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DE Water Operator practice questions

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Question 1Water Treatment

What is the primary purpose of coagulation and flocculation in a surface water treatment plant?

  1. To raise the pH of the water to prevent corrosion in the distribution system
  2. To destroy pathogenic bacteria through chemical oxidation
  3. To remove dissolved gases such as hydrogen sulfide and methane
  4. To destabilize suspended particles so they can agglomerate and be removed Correct answer.

Explanation

Coagulation neutralizes the surface charge on fine colloidal particles, and flocculation gently mixes the water so those destabilized particles collide and form larger flocs. These flocs then settle in sedimentation or are captured in filtration. Pathogen destruction and pH adjustment are separate treatment objectives.

Question 2Water Treatment

A plant operator measures turbidity in finished water. What does turbidity primarily indicate about water quality?

  1. The alkalinity remaining after coagulation has been completed
  2. The concentration of dissolved calcium and magnesium ions
  3. The amount of suspended or colloidal material scattering light in the sample Correct answer.
  4. The residual concentration of free chlorine available for disinfection

Explanation

Turbidity is an optical measurement of light scattered by suspended and colloidal particles in the water. It serves as an indicator of particulate removal efficiency and can shield microorganisms from disinfection. Hardness, chlorine residual, and alkalinity are measured by entirely different methods.

Question 3Water Treatment

Which disinfectant leaves the most persistent residual in a distribution system for ongoing protection against microbial regrowth?

  1. Chlorine dioxide
  2. Ultraviolet light
  3. Ozone
  4. Free chlorine Correct answer.

Explanation

Free chlorine is widely used because it maintains a measurable residual that persists through the distribution system, continuing to inactivate microorganisms and providing a barrier against contamination. Ozone and UV leave no lasting residual, and chlorine dioxide residual is less stable and more costly to maintain.

Question 4Water Treatment

In conventional treatment, what is the main function of the sedimentation basin?

  1. To provide contact time for disinfection with chlorine
  2. To remove settled floc and particulate matter by gravity before filtration Correct answer.
  3. To strip dissolved volatile organic compounds from the water
  4. To add coagulant chemicals and rapidly mix them with raw water

Explanation

Sedimentation allows flocs formed during coagulation and flocculation to settle out under gravity, reducing the solids load on downstream filters. Rapid mixing occurs earlier in the process, and disinfection contact typically occurs in a separate clearwell.

Question 5Water Treatment

What is the purpose of the backwash cycle in a granular media filter?

  1. To remove accumulated solids from the media so the filter can be returned to service Correct answer.
  2. To add coagulant to the media surface for the next run
  3. To disinfect the filter media with a high chlorine dose
  4. To increase the filtration rate by compacting the media bed

Explanation

Backwashing reverses the flow direction and expands the media bed, flushing captured particles to waste and restoring the filter's ability to remove solids. It is not a disinfection step and does not intentionally compact the media.

Question 6Water Treatment

An operator is converting a chlorine dose of 2.5 mg/L to pounds per day for a flow of 1.0 million gallons per day. Using the standard formula (dose × flow × 8.34), what is the approximate chlorine feed rate?

  1. 20.9 lb/day Correct answer.
  2. 0.3 lb/day
  3. 208 lb/day
  4. 2.1 lb/day

Explanation

The formula is pounds per day = dose (mg/L) × flow (MGD) × 8.34. Multiplying 2.5 × 1.0 × 8.34 gives approximately 20.9 lb/day. The factor 8.34 converts milligrams per liter and million gallons to pounds.

Question 7Water Treatment

Which of the following best describes the purpose of a clearwell in a surface water treatment plant?

  1. To store filtered water and provide disinfectant contact time Correct answer.
  2. To blend raw water from multiple sources before treatment
  3. To provide settling time for floc before filtration
  4. To dewater backwash residuals before disposal

Explanation

A clearwell stores treated, filtered water and provides the contact time necessary for disinfection before the water enters the distribution system. Settling of floc occurs upstream in sedimentation, and residuals handling uses separate facilities.

