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HI Water/WW Operator practice questions

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Question 1Water Treatment

Which federal regulation establishes maximum contaminant levels for finished drinking water in Hawaii and across the United States?

  1. The Safe Drinking Water Act and its amendments Correct answer.
  2. The Clean Water Act
  3. The Clean Air Act
  4. The Resource Conservation and Recovery Act

Explanation

The Safe Drinking Water Act authorizes EPA to set national primary drinking water regulations, including maximum contaminant levels, that apply to public water systems nationwide. The Clean Water Act addresses discharges to surface waters rather than finished drinking water quality.

Question 2Water Treatment

A public water system serves 25 or more people year-round. Under the SDWA definition, this system is classified as which type?

  1. A community water system Correct answer.
  2. A transient non-community system
  3. A non-transient non-community system
  4. A private well system

Explanation

A community water system is one that serves at least 25 residents year-round or has at least 15 service connections used by year-round residents. Systems serving transient populations such as restaurants or campgrounds fall under different categories.

Question 3Water Treatment

Chlorine is added to treated water primarily to accomplish which objective?

  1. Reduce total dissolved solids
  2. Adjust the pH to reduce corrosion
  3. Maintain a disinfectant residual that inactivates pathogens throughout distribution Correct answer.
  4. Remove dissolved iron and manganese

Explanation

Primary disinfection inactivates pathogens at the plant, and a residual protects the water as it travels through the distribution system. pH adjustment, iron removal, and TDS reduction are separate treatment goals.

Question 4Water Treatment

In conventional surface water treatment, what is the primary purpose of coagulation and flocculation?

  1. To strip dissolved gases from the water
  2. To raise the alkalinity of the water
  3. To kill bacteria before filtration
  4. To destabilize small particles so they agglomerate into settleable flocs Correct answer.

Explanation

Coagulants such as alum neutralize the surface charge on colloidal particles, allowing them to collide and form larger flocs during flocculation. These flocs are then removed by sedimentation and filtration.

Question 5Water Treatment

A water sample has a pH of 7.0. How is this sample best described?

  1. Neutral Correct answer.
  2. Strongly basic
  3. Strongly acidic
  4. Slightly basic

Explanation

pH 7.0 is the neutral point at 25 degrees Celsius, where hydrogen ion and hydroxide ion activities are equal. Values below 7 are acidic and values above 7 are basic.

Question 6Water Treatment

Which unit expresses the concentration of a contaminant as milligrams per liter in drinking water reporting?

  1. psi
  2. gpm
  3. NTU
  4. mg/L Correct answer.

Explanation

Milligrams per liter is the standard mass-per-volume concentration unit used in drinking water analysis and reporting. NTU measures turbidity, psi measures pressure, and gpm measures flow.

Question 7Water Treatment

What does a turbidity measurement of finished water primarily indicate?

  1. The total alkalinity of the water
  2. The level of dissolved oxygen
  3. The concentration of dissolved calcium
  4. The amount of suspended material that scatters light Correct answer.

Explanation

Turbidity instruments measure light scattered by suspended particles, so the reading reflects particulate matter remaining after treatment. Low finished-water turbidity is a key indicator of effective filtration and pathogen barrier performance.

Question 8Water Treatment

Which type of filter medium is most commonly used in a conventional rapid gravity drinking water filter?

  1. Granular sand and anthracite Correct answer.
  2. Activated carbon only
  3. Diatomaceous earth
  4. Cation exchange resin

Explanation

Dual-media filters typically use a layer of anthracite over sand to improve solids capture and lengthen filter runs. Activated carbon, diatomaceous earth, and ion exchange resin serve other specialized treatment purposes.

Question 9Water Treatment

A treatment plant operator measures a chlorine residual of 0.2 mg/L in the distribution system, below the required minimum. What is the most appropriate immediate action?

  1. Reduce the chlorine dose to save chemical
  2. Flush the system with unchlorinated water
  3. Investigate the cause and adjust chlorination to restore the required residual Correct answer.
  4. Ignore the reading because residuals fluctuate

Explanation

A residual below the regulatory minimum requires prompt investigation of the cause, such as chlorine demand, dosing equipment problems, or long detention time, followed by corrective dosing adjustments. Ignoring the reading or reducing the dose would worsen the deficiency.

