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GA Water/WW Operator practice questions

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Question 1Drinking Water Treatment

Which chemical is most commonly used as the primary coagulant in drinking water treatment?

  1. Sodium fluorosilicate
  2. Aluminum sulfate (alum) Correct answer.
  3. Calcium hydroxide (hydrated lime)
  4. Sodium hypochlorite

Explanation

Alum is the workhorse coagulant because it hydrolyzes in water to form positively charged aluminum species that neutralize the negative surface charge on clay and organic colloids. Once the charge barrier is reduced, particles can collide and stick together during flocculation.

Question 2Drinking Water Treatment

Why is a disinfectant residual maintained in the distribution system after treated water leaves the plant?

  1. To strip out dissolved gases
  2. To improve taste and odor
  3. To prevent regrowth in the pipes Correct answer.
  4. To reduce water hardness

Explanation

Finished water can pick up contamination from main breaks, cross-connections, and biofilm in the distribution system. A persistent residual provides a barrier against bacterial regrowth and any small intrusion that occurs downstream of the plant.

Question 3Drinking Water Treatment

Backwashing a rapid sand filter is performed to accomplish which of the following?

  1. Sterilize the media with chlorine
  2. Increase the media grain size
  3. Raise the filter loading rate
  4. Remove solids trapped in the media bed Correct answer.

Explanation

As water passes through a filter, particles accumulate in the bed and head loss rises while effluent quality degrades. Backwash reverses flow (often with air scour or surface wash) to expand the bed and flush the captured solids to waste, restoring the media for another run.

Question 4Drinking Water Treatment

Under the Surface Water Treatment Rule, filtered water turbidity must never exceed which value?

  1. 10 NTU
  2. 5 NTU
  3. 0.1 NTU
  4. 1 NTU Correct answer.

Explanation

The rule sets a maximum limit of 1 NTU at any time for filtered surface water, with a much tighter limit (0.3 NTU in at least 95 percent of monthly measurements) for conventional and direct filtration plants. Turbidity is used as a proxy because high values indicate that pathogens may be passing through the filters.

Question 5Drinking Water Treatment

What is the typical target fluoride concentration in finished drinking water for the prevention of dental caries?

  1. 4.0 mg/L
  2. 10 mg/L
  3. 0.05 mg/L
  4. 0.7 mg/L Correct answer.

Explanation

About 0.7 mg/L is the commonly used optimal fluoride level for community water fluoridation in warm climates, providing caries protection while avoiding dental fluorosis. The secondary maximum contaminant level of 2.0 mg/L exists to prevent objectionable cosmetic effects.

Question 6Drinking Water Treatment

A jar test is run at the treatment plant in order to determine which of the following?

  1. Optimum coagulant dose and pH Correct answer.
  2. Fluoride feed rate
  3. Filter media grain size
  4. Chlorine demand of finished water

Explanation

A jar test simulates rapid mix, flocculation, and settling on a bench scale at several chemical doses and pH values. The operator selects the dose that produces the clearest supernatant and best-settling floc, then applies that dose to the plant.

Question 7Drinking Water Treatment

In a conventional treatment plant, flocculation is best described as which of the following?

  1. Rapid mixing that disperses coagulant
  2. Gentle mixing to grow larger particles Correct answer.
  3. Passing water through porous media
  4. Settling of floc in a settling basin

Explanation

Flocculation uses slow, gentle agitation so that destabilized particles and microfloc collide and agglomerate into larger, denser floc that can settle. It follows rapid mix, where the coagulant is first dispersed, and precedes sedimentation.

Question 8Drinking Water Treatment

Which chemical is added to finished water to raise its pH?

  1. Aluminum sulfate
  2. Sulfuric acid
  3. Calcium hydroxide Correct answer.
  4. Carbon dioxide

Explanation

Calcium hydroxide (hydrated lime) is a base that neutralizes carbon dioxide and raises pH, and it is widely used for post-treatment pH and stability adjustment. Carbon dioxide and mineral acids move pH in the opposite direction.

Question 9Drinking Water Treatment

Breakpoint chlorination is reached at the point where which condition exists?

