DC Water Operator key terms

The rapid mixing of a chemical such as alum or ferric chloride into raw water so that tiny suspended particles lose their repelling charges and begin to clump together. It is the first step of conventional clarification.

Gentle, slow stirring after coagulation that encourages small destabilized particles to collide and grow into larger, settleable masses called floc. Stirring speed is tapered so floc is not broken apart before settling.

A quiet settling basin where water moves slowly enough that floc and other solids sink to the bottom as sludge. Also called clarification, it removes the bulk of particles before filtration.

The cloudiness of water caused by suspended particles that scatter light. Measured in nephelometric turbidity units, it is a key indicator of filtration performance and disinfection effectiveness because particles can shield pathogens.

A laboratory or online instrument that shines light through a water sample and measures scattered light to report turbidity in nephelometric turbidity units. It must be calibrated with primary standards to keep readings trustworthy.

A bench-scale procedure using several stirred beakers of raw water dosed with different coagulant amounts to find the best chemical dose and mixing conditions before changing full-scale plant operations.

Reversing or scouring flow through a filter to lift and carry away trapped solids so the media regains capacity. Backwash water is usually returned to the head of the plant or otherwise managed.

The product of disinfectant residual concentration and the contact time water spends in the basin, used to demonstrate that a required level of pathogen inactivation has been achieved. Higher temperature and lower pH generally improve disinfection.

The amount of chlorine remaining in treated water after it has reacted with impurities. A free chlorine residual is maintained through the distribution system to prevent regrowth of bacteria and to signal contamination.

Compounds such as trihalomethanes and haloacetic acids that form when chlorine reacts with naturally occurring organic matter. Their formation is controlled by removing organics before disinfection and by managing dose and contact time.

A measure of the carbon bound in natural organic material in water. High levels consume disinfectant, raise byproduct risk, and increase coagulant demand, so treatment targets its removal.

The water's capacity to neutralize acid, mainly from bicarbonate, carbonate, and hydroxide. It buffers pH during coagulation and disinfection, so low-alkalinity water may need lime or caustic addition.

A logarithmic scale from 0 to 14 describing hydrogen ion activity, where 7 is neutral. Treatment processes such as coagulation, disinfection, and corrosion control each perform best within specific pH ranges.

Water that has completed all treatment steps and meets quality standards for entry into the distribution system. Its turbidity, residual, and other parameters are monitored as it leaves the plant.

Treatment adjustments, such as raising pH or adding orthophosphate, that form a protective scale or chemical barrier on pipe walls so lead, copper, and iron do not dissolve into drinking water.

Any actual or potential link between a drinking water system and a source of nonpotable water or contamination. It is controlled by air gaps, backflow preventers, and routine inspections of customer plumbing.

Devices and practices that stop water from flowing opposite to its intended direction, keeping contaminants out of the public main. Common examples are air gaps, reduced pressure zone assemblies, and double check valves.

A large buried pipe that carries treated water through streets to serve fire hydrants and smaller service lines. Its material, diameter, and pressure class determine capacity and repair methods.

The pipe running from the public water main to a customer's meter or building. Ownership rules vary, and leaks or lead material on this line are frequent field concerns for distribution crews.

A device that measures the volume of water delivered to a customer for billing and leak detection. Accuracy checks and proper sizing matter because oversized meters under-register low flows.

A valved connection on a water main used for firefighting and for flushing mains. Crews inspect, lubricate, and flow-test hydrants, and they must be drained properly to avoid freezing damage.

Deliberately releasing water at high velocity through mains and hydrants to scour out sediment, stale water, and biofilm. Flushing is scheduled with attention to chlorine residual and customer impacts.

A portion of a distribution system separated by valves or pumps and held within a defined pressure range. Zones prevent excessive pressure at low elevations and inadequate pressure at high elevations.

A pressure surge caused by abruptly stopping or changing water flow, such as closing a valve too fast. It can crack pipes and damage fittings, so valves are operated slowly and surge protection is installed.

The difference between water produced and water billed, including leaks, flushing, firefighting use, meter error, and unauthorized use. Tracking it helps utilities target leak detection and repair.

A public notice telling customers to boil tap water before drinking or cooking because of a confirmed or suspected contamination event. Utilities issue it under regulatory criteria and lift it only after sampling clears the system.

A group of bacteria used as an indicator of treatment effectiveness and distribution system integrity. Their presence triggers repeat sampling and investigation for contamination or regrowth.

Stormwater and groundwater that enter a sanitary sewer through illegal connections, cracked pipes, and faulty manholes. High flows during storms can overwhelm treatment plants and cause overflows.

A release of untreated sewage from the collection system before it reaches the treatment plant, often caused by blockages, root intrusion, or storm inflow. Overflows must be reported and corrected quickly.

Blowing non-toxic smoke into a sewer reach to reveal illegal storm connections, broken pipe, and leaks into buildings. Crews notify occupants beforehand because smoke can appear in drains.

An access opening in a sewer line that lets crews inspect, clean, and test the pipe. Covers must be secure and confined-space entry procedures followed before anyone descends.

The controlled procedure for entering a manhole, wet well, or vault with limited exit and possible hazardous atmosphere. It requires atmospheric testing, ventilation, an attendant, and rescue provisions.

A pipe that carries wastewater downhill by slope alone, without pumping. Designers set minimum grades so solids stay suspended and the pipe does not clog or develop septic conditions.

A facility with pumps that raise wastewater to a higher elevation so it can continue flowing by gravity. Wet wells, pumps, and controls require regular maintenance and backup power planning.

A pressurized pipe that carries pumped wastewater from a lift station to a gravity sewer or treatment plant. Air release valves and surge control are important because the pipe runs full under pressure.

A toxic, foul-smelling gas produced by anaerobic decay of sewage. It causes odor complaints, corrodes concrete, and creates a serious confined-space hazard at the concentrations found in collection systems.

A wastewater treatment process in which a mixed culture of microorganisms consumes organic matter in an aerated basin, after which solids are settled and partly returned to seed the next batch.

An open tank where air or oxygen is supplied to keep activated sludge mixed and alive while microorganisms break down organic material. Dissolved oxygen is monitored to keep the process healthy.

Settled biological solids collected from the secondary clarifier and pumped back to the aeration basin to maintain the microbial population needed for treatment. Excess is wasted to control solids inventory.

The oxygen dissolved in water and available to aquatic life and to the microbes in an aeration basin. Low levels stress the biomass and can cause odors and poor settling.

The amount of oxygen microorganisms consume while breaking down organic matter in a sample over a set period, usually five days. It is a standard measure of organic strength in wastewater.

The concentration of solid particles suspended in a water or wastewater sample, determined by filtering and drying. It measures effluent quality and the solids loading on treatment units.

The average time biological solids remain in the activated sludge system, controlled by wasting. It influences settling, oxygen demand, and nitrification, so operators adjust wasting to hold a target value.

The biological conversion of ammonia to nitrite and then nitrate by specialized bacteria. It consumes oxygen and alkalinity, and incomplete nitrification can leave toxic ammonia in the effluent.

Adding chlorine or a chlorine compound to wastewater effluent to kill pathogens before discharge. Dose must balance disinfection with the formation of byproducts and toxicity to receiving waters.

Comparing an instrument's reading against a known standard and adjusting it so measurements are accurate. Regular calibration of turbidimeters, pH meters, and flow meters underpins reliable process control.