M or Molar A solution where one gram molecular weight of a compound is dissolved in enough water to make one liter of solution.
macrofauna The large (visible to the naked eye) animals of an area.
macrophytes Large bodied (non-microscopic) vascular aquatic plants.
macro pores Spaces within a geologic material above the water table that are too large to hold water by capillary action. Macro porosity may result in enhanced migration of contaminants into groundwater.
macroscopic organisms Organisms large enough to be seen by the eye without the aid of a microscope.
magistrate A part time or full time court official authorized to try misdemeanor cases without a jury and to perform certain other duties of the court, such as issuing inspection warrants.
magnetic azimuth Azimuth reckoned from the magnetic north or magnetic south. See magnetic direction.
magnetic declination Same as variation.
magnetic direction Direction as indicated by a magnetic compass after correction for deviation but without correction for variation.
mainframe computer A large relatively complex computer. Its capacity far exceeds that of the microcomputer.
main stem The reach of a river or stream formed by the tributaries which flow into it.
major disaster Any natural or man-made disaster, which in the determination of the President of the United States is, of sufficient severity and magnitude to warrant Federal disaster assistance over and above emergency services normally provided.
major flooding A general term indication extensive inundation and property damage. Usually characterized by the evacuation of people and livestock and the closure of both primary and secondary roads.
major modification A term used to define modifications of major stationary sources of emissions with respect to Prevention of Significant Deterioration and New Source Review under the Clean Air Act.
major replacement costs Costs of replacement or rehabilitation of major structural or equipment items within the project life.
majors Large publically owned treatment works (potw) with flows equal to at least one million gallons per day (mgd) or servicing population equal to 10,000 persons; other POTWs having significant water quality impacts.
major stationary sources Term used to determine the applicability of Prevention of Significant Deterioration (PSD) and new source regulations. In a nonattainment area, any stationary pollutant source with potential to emit more than 100 tons per year is considered a major stationary source. In PSD areas, the cutoff level may be either 100 or 250 tons, depending upon the source.
malignant Very dangerous or virulent, causing or likely to cause death. A cancerous growth.
management plan Under the Asbestos Hazard Emergency Response Act (AHERA), a document that each Local Education Agency is required to prepare, describing all activities planned and undertaken by a school to comply with AHERA regulations, including building inspections to identify asbestos-containing materials, response actions, and operations and maintenance programs to minimize the risk of exposure.
managerial controls Methods of nonpoint source pollution control that are derived from managerial decisions, such as changes in application times or rates for agrochemicals.
mandamus A command which a superior court issues to a lower court or a person (including a government agency), ordering it to do its duty.
mandatory recycling A program which by law require consumers to separate trash so that some or all recyclable materials are recovered for recycling rather than going to landfills.
manifest A document issued by the carrier describing the contents of merchandise being transported.
manifest system A procedure in which hazardous materials are identified and tracked as they are produced, treated, transported, and disposed of by a series of permanent, linkable, descriptive documents, i.e., manifests. Commonly referred to as the cradle-to-grave system.
manifold A large pipe to which a series of smaller pipes are connected. Also called a header.
man-made beta particle All radionuclides emitting beta particles or photons, or both, listed and photon emitters in the most current edition of "Maximum Permissible Body Burdens and Maximum Permissible Concentration of Radionuclides in Air or Water for Occupational Exposure," National Bureau of Standards Handbook 69, except the daughter products of thorium-232, uranium-235 and uranium-238.
man-made disaster Any industrial, nuclear, or transportation accident, explosion, power failure, resource shortage, or other condition, except enemy action, resulting from man-made causes, which threaten or cause damage to property, human suffering, hardship or loss of life.
manometer An instrument for measuring pressure. Usually, a manometer is a glass tube filled with a liquid that is used to measure the difference in pressure across a flow-measuring device, such as an orifice or Venturi meter. The instrument used to measure blood pressure is a type of manometer.
mantle A general term for the outer covering of earth material.
manual separation Hand sorting of reyclable or compostable materials in waste.
manufacture To develop a product from materials so as to derive a benefit from the use of the product.
manufacturers formulation See formulation.
marginal utility The extra units of economic output gained from an extra unit of input (marginal cost). A plant that operates at optimum capacity will always have marginal utility equal to marginal cost.
margin of safety Maximum amount of exposure producing no measurable effect in animals (or studied humans) divided by the actual amount of human exposure in a population.
