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OAPEC: Acronym for Organization of Arab Petroleum Exporting Countries founded in 1968 for cooperation in economic and petroleum affairs.

Obligation To Serve: The obligation of a utility to provide electric service to any customer who seeks that service, and is willing to pay the rates set for that service. Traditionally, utilities have assumed the obligation to serve in return for an exclusive monopoly franchise.

Occupancy Sensor:
A control device that senses the presence of a person in a given space, commonly used to control lighting systems in buildings.

Ocean Discharge Waiver:
A variance from Clean Water Act requirements for discharges into marine waters.

Ocean Thermal Gradient (OTG):
Temperature differences between deep and surface water. Deep water is likely to be 25 to 45 degrees Fahrenheit colder. The term also refers to experimental technology that could use the temperature differences as a means to produce energy.

Octane:
A rating scale used to grade gasoline as to its antiknock properties. Also any of several isometric liquid paraffin hydrocarbons, C8H18. Normal octane is a colorless liquid found in petroleum boiling at 124.6 degrees Celsius.

Octane Rating:
A measure of a gasoline's resistance to exploding too early in the engine cycle, which causes knocking. The higher the rating, the lower the chance of premature ignition.

Odor Threshold: The minimum odor of a water or air sample that can just be detected after successive dilutions with odorless water. It is also called threshold odor.

OECD Guidelines: Testing guidelines prepared by the Organization for Economic and Cooperative Development of the United Nations. They assist in the preparation of protocols for studies of toxicology, environmental fate, etc.

Off-Road: Any non-stationary device, powered by an internal combustion engine or motor, used primarily off the highways to propel, move, or draw persons or property, and used in any of the following applications: marine vessels, construction/farm equipment, locomotives, utility and lawn and garden equipment, off-road motorcycles, and off-highway vehicles.

Off-Site Facility: A hazardous waste treatment, storage or disposal area that is located away from the generating site.

Offsets: A concept whereby emissions from proposed new or modified stationary sources are balanced by reductions from existing sources to stabilize total emissions. Greenhouse gas reduction activities are undertaken to compensate for emissions elsewhere

Offstream Use:
Water withdrawn from surface or groundwater sources for use at another place.

Ohm:
A unit of measure of electrical resistance. One volt can produce a current of one ampere through a resistance of one ohm.

Oil and Gas Waste:
Gas and oil drilling muds, oil production brines, and other waste associated with exploration for, development and production of crude oil or natural gas.

Oil Desulfurization:
Widely used precombustion method for reducing sulfur dioxide emissions from oil-burning power plants. The oil is treated with hydrogen, which removes some of the sulfur by forming hydrogen sulfide gas.

Oil Fingerprinting:
A method that identifies sources of oil and allows spills to be traced to their source.

Oil Shale:
A type of rock containing organic matter that produces large amounts of oil when heated to high temperatures.

Oil Spill: An accidental or intentional discharge of oil which reaches bodies of water. Can be controlled by chemical dispersion, combustion, mechanical containment, and/or adsorption. Spills from tanks and pipelines can also occur away from water bodies, contaminating the soil, getting into sewer systems and threatening underground water sources.

Oligopoly:
A few sellers who exert market control over prices.

Oligotrophic Lakes: Deep clear lakes with few nutrients, little organic matter, and a high dissolved-oxygen level.

On-Site Facility: A hazardous waste treatment, storage or disposal area that is located on the generating site.

Onboard Controls:
Devices placed on vehicles to capture gasoline vapor during refueling and route it to the engines when the vehicle is starting so that it can be efficiently burned.

Onconogenicity: The capacity to induce cancer.

One-hit Model: A mathematical model based on the biological theory that a single "hit" of some minimum critical amount of a carcinogen at a cellular target such as DNA can start an irreversible series events leading to a tumor.

Opacity: The amount of light obscured by particulate pollution in the air; clear window glass has zero opacity, a brick wall is 100 percent opaque. Opacity is an indicator of changes in performance of particulate control systems.

OPEC: Acronym for Organization of Petroleum Exporting Countries founded in 1960 for unify and coordinate petroleum polices of the members. Headquarters is in Vienna, Austria.

Open Burning: Uncontrolled fires in an open dump.

Open Dump: An uncovered site used for disposal of waste without environmental controls.

Open Dump:
An unplanned "landfill" that incorporates few if any of the characteristics of a controlled landfill. There is typically no leachate control, no access control, no cover, no management, and many waste pickers.

Operable Unit: Term for each of a number of separate activities undertaken as part of a Superfund site cleanup. A typical operable unit would be the removal of drums and tanks from the surface of a site.