  1. Chlorine demand is met and free chlorine persists Correct answer.
  2. Combined chlorine reaches its peak value
  3. The pH stabilizes at exactly 7.0
  4. The chlorine feed is turned off

Explanation

As chlorine is added, it first satisfies reducing agents and forms chloramines, so almost no free chlorine is measured. After the breakpoint, the ammonia and other demand are destroyed and further chlorine additions appear as free available chlorine.

Question 10Drinking Water Treatment

The CT value used to demonstrate disinfection credit is calculated by multiplying which two quantities?

  1. Chlorine dose times plant flow
  2. Flow rate times filter area
  3. Residual concentration times contact time Correct answer.
  4. Turbidity times contact time

Explanation

CT is the product of the disinfectant residual concentration (C, in mg/L) measured at the outlet of the contactor and the effective contact time (T, in minutes). Effective time is the theoretical detention time multiplied by a baffling factor that accounts for short-circuiting.

Question 11Drinking Water Treatment

Which organism is highly resistant to chlorine disinfection and therefore usually requires a separate barrier such as UV light or ozone?

  1. Cryptosporidium Correct answer.
  2. Escherichia coli
  3. Giardia lamblia
  4. Total coliform bacteria

Explanation

Cryptosporidium oocysts are extremely tolerant of chlorine at normal treatment residuals and pH, so plants rely on physical removal by filtration plus an inactivation step such as UV or ozone. Vegetative bacteria are far more susceptible to chlorine.

Question 12Drinking Water Treatment

In a dual-media filter, anthracite is placed above the sand because anthracite does which of the following?

  1. Dissolves slowly and releases coagulant
  2. Is finer and traps particles at the surface
  3. Has a higher density than sand
  4. Is lower in density with larger grains Correct answer.

Explanation

Anthracite has a specific gravity near 1.5 compared with about 2.65 for sand, so it stays on top during backwash and stratification. The coarser, lighter top layer allows deeper penetration of solids, which uses more of the bed and lengthens filter runs.

Question 13Drinking Water Treatment

In excess-lime softening, the pH must be raised to about 10.5 or higher in order to accomplish which of the following?

  1. Remove dissolved organic carbon
  2. Precipitate magnesium as magnesium hydroxide Correct answer.
  3. Disinfect the water throughout the basin
  4. Precipitate calcium as calcium carbonate

Explanation

Calcium is removed as calcium carbonate at a much lower pH, roughly 9.5 and above. Magnesium does not precipitate appreciably until the pH is driven to about 10.5 to 11, which is why excess lime is used when magnesium removal is required.

Question 14Drinking Water Treatment

A negative Langelier Saturation Index indicates that the water is doing which of the following?

  1. Exactly at calcium carbonate saturation
  2. Supersaturated with dissolved oxygen
  3. Scale-forming and likely to plug pipes
  4. Corrosive and likely to dissolve metal Correct answer.

Explanation

The Langelier Saturation Index compares measured pH with the pH at which calcium carbonate would be exactly saturated. A negative index means the water is undersaturated and tends to dissolve protective scale and metal, while a positive index means it is scale-forming.

Question 15Drinking Water Treatment

Trihalomethanes form primarily when free chlorine reacts with which of the following?

  1. Fluoride added at the plant
  2. Ammonia present in the water
  3. Dissolved iron and manganese
  4. Natural organic matter Correct answer.

Explanation

Chlorine reacts with humic and fulvic acids and other natural organic precursors to produce trihalomethanes and other disinfection byproducts. Reducing precursor concentrations through enhanced coagulation or changing the disinfectant strategy lowers the formation potential.

Question 16Drinking Water Treatment

Packed tower aeration is most effective for removing which of the following from water?

  1. Suspended solids
  2. Volatile compounds such as hydrogen sulfide Correct answer.
  3. Nitrate
  4. Radium

Explanation

Aeration transfers dissolved gases and volatile organics from water to air across a large packing surface area. It is commonly used for hydrogen sulfide, carbon dioxide, radon, and volatile organic chemicals, but it cannot remove nonvolatile dissolved ions.

