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NH Water/Wastewater Operator practice questions

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Question 1Drinking Water Treatment and Distribution

Under New Hampshire drinking water rules, what is the maximum contaminant level for nitrate (as N) in a public water system?

  1. 50 mg/L
  2. 1 mg/L
  3. 5 mg/L
  4. 10 mg/L Correct answer.

Explanation

The federal and New Hampshire primary standard for nitrate measured as nitrogen is 10 mg/L. This limit protects against methemoglobinemia, especially in infants. Systems exceeding it must notify the public and take corrective action.

Question 2Drinking Water Treatment and Distribution

A community water system serving 3,300 people uses free chlorine. Under the Stage 2 Disinfectants and Disinfection Byproducts Rule, which monitoring approach generally applies to the system's TTHM and HAA5 compliance?

  1. Monitoring only when a customer complains of taste or odor
  2. Monitoring at the lowest-DBP location in the distribution system
  3. Monitoring at the entry point only
  4. Monitoring at the highest TTHM and HAA5 locations identified in the IDSE or a similar site plan Correct answer.

Explanation

Stage 2 requires systems to monitor at locations with the highest TTHM and HAA5 formation, determined through the initial distribution system evaluation or an approved site plan. This LRAA-based approach targets worst-case DBP exposure. Entry-point-only or complaint-based sampling would not capture distribution-system formation.

Question 3Drinking Water Treatment and Distribution

What is the primary purpose of adding fluoride to treated drinking water in New Hampshire?

  1. To disinfect the distribution system
  2. To prevent corrosion of lead service lines
  3. To remove dissolved iron and manganese
  4. To reduce the incidence of dental caries Correct answer.

Explanation

Fluoridation is practiced to reduce tooth decay by incorporating fluoride into enamel and promoting remineralization. It is a public health measure, not a treatment for corrosion or disinfection. The target concentration is typically around 0.7 mg/L.

Question 4Drinking Water Treatment and Distribution

A groundwater system chlorinates with free chlorine and reports a measured residual. To determine the chlorine dose required, the operator should account for which relationship?

  1. Dose equals demand divided by residual
  2. Dose equals residual multiplied by demand
  3. Dose equals demand plus residual Correct answer.
  4. Dose equals residual minus demand

Explanation

The applied chlorine dose is consumed partly by chlorine demand in the water and the remainder stays as residual. Therefore dose equals demand plus residual. If a system wants 1.0 mg/L residual and demand is 0.8 mg/L, the dose must be about 1.8 mg/L.

Question 5Drinking Water Treatment and Distribution

A water system operator measures turbidity in filtered water. Under the surface water treatment rules, combined filter effluent turbidity for conventional filtration must generally remain at or below what value in at least 95 percent of monthly measurements?

  1. 5.0 NTU
  2. 0.3 NTU Correct answer.
  3. 1.0 NTU
  4. 0.1 NTU

Explanation

For conventional or direct filtration, combined filter effluent turbidity must be 0.3 NTU or less in at least 95 percent of measurements each month, and must never exceed 1 NTU. These limits confirm that filtration is reliably removing pathogens.

Question 6Drinking Water Treatment and Distribution

During a jar test on a surface water source, the operator observes that floc forms but settles slowly and leaves residual turbidity. Which adjustment is most likely to improve coagulation?

  1. Add more chlorine before coagulation
  2. Increase filter loading rate
  3. Reduce the rapid-mix intensity to zero
  4. Optimize coagulant dose and pH to improve charge neutralization and sweep floc Correct answer.

Explanation

Slow-settling floc and residual turbidity usually indicate that coagulant dose or pH is not optimized for charge neutralization or sweep floc. A jar test series varying dose and pH identifies the best combination. Filter rate and prechlorination do not correct poor coagulation chemistry.

Question 7Drinking Water Treatment and Distribution

What is the primary purpose of a clearwell in a surface water treatment plant?

  1. To store coagulant chemicals
  2. To backwash filters
  3. To provide contact time for disinfection before water enters the distribution system Correct answer.
  4. To aerate water for radon removal

Explanation

The clearwell provides detention time so the disinfectant can inactivate pathogens and meet CT requirements before water is distributed. It also provides finished-water storage. It is not a chemical storage or filter-washing unit.

Question 8Drinking Water Treatment and Distribution

An operator is calculating CT for free chlorine disinfection. If the measured residual is 1.2 mg/L, the contact time is 30 minutes, and the baffling factor is 0.5, what is the CT value in mg/L·min?

