saccharide A simple sugar, combination of sugars, or polymerized sugar.
Sacramento Soil Moisture Accounting Model (SACSMA) A conceptual model that estimates runoff using a water balance to simulate the movement of water through the soil.
sacrificial anode An easily corroded material deliberately installed in a pipe or tank. The intent of such an installation is to give up (sacrifice) this anode to corrosion while the water supply facilities remain relatively corrosion free.
safe Condition of exposure under which there is a “practical certainty” that no harm will result in exposed individuals.
Safe Drinking Water Act Commonly referred to as SDWA. An Act passed by the US Congress in 1974. The Act establishes a cooperative program among local, state, and federal agencies to ensure safe drinking water for consumers. It was Amended in 1986 and reauthorized by Congress in 1996.
safe water Water that does not contain harmful bacteria or toxic materials or chemicals. Water may have taste and odor problems, color, and certain mineral problems and still be considered safe for drinking.
safe yield The annual quantity of water that can be taken from a source of supply over a period of years without depleting the source beyond its ability to be replenished naturally in “wet years.”
Saffir-Simpson Damage-potential Scale A scale, developed in the early 1970s by Herbert Saffir, a consulting engineer, and Robert Simpson, then Director of the National Hurricane Center, to measure the intensity of a hurricane from 1 to 5. The scale categorizes potential damage based on barometric pressure, wind speeds, and storm surge. Scale numbers are available to public safety officials when a hurricane is within 72 hours of landfall. Scale assessments are revised regularly as new observations are made. Public safety organizations are kept informed of new estimates of the hurricane's disaster potential. In practice, sustained surface wind speed (1-minute average) is the parameter that determines the category since storm surge is strongly dependent on the slope of the continental shelf.
salinity 1) The relative concentration of dissolved salts, usually sodium chloride, in a given water. 2) A measure of concentration of dissolved mineral substances in water.
salinity wedge 1) The movement of subsurface saline water into an aquifer or in an estuary. 2) Of a body of sea water under the fresh water.
salmoid Of or related to salmon, trout, char, and allied freshwater and anadromous fishes.
Salmonella A genus of fecal coliform bacteria that includes several pathogenic forms.
salt An ionic substance other than water resulting from the reaction between an acid and a base.
salt marsh Similar to a fresh-water, grass-dominated marsh, but adjacent to marine areas covered periodically (tidally or seasonally) with saline water.
salts The minerals that water picks up as it passes through the air, over and under the ground, and as it is used by households and industries.
salt water Water containing a dissolved salt level of 10,000 to 35,000 mg/L.
salt water encroachment The movement, as a result of human activity, of saline groundwater into an aquifer formerly occupied by fresh water. Passive saline water encroachment occurs at a slow rate owing to a general lowering of the fresh water potentiometric surface. Active saline water encroachment proceeds at a more rapid rate owing to the lowering of the fresh water potentiometric surface below sea level.
salt water intrusion The invasion of fresh surface or groundwater by salt water. If it comes from the ocean, it may be called seawater intrusion.
salvage The utilization of waste materials.
sample 1) A small portion of a substance that when examined, identifies certain characteristics of that substance. 2) A selected subset of a population. A sample may be random or non-random and it may be representative or non-representative.
sampling 1) The process of determining characteristics of a population by collecting and analyzing data from a representative segment of the population. 2) Removal of a sample for determination.
sanctions Actions taken by a government agency for failure to plan or implement a State Improvement Plan (SIP). Such action may be include withholding of highway funds and a ban on construction of new sources of potential pollution.
sanctuary An area, usually set aside by legislation or deed restrictions, for the preservation and protection of organisms.
sand Soil particles between 0.05 and 2.0 mm in diameter.
sand filters, biological Contactors that remove some suspended solids from wastewater. Air and bacteria decompose organic matter filtering through the sand so that cleaner water is collected as filtrate.
sanitary facilities Piping and fixtures, such as sinks, lavatories, showers, and toilets, supplied with potable water and drained by wastewater piping.
sanitary landfill See landfill.
sanitary sewer A sewer that transports only wastewaters (from residences and/or industries) to a wastewater treatment plant. See combined sewer.
sanitary survey 1) An on-site review of the water source, facilities, equipment, operators, and maintenance of a public water system for the purpose of evaluating the adequacy of the facilities for producing and distributing safe drinking water. 2) An investigation of any condition that may affect public health.
sanitary water Also known as gray water. Water discharged from sinks, showers, kitchens, or other nonindustrial operations, but not from commodes.
sanitation Control of physical factors in the human environment that could harm development, health, or survival.
sanitize To reduce the level of microorganisms in materials or on surfaces of objects to levels deemed safe by environmental health specialists or sanitarians.
saprobic Of or related to living forms living in foul, badly polluted, or septic waters.
sapropel Ooze; slimy black or brown sediment of marine, estuarine, or (rarely) lacustrine deposition consisting largely of organic debris. Finely divided, rich in iron and silfide.
saprophyte An organism which lives on dead organic matter. Saprophytes help natural decomposition of organic matter in water.
saprophytic organsims Organisms living on dead or decaying organic matter. They help natural decomposition of the organic solids in was
satellite An earth-orbiting device used for receiving and transmitting signals. Each satellite has a number of transponders which receive the signal and bounce it back to earth, where it is received by any of the dish-shaped earth stations, then transmitted via cable, phone lines, or microwave to its final receiver.
satellite pictures Pictures taken by a weather satellite, such as GOES-9, that reveal information, such as the flow of water vapor, the movement of frontal systems, and the development of a tropical system. Looping individual pictures aids meteorologists in forecasting. One way a picture can be taken is as a visible shot, which is best during times of visible light (daylight). Another way is as an IR (infrared) shot, which reveals cloud temperatures and can be used day or night.
saturated solution A solution that can dissolve no more of a given substance and will not precipitate any of that substance.
saturated zone The subsurface zone where pore spaces are completely filled with water.
saturation 1) The maximum level of material or phase than can be contained in another material or phase. 2) The condition of a liquid (water) when it has taken into solution the maximum possible quantity of a given substance at a given temperature and pressure.
saturator A device which produces a fluoride solution for the fluoridation process. The device is usually a cylindrical container with granular sodium fluoride on the bottom. Water flows either upward or downward through the sodium fluoride to produce the fluoride solution.
savanna (also savannah) Grasslands containing numerous, but isolated trees.
SCADA Supervisory Control and Data Acquisition.
scaling 1) High temperature corrosion resulting in the formation of thick corrosion product layers. 2) Deposition of insoluable materials on metal surfaces, usually inside water boilers or heat exchanger tubes.
scatter diagram A graph in which each dot represents paired values for two continuous variables, with the x-axis representing one variable and the y-axis representing the other; used to display the relationship between the two variables; also called a scattergram.
SCD Soil Conservation District (also called Soil and Water Conservation District in some areas).