marigram A graphic record of the rise and fall of the water. The record is in the form of a curve in which time is generally represented on the abscissa and the height of the tide on the ordinate. See tide curve.
marine Of the sea or ocean.
marine boundary The mean lower low water line (MLLWL) when used as a boundary. Also, lines used as boundaries seaward of and measured from (or points thereon) the MLLWL. See coastal boundary.
marine sanitation device Equipment or processes installed on board a vessel to receive, retain, treat, or discharge sewage and approved for such purposes by the U.S. Coast Guard.
market penetration The extent to which an activity or measure is actually implemented compared to all potential uses or markets.
marginal-cost pricing A method of rate design where prices reflect the costs associated with producing the next increment of supply.
marsh A marsh is commonly differentiated from a swamp on the basis of its herbaceous vegetation (grasses, sedges, reeds, etc.) in contrast to the tree vegetation of swamps. Marshes may be dry and intermittently water covered or they may be permanently water covered.
mascaret French for tidal bore.
mass curve A graph of the cumulative values of a hydrologic quantity (such as precipitation or runoff), generally as ordinate, plotted against time or date.
master cell bank (mcb) A cell seed lot consisting of aliquots of a single culture (in most cases, expanded from a single cell) and stored cryogenically to assure genetic stability.
master metering A large meter at a point of distribution to multiple users or users that could be further submetered. Includes metered wholesale sales.
material category In the asbestos program, broad classification of materials into thermal surfacing insulation, surfacing material, and miscellaneous material.
materials recovery facility A facility that processes residentially collected mixed recyclables into new products available for market.
Material Safety Data Sheet A document that provides pertinent health and safety information and a profile of a particulary hazardous substance or mixture.
material type Classification of suspect material by its specific use or application, e.g., pipe insulation, fireproofing, and floor tile.
mathematical model An analytical, predictive model used to compute pollutant transport, treatment, or removal and used during risk assessment to perform extrapolations.
matric potential Attractive forces of soil particles for water and water molecules for each other.
matrix A rectangular array of terms called elements. It is used to facilitate the study of problems in which the relation between these elements is fundamental. A matrix is usually capable of being subject to a mathematical operation by means of an operator or another matrix according to prescribed rules.
maximum contaminant level (MCL) The maximum permissible level of a contaminant in water which is delivered to the free flowing outlet of the ultimate user of a public water system, except in the case of turbidity where the maximum permissible level is measured at the point of entry into the distribution system. Contaminants added to the water under circumstances controlled by the user are excluded from definition, except those contaminants resulting from the corrosion of piping and plumbing caused by water quality.
maximum contaminant level goal (MCLG) The maximum level of a contaminant in drinking water at which no known or anticipated adverse effect on human health would occur and which allows an adequate margin of safety. Maximum contaminant level goals are nonenforceable health goals.
maximum daily water demand The rate of water usage during the day of maximum water use.
maximum-day demand Total production for the water system on its highest day of production during a year.
maximum envelope of water (MEOW) Describes the predicted areas inundated and amount of storm surge for a particular area during the landfall of a hurricane.
maximum envelope of wind (MEOW) Describes the predicted areas inundated and amount of wind for a particular area during the landfall of a hurricane.
maxiumum spillway discharge Spillway discharge when reservoir is at maximum designed water surface elevation.
maximum tolerated dose The maximum dose that an animal species can tolerate for a major portion of its lifetime without significant impairment or toxic effect other than carcinogenicity.
maximum total trihalomethane potential (MTTP) The maximum concentration of total trihalomethanes produced in a given water containing disinfectant residual after seven days at 25°C or above.
MBAS Methylene-Blue-Active Substances. These substances are used in surfactants or detergents.
MCL See maximum contaminant level.
MCLG See maximum contaminant level goal.
mean A measure of central tendency in statistics. The average value of the values in a set. It is calculated by dividing the sum of the individual values by the number of values in the set. See mean, arithmetic and mean, geometric.
mean areal precipitation (MAP) The average rainfall over a given area, generally expressed as an average depth over the area.
mean, arithmetic The measure of central location commonly called the average. It is calculated by adding together all the individual values in a group of measurements and dividing by the number of values in the group.
mean cell residence time Average time period that a unit of biomass is retained in biological reactors, including the activated sludge process; also known as solids retention time.
mean current hour Same as current hour.
mean depth The average depth of water in a stream channel or conduit. It is equal to the cross-sectional area divided by the surface width.