Question 10Water Treatment

A jar test shows that increasing coagulant dose beyond the optimum produces worsening turbidity. What phenomenon best explains this?

  1. Reduced detention time in the flocculation basin
  2. Higher filter loading rate
  3. Charge reversal causing restabilization of particles Correct answer.
  4. Increased alkalinity from the coagulant

Explanation

Excess coagulant can reverse the particle surface charge, causing repulsion and restabilization instead of floc formation. This is why jar testing is used to find the dose that minimizes settled and filtered turbidity.

Question 11Water Treatment

A clearwell provides 30 minutes of contact time at peak flow, but the required CT value cannot be met at the current chlorine concentration. Which change most directly increases the CT value?

  1. Adding fluoride
  2. Increasing the disinfectant concentration or contact time Correct answer.
  3. Decreasing the pH of the water
  4. Increasing the filtration rate

Explanation

CT is the product of disinfectant residual concentration and contact time, so raising either factor increases the CT value achieved. pH affects the effectiveness of chlorine speciation but does not directly increase CT as a product term.

Question 12Water Treatment

An operator observes that filtered water turbidity spikes immediately after a filter is returned to service following backwash. What is the most likely cause?

  1. Excessive chlorine residual in the filter influent
  2. A failure of the fluoride feed system
  3. Filter ripening and incomplete removal of backwash residuals Correct answer.
  4. A drop in raw water alkalinity

Explanation

After backwash, filters pass a period of filter ripening during which particles are not yet effectively captured, and residual backwash water may carry over. Operators manage this with filter-to-waste, slow starts, or extended backwash, and monitor turbidity closely.

Question 13Water Treatment

A water system reports a lead action level exceedance based on the 90th percentile calculation. What is the required response?

  1. Switch to unchlorinated water
  2. Increase the fluoride dose
  3. Immediately shut down the entire distribution system
  4. Conduct public education and corrosion control treatment evaluation Correct answer.

Explanation

An action level exceedance for lead triggers public education requirements and evaluation or optimization of corrosion control treatment. Lead action levels are not MCLs, so the response is treatment and education rather than system shutdown.

Question 14Water Treatment

Which process is most effective at removing nitrate from drinking water?

  1. Conventional coagulation and sedimentation
  2. Chlorination
  3. Ion exchange or reverse osmosis Correct answer.
  4. Aeration

Explanation

Nitrate is highly soluble and is not removed by conventional coagulation, sedimentation, or disinfection. Treatment options include ion exchange, reverse osmosis, and biological denitrification.

Question 15Water Treatment

A groundwater source contains elevated iron and manganese. Which treatment sequence is most appropriate?

  1. pH reduction followed by aeration
  2. Oxidation followed by filtration Correct answer.
  3. Activated carbon adsorption alone
  4. Coagulation followed by chlorination only

Explanation

Iron and manganese are removed by oxidizing the dissolved forms to insoluble oxides, then filtering the precipitated particles. Chlorine, permanganate, or aeration can serve as the oxidant before filtration.

Question 16Water Treatment

What is the purpose of a corrosion inhibitor such as orthophosphate in drinking water treatment?

  1. To remove turbidity from finished water
  2. To increase the disinfectant residual
  3. To raise the pH of raw water before coagulation
  4. To form a protective film on pipe surfaces that limits metal leaching Correct answer.

Explanation

Orthophosphate forms a sparingly soluble film on the interior of metal pipes, reducing the release of lead and copper into the water. It is applied as part of a corrosion control strategy under the Lead and Copper Rule.

Question 17Water Treatment

A sodium hypochlorite feed system shows declining dose even though the pump stroke is unchanged. Which cause should be investigated first?

  1. A change in fluoride feed rate
  2. A rise in raw water pH
  3. Chemical degradation of the hypochlorite solution Correct answer.
  4. Increased filter run length

Explanation

Sodium hypochlorite loses strength over time, especially when stored warm or in sunlight, so a declining dose at constant pump settings often indicates degraded solution. Operators should verify solution strength by testing and rotate stock.

Question 18Water Treatment

In a distribution system, which condition most commonly causes a loss of chlorine residual?