  1. 36
  2. 0.6
  3. 18 Correct answer.
  4. 30

Explanation

CT equals disinfectant residual times the effective contact time, where effective time is actual time multiplied by the baffling factor. Here CT = 1.2 × 30 × 0.5 = 18 mg/L·min. The baffling factor corrects for short-circuiting in the basin.

Question 9Drinking Water Treatment and Distribution

Which condition most commonly causes a loss of chlorine residual in a distribution system far from the treatment plant?

  1. Low coagulant feed at the plant
  2. High raw water alkalinity at the intake
  3. Excessive filter backwash rate
  4. Long detention time and reaction with pipe deposits and organic matter Correct answer.

Explanation

Chlorine residual decays as water ages in the mains and reacts with biofilm, sediment, and organic material. Dead ends and low-flow areas show the greatest loss. Raw-water and plant-process conditions matter mainly as they affect finished-water quality.

Question 10Drinking Water Treatment and Distribution

What is the minimum recommended separation between a new water main and a sanitary sewer main under standard New Hampshire practice?

  1. No separation is required if both are buried
  2. 25 feet horizontal separation
  3. 10 feet horizontal separation with the water main above the sewer Correct answer.
  4. 2 feet horizontal separation

Explanation

Standard practice calls for at least 10 feet of horizontal separation between water mains and sanitary sewers, with the water main placed above the sewer where possible. Greater separation or special construction is required when these distances cannot be met. This protects against contamination if the sewer leaks.

Question 11Drinking Water Treatment and Distribution

A backflow prevention device installed on a service line to a chemical plant is a reduced-pressure-zone assembly. What makes this device suitable for a high-hazard application?

  1. It uses an air gap inside the meter vault
  2. It has two independently acting check valves with a reduced-pressure zone between them and a relief valve Correct answer.
  3. It relies on a vacuum breaker that must be above grade
  4. It uses a single check valve with no relief port

Explanation

A reduced-pressure-zone assembly provides two check valves separated by a zone that is maintained at lower pressure than the supply, plus a differential relief valve. If either check fails, the relief valve discharges, preventing backflow. This redundancy is why it suits high-hazard connections.

Question 12Drinking Water Treatment and Distribution

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

  1. To increase system pressure permanently
  2. To add fluoride to the distribution system
  3. To test fire hydrant flow capacity only
  4. To remove stagnant water and accumulated sediment and restore disinfectant residual Correct answer.

Explanation

Dead ends accumulate sediment and lose disinfectant residual because water sits stagnant. Routine flushing removes this material and draws fresh treated water into the area. It does not permanently raise pressure or serve as a fluoridation method.

Question 13Drinking Water Treatment and Distribution

A storage tank shows a falling chlorine residual and rising heterotrophic plate count. Which operational response is most appropriate?

  1. Stop all sampling until the next compliance period
  2. Increase the tank's water level and extend detention time
  3. Reduce storage age by improving turnover and inspect for sediment or biofilm Correct answer.
  4. Add phosphate to the tank to raise the residual

Explanation

Rising HPC and falling residual suggest stagnation, sediment buildup, or biofilm in the tank. Improving turnover and cleaning the tank address the cause. Extending detention worsens stagnation, and phosphate is a corrosion inhibitor, not a disinfectant.

Question 14Drinking Water Treatment and Distribution

Which parameter is most directly used to determine whether water is corrosive to distribution piping and plumbing?

  1. Total coliform count
  2. Turbidity
  3. Fluoride concentration
  4. Langelier Saturation Index Correct answer.

Explanation

The Langelier Saturation Index compares measured pH to the calcium-carbonate saturation pH to indicate scaling or corrosive tendency. A negative index suggests corrosivity. Turbidity and coliforms measure particles and bacteria, not corrosion chemistry.

Question 15Drinking Water Treatment and Distribution

Under the Lead and Copper Rule, what is the 90th-percentile action level for lead in first-draw tap samples?

  1. 1.3 mg/L
  2. 0.015 mg/L Correct answer.
  3. 0.05 mg/L
  4. 0.0015 mg/L

Explanation

The lead action level is 0.015 mg/L at the 90th percentile of first-draw samples from high-risk sites. Exceeding it triggers corrosion-control treatment, public education, and additional monitoring. The 1.3 mg/L value is the copper action level.

