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Wastewater Treatment Operator Class I study materials
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Wastewater Treatment Operator Class I practice questions

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Question 1Safety Practices and Hazard Awareness

An operator opening a wet well notices a strong rotten-egg odor that fades away within a few minutes. What is the safest interpretation of this change?

  1. The fading odor shows the well has already been ventilated
  2. Gas generation has stopped, so the well atmosphere is now safe
  3. Hydrogen sulfide may have reached a level that deadens the sense of smell Correct answer.
  4. The odor is being masked by chlorine gas inside the well

Explanation

Hydrogen sulfide at higher concentrations paralyzes the olfactory nerve, so the odor disappears as the danger increases. A decaying gas smell at a wet well is a warning to leave and re-test with a calibrated meter. Odor is never a substitute for atmospheric monitoring.

Question 2Safety Practices and Hazard Awareness

Under OSHA rules, what is the minimum oxygen concentration at which an employee may enter a confined space without supplied-air respiratory protection?

  1. 21.0 percent
  2. 19.5 percent Correct answer.
  3. 23.5 percent
  4. 16.0 percent

Explanation

OSHA defines an oxygen-deficient atmosphere as one containing less than 19.5 percent oxygen by volume. Below that level, entrants must use supplied-air respiratory protection or the space must be ventilated and re-tested.

Question 3Safety Practices and Hazard Awareness

A caustic solution splashes into an operator's eye. How long should the eye be flushed at an emergency eyewash station before medical evaluation?

  1. 5 minutes
  2. 15 minutes Correct answer.
  3. 1 minute
  4. 60 minutes

Explanation

Emergency eyewash standards and first-aid guidance call for flushing the affected eye with tepid water for at least 15 minutes. Flushing is started immediately, before the worker is moved to medical care.

Question 4Safety Practices and Hazard Awareness

A fire involving an energized electrical control panel should be fought with which class of portable extinguisher?

  1. Class A
  2. Class D
  3. Class C Correct answer.
  4. Class B

Explanation

Class C extinguishers are rated for fires in energized electrical equipment because their agents do not conduct electricity. Once the equipment is de-energized, the fire is treated according to the class of burning material present.

Question 5Safety Practices and Hazard Awareness

Who is authorized to remove a lockout device that an employee has attached to an energy-isolating device?

  1. Any supervisor who is on duty at the time
  2. The employee who applied it, following the established removal procedure Correct answer.
  3. The next operator assigned to that piece of equipment
  4. Any employee who holds a key to the facility lock box

Explanation

Lockout/tagout rules require that the device be removed only by the authorized employee who applied it. If that employee is unavailable, removal follows a documented special procedure with employer verification and attempts to contact the worker.

Question 6Safety Practices and Hazard Awareness

When diluting a concentrated acid for a cleaning job, how should the acid and water be combined?

  1. Pour the water into the acid slowly while stirring
  2. Mix equal volumes quickly, then cool the container
  3. Pour the acid slowly into the water while stirring Correct answer.
  4. Add the acid only after the water has been heated

Explanation

Dilution releases heat, and adding water to concentrated acid can boil the acid and cause spattering. Adding acid slowly to water with continuous stirring lets the heat dissipate safely.

Question 7Safety Practices and Hazard Awareness

Before entry into a permit-required confined space, in what order should a direct-reading meter be used to check the atmosphere?

  1. Toxic gases, then oxygen, then flammables
  2. Toxics, then flammables, then oxygen
  3. Flammables, then toxics, then oxygen
  4. Oxygen, then flammables, then toxics Correct answer.

Explanation

Oxygen is tested first because the combustible gas sensor relies on adequate oxygen to give a valid reading. Combustible gas is checked next, then toxic gases such as hydrogen sulfide and carbon monoxide.

Question 8Safety Practices and Hazard Awareness

Chlorine gas is escaping from a cylinder in a below-grade pump room. Where should personnel move to escape the hazard?

