Ensuring Clean Water for California

California Association of Sanitation Agencies

Definition of Terms - D

Records of observations and measurements of physical facts, occurrences and conditions, reduced to written, graphical or tabular form.
(1) An agreed standard point or plane or plane of stated elevation, noted by permanent bench marks on some solid immovable structure, from which elevations are measured or to which they are referred. (2) Any position or element in relation to which others are determined; for example, the horizontal control system used in map making. (3) Any numerical or geometrical quantity or set of such quantities which may serve as a reference or base for other quantities.
Generally solid wastes from natural and man-made sources deposited indiscriminately on land and water.
An obligation resulting from the borrowing of money or from the purchase of goods and services. Debts of governments include bonds, time warrants and floating debt.
debt limit
The maximum amount of gross or net debt which is legally permitted. Generally refers only to General Obligation bonds.
debt service
The amount of money necessary annually: (a) to pay the interest on outstanding debt; (b) to pay the principal of maturing bonded debt not payable from a sinking fund; or (c) to provide a fund for the redemption of bonds payable from a sinking fund.
debt service fund
A fund established to account for the accumulation of resources for, and the payment of, general long-term debt principal and interest.
debt service fund requirements
The amounts of revenue which must be provided for a debt service fund so that all principal and interest payments can be made in full on schedule.
debt service requirement
the amount of money required to pay interest on outstanding debt, serial maturities of principal for serial bonds, and required contributions to accumulate monies for future retirement of term bonds.
The partial or complete reduction of residual chlorine by any chemical or physical process.
The breakdown of complex material into a simpler form by any chemical or biological processes.
decomposition of wastewater
(1) The breakdown of organic matter in wastewater by bacterial action, either aerobic or anaerobic. (2) Chemical or biological transformation of organic or inorganic materials contained in wastewater.
deferred charges
Expenditures not chargeable to the period in which made, but carried on the asset side of the balance sheet, pending amortization or other disposition. They include such items as discount on bond issues. Deferred charges usually involve expenses which are not to be spread over a relatively long period of time and which do not recur regularly in the operation of the enterprise. They are to be distinguished from other prepaid expenses which are usually spread over a short period of time and which recur more or less regularly in the operation of the enterprise.
deferred credits
Credit balances or items spread over subsequent accounting periods either as an addition to income or as a reduction of certain expenses. Payments made in advance represent an example of the latter.
deferred liabilities
Liabilities not elsewhere provided for which are not current in nature and on which payment or other disposition is deferred to a future accounting period. Examples are user's or customer's advances for construction and accrued compensated absences.
deficient work
Work conforming to the plans, specifications, and applicable standards yet is incomplete, insufficient, or lacking in workmanship. See also "Non-conforming Work."
(1) In geology, a process by which wind and water wear down and carry away parts of the surface of the earth, reducing the general elevation. (2) The breakdown of substances by biological action.
(1) The process of removing greases and oils from waste, wastewater, sludge or solid wastes. (2) The industrial process of removing grease and oils from machine parts or iron products.
degree of treatment
A measure of the removal effected by treatment processes with reference to solids, organic matter, BOD, bacteria or any other specified parameter.
deionized water
Water from which anions and cations have been removed by ion exchange.
The biological reduction of nitrate nitrogen to nitrogen gas under anoxic conditions. Also removal of total nitrogen from a system.
A measure of how heavy a substance (solid, liquid or gas) is for its size. Density is expressed in terms of weight per unit volume, that is, grams per cubic centimeter or pounds per cubic foot.
A system of accounting which aims to distribute the cost or other basic value of tangible capital assets over the estimated useful life o the unit in a systematic and rational manner. This is the process of allocation, not of valuation.
depreciation rate
The rate or percentage at which the original cost is allocated over the estimated useful life of an asset.
depressed sewer
A section of sewer constructed lower than adjacent sections to pass beneath a valley, watercourse or other obstruction. It runs full or at pressure greater than atmospheric because its crown is depressed below the hydraulic grade line.
design analysis
In engineering reports, the tabulation and consideration of the physical data present requirements and probable future requirements pertaining to an engineering project. It should include the main features and principles of the design.
design capacity
The flow, usually in million gallons per day, that a treatment plant can effectively treat according to engineering criteria. Usually expressed as both average dry-weather flow and peak wet-weather flow capacity.
designated uses
Those uses specified by the state water quality standards for each water body or segment, whether or not they are being attained. Uses can include coldwater fisheries, public water supply, agriculture, etc.