  1. Low water temperature
  2. High chlorine demand from pipe deposits and long detention time Correct answer.
  3. High source water alkalinity
  4. Presence of fluoride

Explanation

Chlorine residual decays as it reacts with pipe wall deposits, biofilm, and dissolved organics, and it diminishes with long detention time in the system. Operators manage this with booster chlorination and storage tank turnover.

Question 19Water Treatment

A water treatment plant uses powdered activated carbon. What is its primary purpose?

  1. To increase filter loading rate
  2. To adsorb taste- and odor-causing compounds Correct answer.
  3. To soften the water
  4. To disinfect the water

Explanation

Powdered activated carbon is dosed into the treatment train to adsorb organic compounds that cause taste and odor, such as geosmin and MIB. It must be applied at a point where it will not be removed before contacting the target compounds.

Question 20Water Treatment

A plant treats surface water with high turbidity after a storm. Which operational adjustment is most appropriate?

  1. Increase coagulant dose based on jar testing and monitor filter effluent closely Correct answer.
  2. Increase filter loading rate to handle the flow
  3. Reduce coagulant dose to save chemical
  4. Bypass filtration until turbidity drops

Explanation

Storm events raise particulate load, so coagulant demand typically increases and jar testing guides the new dose. Close turbidity monitoring confirms that filters continue to meet performance requirements despite the higher influent load.

Question 21Water Treatment

Which statement best describes the role of a clearwell in a surface water treatment plant?

  1. It removes particles by sedimentation
  2. It backwashes filters
  3. It provides disinfectant contact time and finished water storage Correct answer.
  4. It mixes coagulant into raw water

Explanation

The clearwell stores filtered water and provides the detention time needed for disinfection contact before the water enters distribution. It may also buffer demand variations and support backwash supply.

Question 22Water Treatment

A utility calculates that a filter run has ended because of turbidity breakthrough rather than headloss. What does this indicate?

  1. Particles are passing through the media before the filter becomes hydraulically clogged Correct answer.
  2. The filter media has been completely removed
  3. The filter is operating below design loading
  4. The backwash water was too cold

Explanation

Turbidity breakthrough means the filter is no longer capturing particles effectively even though headloss has not reached its terminal value. Operators must then backwash or take the filter out of service to protect finished water quality.

Question 23Water Treatment

A groundwater system reports a total coliform-positive routine sample. What is the required follow-up under the Total Coliform Rule?

  1. Increase the fluoride dose
  2. Collect repeat samples and test for E. coli, then assess the system for sanitary defects Correct answer.
  3. Do nothing because coliforms are always harmless
  4. Immediately issue a boil water notice for the entire state

Explanation

A total coliform-positive routine sample requires repeat sampling at the same and adjacent locations and E. coli analysis to determine whether the finding is an acute or non-acute violation. The utility then conducts a sanitary survey or assessment to identify and correct the cause.

Question 24Water Treatment

A treatment plant using free chlorine observes that disinfection efficiency drops sharply when pH rises from 7.0 to 8.5. What is the best explanation?

  1. Contact time decreases as pH rises
  2. The fraction of hypochlorous acid decreases as pH rises Correct answer.
  3. Turbidity increases as pH rises
  4. Chlorine demand from iron increases at higher pH

Explanation

Free chlorine exists as hypochlorous acid and hypochlorite ion, and the more effective hypochlorous acid predominates at lower pH. As pH rises, the less effective hypochlorite ion dominates, reducing disinfection efficiency for the same residual.

Question 25Water Treatment

A membrane filtration plant reports a rising transmembrane pressure at constant flow. What is the most likely interpretation?

  1. The permeate pump is oversized
  2. The feed turbidity has decreased
  3. The membrane pore size has enlarged
  4. Membrane fouling is increasing and cleaning or backwash may be needed Correct answer.

Explanation

Transmembrane pressure rises as resistance to flow increases, which typically signals fouling by particles, organics, or scaling. Operators respond with backwash, chemically enhanced cleaning, or pretreatment adjustments to restore performance.

Question 26Water Treatment

Which regulation sets the maximum contaminant levels that a Hawaii public water system must meet for turbidity, disinfection byproducts, and most inorganic chemicals?