Question 16Drinking Water Treatment and Distribution

An operator collects a total coliform-positive routine sample. Under the Revised Total Coliform Rule, what must the system do next?

  1. Shut down all wells until further notice
  2. Immediately issue a boil water order for the entire system
  3. Collect repeat samples and conduct an assessment as required by the positive result Correct answer.
  4. Increase the chlorine dose without any further sampling

Explanation

A routine positive triggers repeat sampling at the site and nearby locations, and may trigger a level 1 or level 2 assessment depending on the pattern. Boil orders and source shutdowns are not automatic for a single positive. Assessment identifies the cause before corrective action.

Question 17Drinking Water Treatment and Distribution

What does a positive presence of E. coli in a distribution sample most likely indicate?

  1. A failure of the fluoride feed system
  2. An error in the turbidity meter calibration
  3. Normal background growth of harmless bacteria
  4. Recent fecal contamination or a serious sanitary defect in the system Correct answer.

Explanation

E. coli is a fecal indicator, so its presence suggests recent fecal contamination or a sanitary defect such as a cross-connection or broken main. It requires immediate follow-up and public notification. It is not normal background flora.

Question 18Drinking Water Treatment and Distribution

A treatment plant uses conventional filtration. Which combination best describes the correct order of processes?

  1. Filtration, coagulation, disinfection, sedimentation
  2. Disinfection, filtration, coagulation, flocculation
  3. Coagulation, flocculation, sedimentation, filtration, disinfection Correct answer.
  4. Sedimentation, disinfection, coagulation, filtration

Explanation

Conventional treatment destabilizes particles with coagulant, gently mixes to form floc, settles floc in sedimentation, and removes remaining particles by filtration. Disinfection follows so that clear, low-turbidity water is disinfected efficiently.

Question 19Drinking Water Treatment and Distribution

An operator notices short filter runs and rapid headloss buildup after a coagulant change. Which cause is most likely?

  1. Excessive clearwell detention time
  2. Underdosing disinfectant in the clearwell
  3. Overdosing coagulant or forming floc that plugs the filter media Correct answer.
  4. Too low a filter loading rate

Explanation

Excess coagulant or poorly conditioned floc can carry onto filters and plug the media, shortening runs and raising headloss quickly. Optimizing dose and floc strength restores run length. Clearwell and disinfection issues do not cause rapid filter headloss.

Question 20Drinking Water Treatment and Distribution

What is the primary reason for maintaining a positive pressure of at least 20 psi throughout a distribution system?

  1. To prevent contamination from entering through leaks and to supply adequate flow Correct answer.
  2. To reduce chlorine demand in the pipes
  3. To increase the fluoride concentration at the tap
  4. To eliminate the need for backflow devices

Explanation

Positive pressure keeps water flowing outward through leaks and joints, preventing contaminated groundwater or soil from entering the main. It also supports adequate flow for domestic and fire use. Pressure does not replace backflow prevention at customer connections.

Question 21Drinking Water Treatment and Distribution

A pump delivers water at 500 gallons per minute. How many gallons does it deliver in 6 hours?

  1. 30,000 gallons
  2. 500 gallons
  3. 180,000 gallons Correct answer.
  4. 3,000 gallons

Explanation

Convert hours to minutes: 6 × 60 = 360 minutes. Multiply by the flow: 500 gpm × 360 min = 180,000 gallons. Keeping units consistent avoids errors in dosage and production calculations.

Question 22Drinking Water Treatment and Distribution

An operator must dose 2 mg/L of a coagulant into a flow of 1.0 million gallons per day. If the chemical is fed as a solution, what information is still needed to set the feed pump rate?

  1. The clearwell baffling factor
  2. The distribution system's pressure
  3. The concentration of the chemical solution and the conversion from mass to volume Correct answer.
  4. The filter loading rate

Explanation

The required mass dose is flow times concentration, but to set a pump in gallons per hour the operator needs the solution strength and the density or conversion factor. Without solution concentration, the mass cannot be converted to a volume feed rate. Filter, clearwell, and pressure data do not determine chemical feed volume.

Question 23Drinking Water Treatment and Distribution

Which action best protects a public water system's finished water from a cross-connection at a customer's irrigation system?

  1. Increase the plant's chlorine residual
  2. Flush the customer's irrigation lines monthly
  3. Require an approved backflow prevention assembly at the service connection Correct answer.
  4. Install a check valve at the treatment plant

Explanation

The most reliable protection is a properly selected and tested backflow prevention assembly at the service connection, matched to the hazard. Plant-side measures and customer flushing do not isolate the public main from a customer's plumbing.