  1. Into the lowest corner of the room
  2. Upwind and to higher ground Correct answer.
  3. Downwind of the room, staying at floor level
  4. Toward the leak to close the cylinder valve by hand

Explanation

Chlorine is about two and a half times heavier than air, so it settles in low areas and spreads downwind. Personnel evacuate crosswind or upwind and move to higher ground rather than running toward the leak.

Question 9Safety Practices and Hazard Awareness

Methane will burn or explode when its concentration in air falls within which approximate range?

  1. 25 to 50 percent by volume
  2. 50 to 100 percent by volume
  3. 5 to 15 percent by volume Correct answer.
  4. 1 to 4 percent by volume

Explanation

Methane has a lower explosive limit of about 5 percent and an upper explosive limit of about 15 percent by volume in air. Between those limits, an ignition source can cause an explosion.

Question 10Safety Practices and Hazard Awareness

Sodium hypochlorite solution is accidentally mixed with an acid in a bucket. What hazard is created?

  1. Oxygen is consumed and the area becomes oxygen deficient
  2. A flammable solvent is produced
  3. Chlorine gas is released Correct answer.
  4. The mixture becomes non-corrosive and safe to handle

Explanation

Acid reacts with hypochlorite to release chlorine gas, which is highly toxic and heavier than air. These chemicals must be stored separately and never combined, even in small amounts or during spill cleanup.

Question 11Safety Practices and Hazard Awareness

Under OSHA general industry rules, fall protection is generally required when an employee works at what height above a lower level?

  1. 4 feet Correct answer.
  2. 3 feet
  3. 2 feet
  4. 10 feet

Explanation

General industry rules require fall protection at heights of 4 feet or more above a lower level, including open-sided floors and platforms around tanks and basins. Construction work uses a different threshold.

Question 12Safety Practices and Hazard Awareness

Employees are working in an excavation for a sewer line. At what depth must a protective system such as sloping or shoring be provided?

  1. 5 feet Correct answer.
  2. 4 feet
  3. 3 feet
  4. 2 feet

Explanation

OSHA requires a protective system for trenches 5 feet deep or more unless the excavation is entirely in stable rock. A competent person must inspect the excavation at least daily and after any change in conditions.

Question 13Safety Practices and Hazard Awareness

An operator collapses in a hot, humid blower building with hot, dry skin and confusion. What should be done first?

  1. Give the worker salt tablets and let the worker rest
  2. Call emergency medical services and begin cooling the worker at once Correct answer.
  3. Return the worker to the crew once sweating stops
  4. Have the worker sit in shade and sip a sports drink

Explanation

Hot, dry skin with confusion indicates heat stroke, a life-threatening emergency. Emergency medical services must be called while aggressive cooling begins immediately.

Question 14Safety Practices and Hazard Awareness

An operator's noise exposure averages 87 dBA over an eight-hour shift. What does OSHA require?

  1. No action until the exposure reaches 100 dBA
  2. The employee be included in a hearing conservation program Correct answer.
  3. The employee be issued respiratory protection for the shift
  4. The employee be removed from the area permanently

Explanation

At an eight-hour time-weighted average of 85 dBA or more, the employer must establish a hearing conservation program including monitoring, audiometric testing, and training. Hearing protection becomes mandatory when exposures reach the higher action level.

Question 15Safety Practices and Hazard Awareness

A hypodermic needle is found lodged in a clogged bar screen. What is the correct practice?

  1. Push the needle through the screen with a gloved hand and keep working
  2. Carry the needle by hand to the first-aid kit
  3. Recap the needle by hand and drop it in the trash
  4. Use tongs or a tool and place the needle in a sharps container Correct answer.

Explanation

Sharps must never be handled by hand; mechanical means are used to pick them up and the item goes directly into a rigid sharps container. Any puncture or exposure is reported and followed by medical evaluation.