meander The winding of a stream channel.
meander belt The area between lines drawn tangential to the extreme limits of fully developed meanders.
mean diurnal tide level (MDTL) A tidal datum. The arithmetic mean of mean higher high water and mean lower low water.
mean, geometric The mean or average of a set of data measured on a logarithmic scale.
mean high water (MHW) A tidal datum. The average of all the high water heights observed over the National Tidal Datum Epoch. For stations with shorter series, simultaneous observational comparisons are made with a control tide station in order to derive the equivalent datum of the National Tidal Datum Epoch.
mean high water line (MHWL) The line on a chart or map which represents the intersection of the land with the water surface at the elevation of mean high water. See shoreline.
mean higher high water (MHHW) A tidal datum. The average of the higher high water height of each tidal day observed over the National Tidal Datum Epoch. For stations with shorter series, simultaneous observational comparisons are made with a control tide station in order to derive the equivalent datum of the National Tidal Datum Epoch.
mean higher high water line (MHHWL) The line on a chart or map which represents the intersection of the land with the water surface at the elevation of mean higher high water.
mean low water (MLW) A tidal datum. The average of all the low water heights observed over the National Tidal Datum Epoch. For stations with shorter series, simultaneous observational comparisons are made with a control tide station in order to derive the equivalent datum of the National Tidal Datum Epoch.
mean sea level (MSL) The average level of the sea, as calculated from a large number of observations taken at equal time intervals. It is the standard level from which all heights are calculated.
mean low water line (MLWL) The line on a chart or map which represents the intersection of the land with the water surface at the elevation of mean low water.
mean low water springs (MLWS) A tidal datum. Frequently abbreviated spring low water. The arithmetic mean of the low water heights occurring at the time of spring tides observed over the National Tidal Datum Epoch.
mean lower low water (MLLW) A tidal datum. The average of the lower low water height of each tidal day observed over the National Tidal Datum Epoch.
mean lower low water line (MLLWL) The line on a chart or map which represents the intersection of the land with the water surface at the elevation of mean lower low water.
mean range of tide (Mn) The difference in height between mean high water and mean low water.
mean rise The height of mean high water above the elevation of chart datum.
mean rise interval (MRI) The average interval between the transit of the Moon and the middle of the period of the rise of the tide.
mean river level A tidal datum. The average height of the surface of a tidal river at any point for all stages of the tide observed over the National Tidal Datum Epoch.
mean sea level (MSL) A tidal datum. The arithmetic mean of hourly heights observed over the National Tidal Datum Epoch. Shorter series are specified in the name; e.g., monthly mean sea level and yearly mean sea level.
mean sun A fictitious sun which is assumed to move in the celestial equator at a uniform speed corresponding to the average angular speed of the real Sun in the ecliptic, the mean sun being alternately in advance and behind the real Sun. It is used as a reference for reckoning mean time, noon of mean local time corresponding to the time of the transit of the mean sun over the local meridian. See equation of time and mean time.
mean tide level (MTL) Same as half-tide level.
mean time Time based upon the hour angle of the mean sun as distinguished from apparent time which is based upon the position of the real Sun. The difference between apparent and mean time is known as the equation of time.
mean water level (MWL) A datum. The mean surface elevation as determined by averaging the heights of the water at equal intervals of time, usually hourly. Mean water level is used in areas of little or no range in tide.
mean water level line (MWLL) The line on a chart or map which represents the intersection of the land with the water surface at the elevation of mean water level.
measured variable A characteristic or component part that is sensed and quantified (reduced to a reading of some kind) by a primary element or sensor.
measure of association A quantified relationship between exposure and disease; includes relative risk, rate ratio, odds ratio.
measure of central location A central value that best represents a distribution of data. Measures of central location include the mean, median, and mode. Also called the measure of central tendency.
measure of dispersion A measure of the spread of a distribution out from its central value. Measures of dispersion used in epidemiology include the interquartile range, variance, and the standard deviation.
mechanical aeration A process using mechanical energy to inject air into water, causing the wastewater to absorb oxygen from the air.
mechanical joint A flexible device that joins pipes or fittings together by the use of lugs and bolts.
mechanical separation Using mechanical means to separate waste into various components.
mechanical turbulence Random irregularities of fluid motion in air caused by buildings or other non-thermal, processes.
media 1) Plural of medium. 2) The porous material in a filter over which processed water or wastewater is uniformly distributed and from which filtrate is collected during treatment.
