fabric filter A cloth device with such limited porosity that suspended particulates are removed from fluids passing through it, such as the separation of dust particles from industrial emissions.
face The external surface of a structure, such as the surface of a dam.
facilities plans Plans and studies related to the construction of treatment works necessary to comply with the Clean Water Act or RCRA. A facilities plan investigates needs and provides information on the cost effectiveness of alternatives, a recommended plan, an environmental assessment of the recommendations, and description of the treatment works, costs, and a completion schedule.
facility emergency coordinator Representative of a facility covered by environmental law who participates in the emergency reporting process with the Local Emergency Planning Committee (lepc).
facultative 1) A condition in which “free” or dissolved oxygen is present only in some places. 2) Able to function both in the presence or absence of free oxygen.
facultative anaerobe An organism that can use either molecular (dissolved) oxygen or oxygen obtained from food material such as sulfate or nitrate ions. In other words, facultative anaerobes can live under aerobic or anaerobic conditions.
facultative bacteria Bacteria that can live under aerobic or anaerobic conditions.
facultative pond The most common type of wastewater treatment pond in current use. The upper portion (supernatant) is aerobic while the bottom is anaerobic. Algae supply most of the oxygen to the supernatant.
fallout See radioactive fallout.
family A category of biological classification ranking above a genus and below an order.
FAQ List of frequently asked questions and their answers.
fathom A unit of measurement equal to six feet used especially to measure water depth.
fatigue A process leading to fracture resulting from repeated stress cycles well below the normal tensile strength. Such failures start as tiny cracks that grow to cause total failure.
fauna The animals of a region taken collectively.
FCIF/QCIF Standards-based display format for communicating between videoconference systems from different vendors.
feasibility study 1) Analysis of the practicability of a proposal; e.g., a description and analysis of potential cleanup alternatives for a site such as one on the National Priorities List. Often the feasibility study recommends selection of a cost-effective alternative. 2) A small-scale investigation of a problem to ascertain whether a proposed research approach is likely to provide useful data.
fecal coliform bacteria Gram-negative bacteria found in the intestines of mammals. Their presence in water or sludge is an indicator of pollution and possible contamination by pathogens. The thermo-tolerant forms of E. coli and Klebsiella which produce a blue colony on a membrane filter when they are cultured on MFC medium and incubated at 44.5°C in EC broth within 24 hours after previous incubation at 35°C in Lauryl tryptose broth.
fecal streptococcus A number of gram-positive bacteria that are species of Lancefield’s group D streptococci such as S. faecalis, S. faecium, S. avium, S. bovis, S. equinus, and S. gallinarum..
fecundity Capacity to produce offspring; in insect ecology, the number of eggs per female that hatch or become larvae.
federal emergency. Any occasion or instance for which, in the determination of the President, Federal assistance is needed to supplement State and local efforts and capabilities to save lives and protect property, public health, and safety.
federal implementation plan A federally implemented plan to achieve attainment of air quality standards, used when a state is unable to develop an adequate plan.
Federal Insecticide, Fungicide, and Rodenticide Act (FIFRA) Federal law first enacted in 1947 and administered by the EPA since 1970. Under FIFRA, EPA registers pesticide products and ensures that they will not present unreasonable risks to human health or the environment when used according to label directions.
Federal Motor Vehicle Control Program All federal actions aimed at controlling pollution from motor vehicles by such efforts as establishing and enforcing tailpipe and evaporative emission standards for new vehicles, testing methods development, and guidance to states operating inspection and maintenance programs.
feed back The circulating action between a sensor measuring a process variable and the controller which controls or adjusts the process variable.
feeder bands In tropical parlance, the lines or bands of thunderstorms that spiral into and around the center of a tropical system. Also known as outer convective bands, a typical hurricane may have three or more of these bands. They occur in advance of the main rain shield and are usually 40 to 80 miles apart. In thunderstorm development, they are the lines or bands of low-level clouds that move or feed into the updraft region of a thunderstorm.
feedlot A confined area for the controlled feeding of animals. Tends to concentrate large amounts of animal waste that cannot be absorbed by the soil and, hence, may be carried to nearby streams or lakes by surface drainage and runoff thereby contributing to water pollution and enrichment.