Question 24Drinking Water Treatment and Distribution

A water system plans to add a new groundwater source. Which contaminant is most important to evaluate when the source is near a former industrial site?

  1. Total dissolved solids only
  2. pH only
  3. Fluoride
  4. Volatile organic compounds such as trichloroethylene Correct answer.

Explanation

Industrial solvents like TCE are common groundwater contaminants and are regulated VOCs. Source approval requires testing for the contaminants associated with nearby land use. Fluoride, TDS, and pH are general parameters but do not target the industrial risk.

Question 25Drinking Water Treatment and Distribution

What is the purpose of an air-release valve on a high-point of a transmission main?

  1. To measure the flow rate
  2. To drain sediment from the main
  3. To introduce chlorine into the main
  4. To release accumulated air that can restrict flow and cause pressure surges Correct answer.

Explanation

Air pockets collect at high points and reduce capacity, and sudden air release can cause damaging surges. Air-release valves vent this air safely. They are not used for sediment draining, chlorination, or flow measurement.

Question 26Drinking Water Treatment and Distribution

In a conventional surface water treatment plant, what is the primary purpose of adding a coagulant such as aluminum sulfate during rapid mix?

  1. To raise the pH of the raw water to the optimum range for disinfection
  2. To kill bacteria before the water reaches the filters
  3. To add hardness and prevent corrosion in the distribution system
  4. To destabilize particle charges so colloids can stick together and form floc Correct answer.

Explanation

Coagulants work by neutralizing the negative surface charges that keep fine colloids apart, allowing them to collide and agglomerate during flocculation. This is a charge-destabilization process, not a disinfection or pH-control step. The resulting floc is then removed by sedimentation and filtration.

Question 27Drinking Water Treatment and Distribution

A gravity filter is operating with a headloss of 8.5 feet when clean and reaches 9.8 feet after several hours. What does this rise in headloss most directly indicate?

  1. The filter media has been lost through the underdrain
  2. Solids are accumulating in the filter bed and restricting flow Correct answer.
  3. The filter effluent turbidity has dropped below 0.1 NTU
  4. The backwash water supply pressure has increased

Explanation

Headloss rises as captured particles clog the pore spaces in the filter media, progressively restricting flow through the bed. When headloss reaches the terminal limit, the filter is taken out of service and backwashed. Effluent turbidity and backwash supply pressure are separate measurements.

Question 28Drinking Water Treatment and Distribution

What is the primary function of a chlorine booster station located in the middle of a distribution system?

  1. To add fluoride at the point of use
  2. To remove disinfection byproducts from the treated water
  3. To restore disinfectant residual that has decayed during travel through the system Correct answer.
  4. To increase the pressure in the distribution mains

Explanation

Chlorine residual decays as water travels through mains because of reactions with pipe surfaces, biofilm, and natural organic matter. A booster station rechlorinates the water to maintain the required residual throughout the system. Booster stations do not generally affect pressure, DBPs, or fluoride.

Question 29Drinking Water Treatment and Distribution

A water system's storage tank has a high water level and the distribution pressure is adequate, yet the tank is not being drawn down overnight as expected. Which condition most likely explains this?

  1. The tank vent is blocked
  2. The tank overflow pipe is undersized
  3. The altitude valve or level control is stuck in the closed position Correct answer.
  4. The tank's cathodic protection system is operating normally

Explanation

A stuck altitude or level-control valve can prevent the tank from discharging into the system even when pressure and level appear normal. The valve regulates fill and draw cycles, so a failure to open during drawdown points to the control valve. Venting, overflow sizing, and cathodic protection do not control tank drawdown.

Question 30Drinking Water Treatment and Distribution

Which unit process in a conventional surface water plant is designed to remove the largest mass of settled floc before the filters?

  1. Clearwell
  2. Rapid mix basin
  3. Flocculation basin
  4. Sedimentation basin Correct answer.

Explanation

Sedimentation (clarification) basins allow floc that has formed during flocculation to settle out under quiescent conditions, removing the bulk of the solids load before filtration. Rapid mix and flocculation only prepare the floc; the clearwell stores disinfected water.