median A measure of central tendency in statistics. The value (or point in a series) in a set of data that divides the ranked values into two equal-sized groups— one consisting of values equal to or smaller than the median, the other consisting of values equal to or greater than the median.
medical surveillance A periodic comprehensive review of a worker’s health status.
medical waste Any solid waste generated in the diagnosis, treatment, or immunization of human beings or animals, in research pertaining thereto, or in the production or testing of biologicals, excluding hazardous waste identified or listed under CFR Part 261 or any household waste as defined in 40 CFR Subsection 261.4 (b) (1).
medium (pl. media) A nutritional formulation used for the growth of microorganisms.
medium-size water system A water system that serves greater than 3,300 and less than or equal to 50,000 persons.
meg A procedure used for checking the insulation resistance on motors, feeders, buss bar systems, grounds, and branch circuit wiring. Also see megger.
megaton An explosive force equivalent to that of 1,000,000 tons (907,000,000 kg) of TNT.
megger (from megohm) An instrument used for checking the insulation resistance on motors, feeders, buss bar systems, grounds, and branch circuit wiring. Also see meg.
megohm Meg means one million, so megohm means one million ohms. A megger reads in million of ohms. See ohm.
meltdown The melting of nuclear fuel.
membrane A thin barrier composed of a substance with limited porosity that only permits passage of small particles such as molecules.
memorandum of understanding (MOU) A formal agreement between government agencies. The agreement does not involve a transfer of funds or a transfer of personal or real property (agreements calling for transfer of funds, or a transfer of personal or real property are considered interagency agreements).
Mendo broth The medium used for the Membrane Filter Procedure.
meniscus The curved top of a column of liquid (water, oil, mercury) in a small tube. When the liquid wets the sides of the container, as with water, the curve forms a valley. When the confining sides are not wetted, as with mercury, the curve forms a hill or upward bulge.
mercury (Hg) A silvery-colored metal, commonly called quicksilver. The term refers to any of the different chemical forms that mercury can take, including methylmercury, Hg zero, and Hg(II).
mercury two Mercury two is the mercury ion. Because it is water soluble and associates with particulates, atmospheric deposition of mercury two is relatively fast, either as dry deposition or in precipitation. Combustion sources can emit both mercury zero and mercury two. Mercury two can be produced in the atmosphere by the oxidation of mercury zero by ozone or other oxidants.
merisitic variation Variation among segments in a segmented animal.
meromictic Lakes that undergo only a partial circulation.
meroplankton Organisms with temporary planktonic phases in their life cycle, e.g., oyster and crab larvae.
mesh One of the openings or spaces in a screen or woven fabric. The value of the mesh is usually given as the number of openings per inch. This value does not consider the diameter of the wire or fabric; therefore, the mesh number does not always have a definite relationship to the size of the hole.
mesic Characterized or pertaining to conditions of medium moisture supply.
mesophile A bacterium that grows best within the temperature range 25°C to 40°C.
mesotrophic Reservoirs and lakes which contain moderate quantities of nutrients and are moderately productive in terms of aquatic animal and plant life.
mesophilic bacteria A group of bacteria that thrive in a temperature range of 68 ° F and 113°F.
messenger rna (mrna) Rna that serves as the template for protein synthesis; it carries the transcribed genetic code from the dna to the protein synthesizing complex to direct protein synthesis. See ribonucleic acid.
metabolism The total chemical and physical processes by which the functional and nutritional activities of an organism are maintained.
metabolite Any product of metabolism, especially a transformed chemical.
metal Any of a class of elementary substances, as gold, silver, or copper, all of which are crystalline when solid, and many of which are characterized by opacity, ductility, conductivity, and a unique luster when freshly fractured. An element yielding positively charged ions in aqueous solution of its salts.
metalimnion The middle layer in a thermally stratified lake or reservoir. In this lake there is a rapid decrease in temperature with depth. Also called the thermocline.
metal ion concentration cell A galvanic cell caused by a difference in metal ion concentration at two locations on the same metal surface.
metastatic Pertaining to the transfer of disease from one organ or part to another not directly connected with it.
meteoric water Water derived from precipitation.
meteorological tides Tidal constituents having their origin in the daily or seasonal variations in weather conditions which may occur with some degree of periodicity. The principal meteorological constituents recognized in the tides are Sa, Ssa, and S1. See storm surge.
meter 1) The metric basic measurement of length equal to 3.3 feet. 2) A device for measuring. 3) An instrument for measuring and recording water volume.
methane A colorless, nonpoisonous, flammable gas created by anaerobic decomposition of organic compounds.