  1. The Clean Water Act national pollutant discharge elimination system permit program
  2. The Clean Air Act stationary source standards
  3. The Resource Conservation and Recovery Act hazardous waste rules
  4. The federal Safe Drinking Water Act and its National Primary Drinking Water Regulations Correct answer.

Explanation

The Safe Drinking Water Act authorizes EPA to set National Primary Drinking Water Regulations, which are health-based limits enforceable on public water systems, and Hawaii adopts them through its drinking water rules. The Clean Water Act governs discharges to surface waters, RCRA governs solid and hazardous waste, and the Clean Air Act governs air emissions, none of which set finished drinking water MCLs.

Question 27Water Treatment

A Hawaii surface water system serves 12,000 people using conventional coagulation, sedimentation, filtration, and disinfection. Under the Surface Water Treatment Rule, which performance requirement applies?

  1. At least 90 percent removal of total organic carbon across the treatment train
  2. At least 99.9 percent removal and inactivation of Giardia and 99 percent of viruses Correct answer.
  3. At least 99.99 percent removal of Cryptosporidium by filtration alone
  4. At least 95 percent reduction of sulfate to below the secondary standard

Explanation

The Surface Water Treatment Rule requires systems using conventional treatment to achieve 3-log (99.9 percent) removal and inactivation of Giardia lamblia and 4-log (99.99 percent) of viruses, commonly summarized as the 3/4-log credit framework. Cryptosporidium is addressed separately by the Long Term 2 Enhanced Surface Water Treatment Rule, and TOC removal is a Stage 2 Disinfectants and Disinfection Byproducts Rule requirement, not the SWTR pathogen goal.

Question 28Water Treatment

An operator collects a routine sample for total coliform analysis from a distribution system tap. Which sampling practice best preserves the sample's integrity before it reaches the laboratory?

  1. Fill the bottle completely, leave no headspace, and chill it during transport
  2. Acidify the sample to pH 2 and hold it for 24 hours before analysis
  3. Add sodium thiosulfate to the bottle, leave headspace, and keep it cool until analysis Correct answer.
  4. Collect the sample without flushing the tap and store it at room temperature

Explanation

Bacteriological sample bottles contain sodium thiosulfate to neutralize chlorine residual so that any organisms present survive to be detected, and the sample is kept cool with headspace to allow mixing and to limit overgrowth or loss. Acidifying a bacteriological sample would kill the target organisms, and room temperature holding allows counts to change before analysis.

Question 29Water Treatment

Which instrument is used to measure the turbidity of finished drinking water by detecting light scattered at 90 degrees from the incident beam?

  1. A colorimeter
  2. A conductivity meter
  3. A pH meter
  4. A nephelometric turbidimeter Correct answer.

Explanation

Nephelometric turbidimeters measure light scattered at approximately 90 degrees, which correlates with the fine particles that cause turbidity in filtered water. Colorimeters measure absorbance of specific wavelengths for chemical concentration, conductivity meters measure ionic conductance, and pH meters measure hydrogen ion activity, none of which quantify suspended particle scattering.

Question 30Water Treatment

A conventional plant is coagulating with aluminum sulfate at pH 6.8 and the operator wants to improve particle removal before filtration. Which operational adjustment is most consistent with good coagulation practice?

  1. Lower the coagulation pH below 4.5 to maximize aluminum solubility
  2. Eliminate flocculation and feed coagulant directly to the filters
  3. Increase filter loading rate to shorten the sedimentation step
  4. Raise the rapid mix intensity and lengthen the slow flocculation period Correct answer.

Explanation

Effective coagulation requires rapid, intense mixing to destabilize particles followed by gentle, prolonged flocculation so collisions build large settleable flocs. Eliminating flocculation or pushing filter rates higher shifts particle load onto the filters, and dropping pH below the aluminum minimum solubility region wastes coagulant and can leave soluble aluminum in the finished water.

Question 31Water Treatment

In a sedimentation basin, an operator observes short-circuiting evidenced by dye reaching the outlet much faster than the theoretical detention time predicts. Which effect should be expected?

