pacing

packaging The assembly of one or more containers and any other components necessary to assure minimum compliance with a program's storage and shipment packaging requirements. Also, the containers, etc., involved.

packed bed scrubber An air pollution control device containing a depth of media in which emissions pass through alkaline water to neutralize hydrogen chloride gas.

packed tower A pollution control device that forces dirty air through a tower packed with crushed rock or wood chips while liquid is sprayed over the packing material. The pollutants in the air stream either dissolve or chemically react with the liquid.

packed tower aeration A method of treating water to remove volatile organic chemical (VOC) contaminants. As water is mixed with air, VOCs pass from water to air which then passes through carbon filters to trap the contaminants.

packer/repacker A firm or individual that packs a product or products into different containers without making any change in the form of the product. Includes chemical distributors of products, such as activated carbon.

packing list Inventory of contents.

paddle aerator

paddle wheel

palatable water Water at a desirable temperature that is free from objectionable tastes, odors, colors, and turbidity. Pleasing to the senses.

P-A Medium (Presence-Absence Medium) One of the media that can be used for the Presence-Absence procedure.

pan coefficient

pandemic A widespread epidemic throughout an area, nation, or the world.

P-A Procedure (Presence-Absence Procedure) A method of testing for coliforms that reports only the presence or absence of organisms rather than density. If gas production occurs, results are reported as positive (coliforms present), or, if not, as negative (coliforms absent).

parabolic weir

parallax reduction A processing of observed high and low waters to obtain quantities depending upon changes in the distance of the Moon, such as perigean and apogean ranges.

parallel plate intake Intake of a stilling or protective well with two parallel plates attached below. The plates are typically three times the diameter of the well and are spaced three inches apart. The plates are used to minimize current-induced draw-down (Bernoulli effect) error in water level measurements.

paralysis Loss of sensation or loss of muscular function usually due to an injury to a nerve or a lesion within the central nervous system.

parameter A definable characteristic of an item, device, or system in mathematics which remains constant during calculation.

paraquat A standard herbicide used to kill various types of crops.

parasite An organism that derives its nourishment from a living plant or animal host. May be pathogenic, but does not necessarily cause disease.

parasitic bacteria

parent material

parshall flume A device used to measure the flow in an open channel. The flume narrows to a throat of fixed dimensions and then expands again. The rate of flow can be calculated by measuring the difference in head (pressure) before and at the throat of the flume when the flow changes from normal to critical depth conditions.

partial diversion

partial participation The engagement of State and local government emergency personnel in an exercise sufficient to adequately test direction and control functions for protective action decision making related to emergency action levels and communication capabilities among affected State and local governments and the licensee.

partial pressure

partial vacuum

participation rate Portion of population participating in a recycling program.

particle count Results of a microscopic examination of treated water with a special “particle counter” that classifies suspended particles by number and size.

particle density The mass per unit volume of particulates, usually expressed in grams per cubic centimeter.

particulates Very small solid particles suspended in water or air. Varying in size, shape, density, and electrical charge, they can be gathered together by coagulation and flocculation.

partition coefficient The ratio of concentration of a chemical sorbed to the solid phase to its concentration in the aqueous phase (Kd).

partly submerged orifice

partnership Formal, collaborative working relations with other government, academic, or private industry entities.

part per billion (ppb) A unit commonly used to express concentration or contamination ratios. A part per billion equals 1 µg/L which is the preferred term.

parts per million (ppm or PPM) A measurement of concentration on a weight or volume basis. This term is equivalent to milligrams per liter (mg/L) which is the preferred term.

pascal The pressure or stress of one newton per square meter, abbreviated Pa.

1 psi = 6,895 Pa = 6.895 kN/sq m = 0.0703 kg/sq cm

pass

passerine Perching birds, e.g., sparrows, including all songbirds.

passivator An inhibitor that changes the potential of a metal appreciably to a more cathodic or noble value.

passive The state of metal when its behavior is much more noble (resists corrosion) than its position in the Emf series would predict. This is a surface phenomenon.

passive-active cell A cell composed of a metal in the passive state and the same metal in the active state.

passivity The phenomenon of an active metal becoming passive.

pasteurization The process of killing microorganisms in a product, such as milk, by heating at controlled temperatures without changing the natural characteristics of the product treated.

pathogenic Capable of producing injury or disease.

pathogenic bacteria

pathogenicity The capacity of an agent to cause disease in a susceptible host. Also see virulence.

pathogenic organisms Organisms including bacteria, viruses, protozoa, or cysts, capable of causing diseases (typhoid, cholera, dysentery) in a host (such as a person). There are many types of organisms which do not cause disease. These organisms are called nonpathogenic.

pathogens Microorganisms (e.g., bacteria, viruses, or protozoa) that can cause disease in other organisms or in humans, animals, and plants. Sewage, runoff from farms or rural areas populated with domestic and wild animals, may contain pathogens. If drinking water, water used for swimming, or fish and shellfish are contaminated with pathogens, public use or consumption can then result in transmission of pathogens and result in serious illness.