Question 31Drinking Water Treatment and Distribution

An operator is calculating the volume of a rectangular clearwell that is 40 feet long, 20 feet wide, and 12 feet deep. What is the volume in cubic feet?

  1. 4,800 cubic feet
  2. 960 cubic feet
  3. 72 cubic feet
  4. 9,600 cubic feet Correct answer.

Explanation

Volume of a rectangular basin equals length times width times depth, so 40 × 20 × 12 equals 9,600 cubic feet. Multiplying by 7.48 gallons per cubic foot would then convert the volume to gallons.

Question 32Drinking Water Treatment and Distribution

What is the purpose of a check valve installed on the discharge line of a distribution pump?

  1. To relieve excessive pressure in the discharge header
  2. To throttle the pump output to a set flow rate
  3. To prevent reverse flow through the pump when it stops Correct answer.
  4. To measure the flow rate leaving the pump

Explanation

A check valve permits flow in one direction only, so it closes when the pump stops and prevents water from flowing backward through the pump. This protects the pump and motor from reverse rotation and water hammer. Throttling, pressure relief, and flow measurement require other devices.

Question 33Drinking Water Treatment and Distribution

A public water system serves 3,300 people. Under the Revised Total Coliform Rule, how many routine coliform samples must the system collect each month for a population of this size?

  1. 2 samples
  2. 5 samples
  3. 1 sample
  4. 3 samples Correct answer.

Explanation

The RTCR sample table requires three routine samples per month for populations from 3,301 to 4,100. Systems serving 1,000 or fewer collect one sample, and the requirement rises in steps as population increases.

Question 34Drinking Water Treatment and Distribution

An operator notices that finished water turbidity rises sharply whenever the raw water temperature drops below 35°F, even though coagulant dose is unchanged. Which explanation is most consistent with this observation?

  1. Cold water reduces filter media depth, shortening filter runs
  2. Cold water slows coagulation kinetics and raises viscosity, so floc forms more slowly and settles less readily Correct answer.
  3. Cold water raises the zeta potential of particles, eliminating the need for coagulant
  4. Cold water increases the solubility of aluminum sulfate, making overdosing likely

Explanation

Low water temperature slows the chemical reactions of coagulation and increases viscosity, which reduces floc collision efficiency and settling velocity. Operators typically respond with adjustments such as a different coagulant, a coagulant aid, or longer flocculation time.

Question 35Drinking Water Treatment and Distribution

A filter has a design loading rate of 4 gpm per square foot and a surface area of 250 square feet. What is the design filtration flow in gallons per minute?

  1. 1,000 gpm Correct answer.
  2. 540 gpm
  3. 62.5 gpm
  4. 250 gpm

Explanation

Filtration rate multiplied by filter area gives total flow: 4 gpm/ft² × 250 ft² equals 1,000 gpm. Loading rate is expressed per unit area, so the area must be multiplied, not divided.

Question 36Drinking Water Treatment and Distribution

A distribution system experiences a sudden pressure drop to 5 psi in a commercial district after a main break. Which immediate action is most important for protecting public health?

  1. Reduce system storage tank levels to relieve pressure on the break
  2. Increase chlorine feed at the treatment plant to 4 mg/L
  3. Flush the affected mains at maximum velocity to restore pressure
  4. Issue a precautionary boil water notice for the affected area and begin coliform sampling Correct answer.

Explanation

A loss of pressure below 20 psi creates a risk of contamination through cross-connections and intrusion, so the system must notify the public and begin sampling to verify water quality. Flushing and raising plant chlorine do not substitute for public notification and verification testing.

Question 37Drinking Water Treatment and Distribution

A groundwater system adds sodium hypochlorite for disinfection and observes a rising concentration of chlorate in the finished water. Which operational change most directly reduces chlorate formation?

  1. Using a fresher hypochlorite solution and storing it cool and out of sunlight Correct answer.
  2. Increasing the hypochlorite feed rate to shorten contact time
  3. Storing the hypochlorite solution in a warm, sunlit area
  4. Switching from liquid hypochlorite to gaseous chlorine without other changes

Explanation

Chlorate forms as hypochlorite degrades, and degradation is accelerated by heat, sunlight, and long storage time. Using fresher solution and storing it cool and dark slows the decay and reduces chlorate. Increasing feed or warm storage would worsen the problem.

Question 38Drinking Water Treatment and Distribution

A water main must be disinfected after repair under standard practice. Which sequence correctly describes the typical procedure?

