Glossary of Terms

Accumulated overdraft. The amount of water necessary to be replaced in the intake area of the groundwater basin to prevent the landward movement of ocean water into the fresh groundwater body.

Acre-foot. af. A common water industry unit of measurement. An acre-foot is 325,851 gallons, or the amount of water needed to cover one acre with water one foot deep. An acre-foot serves annual needs of two typical California families

Advanced treatment. Additional treatment processes used to clean wastewater even further following primary and secondary treatment. Also known as tertiary treatment.

Alluvium. A stratified bed of sand, gravel, silt, and clay deposited by flowing water.

Annexation. The inclusion of land within a government agency's jurisdiction.

Annual overdraft. The quantity by which the production of water from the groundwater supplies during the water year exceeds the natural replenishment of such groundwater supplies during the same water year.

Aquifer. An underground geologic formation of rock, soil or sediment that is naturally saturated with water; an aquifer stores groundwater.

Arid: Dry; deserts are arid places. Semi-arid refers to a place that is almost as dry as a desert.

Artesian. An aquifer in which the water is under sufficient pressure to cause it to rise above the bottom of the overlying confining bed, if opportunity to do so should be provided.

Artificial recharge. The addition of surface water to a groundwater reservoir by human activity, such as putting surface water into recharge basins. (See also: groundwater recharge and recharge basin.)

Base flow. The portion of river surface flow which remains after deduction of storm flow and/or purchased imported water.

Biofouling. The formation of bacterial film (biofilm) on fragile reverse osmosis membrane surfaces.

BMP. Best Management Practice. An engineered structure or management activity, or combination of these, that eliminates or reduces and adverse environmental effects.

Brown Act. Ralph M. Brown Act enacted by the State legislature governing all meetings of legislative bodies. Also know as the Open Meeting requirements.

CERCLA. Comprehensive Environmental Response, Compensation and Liability Act. This federal law establishes the Superfund program for hazardous waste sites. It provides the legal basis for the United States EPA to regulate and clean up hazardous waste sites, and if appropriate, to seek financial compensation from entities responsible for the site.

Chloramines. A mixture of ammonia and chlorine used to purify water of harmful substances.

Clarify: To make clear or pure by separation and elimination of suspended solid material.

Coagulation: The clumping together of solids so they can more easily be settled out or filtered out of water. A chemical called aluminum sulfate (alum) is generally used to aid coagulation in water treatment and reclamation.

Colored water. Groundwater extracted from the basin that is unsuitable for domestic use without treatment due to high color and odor exceeding drinking water standards.

Condensation: The process of water vapor (gas) changing into liquid water. An example of condensation can be seen in the tiny water droplets that form on the outside of a glass of iced tea as warmer air touches the cooler glass.

Confined aquifer. An aquifer that is bound above and below by dense layers of rock and contains water under pressure.

Conjunctive use. TStoring imported water in a local aquifer, in conjunction with groundwater, for later retrieval and use.

Contaminate: To make unclean or impure by the addition of harmful substances.

Deep percolation. The percolation of surface water through the ground beyond the lower limit of the root zone of plants into a groundwater aquifer.

Degraded water. Water within the groundwater basin that, in one characteristic or another, does not meet primary drinking water standards.

Delta. Where the rivers empty; an outlet from land to ocean, also where the rivers deposit sediment they carry forming landforms.

Denitrification. The physical process of removing nitrate from water through reverse osmosis, microfiltration, or other means.

Desalting (or desalination). Removing salts from salt water by evaporation or distillation. Specific treatment processes, such as reverse osmosis or multi-stage flash distillation, to demineralize seawater or brackish (saline) waters for reuse. Also sometimes used in wastewater treatment to remove salts other pollutants.

Drainage basin. The area of land from which water drains into a river, for example, the Sacramento River Basin, in which all land area drains into the Sacramento River. Also called catchment area, watershed, or river basin.

DVL. Diamond Valley Lake. Metropolitan’s major reservoir near Hemet, in southwestern Riverside County.

DWR. California Department of Water Resources. Guides development and management of California’s water resources; owns and operates State Water Project and other water-development facilities.

East Side Reservoir Project. A Metropolitan Water District project in Riverside County for the storage of imported water.

Endangered Species. A species of animal or plant threatened with extinction.

Ecosystem. Where living and non-living things interact (coexist) in order to survive.

Effluent. Wastewater or other liquid, partially or completely treated or in its natural state, flowing from a treatment plant.

Evaporation. The process that changes water (liquid) into water vapor (gas).

Evapotransporation. The quantity of water transpired (given off), retained in plant tissues, and evaporated from plant tissues and surrounding soil surface. Quantitatively, it is expressed in terms of depth of water per unit area during a specified period of time.

Filtration: The process of allowing water to pass through layers of a porous material such as sand, gravel or charcoal to trap solid particles. Filtration occurs in nature when rain water soaks into the ground and it passes through hundreds of feet of sand and gravel. This same natural process of filtration is duplicated in water and wastewater treatment plants, generally using sand and coal as the filter media.