A single entity performs both the design and the construction services for a project.
Independent consulting engineering firm provides the design and development of construction documents to the owner. Owner requests bid proposals from consrtuctors and contracts with the selected bidder. This is also referred to as the "conventional project delivery system."
design criteria
(1) Engineering guidelines specifying construction details and materials. (2) Objectives, results or limits which must be met by a facility, structure or process in performance of its intended functions.
design loadings
Flow rates and constituent concentrations which determine the design of a process unit or facility necessary for proper operation.
detention time
The period of time that a water or wastewater flow is retained in a basin, tank or reservoir for storage or completion of physical, chemical or biological reaction.
dewatered biosolids (sludge)
The solid residue remaining after removal of some or most of the water from a wet biosolids by evaporation, draining, or filtering. Dewatering is distinguished from thickening in that dewatered biosolids may be transported by solids handling procedures.
The process of partially removing water; may refer to removal of water from a basin, tank, reservoir or other storage unit, or to separation of water from solid material.
diffused air
Small air bubbles formed below the surface of a liquid to transfer oxygen to the liquid.
(1) A porous plate, tube or other device through which air is forced and divided into minute bubbles for diffusion in liquids. Commonly made of carborundum, alundum, metal or plastic materials. (2) That portion of an outfall pipe that distributes effluent into the receiving waters such that maximum dilution is achieved.
A tank or other vessel for the storage and anaerobic or aerobic decomposition of organic matter present in biosolids.
digester gas
The gases resulting from the anaerobic digestion of wastewater. Principally composed of carbon dioxide, methane, and hydrogen sulfide.
digested sludge
Sludge digested under either aerobic or anaerobic conditions until the volatile content has been reduced to the point at which the solids are relatively nonputrescible and inoffensive.
(1) The biological decomposition of organic matter in sludge, resulting in partial liquefaction, mineralization and volume reduction. (2) The process carried out in a digester.
Disposal of wastewater or treated effluent by discharge to and dispersion in a receiving water with resulting reduction in concentrations of constituents, while accounting for background levels and natural assimilation processes.
dilution factor
The ratio of the quantity of untreated wastewater or partly or completely treated effluent to the average quantity of diluting water available at the point of disposal or at any point under consideration; usually expressed in percentage.
direct costs
(1) Any cost that can be identified specifically with a particular cost objective or any cost that can be directly identified with a particular grant or contract. (2) The field costs directly attributed to the construction of a project, including labor, material, equipment, subcontracts and their associated costs.
direct debt
Debt of the issuing agency.
direct labor
Labor directly expended or applied in productive operations, as distinguished from that not directly connected with a productive process.
direct net debt
Gross direct debt less debt that is self-supporting from revenues which flow outside the general fund.
disallowed costs
Defined by the Inspector General Act Amendments of 1988 as questioned costs that management, in a management decision, has sustained or agreed should not be charged to the government.
With respect to wastewaters, the release of treated, partially treated or untreated wastewaters into the environment, whether accidentally or by design.
(1) One who discharges wastewater. (2) Any person who discharges waste which could affect the quality of waters of the State.
discharge permit
Formal authorization, issued by a state or federal regulatory agency stipulating conditions under which effluent may be released into the environment. See also "National Pollutant Discharge Elimination System (NPDES) Permit".
A substance used for disinfection and in which disinfection has been accomplished.
disinfected wastewater
Wastewater to which a disinfecting agent has been added.
(1) The killing or inactivation of waterborne fecal and pathogenic bacteria and viruses in potable water supplies or wastewater effluent with a disinfectant; an operational term that must be defined within limits, such as achieving an effluent with no more than 200 colonies fecal coliform per 100 ml. (2) The killing of the larger portion of microorganisms, excluding bacterial spores, in or on a substance with the probability that all pathogenic forms are killed, inactivated or otherwise rendered non-virulent.
Release or discharge to the environment.
dissolved air flotation
A separation process in which air bubbles emerging from a supersaturated solution become attached to suspended solids in the liquid undergoing treatment and float them up to the surface. A skimming mechanism removes the solids which then typically become part of the biosolids handling process.
dissolved oxygen (DO)
The oxygen dissolved in water, wastewater or other liquid, usually expressed in milligrams per liter or percent of saturation.
dissolved solids
Solids in solution that cannot be removed by filtration; for example, NaCl; determined by evaporating the water at 103 °C.
