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

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Question 1Collection System Operation and Maintenance

During high-pressure jetting of a gravity sewer, from which manhole is the nozzle normally inserted, and in which direction is it fed?

  1. Upstream manhole, fed downstream with flow
  2. Nearest manhole, worked outward in both directions
  3. Downstream manhole, fed upstream against flow Correct answer.
  4. Either manhole, with the nozzle always pointed down

Explanation

Jetting normally starts at the downstream manhole and the nozzle is fed upstream so the returning water carries loosened debris back to the manned manhole for removal. Working upstream also lets the crew follow the hose into the pipe rather than being pushed by the debris.

Question 2Collection System Operation and Maintenance

Smoke testing of a sanitary sewer is primarily performed to

  1. check pipe deflection under traffic loading
  2. find inflow sources such as roof leaders Correct answer.
  3. determine the slope of the gravity main
  4. measure dry-weather flow depth in the pipe

Explanation

Smoke is blown into the sewer and escapes wherever there is a direct connection or an opening to the surface, revealing roof downspouts, yard drains, broken pipes and missing cleanout caps. The smoke itself is harmless and does not measure hydraulic or structural properties.

Question 3Collection System Operation and Maintenance

Before an operator enters a sanitary sewer manhole, the minimum required action is to

  1. wait for a calm, dry day so the gases can disperse
  2. test the atmosphere and station an attendant outside Correct answer.
  3. flush the manhole with clean water until the odor is gone
  4. prop the cover open for a few minutes and then descend quickly

Explanation

Sewer manholes are permit-required confined spaces, so entry requires atmospheric testing before and during entry, a retrieval system, and an attendant stationed outside who does not enter. Odor is not a reliable indicator of safe air.

Question 4Collection System Operation and Maintenance

A roof downspout that is plumbed directly into a sanitary sewer manhole is an example of

  1. inflow from a direct stormwater connection Correct answer.
  2. infiltration from groundwater
  3. surcharge from a downstream restriction
  4. exfiltration from a cracked pipe

Explanation

Inflow is stormwater that enters the sanitary sewer directly through connections such as roof leaders, yard drains and area drains. Infiltration, by contrast, seeps in through defective joints, cracks and manhole walls.

Question 5Collection System Operation and Maintenance

In a gravity sewer, the most severe sulfuric-acid attack caused by hydrogen sulfide typically occurs

  1. in the middle of the pipe wall at the spring line
  2. evenly around the entire circumference
  3. at the invert, below the water line
  4. at the crown, above the water line Correct answer.

Explanation

Hydrogen sulfide released from the wastewater collects in the moist headspace, where bacteria convert it to sulfuric acid on the damp surface above the water line. As a result, the crown of concrete and metal pipe corrodes first.

Question 6Collection System Operation and Maintenance

When excavating a trench in an unpaved area, excavated spoil should be placed

  1. directly against the trench edge to build a windrow
  2. in the trench, behind the pipe, as backfill
  3. back from the edge so it cannot fall in Correct answer.
  4. on the far side of any nearby guardrail

Explanation

Spoil, tools and materials must be kept back from the trench edge, commonly at least 2 feet, so they neither overload the sides nor drop onto workers below. Staging backfill inside the trench during excavation blocks access and egress.

Question 7Collection System Operation and Maintenance

On a lift station pump discharge, the check valve is installed mainly to

  1. throttle the pump to the desired flow rate
  2. trap rags and solids before they reach the pump
  3. relieve excessive pressure in the force main
  4. keep flow from running back into the wet well Correct answer.

Explanation

A check valve closes when the pump stops so the column of wastewater in the force main does not drain back into the wet well or spin the pump backwards. Flow control is handled by a separate throttling valve.

Question 8Collection System Operation and Maintenance

A lift station high-level alarm activates. What is the most appropriate first action for the operator on call?

  1. Reset the alarm and wait to see if it repeats
  2. Close the discharge gate valve to take the pumps off line
  3. Turn off the alarm and log it at the end of the shift
  4. Check the station and find the cause Correct answer.

Explanation

A high-level alarm warns that a station may overflow, so the operator must reach the station, verify the level and identify the cause, such as pump failure, power loss, a plugged discharge or faulty controls. Corrective action is taken before the wet well spills.

Question 9Collection System Operation and Maintenance

At high concentrations, hydrogen sulfide is especially dangerous in sewers because it

  1. is heavier than air and cannot be ventilated out
  2. has a sweet smell that operators mistake for methane
  3. causes the pipe walls to expand and crack
  4. deadens smell at levels that can still be fatal Correct answer.

Explanation

Hydrogen sulfide causes olfactory fatigue, so workers stop detecting the rotten-egg odor while the gas is still at hazardous concentrations. Monitoring with a calibrated instrument, not the nose, is required.