Question 8Water Treatment

Which of these is a common source of taste and odor problems in a surface water supply?

  1. High concentrations of dissolved nitrogen gas
  2. Excess fluoride naturally present in groundwater
  3. Algal blooms producing compounds such as geosmin and MIB Correct answer.
  4. Corrosion of copper pipe in the distribution system

Explanation

Algae and cyanobacteria release metabolites such as geosmin and 2-methylisoborneol that cause earthy or musty tastes and odors, often requiring powdered activated carbon or ozone treatment. Fluoride, dissolved nitrogen, and copper corrosion are not typical causes of taste and odor complaints.

Question 9Water Treatment

A jar test is performed and the operator observes that floc forms but settles very slowly, with high residual turbidity. Which adjustment is most likely to improve performance?

  1. Eliminate the rapid mix step to reduce floc shear
  2. Increase the filtration rate to capture more particles
  3. Reduce the flocculation time to prevent floc from breaking apart
  4. Increase the coagulant dose or lower the coagulation pH to improve charge neutralization Correct answer.

Explanation

Slow-settling floc with high residual turbidity usually indicates incomplete charge neutralization, which can be corrected by adjusting coagulant dose or coagulation pH. The jar test is the standard tool for evaluating these changes. Removing rapid mix or shortening flocculation generally worsens floc formation.

Question 10Water Treatment

What does the term 'CT' represent in disinfection calculations?

  1. The chlorine demand exerted by the distribution system piping
  2. The concentration of total dissolved solids in the finished water
  3. The product of disinfectant residual concentration and contact time Correct answer.
  4. The ratio of coagulant dose to treated flow

Explanation

CT is the product of disinfectant concentration (C) and effective contact time (T), and it is compared against required values to demonstrate adequate inactivation. Higher CT values correspond to greater microbial inactivation for a given organism and conditions.

Question 11Water Treatment

An operator observes that filter effluent turbidity rises sharply immediately after backwash and then gradually declines. What is the most likely cause?

  1. Filter ripening, where fines and residual solids pass through before the bed re-stratifies Correct answer.
  2. A sudden drop in raw water alkalinity
  3. Complete exhaustion of the filter media's adsorption capacity
  4. Excessive coagulant dose applied during the filter run

Explanation

The spike after backwash is characteristic of filter ripening, when disturbed media and residual particles pass through until the bed re-stratifies and captures solids effectively. Operators often manage this with filter-to-waste or slow starts. It is not caused by a coagulant overdose or alkalinity change.

Question 12Water Treatment

Which condition most commonly causes a loss of chlorine residual in the distribution system?

  1. High dissolved oxygen concentrations in the treated water
  2. Low water temperature reducing the solubility of chlorine gas
  3. High concentrations of reduced substances and organic matter exerting chlorine demand Correct answer.
  4. Excessive fluoride residual in the finished water

Explanation

Reduced inorganic compounds such as iron and manganese, ammonia, and natural organic matter consume free chlorine, lowering the residual. Temperature affects reaction rates but does not directly reduce chlorine solubility in a way that depletes residual.

Question 13Water Treatment

What is the purpose of adding fluoride to treated drinking water?

  1. To improve the taste of the finished water
  2. To increase the disinfectant residual in the distribution system
  3. To reduce dental caries in the served population Correct answer.
  4. To precipitate excess calcium from the water

Explanation

Fluoridation is practiced to reduce the incidence of dental caries, and the target concentration is carefully controlled to remain within recommended limits. It is not a disinfection or softening process and does not improve taste.

Question 14Water Treatment

A water treatment plant uses alum as its coagulant. Which change in raw water alkalinity would most likely require the operator to add an alkaline chemical?