Optimal Corrosion Control Treatment:
An erosion control treatment that minimizes the lead and copper concentrations at users' taps while also ensuring that the treatment does not cause the water system to violate any national primary drinking water regulations.

Optimization:
An act, process or methodology of making something (as a design, system or decision) as fully perfect, functional or effective as possible.

Options: An option is a contractual agreement that gives the holder the right to buy (call option) or sell (put option) a fixed quantity of a security or commodity (for example, a commodity or commodity futures contract), at a fixed price, within a specified period of time. May either be standardized, exchange-traded, and government regulated, or over-the-counter customized and non-regulated.

Oral Toxicity: Ability of a pesticide to cause injury when ingested.

Organic: 1. Referring to or derived from living organisms. 2. In chemistry, any compound containing carbon.

Organic Chemicals/Compounds:
Naturally occurring (animal or plant-produced or synthetic) substances containing mainly carbon, hydrogen, nitrogen, and oxygen.

Organic Matter:
Carbonaceous waste contained in plant or animal matter and originating from domestic or industrial sources.

Organic Matter:
Organic matter in the soil is made up of living organisms, plant and animal residue, and decomposing products. In general, it only represents between 0.5% and 10% of the soil's mass. Organic matter disappears as a result of erosion, clearing or natural oxidation. However, it boosts fertility and plays an essential role in the stability of the ecosystem. It, therefore, fulfills important environmental functions (preserving soil, protecting water resources and trapping carbon).

Organic Soil Improver:
A stable, dry product with high agricultural value. Organic soil improvers are generated by composting organic waste, which includes food waste, green waste, and wastewater treatment sludge. Rich in humus, it is applied to land to improve various soil properties:

physical: stabilization, aeration, and erosion resistance;

chemical: fertilization and addition of trace elements;

biological: strengthening of plant resistance and the soil's

biological activity.

Organic Waste:
Technically, waste containing carbon, including paper, plastics, wood, food wastes, and yard wastes. In practice in MSWM, the term is often used in a more restricted sense to mean a material that is more directly derived from plant or animal sources, and which can generally be decomposed by microorganisms.

Organism: Any form of animal or plant life.

Organophosphates: Pesticides that contain phosphorus; short-lived, but some can be toxic when first applied.

Organophilic:
A substance that easily combines with organic compounds.

Organotins: Chemical compounds used in anti-foulant paints to protect the hulls of boats and ships, buoys, and pilings from marine organisms such as barnacles.

Orientation: The position of a building relative to the points of a compass.

Original Equipment Manufacturer (OEM):
Refers to the manufacturers of complete vehicles or heavy-duty engines, as contrasted with remanufacturers, converters, retrofitters, up-fitters, and re-powering or rebuilding contractors who are overhauling engines, adapting or converting vehicles or engines obtained from the OEMs, or exchanging or rebuilding engines in existing vehicles.

Original Generation Point:
Where regulated medical or other material first becomes waste.

Osmosis:
The passage of a liquid from a weak solution to a more concentrated solution across a semi permeable membrane that allows passage of the solvent (water) but not the dissolved solids.

Other Ferrous Metals: Recyclable metals from strapping, furniture, and metal found in tires and consumer electronics but does not include metals found in construction materials or cars, locomotives, and ships.

Other Glass:
Recyclable glass from furniture, appliances, and consumer electronics. It does not include glass from transportation products (cars trucks or shipping containers) and construction or demolition debris.

Other Nonferrous Metals:
Recyclable nonferrous metals such as lead, copper, and zinc from appliances, consumer electronics, and non-packaging aluminum products. It does not include nonferrous metals from industrial applications and construction and demolition debris.

Other Plastics: Recyclable plastic from appliances, eating utensils, plates, containers, toys, and various kinds of equipment. It does not include heavy-duty plastics such as yielding materials.

Other Solid Waste: Recyclable nonhazardous solid wastes, other than municipal solid waste, covered under Subtitle D of RARA.

Other Wood:
Recyclable wood from furniture, consumer electronics cabinets, and other non-packaging wood products. Does not include lumber and tree stumps recovered from construction and demolition activities, and industrial process waste such as shavings and sawdust.

Outage (Electric Utility):
An interruption of electric service that is temporary (minutes or hours) and affects a relatively small area (buildings or city blocks).

Outdoor Air Supply:
Air brought into a building from outside.

Outer Continental Shelf (OCS): The submerged lands extending from the out limit of the historic territorial sea (typically three miles) to some undefined outer limit, usually a depth of 600 feet. In the United States, this is the portion of the shelf under federal jurisdiction.

Outfall: The place where effluent is discharged into receiving waters.

