AK Water Operator key terms

An underground layer of rock, sand, or gravel that holds and transmits groundwater in quantities useful for wells. Confined aquifers sit beneath an impermeable layer; unconfined aquifers have a water table open to recharge.

The upper surface of the saturated zone in an unconfined aquifer, where water pressure equals atmospheric pressure. Its depth rises and falls with recharge and pumping, affecting well yield and contamination vulnerability.

A state-conducted evaluation of a public water system's source water to identify the origins of water, potential contaminant sources nearby, and the system's susceptibility to contamination. Results inform monitoring waivers and protection planning.

The land surface and subsurface zone around a public well through which contaminants could travel to reach the well. Delineated areas support local controls on land use and chemical storage.

The cloudiness of water caused by suspended particles such as clay, silt, organic matter, and microorganisms. Measured in nephelometric turbidity units, it is a key indicator of filtration performance and microbial risk.

The maximum amount of a pollutant a water body can receive and still meet water quality standards, allocated among point and nonpoint sources. Used under the Clean Water Act to restore impaired waters that may serve as drinking water sources.

A treatment step in which a chemical such as alum or ferric chloride is rapidly mixed into water to neutralize the electrical charges that keep small particles apart. Destabilized particles then clump together in flocculation.

Gentle, prolonged stirring of coagulated water that encourages destabilized particles to collide and gather into larger, settleable masses called floc. Adequate time and mixing energy are needed for floc to grow without breaking apart.

A tank or clarifier where water moves slowly enough for floc and other suspended solids to settle to the bottom as sludge. Detention time, flow distribution, and sludge removal affect settled water quality.

The granular material, commonly sand, anthracite, or a mixed bed, through which water passes to remove remaining particles. Media depth, grain size, and uniformity determine filtration rate and particle capture.

A reverse, upward flow of water, often aided by air scour, that lifts and cleans filter media by carrying trapped solids to waste. Backwash frequency and effectiveness are tracked to protect filter performance.

A practice of diverting the first filtered water after backwash to waste rather than to finished water storage. It prevents a spike of particles and pathogens from entering the distribution system during filter ripening.

The product of disinfectant residual concentration in milligrams per liter and contact time in minutes, used to measure disinfection exposure. Required CT values vary by disinfectant, temperature, pH, and target organism.

The concentration of disinfectant remaining in treated water after a specified contact time. A detectable residual must be maintained throughout the distribution system to guard against contamination and regrowth.

A way of expressing pathogen reduction as powers of ten, so one log means a 90 percent reduction, two logs 99 percent, and three logs 99.9 percent. Treatment rules set required log credits for viruses, Giardia, and Cryptosporidium.

Chemicals such as trihalomethanes and haloacetic acids that form when disinfectants react with naturally occurring organic matter and bromide in water. Their formation is managed by controlling precursors and disinfectant dose.

A measure of the carbon bound in dissolved and particulate organic compounds in water. It serves as a precursor indicator for disinfection byproduct formation and as a gauge of source water quality.

A protozoan parasite that forms oocysts highly resistant to chlorine disinfection and can cause gastrointestinal illness. Utilities rely on filtration, ultraviolet light, or ozone for control and monitor source water for it.

Any actual or potential link between a potable water system and a source of nonpotable fluid or contamination. Backflow through such links is prevented with air gaps, reduced-pressure assemblies, and routine surveys.

A testable device, such as a reduced-pressure principle assembly or double check valve, installed to stop reverse flow of contaminated water into the potable system. Assemblies must be tested periodically by certified personnel.

A public health advisory telling customers to boil tap water before drinking, cooking, or brushing teeth because of confirmed or suspected microbial contamination. Utilities issue it with health authorities and lift it after corrective action and testing.

A group of bacteria used as indicators of treatment effectiveness and possible fecal contamination in drinking water. Total coliform presence triggers repeat sampling; E. coli presence signals a serious health risk.

A microbiological method that reports whether coliform bacteria are detected in a sample rather than counting colonies. It is used for routine compliance monitoring of distribution system water.

A method that estimates the number of bacteria able to grow on a nutrient medium, reflecting general bacterial regrowth in distribution water. Elevated counts can indicate loss of residual or biofilm problems.

Written documentation recording who collected, handled, and transported a water sample and when, ensuring its integrity for regulatory testing. Missing or broken custody records can invalidate compliance results.

The unit reported by a turbidimeter that measures light scattered at 90 degrees by particles in a sample. Regulatory limits for filtered water are expressed in these units and compared to maximum values.

The highest concentration of a regulated contaminant legally allowed in water delivered to customers. Primary levels protect health; secondary levels address aesthetics such as taste, odor, and color.

A required treatment process or practice, such as filtration or corrosion control, used when a contaminant cannot be reliably measured at low levels. Compliance is judged by following the specified method rather than meeting a numeric limit.

An annual water quality report that community water systems deliver to customers, listing detected contaminants, their levels, and health effects. It must be distributed by the regulatory deadline and made publicly available.

A regulation requiring systems to sample tap water at high-risk sites and, if action levels are exceeded, apply corrosion control, public education, and possible pipe replacement. It targets plumbing materials rather than source water.

A chemical such as orthophosphate or silicate dosed into water to form a protective film on pipe surfaces and reduce metal release. Dose and pH are adjusted based on water chemistry and monitoring results.

A layer of microorganisms attached to pipe walls and equipment surfaces and held together by a slimy matrix. Biofilm shelters pathogens, consumes disinfectant residual, and can harbor taste and odor problems.

A pressure surge caused by a sudden change in flow velocity, such as rapid valve closure or pump shutdown, that travels through piping as a shock wave. It can damage pipes and fittings and is controlled with slow-closing valves and surge protection.

A device that automatically lowers downstream pressure to a set value regardless of upstream fluctuations. It protects distribution piping and customer plumbing from excessive pressure.

A graph showing the relationship between a pump's flow rate and the head it develops at a given speed. It is compared with the system curve to find the operating point.

A plot of the total head required to move water through a piping system at various flow rates, including static lift and friction losses. Where it crosses the pump curve defines actual operating flow and head.

The absolute pressure margin at a pump suction that keeps water from vaporizing and cavitating. Available margin must exceed the pump's required margin, or the pump will lose capacity and suffer damage.

The formation and collapse of vapor bubbles in a pump when local pressure drops below the liquid's vapor pressure. It causes noise, vibration, and pitting damage and is corrected by improving suction conditions.

The energy of water expressed as the height of a column it could support, measured in feet or meters. It allows pressures and elevations to be compared directly in hydraulic calculations.

Force per unit area exerted by water, commonly reported in pounds per square inch at a distribution point. One psi corresponds to about 2.31 feet of water head.

The average time water spends in a tank or process unit, calculated as volume divided by flow rate. It governs settling, disinfection contact, and chemical reaction completion.

A space large enough to enter, with limited entry or exit, not designed for continuous occupancy, such as a vault or wet well. Entry requires hazard evaluation, atmospheric testing, an attendant, and a permit.

A procedure that isolates hazardous energy sources with locks and tags before maintenance so equipment cannot start unexpectedly. Each worker applies a personal lock, and only the person who applied it removes it.