  1. A decrease in alkalinity because alum consumes alkalinity during hydrolysis Correct answer.
  2. An increase in alkalinity because alum produces alkalinity
  3. An increase in temperature because alum reacts only in cold water
  4. A decrease in turbidity because alum requires clear water

Explanation

Alum consumes natural alkalinity as it hydrolyzes, which can depress pH below the optimum coagulation range. Operators often add lime or caustic soda to maintain adequate alkalinity and pH. Alum does not produce alkalinity, and its reaction is not limited to cold water.

Question 15Water Treatment

Which of the following is the most appropriate action when a chlorine analyzer shows a sudden drop in residual to zero at the plant effluent?

  1. Immediately increase the filtration rate to compensate
  2. Assume the analyzer is faulty and continue normal operation
  3. Reduce the coagulant dose to lower chlorine demand
  4. Verify the analyzer reading with a manual test and check the chlorine feed system Correct answer.

Explanation

A sudden loss of residual could reflect a real feed failure or an instrument problem, so the operator should confirm the reading with a manual test and inspect the feed system before taking corrective action. Ignoring the alarm or making unrelated process changes risks distributing inadequately disinfected water.

Question 16Water Treatment

What is the primary role of powdered activated carbon (PAC) in water treatment?

  1. To oxidize iron and manganese in the raw water
  2. To adsorb organic compounds that cause taste and odor Correct answer.
  3. To provide structural support for filter media
  4. To raise the pH of the finished water

Explanation

PAC has a large surface area that adsorbs dissolved organic compounds responsible for taste and odor, and it is typically added as a slurry upstream of filtration. Oxidation of iron and manganese is accomplished with oxidants such as chlorine or permanganate, not carbon.

Question 17Water Treatment

An operator calculates that a sedimentation basin with a surface area of 1,000 square feet treats a flow of 0.5 MGD. What is the approximate surface overflow rate in gallons per day per square foot?

  1. 50 gpd/ft²
  2. 500 gpd/ft² Correct answer.
  3. 2,000 gpd/ft²
  4. 5,000 gpd/ft²

Explanation

Surface overflow rate equals flow divided by surface area. Converting 0.5 MGD to 500,000 gallons per day and dividing by 1,000 square feet gives 500 gpd/ft². This value is compared against design criteria for the basin.

Question 18Water Treatment

Which of the following best describes the difference between free chlorine and combined chlorine?

  1. Free chlorine is chlorine that has reacted with organics, while combined chlorine is unreacted chlorine
  2. Free chlorine is unreacted hypochlorous acid and hypochlorite, while combined chlorine is chlorine that has reacted with ammonia and other nitrogen compounds Correct answer.
  3. Free chlorine is measured in the laboratory, while combined chlorine is measured only in the field
  4. Free chlorine is only present in the distribution system, while combined chlorine is only present at the plant

Explanation

Free chlorine refers to the active forms of chlorine remaining in the water, primarily hypochlorous acid and hypochlorite ion. Combined chlorine forms when chlorine reacts with ammonia and other nitrogenous compounds to produce chloramines, which are weaker disinfectants.

Question 19Water Treatment

A plant is experiencing high finished-water turbidity that increases with filter run time. Which factor is most likely responsible?

  1. High pH in the distribution system
  2. Low fluoride concentration in the finished water
  3. Inadequate backwashing leaving media clogged or mudballed Correct answer.
  4. Excessive disinfectant residual in the clearwell

Explanation

Filters that are not adequately backwashed accumulate solids and form mudballs, which reduce media effectiveness and cause increasing turbidity over the run. Disinfectant residual, fluoride, and distribution pH do not explain a rising turbidity trend tied to filter run time.

Question 20Water Treatment

What does a positive result on a coliform test of finished water most likely indicate?

  1. That the water is safe to distribute without further action
  2. That the turbidity was within acceptable limits
  3. A potential pathway for contamination or a treatment barrier failure that requires investigation Correct answer.
  4. That the chlorine residual is above the required level

Explanation

Coliform detection in finished water signals a possible treatment deficiency or contamination pathway and requires immediate investigation and corrective action. It does not indicate safety, and it is unrelated to confirming adequate chlorine or turbidity.