Question 16Safety Practices and Hazard Awareness

What must be done with a direct-reading gas meter before each day's use?

  1. It must be bump tested with a known test gas to confirm sensor and alarm response Correct answer.
  2. It must be rinsed with clean water and stored damp
  3. It must be recharged for eight hours before the shift
  4. It must be returned to the manufacturer for recalibration

Explanation

A bump test briefly exposes the sensors to a known gas concentration and verifies that both the reading and the alarm respond. Manufacturer instructions generally require this check before each day's use, with periodic full calibration in addition.

Question 17Safety Practices and Hazard Awareness

Why is an air-purifying respirator unsuitable for entry into a confined space with an unknown atmosphere?

  1. It cannot add oxygen and is prohibited in immediately dangerous atmospheres Correct answer.
  2. It requires a compressed-air cylinder the wearer cannot lift
  3. Its cartridges clog quickly when the air is humid
  4. It removes gases but not airborne particles

Explanation

Air-purifying respirators only filter contaminants out of the air; they cannot supply oxygen and are not permitted in oxygen-deficient or immediately dangerous to life or health atmospheres. An unknown atmosphere must be treated as potentially IDLH until testing proves otherwise.

Question 18Safety Practices and Hazard Awareness

An entrant collapses inside a wet well that tested low in oxygen. What should the attendant do first?

  1. Ventilate for a minute, then climb down the ladder to help
  2. Call for trained rescue help and attempt non-entry retrieval with the tripod and line Correct answer.
  3. Enter with a spare self-contained breathing apparatus and drag the entrant out
  4. Call down to the entrant and wait for a reply before acting

Explanation

The attendant must never enter the space; untrained rescue attempts are a leading cause of multiple fatalities in confined spaces. The correct response is to summon trained rescue and use the retrieval line and tripod for non-entry rescue.

Question 19Safety Practices and Hazard Awareness

A meter reads 23.8 percent oxygen inside a tank that was purged with bottled oxygen. Why is entry refused despite the reading being above normal?

  1. The reading actually shows the tank is oxygen deficient
  2. Oxygen above 23.5 percent sharply increases the risk of fire Correct answer.
  3. The meter is faulty whenever it reads above 21 percent
  4. Oxygen-enriched air is harmful only after several hours of exposure

Explanation

An atmosphere above 23.5 percent oxygen is classified as oxygen enriched, and materials such as clothing and grease ignite and burn far more readily in it. The space must be ventilated with fresh air and re-tested before entry.

Question 20Safety Practices and Hazard Awareness

A combustible gas meter reads 20 percent of the lower explosive limit in a pump room. What action is appropriate?

  1. Stop work, ventilate the space, and find the source of the gas Correct answer.
  2. Wait until the reading passes 50 percent of the lower limit before leaving
  3. Continue working, but post a second operator to watch the meter
  4. Continue working, because 20 percent of the lower limit is far from explosive

Explanation

Common practice sets 10 percent of the lower explosive limit as the action level at which work stops and the space is ventilated. At 20 percent, the room already holds roughly 1 percent methane by volume, since the lower limit for methane is about 5 percent.

Question 21Rules, Regulations, and Administration

What is the maximum term for an NPDES permit issued to a publicly owned treatment works?

  1. Five years Correct answer.
  2. Three years
  3. Ten years
  4. Seven years

Explanation

The Clean Water Act and 40 CFR 122.46 limit NPDES permits to a fixed term not exceeding 5 years. The permit is then reissued or renewed after a new application and review.

Question 22Rules, Regulations, and Administration

A POTW's NPDES permit expires on December 31. At least how many days before that date must the facility submit a complete renewal application?

  1. 270 days
  2. 90 days
  3. 180 days Correct answer.
  4. 365 days

Explanation

40 CFR 122.21(d) requires an operator to submit a new application at least 180 days before an existing NPDES permit expires. Filing late can affect permit coverage and enforcement status.