SCFM Cubic feet of air per minute at Standard Conditions of temperature (0° C), pressure (14.7 psia), and humidity (50% relative humidity).
schedule, pipe A sizing system of arbitrary numbers that specifies the inside diameter (I.D.) and outside diameter (O.D.) for each diameter pipe. This term is used for steel, wrought iron, and some types of plastic pipe. Also used to describe the strength of some types of plastic pipe.
Schiff reaction Used as a sensitive test for an aldehyde.The formation of a red-violet color with basic fuchsin (decolorized with SO2) in the presence of an aldehyde.The reagent is incorporated into Endo media.
schistosomiasis A disease produced by invasion of the human body by Schistosoma which infects humans and snails in tropical waters.
Science Advisory Board A group of external scientists who advise EPA on science and policy.
scientific classification See taxonomy.
scrap Materials discarded from manufacturing operations that may be suitable for reprocessing.
screening 1) Use of screens to remove coarse floating and suspended solids from sewage. 2) The use of preliminary examination or data to select a desired result.
scrubber An air pollution device that uses a spray of water or reactant or a dry process to trap pollutants in emissions.
SCS Soil Conservation Service.
scum An accumulation of a floating layer on the water or wastewater surface of treatment units that consists of grease, fats, foam, fibers, etc.
scum collector A mechanical device for skimming and removing scum from the surface of a settling tank and passing it into a scum trough for removal and return for further tratment.
SDWA Safe Drinking Water Act.
search engines Permits searching of documents and databases accessible on the Internet. Search engines can be set up to search only content within one Web site or to search the entire Internet. Many search engine developers have their own web sites such as Lycos and Alta Vista. In addition to search engines there are index sites such as Yahoo, where links to Web sites are organized into categories so that you can browse categories rather than guessing at search terms.
seasonal rate A pricing structure for which the dollar amount charged per unit of water (such as dollars per gallon) varies by season of use; usually higher rates are charged in the season of peak demand.
seasonality Phenomena that show cyclic or repeated behavior according to the season.
Secchi disk A flat, white disc lowered into the water by a rope until it is just barely visible. At this point, the depth of the disc from the water surface is the recorded Secchi disk transparency.
secondary attack rate. A measure of the frequency of new cases of a disease among the contacts of known cases.
secondary drinking water regulations Nonenforceable regulations applying to public water systems that specify the maximum contaminant levels, that, in the judgment of EPA, are required to protect the public welfare. These regulations apply to any contaminant that may adversely affect the odor or appearance of such water and consequently may cause people served by the system to discontinue its use.
secondary materials Materials that have been manufactured and used at least once and are to be used again.
Secondary Maximum Contaminant Level Secondary MCLs for various water quality indicators that are established to protect public health. Also SMCL.
secondary standards National ambient air quality standards designed to protect welfare, including effects on soils, water, crops, vegetation, manmade materials, animals, wildlife, weather, visibility, and climate, damage to property, transportation hazards, effects on economic values, and on personal comfort and well-being.
secondary treatment The second step, following primary treatment, in most waste treatment systems in which bacteria and other microorganisms oxidize the organic parts of the wastes. It is accomplished by bringing together waste, bacteria, and oxygen in contactors or in the activated sludge processes. This treatment flocculates colloidal solids and develops settleable solids so that 90 percent of the oxygen-demanding substances are removed through secondary clarification. Typically, disinfection is the final stage of treatment for secondary effluent.
secondary wastewater treatment facility A process that reduces conventional biochemical oxygen demand (BOD5) and suspended solids (TSS) to a greater level than that achieved by a primary treatment. Wastewater is processed through biological treatment processes which typically produces effluent BOD5 and TSS concentrations of 30 mg/L or less each. See wastewater treatment works.
secondary water source Any approved water source, other than a waterworks' primary source, connected to or available to that waterworks for emergency or other nonregular use.
second-day foot (sdf) The volume of water represented by a flow of one cubic foot per second (cfs) for 24 hours; equal to 86,400 cubic feet.
second stage Additional reactions or treatment that follow immediately after an initial occurrence that is necessary for the additional reactions or treatment to develop.
secular trend Changes over a long period of time, generally years or decades.
secure maximum contaminant level Maximum permissible level of a contaminant in water delivered to the free flowing outlet of the ultimate user or of contamination resulting from corrosion of piping and plumbing caused by water quality.
sedge meadow A vegetation (usually in wet situations) consisting of low, grass-like plants belonging to the family Cyperaceae; distinguished from grasses by having stems triangular in cross-section.
sediment Any usually finely divided organic and/or mineral matter deposited by air or water in nonturbulent areas.
sedimentation A water treatment process in which solid particles settle out of the water being treated in a large clarifier or sedimentation basin.
sedimentation tank A clarifier to which wastewater is introduced in a controlled manner so that suspended solids settle out to the bottom or float to the top as scum. The scum is skimmed off the top and the solids on the bottom are removed to sludge handling and treatment. The effluent is withdrawn at a controlled rate from the tank for additional processing.
sediment yield The quantity of sediment arriving at a specific location.
seed protectant A chemical applied before planting to protect seeds and seedlings from disease or insects.
seepage The percolation or trickling of water (or other liquid) through the soil from unlined channels, ditches, watercourses, and water storage facilities. A seepage lake has no visible surface inflow.
seepage meter A device used to measure leakage from underlying aquifers into stream beds or through emergence of groundwater into a stream channel.
seiche An internal wave that oscillates in lakes, gulfs, or bays over periods of a few minutes to hours, resulting from wind, tidal forces, or (rarely) seismic activity. Oscillation is most dramatic and most likely to cause damage after the wind has dropped.
seismic methods Exploration of subsurface geologic structures by means of seismic waves that are induced at the surface.
seize up Seize up occurs when an engine or motor overheats and a part expands to the point where the engine/motor will not run. Also called freezing.
selective corrosion The selective corrosion of certain alloying constituents from an alloy (as dezincification) or in an alloy (as internal oxidation).
selective pesticide A chemical designed to affect only certain types of pests, leaving other plants and animals unharmed.
self-supplied water Water withdrawn from a surface- or ground-water source by a user rather than being obtained from a public supply.
semi-confined aquifer An aquifer that is partially confined by a soil layer (or layers) of low permeability through which recharge and discharge can occur.
semi-permeable Describing molecular transfer across a membrane that acts as a barrier to larger particles.
senescence The aging process. Sometimes used to describe lakes or other bodies of water in advanced stages of eutrophication.
sensitivity The ability of a system to detect epidemics and other changes in disease occurrence. The proportion of persons with disease who are correctly identified by a screening test or case definition as having disease.
sensitivity analysis An analysis of how sensitive outcomes are to changes in the assumptions.
sensor An instrument that measures (senses) a physical condition or variable of interest. Floats and thermocouples are examples of sensors. Also called a primary element.
sentence The judgment formally pronounced by the court upon the defendant after his conviction in a criminal prosecution, awarding the punishment to be inflicted.
sentinel surveillance A monitoring method that employs a surrogate indicator for a public health problem, allowing estimation of the magnitude of the problem in the general population.
sepsis The presence of pathogenic microorganisms or their toxins in the blood or other tissues.