Question 17Drinking Water Treatment

Which membrane process is designed to remove dissolved salts and is commonly called desalination?

  1. Ultrafiltration
  2. Granular media filtration
  3. Microfiltration
  4. Reverse osmosis Correct answer.

Explanation

Reverse osmosis uses a dense membrane and applied pressure to separate dissolved ions from water, making it the standard process for desalting brackish water and seawater. Microfiltration and ultrafiltration have larger pores that reject particles and microorganisms but pass dissolved salts.

Question 18Drinking Water Treatment

Compared with free chlorine, monochloramine provides which of the following advantages?

  1. A longer-lasting residual with fewer THMs Correct answer.
  2. Higher trihalomethane formation
  3. No measurable disinfection ability
  4. A stronger and faster kill of bacteria

Explanation

Monochloramine is a weaker but more stable disinfectant, so it persists longer in large distribution systems and forms far fewer trihalomethanes because it reacts less with organic matter. It must be formed by adding chlorine and ammonia in the correct ratio and is not a strong primary disinfectant.

Question 19Drinking Water Treatment

When alum is added to a low-alkalinity water, the pH of the water typically does which of the following?

  1. It rises then falls to zero
  2. It drops because alum consumes alkalinity Correct answer.
  3. It stays essentially unchanged
  4. It increases because alum is basic

Explanation

Alum hydrolysis releases hydrogen ions that react with bicarbonate alkalinity, so pH and alkalinity both decrease as the coagulant demand is satisfied. Plants treating low-alkalinity water must add lime or caustic to maintain the pH needed for effective coagulation.

Question 20Drinking Water Treatment

A typical backwash of a rapid sand filter expands the media bed by approximately what amount?

  1. No expansion is needed
  2. 20 to 50 percent Correct answer.
  3. 100 to 150 percent
  4. 2 to 5 percent

Explanation

Backwash rates are set high enough to expand the bed about 20 to 50 percent so that trapped solids can be scoured free and carried to waste. Excessive expansion wastes water and can wash media over the troughs, while too little expansion leaves the bed packed with dirt.

Question 21Drinking Water Treatment

A clearwell provides 40 minutes of theoretical detention time with a baffling factor of 0.5. If the free chlorine residual at the clearwell outlet is 1.5 mg/L, what is the CT value in mg-min/L?

  1. 30 Correct answer.
  2. 20
  3. 45
  4. 60

Explanation

Effective contact time equals theoretical time multiplied by the baffling factor: 40 min times 0.5 equals 20 minutes. CT is then the residual times that effective time, or 1.5 mg/L times 20 min, which equals 30 mg-min/L.

Question 22Drinking Water Treatment

A water has a chlorine demand of 1.8 mg/L. What applied dose is required to leave a free chlorine residual of 0.5 mg/L?

  1. 1.3 mg/L
  2. 0.5 mg/L
  3. 2.3 mg/L Correct answer.
  4. 1.8 mg/L

Explanation

The applied dose must satisfy the demand before any free residual can persist, so dose equals demand plus desired residual. Adding 1.8 mg/L of demand to 0.5 mg/L of target residual gives an applied dose of 2.3 mg/L.

Question 23Drinking Water Treatment

Filter effluent turbidity is often elevated immediately after backwashing. What is the most common operational practice to protect the distribution system during this period?

  1. Backwash the filter a second time at once
  2. Increase the coagulant dose permanently
  3. Filter to waste until turbidity is normal Correct answer.
  4. Add extra chlorine to the filtered water

Explanation

Right after backwash the bed is disturbed and the first water through carries a slug of particles, a period known as filter ripening. Diverting that water to waste, or slowly ramping flow while wasting, keeps the turbidity spike out of the clearwell and distribution system.

Question 24Drinking Water Treatment

When the coagulant dose greatly exceeds the optimum, filtered water turbidity can increase because of which of the following?