  1. Chlorinate the main and place it in service without flushing or sampling
  2. Flush the main, chlorinate to a high concentration, hold for the required contact time, then flush and sample for coliforms Correct answer.
  3. Chlorinate the main, sample immediately, then flush to remove the chlorine
  4. Flush the main, sample for coliforms, then chlorinate if results are positive

Explanation

Main disinfection involves flushing to remove debris, applying a high chlorine concentration (often 50 mg/L for new mains), holding for the specified contact time, then flushing and collecting bacteriological samples before service. Sampling before disinfection or omitting the hold time would not verify safe water.

Question 39Drinking Water Treatment and Distribution

An operator measures a chlorine residual of 0.8 mg/L as free chlorine at a tap, but a DPD test on the same sample shows a total chlorine reading of 1.4 mg/L. What does the difference between total and free chlorine most likely represent?

  1. The combined chlorine fraction, largely chloramines Correct answer.
  2. An error caused by using a colorimeter instead of a spectrophotometer
  3. The amount of chlorine lost to evaporation during sampling
  4. The concentration of fluoride in the water

Explanation

Total chlorine equals free chlorine plus combined chlorine, so the 0.6 mg/L difference represents combined chlorine, mainly chloramines formed when chlorine reacts with ammonia. Combined chlorine is a weaker disinfectant and is monitored to confirm adequate free residual.

Question 40Drinking Water Treatment and Distribution

A system using free chlorine wishes to maintain a CT of at least 30 mg/L·min for a 3-log inactivation of Giardia. If the measured residual is 1.5 mg/L, what contact time is required?

  1. 20 minutes Correct answer.
  2. 10 minutes
  3. 30 minutes
  4. 45 minutes

Explanation

CT equals residual concentration multiplied by contact time, so contact time equals CT divided by residual: 30 mg/L·min ÷ 1.5 mg/L equals 20 minutes. This assumes the residual is maintained throughout the contact basin.

Question 41Drinking Water Treatment and Distribution

A water system plans to install a new 12-inch ductile iron main in a trench where the horizontal distance to an existing sanitary sewer main is 8 feet. Under standard New Hampshire separation guidance, what is the most appropriate action?

  1. Reduce the water main diameter to 8 inches to satisfy separation requirements
  2. Relocate the water main or sewer to achieve the required horizontal separation, or use an approved alternative such as encasement Correct answer.
  3. Install the water main as planned because 8 feet exceeds the 10-foot minimum
  4. Backfill the trench with native soil and proceed without further review

Explanation

Standard separation guidance calls for at least 10 feet of horizontal separation between a new water main and a sanitary sewer, with alternatives such as encasement or relocation when that cannot be met. Eight feet does not satisfy the minimum, so the design must be changed or an approved alternative used.

Question 42Drinking Water Treatment and Distribution

A storage tank inspection reveals that the interior coating is blistering and the steel beneath shows rust. Which action is most appropriate?

  1. Add a corrosion inhibitor to the distribution system without repairing the tank
  2. Lower the tank water level permanently to keep the coating submerged
  3. Schedule the tank for recoating and repair of the affected steel Correct answer.
  4. Increase the chlorine residual in the tank to stop the corrosion

Explanation

Blistering coating and rust indicate coating failure and active corrosion of the steel, which requires surface preparation and recoating to restore protection. Chemical adjustments alone cannot repair failed coating or structural deterioration.

Question 43Drinking Water Treatment and Distribution

An operator is troubleshooting a distribution system where chlorine residual is low at the far ends of the system but normal near the plant. Which factor is the most likely cause?

  1. High water age and long travel time allowing chlorine decay Correct answer.
  2. A malfunctioning fluoride feed system
  3. Excessive chlorine demand in the treatment plant clearwell
  4. Low source water turbidity

Explanation

Water that spends a long time in the distribution system loses chlorine through reactions with pipe walls, sediment, and biofilm, so residual is lowest at distant points. Reducing water age through flushing, looping, or storage management is the usual remedy. Plant clearwell demand or fluoride feed would not produce this spatial pattern.

Question 44Drinking Water Treatment and Distribution

A system must feed 25 pounds per day of a coagulant. The chemical is supplied as a solution containing 1.5 pounds of active ingredient per gallon. What feed rate in gallons per day is required?