septage The liquid and semisolid contents removed by pumping from a septic tank.
septic A condition produced by bacteria when all oxygen supplies are depleted. If severe, bottom deposits and water turn black, give off foul odors, and the water has a greatly increased chlorine demand.
septic system An onsite system designed to treat and dispose of domestic sewage; a typical septic system consists of a tank that receives waste from a residence or business and a system of subsurface distribution lines for disposal of the liquid effluent (that remains after primary treatment) by percolation down through the soil profile.
septic tank An underground storage tank providing some primary treatment for wastes from homes not connected to a collection system sewer line. Waste goes directly from the home to the tank (on-site system). The typical tank size for a single family structure or residence would be 750 to 1,000 gallons.
septum 1) A disk, usually made out of Teflon, used to seal a vial and held in place with a cap. 2) A permeable support for a filter media or layer.
sequenching batch reactor (SBR) A biological reactor in which the aeration and mixing devices are periodically turned off and clarified supernatent is withdrawn at the surface through a decanting device.
sequestration A chemical complexing (forming or joining together) of metallic cations (such as iron) with certain inorganic compounds, such as phosphate. Sequestration prevents the precipitation of the metals (iron). Also see chelation.
serotypes A taxonomic subdivision of microorganisms as determined by constituent antigens.
service territory The geographic area served by a water utility.
sequelae Morbod conditions following as a consequence of a disease.
seral (stages) Developmental, temporary communities in a sere; not fixed.
sere A developmental series of communities that can be verified during succession; one of a chain of seral changes containing the initial (pioneer), one or more transitional stages, and a single (often hypothetical) climax stage.
service The delivery of a writ, subpoena, notice, injunction, or other court order by an authorized person, to a person, thereby officially notifying him of some action or step which he is commanded to take or not to take.
service connection The point of delivery of water to a customer's building service line as follows: (a) if a meter is installed, the service connection is the downstream side of the meter; (b) if a meter is not installed, the service connection is the point of connection to the waterworks; and (c) when the water purveyor is also the building owner, the service connection is the entry point to the building.
service connector The pipe that carries tap water from a public water main to a building.
service line sample 1) A one-liter sample of water collected, in accordance with CFR Section 141.86(b)(3) of the code of Federal Regulations, that has been standing for at least six hours in a service line. 2) A one-liter sample of water, collected in accordance with 12 VAC 5-590-370 B 6 a (2) (c), of the Waterworks Regulations, that has been standing for at least 6 hours in a service line.
service pipe The pipeline extending from the water main to the building served or to the consumer's system.
sessile Stationary; attached; nonmoving. In botany, nonstalked.
seston 1) Particulate material including plankton (living and dead) and detritus or tripton retained by fine-meshed nets. 2) A collective term designating everything that floats or is suspended in the water.
set point The position at which the control or controller is set. This is the same as the desired value of the process variable.
setteable matter See settleable solids.
setteable solids The suspended matter in wastewater that will not stay in suspension during a preselected settling period, either settling to the bottom or floating to the top.
settled wastewater Wastewater from which most of the settleable solids have been removed by sedimentation.
settling chamber A series of screens placed in the way of flue gases to slow the stream of air, thus helping gravity to pull particles into a collection device.
settling tank Awastewater clarifier designed to retain a design flow rate for a period of detention time sufficient to remove a maximum amount of setteable solids. The clarified effluent is removed at a low velocity for further processing.
7Q10 Seven-day, consecutive low flow with a ten-year return frequency; the lowest stream flow for seven consecutive days that would be expected to occur once in ten years.
severe thunderstorm warning Indicates that severe thunderstorms have been sighted or indicated on radar.
severe thunderstorm watch Indicates that conditions are favorable for lightning, damaging winds greater than 58 miles an hour and hail and/or heavy rainfall.
sewage The used water and solid matter that flow from home plumbing systems through sewers to a wastewater treatment works. The preferred term is wastewater, but wastewater can also contain industrial wastes and significant infiltration and inflow.
sewage lagoon See lagoon.
sewage sludge A mixture of solids and wastewater produced at a publicly owned treatment works, the use or disposal of which is regulated under the Clean Water Act.
sewer An underground system of conduits (pipes and/or tunnels) that collect and transport wastewaters and/or runoff; gravity sewers carry free-flowing water and wastes; pressurized sewers carry pumped wastewaters under pressure. Any pipe or conduit used to convey sewage or industrial waste streams.
sewerage The entire system of sewage collection, treatment, and disposal.
sewerage system The network of sewers or collection system that carries sewage from point of origin to point of treatment.
shareware Computer software developed for the public domain, which can be used or copied without infringing copyright. Programmers typically get paid a small one time fee from users who find the software useful.
sharps Hypodermic needles, syringes, pasteur pipettes, scalpel blades, blood vials, needles with tubing attached, and culture dishes used in animal or human patient care or treatment, or in medical, research, or industrial laboratories. Also included are other types of broken glassware that were in contact with infectious agents.
shell fish Aquatic animals, usually mollusks, having an external shell or exoskeleton.
shelter period The period in which people are forced to evacuate their homes. This time may vary from several hours to a couple of days depending upon the severity of the hurricane.
shielding Any material between a radiation source and a radiation receptor.
Shigella A genus of bacteria within the Salmonella family that is pathogenic causing dysentery.
shipper Firm or individual responsible for introducing merchandise into interstate commerce by way of transport and does not act as a manufacturer, repacker, distributor, etc.
shoal 1) A shallow place in a body of water. 2) A mass of plankton or fish (from school).
shock load The arrival at a water treatment plant of raw water containing unusual amounts of algae, colloidal matter, color, suspended solids, turbidity, or other pollutants.
shock wave See blast effect.
short-circuiting A condition that occurs in tanks or basins when some of the water travels faster than the rest of the flowing water. This is usually undesirable since it may result in shorter contact, reaction, or settling times in comparison with the theoretical (calculated) or presumed detention times.
shrub A woody perennial of smaller height than a tree.
side water depth (SWD) The depth of water measured along a vertical exterior wall.
sieve To use progressively smaller openings in screens so as to separate or classify particles of different sizes.
sievert (Sv) The radiation dose unit of the international system of units. One sievert equals 100 rem.
sign Objective evidence of a disease.
signal The volume or product-level change produced by a leak in a tank.
signal words The words used on a pesticide label to indicate level of toxicity.
significant deterioration Pollution resulting from a new source in previously “clean” areas. See prevention of significant deterioration.
significant municipal facilities Those publicly owned sewage treatment plants that discharge a million gallons per day or more and are therefore considered by states to have the potential for to substantially effect the quality of receiving waters.
significant non-compliers (SNC) Community waterworks, nontransient noncommunity waterworks, and transient noncommunity waterworks, serving over 500 people, that have more serious, frequent, or persistent violations. The criteria which designate a system as a SNC vary by contaminant. Also see Significant Violations.
significant threshold shift A shift in hearing threshold, outside the range of audiometric testing variability (+5 dB), that warrants follow-up action to prevent further hearing loss. NIOSH recommends that a change in hearing threshold of 15 dB for the worse at any frequency (0.5, 1, 2, 3, 4, or 6 kHz) that is repeated for the same ear and frequency to meet the criteria for significant threshold shift.
significant violations Violations by point source dischargers of sufficient magnitude or duration to be a regulatory compliance and enforcement priority.
silica A mineral composed of silicon and oxygen such as sand.
silt Soil particles between 0.002 and 0.05 millimeters in approximate diameter.
siltation Referring to the deposition of silt-sized particles.