fen A type of wetland that accumulates peat deposits, but far less acidic than bogs, deriving most of their water from groundwater rich in calcium and magnesium.
fence The hearing threshold level above which a hearing loss is considered to have occurred.
fence diagram A projection of known stratigraphic columns to show the lateral thicknesses and interrelationships of geologic units.
fermentation The oxidation of carbohydrates and carbohydrate-like compounds in the absence of oxygen by enzyme action of microorganisms.
fertilization Sexual union at the cellular level; fusion of the nuclei of a male and female gamete.
fertilizer Any substance, like manure, used to enrich the soil through the addition of nutrients that support crop production.
fetch 1) At sea, the length of open water across which the wind is blowing, i.e., the distance from the weather shore which largely determines the height of the waves. 2) The distance of the water or the homogenous type surface over which the wind blows without appreciable change in direction.
fiat A command; order directing some legal act to be done.
fiber optic cable Bundled glass rods (fibers) that are extremely thin and flexible and are capable of transmitting voice, video, and data signals in either analog or digital formats. This is accomplished with very little loss in signal quality. A single glass fiber can carry the equivalent of 100 channels of television or 100,000 telephone calls, with even more capacity possible by encasing many fibers within a cable.
Fick's First Law An equation describing the rate at which a gas transfers into solution. The change in concentration of gas in solution is proportional to the product of an overall mass transfer coefficient and the concentration gradient.
Fick's Second Law An equation relating the change of concentration with time due to diffusion to the change in concentration gradient with distance from the source of concentration.
fidelity The degree to which species are confined to certain communities.
field area The “wetted area” where treatment occurs in a land application system.
field capacity (field moisture capacity) The moisture content of the soil in the field two or three days after having been saturated and after free drainage has practically ceased; the quantity of water held in a soil by capillary action after the gravitational or free water has been allowed to drain; expressed as moisture percentage, dry weight basis.
field deficiency (field moisture deficiency) The quantity of water, which would be required to restore the soil moisture to field moisture capacity.
field trip blank Reagent or distilled bottled water transferred to a sample container in the field and treated as a sample in all respects. The field trip blank allows the laboratory to determine whether interferences are present in the field environment.
FIFRA pesticide ingredient An ingredient of a pesticide that must be registered under the Federal Insecticide, fungicide, and Rodenticide Act. Products making pesticide claims must be registered under FIFRA are subject to labeling and use requirements.
filamentous Microbiological growth composed of thread-like structures.
filamentous bacteria Bacteria that grow in a thread or filamentous form.
filiform corrosion See underfilm corrosion.
fill dam Any dam constructed of excavated natural materials or of industrial wastes.
filling 1) Depositing soil, mud, and/or other materials into aquatic areas to create more dry land usually for agricultural or commercial development purposes, often with ecological consequences. 2) Used in describing the history of a low-pressure system or an area of cyclonic circulation, it means an increase in the central pressure of the system. Although it usually describes the action of a pressure system on a constant pressure chart, it also means a surface low is decreasing in cyclonic circulation and losing its characteristics.
film A thin surface layer that may or may not be visible.
filter The use of porous media, from a bed of stone or sand to a layer of cloth or membrane, to remove particulates from fluids.
filter backwash The water containing the material obtained by reversing the flow of water through a filter to dislodge the particles that have been retained on it.
filter flooding The filling of a trickling filter contactor to an elevation above the top of the medium by closing all outlets, in order to control the nuisance of filter flies.
filter strip A strip or area of vegetation used for removing sediment, organic matter, and other pollutants from surface runoff and wastewater.
filtration A process for removing suspended particulate matter from water by passage through a porous medium or media.
final order The last order, issued by the court in a lawsuit, that terminates the action.
financial assurance for closure Documentation or proof that an owner or operator of a facility such as a landfill or other waste repository is capable of paying the projected costs of closing the facility and monitoring it afterwards as provided in RCRA regulations.
finding of no significant impact (FNSI) A document, based on the results of an environmental assessment, prepared by a regulatory agency showing why a proposed action would not have a significant impact on the environment and thus would not require preparation of an Environmental Impact Statement.