Question 10Collection System Operation and Maintenance

Before running a CCTV inspection camera through a gravity main, the crew should

  1. Clean the pipe and lower the flow for a clear view Correct answer.
  2. Raise the flow by opening an upstream diversion
  3. Remove all manhole steps ahead of the camera run
  4. Fill the pipe with clean water to lubricate the camera

Explanation

Debris, grease and standing flow hide defects, so a main is normally cleaned and the flow reduced by damming or diversion before inspection. The camera then sees the full pipe wall and can be moved at a controlled speed.

Question 11Collection System Operation and Maintenance

Where along a force main is an air release valve normally installed?

  1. Every 50 feet regardless of profile
  2. At high points, where air pocketing occurs Correct answer.
  3. At the lowest point, where solids settle
  4. Just downstream of the pump check valve

Explanation

Air entrained or released from wastewater collects at the high points of the force main profile, forming pockets that increase head loss, aggravate surge and reduce capacity. Air release valves are placed there to bleed that air off.

Question 12Collection System Operation and Maintenance

A drop manhole is used where

  1. groundwater is too high to set a normal manhole base
  2. a steep incoming sewer would plunge into the manhole Correct answer.
  3. a large trunk line must be vented to the surface
  4. a gravity main must reverse direction in a short distance

Explanation

When an incoming sewer is too steep for the outlet, a drop connection carries the flow down the side of the manhole to the outlet elevation. This reduces turbulence, splashing, corrosion and odor release caused by a free-falling stream.

Question 13Collection System Operation and Maintenance

Roots that have intruded into a sewer joint are most commonly removed by

  1. Cutting with a mechanical tool or jetting nozzle Correct answer.
  2. Raising the flow velocity in the reach by opening a diversion
  3. Flushing with low-pressure water for several days
  4. Pouring a strong caustic solution into the manhole

Explanation

Roots are cut out mechanically with a root saw, chain flail or root-cutting nozzle on a jetter, then often controlled chemically with a foamed herbicide to limit regrowth. Cutting alone restores capacity immediately.

Question 14Collection System Operation and Maintenance

Heavy sand and grit in a gravity line are usually removed with

  1. A dye test followed by flushing
  2. A smoke blower at the upstream manhole
  3. A bucket machine working from the manholes Correct answer.
  4. A foam swab pulled through the pipe

Explanation

A bucket machine scoops heavy material from the line and hauls it to the surface, and jetters with the proper nozzle flush sand to a manhole for removal. Light tools and testing methods do not move a bed of grit.

Question 15Collection System Operation and Maintenance

During a routine manhole inspection, a corroded, loose frame is best addressed by

  1. Noting it for the next five-year inspection cycle
  2. Reporting it for frame and cover repair Correct answer.
  3. Packing the gap with mortar and painting the frame
  4. Temporarily covering the manhole with a steel plate

Explanation

A loose, deteriorated frame is both a traffic and a structural hazard and can admit surface water, so it is documented and scheduled for repair or replacement. Inspection findings that affect safety or inflow are not deferred.

Question 16Collection System Operation and Maintenance

At a gravity sewer manhole that produces nuisance odors, activated carbon is used to

  1. Raise the pH of the wastewater to stop sulfide formation
  2. Add oxygen to the sewage so sulfides are oxidized
  3. Mask the odor with a stronger, more pleasant fragrance
  4. Adsorb odorous compounds from the air stream Correct answer.

Explanation

Carbon adsorbs odorous gases such as hydrogen sulfide from the air pulled out of the manhole before it is discharged. Liquid-phase methods, such as oxygen or nitrate addition and pH control, treat the wastewater itself.

Question 17Collection System Operation and Maintenance

When a sanitary sewer overflow is discovered, the operator's first priority is to

  1. Notify the media about the discharge volume
  2. Stop and contain the spill Correct answer.
  3. Complete the written report for the regulator
  4. Photograph the spill from every angle

Explanation

Immediate action is to stop the flow and contain the spill so it does not reach surface water, ditches or the public. Notification, documentation and cleanup follow once the discharge is controlled.

Question 18Collection System Operation and Maintenance

Gravity sanitary sewers are designed with a minimum velocity near 2 ft/s mainly to

  1. Prevent solids from settling and depositing Correct answer.
  2. Limit the formation of hydrogen sulfide
  3. Protect the pipe from abrasion by grit
  4. Keep the pipe crown from corroding

Explanation

About 2 ft/s (0.6 m/s) is the self-cleansing velocity that keeps suspended solids moving so they do not settle and form blockages. High velocities, by contrast, are what cause abrasion and release of dissolved gases.