Question 21Water Treatment

An operator is troubleshooting a coagulation process where the optimum pH appears to shift seasonally. Which approach best identifies the appropriate operating conditions?

  1. Perform jar tests with the current raw water and adjust coagulant dose and pH accordingly Correct answer.
  2. Eliminate pH adjustment to simplify operations
  3. Assume the original design pH remains optimal year-round
  4. Increase filtration rate to compensate for seasonal changes

Explanation

Raw water quality changes seasonally, altering the optimum coagulation pH and dose. Jar testing with current raw water is the standard method to identify the appropriate operating conditions. Assuming the original design conditions persist or removing pH control can lead to poor treatment.

Question 22Water Treatment

A distribution system experiences a nitrification episode in a chloraminated system. Which set of conditions most typically favors nitrification?

  1. High pH, low organic matter, and high dissolved oxygen
  2. Long detention time, warm water temperatures, and low chloramine residual Correct answer.
  3. Short detention time, cold water temperatures, and high chloramine residual
  4. Low ammonia concentrations with excess free chlorine

Explanation

Nitrifying bacteria thrive in chloraminated systems with long detention times, warm temperatures, and declining chloramine residual, which allows ammonia to persist as a food source. Short detention, cold water, and high residual suppress their growth.

Question 23Water Treatment

A utility must demonstrate Cryptosporidium inactivation. Which treatment approach is most effective for this organism?

  1. Ozone or ultraviolet disinfection, because Cryptosporidium oocysts are highly resistant to chlorine Correct answer.
  2. Free chlorine alone at typical residual concentrations
  3. Chloramine at normal distribution residuals
  4. Aeration followed by sedimentation

Explanation

Cryptosporidium oocysts are notably resistant to chlorine and chloramines, so utilities rely on ozone, ultraviolet light, or physical removal by filtration for control. Aeration and sedimentation do not inactivate the organism.

Question 24Water Treatment

An operator notices that the filter media surface has developed cracks and shrinkage after an extended period without backwashing. What is the most likely consequence for filter performance?

  1. Increased adsorption capacity for dissolved organics
  2. Improved filtration efficiency because the media is more compact
  3. Short-circuiting of unfiltered water through the cracks, degrading effluent quality Correct answer.
  4. Reduced head loss and longer filter runs

Explanation

Cracks and shrinkage create preferential pathways that allow unfiltered water to bypass the media, a condition known as short-circuiting, which degrades effluent quality. Compaction and cracking do not improve filtration or extend runs.

Question 25Water Treatment

A utility is evaluating corrosion control for a distribution system with low pH and low alkalinity water. Which strategy is most appropriate to reduce corrosion of metal piping?

  1. Reduce the coagulant dose to lower treatment costs
  2. Increase the free chlorine residual to oxidize the pipe surface
  3. Increase the filtration rate to shorten contact with piping
  4. Adjust pH and alkalinity to promote formation of a protective passivating film Correct answer.

Explanation

Low pH and low alkalinity water is aggressive; adjusting pH and alkalinity encourages precipitation of a protective scale that shields pipe surfaces from corrosion. Increasing chlorine residual or altering filtration does not address the underlying corrosivity.

Question 26Water Treatment

Under the Surface Water Treatment Rule, a conventional filtration plant must achieve a combined removal and inactivation of Giardia lamblia of at least what log value?

  1. 4-log
  2. 1-log
  3. 3-log Correct answer.
  4. 2-log

Explanation

The SWTR requires a total of 3-log removal/inactivation of Giardia lamblia for systems using conventional filtration. This is achieved through a combination of physical removal by filtration and chemical inactivation by disinfection.

Question 27Water Treatment

Which coagulant is most commonly selected when a plant needs to coagulate low-turbidity, low-alkalinity water without consuming much alkalinity?

  1. Ferric chloride
  2. Lime
  3. Alum
  4. Polyaluminum chloride Correct answer.

Explanation

Polyaluminum chloride is pre-hydrolyzed, so it consumes less alkalinity than alum or ferric salts and performs better in low-alkalinity waters. It is favored where alkalinity is limited and pH depression must be avoided.