Method 18 A test method which uses gas chromatographic techniques to measure the concentration of volatile organic compounds in a gas stream.
Method 24 A reference method to determine density, water content and total volatile content (water and VOC) of coatings.
Method 25 A reference method to determine the VOC concentration in a gas stream.
method blank A portion of reagent water analyzed as if it were a sample.
methoxychlor A pesticide which causes adverse health effects in domestic water supplies and is also toxic to freshwater and marine aquatic life. The chemical name for methoxychlor is 2,2-bis (p-methoxyphenol)-1,1,1-trichloroethane.
methylmercury Any of several extremely toxic compounds formed from metallic mercury by the action of microorganisms and capable of entering the food chain.
methyl orange alkalinity A measure of the total alkalinity in a water sample. The alkalinity is measured by the amount of standard sulfuric acid required to lower the pH of the water to a pH level of 4.5, as indicated by the change of color of methyl orange from orange to pink. Methyl orange alkalinity is expressed as milligrams per liter equivalent calcium carbonate.
Metonic cycle A period of almost 19 years or 235 lunations. Devised by Meton, an Athenian astronomer who lived in the fifth century B.C., for the purpose of obtaining a period in which new and full Moon would recur on the same day of the year. Taking the Julian year of 365.25 days and the synodic month as 29.530,588 days, we have the l9-year period of 6,939.75 days as compared with the 235 lunations of 6,939.69 days, a difference of only 0.06 day.
MF Procedure (Membrane Filter Procedure) A test for coliform bacteria that involves filtering the water sample to capture the bacteria, then incubating the filter in Mendo broth to encourage growth of coliforms and counting the number of colonies that grow on the filter. Colonies are submitted to the Verified Test to assure quality control. The results may be reported as the number of coliform colonies per 100 mL of water (for internal use by the water system) or as the presence or absence of total coliforms for US Environmental Protection Agency microbiological compliance testing.
mg/L Milligrams per liter.
microbial growth The activity and growth of microorganisms, such as bacteria, algae, diatoms, plankton, and fungi.
microbial pesticide A microorganism that is used to control a pest, but of minimum toxicity to man.
microbiota The microscopic organisms present in an area or volume. Also referred to as biomass.
microclimate Conditions of moisture, temperature, etc., as influenced by the topography, vegetation, etc.
microcomputer A computer with a microprocessor chip-based processing unit. Microcomputers are the original personal computers that many people use at home and at work.
microenvironment (habitat) A small or restricted set of distinctive environmental conditions, such as a dead animal or a fallen log.
microflora The microscopic plants present in an area or volume.
microgram One-millionth of a gram (3.5 x 10-8 oz. = 0.000000035 oz.).
micrograms per liter (µg/L) One microgram of a substance dissolved in each liter of water. This is equal to parts per billion (ppb) since one liter of water is equal in weight to one billion micrograms.
microheterogeneity Slight differences in large, complex macromolecules that result in a population of closely related but not identical structures.
micrometer A unit of measurement: 1/1000 millimeter or 1/25,400 inch. Designated by µm; sometimes referred to as micron.
micron A unit of length. One-millionth of a meter or one-thousandth of a millimeter. One micron equals 0.00004 of an inch.
micronutrients Inorganic nutrients required in only trace amounts.
microorganism An animal or plant life form of microscopic dimensions that can be seen only with the aid of a microscope.
microphyte The smaller algae, e.g., diatoms.
microwave High-frequency radio waves used for point-to-point and omnidirectional communication of audio, data, and video signals. Microwave frequencies require direct line of sight to operate. Obstructions in the path usually distort or block the signal. Growth of fiber optic networks have tended to curtail the growth and use of microwave relays.
midextreme tide An elevation midway between extreme high water and extreme low water occurring in any locality.
midrange The halfway point or midpoint in a set of observations. For most types of data, it is calculated as the sum of the smallest observation and the largest observation, divided by two. For age data, one is added to the numerator. The midrange is usually calculated as an intermediate step in determining other measures.
migration A regular movement from one region to another.
mil A unit of length equal to 0.001 of an inch. The diameter of wires and tubing is measured in mils, as in the thickness of plastic sheeting.
millibar (MB) A metric measurement of atmospheric pressure used by the National Weather Service.. Standard surface pressure is 1,013.2 millibars.