  1. Complete elimination of the sludge blanket
  2. Higher coagulant demand with no change in settled turbidity
  3. Reduced effective settling time and poorer particle removal Correct answer.
  4. Increased solids capture because of longer actual contact

Explanation

Short-circuiting means a portion of the flow travels from inlet to outlet in less than the theoretical detention time, so particles have less time to settle and effluent quality degrades. The remaining basin volume becomes quiescent and may develop stagnant zones and sludge accumulation, but the net effect on settled water is poorer, not improved, particle removal.

Question 32Water Treatment

Which filter backwash practice best restores a rapid gravity filter after solids have accumulated in the media?

  1. Backwash with filtered water at full service rate for several hours
  2. Disinfect the media with chlorine without any hydraulic washing
  3. Apply an air scour followed by an upflow water wash at a rate that expands the bed Correct answer.
  4. Backwash with a short low-rate water wash that leaves the bed unexpanded

Explanation

Effective backwash uses air scour to break up surface deposits and media packing, followed by upflow water at a rate that expands the bed so that trapped floc and particles are released and carried to waste. An unexpanded bed leaves deposits in place, and extended high-rate washing wastes water while risking media loss and stratification.

Question 33Water Treatment

A plant uses free chlorine for primary disinfection and the operator must verify that the required CT has been achieved. Which two measurements define the CT value?

  1. pH and total alkalinity
  2. Turbidity and the filter loading rate
  3. Coagulant dose and settled water color
  4. Residual disinfectant concentration and the contact time at the applicable peak flow Correct answer.

Explanation

CT is the product of the disinfectant residual concentration measured at the outlet of the contact basin and the effective contact time, corrected for baffling and evaluated at peak flow. Turbidity, filter rate, pH, alkalinity, and coagulant dose influence treatment performance but are not the two terms that define the CT calculation itself.

Question 34Water Treatment

A distribution system operator measures a free chlorine residual of 0.2 mg/L at a location where the state requires a detectable residual throughout the system. Which action is most appropriate?

  1. Flush the main and resample without notifying anyone
  2. Investigate for causes of decay and adjust chlorination to restore the required residual Correct answer.
  3. Record the result and take no action because a residual was detected
  4. Increase the fluoride feed to compensate

Explanation

A residual below the required minimum is a deficiency that must be corrected, so the operator should look for causes such as high water age, nitrification, sediment demand, or excessive storage time and then adjust chlorination or flushing to restore compliance. Simply recording the value leaves the system out of compliance, and fluoride has no bearing on chlorine residual.

Question 35Water Treatment

A groundwater system adds chlorine before the water enters a storage tank. Which condition in the tank most directly consumes free chlorine and can cause residual loss?

  1. Accumulated sediment and biofilm on tank surfaces Correct answer.
  2. A tank overflow set at the correct elevation
  3. A properly functioning altitude valve
  4. A tank vent screened against insects

Explanation

Sediment, biofilm, and corrosion deposits in a storage tank exert chlorine demand as the water contacts them, and long storage times compound the loss through decay and reactions with natural organic matter. Properly operating valves, overflows, and screened vents are normal design features and do not themselves consume disinfectant.

Question 36Water Treatment

A utility plans to use a groundwater source containing 1.5 mg/L of iron and 0.3 mg/L of manganese. Which treatment approach is most appropriate?

  1. Aeration alone with no subsequent filtration
  2. Ion exchange softening as the only treatment step
  3. Oxidation followed by filtration to remove the precipitated metals Correct answer.
  4. Ultraviolet irradiation as the sole treatment

Explanation

Soluble ferrous iron and manganous manganese must be oxidized to their insoluble forms, typically with aeration, chlorine, or potassium permanganate, and then removed by filtration. Aeration without filtration leaves precipitated particles in the water, and UV irradiation does not oxidize or remove metals.

Question 37Water Treatment

Which process is designed primarily to reduce dissolved organic carbon and disinfection byproduct precursors in surface water before disinfection?

  1. Enhanced coagulation with alum or ferric salts
  2. Powdered activated carbon addition
  3. Membrane softening
  4. Granular activated carbon adsorption Correct answer.

Explanation

Granular activated carbon adsorbs dissolved organic matter and taste and odor compounds as water passes through the bed, making it a principal barrier for dissolved organics and disinfection byproduct precursors. Enhanced coagulation removes a portion of organics by charge neutralization and precipitation, but GAC is the dedicated adsorption process for dissolved species.