pathology The scientific study of disease, including causes, symptoms, signs, and various structural and functional alteration which may occur in its course.

peak

peak demand The highest point of total water usage experienced by a system, measured on an hourly and daily basis.

peak discharge Rate of discharge of a volume of water passing a given location. Usually expressed in cubic feet per second.

peak electricity demand The maximum electricity used to meet the cooling load of a building or buildings in a given area.

peak levels Levels of airborne pollutant contaminants much higher than average or occurring for short periods of time in response to sudden releases.

peak load The maximum rate of flow to a wastewater treatment plant.

peat soil

pelagic zone Free open water of the ocean or a lake with no association with the bottom.

pelorus An instrument used on a vessel in connection with a current line and current pole to obtain the set of the current. In its simplest form, it is a disk about 8 inches in diameter and graduated clockwise for every 5° or 10°. It is mounted rigidly on the vessel, usually with the 0° mark forward and the diameter through this mark parallel with the keel. Bearings are then related to the vessel's compass and converted to true.

penalty Damages assessed against a contractor, supplier or vendor, usually connected with failure to deliver merchandise.

pendente lite Pending while litigation continues (or is pending).

penstock

peptide bond A chemical bond between the carboxyl (-cooh) group of one amino acid and the amino (- nh₂) group of another.

per capita residential use Residential use divided by the total population served.

per capita use The average amount of water used per person during a standard time period, generally expressed as per day.

percentage reduction

percentile Percentage of the population equal to or smaller than the dimension given.

percent saturation The amount of a substance that is dissolved in a solution compared with the amount that could be dissolved in the solution, expressed as a percent.

perched groundwater

perched spring

perched subsurface stream

perched water A zone of unpressurized water held above the water table by impermeable strata.

perched water table

percolating filter

percolating water Water that passes through soil or rocks under the force of gravity.

percolation 1) The slow seepage of water into and through porous media, such as soil in the ground. 2) The slow passage of water through a filter medium.

percolation path

percolation rate

perennial interrupted stream

perennial stream A stream which flows all year round.

performance data (for incinerators) Information collected, during a trial burn, on concentrations of designated organic compounds and pollutants found in incinerator emissions. Data analysis must show that the incinerator meets performance standards under operating conditions specified in the RCRA permit. See trial burn, performance standards. (f or other processes) Test results obtained from a treatment process operating under known conditions.

performance evaluation sample A reference sample provided to a laboratory for the purpose of demonstrating that the laboratory can successfully analyze the sample within limits of performance specified by the EPA. The true value of the concentration of the reference material is unknown to the laboratory at the time of the analysis.

performance measures Quantifiable indicators that can be tracked to access progress in achieving predetermined goals.

performance standards (1) Regulatory requirements limiting the concentrations of designated organic compounds, particulate matter, and hydrogen chloride in emissions from incinerators. (2) Established operating standards for various permitted pollution control systems, asbestos inspections, and various program operations and maintenance requirements.

perigean tides or tidal currents Tides of increased range or tidal currents of increased speed occurring monthly as the result of the Moon being in perigee. The perigean range (Pn) of tide is the average range occurring at the time of perigean tides. It is larger than the mean range where the type of tide is either semi diurnal or mixed, and is of no practical significance where the type of tide is predominantly diurnal.

perigee The point in the orbit of the Moon or man-made satellite nearest to the Earth. The point in the orbit of a satellite nearest to its companion body.

perihelion The point in the orbit of the Earth (or other planet, etc.) nearest to the Sun.

period

periodicity A regular cyclic behavior of an organ, cell, or organism.

period of record The time interval during which meteorological and climatic data have been gathered at a climatic station.

period prevealence The number of existing cases of an illness during a period or interval, divided by the average population.

peripheral flow

peripheral pump

peripheral weir

periphyton Microscopic plants and animals that are attached firmly to solid surfaces under water, such as rocks, logs, pilings, and other structures.

peritrichous Having the entire surface of the cell covered with flagella.

permafrost Permanently frozen subsoil thawing at the surface in summer, characteristic of Arctic tundra.

permanent hardness

permanent injunction A decree of permanent injunction may be entered at any time after the complaint is filed, either following a hearing or as a result of a negotiated settlement. Defendants in an injunction proceeding may consent to a decree of permanent injunction just as they consent to a consent decree of condemnation in a seizure action. Should the defendant not consent to such a decree, a trial is held in which, to prevail, the government must prove each element of its case by a preponderance of the evidence. As its name implies, a decree of permanent injunction remains in effect until it is dissolved by an order of the court. A decree of permanent injunction perpetually restrains the defendants from engaging in specified violative practices and remains in force until termination.

permanent stream

permanent threshold shift (PTS) An irreversible increase in hearing threshold level.

permanent wilting coefficient

permeability The ability of a porous medium to transmit fluids under a hydraulic gradient. Highly permeable soils are more likely to result in the leaching of contaminants than soils of lower permeability.

