SC Water/Wastewater Operator key terms

A measure of how much suspended material clouds water, reported in nephelometric turbidity units. High turbidity can shield pathogens from disinfectants and usually signals a problem upstream in treatment.

The land area that drains rain and snowmelt into a particular stream, lake, or reservoir. Land use and activities within that area strongly affect raw water quality at the intake.

An underground layer of sand, gravel, or rock that holds and transmits usable quantities of groundwater. Wells draw from aquifers, which are usually lower in turbidity and organic matter than surface supplies.

The concentration of dissolved calcium and magnesium in water, usually reported as milligrams per liter of calcium carbonate. Hard water forms scale in pipes and heaters and consumes soap.

The amount of carbon bound in natural organic matter in a water sample. TOC drives disinfectant demand, can cause tastes and odors, and serves as a precursor for disinfection byproducts.

A group of organisms used as indicator bacteria because their presence suggests contamination and the possible presence of pathogens. Total coliform, fecal coliform, and E. coli are reported under drinking water and wastewater rules.

The rapid mixing of a chemical such as alum into water to neutralize the electrical charges that keep small particles apart, allowing them to begin clumping together.

Gentle, slow stirring that encourages small destabilized particles to collide and grow into larger settleable clumps called floc after a coagulant has been added.

A quiet settling basin where gravity pulls floc and other solids to the bottom, producing clearer overflow and a sludge underflow that must be removed and treated.

Passing water through granular media such as sand, anthracite, or mixed beds to remove remaining particles. Filtration is the final particle barrier before disinfection in a conventional plant.

Reversing flow upward through a filter at a high rate to expand the bed and wash out trapped solids. Backwashing restores head loss and is usually followed by a filter-to-waste or ripening period.

A bench-scale test that doses several beakers of raw water with different coagulant amounts and mixing conditions to identify the best chemical dose and pH.

A pressure surge caused by a sudden change in flow velocity, such as a fast-closing valve or a pump trip. It can crack mains and damage fittings, so surge control is designed into the system.

Any actual or potential link between a drinking water system and a source of contamination, such as a submerged hose or a boiler feed line. Cross-connections are controlled through backflow prevention.

A device such as a reduced-pressure-zone assembly or a vacuum breaker that stops water from reversing direction and carrying contamination into the drinking water distribution system.

Groundwater that leaks into sewers plus rainwater and drainage that enters through illegal connections, broken manholes, or sump pumps. I/I overloads collection systems and treatment plants during storms.

An unauthorized release of raw sewage from the collection system before it reaches the treatment plant, often caused by blockages, root intrusion, or wet-weather flows. It is reportable to regulators.

A collection-system facility with pumps and a wet well that raises wastewater to a higher elevation so gravity flow can continue on toward the treatment plant.

A treatment process in which aeration mixes wastewater with a concentrated community of microorganisms that consume organic matter, followed by clarification that separates the biomass for return or wasting.

The amount of oxygen microorganisms consume while breaking down organic matter in a sample over five days at 20 degrees Celsius, a standard measure of wastewater strength and plant performance.

The concentration of suspended solids, mostly bacteria, in the aeration basin. MLSS is combined with other data to set wasting rates and control sludge age.

A settling tank after biological treatment where microorganism floc settles out, producing a clear effluent and a return activated sludge stream that is sent back to the aeration basin.

The concentration of chlorine remaining in water after the initial demand is satisfied. Free residual protects the distribution system, and regulations set both minimum targets and maximum limits.

The product of disinfectant concentration and contact time, adjusted for temperature and pH, used to demonstrate that a required level of pathogen inactivation has been achieved.

A group of disinfection byproducts, including chloroform, formed when chlorine reacts with natural organic matter. THM levels are limited by regulation and controlled by removing precursors before chlorination.

A disinfectant formed by adding chlorine and ammonia together. It lasts longer in distribution systems but is a weaker primary disinfectant and must be managed to limit nitrification.

Removing or neutralizing chlorine from water before discharge, commonly with sulfur dioxide or sodium bisulfite, to protect receiving streams and aquatic life from toxic effects.

Vapor bubbles forming and collapsing in a pump because of low pressure at the impeller eye, producing noise, vibration, and metal damage. It is prevented by maintaining adequate net positive suction head.

The absolute pressure head at the pump suction minus the liquid vapor pressure, expressed in feet. Available NPSH must exceed the pump's required NPSH to avoid cavitation.

A graph showing the flow a pump delivers at each head. The operating point occurs where the pump curve intersects the system curve.

A space large enough for a worker to enter, with limited entry or exit, and not designed for continuous occupancy. Examples include manholes, wet wells, and digesters.

A confined space containing a hazardous atmosphere, engulfment potential, or another serious hazard, requiring an entry permit, atmospheric testing, an attendant, and rescue provisions before entry.

A procedure that isolates hazardous energy with locks and tags before maintenance, preventing accidental start-up or release of stored energy that could injure workers.

A toxic, flammable gas with a rotten-egg odor produced by anaerobic decay of sewage. It deadens the sense of smell at higher concentrations and is a leading cause of confined-space fatalities.

The highest concentration of a regulated contaminant allowed in drinking water delivered to customers, set as close to the health goal as is technically and economically feasible.

A periodic report submitted to the permitting agency listing sampling results and calculated limits from an NPDES permit, signed by a responsible official who certifies its accuracy.

An annual report that community water systems must deliver to customers, summarizing source water, detected contaminants, compliance status, and health effects information.

The average time water remains in a tank or basin, calculated as volume divided by flow rate. It is a core operator math calculation used for chlorine contact and settling design.

The fraction of a pollutant removed by a process, calculated as influent concentration minus effluent concentration, divided by influent concentration, times one hundred. It is used to judge treatment performance.