laboratory control standard

laboratory trip blank Reagent water placed in a sample container in the laboratory and sent to the field collection area. The container is unopened, but treated as a sample in all respects. The laboratory trip blank allows the laboratory to determine whether interferences are introduced into the sample during shipment. Also called shipping blank or travel blank. See field trip blank.

Labrador Current A North Atlantic Ocean current setting southeastward along the east coasts of Baffin Island, Labrador, and Newfoundland.

lactose A carbohydrate (disaccharide) sometimes known as milk sugar. On hydrolysis, it is split into glucose and galactose.

lacustrine Originating in or inhabiting a lake.

lag 1) The measure of the time between the center of mass of precipitation to the center of mass of runoff (on the hydrograph). 2)

lag, basin Basin lag is a function of not only basin characteristics, but also of storm intensity and movement. Some hydrologic texts define lag from the center of mass of rainfall to the hydrograph peak.

lagging of tide The periodic retardation in the time of occurrence of high and low water due to changes in the relative positions of the Moon and Sun.

lagoon 1) A water body in a depression back of an offshore bar, a beach ridge or shore dune, with these geomorphic features acting as barriers or dams. 2) A man-made excavation with side and bottom impervious surfaces or liners to maintain an established volume of water or wastewater.

lag phase The initial period of slow microorganism growth after a medium is first inoculated with a bacterial culture.

Lagrangian measurement Observation of a current with a device flowing with the current.

lag time 1) The delay between some event and its effect. 2) The time it takes a flood wave to move downstream.

lake A large body of water contained in a depression of the earth's surface and supplied from hydrological drainage of a larger area. Locally it may be called a pond.

lake turnover The complete top-to-bottom circulation of water in a lake that occurs when the density of the surface water is the same or slightly greater that at the lake bottom; most temperate zone lakes circulate in the spring and again in the fall.

laminar Smooth, non-turbulent.

laminar flow Streamline flow in which successive flow particles follow similar path lines and head loss varies with velocity to the first power.

LAN See Local Area Network.

land application The discharge of wastewater or treated residual matter onto the ground surface or incorporated into the upper soil layer for treatment or reuse by irrigation or as a soil amendment.

land farming (of waste) A land application process in which waste matter is deposited on (or in) the soil and is degraded naturally by microbes.

landfall The term used to describe where the hurricane eye actually passes over land, usually used to describe the continental States rather than islands in the Caribbean.

landfill Facility in which solid waste from municipal and/or industrial sources is disposed; sanitary landfills are those that are operated in accordance with environmental protection standards.

landscape The traits, patterns, and structure of a specific geographic area, including its biological composition, its physical environment, and its anthropogenic or social patterns. An area where interacting ecosystems are grouped and repeated in similar form.

landscape characterization Documentation of the traits and patterns of the essential elements of the landscape.

landscape ecology The study of the distribution patterns of communities and ecosystems, the ecological processes that affect those patterns, and changes in pattern and process over time.

landscape indicator A measurement of the landscape, calculated from mapped or remotely sensed data, used to describe spatial patterns of land use and land cover across a geographic area. Landscape indicators may be useful as measures of certain kinds of environmental degradation such as forest fragmentation.

land treatment A land application process in which treated effluent is periodically applied in controlled amounts to an established field area in a manner designed to protect public health and prevent violations of water quality standards.

Langelier Index (L.I.) An index reflecting the equilibrium pH of a water with respect to calcium and alkalinity. This index is used in stabilizing water to control both corrosion and the deposition of scale. Langelier Index = pH - pH_s

where pH = actual pH of the water and pH_s = pH at which the water having the same alkalinity and calcium content is just saturated with calcium carbonate.

large quantity generator Person or facility generating more than 2,200 pounds of hazardous waste per month. Such generators produce about 90 percent of the nation's hazardous waste, and are subject to all RCRA requirements.

large-volume user A water customer, usually industrial or wholesale, whose usage is substantial to other users; large-volume users may present unique peaking or other demand characteristics.

large water system A waterworks that serves more than 50,000 persons.