Silurian Of the period of the Paleozoic era characterized by the appearance of land plants; also, of the rocks of that period.
silviculture The care and cultivation of forest trees.
simplex video One-way video communication capable of origination and reception, though not simultaneously.
simulate To reproduce the action of some process, usually on a smaller scale.
simulation The representation of physical systems and phenomena by computers, models, or other equipment. The model or computer representation is manipulated to imitate significant aspects of a situation.
single centrifugal pump
single-family structure A building constructed as a single-family residence that is currently used as either a residence or a place of business.
single-stage digestion
single-stage pump A pump that has only one impeller. A multi-stage pump has more than one impeller.
sink A place in the environment where a compound or material collects. See reservoir.
sinking Controlling oil spills by using an agent to trap the oil and sink it to the bottom of the body of water where the agent and the oil are biodegraded.
SIP call The action requiring a state to resubmit all or part of its State Implementation Plan to demonstrate attainment of the required national air quality standards within the statutory deadline. See state implementation plans.
site 1) An area or place within the jurisdiction of the EPA and/or a state. 2) The location at which there is one or more commercial nuclear power plants. A nuclear power plant is synonymous with a nuclear power facility.
site assessment program A means of evaluating hazardous waste sites through preliminary assessments and site inspections to develop a Hazard Ranking System score.
site inspection 1) An on-site confirmation of the land application, site specific information contained in a biosolids use permit application. 2) The collection of information from a contaminated site to determine the extent and severity of hazards posed by the site. It follows and is more extensive than a preliminary assessment.
site safety plan A crucial element in all removal actions, it includes information on equipment being used, precautions to be taken, and steps to take in the event of an on-site emergency.
site-specific studies Studies that pertain to one unique location and not generally applicable to elements of another location.
siting The process of choosing a location for a facility.
skewed A distribution that is asymmetrical.
skid mount A platform of horizontal structure on runners that facilitates the movement of heavy equipment.
skimming Using a machine to remove oil or scum from the surface of water.
slake To mix with water with a true chemical combination (hydrolysis) taking place, such as in the slaking of lime.
sleet A type of precipitation consisting of transparent or translucent pellets of ice 5 mm or less in diameter. Sleet forms when raindrops fall through a layer of below-freezing air near the earth's surface.
sleeve
slope The slope or inclination of a trench bottom or a trench side wall is the ratio of the vertical distance to the horizontal distance or "rise or run." Also see grade (2).
SLOSH (SEA, LAKE AND OVERLAND SURGES FROM HURRICANES) A computerized model that is able to estimate the overland tidal surge heights and winds that result from hypothetical hurricanes with selected characteristics in pressure, size, forward speed, track and winds. The resultant tidal surge is then applied to a specific locale's shoreline, incorporating the unique bay and river configurations, water depths, bridges, roads and other physical features. The model estimates open coastline heights as well as surge heights over land, thus predicting the degree of propagation or run-up of the surge into inland areas.
slough 1) A wet place of deep mud or mire or a temporary or permanent lake usually found on or at the edge of the flood plain of a river. 2) Something that is shed or to shed or cast off.
sloughing The dropping or washing off of biofilm from contactor media.
slow sand filter
slow sand filtration A process involving passage of raw water through a bed of sand at low velocity (generally less than 0.4 m/hr) resulting in substantial particulate removal by physical and biological mechanisms.
sludge 1) The mixture of settleable solids, dissolved solids, and wastewater (a semi-fluid mass) separated from water or wastewater during processing or treatment. 2) The soft soupy bottom deposits of organic and inorganic deposit accumulating on the bottoms of streams and lakes.
sludge age A measure of the length of time a particle of suspended solids has been undergoing aeration in an activated sludge process.
sludge blanket A layer of sludge suspended within an enclosed body of wastewater, such as a settling tank.
sludge digester A reactor with extended detention and mixing during which complex organic substances like sewage sludge are biologically degraded. During these reactions, energy is released and much of the sewage is converted to methane, carbon dioxide, and water through aerobic or anaerobic biological oxidation.
sludge digestion A process by which organic matter in sludge is converted into a more stable form by anaerobic or aerobic organisms.
sludge density index The reciprocal of the sludge volume index (SVI) multiplied by 100 (i.e., 1/SVI x 100).
sludge gasification A process in which soluble and suspended organic matter in sludge are converted into a gas.
sludge volume index (SVI) The ratio of the volume in milliliters of sludge settled from a 1,000-mL sample in 30 minutes to the concentration of mixed liquor in milligrams per liter multiplied by 1,000.
slug plezometer test A single well test to determine the in-situ hydraulic conductivity of an aquifer by the instantaneous addition of a known quantity (i.e., slug) of water into a well and the subsequent measurement of the resulting recovery time.
sluice To divert water or wastewater into a channel through the use of regulated openings or gates.
slurry A watery mixture or suspension of insoluble (not dissolved) matter; a thin watery mud or any substance resembling it (such as a grit slurry or lime slurry).
small craft advisory An advisory issued for marine interests, especially for operators of small boats or other vessels. Conditions include wind speeds between 20 knots (23 mph) and 34 knots (39 mph). Issued up to 12 hours ahead of conditions.
small quantity generator (SQG) A person or enterprise that produces 220-2200 pounds per month of hazardous waste. SOGs are required to keep more records than conditionally exempt generators. SQGs include automotive shops, dry cleaners, photographic developers, and a host of other small businesses. See conditionally exempt generators.
small waterworks A waterworks that serves 3,300 persons or fewer.
SMCL Secondary Maximum Contaminant Level.
smelter A facility that melts or fuses ore, often with an accompanying chemical change, to separate its metal content.
smelting Fusion or melting process in order to separate metals.
smog Air pollution associated with oxidants. See photochemical smog.
smoke Particles suspended in an emission of exhaust after incomplete combustion that interferes with light transmission.