Question 38Water Treatment

A plant is treating a surface water with a high concentration of natural organic matter and must control disinfection byproduct formation. Which operational strategy is most appropriate?

  1. Reduce precursor concentrations before chlorine addition and minimize chlorine contact with organics Correct answer.
  2. Switch to a prechlorination step ahead of coagulation
  3. Increase the water temperature to drive off the organics
  4. Increase the chlorine dose early in the treatment train to oxidize the organics

Explanation

Trihalomethanes and haloacetic acids form when chlorine reacts with natural organic matter, so the practical controls are removing precursors before chlorination and limiting chlorine contact with organics. Prechlorination ahead of coagulation actually increases precursor contact with chlorine and can raise byproduct formation, and heating large water volumes is not a treatment option.

Question 39Water Treatment

A plant applies powdered activated carbon to control earthy and musty taste and odor compounds. Which operational consideration most affects its effectiveness?

  1. The clearwell baffle configuration
  2. The filter media effective size
  3. Contact time and the point of application relative to other chemicals Correct answer.
  4. The fluoride concentration in the finished water

Explanation

Powdered activated carbon needs sufficient contact time to adsorb taste and odor compounds before it is removed by sedimentation or filtration, and applying it at the right point avoids interference from other treatment chemicals. Fluoride concentration, filter media size, and clearwell baffling do not determine PAC adsorption performance.

Question 40Water Treatment

A treatment plant has a clearwell with a baffling factor of 0.5 and a theoretical detention time of 120 minutes at peak flow. What effective contact time should be used in the CT calculation?

  1. 240 minutes
  2. 30 minutes
  3. 120 minutes
  4. 60 minutes Correct answer.

Explanation

Effective contact time is the theoretical detention time multiplied by the baffling factor, so 120 minutes times 0.5 equals 60 minutes. Dividing by the factor or ignoring it would overstate the disinfection credit and could lead to a false conclusion that the required CT has been met.

Question 41Water Treatment

An operator is preparing to disinfect a newly installed water main before placing it in service. Which practice is standard for new main disinfection?

  1. Disinfect the main with ultraviolet light applied at the service connection
  2. Flush the main with finished water and place it in service without disinfection
  3. Fill the main with a high-strength chlorine solution, hold it for the specified contact time, then flush and sample for bacteriological quality Correct answer.
  4. Add chlorine only after the main has been in service for a week

Explanation

New mains are disinfected by filling with a concentrated chlorine solution, holding it for the required contact period, flushing to remove the chlorinated water, and then collecting bacteriological samples before the main is placed in service. Skipping disinfection or delaying it until after service risks introducing contamination into the distribution system.

Question 42Water Treatment

A distribution system experiences a pressure drop below the required minimum during a main break repair. What is the primary water quality concern that follows?

  1. Loss of fluoride residual throughout the system
  2. Reduced turbidity at customer taps
  3. Increased chlorine residual in the affected area
  4. Potential for backflow and intrusion of contaminated groundwater into the system Correct answer.

Explanation

When system pressure falls below atmospheric or below the required minimum, a pressure gradient can allow contaminated groundwater or soil water to enter through leaks, breaks, and cross connections. Utilities respond with boil water notices, flushing, and increased disinfection until bacteriological samples confirm the system is safe.

Question 43Water Treatment

A water system must monitor for lead and copper at customer taps. Which sampling approach is required under the Lead and Copper Rule?

  1. Samples collected only from the service line at the curb stop
  2. Composite samples collected from the treatment plant finished water
  3. Flowing samples collected after the tap has run for five minutes
  4. First-draw samples collected after water has stood in the plumbing for at least six hours Correct answer.

Explanation

The Lead and Copper Rule targets the highest-risk water at the customer tap, so first-draw samples are collected after the water has stood motionless in the plumbing for at least six hours, capturing metal that has leached from pipes and solder. Flowing samples and plant finished water samples do not represent the stagnation conditions that drive exposure.

Question 44Water Treatment

A plant using free chlorine for disinfection finds that the required CT cannot be met at the current pH and residual. Which adjustment is most likely to improve disinfection efficiency without changing the physical contact basin?