Question 23Rules, Regulations, and Administration

Under NPDES regulations, what is the minimum period a permittee must keep monitoring records and copies of reports required by the permit?

  1. 3 years Correct answer.
  2. 1 year
  3. 7 years
  4. 6 months

Explanation

40 CFR 122.41(j)(2) requires records of monitoring and copies of required reports to be retained for at least 3 years from the date of the sample, measurement, report, or application. A permit may require a longer period.

Question 24Rules, Regulations, and Administration

Federal secondary treatment standards for POTWs set monthly average effluent limits for BOD5 and TSS at which levels?

  1. 30/30 mg/L with at least 85% removal Correct answer.
  2. 15/15 mg/L with 95% removal
  3. 20/20 mg/L with 90% removal
  4. 45/45 mg/L with no removal requirement

Explanation

40 CFR Part 133 establishes secondary treatment limits of 30 mg/L for BOD5 and 30 mg/L for TSS as monthly averages, with at least 85% removal of each. Weekly averages and pH limits also apply.

Question 25Rules, Regulations, and Administration

The NPDES permit program that regulates wastewater discharges is established under which federal law?

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

Explanation

The Clean Water Act authorizes EPA and approved states to issue NPDES permits for discharges of pollutants to waters of the United States. The Safe Drinking Water Act addresses public water systems, not wastewater discharges.

Question 26Rules, Regulations, and Administration

A permittee discovers a noncompliance that may endanger human health or the environment. Within what time must the permittee orally notify the permitting authority?

  1. 5 days
  2. 30 days
  3. 24 hours Correct answer.
  4. 2 hours

Explanation

40 CFR 122.41(l)(6)(i) requires oral notice as soon as possible, but no later than 24 hours after the permittee becomes aware of the noncompliance. A written report is generally required within 5 days unless the authority waives it.

Question 27Rules, Regulations, and Administration

To claim an affirmative defense for an upset, a permittee must show that the upset was:

  1. caused by an unusual influent flow increase that the operator did not anticipate or record in the logbook
  2. unintentional and not caused by careless operation, inadequate maintenance, or inadequate facilities Correct answer.
  3. reported to the local newspaper within 24 hours of the discharge event
  4. documented only in the annual report rather than in the daily operating record kept at the plant

Explanation

An upset defense requires the permittee to show that the upset was unintentional, the facility was properly operated and maintained, and the upset was not caused by careless or improper operation, inadequate maintenance, or inadequate facilities. Notice and reporting conditions also apply.

Question 28Rules, Regulations, and Administration

Generally, a POTW is required to develop an approved pretreatment program when its design flow exceeds which threshold and it receives pollutants from industrial users?

  1. 10 MGD regardless of the type of industrial users
  2. 1 MGD and it has at least one industrial user
  3. 3 MGD and it treats wastewater from more than one municipality
  4. 5 MGD and industrial users discharge pollutants to it Correct answer.

Explanation

40 CFR 403.8(a) uses a 5 MGD design-flow threshold for POTWs that receive pollutants from industrial users which pass through or interfere with treatment. Smaller POTWs may also be required to develop a program when categorical industrial users discharge to them.

Question 29Rules, Regulations, and Administration

Categorical pretreatment standards regulate industrial users at what point in the process?

  1. At the POTW outfall after secondary treatment is complete
  2. Only when the POTW's local limit is less stringent than the federal standard
  3. At the POTW headworks after all waste streams have been combined
  4. At the end of the industrial process, before any dilution with other waste streams Correct answer.

Explanation

Categorical standards are technology-based limits that apply at the end of the industrial process before the waste stream is diluted. Dilution is not an acceptable substitute for treatment.