larva An early developmental stage of an animal which changes structurally when it becomes an adult, e.g., a tadpole or caterpillar.

latency Time from the first exposure to a chemical until the appearance of a toxic effect.

latency period A period of subclinical or inapparent pathologic changes following exposure, ending with the onset of symptoms of chronic disease.

latent energy

latent heat The heat (energy) absorbed or released as water changes between the gas (water vapor), the liquid (water droplets), and the solid (ice) state.

latent period The time interval between exposure to toxic chemical agents and the onset of signs and symptoms of illness.

lateral sewers Sewage collection pipelines only serving individual homes and businesses. Not to be confused with submains that receive flow from two or more laterals.

latitude The angular distance between a terrestrial position and the equator measured northward or southward from the equator along a meridian of longitude.

laundering weir Sedimentation basin overflow weir. A plate with V-notches along the top to assure a uniform exit or effluent velocity in order to avoid short circuiting.

launders Sedimentation basin and filter discharge channels, consisting of overflow weir plates (in sedimentation basins) and conveying troughs.

leak detection Methods for identifying water leakage in pipes and fittings.

leeward The side of an object or obstacle, such as a ship's sail, a mountain, or a hill, furthest away from the wind, and therefore, protected from the direct force of the wind. The opposite of windward.

lethal concentration 50% (LC50) The concentration of a chemical in air or water which is expected to cause death in 50% of test animals living in that air or water; lethal concentration.

lethal dose 50% (LD50) The dose of a chemical taken by mouth or absorbed by the skin which is expected to cause death in 50% of the test animals so treated; lethal dose.

leachate A liquid that has been contaminated as it passes through wastes, agricultural pesticides, or fertilizers.

leachate collection system A system that gathers leachate and pumps it to the surface for treatment.

leaching The process by which soluble substances are dissolved and leachate is transported on or through the soil. Leaching may occur in farming areas, feedlots, and landfills and may result in hazardous substances entering surface water, groundwater, or soil.

lead (Pb) A heavy metal that is hazardous to health if breathed or swallowed. Its use in gasoline, paints, and plumbing compounds has been sharply restricted or eliminated by federal laws and regulations. See heavy metals.

lead service line A service line made of lead which connects the water main to the building inlet and any lead pigtail, gooseneck, or other fitting which is connected to such lead line.

leaky aquifer A low-permeability layer that can transmit water at sufficient rates to furnish some recharge to a well pumping from an adjacent aquifer.

leap year A calendar year containing 366 days. According to the present Gregorian calendar, all years with the date-number divisible by 4 are leap years, except century years. The latter are leap years when the date-number is divisible by 400.

legal status The legal constitution of a business enterprise as to whether it is a corporation, partnership, cooperative, or sole-ownership.

legionella A genus of bacteria, some species of which have caused a type of pneumonia called Legionnaires Disease.

length The distance in the direction of flow between two specific points along a river, stream, or channel.

lentic Still or slowly flowing water situations, e.g., ponds, lakes, and swamps.

lentic system A nonflowing or standing body of fresh water, such as a lake or pond. Compare to lotic system.

lesion A pathological or traumatic discontinuity of tissue or loss of function of a part.

lethal Deadly; fatal.

levee A long, narrow embankment usually built to protect land from flooding. If built of concrete or masonary the structure is usually referred to as a flood wall. Levees and floodwalls 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.

level controls A float device (or pressure switch) which senses changes in a measured variable and opens or closes a switch in response to that change. In its simplest form, this control might be a floating ball connected mechanically to a switch or valve such as is used to stop water flow into a toilet when the tank is full.

level of concern (LOC) The concentration in air of an extremely hazardous substance above which there may be serious immediate health effects to anyone exposed to it for short periods

level of no motion A level (or layer) at which it is assumed that an isobaric surface coincides with a geopotential surface. A level (or layer) at which there is no horizontal pressure gradient force.

level surface See geopotential surface as preferred term.

leverage The use of capitalization grants as the security for the sale of state bonds.