milligram One-thousandth of a gram (3.5 x 10-5 oz. = 0.000035 oz.).
milligrams per liter (mg/L) A measure of concentration of a dissolved substance. A concentration of one mg/L means that one milligram of a substance is dissolved in each liter of water. For practical purposes, this unit is equal to parts per million (ppm) since one liter of water is equal in weight to one million milligrams. Thus a liter of water containing ten milligrams of calcium has ten parts of calcium per one million parts of water, or ten parts per million (10 ppm).
milliliter One-thousandth of a liter.
millimicron A unit of length equal to 10-3 microns (one-thousandth of a micron), 10-6 millimeters, or 10-9 meters; correctly called a namometer, nm.
million-gallons per day (MGD) A measure of water flow; 1.54723 cubic feet per second or 3.0689 acre-feet per day.
mineralization The microbial conversion of an element from an organic to an inorganic state.
minimal area The smallest area upon which a community reaches its mature or developed stage, including all of its characteristic components.
minimization A comprehensive program to minimize or eliminate wastes; usually applied to wastes at their point of origin. See waste minimization.
minimum quantification limit (MQL) The lowest concentration of an analyte in a sample that could be reliably measured and reported as a detection with a measured concentration.
minimum reporting limit (MRL) The lowest concentration of an analyte that could reliably be reported as a detection of an analyte, established as one-half the MQL. Analytes detected at a concentration between one-half the MQL and the MQL are reported as detected, without a measured concentration.
mining an aquifer Withdrawal of groundwater over a period of time that exceeds the rate of recharge of the aquifer.
mining water use Water use for the extraction of minerals occurring naturally including solids, such as coal and ores; liquids, such as crude petroleum; and gases, such as natural gas. Also includes uses associated with quarrying, well operations (dewatering), milling (crushing, screening, washing, floatation, and so forth), and other preparations customarily done at the mine site or as part of a mining activity. Does not include water used in processing, such as smelting, refining petroleum, or slurry pipeline operations. These uses are included in industrial water use.
minor flooding A general term indicating minimal or no property damage but possibly some public inconvenience.
minors Publically owned treatment works with flows less than one million gallons per day.
miscellaneous ACM Interior asbestos-containing building material or structural components, members or fixtures, such as floor and ceiling tiles; does not include surfacing materials or thermal system insulation.
miscible liquids Two or more liquids that can be mixed and will remain mixed under normal conditions.
missed detection The situation that occurs when a test indicates that a tank’s integrity is tight when in fact it is leaking.
mission The specific task or responsibility that a person or a body of persons is assigned to do or fulfill.
mist Liquid particles measuring 40 to 500 microns, formed by condensation of vapor. By comparison, fog particles are smaller than 40 microns.
mitigation 1) Actions taken to prevent or reduce the severity of harm. 2) Alleviation; abatement or diminution of a penalty or punishment imposed by law, as a result of the circumstances surrounding the crime, or the acts of the defendant.
mixed current Type of tidal current characterized by a conspicuous diunal inequality in the greater and lesser flood strengths and/or greater and lesser ebb strengths. See flood current and ebb current.
mixed funding Settlements in which potentially responsible parties and EPA share the cost of a response action.
mixed liquor A mixture of activated sludge and waters containing organic matter that is developed during the activated sludge process.
mixed liquor suspended solids (MLSS) Defined by testing method. May be roughly defined as non- filterable, solid particles in mixed liquor.
mixed liquor volatile suspended solids (MLVSS) Defined by testing method. May be roughly defined as that part of the mixed liquor suspended solids that is combustible.
mixed tide Type of tide characterized by a conspicuous diurnal inequality in the higher high and lower high waters and/or higher low and lower low waters.
mixed-use meter A meter measuring water for more than one type of end use (such as indoor and outdoor use).
mixotrophic Fed by several alternative modes of nutrition; usual for some one-celled animals and plants.