  1. Excess coagulant restabilizes the particles Correct answer.
  2. The floc becomes too dense to settle out
  3. Alkalinity rises sharply in the filter
  4. The filter media begins to dissolve

Explanation

Overdosing reverses the charge on the particles, so they repel one another again instead of aggregating, a condition called restabilization. Unreacted coagulant can also pass through as a precipitate, adding to finished-water turbidity.

Question 25Drinking Water Treatment

Why does the chlorine CT required for a given level of Giardia inactivation increase as water temperature decreases?

  1. Giardia cells grow larger in cold water
  2. Disinfection is slower in cold water Correct answer.
  3. Chlorine demand rises as pH falls
  4. Turbidity automatically rises in winter

Explanation

Chemical disinfection rates fall with temperature, so a colder water needs a higher residual, a longer contact time, or both to achieve the same log inactivation. CT tables in the regulations reflect this by assigning larger required CT values at lower temperatures.

Question 26Drinking Water Treatment

In a conventional surface water treatment plant, the main purpose of the sedimentation basin is to:

  1. inactivate pathogens with chlorine
  2. add fluoride for dental health
  3. remove dissolved minerals by ion exchange
  4. settle floc particles by gravity Correct answer.

Explanation

Sedimentation follows coagulation and flocculation and relies on gravity to remove floc particles that are denser than water. It does not disinfect, demineralize, or fluoridate the water.

Question 27Drinking Water Treatment

Rapid sand filters are backwashed primarily to:

  1. increase the filter run length
  2. disinfect the filter media with chlorine
  3. remove captured solids and restore flow Correct answer.
  4. add filter aid to the media surface

Explanation

Solids accumulate in the filter bed and cause headloss to rise; backwashing reverses flow to expand the bed and flush those solids to waste. Disinfection and filter-aid addition are separate operations.

Question 28Drinking Water Treatment

Fluoride is added to drinking water primarily to:

  1. reduce the incidence of tooth decay Correct answer.
  2. improve taste and odor
  3. soften hard water
  4. prevent corrosion of pipes

Explanation

Fluoride is fed to reduce dental caries, with the target concentration set to balance benefit and risk. It is not used for taste, softening, or corrosion control.

Question 29Drinking Water Treatment

The primary purpose of disinfection in drinking water treatment is to:

  1. remove turbidity-causing particles
  2. inactivate disease-causing microorganisms Correct answer.
  3. reduce water hardness
  4. control corrosion in distribution pipes

Explanation

Disinfection destroys or inactivates pathogens that could cause waterborne disease. Turbidity removal, softening, and corrosion control are separate treatment objectives.

Question 30Drinking Water Treatment

A coagulant such as aluminum sulfate primarily destabilizes suspended particles by:

  1. adding alkalinity to the water
  2. neutralizing their negative surface charge Correct answer.
  3. raising the water pH above 10
  4. oxidizing dissolved organic matter

Explanation

Suspended particles carry negative surface charges that keep them apart; alum and other coagulants neutralize those charges so particles can collide and form floc. Raising pH, adding alkalinity, and oxidizing organics are not the primary coagulation mechanism.

Question 31Drinking Water Treatment

The weir loading rate of a sedimentation basin is calculated by dividing the plant flow rate by the:

  1. total length of the effluent weirs Correct answer.
  2. detention time in hours
  3. basin side-water depth
  4. basin surface area

Explanation

Weir loading rate is the flow per unit length of effluent weir, usually expressed as gallons per day per foot of weir. Dividing by surface area gives the surface overflow rate, not the weir loading rate.

Question 32Drinking Water Treatment

The effective size of filter media is the sieve opening through which what percentage of the media passes?

  1. 90 percent
  2. 10 percent Correct answer.
  3. 60 percent
  4. 50 percent

Explanation

Effective size is the d10 value, the sieve size through which 10 percent of the media by weight passes. The d60 value is used with d10 to calculate the uniformity coefficient.

Question 33Drinking Water Treatment

A filter run should be terminated when:

  1. the filter has operated for exactly 24 hours
  2. the backwash water tank is full
  3. headloss reaches its limit or turbidity breaks through Correct answer.
  4. the effluent turbidity is 0.05 NTU

Explanation

A filter run ends when headloss reaches the available driving head or when effluent turbidity breaks through, because continued operation can degrade water quality. A fixed time, low turbidity, or backwash tank level is not the controlling criterion by itself.