Flocculation. A chemical process involving addition of a coagulant to assist in the removal of turbidity in water.

Forebay. A reservoir or pond situated at the intake of a pumping plant or power plant to stabilize water level; also, a portion of a groundwater basin where large quantities of surface water can recharge the basin through infiltration.

Gray water reuse. Reuse, generally without treatment, of domestic type wastewater for toilet flushing, garden irrigation and other nonpotable uses. Excludes water from toilets, kitchen sinks, dishwashers, or water used for washing diapers.

Green Acres Project (GAP). A 7.5 million gallons per day (Mgd) water reclamation project that serves tertiary treated recycled water to irrigation and industrial users in Costa Mesa, Fountain Valley, Huntington Beach, Newport Beach, and Santa Ana.

Groundwater. Water that has percolated into natural, underground aquifers; water in the ground, not water puddled on the ground.

Groundwater basin. A groundwater reservoir defined by all the overlying land surface and the underlying aquifers that contain water stored in the reservoir. Boundaries of successively deeper aquifers may differ and make it difficult to define the limits of the basin.

Groundwater mining. The withdrawal of water from an aquifer in excess of recharge over a period of time. If continued, the underground supply would eventually be exhausted or the water table could drop below economically feasible pumping lifts.

Groundwater overdraft. The condition of a groundwater basin in which the amount of water withdrawn by pumping exceeds the amount of water that recharges the basin over a period of years during which water supply conditions approximate average.

Groundwater recharge. The action of increasing groundwater storage by natural conditions or by human activity. See also: Artificial recharge.

Groundwater Replenishment System. A joint project of the Orange County Water District and the Orange County Sanitation District that will provide up to 100,000 acre-feet of reclaimed water annually. The high-quality water will be used to expand an existing underground seawater intrusion barrier and to replenish the groundwater basin underlying north and central Orange County.

Groundwater table. The upper surface of the zone of saturation (all pores of subsoil filled with water), except where the surface if formed by an impermeable body.

Hydrologic balance. An accounting of all water inflow to, water outflow from, and changes in water storage within a hydrologic unit over a specified period.

Hydrologic cycle. The process by which water constantly circulates from the ocean, to the atmosphere, returning to the earth in some form of precipitation, and finally returning to the ocean.

Imported water. Water that has originated from one hydrologic region and is transferred to another hydrologic region.

Inflatable rubber dams. Designed to replace temporary sand levees that wash out during heavy storm flow, the dams hold back high-volume river flows and divert the water into the off-river system for percolation.

Influent: Water or wastewater entering a treatment plant, or a particular stage of the treatment process.

Irrigation: Applying water to crops, lawns or other plants using pumps, pipes, hoses, sprinklers, etc.

Leach. To remove components from the soil by the action of water trickling through.

MCL. Maximum contaminant level set by EPA for a regulated substance in drinking water.According to health agencies, the maximum amount of a substance that can be present in water that's safe to drink and which looks, tastes and smells good.

Microfiltration. A physical separation process where tiny, hollow filaments members separate particles from water.

Non-point source pollution. Pollution that is so general or covers such a wide area that no single, localized source of the pollution can be identified.

Organism: Any individual form of life, such as a plant, animal or bacterium.

Perched groundwater. Groundwater supported by a zone of material of low permeability located above an underlying main body of groundwater with which it is not hydrostatically connected.

Percolation. The downward movement of water through the soil or alluvium to the groundwater table.

Permeability. The capability of soil or other geologic formations to transmit water.

Point source. A specific site from which waste or polluted water is discharged into a water body, the source of which is identified. See also: non-point source.

Precipitation: Water from the atmosphere that falls to the ground as a liquid (rain) or a solid (snow, sleet, hail).

Primary treated water. First major treatment in a wastewater treatment facility, usually sedimentation but not biological oxidation.

Primary treatment: Removing solids and floating matter from wastewater using screening, skimming and sedimentation (settling by gravity).

Prior appropriation doctrine. Allocates water rights to the first party who diverts water from its natural source and applies the water to beneficial use. If at some point the first appropriator fails to use the water beneficially, another person may appropriate the water and gain rights to the water. The central principle is beneficial use, not land ownership.

Recharge. The physical process where water naturally percolates or sinks into a groundwater basin.

Recharge basin. A surface facility, often a large pond, used to increase the infiltration of surface water into a groundwater basin.

Reclaimed wastewater. Wastewater that becomes suitable for a specific beneficial use as a result of treatment. See also: wastewater reclamation.

Reclamation project. A project where water is obtained from a sanitary district or system and which undergoes additional treatment for a variety of uses, including landscape irrigation, industrial uses, and groundwater recharge.

Recycling. A type of reuse, usually involving running a supply of water through a closed system again and again. Legislation in 1991 legally equates the term "recycled water" to reclaimed water.