Mm Lunar monthly constituent. This constituent expresses the effect of irregularities in the Moon's rate of change of distance and speed in orbit.
mobile incinerator systems Hazardous waste incinerators that can be transported from one site to another.
mobile source Any non-stationary source of air pollution such as cars, trucks, motorcycles, buses, airplanes, locomotives.
mode A measure of central tendency in statistics. The value in a set of data that occurs most frequently.
model A simplified representation of an operation, containing only those aspects of primary importance to the problem under study. The means of representation may vary from a set of mathematical equations or a computer program to a purely verbal description of the situation.
modeling Use of mathematical equations to simulate and predict real events and processes.
model plant A hypothetical plant design used for developing economic, environmental, and energy impact analyzes as support for regulations or regulatory guidelines.
model stability The choice of variables included in the population model.
model validation The evaluation of the predictability of the model (i.e., the model form together with the model parameter estimates).
modem Equipment that converts digital signals into analog signals for purpose of transmission over a telephone line. Signal is then converted back to digital form so that it can be processed by a receiving computer. Modems are typically used to link computers via telephone lines. Short for modulator-demodulator. Typical modems for home use are 14.4 kbps. 14 kilobytes per second translates into a transmission or receiving rate of approximately 1600 bytes per second.
moderate flooding The inundation of secondary roads; transfer to higher elevation necessary to save property. Some evacuation may be required.
modus operandi Manner of working.
MOE Margin of exposure.
moisture equivalent The ratio, stated as a percentage, of the weight of water which the soil, after saturation, will retain against a centrifugal force 1,000 times the force of gravity, to the weight of the soil when dry.
molar or molarity (M) A molar solution consists of one gram molecular weight of a compound dissolved in enough water to make one liter of solution. A gram molecular weight is the molecular weight of a compound in grams. For example, the molecular weight of sulfuric acid (H2SO4) is 98. A one M solution of sulfuric acid would consist of 98 grams of H2SO4 dissolved in enough distilled water to make one liter of solution.
mold A fungus characterized by a thread-like or filamentous structure.
mole The molecular weight of a substance usually expressed in grams.
molecular weight The molecular weight of a compound in grams is the sum of the atomic weights of the elements in the compound. The molecular weight of sulfuric acid (H2SO4) is 98.
Element Atomic Weight Number of Atoms Molecular Weight
H 1 2 2
S 32 1 32
O 16 4 64
molecule The smallest division of a compound that still retains or exhibits all the properties of the substance.
mollusc, mollusk Any of a phylum of invertebrate animals including oysters, clams, mussels, snails, slugs, squids, octupi, whelks, and other shellfish.
molten salt reactor A thermal treatment unit that rapidly heats waste in a heat-conducting fluid bath of carbonate salt.
monition A formal order commanding something be done or not done.
monitoring The periodic measuring of concentrations of substances in environmental media or in human or other biological tissues.
monitoring wells Wells used to collect groundwater samples for analysis to determine the amount, type, and spread of contaminants in groundwater.
monoclonal antibodies 1) Man-made clones of a molecule, produced in quantity for medical or research purposes. 2) Molecules of living organisms that selectively find and attach to other molecules to which their structure conforms precisely. This could also apply to equivalent activity by chemical molecules. Also called MABs and MCAs.
monoculture Cultivation of land in a single crop.
monomer A molecule of low molecular weight capable of reacting with identical or different monomers to form polymers.
monomictic Lakes and reservoirs which are relatively deep, do not freeze over during the winter months, and undergo a single stratification and mixing cycle during the year. These lakes and reservoirs usually become destratified during the mixing cycle, usually in the fall of the year.
monospecific Of or related to a single species of organism.
monovalent Having a valence of one, such as cuprous (copper) ion, Cu+.
Monte Carlo Method
month The period of the revolution of the Moon around the Earth. The month is designated as siderial, tropical, anomalistic, nodical, or synodical according to whether the revolution is relative to a fixed star, vernal equinox, perigee, ascending node, or Sun. The calendar month is a rough approximation to the synodical month.
moratorium A period, during the negotiation process, of 60-90 days during which EPA and potentially responsible parties may reach settlement, but no site response activities can be conducted.
morbidity The incidence (measured frequency) of disease in a population; the illness rate.
morbidity rate A measure of the frequency of illness or disease in a population. There are two major groups of morbidity rates, incidence and prevalence rates.
moribund In a dying state.
morphology The study of the form and structure, but not the functions, of an organism.
mortality 1) Death in a population. 2) The death rate.
mortality rate A measure of the frequency of deaths within a particular population during a specified time interval. If deaths from all causes are included, the rate is called a crude death rate; if only deaths from a specific cause are included, the rate is called a cause-specific death rate. A case fatality rate is a measure of the frequency of deaths due to a particular disease among members of a population who have the disease.