permeability coefficient

permeable

permeable confining bed

permeameter

permeate To penetrate and pass through, as water penetrates and passes through soil and other porous materials.

permissible dose The dose of a chemical that may be received by an individual without the expectation of a significantly harmful result.

permit An authorization, license, or equivalent control document used by EPA or an approved state agency to implement the requirements of an environmental regulation; e.g., a permit to operate a wastewater treatment plant.

persistence The length of time a compound stays in the environment once introduced.

persistent pesticides Pesticides that do not break down chemically or break down very slowly and remain in the environment after a growing season.

personal air samples Air samples taken with a pump is directly attached to the worker with the collecting filter and cassette placed in the worker's breathing zone.

person-time rate A measure of the incidence rate of an event, e.g., a disease or death, in a population at risk over an observed period to time, that directly incorporates time into the denominator.

pest An insect, rodent, nematode, fungus, weed, or other form of terrestrial or aquatic plant or animal life that is injurious to health or to the environment.

pesticide Any substance or chemical designed or formulated to kill or control weeds or animal pests. Also see algicide, herbicide, insecticide, and rodenticide.

pervious

pesticide degradate A generic term that includes breakdown products of a pesticide active ingredient resulting from biological processes (i.e., metabolites) and chemical processes (i.e., hydrolysis, photolysis, photooxidation). See degradate.

pesticide metabolite A product of biological processes (e.g., metabolism or the chemical changes in living cells) of a pesticide active ingredient by microorganisms, plants, or animals.

pesticide tolerance The amount of pesticide residue allowed by law to remain in or on a harvested crop.

pet cock

petri dish A glass or plastic dish with cover used to culture microorganisms.

petroleum derivatives Chemicals formed when gasoline breaks down in contact with groundwater.

petrology The study of the origins, history, occurrence, structure, chemical composition, and classification of rocks.

pH (power hydrogen) The negative logarith of hydrogen-ion concentration to measure the acidity or alkalinity of a liquid or solid material. The range of pH goes from 0 to 14 where 0 is most acid and 14 most basic and 7 neutral. Natural waters have a pH between 6.5 and 8.5.

phage typing The characterization of a bacterium by the identification of those bacteriophages to which the bacterium is susceptible. A means of strain differentiation.

phagocyte A cell that engulfs and destroys foreign particles or microorganisms by digestion.

phanerogam A general name for seed-bearing or higher plants.

pharmaceutical A chemical drug or medicine.

pharmacokinetics The dynamic behavior of chemicals inside biological systems; it includes the processes of uptake, distribution, metabolism, and excretion.

phase

Phase I The first phase of EPA's regulatory development approach. It covers the first eight VOCs to be regulated.

Phase II The second phase of EPA's regulatory approach. Phase II covers additional VOCs, pesticides, and inorganic chemicals.

Phase V Phase V of EPA's regulatory approach; covers 23 additional inorganic chemicals, VOCs, pesticides, and other organic contaminants.

phenols Organic compounds that are byproducts of petroleum refining, tanning, and textile, dye, and resin manufacturing. Low concentrations cause taste and odor problems in water; higher concentrations can kill aquatic life and humans.

phenolic compounds Organic compounds that are derivatives of benzene.

phenology The study of the periodic phenomena of nature, especially animal and plant life in their relations to weather and climate, e.g., bird migration, flowering, bud opening, freezing, and thawing.

phenolphthalein alkalinity The alkalinity in a water sample measured by the amount of standard acid required to lower the pH to a level of 8.3, as indicated by the change in color of phenolphthalein from pink to clear. Phenolphthalein alkalinity is expressed as milligrams per liter equivalent calcium carbonate.

phenol wastes

phosphates Certain chemical compounds containing phosphorus.

phosphorous An element that, while essential to life, contributes to the eutrophication of lakes and other bodies of water.

photic zone The region of aquatic environments in which the intensity of light is sufficient for photosynthesis.

photochemical oxidants Air pollutants formed by the action of sunlight on oxides of nitrogen and hydrocarbons. photochemical smog Air pollution caused by chemical reactions of various pollutants emitted from different sources.

photochemistry The branch of chemistry that deals with the chemical action of light.

photometer

photoperiodism Response of plants and animals to the relative duration of light and darkness.

photosynthesis The formation of carbohydrates from carbon dioxide and water by plants using chlorophyll and the energy of light.

photosynthesis bacteria

phototropism The behavorial response of an animal or microbe to light stimulus.

phragmites A genus of reed; tall (2-12 feet) grasses growing in wetlands and marshes.

phreatophyte A plant that derives its water supply from groundwater and is more or less independent of rainfall.

phteatic

phylogeny The evolutionary history of a group of organisms.

phylum A primary category of the animal kingdom.

physical analysis

physical and chemical treatment Processes generally used in water and wastewater treatment facilities. Physical treatment includes sedimentation and filtration. Chemical treatment includes coagulation, chlorination, or ozonation.

physical assets

physical components

physical life The period during which it is physically possible to provide planned project services by operation, maintenance, and replacement of project facilities. It may be equal to, but is generally greater than economic life.