finished water Water that has passed through a water treatment plant; all the treatment processes are completed or "finished." This water is ready to be delivered to consumers. Also called product water.
first cost The total project construction cost including costs of lands, relocations, engineering, design, administration, and supervision.
first draw The water that immediately comes out when a tap is first opened. This water is likely to have the highest level of lead contamination from plumbing materials.
first draw sample A one-liter sample of tap water, collected in accordance with CFR Section 141.86(b)(2), that has been standing in plumbing pipes at least six hours and is collected without flushing the tap.
first reduction A method of determining high and low water heights, time intervals, and ranges from an arithmetic mean without adjustment to a long-term series through simultaneous observational comparisons.
fiscal year It is the budget year used for programming and funding. The Federal fiscal year commences October 1 of one year and ends September 30 of the succeeding year. The State fiscal year commences July 1 of one year and ends June 30 of the succeeding year.
Fish and Wildlife Service A regulatory component within the department of interior concerned with enforcement of laws protecting endangered and protected species.
fish elevator
fishery Of or related to fish populations as the basis of an industry, recreational or commercial.
fish hatchery water use Water used for raising fish for later release.
fish kill Pertaining to the sudden death of fish population.
fission The splitting of an atom resulting in the release of neutrons, energy, and two or more similar atoms.
fission, binary Single nuclear division followed by division of the cytoplasm to form two daughter cells of equal size.
fission product An atom produced through the splitting of a larger atom.
fixed charge The portion of a water bill that does not vary with water usage.
fixed costs 1) Costs associated with the project investment and amortization of the investment. 2) The costs associated with water service that do not vary with the amount of water produced or sold.
fixed spray nozzle A cone-shaped spray nozzle used to distribute wastewater over the filter media.
fix, sample A sample is fixed in the field by adding chemicals that prevent the water quality indicators of interest in the sample from changing before final measurements are performed later in the lab.
flagellates Microorganisms that move by the action of tail-like projections.
flagellum A whip-like attachment on cells used as an organ for mobility.
flame polished Melted by a flame to smooth out irregularities. Sharp or broken edges of glass are rotated in a flame until the edge melts slightly and becomes smooth.
flammable liquid A liquid with a flash point below 100°F and having a vapor pressure not exceeding 40 p.s.i.g. absolute at 100°F.
flare A control device that burns hazardous materials to prevent their release into the environment; may operate continuously or intermittently, usually on top a stack.
flashboards A length of timber, concrete, or steel placed on the crest of a spillway to raise the retention water level but which may be quickly removed in the event of a flood by a tripping device, or by deliberately designed failure of the flashboard or its supports.
flash flood A flood which follows within a few (usually less than six) hours of heavy or excessive rainfall, dam or levee failure, or the sudden release of water impounded by an ice jam.
flash flood guidance (FFG) An internal NWS product which indicates the amount of rainfall in a given amount of time (usually less than 6 hours) which most likely will produce flash flooding in a given area.
flash flood statement (FFS) A statement issued by the NWS which provides follow-up information on flash flood watches and warnings.
flash flood table A table of pre-computed forecast crest stage values for small streams for a variety of antecedent moisture conditions and rain amounts. Soil moisture conditions are often represented by flash flood guidance values. In lieu of crest stages, categorical representations of flooding (minor, moderate, major) may be used on the tables.
flash flood warning (FFW) A warning issued by the NWS to warn of flash flooding that is imminent or occurring.
flash flood watch (FFA) A statement issued by the NWS which alerts communities to the possibility of flash flooding in specified areas.
flights Scraper boards, made from redwood or other rot resistant woods, used to collect and move settled sludge or floating scum.
float well A stilling well in which the float of a float-actuated gauge operates. See stilling well.
floc 1) Aggregates of microorgansims of bacteria and particulate impurities that are bound through coagulation to forma settleable cluster. Developed in flocculation tanks, reactors, and settling or sedimentation basins. 2) A cluster of frazil particles
flocculating tank
flocculation The development of flocs in water and wastewater by gentle mixing after the addition of coagulant chemicals to form larger particles.
floe Ice which has been flooded by melt water or river water and is heavily loaded by water and wet snow.