SNARL Suggested No Adverse Response Level.
snow water equivalent The water equivalent of snow is the depth of water that would be obtained by melting the snow cover.
soda ash A compound composed of sodium carbonate.
sodic soil A soil that contains sufficient sodium to interfere with the growth of most crop plants and, in which, the exchangeable sodium percentage is 15 or more.
sodium carbonate A metal salt used to provide alkalinity when added to water and wastewater.
sodium hydroxide A strong base used to neutralize acids.
sodium hypochlorite A chlorine containing compound often used in dry form or generated where used.
soft detergents Cleaning agents that break down in nature.
soft water Water having low concentrations of calcium and magnesium ions. According to the US Geological Survey guidelines, soft water is water having a hardness of 60 milligrams per liter or less.
software programs Computer programs; the list of instructions that tell a computer how to perform a given task or tasks.
soil The natural, weathered, unconsolidated, mineral, and organic matter on the surface of the earth; it is a medium for the growth of plants.
soil absorption field A subsurface area containing a trench or bed that has a minimum depth of 12 inches of clean stones and a system of distribution piping through which treated sewage may seep into the surrounding soil for further treatment and disposal.
soil aggregation The lumping together of soil particles into a coherent mass.
soil conditioner An organic material like humus or compost that helps soil absorb water, build a bacterial community, and take up mineral nutrients.
Soil Conservation District (also called Soil and Water Conservation District) A local government entity within a defined water or soil protection area that provides assistance to farmers and other local residents in conserving natural resources, especially soil and water.
Soil Conservation Service An former agency of the US Department of Agriculture now called the Natural Resources Conservation Service (NRCS) that provides technical assistance for resource conservation to farmers, other federal, state, and local agencies, and to local soil conservation districts.
soil discharge of groundwater
soil erodibility A measure of the soil's susceptibility to raindrop impact, runoff, and other erosional processes.
soil gas Gaseous elements and compounds in the small spaces between particles of the earth and soil. Such gases can be moved or driven out under pressure.
soil moisture Water diffused in the upper part of the soil mantle that is lost by the transpiration of plants or by soil evaporation.
soil moisture content The portion of water in a soil that can be readily absorbed by plant roots. It is the amount of water released between in situ field capacity and the permanent wilting point.
soil organism An organism ordinarily found living and reproducing in the soil.
soil profile A vertical section of the earth's highly weathered upper surface often showing several distinct layers or horizons.
soil sterilant A chemical that temporarily or permanently prevents the growth of all plants and animals. depending on the chemical.
soil structure The arrangement of soil particles into aggregates.
soil temperature Soil temperature measures the hotness or coldness of soil. Soil temperature is very important to the agricultural industry. Most seeds require a certain soil temperature in order to germinate. Soil temperatures are commonly measured at 2, 4, 8, 20, 40, 60, and 120 inches with the 4 inch reading being the most frequently observed.
soil texture The proportions of soil particles (sand, silt, and clay) in a soil profile.
soil water That water present in the soil pores in an unsaturated (aeration) zone above the groundwater table. Such water may be either lost by evapotranspiration or percolation to the groundwater table.
solar outage Solar outages occur when an antenna is looking at a satellite, and the sun passes behind or near the satellite and within the field of view of the antenna. The field of view is usually wider than the beamwidth. Solar outages can be exactly predicted as to the timing of each site.
solar radiation The total amount of energy emitted by the sun.
solar radiation, incoming Incoming solar radiation is the total electromagnetic radiation emitted by the sun striking the earth.
solder A metallic compound used to seal the joints between pipes. Until recently, solder contained 50% lead. The use of lead solder containing more than 20 percent lead is now prohibited for pipes carrying potable water.
sole source aquifer An aquifer that supplies 50% or more of the drinking water of an area.
solenoid A magnetically (electrical coil) operated mechanical device. Solenoids can operate a small valve or switch.
solidification and stabilization Removal of waste from a wastewater and changing it chemically to make it less permeable and susceptible to transport by water.
solids loading The weight or mass of solids applied to a treatment process per unit time and process capacity.
solids retention time (SRT) The average residence time of suspended solids in a biological waste treatment system, equal to the weight of suspended solids in the system divided by the total weight of suspended solids leaving the system per unit time.
solid waste Non-liquid, non-soluble materials ranging from municipal garbage to industrial wastes that contain complex and sometimes hazardous substances. Solid wastes also include sewage sludge, agricultural refuse, demolition wastes, and mining residues. Technically, solid waste also refers to liquids and gases in containers.
solid waste disposal The final placement of refuse that is not salvaged or recycled.
solid waste management Supervised handling of waste materials from their source through recovery processes to disposal.
solubility The amount of one substance that will dissolve in another to produce a saturated solution.
soluble Capable of dissolving readily.
solum Upper weatherd part of the soil (A and B horizons).
solute A dissolved substance.
solution A liquid mixture of dissolved substances. In a solution, it is impossible to see all the separate parts.
solvent A liquid in which a substance is dissolved.
soot Carbon dust formed by incomplete combustion.
sorb To take up and hold either by absorption or adsorption.
sorption A surface phenomenon which may be either absorption or adsorption, or a combination of both; often used when the specific mechanism is not known.
sound An auditory sensation evoked by oscillations in pressure in a medium with elasticity and viscosity (e.g., air).
sounding tube A pipe or tube used for measuring the depths of water.
sound intensity The average rate at which sound energy is transmitted through a unit area normal to the direction of sound propagation.
sound intensity level (SIL) The sound intensity level, in decibels, of a sound is 10 times the logarithm to the base 10 of the ratio of the sound intensity to the reference sound intensity. For sound transmitted in air, the reference sound intensity is 10-12 watts per square meter.
SIL = 10*log(I/I0)
where I = sound intensity
I0 = reference sound intensity
sound pressure The total instantaneous pressure at a point in the presence of a sound wave minus the static pressure at that point.
sound pressure level (SPL) The sound pressure level, in decibels, of a sound is 10 times the logarithm to the base 10 of the ratio of the sound pressure squared to the reference sound pressure squared. For sound transmitted in air, the reference sound pressure is 20 micropascal (:Pa).
SPL = 10*log(P2/P02)
SPL = 10*log(P/P0)2
SPL = 20*log(P/P0)
where P = sound pressure
P0 = reference sound pressure
source of infection The person, animal, or substance from which an infectious agent is transmitted to a host.
source meter A meter used to record water withdrawn from a surface water or groundwater source or purchased from a wholesale supplier.
source reduction Reducing the amount of materials entering the waste stream by redesigning products or patterns of production or consumption (e.g., using returnable beverage containers). Synonymous with waste reduction.
source separation Segregating various wastes at the point of generation (e.- g., separation of paper, metal and glass from other wastes to make recycling simpler and more efficient.)
span The scale or range of values an instrument is designed to measure. Also see range.
sparger
spawning beds Those places in which the eggs of aquatic animals lodge or are placed during or after fertilization.
special marine warning A warning for hazardous weather conditions, usually short and not adequately covered by existing marine warnings. Such conditions include sustained winds or gusts of 35 knots or more for 2 hours or less.
special review The regulatory process through which existing pesticides suspected of posing unreasonable risks to human health, non-target organisms, or the environment are referred for review. Formerly known as Rebuttable Presumption Against Registration (RPAR). Such review requires an intensive risk/benefit analysis with opportunity for public comment.
special waste Items such as household hazardous waste, bulky wastes (refrigerators, pieces of furniture, etc.) tires, and used oil.
species 1. A distinct type or appearance. 2) A taxonomic category of biological classification ranking immediately below the genus (subgenus). Dominant species, see dominant; rare species, an unusual species in an area.
