or fungi injected into compost to start biological action. 2. A medium containing organisms, usually bacteria or a virus, that is introduced into cultures or living organisms. Inorganic Chemicals: Chemical substances of mineral origin, not of basically carbon structure. Insecticide: A pesticide compound specifically used to kill or prevent the growth of insects. Inspection and Maintenance (I/M): 1. Activities to ensure that vehicles' emission controls work properly. 2. Also applies to wastewater treatment plants and other anti-pollution facilities and processes. Institutional Waste: Waste generated at institutions such as schools, libraries, hospitals, prisons, etc. Instream Use: Water use taking place within a stream channel; e.g., hydro-electric power generation, navigation, water quality improvement, fish propagation, recreation. Integrated Exposure Assessment: Cumulative summation (over time) of the magnitude of exposure to a toxic chemical in all media. Integrated Pest Management (IPM): A mixture of chemical and other, non-pesticide, methods to control pests. Integrated Waste Management: Using a variety of practices to handle municipal solid waste; can include source reduction, recycling, incineration, and landfilling. Interceptor Sewers: Large sewer lines that, in a combined system, control the flow of sewage to the treatment plant. In a storm, they allow some of the sewage to flow directly into a receiving stream, thus keeping it from overflowing onto the streets. Also used in separate systems to collect the flows from main and trunk sewers and carry them to treatment points. Interface: The common boundary between two substances such as a water and a solid, water and a gas, or two liquids such as water and oil. Interfacial Tension: The strength of the film separating two immiscible fluids (e.g. oil and water) measured in dynes per, or millidynes per centimeter. Interim (Permit) Status: Period during which treatment, storage and disposal facilities coming under RCRA in 1980 are temporarily permitted to operate while awaiting a permanent permit. Permits issued under these circumstances are usually called "Part A" or "Part B" permits. Internal Dose: In exposure assessment, the amount of a substance penetrating the absorption barriers (e.g. skin, lung tissue, gastrointestinal tract) of an organism through either physical or biological processes. (See: absorbed dose) Interstate Carrier Water Supply: A source of water for drinking and sanitary use on planes, buses, trains, and ships operating in more than one state. These sources are federally regulated. Interstate Commerce Clause: A clause of the U.S. Constitution which reserves to the federal government the right to regulate the conduct of business across state lines. Under this clause, for example, the U.S. Supreme Court has ruled that states may not inequitably restrict the disposal of out-of-state wastes in their jurisdictions. Interstate Waters: Waters that flow across or form part of state or international boundaries; e.g. the Great Lakes, the Mississippi River, or coastal waters. Interstitial Monitoring: The continuous surveillance of the space between the walls of an underground storage tank. Intrastate Product: Pesticide products once registered by states for sale and use only in the state. All intrastate products have been converted to full federal registration or canceled. Inventory (TSCA): Inventory of chemicals produced pursuant to Section 8 (b) of the Toxic Substances Control Act. Inversion: A layer of warm air that prevents the rise of cooling air and traps pollutants beneath it; can cause an air pollution episode. Ion: An electrically charged atom or group of atoms. Ion Exchange Treatment: A common water-softening method often found on a large scale at water purification plants that remove some organics and radium by adding calcium oxide or calcium hydroxide to increase the pH to a level where the metals will precipitate out. Ionization Chamber: A device that measures the intensity of ionizing radiation. Ionizing Radiation: Radiation that can strip electrons from atoms; e.g. alpha, beta, and gamma radiation. IRIS: EPA's Integrated Risk Information System, an electronic data base containing the Agency's latest descriptive and quantitative regulatory information on chemical constituents. Irradiated Food: Food subject to brief radioactivity, usually gamma rays, to kill insects, bacteria, and mold, and to permit storage without refrigeration. Irradiation: Exposure to radiation of wavelengths shorter than those of visible light (gamma, x-ray, or ultra- violet), for medical purposes, to sterilize milk or other foodstuffs, or to induce polymerization of monomers or vulcanization of rubber. Irreversible Effect: Effect characterized by the inability of the body to partially or fully repair injury caused by a toxic agent. Irrigation: Applying water or wastewater to land areas to supply the water and nutrient needs of plants. Irrigation Efficiency: The amount of water stored in the crop root zone compared to the amount of irrigation water applied. Irrigation Return Flow: Surface and subsurface water which leaves the field following application of irrigation water. Irritant: A substance that can cause irritation of the skin, eyes, or respiratory system. Effects may be acute from a single high level exposure, or chronic from repeated low-level exposures to such compounds as chlorine, nitrogen dioxide, and nitric acid. Isoconcentration: More than one sample point exhibiting the same isolate concentration. Isopleth: The line or area represented by an isoconcentration. Isotope: A variation of an element that has the same atomic number of protons but a different weight because of the number of neutrons. Various isotopes of the same element may have different radioactive behaviors, some are highly unstable.. Isotropy: The condition in which the hydraulic or other properties of an aquifer are the same in all directions.