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P

PACKED TOWER—(Air Quality) An air pollution control device in which contaminated air is passed through a tower containing substances (packing) possessing large surface area. Water is passed over the packing material in a countercurrent fashion, i.e., in a direction opposite to the passage of the air, and the air contaminants are then absorbed into the liquid. Also referred to as Absorption Tower, Spray Tower, or Tray Tower.

PACKED TOWER AERATION—(Water Quality) A process for the removal of organic contaminants from groundwater. The groundwater flows downward inside a tower filled with materials (the packing) over a large surface area. Air is introduced at the bottom of the tower and is forced upward past the falling water. Individual organic contaminants are transferred from the water to the air, according to the gas and water equilibrium concentration values of each contaminant. Also referred to as Air Stripping.

PACKER—A device lowered into a well to produce a fluid-tight seal.

PACK ICE—Floating ice that has been driven together into a single mass.

PAHRANAGAT NATIONAL WILDLIFE REFUGE (NWR) [Nevada]—One of the nine National Wildlife Refuges (NWR) located in the State of Nevada, the Pahranagat NWR is located approximately 90 miles north of Las Vegas, Nevada, at the northern end of the Desert National Wildlife Refuge and consists of 5,380 acres (8.4 square miles) of marshes, open water, native grass meadows and cultivated croplands. Established in 1964, the Pahranagat NWR hosts numerous waterfowl and other migratory birds on the Pacific Flyway, which stretches from Alaska and Canada to Mexico. The name "Pahranagat" comes from the Paiute Indian word meaning "place of many waters." Also see National Wildlife Refuge (NWR) System and National Wildlife Refuges (NWR) [Nevada].

PALATABLE WATER—Water, at a desirable temperature, that is free from objectionable tastes, odors, colors, and turbidity.

PALEONTOLOGY—The study of fossils of animal and plant life that existed in remote geological times. The study of these remains enables scientists to trace the evolutionary history of extinct as well as contemporary organisms. Paleontologists also play a major role in unraveling the stratigraphic mysteries of the earth's crust and by using detailed information on how fossils are distributed in sedimentary strata, they help prepare accurate geologic maps, which are essential in the search for oil, water, and minerals.

PALEOPEDOLOGY—The study of fossil soils. Also see Pedology.

PALUSTRINE—Pertaining to a Marsh or Wetlands; wet or marsh habitats.

PALUSTRINE WETLANDS—Used in the wetlands classification system by the U.S. Fish and Wildlife Service (USFWS) to refer to wetlands that are vegetated-dominated by trees, shrubs, herbaceous plants, mosses or lichens. See Wetlands (General), Wetlands (COE and EPA), Wetlands (USFWS), Wetlands (NRCS), Wetlands, Palustrine, and Wetlands, Benefits. [See Appendix W-2 for an explanation of the Wetland and Deepwater Habitat Classification System according to U.S. Fish and Wildlife Service (USFWS) criteria and more detailed information of these systems.

PAMs—See Polyacrylamides (PAMs).

PAN—(1) A basin or depression in the earth, often containing mud or water. (2) A natural or artificial basin used to obtain salt by evaporating brine. Also referred to as Hardpan.

PAN EVAPORATION—Evaporation in inches from a standard Weather Bureau Class A pan. See Evaporation Pan.

PARALYTIC SHELLFISH POISONING (PSP)—A pathological condition in humans caused by the consumption of certain marine mussels or clams that have fed on planktonic dinoflagellates belonging to the genus Gonyaulax. The mussels or clams become contaminated with a neurotoxin produced by the dinoflagellates, and subsequent consumption by humans results in respiratory or gastrointestinal distress. The condition occurs in conjunction with the phenomenon known as the Red Tide, a bloom of dinoflagellate population in marine waters.

PARAMETER—(1) A variable, measurable property whose value is a determinant of the characteristics of a system. (2) (Statistics) Fundamentally, the parameter represents the true value of the characteristic of a sample or population. The estimate of a parameter, called a statistic, is a measurement of a sample of the population. The parameters in an Econometric Model (Regression Analysis) describe the relationship between the variations in the Dependent Variable, or the variable to be explained, and the variations in the Independent, or Explanatory Variable(s). For example, in the simple expression of cause and effect

Yt = a + ßXt + et

the constant term, a (alpha), and the coefficient term, ß (beta), define the (fixed) parameters of this econometric model and will be tested, statistically, to determined if the relationship is valid, i.e., is there exists a causal (i.e., cause and effect) relationship, or if the variations in the dependent variable are based on chance (random).

PARAPET WALL—A solid wall built along the top of a dam for ornament, for the safety of vehicles and pedestrians, or to prevent overtopping.

PARENT MATERIAL—The unconsolidated and more or less chemically weathered mineral or organic matter from which the Solum of soils is developed by Pedogenic processes.

PARHELIC CIRCLE—A luminous halo visible at the height of the sun and parallel to the horizon, caused by the sun's rays reflecting off atmospheric ice crystals. Also referred to as a Parhelic Ring.

PARSHALL FLUME—A device used to measure the flow of water in an open channel.

PARTIAL DURATION FLOOD SERIES—A list of all flood peaks that exceed a chosen base stage or discharge, without regard for the number occurring in a year. Also referred to as Basic-Stage Flood Series or Floods Above a Base.

PARTIAL PENETRATION—A well constructed in such a way that it draws water directly from a fractional part of the total thickness of the aquifer. The fractional part may be located at the top, the bottom, or anywhere else in the aquifer.

PARTIAL PRESSURE—In a mixture of gases, the pressure exerted by each gas independently of the other gases.

PARTICLE COUNT—(Water Quality) Results of a microscopic examination of treated water with a special "particle counter" that classifies suspended particles by number and size.

PARTICLE SIZE—The diameter (usually the intermediate diameter), in millimeters, of suspended sediment or bed material determined by either sieve or other sedimentation methods.

PARTICLE SIZE CLASSIFICATION—Agrees with recommendations made by the American Geophysical Union Subcommittee on Sediment Terminology. The particle size classification is as follows:

[1] Clay—0.00024-0.004 millimeters (mm);
[2] Silt—0.004-0.062 mm;
[3] Sand—0.062-2.0 mm; and
[4] Gravel—2.0-64.0 mm.

PARTICULATE LOADING—The mass of Particulates per unit volume of water.

PARTICULATE MATTER—(Water Quality) In water pollution, particulate matter describes solid material in either the solid or dissolved states.