flood An overflow of lands not normally covered by water and that are used (or usable) by man. Floods have two essential characteristics— the inundation of land is temporary and the land is adjacent to or inundated by overflow from a river, stream, ocean, lake, or other body of standing water. See flood plain.
flood axis The average set of the tidal current at strength of flood.
flood control storage Space available in a reservoir for storing runoff to prevent downstream flood damages.
flood crest The maximum stage or elevation reached by the waters of a flood at a given location.
flood current The movement of a tidal current toward the shore or up a tidal river or estuary. In the mixed type of reversing current, the terms greater flood and lesser flood are applied respectively to the two flood currents of greater and lesser speed of each day. The expression maximum flood is applicable to any flood current at the time of greatest speed. See flood strength.
flood damages Flood damages may be classified as tangible and intangible. The former are those subject to monetary evaluation and the latter include loss of life, health, and scenic or historic values not readily identified in monetary terms. Tangible damages include physical losses, flood emergency costs, and business or financial losses. These tangible losses are referred to frequently as primary damages in contrast to secondary damages (or losses to business not otherwise related to the direct effect of the conditions under study).
flood duration curve A cumulative frequency curve that shows the percentage of time that specified discharges are equaled or exceeded.
flood frequency curve 1) A graph showing the number of times per year on the average, plotted as abscissa, that floods of magnitude, indicated by the ordinate, are equaled or exceeded. 2) A similar graph but with recurrence intervals of floods plotted as abscissa.
flooding A general and temporary condition of partial or complete inundation of normally dry land areas from the overflow of inland or tidal water or rapid accumulation or runoff of surface waters from any source.
flood interval The interval between the transit of the Moon over the meridian of a place and the time of the following flood strength.
flood-level rim The edge of the receptacle from which water overflows.
flood loss reduction measures The strategy for reducing flood losses. There are four basic strategies: prevention, property protection, emergency services, and structural projects. Each strategy incorporates different measures that are appropriate for different conditions.
flood of record The highest observed river stage or discharge at a given location during the period of record keeping.
flood peak The highest value of the stage or discharge attained by a flood—peak stage or peak discharge. Flood crest has nearly the same meaning, but connotes the top of the flood wave.
floodplain The flat or nearly flat land on the floor of a stream valley or tidal area that is covered by water during floods.
floodplain management The combination of efforts both political and physical to reduce long-term flood damages.
flood potential outlook A statement issued by the NWS which alerts communities to the possibility of river flooding along specified reaches or near specified forecast points.
flood prevention Measures taken in order to keep flood problems from getting worse. Planning, land acquisition, river channel maintenance, wetlands protection, and other regulations all help modify development on floodplains and watersheds to reduce their susceptibility to flood damage. Preventive measures are usually administered by the building, zoning, planning and/or code enforcement offices of the local government.
flood problems Problems and damages which occur during a flood as a result of human development and actions. Flood problems result from inappropriate development in the floodplain (e.g., building too low, too close to the channel, or blocking flood flows). Development in the watershed that increases flood flows and creates a larger floodplain; or a combination of the previous two.
flood profile A graph of elevation of the water surface of a river in flood, plotted as ordinate, against distance, measured in the downstream direction, plotted as abscissa. A flood profile may be drawn to show elevation at a given time, crests during a particular flood, or to show stages of concordant flows.
floodproofing The process of protecting a building from flood damage on site. Floodproofing can be divided into wet and dry floodproofing. In areas subject to slow-moving, shallow flooding, buildings can be elevated, or barriers can be constructed to block the water's approach to the building. These techniques have the advantage of being less disruptive to the neighborhood. It must be noted that during a flood, a floodproofed building may be isolated and without utilities and therefore unusable, even though it has not been damaged.
flood-protection works
flood routing The process of determining progressively the timing, shape, and amplitude of a flood wave as it moves downstream to successive points along the river.
flood stage The stage or elevation at which overflow of the natural banks of a stream or body of water begins in the reach or area in which the elevation is measured.
flood statement A statement issued by the NWS which provides follow-up information on river flooding.
flood strength Phase of the flood tidal current at the time of maximum speed. Also, the speed at this time. See strength of current.