Reservoir.A place where water is stored until it is needed. A reservoir can be an open lake or an enclosed storage tank.

Reverse osmosis. (RO) A method of removing salts or other ions from water by forcing water through a semi-permeable membrane.

Runoff. Liquid water that travels over the surface of the Earth, moving downward due to the law of gravity; runoff is one way in which water that falls as precipitation returns to the ocean.

Safe yield. The maximum quantity of water that can be withdrawn from a groundwater basin over a long period of time without developing a condition of overdraft. Sometimes referred to as sustained yield.

Salinity. Generally, the concentration of mineral salts dissolved in water. Salinity may be measured by weight (total dissolved solids - TDS), electrical conductivity, or osmotic pressure. Where seawater is known to be the major source of salt, salinity is often used to refer to the concentration of chlorides in the water.

STSS (Short Term Seasonal Storage) financially encourages agencies with local groundwater production capabilities to produce a higher percentage of their demand in the summer from their local groundwater supplies, thus ÒshiftingÓ a portion of their demand on the MWD system from the summer to winter;

LTSS (Long Term Seasonal Storage) financially encourages retail agencies to take and store additional amounts of MWD water above their normal annual demands for later use;

Replenishment Water provides less expensive interruptible water that is generally available and used to increase the operating yield of groundwater basins.

Seawater intrusion. The movement of salt water into a body of fresh water. It can occur in either surface water or groundwater basins.

Seawater barrier. A physical facility or method of operation designed to prevent the intrusion of salt water into a body of freshwater.

Secondary treatment. The biological portion of wastewater treatment which uses the activated sludge process to further clean wastewater after primary treatment. Generally, a level of treatment that produces 85 percent removal efficiencies for biological oxygen demand and suspended solids. Usually carried out through the use of trickling filters or by the activated sludge process.

Settle: To clarify water by causing impurities or solid material to sink to the bottom of the container.

Sewer: The system of pipes that carries wastewater from homes and businesses to a treatment plant or reclamation plant. Sewers are separate from storm drains, which is a system of drains and pipes that carry rain water from urban streets back to the ocean. Overwatering your yard can also cause water to run into the streets and into storm drains. Storm drain water is not treated before it is discharged.

Sludge: The solids that remain after wastewater treatment. This material is separated from the cleaned water, treated and composted into fertilizer. Another word for sludge is biosolids.

Storm Drain: The system of pipes that carries rain water from urban streets back to the ocean. Overwatering your yard can also cause water to run into the streets and into storm drains. Storm drain water is not treated before it is discharged. Storm drains are separate from sewers, which is a separate system of pipes to carry wastewater from homes and businesses to a treatment plant or reclamation plant for cleaning.

Storm flow. Surface flow originating from precipitation and run-off which has not percolated to an underground basin.

SWP. State Water Project. An aqueduct system that delivers water from northern California to central and southern California.

TDS. Total dissolved solids. A quantitative measure of the residual minerals dissolved in water that remain after evaporation of a solution. Usually expressed in milligrams per liter.

Tertiary treatment. The treatment of wastewater beyond the secondary or biological stage. Normally implies the removal of nutrients, such as phosphorous and nitrogen, and a high percentage of suspended solids.

THM. Trihalomethanes. Any of several synthetic organic compounds formed when chlorine or bromine combine with organic materials in water.

Transpiration. The process in which plant tissues give off water vapor to the atmosphere as an essential physiological process.

Ultraviolet light disinfection. A disinfection method for water that has received either secondary or tertiary treatment used as an alternative to chlorination.

VOC. Volatile organic compound. A chemical compound which evaporates readily at room temperature and contains carbon.

Wastewater. Water that has been previously used by a municipality, industry or agriculture and has suffered a loss of quality as a result.

Water Cycle: The continuous process of surface water (puddles, lakes, oceans) evaporating from the sun's heat to become water vapor (gas) in the atmosphere. Water condenses into clouds and then falls back to earth as rain or snow (precipitation). Some precipitation soaks into the ground (percolation) to replenish groundwater supplies in underground aquifers.

Water Factory 21 (WF-21). Orange County Water District's advanced wastewater treatment plant.

Water rights. A legally protected right to take possession of water occurring in a natural waterway and to divert that water for beneficial use.

Water year (USGS). The period between October 1 of one calendar to September 30 of the following calendar year.

Watermaster. A court appointed person(s) that has specific responsibilities to carry out court decisions pertaining to a river system or watershed.

Water Reclamation: The treatment of wastewater to make it suitable for a beneficial reuse, such as landscape irrigation. Also called water recycling.

Watershed. The total land area that from which water drains or flows to a river, stream, lake or other body of water.

Weir box. A device to measure and/or control surface water flows in streams or between a series of ponds.

Wellhead treatment. Water quality treatment of water being produced at the well site.

Wetland: Any area in which the water table stands near, at, or above the land surface for at least part of the year. Such areas are characterized by plants that are adapted to wet soil conditions.