426DARCY’S LAW: (Q=KIA) A fundamental equation used in the groundwater sciences to
determine aquifer characteristics, where Q=Flux, K=Hydraulic Conductivity (Permeability), I =
Hydraulic Gradient (change in head), and A = Cross Sectional Area of flow.
DECOMPOSE: To decay or rot.
DECOMPOSITION OF ORGANIC MATERIAL: The decomposition of organic material in water
produces taste and odors.
DEIONIZATION: The removal of ions, and in water's case mineral ions such as sodium, iron and
calcium.
DELIQUESCENE: Substances that absorb water from the atmosphere to form liquid solutions.
DEMINERALIZATION PROCESS: Mineral concentration of the feed water is the most important
consideration in the selection of a demineralization process. Acid feed is the most common
method of scale control in a membrane demineralization treatment system.
DENTAL CARIES PREVENTION IN CHILDREN: The main reason that fluoride is added to a
water supply.
DEPOLARIZATION: The removal of hydrogen from a cathode.
DEPOSITION: Settling of particles within a solution or mixture.
DESICCANT: When shutting down equipment which may be damaged by moisture, the unit may
be protected by sealing it in a tight container. This container should contain a desiccant.
DESORPTION: Desorption is a phenomenon whereby a substance is released from or through a
surface. The process is the opposite of sorption (that is, adsorption and absorption). This occurs
in a system being in the state of sorption equilibrium between bulk phase (fluid, i.e. gas or liquid
solution) and an adsorbing surface (solid or boundary separating two fluids). When the
concentration (or pressure) of substance in the bulk phase is lowered, some of the sorbed
substance changes to the bulk state. In chemistry, especially chromatography, desorption is the
ability for a chemical to move with the mobile phase. The more a chemical desorbs, the less likely
it will adsorb, thus instead of sticking to the stationary phase, the chemical moves up with the
solvent front. In chemical separation processes, stripping is also referred to as desorption as one
component of a liquid stream moves by mass transfer into a vapor phase through the liquid-vapor
interface.
DETENTION LAG: Is the period of time between the moment of change in a chlorinator control
system and the moment when the change is sensed by the chlorine residual indicator.
DEVELOPMENT: The cleaning of the well and bore once construction is complete.
DIATOMACEOUS EARTH: A fine silica material containing the skeletal remains of algae.
DIPOLE: Electric or magnetic separation of charge.
DIPOLE MOMENT: The polarity of a polar covalent bond.
DIRECT CURRENT: A source of direct current (DC) may be used for standby lighting in a water
treatment facility. The electrical current used in a DC system may come from a battery.
DISINFECT: The application of a chemical to kill most, but not all, microorganisms that may be
present. Chlorine is added to public water drinking systems drinking water for disinfection.
Depending on your state rule, drinking water must contain a minimum of 0.2 mg/L free chlorine.
Disinfection makes drinking water safe to consume from the standpoint of killing pathogenic
microorganisms including bacteria and viruses. Disinfection does not remove all bacteria from
drinking water, but the bacteria that can survive disinfection with chlorine are not pathogenic
bacteria that can cause disease in normal healthy humans.
DISINFECTION BY-PRODUCTS (DBPs): The products created due to the reaction of chlorine
with organic materials (e.g. leaves, soil) present in raw water during the water treatment process.
The EPA has determined that these DBPs can cause cancer. Chlorine is added to drinking water
to kill or inactivate harmful organisms that cause various diseases. This process is called
disinfection. However, chlorine is a very active substance and it reacts with naturally occurring
substances to form compounds known as disinfection byproducts (DBPs). The most common
DBPs formed when chlorine is used are trihalomethanes (THMs), and haloacetic acids (HAAs).
DISINFECTION: The treatment of water to inactivate, destroy, and/or remove pathogenic
bacteria, viruses, protozoa, and other parasites.
Dissolution: The chemical and physical process of dissolving rock. Typically, limestone or
carbonate rocks can be dissolved via the percolation or movement of groundwater that, in its
infancy, is slightly acidic. As time goes on, the rock may also be physically worn away by the