licensure A method of regulation whereby the Commonwealth, through the issuance of a license, authorizes a person possessing the character and minimum skills to engage in the practice of a profession or occupation which is unlawful to practice without a license.

life cycle The series of changes or stages undergone by an organism from fertilization, birth, or hatching to reproduction of the next generation.

life-cycle cost The overall cost for a particular program or system over the time period corresponding to the estimated life of the program or system. Costs include direct and indirect initial costs as well as recurring or periodic costs for operations and maintenance.

lifelines

life span The expected useful life of a supply-side or demand-side project, measure, or practice. (The life span may not be identical to useful life for tax purposes.)

life system (rare) A population and the environment that influences it; see ecosystem.

lifetime exposure Total amount of exposure to a substance that a human would receive in a lifetime (usually assumed to be 70 years).

life zone (rare) An altitudinal or latitudinal zone defined by climatic characteristics and having certain plants and animals, especially birds and mammals.

lift In a sanitary landfill, a compacted layer of solid waste and the top layer of cover material.

lifting station See pumping station.

ligase Enzyme used to join dna molecules.

lime Calcium oxide (CaO) or quicklime, prepared by heating calcium carbonate thus driving off carbon dioxide.

limestone scrubbing Use of a limestone and water solution to remove gaseous stack-pipe sulfur before it reaches the atmosphere.

Limited Automatic Report Collector (LARC) An electronic device which interfaces a river or precipitation gage with a telephone line making it possible for remote computers to call a gaging site and retrieve data.

limited degradation An environmental policy permitting some degradation of natural systems, but terminating at a level well beneath an established health standard.

limiting factor An environmental factor or factors that limit distribution and/or abundance of an organism or its population, i.e., the factor that is closest to the physiological limits of tolerance of that organism.

limnetic zone 1) The open water zone of a lake or pond from the surface to the depth of effective light penetration. 2) Offshore, areas shallow enough to support rooted aquatic plants.

limnology The science that deals with lakes and, by extension, with all inland waters. It is concerned especially with the biology of the waters and bottoms.

lindane A pesticide that causes adverse health effects in domestic water supplies and is also toxic to freshwater and marine aquatic life.

linearized multistage model Derivation of the multistage model where the data are assumed to be linear at low doses.

liner 1) A relatively impermeable barrier designed to prevent leaching from a volume of contained wastes or polluted liquid. 2) An insert or sleeve for sewer pipes to prevent leakage or infiltration.

lining A coating of concrete, rubber, or plastic to a canal, tunnel, shaft or reservoir to provide water-tightness, prevent erosion, reduce friction, or support the periphery of the structure.

links A graphic, line of text, or both on a Web page that connects to another page on the same Web site or to one on a Web server located anywhere in the world. Links are "clicked on" to go to the Web page they specify.

lipid solubility The maximum concentration of a chemical that will dissolve fatty substances. Lipid soluble substances are insoluble in water. They will very selectively disperse through the environment via uptake in living tissue.

liquefaction The transformation of large solid particles of sludge into either a soluble or finely dispersed state.

liquid chlorine A liquefied, compressed gas as shipped in commerce. Note: The term liquid chlorine is sometimes used to describe a hypochlorite solution often employed for swimming pool sanitation. This use of the term is incorrect.

liquid injection incinerator Commonly used system that relies on high pressure to prepare liquid wastes for incineration breaking them up into tiny droplets to allow easier combustion.

listed waste Wastes listed as hazardous under RCRA but which have not been subjected to the Toxic Characteristics Listing Process because the dangers they present are considered self-evident.