  1. Lower the pH to shift the chlorine equilibrium toward hypochlorous acid Correct answer.
  2. Raise the pH to increase the hypochlorite ion fraction
  3. Increase the finished water turbidity
  4. Reduce the chlorine residual to lower demand

Explanation

Free chlorine exists as hypochlorous acid and hypochlorite ion, and hypochlorous acid is the far more effective disinfectant, so lowering pH within the allowable range increases the active fraction and improves inactivation. Raising pH shifts the balance toward the less effective ion, and reducing residual or increasing turbidity both reduce disinfection effectiveness.

Question 45Water Treatment

An operator observes a white, scale-like deposit on the interior of a distribution main in an area with hard water. Which water quality parameter is most closely associated with this condition?

  1. Elevated nitrate and low alkalinity
  2. Low total dissolved solids and negative Langelier index
  3. High dissolved oxygen and low pH
  4. High calcium carbonate saturation and positive Langelier index Correct answer.

Explanation

Scale deposits form when water is supersaturated with respect to calcium carbonate, indicated by a positive Langelier saturation index and high calcium and alkalinity. Low pH and a negative index indicate corrosive water that tends to dissolve rather than deposit scale.

Question 46Water Treatment

A conventional plant treats surface water and must report filtered water turbidity. Which measurement location best represents the performance of the filtration barrier?

  1. Combined filter effluent or individual filter effluent from each filter Correct answer.
  2. Finished water in the clearwell after disinfection
  3. Settled water at the sedimentation basin outlet
  4. Raw water at the plant intake

Explanation

Filtered water turbidity, measured at the combined filter effluent or at each individual filter, directly reflects particle passage through the filtration barrier and is the value used for treatment technique compliance. Raw, settled, and clearwell samples describe upstream conditions or storage but not filter performance.

Question 47Water Treatment

A membrane filtration plant reports a steady rise in transmembrane pressure at constant permeate flow over several weeks. What is the most likely interpretation?

  1. The permeate pump has been turned off
  2. The membrane has developed larger pores and is passing more water
  3. Fouling or scaling is accumulating on the membrane surface, increasing resistance Correct answer.
  4. The feed water turbidity has decreased to near zero

Explanation

At constant flow, a rising transmembrane pressure means the membrane resistance has increased, which is characteristic of fouling by particulates, organics, or scale. The operator should review pretreatment and cleaning frequency, and confirm integrity separately with pressure decay or turbidity testing.

Question 48Water Treatment

A utility is required to reduce the concentration of radium-226 in a groundwater supply. Which treatment process is commonly used for radium removal?

  1. Ultraviolet irradiation
  2. Aeration followed by sand filtration
  3. Cation exchange softening or reverse osmosis Correct answer.
  4. Granular activated carbon adsorption

Explanation

Radium is a dissolved cation that is removed effectively by cation exchange softening and by reverse osmosis, which reject dissolved ions. GAC, aeration, and UV do not remove dissolved radium and are used for organics, gases, and disinfection respectively.

Question 49Water Treatment

A plant uses sodium fluoride to fluoridate finished water. Which operational practice is most important for safe and compliant fluoridation?

  1. Accurately metering feed and continuously monitoring the finished water fluoride concentration Correct answer.
  2. Feeding fluoride only when turbidity exceeds 1 NTU
  3. Using the fluoride feed pump to control pH
  4. Adding fluoride upstream of coagulation to improve mixing

Explanation

Fluoride is added at a controlled concentration near 0.7 mg/L, and overfeeding can cause dental fluorosis or acute illness, so accurate metering with continuous monitoring and alarms is essential. Fluoride feed should be applied where mixing is good and should not be tied to turbidity or used as a pH control chemical.

Question 50Water Treatment

Which unit process in a conventional surface water plant is designed to remove settleable floc formed during coagulation and flocculation?

  1. Clearwell
  2. Sedimentation basin Correct answer.
  3. Filter underdrain
  4. Chemical feed room

Explanation

The sedimentation basin provides quiescent conditions and detention time so that floc formed in coagulation and flocculation can settle to the bottom as sludge before the water reaches the filters. The clearwell stores disinfected water, the underdrain supports filter media and collects filtered water, and the chemical feed room houses dosing equipment.