species composition The kinds and numbers of species occupying an area.
species diversity The number of species or other kinds in an area and, for purposes of quantification, to their relative abundance as well.
species diversity index Any of several mathematical indices that express, in one term, the number of kinds of species and the relative numbers of each in an area.
specific activity The amount of radioactivity of a material per unit mass.
specific conductance A rapid method of estimating the dissolved-solids content of a water supply. The measurement indicates the capacity of a water sample to carry an electric current, which is related to the concentration of ionized substances in water. Also called conductance.
specific gravity The ratio of the weight of a particle, substance, or chemical solution to the weight of water. Water has a specific gravity of 1.000 at 4°C (39°F). Particulate in raw water may have a specific gravity of 1.005 to 2.5.
specificity The proportion of persons without disease who are correctly identified by a screening test or case definition as not having disease.
specific oxygen uptake rate (SOUR) The dissolved oxygen depletion characteristics of biomass and sludge, measured in mg/L per hour.
specific retention The ratio of the volume of water that a given body of rock or soil will hold against the pull of gravity to the volume of the body itself. It is usually expressed as a percentage.
specific yield The ratio of the water drained from a rock under the influence of gravity, or removed by pumping, to the total volume of rock voids or pore space in the drained rock.
spectrophotometer An analytical instrument that measures the light or radiation adsorption characteristics of liquids at specific wavelengths.
Sphaerotilus A filamentous bacteria that when present as a large fraction of biomass will produce nonsettleable conditions referred to as sludge bulking.
spiked sample A water sample to which a known quantity of a contaminant has been added so that the accuracy of the laboratory analysis can be determined.
spill prevention control and countermeasures plan (SPCP) Plan covering the release of hazardous substances as defined in the Clean Water Act.
spillway Any passageway, channel, or structure designed primarily to discharge excess water from a reservoir. A controlled spillway is equipped with crest gates, stoplogs, or other movable structures to permit various degrees of variation in outflow rates.
spillway crest The elevation of the highest point of a spillway.
spiral rainbands Bands of thunderstorms that spiral inward towards the center, where they wrap themselves around the eye.
spirillium A spiral or corkscrew-shaped bacterium.
split samples A sample which is divided into two or more portions for analysis by two or more laboratories
spoil Excavated material, such as soil from the trench of a water main or muck dredged from underwater deposits.
sporadic A disease that occurs infrequently and irregularly.
spore The reproductive body of certain organisms that is capable of giving rise to a new organism either directly or indirectly. A viable (able to live and grow) body regarded as the resting stage of an organism. A spore is usually more resistant to disinfectants and heat than most organisms; a primitive unicellular reproductive body.
spot map A map that indicates the location of each case of a rare disease or outbreak by a place that is potentially relevant to the health event being investigated, such as where each case lived or worked.
spray irrigation The application of treated wastewater in a spray for land treatment.
spray tower scrubber A device that sprays alkaline water into a chamber where acidic gases present to aid in the neutralizing of the gas.
spring Groundwater seeping out of the earth where the water table intersects the ground surface.
spring line Theoretical center of a pipeline. Also, the guideline for laying a course of bricks.
spring melt/thaw The process by which warm temperatures melt winter snow and ice. The melt can result in abnormally large amounts of acidity entering streams and rivers, sometimes causing fish kills.
squall A sudden increase of wind speed by at least 18 miles per hour (16 knots) and rising to 25 miles per hour (22 knots) or more and lasting for at least one minute.
stability (ecological) The tendency of systems, especially ecosystems, to persist, relatively unchanged, through time; also the persistence of a system; the inverse of its turnover time.
stabilization 1) Equalization with time. 2) The production of water that is exactly saturated with calcium carbonate. 3) Conversion of the active organic matter in sludge into a more stabilized waste.
stabilization ponds An excavated, uniformly shaped, and lined basin, about ten feet in average depth, providing weeks of detention time for a raw sewage influent that is biologically oxidized by a dilute biomass of bacteria and algae. Dissolved oxygen is provided by algal photosynthesis and surface reaeration. See lagoons.
stabilize To convert to a form that resists change. Organic material is stabilized by bacteria that convert the material to gases and other relatively inert substances.
stabilized waste A waste that has been treated or decomposed to the extent that, if discharged or released, its rate and state of decomposition would be such that the waste would not cause a nuisance or odors.
stable air A motionless mass of air that holds instead of dispersing pollutants.
stack A chimney, smokestack, or vertical pipe that discharges used air.
stack effect Air, as in a chimney, that moves upward because it is warmer than the ambient atmosphere.
stack gas See flue gas.
stack-unit maps A map showing the areal distribution of geologic materials based on their order of occurrence to a specified depth.
stage 1) In hydrology, the height of the water surface above or below an arbitrary datum; a gage height. 2) As a physiographic term, stage refers to a period of phase (youthful stage or mature stage) in the cycle of erosion, such as the development of a shoreline. 3) A period in the life history of a lake marking periods of geologic history. 4) A process that is followed or preceded by a similar process to accomplish progressive changes, such as a treatment process.
stage II controls Systems placed on service station gasoline pumps to control and capture gasoline vapors during refueling.
stage-discharge curve See rating curve.
stagnation Lack of motion in a mass of air or water that holds pollutants in place.
stand An aggregation of plants, usually trees, standing in a limited definite area.
standard 1) The value determined to provide a desired or required level or quality. 2) A physical or chemical quantity whose value is known exactly and is used to calibrate or standardize instruments. 3) Criterion. Also see reference.
standard deviation The most widely used measure of dispersion of a frequency distribution, equal to the positive square root of the variance.
standard error [of the mean] The standard deviation of a theoretical distribution of sample means about the true population mean.
standardize To compare with a standard. 1) In wet chemistry, to find out the exact strength of a solution by comparing it with a standard of known strength. 2) To set up an instrument or device through detection of a standard. This allows you to adjust the instrument so that it reads accurately or enables you to apply a correction factor to the readings.
Standard Methods Same as Standard Methods for the Examination of Water and Wastewater.
Standard Methods for the Examination of Water and Wastewater A joint publication of the American Public Health Association, American Water Works Association, and the Water Environment Federation that outlines the accepted procedures used to analyze the impurities in water and wastewater.
standard-rate filter A trickling filter biological reactor receiving conventional hydraulic and organic loading from a combined primary effluent and recirculation flow
standards (permits) Accepted values that impose limits on the amount of pollutants or emissions produced that can be discharged into the environment.
standard sample That portion of finished drinking water that is examined for the presence of coliform bacteria. The minimum amount collected must be greater than 100 mL.
standard solution A solution in which the exact concentration of a chemical or compound is known.
standard surface pressure The measurement of one atmosphere of pressure under standard conditions. It is equivalent to 1,013.25 millibars, 29.92 inches of mercury, 760 millimeters of mercury, 14.7 pounds per square inch, or 1.033 grams per square centimeter.
standing crop The biological mass (biomass) of certain or all living organisms of an area or volume at some specific time, i.e., what could be harvested.
staphylococci A genus of gram positive, coccoid (spherical) bacteria arranged in irregular, grape-like clusters, including a number of pathogenic forms such as S. pyogenes.
starters Devices used to start up large motors gradually to avoid severe mechanical shock to a driven machine and to prevent disturbance to the electrical lines (causing dimming and flickering of lights).
start of a response action The point in time when there is a guarantee or set-aside of funding either by federal agencies, states or principal responsible parties in order to begin response actions at a contaminated site.
stasis Stagnation or inactivity of the life processes within organisms.
state The agency of the State or Tribal government that has jurisdiction over public water systems. During any period when a State or Tribal government does not have primary enforcement responsibility pursuant to the Safe Drinking Water Act, the term “State” means the Regional Administrator, US Environmental Protection Agency.