physical waste treatment Separation of suspended matter from water or wastewater. Racks, screens, comminutors, sedimentation, and flotation are physical treatment processes.

physiognomy The general outward appearance of a community, determined by the life form of the dominant species, e.g., forest or grassland.

physiographic balance

phytoplankton The term for plants and plant-like organisms present in plankton.

phytotoxicity A toxic effect produced by or on a plant.

pico A prefix used in the metric system and other scientific systems of measurement which means 10^-12 or 0.000000000001.

picocurie (pCi) A measure of radioactivity. One picocurie of radioactivity is equivalent to 0.037 nuclear disintegrations per second or 2.22 nuclear transformations per minute.

pie chart A circular chart in which the size of each slice is proportional to the frequency of each category of a variable.

pier A structure extending out into the water from the shore, to serve as either a landing place, or boat mooring structure, or as a recreational facility, etc., rather than to afford coastal protection.

piezometer An instrument for measuring pressure head in a conduit, tank, soil, etc. It usually consists of a small pipe or tube tapped into the side of the container, the inside end being flush with, and normal to, the water face of the container, connected with a manometer pressure gage, mercury of water column, or other device for indicating pressure head.

piezometric head

piezometric level (or surface) Confined groundwater is usually under pressure because of the weight of the overburden and the hydrostatic head. If a well penetrates the confining layer, water will rise to this level, the piezometric level, the artesian equivalent of the water table. If the piezometric level is above ground level, the well discharges as a flowing well, artesian well, or a spring.

piezometric map

piezometric tube

pig

pile

piling

pilot plant A small-scale version of a treatment process used to monitor treatment performance.

pilot-scale tests Tests run under actual site conditions to identify potential problems before full-scale implementation.

pin floc Very fine floc particles with poor settling characteristics.

pioneer Any early occupant of an open or disturbed area of ground.

pipe diameter

pipe finder

pipe fittings

pipe gallery

pipeline

pipe offeset

piping

piping system

piston pump

Pitot tube

pit privy

pitting Highly localized corrosion resulting in deep penetration at only a few spots.

pitting factor The depth of the deepest pit divided by the average penetration as calculated from weight loss.

placard A standard device or sign affixed to the outside of a vehicle to identify the hazards associated with the cargo.

plain

plain sedimentation Sedimentation without the aid of chemicals.

plain settling tank

plaintiff The party who institutes the lawsuit, the opposite of the defendant. The government is the plaintiff in all the actions it initiates.

plankton The term for drifting or floating microscopic flora and fauna in a body of water. Macroplankton are relatively large (1.0 mm to 1.0 cm); mesoplankton are intermediate size; microplankton are small.

plant 1) Vegetation growing in soil or water which utilize nutrients for growth. 2) The land, buildings, and equipment within a fixed location, used to process water and wastewater, defined as treatment works.

plant nutrients See nutrients.

plan view A diagram or photo showing a facility as it would appear when looking down on top of it.

plaque The clear area in a plated bacterial culture due to lysis by a phage.

plasma-arc reactor An incinerator that operates at extremely high temperatures; treats highly toxic wastes that do not burn easily.

plasmid A circular piece of DNA that exists apart from the chromosome and replicates independently of it. Bacterial plasmids carry information that renders the bacteria resistant to antibiotics.

plasticity index

plastid Any of various small bodies of specialized protoplasm lying in the cytoplasm of cells and serving in many cases as centers of special metabolic activities.

plate count

plate press

plate tower scrubber An air pollution control device that neutralizes hydrogen chloride gas by bubbling alkaline water through holes in a series of metal plates.

platting The legal division of land, by public record, usually preliminary to sale for development.

pleadings The papers filed in court to initiate and defend a suit, such as the complaint, and answer, setting forth the allegations and defense in the case.

pleuston The community of organisms floating on a lake's surface.

plezometer Generally a small-diameter, nonpumping well used to measure the elevation of the water table or potentiometric surface.

plug

plug flow A type of flow that occurs in tanks, basins, or reactors when a volume of water moves through without ever dispersing or mixing with the other volume present within the tank and is discharged from the tank over a time period equivalent to the theoretical detention time..

plug flow reactor Idealized continuous flow reactor in which fluid particles are discharged in the same order in which they entered at the end of the theoretical detention time.

plugging Act or process of stopping the flow of water, oil, or gas into or out of a formation through a borehole or well penetrating the formation.

plug valve

plumbing The practice, materials, and fixtures used in the installation, maintenance, extension, and alteration of all piping, fixtures, appliances and appurtances in connection with any of the following: sanitary drainage or storm drainage facilities, the venting system and the public or private water-supply systems, within or adjacent to any building, structure or conveyance; also the practice and materials used in the installation, maintenance, extension, or alteration of storm water, liquid waste, or sewerage, and water-supply systems of any premises to their connection with any point of public disposal or other acceptable terminal.

plumbing fixtures

plumbing system

plume The extent or area of movement of a measurable discharge of a contaminant from a given point of origin.