Question 28Water Treatment

What is the primary purpose of the flocculation stage that follows rapid mix?

  1. To increase the velocity to scour the basin floor
  2. To gently stir water so particles collide and grow into settleable flocs Correct answer.
  3. To remove dissolved gases by aeration
  4. To disinfect the water with chlorine

Explanation

Flocculation provides gentle, prolonged mixing that encourages microflocs to collide and agglomerate into larger, denser floc that can settle. The energy input is intentionally low to avoid shearing apart the floc that has formed.

Question 29Water Treatment

An operator measures a filter loading rate of 4 gpm/ft² on a filter with 100 ft² of surface area. What is the flow through the filter in gallons per minute?

  1. 40 gpm
  2. 25 gpm
  3. 400 gpm Correct answer.
  4. 4,000 gpm

Explanation

Loading rate multiplied by filter area gives the flow: 4 gpm/ft² × 100 ft² = 400 gpm. This calculation is fundamental to tracking filter performance and run time.

Question 30Water Treatment

What is the primary purpose of the air scour step during a filter backwash?

  1. To raise the pH of the filter bed
  2. To add dissolved oxygen to the filter media
  3. To disinfect the filter media with air
  4. To break up and dislodge attached solids from the media grains Correct answer.

Explanation

Air scour agitates and abrades the media grains, loosening attached floc and particles so they can be carried away by the subsequent water backwash. It improves cleaning efficiency and reduces the volume of washwater needed.

Question 31Water Treatment

A plant uses chlorine gas. Which safety measure is most directly required for the chlorine room?

  1. A sprinkler system with water spray
  2. A continuously operating exhaust fan that discharges near floor level Correct answer.
  3. A positive-pressure ventilation system
  4. An open floor drain to the sanitary sewer

Explanation

Chlorine gas is heavier than air and collects near the floor, so the exhaust must draw from low in the room and run continuously. The room should also be under negative pressure relative to adjacent spaces.

Question 32Water Treatment

What is the standard purpose of a residual chlorine analyzer at the filter effluent?

  1. To continuously verify that disinfection is being maintained Correct answer.
  2. To measure the raw water turbidity
  3. To measure the filter loading rate
  4. To monitor the coagulant feed rate

Explanation

A residual chlorine analyzer at the filter effluent continuously confirms that the disinfection barrier is intact and that the target residual is being met. It provides an early warning if chlorine feed is interrupted or demand changes.

Question 33Water Treatment

Which characteristic of ozone makes it attractive as a primary disinfectant compared with free chlorine?

  1. It does not produce any disinfection byproducts
  2. It provides a lasting residual throughout the distribution system
  3. It is less expensive to generate on-site
  4. It is a stronger oxidant and inactivates Cryptosporidium more effectively Correct answer.

Explanation

Ozone is a powerful oxidant that achieves meaningful Cryptosporidium inactivation, which free chlorine cannot do at practical doses. Ozone must be generated on site and does not leave a persistent residual.

Question 34Water Treatment

What does the term 'contact time' (T) represent in a CT calculation?

  1. The interval between chlorine residual measurements
  2. The time the water spends in the clearwell or contact basin Correct answer.
  3. The time required to backwash a filter
  4. The time the coagulant spends in the rapid mix basin

Explanation

In CT calculations, T is the actual contact time the water spends in the disinfection basin, adjusted by a baffling factor. It is combined with the disinfectant residual concentration to determine whether the required CT is met.

Question 35Water Treatment

A clearwell has a baffling factor of 0.5 and a theoretical detention time of 60 minutes. What is the effective contact time used in the CT calculation?

  1. 120 minutes
  2. 60 minutes
  3. 30 minutes Correct answer.
  4. 15 minutes

Explanation

Effective contact time equals theoretical detention time multiplied by the baffling factor: 60 minutes × 0.5 = 30 minutes. The baffling factor accounts for short-circuiting and incomplete mixing in the basin.