  1. 1.5 gallons per day
  2. 37.5 gallons per day
  3. 16.7 gallons per day Correct answer.
  4. 25 gallons per day

Explanation

Divide the required mass by the concentration: 25 lb/day ÷ 1.5 lb/gal equals about 16.7 gal/day. This converts a mass feed requirement into a volumetric feed rate for the chemical metering pump.

Question 45Drinking Water Treatment and Distribution

A water system is evaluating a new well that draws from an aquifer under the influence of surface water. Which regulatory determination is most important before placing the source in service?

  1. Whether the well requires filtration and disinfection as a groundwater under the direct influence of surface water Correct answer.
  2. Whether the well can be exempted from all monitoring because it is a groundwater source
  3. Whether the well water needs fluoridation before any other treatment
  4. Whether the well can supply water without a coliform monitoring schedule

Explanation

A groundwater source under the direct influence of surface water is subject to surface water treatment requirements, including filtration and disinfection, because of the risk of pathogen contamination. The determination must be made before the source is used.

Question 46Drinking Water Treatment and Distribution

A distribution system has a history of red water complaints after main flushing or during high-demand periods. Which condition is the most likely cause?

  1. Unlined or corroded iron mains releasing corrosion products when flow or water chemistry changes Correct answer.
  2. A storage tank with an oversized vent
  3. Excessively high chlorine residual throughout the system
  4. A fluoride feed rate that is too low

Explanation

Red water is typically caused by iron corrosion products being disturbed or mobilized when flow velocity, direction, or water chemistry changes in unlined or corroded iron mains. Flushing and corrosion control are the usual responses.

Question 47Drinking Water Treatment and Distribution

A system is required to maintain a minimum residual disinfectant of 0.2 mg/L in the distribution system. A sample collected at a remote location shows 0.1 mg/L free chlorine. What is the most appropriate response?

  1. Record the result as compliant because the sample was at a remote location
  2. Discontinue monitoring at that location because residual is naturally lower there
  3. Add fluoride at that location to raise the chlorine residual
  4. Investigate the cause, increase or adjust disinfection, flush the area, and resample to confirm residual Correct answer.

Explanation

A residual below the required minimum is a compliance concern that requires investigation and corrective action, such as adjusting disinfection, flushing, or reducing water age, followed by resampling. Remote location does not exempt a sample from the minimum residual requirement.

Question 48Drinking Water Treatment and Distribution

An operator is evaluating a treatment plant that uses ozone for primary disinfection. Which operational concern is most specific to ozone compared with free chlorine?

  1. Ozone must be generated on site and does not persist as a residual in the distribution system Correct answer.
  2. Ozone cannot be used with a clearwell
  3. Ozone provides no disinfection credit for viruses
  4. Ozone raises the pH of the water and requires acid addition

Explanation

Ozone is an unstable gas that must be generated on site and decomposes quickly, so it provides little or no lasting residual in the distribution system. Systems using ozone typically add chlorine or chloramines to maintain a residual. Ozone is a strong virucide and does not require acid for pH control.

Question 49Drinking Water Treatment and Distribution

A filter is beginning to show turbidity breakthrough before the terminal headloss is reached. Which combination of actions is most appropriate?

  1. Delay backwashing until terminal headloss is reached regardless of turbidity
  2. Backwash the filter, check coagulant dose and floc strength, and consider filter-to-waste until turbidity is acceptable Correct answer.
  3. Increase the filtration rate to push the turbidity through the bed faster
  4. Reduce the chlorine dose to lower turbidity

Explanation

Early turbidity breakthrough indicates that floc is penetrating the bed, often because of coagulant dose, floc strength, or media condition problems. The filter should be backwashed and the upstream chemistry evaluated, with filter-to-waste used to protect finished water until turbidity is acceptable.

Question 50Drinking Water Treatment and Distribution

A system using chloramines for secondary disinfection experiences a nitrification episode in a storage tank. Which set of indicators and responses is most appropriate?

  1. Rising free ammonia and falling chloramine residual; increase tank turnover, flush, and adjust the chlorine-to-ammonia ratio Correct answer.
  2. Falling free ammonia and rising chloramine residual; reduce tank turnover and stop flushing
  3. Falling turbidity and rising pressure; reduce disinfection
  4. Rising fluoride and falling pH; add more fluoride

Explanation

Nitrifying bacteria consume ammonia and chloramine, so free ammonia rises while total chlorine residual falls. Operators respond by improving turnover, flushing, and adjusting the chlorine-to-ammonia ratio to reestablish a stable chloramine residual.