Question 30Rules, Regulations, and Administration

Under 40 CFR Part 503, Class A biosolids may meet the fecal coliform alternative when the density is less than:

  1. 100 MPN per gram of dry solids
  2. 1,000 MPN per gram of dry solids Correct answer.
  3. 10,000 MPN per gram of dry solids
  4. 1 MPN per gram of dry solids

Explanation

Class A pathogen reduction under Part 503 allows a fecal coliform density below 1,000 MPN per gram of total solids on a dry-weight basis. The alternative is Salmonella below 3 MPN per 4 grams of dry solids.

Question 31Rules, Regulations, and Administration

What is the main purpose of a slug discharge control plan in a POTW pretreatment program?

  1. To identify every industrial user that needs an individual categorical permit
  2. To document the annual budget for pretreatment staffing and laboratory testing
  3. To reduce the volume of stormwater entering the sanitary sewer during heavy rain
  4. To prevent accidental discharges that could interfere with or pass through the treatment plant Correct answer.

Explanation

A slug control plan is intended to prevent accidental or unauthorized discharges of pollutants that could cause interference, pass-through, or harm to the POTW. It includes controls such as inspections, monitoring, and response procedures.

Question 32Rules, Regulations, and Administration

A whole effluent toxicity (WET) test is designed to:

  1. identify the specific chemical compound responsible for toxicity in the effluent
  2. measure only the chlorine residual remaining in the effluent after disinfection
  3. determine the BOD5 concentration of the effluent sample
  4. measure the combined toxic effect of the effluent on test organisms Correct answer.

Explanation

WET tests expose aquatic test organisms to the whole effluent and measure effects such as survival, growth, or reproduction. The test evaluates the combined effect of all constituents, not a single chemical.

Question 33Rules, Regulations, and Administration

In NPDES regulations, a bypass is best defined as:

  1. the removal of sludge from a treatment unit for disposal
  2. the discharge of effluent that exceeds a permit limit
  3. the intentional diversion of waste from part of the treatment works Correct answer.
  4. the unintentional overflow of untreated sewage from a manhole onto the ground

Explanation

40 CFR 122.41(m)(1) defines bypass as the intentional diversion of waste streams from any portion of a treatment facility. Bypasses are restricted and must meet notice and reporting requirements.

Question 34Rules, Regulations, and Administration

A total maximum daily load (TMDL) for an impaired waterbody includes which components?

  1. only the permitted point-source discharges located in the watershed above the impaired segment
  2. the design flow and treatment efficiency of each municipal wastewater plant in the basin
  3. the total annual permit fees that the state collects from all dischargers in the watershed
  4. waste load allocations, load allocations, a margin of safety, and background Correct answer.

Explanation

A TMDL is the maximum amount of a pollutant that a waterbody can receive and still meet water quality standards. It is allocated among point sources (waste load allocations), nonpoint sources (load allocations), natural background, and a margin of safety.

Question 35Rules, Regulations, and Administration

Under 40 CFR Part 503, the annual report for land application of sewage sludge is due by which date?

  1. January 31
  2. December 31
  3. March 1
  4. February 19 Correct answer.

Explanation

Part 503 requires the person who prepares sewage sludge for land application to submit an annual report to the permitting authority by February 19. The report documents quantities, site information, and compliance with management practices.

Question 36Rules, Regulations, and Administration

For an anticipated bypass that is to be covered by an affirmative defense, the permittee must notify the permitting authority at least how many days before the bypass, if possible?

  1. 10 days Correct answer.
  2. 5 days
  3. 2 days
  4. 7 days

Explanation

40 CFR 122.41(m)(4) requires notice of an anticipated bypass at least 10 days before the bypass, if possible, as a condition of the affirmative defense. If advance notice is not possible, the permittee must notify orally within 24 hours and follow up in writing.

Question 37Collection Systems and Influent Flow

What is the commonly accepted minimum self-cleaning velocity for a gravity sanitary sewer carrying domestic wastewater?