floodwall A long, narrow concrete, or masonry embankment usually built to protect land from flooding. If built of earth the structure is usually referred to as a levee. Floodwalls and levees confine streamflow within a specified area to prevent flooding. The term "dike" is used to describe an embankment that blocks an area on a reservoir or lake rim that is lower than the top of the dam.
flood warning A warning issued by the NWS to warn of river flooding which is imminent or occurring. A flood warning is issued when a river first exceeds its flood stage, and it may be reissued if a new river forecast for a forecast point or reach is significantly higher than a previous forecast.
flood wave A distinct rise in stage culminating in a crest and followed by recession to lower stages.
floodway The channel of a river or stream and those parts of the flood plains, adjoining the channel, that are required to carry and discharge the flood water of any river or stream.
floor sweep Capture of heavier-than-air gases that collect at floor level.
flora Plants. Organisms of the plant kingdom. Specifically, the plants growing in a geographic area.
Florida Current A North Atlantic Ocean current setting northward along the south-east coast of the United States. A segment of the Gulf Stream System, the Florida Current extends from the Straits of Florida to the region off Cape Hatteras.
flow 1)2)3)4)5) The British equivalent of the United States total current. Flow is the combination of their tidal stream and current.
flowage The volume or dimensions of the water of a stream. Flowage land is that which will be covered by the water impounded by a proposed dam.
flowage easement The right to flood a tract of land to a designated level, usually sold voluntarily. The landowner may reserve the right to enter upon and use the entire flowage for riparian purposes, but always retains ownership to the bottom land on his tract. The right to flood land usually embodies the right to manipulate water level.
flow-direction The vector in which the water in an aquifer moves.
flowing well A well drilled into a confined aquifer with enough hydraulic pressure for the water to flow to the surface without pumping. Also called an artesian well.
flow meter A gauge indicating the velocity of a liquid moving through a treatment plant or through various industrial processes.
flow-net analysis Study to determine a set of interacting equipotential lines and flow lines representing a twodimensional steady flow through porous media.
flow rate Fluid movement in volume per time, such as the rate expressed in gallons or liters per hour at which a liquid passes through a channel.
flow tube A calibrated flow measuring device made for a specific range of flow velocities and fluids.
fluctuation A change in level.
flue gas The air coming out of a chimney after combustion in the burner it is venting.
flue gas desulfurization A technology that employs a sorbent, usually lime or limestone, to remove sulfur dioxide from the gases produced by burning fossil fuels.
fluidized A mass of solid particles that is made to flow like a liquid by injection of water or gas is said to have been fluidized. In water treatment, a bed of filter media is fluidized by backwashing water through the filter.
fluidized bed incinerator An incinerator, used mainly for destroying municipal sludge, that uses a bed of hot sand or other granular material to transfer heat directly to waste.
flume A natural or man-made channel that diverts water.
fluorescence The property of absorbing light of a particular wave length and then emitting light of a different color and wave length.
fluoridation The addition of a chemical to increase the concentration of fluoride ions in drinking water to a predetermined optimum limit to reduce the incidence (number) of dental caries (tooth decay) in children. Defluoridation is the removal of excess fluoride in drinking water to prevent the mottling (brown stains) of teeth.
fluorides Gaseous, solid, or dissolved compounds containing fluorine that result from industrial processes.
fluorocarbon (FC) Any of a number of organic compounds analogous to hydrocarbons in which one or more hydrogen atoms are replaced by fluorine. FCs containing chlorine are called chlorofluorocarbons (CFCs).
fluorosis An abnormal condition caused by excessive intake of fluoride, characterized chiefly by the mottling of the teeth.
flush 1) To open a cold-water tap to clear out all the water which may have been sitting for a long time in the pipes. In new homes, to flush a system means to send large volumes of water gushing through the unused pipes to remove loose particles of solder and flux. 2) To force large amounts of water through liquid to clean out piping or tubing, storage or process tanks.
flushing A method to clean water distribution lines. Hydrants are opened and water with a high velocity flows through the pipes, removes deposits from the pipes, and flows out the hydrants.
flushing time The time required to remove or reduce (to a permissible concentration) any dissolved or suspended contaminant in an estuary or harbor.
flushometer valve A device which discharges a predetermined quantity of water to fixtures for flushing purposes and is actuated by direct water pressure.
fluvial Applied to plants growing on streams.
flux 1) A flowing or flow of liquid, gas, energy, etc. 2) The rate of movement of mass through a unit cross-sectional area per unit time in response to a concentration gradient or some advective force.
fly ash Non-combustible residual particles expelled by flue gas.
flyway The route taken by migratory birds, usually waterfowl, during migration.