State Emergency Response Commission (SERC) Commission appointed by the governor according to the requirements of SARA Title III. The SERCs designate emergency planning districts, appoint local emergency planning committees, and supervise and coordinate their activities.
state implementation plans (SIP) Approved state plans for the establishment, regulation, and enforcement of air pollution standards.
state of emergency The condition declared by the Governor when in his judgment, a disaster in any part of the state is of sufficient severity and magnitude to warrant State disaster assistance and resources otherwise unavailable to the stricken area.
State Revolving Fund (SRF) State loan funds for utilities established under the Safe Drinking Water Act. Also Drinking Water State Revolving Fund.
static head When water is not moving, the vertical distance (in feet) from a specific point to the water surface is the static head.
static pile A mixture of treated sewage sludge and bulking agent established for stability and ease of aeration for composting into a product to be used as a soil conditioner.
static pressure The static head multiplied by a density factor to establish the force per area at a point. The static pressure in psi is the static head in feet times 0.433 psi/ft. Also see dynamic pressure.
static water depth The vertical distance in feet from the centerline of the pump discharge down to the surface level of the free pool while no water is being drawn from the pool or water table.
static water level 1) The elevation or level of the water table in well when the pump is not operating. 2) The level or elevation to which water would rise in a tube connected to an artesian aquifer, or basin, or conduit under pressure.
stationary front The boundary between two air masses, neither of which is replacing the other.
stationary phase The interval which follows the growth phase during which the number of living bacteria remains constant. As many organisms die as are formed.
stationary source A fixed-site producer of pollution, mainly power plants and other facilities using industrial combustion processes.
statistics 1) The subject that deals with collecting, organizing, summarizing, presenting, and analyzing data, as well as drawing conclusions on the basis of such analysis. 2) A value or measure of some property of a sample, such as the mean. 3) A term for data.
stator The portion of a machine that contains the stationary (nonmoving) parts that surround the moving parts (rotor).
statute mile Commonly known as a ground mile; 5,280 feet.
statute of limitation The period in which any contemplated legal action must be brought.
steady state A condition of equilibrium where the output of a process tracks uniformly with the input.
steam generator The component used in a pressurized water reactor that transfers the heat generated in the primary system (by the reactor core) to the secondary cooling water and hence to the turbine.
stenohaline Of or related to those organisms that can endure only a narrow range of salt in solution.
stenothermal Describing a species restricted to a narrow range of temperatures.
stenotopic With narrow limits of tolerance to varied conditions.
step aeration A type of activated sludge reactor, in which influent and recycled biomass is introduced sequentially at several points along the length of the reactor or aeration basin.
sterile Free of living organisms.
sterilization The treatment of a material, usually by the means of heat or chemicals, which kills or removes any or all forms of life. The act of making something sterile.
stiff diagram A geographic means of presenting the chemical analysis of the major cations and anions of a water sample.
stochastic Based on the assumption that the actions of a chemical substance results from probable events.
stoichiometric Chemical reactions in which products are in direct proportion to reactants in terms of weight.
storage 1) The retention of drinking water from a source or distribution system to meet future operating and pressure demands for supply. 2) Inline or offline containment or holding of waste pending treatment or disposal, as in containers, tanks, waste piles, and surface impoundments. 3) The temporary deposit of a chemical in body tissue or in an organ. Storage is just one facet of chemical bioaccumulation. The term also applies to other natural processes, such as the storage of fat in hibernating animals or the storage of starch in seeds.
storativity Coefficient of storage. The volume of water an aquifer releases from or takes into storage per unit surface area of the aquifer per unit change in head. In unconfined aquifers, it is equal to the specific yield. In confined aquifers, the storage coefficient depends on elastic compression of the aquifer and is usually less than 10-3.
storm An individual low-pressure disturbance, complete with winds, clouds, and precipitation. Examples include thunderstorms, tornadoes, or even tropical cyclones. The name is associated with destructive or unpleasant weather.
storm hydrograph A hydrograph representing the total flow or discharge past a point for a particular rain event.
storm sewer A system of pipes (separate from sanitary sewers) that carries only water runoff from land surfaces and from structures and roads containing materials of limited permeability and transports this flow to a discharge point.
storm surge An abnormal rise in sea level accompanying a hurricane or other intense storm, and whose height is the difference between the observed level of the sea surface and the level that would have occurred in the absence of the cyclone. Storm surge is usually estimated by subtracting the normal or astronomic high tide from the observed storm tide. Note waves on top of the storm surge will create an even greater high-water mark.
storm tide The actual level of seawater resulting from the astronomic tide combined with the storm surge. If the storm comes ashore during astronomical low tide, the surge will be decreased by the amount of the low tide. If the storm makes landfall during astronomical high tide, the surge will be that much higher.
storm tracks The path or tracks generally followed by a cyclonic disturbance.
storm warning A warning of 1-minute sustained surface winds of 48 kt (55 mph or 88 kph) or greater, either predicted or occurring, not directly associated with tropical cyclones.
strain A group of organisms of the same species having distinctive characteristics, but not usually considered a separate breed or variety.
strategic plan The document used by an organization to align efforts with the organization's mission and focus resources towards long-term goals and objectives.
stratification 1) The natural division of the plant community into superposed strata or layers. 2) The division of a body of water into two or more depth zones, as in thermal stratification. 3) The formation of separate layers (of temperature, plant, or animal life) in a lake or reservoir. Each layer has similar characteristics such as all water in the layer has the same temperature.
stratification, thermal The division of water or air into layers or depth zones of different temperatures and/or densities.
stratosphere The portion of the atmosphere 10-to-25 miles above the earth's surface.
stray current corrosion Corrosion that is caused by stray currents from some external source.
streamflow Water flowing in the stream channel.
stream recession length The time required for a stream, which has experienced a rise, to fall to its normal, or baseflow stage.
streptococci A genus of gram positive bacteria coccoid bacteria that often forms into chains of cells. A number of the four types of these organisms are pathogenic, including S. pyogenes that can cause scarlet and rheumatic fever in man.
stress The result or consequent state of a physical, chemical, or social stimulus on an organism or system; a state of strain resulting from stress.
strip cropping A crop production system that involves planting alternating strips or row crops and close-growing forage crops; the forage strips intercept and slow runoff from the less protected row crop strips.