Question 34Drinking Water Treatment

Turbidity in filtered water can interfere with disinfection because particles:

  1. raise the water temperature
  2. reduce the CT value to zero
  3. consume all the applied chlorine instantly
  4. shield microorganisms from the disinfectant Correct answer.

Explanation

Particles can shield attached microorganisms from chlorine and also exert chlorine demand, so filtered water must be low in turbidity for disinfection to work reliably. Turbidity does not instantly consume all chlorine or reduce CT to zero.

Question 35Drinking Water Treatment

Sludge produced by lime softening is composed mainly of:

  1. sodium chloride
  2. activated carbon
  3. aluminum hydroxide
  4. calcium carbonate Correct answer.

Explanation

Lime softening precipitates calcium as calcium carbonate and, at higher pH, magnesium as magnesium hydroxide; the sludge is mainly calcium carbonate. Sodium chloride, activated carbon, and aluminum hydroxide are not the main softening sludge.

Question 36Drinking Water Treatment

Adding a polyphosphate to finished water is intended primarily to:

  1. remove dissolved iron and manganese
  2. increase the fluoride residual
  3. form a protective film on pipe surfaces Correct answer.
  4. disinfect the distribution system

Explanation

Polyphosphates and silicates can form a thin protective film on pipe surfaces that limits corrosion and metal release. They are not disinfectants, iron/manganese removers, or fluoride sources.

Question 37Drinking Water Treatment

Powdered activated carbon for taste and odor control is usually added:

  1. after final disinfection
  2. to the finished water storage tank
  3. early in the treatment train, before coagulation Correct answer.
  4. inside the clearwell

Explanation

PAC adsorbs taste- and odor-causing compounds and is usually contacted early, often before coagulation, so it has time to work before the carbon is removed with the sludge. Adding it after disinfection or in clearwells limits contact and can waste chlorine.

Question 38Drinking Water Treatment

A sudden increase in differential pressure across an ultrafiltration membrane, with permeate quality unchanged, most likely indicates:

  1. complete removal of dissolved salts
  2. membrane rupture
  3. membrane fouling or cake buildup Correct answer.
  4. decreased feed turbidity

Explanation

A rising differential pressure at stable permeate quality points to fouling or cake buildup that restricts flow through the membrane. Membrane rupture would normally degrade permeate quality, and dissolved-salt removal is not expected for UF.

Question 39Drinking Water Treatment

Ozone is a strong primary disinfectant, but it is usually followed by a secondary disinfectant because ozone:

  1. does not inactivate viruses
  2. leaves little or no persistent residual Correct answer.
  3. produces a permanent chlorine residual
  4. raises the pH excessively

Explanation

Ozone decomposes quickly in treated water, leaving little or no residual to protect the distribution system. A persistent secondary disinfectant such as chlorine or chloramine is therefore normally added.

Question 40Drinking Water Treatment

After excess-lime softening, recarbonation is used mainly to:

  1. lower the pH and stabilize the water Correct answer.
  2. remove sulfate by precipitation
  3. disinfect the softened water
  4. increase the pH and precipitate more magnesium

Explanation

Excess-lime softening raises pH and precipitates calcium and magnesium; recarbonation with carbon dioxide lowers the pH to a stable range and helps prevent scale or corrosion. It is not a disinfection or sulfate-removal step.

Question 41Drinking Water Distribution

What is the minimum free chlorine residual that a Georgia public water system must maintain in the distribution system when using free chlorine?

  1. 1.0 mg/L
  2. 0.2 mg/L Correct answer.
  3. 2.0 mg/L
  4. 0.5 mg/L

Explanation

Georgia rules require a detectable free chlorine residual of at least 0.2 mg/L throughout the distribution system when free chlorine is used. This residual helps prevent microbial regrowth and indicates that disinfection is being maintained.

Question 42Drinking Water Distribution

What is the primary purpose of a thrust block installed at a water main bend?