F/M ratio Food to microorganism ratio; the amount of food (organic matter as BOD or COD) available per mass of microorganisms.
fog 1) A visible collection of minute water droplets suspended in the atmosphere near the earth's surface. Fog reduces visibility below one kilometer (0.62 miles). 2)
fogging Applying a pesticide by rapidly heating the liquid chemical so that it forms very fine droplets that resemble smoke or fog. Used to destroy mosquitoes, black flies, and similar pests.
follow-up monitoring Monitoring required after a PWS installs treatment. Follow-up monitoring is required for lead, copper, and other water quality parameters.
food chain Animals linked together by the succession of food sources and all dependent , in the long run, on plants.
food web See food chain. Implies many cross connections to the food chain rather than straight-line connections.
footcandle (fc) The unit of illumination when the foot is taken as the unit of length. It is the illumination on the surface of one square foot of area on which there is a uniformly distributed flux of one lumen, or the illumination produced on a surface all points of which are at a distance of one foot from a directionally uniform point source of one candela.
footlambert (fL) A unit of luminance (photometric brightness) equal to 1/pi candela per square foot, or to the uniform luminance of a perfectly diffusing surface emitting or reflecting light at the rate of one lumen per square foot, or to the average luminance of any surface emitting or reflecting light at that rate.
footprint The area of the earth's surface where a particular satellite's signal can be received. A footprint can cover one-third of the globe, but is usually less.
foot valve A special type of check valve located at the bottom end of the suction pipe on a pump. This valve opens when the pump operates to allow water to enter the suction pipe, but closes when the pump shuts off to prevent water from flowing out of the suction pipe.
forage Search for, pursue, capture, and ingest food.
forage fish Fish eaten by other fish.
forb An herbaceous plant, not a grass.
forced wave A wave generated and maintained by a continuous force. See gravity wave.
forebay 1) An extra storage space provided near an inlet of a wet pond or constructed wetland to trap incoming sediments before they accumulate in the pond. 2) The water behind (upstream) of a dam. 3) A lake or water impoundment (reservoir) at the end of a diversion canal or conduit and before the entrance to the powerplant.
forecast A statement of expected future occurrences. Weather forecasting includes the use of objective models based on certain atmospheric parameters, along with the skill and experience of a meteorologist. Also called a prediction.
forecast crest The highest elevation of a river stage expected during a specific storm event.
forest An association dominated by trees, usually defined as woody plants over ten meters tall.
forest cover type All trees and other woody underbrush covering the ground in a forest. Includes trees, herbs and shrubs, litter, and the remain of rich humus of partly decayed vegetable matter at the surface of the soil.
forest game Any forest animal usually a mammal or bird, upon which hunting is regulated by law.
forest type A forest stand community or association, essentially similar throughout its extent with regard to composition and development under equivalent conditions.
forfeiture of bond The loss of a bond as a result of a failure to perform the conditions agreed upon when the bond was made.
formaldehyde A colorless, pungent, and irritating gas, CH20, used chiefly as a disinfectant and preservative and in synthesizing other compounds like resins.
formation A group of similar consolidation (that is, relatively solid) rocks of unconsolidated (that is relatively loose) minerals.
formulation A list of substances or component parts as described by the maker of a coating, pesticide, or other product containing chemicals or other substances.
fortnight The time elapsed between the new and full moons. Half a synodic month of 14.765,294 days. See synodical month.
forward speed The rate of movement (propagation) of the hurricane eye in miles per hour or knots.
fossil Any remains, impression, cast, or trace of an animal or plant of a past geological period. The term is generally restricted to parts which have been petrified or converted to stone.