  1. 4 ft/s
  2. 6 ft/s
  3. 2 ft/s Correct answer.
  4. 1 ft/s

Explanation

Gravity sanitary sewers are designed to produce a velocity of at least 2 ft/s (about 0.6 m/s) at design flow. At this velocity, grit and organic solids remain suspended and are carried downstream instead of depositing in the pipe. Lower velocities allow solids to settle and cause stoppages.

Question 38Collection Systems and Influent Flow

Groundwater that seeps into a sanitary sewer through cracked pipe joints and defective manholes is best described as which of the following?

  1. Infiltration Correct answer.
  2. Inflow
  3. Exfiltration
  4. Backflow

Explanation

Infiltration is groundwater that enters the sewer system through defects such as cracked pipe, open joints, and deteriorated manholes. It is distinguished from inflow, which is surface water or storm water that enters directly through connections such as roof drains and catch basins. Infiltration rises and falls with the groundwater table, so it is often seen as a steady wet-weather and seasonal base increase.

Question 39Collection Systems and Influent Flow

Which device is commonly installed at the headworks of a treatment plant to measure the flow of wastewater in an open channel?

  1. Parshall flume Correct answer.
  2. Magnetic flow meter
  3. Orifice plate
  4. Rotameter

Explanation

A Parshall flume is a fixed-throat open-channel structure in which flow rate is determined from the depth of water at a specified measuring point. Because it has no moving parts and passes solids readily, it is widely used at plant headworks. The depth reading is converted to flow using the flume's published rating table.

Question 40Collection Systems and Influent Flow

What is the primary purpose of a manhole in a gravity sewer system?

  1. Continuous venting of sewer gases
  2. Crew access for cleaning and inspection Correct answer.
  3. Measurement of wastewater velocity
  4. Storage of peak wastewater flow during storms

Explanation

Manholes are placed at changes in direction, grade, pipe size, and at intervals along straight runs so that crews can enter or reach the sewer for cleaning, inspection, and repair. They also provide ventilation and a point to rod or jet the line. Their design is based on access, not on flow storage or velocity measurement.

Question 41Collection Systems and Influent Flow

Where in a conventional treatment plant is grit normally removed?

  1. At the headworks, before primary tanks Correct answer.
  2. In the aeration basin
  3. In the secondary clarifier after aeration
  4. In the anaerobic digester

Explanation

Grit is heavy, abrasive material such as sand and eggshells that must be removed early so it does not wear pumps, clog pipes, or accumulate in tanks. Grit removal is therefore placed at the headworks, ahead of primary treatment and downstream of the bar screens. Removing it later would allow abrasion and deposits throughout the plant.

Question 42Collection Systems and Influent Flow

A sewer line drops 2.5 feet over a horizontal run of 500 feet. What is its slope expressed as a percent grade?

  1. 5.0%
  2. 0.05%
  3. 0.50% Correct answer.
  4. 0.25%

Explanation

Percent grade equals the fall divided by the run, multiplied by 100. Here, 2.5 ft divided by 500 ft equals 0.005, which is 0.50 percent. Expressing slope as a decimal fraction (0.005 ft/ft) is equivalent and is also used in the Manning equation.

Question 43Collection Systems and Influent Flow

A community generates an average daily flow of 1.2 MGD, and the design peaking factor is 2.5. What peak flow must the collection system and headworks be able to handle?

  1. 1.45 MGD
  2. 0.48 MGD
  3. 2.4 MGD
  4. 3.0 MGD Correct answer.

Explanation

Peak flow is found by multiplying the average daily flow by the peaking factor: 1.2 MGD times 2.5 equals 3.0 MGD. Collection mains and headworks must be sized for this peak, since hydraulic capacity is governed by the highest flows, not averages. Peaking factors are larger for small communities and decrease as population grows.

Question 44Collection Systems and Influent Flow

Which condition is the most common cause of a sewage pump in a wet well short-cycling?