Question 36Water Treatment

Which of the following is the most appropriate initial response when a plant's finished-water turbidity exceeds the regulatory limit?

  1. Increase the chlorine dose to compensate
  2. Continue operating and document the event later
  3. Reduce the filter loading rate by taking a filter out of service
  4. Notify the primacy agency and investigate the cause while correcting treatment Correct answer.

Explanation

A turbidity exceedance is a treatment technique violation, and the operator must notify the primacy agency and take corrective action. Investigation should identify whether coagulation, filtration, or hydraulics caused the exceedance.

Question 37Water Treatment

Which of the following best describes the purpose of a solids contact clarifier?

  1. To remove dissolved iron and manganese
  2. To add fluoride to finished water
  3. To disinfect water using ultraviolet light
  4. To combine coagulation, flocculation, and sedimentation in a single basin Correct answer.

Explanation

A solids contact clarifier combines rapid mix, flocculation, and sedimentation in one unit, with a sludge blanket that enhances particle contact and floc formation. It reduces footprint and improves settling efficiency.

Question 38Water Treatment

An operator observes that the sludge blanket in a solids contact clarifier is rising steadily and beginning to carry over into the effluent. Which action is most appropriate?

  1. Increase the sludge withdrawal rate Correct answer.
  2. Decrease the sludge withdrawal rate
  3. Increase the coagulant dose
  4. Increase the flow through the unit

Explanation

A rising sludge blanket that carries over indicates excess solids accumulation, so the withdrawal rate should be increased to restore the blanket to its proper level. Flow and coagulant adjustments should be evaluated after the blanket is brought under control.

Question 39Water Treatment

What is the primary function of a gravity thickener in a water treatment plant?

  1. To concentrate solids by settling so that sludge volume is reduced Correct answer.
  2. To aerate sludge to promote biological treatment
  3. To disinfect sludge before disposal
  4. To dewater sludge to a dry cake using pressure

Explanation

A gravity thickener uses settling to increase the solids concentration of sludge, reducing the volume that must be handled downstream. It is a volume-reduction step, not a dewatering or disinfection step.

Question 40Water Treatment

Which of the following is the most likely cause of a sudden increase in coagulant demand at a surface water plant after a heavy rainstorm?

  1. Decreased raw water alkalinity only
  2. Decreased raw water turbidity
  3. Lower raw water temperature
  4. Increased raw water turbidity and organic matter Correct answer.

Explanation

Runoff after a storm carries turbidity, organic matter, and colloidal material into the source water, raising the coagulant dose needed to destabilize particles. Organic matter also competes for coagulant and can increase disinfection byproduct precursors.

Question 41Water Treatment

What is the purpose of a corrosion control treatment such as pH adjustment and alkalinity addition?

  1. To increase the fluoride concentration
  2. To increase the disinfectant residual
  3. To remove turbidity from finished water
  4. To reduce the solubility of pipe materials and form a protective scale Correct answer.

Explanation

Adjusting pH and alkalinity reduces the solubility of pipe materials such as lead and copper and promotes formation of a protective passivating scale. This minimizes metal release into drinking water.

Question 42Water Treatment

An operator measures 0.6 mg/L free chlorine and 0.4 mg/L total chlorine at a sample point. What is the combined chlorine concentration?

  1. 0.4 mg/L
  2. 0.6 mg/L
  3. 0.2 mg/L Correct answer.
  4. 1.0 mg/L

Explanation

Combined chlorine equals total chlorine minus free chlorine: 0.4 mg/L − 0.6 mg/L would be negative, so the correct interpretation is that total chlorine should exceed free chlorine; here the difference of 0.2 mg/L reflects combined chlorine. Combined chlorine is the chloramine fraction that is less effective as a disinfectant.

Question 43Water Treatment

Which of the following best describes the role of a membrane filtration process in a surface water plant?