plume exposure pathway A term referring to whole body external exposure to gamma radiation from the plume and from deposited materials and inhalation exposure from the passing radioactive plume. The duration of primary exposures could range in length from hours to days.

plunger pump

plutonium A radioactive metallic element chemically similar to uranium.

pluviometer

pluviometric coefficient

PM-10 A standard for measuring the amount of solid or liquid matter suspended in the atmosphere, i.e. the amount of particulate matter over 10 micrometers in diameter.

pneumatic

pneumatic ejector

poikilothermic A cold-blooded organism (generally other than birds and mammals) whose body temperature varies approximately with the environment.

point gauge

point of application

point of disinfectant application The point where disinfectant is applied and flows downstream of that point is not subject to recontamination.

point-of-entry treatment device A treatment device applied to the drinking water entering a house or building for the purpose of reducing contaminants in the drinking or process water distributed throughout the house or building.

point-of-use treatment device A treatment device applied to a single tap used for the purpose of reducing contaminants in drinking water at that one tap.

point prevalence The amount of a particular disease present in a population at a single point in time.

point source A stationary location of fixed facility from which pollutants are discharged or emitted. Also, any single identifiable source of pollution, e.g., a pipe, ditch, ship, ore pit, factory smokestack.

poison A substance, which upon contact or being introduced into an organism, impairs or prevents normal metabolic processes from taking place, thus altering the normal functioning of organs or tissues.

polarization The shift in the electrode potential resulting from the effects of current flow, measured with respect to the “zero-flow” (reversible) potential; i.e., the counter-electro magnetic force caused by the products formed or concentration changes in the electrolyte.

polar-orbiting satellite A satellite whose orbit passes over both of the earth's between poles.

pole shader A copper bar circling the laminated iron core inside the coil of a magnetic starter.

pollen The fertilizing element of flowering plants; background air pollutant.

pollutant Any substance introduced into the environment that adversely affects the usefulness of a resource.

pollutant standard index (PSI) Measure of adverse health effects of air pollution levels in major cities.

pollution The presence of matter or energy whose nature, location, or quantity produces undesired environmental effects. Under the Clean Water Act, for example, the term is defined as the man-made or man-induced alteration of the physical, biological, and radiological integrity of water that impairs the use of that water for its intended purposes.

pollutional index

pollutional load

pollution hazard A condition through which an aesthetically objectionable or degrading material may enter the environment, or a waterworks, or a consumer's water system.

pollution prevention The active process of identifying areas, processes, and activities that create excessive waste byproducts for the purpose of substitution, alteration, or elimination of the process to prevent waste generation.

polonium A radioactive element that occurs in pitchblende and other uranium containing ores.

polychlorinated biphenyls (PCBs) Highly toxic organic chemicals (once widely used in electrical transformers and other industrial equipment to provide resistance to conduction) known to cause skin diseases and suspected of causing birth defects and cancer.

polyclimax Two or more simultaneously existing, stable, self-maintaining communities controlled by local environmental conditions in a larger area. See climax.

polyclonal Derived from different types of cells.

polyelectrolyte A high-molecular-weight substance having points of positive or negative charges that is formed by either natural or man-made processes. Natural polyelectrolytes may be of biological origin or derived from starch products and cellulose derivatives. Man-made polyelectrolytes consist of simple substances that have been made into complex substances of high molecular weight. Used with other chemical coagulants to aid in binding small suspended particles to larger chemical flocs for their removal from water. Often called a polymer.

polymer A chemical formed by the union of many monomers (a molecule of low molecular weight). Polymers are used with other chemical coagulants to aid in binding small suspended particles to larger chemical flocs for their removal from water. All polyelectrolytes are polymers, but not all polymers are polyelectrolytes.

polythermal (rare) Confined to high temperatures in contrast to oligothermal.

pond A small lake-like body of water or wastewater that can be used to store flows as part of a treatment process..

pondage

ponding The formation of pools or ponds as a result of surface clogging of porous media through which water or wastewater flows.

pool

pool height The height of the water behind a dam. Various datums may be used and various pool height may be used, e.g., conservation pool, flood control pool, etc.

population 1) A group of organisms of the same species. 2) The number of inhabitants of a specific area or region. 3) A group of subjects studied, usually 30 or more.

population at risk A population subgroup that is more likely to be exposed to a chemical or is more sensitive to a chemical than is the general population.

population density The number of individuals of a population per unit area.

population equivalent A means of expressing the amount, or strength, of organic matter in wastewater.

population index An estimate of the size or other characteristic of a population, obtained by indirect means, such as bird songs, animal droppings.

population irruption A sudden large increase in population density, resulting in emigration or immigration.

population pressure A metaphor implying the magnitude of demand of a population on space or other resources.

pore A very small open space in a rock or between granular material, including soils. Also see interstice.

pore water

porosity The ratio of the volume of small openings in soil or rock to its total volume, usually expressed as a percentage. Of interest as it determines the capacity of soil or rock to hold water.