  1. Float on and off setpoints are too close Correct answer.
  2. The wet well working volume is far larger than needed
  3. The impeller is badly worn
  4. The check valve is stuck open

Explanation

The volume pumped per cycle equals the wet well surface area multiplied by the vertical distance between the pump-on and pump-off levels. If those levels are set close together, only a small volume is pumped each cycle, so the pump starts and stops rapidly. Short cycling overheats motors and shortens the life of starters and pumps.

Question 45Collection Systems and Influent Flow

Hydrogen sulfide in a gravity sewer is most damaging to concrete pipe because it does which of the following?

  1. Causes the pipe invert to swell and crack badly
  2. Forms sulfuric acid at the pipe crown Correct answer.
  3. Softens the pipe bedding material
  4. Reacts with grit to form hard scale

Explanation

Hydrogen sulfide escapes into the headspace and is converted by bacteria on moist concrete surfaces to sulfuric acid. The acid attacks the concrete above the waterline, so the crown and upper walls of the pipe are eaten away. This corrosion is worst in warm, slow-moving, septic sewage.

Question 46Collection Systems and Influent Flow

In a combined sewer system, a combined sewer overflow occurs under which condition?

  1. Rainfall plus sewage exceeds interceptor capacity Correct answer.
  2. Groundwater leaks in much faster than the pumps can handle it
  3. Sewage is stronger than the plant can treat
  4. A force main loses pressure and drains back

Explanation

A combined sewer carries both sanitary sewage and storm water in one pipe. When rain adds enough flow that the total exceeds the capacity of the interceptor sewer or treatment plant, the excess is discharged at a designed overflow point. Infiltration alone and strength of the sewage do not govern overflow occurrence.

Question 47Collection Systems and Influent Flow

Why is flow-proportional composite sampling preferred over time-proportional sampling for characterizing plant influent?

  1. It removes the need to refrigerate any of the collected samples
  2. It requires far fewer aliquots per day
  3. It measures BOD directly in the field
  4. Aliquot size follows flow, so the composite represents mass load Correct answer.

Explanation

In flow-proportional sampling, the volume of each aliquot is tied to the flow passing at that moment, so high-flow periods contribute proportionally more sample. The resulting composite represents the total mass of pollutant delivered, which is what load calculations and permit reporting require. Time-proportional composites over-weight low-flow periods.

Question 48Collection Systems and Influent Flow

Where should an air release valve be installed on a wastewater force main?

  1. At low points of the profile
  2. Only at the pump discharge
  3. At every joint along the line
  4. At high points of the profile Correct answer.

Explanation

Air entrained or released from wastewater collects at the highest points of a force main profile. If it is not vented, it can air-bind the line, reduce capacity, raise pumping head, and cause surge when it suddenly moves. Air release valves are therefore placed at high points, with combination air-and-vacuum valves where column separation is a concern.

Question 49Collection Systems and Influent Flow

Smoke testing of a sanitary sewer is primarily performed to do which of the following?

  1. Locate inflow sources and illegal connections Correct answer.
  2. Measure flow velocity in the line
  3. Measure how much groundwater leaks into the line
  4. Assess the structural condition of the wall

Explanation

Smoke is blown into a section of sewer and escapes wherever there is a direct connection or defect open to the surface, such as roof drains, area drains, and broken laterals. Observers on the surface then map where smoke appears, identifying sources of clear-water inflow. The test is qualitative and does not quantify leakage or evaluate wall condition.

Question 50Collection Systems and Influent Flow

For a circular pipe flowing full at the same slope and roughness, approximately how much does capacity increase if the diameter is doubled?

  1. About 4 times
  2. About 2 times
  3. About 6.3 times Correct answer.
  4. About 16 times

Explanation

In the Manning equation, area varies with the square of diameter and hydraulic radius varies with diameter, so capacity of a full circular pipe varies as diameter to the 8/3 power. Doubling the diameter gives 2 raised to the 8/3, which is about 6.3. The extra gain beyond the 4-fold area increase comes from the larger hydraulic radius.