  1. Resist longitudinal forces from changes in flow direction Correct answer.
  2. Provide electrical grounding for the pipe
  3. Measure pressure changes in the main
  4. Support the weight of the pipe

Explanation

Thrust blocks transfer unbalanced hydraulic forces at bends, tees, reducers, and dead ends into undisturbed soil. Without adequate restraint, these forces can separate pipe joints or cause movement.

Question 43Drinking Water Distribution

Which valve type is most commonly used for stop-and-start isolation of distribution mains?

  1. Needle valve
  2. Pressure relief valve
  3. Gate valve Correct answer.
  4. Globe valve

Explanation

Gate valves are widely used for isolation because they have low head loss when fully open and provide a straight-through flow path. They are intended for fully open or fully closed service, not for throttling.

Question 44Drinking Water Distribution

Which backflow prevention device is designed for a high-hazard connection such as an irrigation system with chemical injection?

  1. A reduced pressure zone assembly Correct answer.
  2. A double check valve assembly with test cocks
  3. A vacuum breaker
  4. An atmospheric vacuum breaker for hose bibbs

Explanation

A reduced pressure zone assembly maintains a reduced pressure zone between the potable supply and the hazardous system. It is used for high-hazard connections because it protects against both backpressure and backsiphonage.

Question 45Drinking Water Distribution

What is the main purpose of flushing a dead-end water main?

  1. Increase pressure throughout the entire system
  2. Reduce water age in the treatment plant clearwell
  3. Disinfect the source water at the treatment plant
  4. Remove stagnant water and sediment and restore disinfectant residual Correct answer.

Explanation

Dead-end mains can accumulate sediment and stagnant water, which reduces disinfectant residual and can cause water quality complaints. Flushing replaces the stagnant water with fresh treated water.

Question 46Drinking Water Distribution

Why is proper pipe bedding material placed under and around a new water main?

  1. To increase flow velocity inside the pipe
  2. To provide a smooth surface for painting the pipe
  3. To serve as a thrust restraint at bends
  4. To support the pipe and protect it from sharp rocks Correct answer.

Explanation

Bedding provides uniform support along the pipe barrel and protects the pipe and coating from sharp rocks or debris. Proper bedding helps prevent point loading, settlement, and damage during backfilling.

Question 47Drinking Water Distribution

A pressure gauge reads 72 psi. What is the approximate equivalent head in feet of water?

  1. 230 feet
  2. 72 feet
  3. 166 feet Correct answer.
  4. 31 feet

Explanation

One psi is equivalent to about 2.31 feet of water head. Multiplying 72 psi by 2.31 gives approximately 166 feet of head.

Question 48Drinking Water Distribution

What is the function of a curb stop on a water service line?

  1. Shut off water to an individual service line Correct answer.
  2. Measure customer water usage
  3. Release air from a water main
  4. Control flow at a fire hydrant

Explanation

A curb stop is a valve installed on the service line, usually near the property line, to shut off water to an individual customer. It allows maintenance or disconnection without shutting down the main.

Question 49Drinking Water Distribution

What is the standard disinfection practice for a newly installed water main before it is placed in service?

  1. 50 mg/L free chlorine for 24 hours Correct answer.
  2. 25 mg/L free chlorine for 12 hours
  3. 10 mg/L free chlorine for 24 hours
  4. 100 mg/L free chlorine for 1 hour

Explanation

New water mains are typically disinfected with a strong chlorine solution, commonly 50 mg/L free chlorine for 24 hours, followed by flushing and bacteriological sampling. The high concentration provides adequate disinfection of the pipe interior.

Question 50Drinking Water Distribution

If distribution system pressure falls below 20 psi, what is the most appropriate immediate action?

  1. Issue a boil water notice and notify EPD Correct answer.
  2. Flush all hydrants in the affected area
  3. Increase the chlorine dose at the plant only
  4. Continue normal operations and monitor pressure

Explanation

Pressure below 20 psi creates a risk of backflow and contamination entering the distribution system. The system should issue a boil water notice and notify the primacy agency while investigating and correcting the cause.