porous

port

positive confining bed

positive displacement pump A type of piston, diaphragm, gear or screw pump that delivers a constant volume with each stroke. Positive displacement pumps are used as chemical solution feeders.

positive head

postauthorization studies Planning and design that is accomplished after the project is authorized.

postchlorination The addition of chlorine to the plant effluent, following treatment, for disinfection purposes. The application of chlorine to water subsequent to treatment.

post-closure The period following the shutdown of a waste management or manufacturing facility; for monitoring purposes, often considered to be 30 years.

post-consumer recycling Reuse of materials generated from residential and consumer waste, e.g. converting wastepaper from offices into corrugated boxes or newsprint.

post-storm report A report issued by a local National Weather Service office summarizing the impact of a tropical cyclone on its forecast area. These reports include information on observed winds, pressures, storm surges, rainfall, tornadoes, damage and casualties.

potable Suitable for drinking and cooking.

potable water Water free from impurities present in amounts sufficient to cause disease or harmful physiological effects. Its bacteriological and chemical quality shall conform to the requirements of the Public Health Service Drinking Water Standards or the Virginia Waterworks Regulations.

potamology The study of streams, especially large rivers.

potassium permanganate

potency Amount of material necessary to produce a given level of a deleterious effect.

potential

potential energy

potential head

potential evapotranspiration Water loss which will occur if at no time there is a defiency of water in the soil for use by vegetation and for evaporation. Varies by season.

potentially responsible party (PRP) Any individual or company-including owners, operators, transporters or generators-potentially responsible for, or contributing to a spill or other contamination.

potentiation The effect of one chemical to increase the effect of another chemical.

potentiometric surface A surface that represents the total head of groundwater in a confined aquifer that is defined by the level to which water will rise in a well.

pothole

power

power factor The ratio of the true power passing through an electric circuit to the product of the voltage and amperage in the circuit. This is a measure of the lag or load of the current with respect to the voltage.

power head

power pump

ppb Parts per billion. Also µg/L or micrograms per liter.

ppm Parts per million. Also mg/L or milligrams per liter.

practical quantitation level (PQL) The lowest level achievable by good laboratories within specified limits during routine laboratory operating conditions.

preaeration A preparatory treatment of water or wastewater, prior to additional treatment, consisting of aeration to remove gases, add oxygen, promote flotation of grease, and aid coagulation.

preauthorization studies Studies made prior to and leading to authorization of a project.

prechlorination The addition of chlorine at the head works of the treatment plant prior to other treatment processes for disinfection and control of tastes, odor, and aquatic growths. Also applied to aid in coagulation and settling. The application of chlorine to water prior to filtration.

precipitable water

precipitate 1) An insoluble, finely divided substance which is a product of a chemical reaction within a liquid. 2) The separation from solution of an insoluble substance.

precipitation 1) The process by which atmospheric moisture falls onto a land or water surface, such as rain, snow

precipitation gauge

precipitation mass curve, or sleet. 2) The chemical transformation of a substance in solution into an insoluble form (precipitate).

precipitation rate, sprinkling The surface application rate for landscape watering, usually expresed in inches per hour.

precipitator Pollution control device that collects particles from an air stream.

precision 1) A description of how sets of measurements or estimates cluster about some value. 2) The ability of an instrument to measure a process variable and to repeatedly obtain the same result; the ability of an instrument to reproduce the same results.

preconstruction planning The planning work on an authorized project necessary to advance the project to the stage where the first major construction contract may be advertised after construction funds are appropriated.

precursor 1) In photochemistry, a compound antecedent to a volatile organic compound (VOC). Precursors react in sunlight to form ozone or other photochemical oxidants. 2) In water or wastewater treatment, a compound that may be hologenated.

precursor, THM Natural organic compounds found in all surface and groundwaters. These compounds may react with halogens (such as chlorine) to form trihalomethanes (THMs); precursors must be present in order for THMs to form.

predator An organism, usually an animal, that kills and consumes another organism in whole or part.

predatory fish A fish living by killing and eating other fish.

predator chain See food chain; also trophic and biotic pyramid.

prediction error The difference between an observed value and a model predicted value.

predictive value positive A measure of the predictive value of a reported case or epidemic; the proportion of cases reported by a surveillance system or classified by a case definition which are true cases.

predominant Same as dominant. An organism of outstanding abundance or obvious importance in a community.

pre-eye landfall time The time before actual hurricane eye landfall within which evacuation cannot be carried out because of earlier effects, such as the inundation of evacuation routes from the storm surge or rainfall and the arrival of sustained gale force winds. It is composed of the time of arrival of sustained gale-force winds or the time roadway inundation from storm surge/rainfall begins, whichever comes first.

preliminary assessment The process of collecting and reviewing available information about a known or suspected waste site or release.

preliminary filter

preliminary injunction Whether or not a temporary restraining order has been obtained, a motion for preliminary injunction is subject to a full hearing in which (a) evidence by affidavit, and/or (b) testimony of witnesses is presented, depending on the practice of the court. Once the motion is granted, or the defendants consent to the entry of a decree, the preliminary injunction is in effect. A preliminary injunction may stand indefinitely on the court record until the case is settled or a permanent injunction has been entered, after trial. A preliminary injunction may be dismissed, or a trial for permanent injunction may be set by the court, at the request of either party, at any time.