fossil fuel Any combustible organic material as oil, coal, or natural gas, derived from fossils.
fouling A term used to describe the covering of submerged surfaces by marine growths, such as barnacles.
fragile Easily broken or disrupted, usually refers to communities or an ecosystem particularly susceptible to disruption by man.
fragipan A loamy, dense, brittle subsurface horizon that is very low in organic matter and clay, but is rich in silt or very fine sand. The layer is seemingly cemented and is slowly or very slowly permeable.
frame rate Frequency with which video frames are displayed on a monitor, typically described in frames-per-second (fps). Higher frame rates improve the appearance of video motion. Broadcast TV (full-motion video) is 30 frames-per-second.
FRDS A data base maintained by EPA's Office of Drinking Water (ODW) that contains information on all public water supply systems in the US. Soon to be replaced by SDWIS, the Safe Drinking Water Information System.
free available chlorine That portion of the total residual chlorine remaining in water at the end of a specified contact period which will react chemically and biologically as hypochlorous acid or hypochlorite ion.
free available residual chlorine That portion of the total available residual chlorine composed of dissolved chlorine gas (Cl2), hypochlorous acid (HOCl), and/or hypochlorite ion (OCL- ) remaining in water after chlorination. This does not include chlorine that has combined with ammonia, nitrogen, or other compounds.
free board 1) The vertical distance from the normal water surface to the top of the confining wall. 2) The vertical distance from the media surface to the outlet, such as the underside of a trough in a sand filter. This distance is also called available expansion.
free product A petroleum hydrocarbon in the liquid ("free" or non-aqueous) phase (see also non-aqueous phase liquid, NAPL).
free residual chlorine level The concentration of chlorine in water that is not combined with other constituents and thus serves as an effective disinfectant.
free residual chlorination The application of chlorine to water to produce a free available chlorine residual equal to at least 80 percent of the total residual chlorine (sum of free and combined available chlorine residual).
free water surface A water surface that is at atmospheric pressure.
free wave A wave that continues to exist after the generating force has ceased to act.
freeze A freeze occurs at any time the surface air temperature reaches 28 degrees or less. This temperature causes damage to most vegetation except certain species which are resistant to freezing.
freeze free period The number of consecutive days where the air temperature does not fall below 28 degrees Fahrenheit.
freeze free period, killing The number of consecutive days where the air temperature does not fall below 24 degrees Fahrenheit.
freeze, killing A killing freeze occurs at or below 24 degrees Fahrenheit and causes permanent damage to almost all vegetation.
freight bill (f/b) The document stating the transportation charges incurred by the carrier (a bill for the freight charges on a shipment). Next to a bill of lading, the freight bill is the most authentic document that supports movement of a shipment in interstate commerce.
French drain
frequency 1) The number of observations or measures in one of the class intervals of a frequency distribution. 2) The number of times that a function occurs per unit time. For sound, the unit is cycles per second, or Hertz (Hz). 3) likelihood of occurrence.
frequency distribution A complete summary of the frequencies of the values or categories of a variable; often displayed in a two column table: the left column lists the individual values or categories, the right column indicates the number of observations in each category.
frequency polygon A graph of a frequency distribution with values of the variable on the x-axis and the number of observations on the y-axis; data points are plotted at the midpoints of the intervals and are connected with a straight line.
freshet An overflowing of a stream swollen by heavy rain or melted snow, usually occurring in the spring.
fresh water High quality water that generally contains less than 1,000 milligrams per liter of dissolved solids. More than 500 mg/L of dissolved solids is undesirable for drinking and many industrial uses.
friable Easily crumbled, not cohesive or sticky.
friable asbestos Any material containing more than one percent asbestos, and that can be crumbled or reduced to powder by hand pressure.
friction losses The head, pressure or energy (they are the same) lost by water flowing in a pipe or channel as a result of turbulence caused by the velocity of the flowing water and the roughness of the pipe, channel wall, and restrictions caused by fittings. Water flowing in a pipe loses pressure or energy as a result of friction losses. Also see head loss.
front The boundary between two dissimilar air masses.