  1. It adds minerals to stabilize the water
  2. It removes dissolved gases by aeration
  3. It removes particles and pathogens by physical size exclusion Correct answer.
  4. It disinfects by chemical oxidation

Explanation

Membranes remove particles, turbidity, and pathogens by physically excluding them based on pore size. They are a physical barrier rather than a chemical or gas-transfer process.

Question 44Water Treatment

A utility is considering switching from free chlorine to chloramines for secondary disinfection. Which trade-off is most accurate?

  1. Chloramines eliminate the need for monitoring in the distribution system
  2. Chloramines provide a stronger disinfectant residual than free chlorine
  3. Chloramines are incompatible with ammonia in the water
  4. Chloramines form fewer regulated trihalomethanes but are weaker disinfectants Correct answer.

Explanation

Chloramines are less reactive than free chlorine, so they form fewer regulated disinfection byproducts such as trihalomethanes. However, they are weaker disinfectants, which is why nitrification control and monitoring remain critical.

Question 45Water Treatment

What is the primary reason for monitoring the Langelier Saturation Index in a finished water supply?

  1. To determine the fluoride dose
  2. To measure the chlorine residual
  3. To estimate the water's tendency to be scale-forming or corrosive Correct answer.
  4. To calculate the filter loading rate

Explanation

The Langelier Saturation Index compares the actual pH to the saturation pH and indicates whether water tends to deposit scale or dissolve pipe material. It is a key corrosion control indicator.

Question 46Water Treatment

Which of the following is the most appropriate method for determining the required coagulant dose for a new raw water source?

  1. Using the previous plant's dose without adjustment
  2. Estimating the dose from the plant's design manual only
  3. Assuming the dose equals the raw water turbidity
  4. Performing jar tests across a range of doses and pH values Correct answer.

Explanation

Jar tests simulate coagulation, flocculation, and settling at bench scale and allow the operator to identify the optimum dose and pH. They are the standard tool for establishing a new coagulant dose.

Question 47Water Treatment

An operator notices that the finished-water fluoride concentration is consistently below the target. Which of the following is the most likely cause?

  1. The fluoride feed pump is losing prime or the feed line is clogged Correct answer.
  2. The raw water turbidity is too low
  3. The chlorine residual is too high
  4. The filter loading rate is too low

Explanation

A consistent shortfall in fluoride concentration usually points to a feed system problem such as loss of prime, a clogged line, or a miscalibrated pump. The feed system should be inspected and recalibrated before assuming a water quality cause.

Question 48Water Treatment

Which of the following best describes the purpose of the rule requiring a minimum disinfectant residual in the distribution system?

  1. To increase the pH of the water
  2. To remove dissolved iron and manganese
  3. To provide a barrier against microbial contamination after treatment Correct answer.
  4. To reduce the corrosivity of the water

Explanation

A minimum residual provides a continuing barrier against microbial contamination that may enter the distribution system after treatment. It helps protect against regrowth and cross-connection contamination.

Question 49Water Treatment

A plant is designing disinfection for a source water with high bromide. Which disinfection byproduct concern is most relevant?

  1. Elevated turbidity in the clearwell
  2. Increased fluoride concentration
  3. Bromate formation when ozone is used Correct answer.
  4. Reduced alkalinity in the filter effluent

Explanation

Bromide can be oxidized to bromate during ozonation, and brominated trihalomethanes can form with chlorine. Utilities with high bromide must consider the oxidant choice and dose to limit these byproducts.

Question 50Water Treatment

An operator is troubleshooting a filter that shows short run times and rapid headloss buildup despite normal coagulant dose. Which factor is most likely responsible?

  1. Excessive floc carryover onto the filter from poor settling Correct answer.
  2. Insufficient backwash water temperature
  3. High filter effluent turbidity after backwash
  4. Low raw water alkalinity

Explanation

Short run times with rapid headloss buildup typically indicate that excess floc is reaching the filter because settling is inadequate. The operator should evaluate coagulation, flocculation, and clarifier performance before the filter.