ListServ Mailing list program for communicating with other people who have subscribed to the same list. Using E-mail, you can participate in listservs pertaining to your topics of interest. When you submit a message to the server your message is relayed to all those on the listserv. You receive messages from other participants via E-mail. It is similar to computer conferencing, but a listserv is asynchronous.

lithologic correlation Verifying results of an analytic method through direct study of the macroscopic features of a rock (e.g., its texture or petrology).

lithology The study of the chemical composition and structure of rocks, especially with characteristics that can be studied without a high magnification; also a study of the character of rock formations.

lithosphere A general term for the outer layer of the earth. A wind blown deposit of silty soil having little or no stratification.

litigation The act or process of carrying on a lawsuit.

litter The highly visible portion of solid waste carelessly discarded outside the regular garbage and trash collection and disposal system.

littoral Of the shoreward region of a body of water in which light penetrates to the bottom; in lakes or ponds, from shoreline to the lakeward limit of rooted aquatic plants; in oceans, from shoreline to a depth of 200 meters.

littoral current A current in the littoral zone such as a long shore or rip current.

littoral zone 1) That portion of a body of fresh water extending from the shoreline lakeward to the limit of occupancy of rooted plants. 2) The strip of land along the shoreline between high and low water levels. 3) In coastal engineering, the area from the shoreline to just beyond the breaker zone. 4) In biological oceanography, it is that part of the benthic division extending from the high water line out to a depth of about 200 meters. The littoral system is divided into a eulittoral and sublittoral zone, separated at a depth of about 50 meters. Also, frequently used interchangeably with intertidal zone.

live capacity The total amount of storage capacity available in a reservoir for all purposes, from the dead storage level to the normal water or normal pool level surface level. Does not include surcharge, or dead storage, but does include inactive storage, active conservation storage and exclusive flood control storage.

livestock water use Water for livestock watering, feed lots, dairy operations, fish farming, and other on-farm needs. Livestock as used here includes cattle, sheep, goats, hogs, and poultry. Also included are animal specialties. See also rural water use and animal specialties water use.

loading 1) The quantity of a substance entering the environment (soil, water, or air). 2) Quantity of material applied to a device at one time.

load management Methods for managing levels and patterns of usage to optimize system resources and facilities.

LOAEL Lowest-observed-adverse-effect level; the lowest dose in an experiment which produced an observable adverse effect.

local action Corrosion due to action of local cells, i.e., galvanic cells caused by nonumiformities between two adjacent areas at a metal surface exposed to an electrolyte.

local action statement A release prepared by a National Weather Service Forecast Office in or near a threatened area giving specific details for its area of responsibility.

local area network (LAN) Communications network connecting computers by wire, cable, or fiber optics link. Usually serves parts of an organization located close to one another, generally in the same building or within 2 miles of one another. Allows users to share software, hardware and data.

local cell A galvanic cell caused by small differences in composition in the metal ion concentration at two locations on the same metal surface.

local education agency (LEA) In the asbestos program, an educational agency at the local level that exists primarily to operate schools or to contract for educational services, including primary and secondary public and private schools. A single, unaffiliated school can be considered an LEA for AHERA purposes.

local emergency The condition declared by the local governing body when in their judgment a disaster is of sufficient magnitude to warrant coordinated local governing action to prevent or alleviate damage.

Local Emergency Planning Committee (lepc) A committee appointed by the state emergency response commission as required by SARA Title III, to formulate a comprehensive emergency plan for its jurisdiction.

local flooding Flooding conditions over a relatively limited (localized) area.

local government Boroughs, cities, counties, municipalities, towns, and other local jurisdictions within the state. plume

local time Time in which noon is defined by the transit of the Sun over the local meridian as distinguished from standard time which is based upon the transit of the Sun over a standard meridian. Local time may be either mean or apparent, according to whether reference is to the mean or actual Sun. Local time was in general use in the United States until 1883, when standard time was adopted. The use of local time in other parts of the world has also been practically abandoned in favor of the more convenient standard time.

locus The site of a gene on a chromosome.

log and safety boom A net-like device installed in a reservoir, upstream of the principal spillway, to prevent logs, debris, and boaters from entering a water discharge facility or spillway.

logarithm The exponent that indicates the power to which a number must be raised to produce a given number. For example, if B² = N, the 2 is the logarithm of N (to the base B) or 10² = 100 and log₁₀100 = 2. Also abbreviated to “log.”

logging on Connecting to a computer network, typically through the use of a personalized identification code.

log growth phase The period of time when the mass of microorganisms is doubling at regular intervals.