Outside Air: Air taken from outdoors and not previously circulated through the HVAC system.

Over Generation: A condition that occurs when total PX participant demand is less than or equal to the sum of regulatory must-take generation, regulatory must-run generation, and reliability must-run generation.

Overburden: Rock and soil cleared away before mining.

Overdraft: The pumping of water from a groundwater basin or aquifer in excess of the supply flowing into the basin; results in a depletion or "mining" of the groundwater in the basin.

Overfire Air: Air forced into the top of an incinerator or boiler to fan the flames.

Overflow Rate: One of the guidelines for the design of the settling tanks and clarifiers in a treatment plant; used by plant operators to determine if tanks and clarifiers are over or under-used.

Overhang:
Any horizontal projection that serves as a shading element for a window.

Overland Flow:
A land application technique that cleanses waste water by allowing it to flow over a sloped surface. As the water flows over the surface, contaminants are absorbed and the water is collected at the bottom of the slope for reuse.

Oversized Regulated Medical Waste:
Medical waste that is too large for plastic bags or standard containers.

Overturn: One complete cycle of top to the bottom mixing of previously stratified water masses. This phenomenon may occur in spring or fall, or after storms, and results in uniformity of chemical and physical properties of water at all depths.

Oxidant:
A collective term for some of the primary constituents of photochemical smog.

Oxidation: The chemical addition of oxygen to break down pollutants or organic waste; e.g., destruction of chemicals such as cyanides, phenols, and organic sulfur compounds in sewage by bacterial and chemical means.

Oxidation Pond: A man-made (anthropogenic) body of water in which waste is consumed by bacteria, used most frequently with other waste-treatment processes; a sewage lagoon.
Oxidation-Reduction Potential: The electric potential required to transfer electrons from one compound or element (the oxidant) to another compound (the reductant); used as a qualitative measure of the state of oxidation in water treatment systems.

Oxygenate: A term used in the petroleum industry to denote octane components containing hydrogen, carbon, and oxygen in their molecular structure. It includes ethers such as MTBE and ETBE and alcohols such as ethanol or methanol. The oxygenate is a prime ingredient in reformulated gasoline. The increased oxygen content given by oxygenates promotes a complete combustion, thereby reducing tailpipe emissions.

Oxygenated Fuels: Gasoline which has been blended with alcohols or ethers that contain oxygen in order to reduce carbon monoxide and other emissions.

Oxygenated Solvent:
An organic solvent containing oxygen as part of the molecular structure. Alcohols and ketones are oxygenated compounds often used as paint solvents.

Ozonation/Ozonator:
Application of ozone to water for disinfection or for taste and odor control. The Ozonator is the device that does this.

Ozone: A kind of oxygen that has three atoms per molecule instead of the usual two. Ozone is a poisonous gas, but the ozone layer in the upper atmosphere shields life on earth from deadly ultraviolet radiation from space. The molecule contains three oxygen atoms (O3).

Ozone (O3): Found in two layers of the atmosphere, the stratosphere, and the troposphere. In the stratosphere (the atmospheric layer 7 to 10 miles or more above the earth's surface) ozone is a natural form of oxygen that provides a protective layer shielding the earth from ultraviolet radiation. In the troposphere (the layer extending up 7 to 10 miles from the earth's surface), ozone is a chemical oxidant and major component of photochemical smog. It can seriously impair the respiratory system and is one of the widest spread of all the criteria pollutants for which the Clean Air Act required EPA to set standards. Ozone in the troposphere is produced through complex chemical reactions of nitrogen oxides, which are among the primary pollutants emitted by combustion sources; hydrocarbons, released into the atmosphere through the combustion, handling and processing of petroleum products; and sunlight.

Ozone Depleting Substance (ODS):
Substances that release chlorine or bromine atoms when they break down which deplete the ozone.

Ozone Depletion: Destruction of the stratospheric ozone layer which shields the earth from ultraviolet radiation harmful to life. This destruction of ozone is caused by the breakdown of certain chlorine and/or bromine containing compounds (chlorofluorocarbons or halons), which break down when they reach the stratosphere and then catalytically destroy ozone molecules.

Ozone Hole: A thinning break in the stratospheric ozone layer. Designation of the amount of such depletion as an "ozone hole" is made when the detected amount of depletion exceeds fifty percent. Seasonal ozone holes have been observed over both the Antarctic and Arctic regions, part of Canada, and the extreme north-eastern United States.

Ozone Layer: The protective layer in the atmosphere, about 15 miles above the ground, that absorbs some of the sun's ultraviolet rays, thereby reducing the amount of potentially harmful radiation that reaches the earth's surface.