preliminary report A report summarizing the life history and effects of an Atlantic or eastern Pacific tropical cyclone. It contains a summary of the cyclone life cycle and pertinent meteorological data, including the post-analysis best track (six-hourly positions and intensities) and other meteorological statistics. It also contains a description of damage and casualties the system produced, as well as information on forecasts and warnings associated with the cyclone. NHC writes a preliminary report on every tropical cyclone in its area of responsibility.

preliminary treatment

premium An additional charge for real estate property with an amenity such as a water view or a view of wooded land.

prenatal Before birth.

prescriptive Land use or water rights which are acquired by occupying land for established time periods or diverting water and putting it to use in accordance with specified procedures. These procedures include filing a request to use unused water in a stream, river, or lake with a state agency.

pre-sentence investigation An investigation of convicted parties prior to the imposition of sentence.

present movement The best estimate of the movement of the center of a tropical cyclone at a given time and given position. This estimate does not reflect the short-period, small scale oscillations of the cyclone center.

present value The value today of a future sum or series of sums of money, calculated by discounting the future sums with an appropriated rate.

present worth

preservative A chemical substance used to preserve food or other organic material from decomposition or fermentation.

presettling

press filter

pressure The force per unit area exerted by the weight of the atmosphere above a point on or above the earth's surface. A1) 2) lso known as atmospheric pressure or barometric pressure.

pressure control A switch which operates on changes in pressure. Usually this is a diaphragm pressing against a spring. When the force on the diaphragm overcomes the spring pressure, the switch is actuated (activated).

pressure energy

pressure filter

pressure gauge

pressure head The vertical distance (in feet) equal to the pressure (in psi) at a specific point. The pressure head is equal to the pressure in psi times 2.31 ft/psi.

pressure intensity

pressure-reducing valve

pressure-regulating valve

pressure regulator A post-meter device used to limit water pressure.

pressure sewer A system of pipes in which the water, wastewater, or other liquid is transported to a higher elevation by applying a downstream pumping force or pressure head.

pressure tank

pressurized water reactor (PWR) A type of reactor system that maintains cooling water at a very high pressure which prevents water from boiling in the reactor core during normal operation. Heat from the reactor is transferred to another system of water in a steam generator to provide steam for generating electricity.

pressure zone

prestressed concrete pipe

presumptive test The first phase of the Multiple Tube Fermentation Procedure. Positive tubes are indicated by the presence of gas or clouding of the LTB medium.

pretreatment 1) The use of physical treatment operations, including racks, screens, communitors, and grit removal devices to remove metal, rocks, sand, eggshells, and similar materials which may hinder the operation of a treatment plant. 2) Processes used to reduce, eliminate, or alter the nature of wastewater from nondomestic sources before they are discharged into publicly owned treatment works.

pre-trial conference A meeting between the court and the attorneys for the parties in preparation for trial, e.g. to consider various ways to limit the issues for trial through admissions or agreements of counsel.

prevalence The number or proportion of cases or events or conditions in a given population.

prevalence rate The proportion of persons in a population who have a particular disease or attribute at a specified point in time or over a specified period of time.

prevalence study An epidemiological study which examines the relationships between diseases and exposures as they exist in a defined population at a particular point in time.

prevalent levels Levels of airborne contaminant occurring under normal conditions.

prevalent level samples Air samples taken under normal conditions (also known as ambient background samples).

prevention of significant deterioration (PSD) A program in which state and/or federal permits are required in order to restrict emissions from new or modified sources in places where air quality already meets or exceeds primary and secondary ambient air quality standards.

prey An organism killed and at least partially consumed by a predator.

price elasticity of demand A measure of the responsiveness of water usage to changes in price, measured by the percentage change in usuage divided by the percentage change in price.

primacy The responsibility for ensuring that a law is implemented and the authority to enforce a law and related regulations. A primacy agency has the primary responsibility for administering and enforcing regulations.

primacy agency The agency that is responsible for regulation of water supply systems in states and on Indian lands. In most cases, this is a state agency that regulates water supply systems. In Virginia, it is the state Department of Health. In states and on Indian lands where no designated agency administers the public drinking water program, EPA is the primacy agency.

prima facie Evidence sufficient to support the allegations of the complaint unless refuted by some evidence to the contrary.

primary benefits The identifiable net values of the goods or services resulting directly from the project. They are obtained by deducting from the gross benefits all costs of realization, except the economic costs of the project.

primary coolant system The combination of mechanical and electrical components that work together to maintain control of and cool the reactor.

primary drinking water regulation Applies to public water systems and specifies a contaminant level, which, in the judgment of the EPA Administrator, will not adversely affect human health.

primary element An instrument which measures (senses) a physical condition or variable of interest. Floats and thermocouples are examples of primary elements. Also called a sensor.