log inactivation (log removal) Means that a 99.9% reduction is a 3-log inactivation; a 99.99% reduction is a 4-log inactivation.

log line A graduated line used to measure the speed of a vessel through the water or to measure the velocity of the current from a vessel at anchor. See current line.

log phase The stage of bacterial growth where the cells divide steadily at a constant rate. If the logarithm of the number of cells is plotted against time, the result is a straight line. This is the phase of maximum growth.

log-rate filter A biological contactor designed to be operated with a hydraulic load of 25 to 100 gpd/sq. ft. of media surface. Also called standard-rate filter.

longitude Angular distance in a great circle of reference reckoned from an accepted origin to the projection of any point on that circle. Longitude on the Earth's surface is measured on the Equator east and west of the meridian of Greenwich and may be expressed either in degrees or in hours, the hour being taken as the equivalent of 15° of longitude. Celestial longitude is measured in the ecliptic eastward from the vernal equinox. The mean longitude of a celestial body moving in an orbit is the longitude that would be attained by a point moving uniformly in the circle of reference at the same average angular velocity as that of the body, with the initial position of the point so taken that its longitude would be the same as that of the body at a certain specified position in its orbit. With a common initial point, the mean longitude of a body will be the same in whatever circle it may be reckoned.

long period constituent A tidal or tidal current constituent with a period that is independent of the rotation of the Earth but which depends upon the orbital movement of the Moon or the Earth. The principal lunar long period constituents have periods approximating the month and half month, and the principal solar long period constituents have periods approximating the year and half year.

long period waves (long waves) Forced or free waves whose lengths are much longer than the water depth. See tidal wave and tsunami.

longshore current A current paralleling the shore largely within the surf zone. It is caused by the excess water brought to the zone by the small net mass transport of wind waves. Long shore currents feed into rip currents. See progressive wave.

long-term storage dams Reservoirs used for recreational use or storage of irrigation, municipal or industrial water. Because water is impounded on a "permanent" basis, the design of these dams is more complex than for tailings or flood control detention dams. A long-term storage dam may include an impermeable core surrounded by shell materia, have many types of drains and filters, outlet works, with gates and valves, seepage collection boxes, and possibly several spillways. The capacity of the spillway is dependant upon the downstream hazard potential.

Loop Current A current setting clockwise in the Gulf of Mexico. It enters through the Yucatan Channel from the Caribbean Sea and leaves through the Straits of Florida.

loop of stationary wave That portion of the oscillating area where the vertical movement is greatest.

losses (water) Metered source water less revenue-producing water and authorized unmetered water uses.

lotic Of or related to rapid water situations, living in waves or currents.

lotic system A flowing body of fresh water, such as a river or stream. Compare lentic system.

low A region of low pressure.

lower explosive limit (LEL) The point at which the concentration of a gas in air is sufficiently large to result in an explosion if an ignition source is present.

lower high water (LHW) The lowest of the high waters of any specified tidal day due to the declination Al effects of the Moon and Sun.

lower low water (LLW) The lowest of the low waters (or single low water) of any specified tidal day due to the declination Al effects of the Moon and Sun.

lower low water datum (LLWD) An approximation of mean lower low water that has been adopted as a standard reference for a limited area and is retained for an indefinite period regardless of the fact that it may differ slightly from a better determination of mean lower low water from a subsequent series of observations. Used primarily for river and harbor engineering purposes. Columbia River lower low water datum is an example.

lowest achievable emission rate The rate of emissions that reflects (a) the most stringent emission limitation in the implementation plan of any state for such source unless the owner or operator demonstrates such limitations are not achievable; or (b) the most stringent emissions limitation achieved in practice, whichever is stricter. A proposed new or modified source may not emit pollutants in excess of existing new source standards.

lowest-observed-adverse-effect-level The lowest dose in an experiment that produces an observable adverse effect.

lowland flooding Inundation of low areas near a river, often rural but may also occur in urban areas.

low-level invest An investigative mission for tropical disturbances to: 1) determine the existence or non-existence of a "closed circulation" (winds blowing in a complete circle); 2) supply weather observations in required areas, and; 3) determine the vortex center, if any. These missions are flown at 500 to 1500 feet.