strip mining A process that uses large earth-moving machines to scrape soil or rock away from mineral deposits just under the earth's surface.
structural control A practice that involves design and construction of a facility to mitigate the adverse impact of urban runoff, and often requires maintenance.
structural deformation Distortion of the walls of a tank after liquid has been added or removed.
stuck Used to describe a digester that does not decompose organic matter properly, characterized by low gas production, high volatile acid ti alkalinity relationship, and poor liquid-solids separation.
subacute A zone between acute and chronic, denoting the course of a disease.
subchronic Of intermediate duration, usually used to describe studies or levels of exposure between five and 90 days.
subclimax A stage in a community’s development, i.e., the succession before its final (climax) stage; a community simulating climax because of its further development being inhibited by some disturbing factor, such as fire or poor soil.
sublimation A process by which solids will volatilize.
sublittoral Below the lake or seashore; the area between the low-tide mark and 20 fathoms.
submerged aquatic vegetation (SAV) Aquatic vegetation that cannot withstand excessive drying and, therefore, live with their leaves at or below the water surface.
submergence The distance between the water surface and the media surface in a filter.
submetering Metering for units comprising a larger service connection, such as apartments in a multifamily building.
subpoena A document, issued by the clerk of court which, when delivered to the person armed therein, requires him to appear in court, or at a deposition, or before a grand jury.
subpoena duces tecum Same as a subpoena with the requirement that the person bring with him certain records or items named in the subpoena.
subsidence Sinking or settling of the ground surface due to natural or anthropogenic causes, such as loss of fluid pressure or removal of underlaying subsurface support. Surface material is displaced vertically downwards with little or no horizontal movement. One anthropogenic cause of subsidence is groundwater pumpage from unconsolidated aquifers that greatly exceed the recharge rate and depletes the aquifer.
substrate 1) The layer of organic matter or medium that supports the growth of organisms. 2) The substance, usually a protein, acted upon by an enzyme. 3) A foundation or supporting layer.
subtropical The region between the tropical and temperate regions, an area between 35 and 40 degrees North and South latitude. This is generally an area of semi-permanent high pressure that exists and is where the Azores and North Pacific Highs may be found.
subtropical cyclone A low pressure system that develops over subtropical waters that initially has a non-tropical circulation but in which some elements of tropical cyclone cloud structure are present. Subtropical cyclones can evolve into tropical cyclones.
subtropical depression A subtropical cyclone in which the maximum sustained surface wind speed (using the U.S. 1-minute average) is 38 mph (33 knots) or less.
subtropical high A semi-permanent high-pressure region near 30 degrees latitude.
subtropical storm A subtropical cyclone in which the maximum sustained surface wind speed (using the U.S. 1-minute average) is 39 mph (34 knots) or more.
succession The replacement of one community by another; the definition includes the possibility of retrograde succession. Plant succession is the replacement of one kind of a plant by another. Primary succession is succession that begins on bare, unmodified substrate. Secondary succession is succession that occurs on formerly vegetated areas (or having an already developed soil) after disturbance or clearing.
suction lift The negative pressure, in feet (meters) of water or inches (centimeters) of mercury vacuum, on the suction side of the pump. The pressure can be measured from the centerline of the pump down to the elevation of the hydraulic grade line on the suction side of the pump.
sufficient cause A causal factor or collection of factors whose presence is always followed by the occurrence of the effect (of disease).
suggested no adverse response level The concentration of a chemical in water that is expected not to cause an adverse health effect. Also SNARL.
sulfate-reducing bacteria
sulfur dioxide (SO2) A pungent, colorless, gaseous pollutant formed primarily by the oxidation of sulfur, such as in anaerobic biological decomposition, and combustion of fossil fuels.
sulfur dioxide detector An instrument similar to a chlorine detector except that it is calibrated to detect sulfur dioxide concentrations in air.
summary judgment A judgment given to one party or the other without the necessity of a formal trial. This may be done when the record before the court shows there are no genuine issues of fact that are in dispute. It is literally "summarily deciding" the case.
summons A document which is served upon the defendant along with the complaint, advising him that a case has been filed against him, and requiring him to appear and answer the complaint.
sump A pit or tank that catches liquid runoff for drainage or disposal.
sump pump A mechanical device for removing water or wastewater from a sump or wet well. It may be energized by air, water, steam, or electric motors.
superchlorination Chlorination with doses that are deliberately selected to produce free or combined residuals so large as to require dechlorination.
supercritical flow
supercritical water A type of thermal treatment using moderate temperatures and high pressures to enhance the ability of water to break down large organic molecules into smaller, less toxic ones. Oxygen injected during this process combines with simple organic compounds to form carbon dioxide and water.
Superfund The program operated under the legislative authority of CERCLA and SARA that funds and carries out solid waste emergency and long-term removal and remedial activities. Activities include establishing the National Priorities List, site investigation sites for inclusion on the list, priority determination, cleanup, and other remedial actions.
supernatant Liquid removed from above a depth of settled suspended solids or sludge. Supernatent commonly refers to the liquid between the sludge on the bottom and the water surface of a basin or container.
supersaturated An unstable condition of a solution (water) in which the solution contains a substance at a concentration greater than the saturation concentration for the substance.
supersaturated solution A solution that contains more of one substance that needed to be saturated.
supplier of water Any person who owns or operates a public water system.
supply management Measures used by the utility to improve the efficiency of production, transmission, and distribution facilities.
surcharge A special charge on a water bill used to send customers a specific pricing signal and recover costs associated with a particular activity.
surface aerator A mechanical mixing device situated on floats or fixed supports in a large basin of water or wastewater which imparts dissolved oxygen into the fluid through turbulent agitation of flow pumped from an affected depth up to the surface and into the air above the surface.
surface impoundment Treatment, storage, or disposal of liquid hazardous wastes in ponds.
surface loading One of the guidelines for the design of settling tanks and clarifiers in treatment plants. Used by operators to determine if tanks and clarifiers are hydraulically over- or underloaded. Also called overflow rate and equivalent to the influent flow divided by the basin surface area.
surface pump A mechanism for removing water or wastewater from a sump or wet well.
surface runoff Precipitation, snow melt, or irrigation in excess of what can infiltrate the soil surface and be stored in small surface depressions; runoff is a major transporter of nonpoint source pollutants.
surface water All water naturally open to the atmosphere (rivers, lakes, reservoirs, streams, impoundments, seas, estuaries, etc.) and all springs, wells, or other collectors that are directly influenced by surface water.
surfacing ACM Asbestos-containing material that is sprayed or troweled on or otherwise applied to surfaces, such as acoustical plaster on ceilings and fireproofing materials on structural members.
surfactant Abbreviation for surface-active agent. The active agent in detergents that possesses a high cleaning ability due to its ability to emulsify fats, oils, and grease.
surge chamber A chamber or tank connected to a pipe and located at or near a valve that may quickly open or close or a pump that may suddenly start or stop. When the flow of water in a pipe starts or s