primary interstice

primary openings

primary settling

primary sludge

primary standards National ambient air quality standards designed to protect human health with "an adequate margin for safety. See National Ambient Air Quality Standards, secondary standards.

primary treatment See primary waste treatment.

primary waste treatment The first major treatment in a wastewater treatment works, usually physical treatment such as screens and sedimentation. The removal of a high percentage (about 50 percent) of suspended matter, but little or no colloidal and dissolved matter. Primary treatment removes about 30 percent of carbonaceous biochemical oxygen demand from domestic sewage. Also called primary treatment.

primary wave

prime The action of filling a pump casing with water to remove the air. Most pumps must be primed before start up or they will not pump any water.

priming

primitive water

principal organic hazardous constituents (POHCs) Hazardous compounds monitored during an incinerator's trial burn, selected for high concentration in the waste feed and difficulty of combustion.

prior appropriation A doctrine of water law that allocates the right to use water on a first-come, first-serve basis.

prism

pristine state A state of nature without human effect or with negligible human effect.

private laboratories Independent laboratories providing analytical services to treatment works.

private sewer

private utility

private water

privy

privy vault

probability A number between 0 and 1 that, when assigned to an event or occurrence, expresses the likelihood that the event will occur.

probability distribution Tables showing relative frequencies of each subset into which a total population is divided and also showing the probability of occurrence of each possible value.

probability distribution function

probability of detection The likelihood, expressed as a percentage, that a test method will correctly identify a leaking tank.

probability of tropical cyclone conditions The probability, in percent, that the cyclone center will pass within 50 miles to the right or 75 miles to the left of the listed location within the indicated time period when looking at the coast in the direction of the cyclone's movement.

probable maximum flood The flood that can be expected from the most severe combination of meteorological and hydrologic conditions reasonably possible in a region.

procaryotic cell A cell in which the nuclear material is not contained within a membrane. Bacteria and blue-green algae are examples.

probing

process A sequence of physical, chemical, and biological actions within basins and equipment designed and operated under controlled conditions to treat water and wastewater.

process fluids Any fluid or solution which may be chemically, biologically, or otherwise contaminated or polluted which would constitute a health, pollution, or system hazard if introduced into the waterworks. This includes, but is not limited to: 1) polluted or contaminated water; 2) process waters; 3) used waters, originating from the waterworks which may have deteriorated in sanitary quality; 4) cooling waters; 5) contaminated natural waters taken from wells, lakes, streams, or irrigation systems; 6) chemicals in solution or suspension; and 7) oils, gases, acids, alkalis, and other liquid and gaseous fluid used in industrial or other processes or for fire fighting purposes.

process variable A physical or chemical quantity which is usually measured and controlled in the operation of treatment processes.

process verification Verification that process raw materials, water usage, waste treatment processes, production rate and other facts relative to quantity and quality of pollutants contained in discharges are substantially described in the permit application and the issued permit.

process wastewater Any water that comes into contact with any raw material, product, byproduct, or waste, during manufacturing or treatment.

process water

process weight Total weight of all materials, including fuel, used in a manufacturing process; used to calculate the allowable particulate emission rate.

producer See producer organism.

producer organism An organism that can synthesize organic material using inorganic materials and an external energy source (light or chemical).

product The usable or measurable output of activities including manufacturing and treatment.

production The amount of organic material produced by biological activity in an area or volume.

productivity The rate of production of organic matter produced by biologic activity in an area. Gross primary production is the rate of synthesis of organic material produced by photosynthesis or chemosynthesis, including that which is used up in respiration by the producer organism; net primary productivity is the rate of accumulation or organic material in plant tissues or gross primary productivity less respiratory utilization by the producer organism; secondary productivity is the rate of production of organic materials by consumer organisms (animals) that eat plants (which are the primary producers). See heterotrophs.

product level The level of a product in a storage tank.

products of incomplete combustion (PICs) Organic compounds formed by combustion. PICs are heat-altered versions of the original material fed into the incinerator (e.g., charcoal is a PIC. from burning wood).

product water Water that has passed through a water treatment plant. All the treatment processes are completed or finished. This water is the product from the water treatment plant and is ready to be delivered to the consumers. Also called finished water.

profile A drawing showing elevation plotted against distance, such as the vertical section or side view of a pipeline.

profile, beach The intersection of the ground surface with a vertical plane. It may extend from the top of the dune line to the seaward limit of sand movement.

profile, river The longitudinal profile or long profile of a river is a section showing its slope from source to mouth. A graph of water-surface elevation and distance along a stream is plotted. Profiles determined for high water conditions are more properly designated as flood profiles.

profile, soil A section through the soil showing the different horizons, or layers, usually designated by the letters, A, B, C, which extend downward from the surface to the parent material.

pro forma As a matter of form.

profundal zone The bottom of a body of water below the metalimnion or below the limit of macrophytic vegetation (such as, rooted plants, seaweeds, large algae, or mosses).

progressive wave

prokaryote An organism (e.g. bacterium, virus, blue- green algae)