MOS See margin of safety.
mosaic A patchwork pattern of distribution of habitats or communties.
most probable number (MPN) Usually applied to tube fermentation procedures for coliforms and fecal streptococci. It is an index of the number of bacteria (coliforms, etc.) that, more probably than any other number, would give the results shown by the laboratory examination. MPN is not an actual enumeration.
motile Capable of self-propelled movement. A term that is sometimes used to distinguish between certain types of organisms found in water.
motion An application to a court, either written or oral, for a rule or order.
motor efficiency The ratio of energy delivered by a motor to the energy supplied to it during a fixed period or cycle. Motor efficiency ratings will vary depending upon motor manufacturer and usually will range from 88.9 to 90.0 percent.
movable bed A stream bed made up of materials readily transportable by the stream flow.
movable bed stream This type of stream is most common where steep slopes and lack of vegetation result in a lot of erosion. During a flood, a channel may be eroded more deeply, or it may become filled with sediment and move to a different location.
MPEG (Moving Picture Experts Group) The standard for compression and storage of motion video, for example, videos available though the World Wide Web.
MPN See most probable number.
MTD Maximum tolerated dose. The dose that an animal species can tolerate for a major portion of its lifetime without significant impairment or toxic effect other than carcinogenicity.
MTF (Multiple Tube Fermentation) A series of tests used to determine the presence and approximate density of coliform bacteria in a water sample, e.g., the MPN or P/A procedures. The test is based on the property of coliform bacteria to form gas when fermenting lactose.
muck soils Earth made from decaying plant material.
mudballs Material that is approximately spherical in shape and varies from pea-sized up to two or three inches in diameter. This material forms in filters and gradually increases in size when not removed by the backwashing process.
muffle furnace A small oven capable of temperatures up to 600°C used in laboratories to incinerate samples to determine there volatile and/or fixed solids content.
mulch Any vegetable substance spread or allowed to remain on the soil surface to conserve moisture and shield soil particles from the erosive forces of raindrops and runoff.
multimedia Systems that support the interactive use of text, audio, still images, video, and graphics. Each of these elements must be converted in some way from analog form to digital form before they can be used in a computer application. Thus, the distinction of multimedia is the convergence of previously diverse systems.
multiple tide staff A succession of tide staffs on a sloping shore so placed that the vertical graduations on the several staffs will form a continuous scale referred to the same datum.
multiplex The act of combining input signals from many sources onto a single communications path, or the use of a single path for transmitting signals from several sources. Advantages of multiplexing is that it doubles the capacity of television transmission and allows for simultaneous feed of independent programs for two audiences.
multi-point videoconference A video conference with 3 or more sites. Sites must connect via a video bridge.
multipurpose reservoir A reservoir constructed and equipped to provide storage and release of water for two or more purposes such as flood control, power development, navigation, irrigation, recreation, pollution abatement, domestic water supply, etc.
multistage pump A pump that has more than one impeller. A single-stage pump has one impeller.
multistage remote sensing A strategy for landscape characterization that involves gathering and analyzing information at several geographic scales, ranging from generalized levels of detail at the national level through high levels of detail at the local scale.
multiple use Use of land for more than one purpose, i.e., grazing of livestock, wildlife production, recreation, watershed, and timber production. Also applies to bodies of water for recreational purposes, fishing, and water supply.
multistage model Mathematical model based on the multistage theory of the carcinogenic process which yields risk estimates either equal to or less than the one-hit model.
municipal discharge Discharge of effluent from publically owned wastewater treatment works (POTWs) that receive wastewater from households, commercial establishments, and industries. Combined sewer/separate storm overflows are included in this category.
municipal sewage Wastes (mostly liquid) originating from a community; may be composed of domestic wastewater and/or industrial wastewater.
mushroom valve
muskeg Moss-covered countryside or continuous boggy ground.
mutagen An agent that causes a permanent genetic change in a cell other than that which occurs during normal genetic recombination.
mutagenicity The capacity of a chemical or physical agent to cause permanent alteration of the genetic material within living cells.
mutagenesis The induction of genetic mutation by physical or chemical means to obtain a characteristic desired by researchers.
mutation A change in the genetic material, either of a single base pair (point mutation) or in the number or structure of the chromosomes.
mutualism A form of interrelationship between two organisms in which both involved organisms benefit. See symbiosis.
mycelium A mass of thread-like, branched filaments called hyphae. They are the vegetative body of a fungus.
myeloma Tumor cell line derived from a lymphocyte.