low-level radioactive waste (LLRW) Wastes less hazardous than most of those associated with nuclear reactor; generated by hospitals, research laboratories, and certain industries. See high-level radioactive wastes.

low NOx burners One of several combustion technologies used to reduce emissions of nitrogen oxides (Nox).

low-pressure system An area of a relative pressure minimum that has converging winds and rotates in the same direction as the earth. This is counterclockwise in the Northern Hemisphere and clockwise in the Southern Hemisphere. Also known as an cyclone, it is the opposite of an area of high pressure, or a anticyclone. See closed low, cold low, and cut-off low for further examples.

low tide Same as low water.

low water (LW) The minimum height reached by a falling tide. The low water is due to the periodic tidal forces and the effects of meteorological, hydrologic, and/or oceanographic conditions. For tidal datum computational purposes, the minimum height is not considered a low water unless it contains a tidal low water.

low water datum An approximation to the plane of mean low water that has been adopted as a standard reference plane for a limited area and is retained for an indefinite period regardless of the fact that it may differ slightly from a better determination of mean low water from a subsequent series of observations. Used primarily for river and harbor engineering purposes.

low water equinoctial springs Low water springs near the times of the equinoxes.

low water inequality See diurnal inequality.

low water interval (LWI) See lunitidal interval.

low water line The intersection of the land with the water surface at an elevation of low water.

low water-use landscaping Use of plant materials that are appropriate to an area’s climate and growing conditions (usually native and adaptive plants.) See Xeriscape™.

LTB (Lauryl Tryptose Broth) The medium used for the Presumptive Test of the Multiple Tube Fermentation (MTF) Procedure.

lunar cycle An ambiguous expression which has been applied to various cycles associated with the Moon's motion.

lunar day The time of the rotation of the Earth with respect to the Moon, or the interval between two successive upper transits of the Moon over the meridian of a place. The mean lunar day is approximately 24.84 solar hours in length, or 1.035 times as great as the mean solar day.

lunar interval The difference in time between the transit of the Moon over the meridian of Greenwich and a local meridian. The lunar interval equals the difference between the local and Greenwich interval of a tide or current phase.

lunar month Same as synodical month.

lunar nodes The points where the plane of the Moon's orbit intersects the ecliptic. The point where the Moon crosses in going from south to north is called the ascending node and the point where the crossing is from north to south is called the descending node. References are usually made to the ascending node which, for brevity, may be called the node.

lunar tide That part of the tide on the Earth due solely to the Moon as distinguished from that part due to the Sun.

lunar time Time based upon the rotation of the Earth relative to the Moon. See lunar day.

lunation Same as synodical month.

lunicurrent interval The interval between the Moon's transit (upper or lower) over the local or Greenwich meridian and a specified phase of the tidal current following the transit. Examples are strength of flood interval and strength of ebb interval, which may be abbreviated to flood interval and ebb interval, respectively.

lunitidal interval The interval between the Moon's transit (upper or lower) over the local or Greenwich meridian and the following high or low water. The average of all high water intervals for all phases of the Moon is known as mean high water lunitidal interval and is abbreviated to high water interval (HWI). Similarly, mean low water lunitidal interval is abbreviated to low water interval (LWI).

lux (lx) The International System (SI) unit of illumination. It is the illumination on a surface one square meter in area on which there is a uniformly distributed flux of one lumen, or the illumination produced at a surface all points of which are at a distance of one meter from a uniform point source of one candela

lymphokines Ssubstances released predominantly from t-lymphocytes after reaction with the specific antigen. Lymphokines are biologically highly active and will cause chemotaxis and activation of macrophages and other cell mediated immune reactions. Gamma-interferon is a lymphokine.

lysimeter A device to measure the quantity or rate of downward water movement through a block of soil usually undisturbed, or to collect such percolated water for quality analysis.

lysis The process whereby a cell wall breakdown occurs releasing cellular content into the surrounding environment. Destruction of bacteria by infective phage.