frost The process of deposition of frozen atmospheric water vapor on surfaces whose surface air temperature is below 32 degrees Fahrenheit. A frost can occur at anytime the surface air temperature falls to 32 degrees Fahrenheit or less.
frost, first The first date following the growing season that the minimum temperature drops below an index temperature, usually 32 degrees Fahrenheit. The first frost usually occurs in the fall of the year, but it may occur during the winter months, or in some locations may not occur at all.
frost free period Frost free period is the number of consecutive days where the surface air temperature does not fall below 32 degrees Fahrenheit.
frost, last Last Frost is the last date preceding the growing season that the minimum temperature drops below an index temperature, usually 32 degrees Fahrenheit. The last frost usually occurs in the spring of the year but may occur very early in the summer or not at all in some locations. First and Last frosts are analyzed at three temperatures (32, 28, and 24 degrees Fahrenheit) specifically relating to damage caused to vegetation by the sub-freezing temperatures.
frostproof closet A hopper with no water in the bowl and with the trap and water supply control valve located below the frost line.
fuel assembly A number of nuclear fuel rods grouped together.
fuel cladding A long metal tube encasing the nuclear fuel rod. Cladding is designed to prevent fission products, that migrate from the nuclear fuel, from escaping to the primary coolant system.
fuel economy standard The Corporate Average Fuel Economy Standard (CAFE), effective in 1978, that imposed a miles-per-gallon floor for motor vehicles.
fuel efficiency The proportion of the energy released on combustion of a fuel that is converted into useful energy.
fuel pellet A cylindrical pellet of nuclear fuel typically consisting of uranium dioxide.
fuel rod A stack of cylindrical fuel pellets encased in fuel cladding.
fuel switching 1) A precombustion process whereby a low-sulfur coal is used in place of a higher sulfur coal in a power plant to reduce sulfur dioxide emissions. 2) Illegally using leaded gasoline in a car designed to use only unleaded.
fugitive emissions Emissions not caught by a capture system.
Fujita Scale (F Scale) A scale of wind damage intensity in which wind speeds are inferred from an analysis of wind damage:
F0 (weak): 40- 72 mph, light damage.
F1 (weak): 73-112 mph, moderate damage.
F2 (strong): 113-157 mph, considerable damage.
F3 (strong): 158-206 mph, severe damage.
F4 (violent): 207-260 mph, devastating damage.
F5 (violent): 261-318 mph, incredible damage (rare)
Fujiwhara effect A binary interaction where tropical cyclones within a certain distance (300-750 nautical miles depending on the sizes of the cyclones) of each other begin to rotate about a common midpoint.
full-motion video Equivalent to broadcast television video with a frame rate of 30 fps. Images are sent in real time and motion is continuous. Unlike compressed video signals (which tend to be blurry), full-motion video refers to high-quality signals, similar to what is received over a television set.
full participation A term that refers to an exercise in which:
(1) State and local government emergency personnel are engaged in sufficient numbers to verify the capability to respond to the actions required by the accident scenario;
(2) the integrated capabilitity to adequately assess abd respond to an accident at a commercial nuclear power plant is tested;
(3) the implementation of the observable portions of State and/or local plans is tested.
fume 1) The particulate, smoke-like emanation from the surface of heated metals. 2) Also the vapors evolved from the concentrated acids (sulfuric, nitric); from evaporating solvents; or as the result of combustion or any other decomposition reaction.
fumigant A pesticide vaporized to kill pests, usually used in buildings and greenhouses.
functional equivalent A term used to describe EPA’s decision-making process and its relationship to the environmental review conducted under the national Environmental Policy Act (nepa). A review is considered functionally equivalent when it addresses the substantive components of a NEPA review.
fungi Thallophytic plants lacking chlorophyll, roots, stems, and leaves. They are molds with a filamentous structure. They occur in natural waters and best grow in the absence of light. Their decomposition may cause objectionable tastes and odors in water.
fungicide An agent which kills or inhibits the growth of fungi.
fungistat A chemical that keeps fungi from growing.
furrow irrigation Irrigation method in which water travels through the field by means of small channels between each row or groups of rows.
future liability Potential responsible party’s obligation to pay for additional response activities beyond those specified in the Record of Decision or Consent Decree.