(1) Occurring during a 24-hr period, as in "diurnal variation". (2) Occurring during the daytime (as opposed to night time). (3) In tidal hydraulics, having a period or cycle of approximately one tidal day.
diurnal fluctuation
(1) The cyclic rise and fall of the water table or streamflow during a 24-hour period in response to changes in evapotransporation draft from groundwater. (2) Any daily variation in a groundwater characteristic such as flow, BOD or suspended solids.
diversion manhole
A manhole equipped with a device for diverting a portion of the total flow to another sewer, conduit, or receiving waters.
The number and relative abundance of biological taxa in a specified location.
dissolved oxygen (DO)
The amount of oxygen dissolved in water or other liquids, usually expressed as mg/L or percent saturation.
A term used to distinguish municipal (household) water or wastewater services from commercial and industrial water or wastewater. Term sometimes used to include commercial component.
domestic consumption
The quantity, or quantity per capita, of water supplied in a municipality or district for domestic uses or purposes during a given period, usually one day. It is usually taken to include all uses included within the term municipal use of water, and quantity wasted, lost or otherwise unaccounted for.
domestic wastewater
Wastewater derived principally from dwellings, business buildings, institutions and the like. It may or may not contain groundwater, surface water or storm water.
domestic wastewater treatment
Reduction or removal of insoluble and dissolved constituents from the liquid wastes from dwelling, business building, institutions, etc.
A specified quantity of a material applied to a specified quantity of a second material; for example, mg/L alum applied as a coagulant in water purification, or mg/L of chlorine used in disinfection.
(1) A conduit or channel constructed to carry off, by gravity, liquids other than wastewater, including surplus underground, storm or surface water. It may be an open ditch, lined or unlined, or a buried pipe. (2) In plumbing, any pipe which carries water or wastewater in a building drainage system.
drainable biosolids
Biosolids that can be dewatered readily by gravity.
(1) The magnitude of the change in surface elevation of a body of water as a result of the withdrawal of water. (2) The magnitude of the lowering of the water surface in a well or of the water table of piezometric surface adjacent to the well, resulting from the withdrawal of water from the well by pumping. (3) In a continuous water surface with accelerating flow, the difference in elevation between downstream and upstream points.
drawdown curve
In well or groundwater drainage hydraulics, a profile of the piezometric surface of the water table relating drawdown to distance from pumping well under a given set of pumping conditions.
Graphic representations showing the relationships, geometry and dimension of the elements of the work.
Removal of mud from the bottom of waterbodies using a scooping or suction machine or other device. This disturbs the ecosystem and causes silting that can kill aquatic life. Dredging of contaminated muds can expose aquatic life to heavy metals and other toxics.
drinking water standards
Standards that define allowable concentrations of coliforms and certain chemicals, physical characteristics and radioactivity in drinking water. They are prescribed by federal, state or local authorities and also contain sampling monitoring and reporting requirements.
drop manhole
A manhole configuration used if an incoming sewer is considerably higher than the outgoing. A tee or elbow from the incoming sewer drops the wastewater through a vertical pipe into the manhole at the outgoing sewer elevation.
dry feeder
A feeder for dispensing a chemical or other fine material in the solid state to water or wastewater at a rate controlled manually or automatically by the rate of flow. The constant rate may be either volumetric or gravimetric.
drying beds
Confined, underdrained shallow layers of sand, gravel, fabricated drainage media, or paved beds on which wet biosolids are distributed for draining and air drying. Also applies to underdrained, shallow, dyked, earthen structures used for drying biosolids.
dry weather flow
(1) The flow of wastewater in a combined sewer during dry weather. Such flow consists mainly of wastewater, with no storm water included. (2) The flow of water in a stream during dry weather, usually contributed entirely by groundwater. This is also called "base flow."
dual-media filters
Deep-bed filters utilizing discrete layers of dissimilar media, such as anthracite and sand, placed one on top of the other.
dynamic head
(1) When there is flow: (a) the head at the top of a waterwheel; (b) the height of the hydraulic grade line above the top of a waterwheel; (c) the head against which a pump works. (2) That head of fluid which would produce statically the pressure of a moving fluid. (3) Dynamic head = total head - static head.
definition of terms


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