Question 19Collection System Operation and Maintenance

Pigging a force main is performed to

  1. Increase the pressure rating of the pipeline
  2. Measure the wastewater flow rate in the main
  3. Remove grease and debris from the wall Correct answer.
  4. Test the pipe for leaks with pressurized air

Explanation

A pig is driven through the force main by the flow or by pumped water and scrapes accumulated grease, grit and sediment from the pipe wall, restoring capacity. Pigs are also used for dewatering and filling, but cleaning is the common maintenance purpose.

Question 20Collection System Operation and Maintenance

A full-flowing gravity sewer carries flow at velocity V on slope S. If the slope is increased to 4S while the pipe and roughness stay the same, the new velocity is approximately

  1. 16V
  2. 2V Correct answer.
  3. 4V
  4. 0.5V

Explanation

Manning's equation makes velocity proportional to the square root of slope, so the new velocity is V times the square root of 4, which is 2V. The area and hydraulic radius do not change in full flow.

Question 21Collection System Operation and Maintenance

Wastewater held for long periods in a force main most commonly leads to

  1. Septic conditions and sulfide formation Correct answer.
  2. Increased dissolved oxygen and a sweeter discharge
  3. Lower head loss through the pipeline
  4. Reduced grease buildup on the pipe wall

Explanation

Long detention in a full force main consumes oxygen and lets anaerobic sulfate-reducing bacteria produce sulfide. When the flow discharges into a gravity sewer, hydrogen sulfide is released and forms sulfuric acid on the crown.

Question 22Collection System Operation and Maintenance

A lift station pump makes a rattling, gravel-like noise and loses capacity. The most likely cause is

  1. The motor is running at half speed
  2. Cavitation from a restricted or starved suction Correct answer.
  3. The wet well level is above the high-level float
  4. The check valve is stuck open

Explanation

Cavitation occurs when absolute pressure at the impeller eye drops below the vapor pressure of the liquid, so bubbles collapse against the impeller and produce noise, vibration and erosion with a loss of head. A plugged intake, air leak or low wet well level are common causes.

Question 23Collection System Operation and Maintenance

In a deep, undisturbed manhole, which gas would tend to be found at the greatest concentration near the bottom?

  1. Carbon monoxide, which is about as heavy as air
  2. Nitrogen, because it is completely inert
  3. Hydrogen sulfide, which is heavier than air Correct answer.
  4. Methane, because it is lighter than air

Explanation

Hydrogen sulfide has a molecular weight of about 34, so it is denser than air and collects in low-lying areas such as wet wells, vaults and the bottoms of deep manholes. Methane, being much lighter than air, rises and gathers under covers.

Question 24Collection System Operation and Maintenance

A pump at a lift station starts and stops every 30 seconds while the inflow rate is steady. The most likely cause is

  1. The discharge pressure is lower than design
  2. The pump impeller is worn and delivers much less flow
  3. The off level is set too close to the on level Correct answer.
  4. The inflow to the station has increased sharply

Explanation

Short cycling with steady inflow means the working volume between start and stop levels is too small, either because the float settings are too close together or because a leaking check valve drains the wet well back. Excess cycling overheats motors and shortens pump life.

Question 25Collection System Operation and Maintenance

Flow in a gravity sewer is being measured continuously at a temporary site. A flume is often preferred to a sharp-crested weir because a flume

  1. Is unaffected by the velocity of approach
  2. Passes solids and needs less upstream ponding Correct answer.
  3. Measures depth without any primary device
  4. Can be installed only in pipes smaller than 12 inches

Explanation

A flume accelerates flow through a shaped throat, so it operates with a small head loss and lets solids and grit pass, which suits raw wastewater. A sharp-crested weir needs a quiet pool upstream and tends to collect debris on the crest.

Question 26Collection System Operation and Maintenance

Before entering a sewer manhole, an operator must first:

  1. Place a traffic cone and proceed with the inspection
  2. Test oxygen, flammable gas, and hydrogen sulfide Correct answer.
  3. Lower a worker on a rope before testing the air
  4. Open the cover and enter as soon as the space is ventilated

Explanation

Confined-space entry requires atmospheric testing before anyone enters. Ventilation may be part of preparation, but it does not replace testing for oxygen, flammable gas, and hydrogen sulfide.

Question 27Collection System Operation and Maintenance

Before removing a jammed rag from a lift station pump, the operator should:

  1. De-energize and lock out the pump motor Correct answer.
  2. Reverse the pump rotation to clear the rag
  3. Notify the laboratory that the pump is offline
  4. Close the discharge valve and open the wet well hatch

Explanation

The pump must be isolated from all energy sources before anyone reaches into it. A pump can start automatically unless the motor is locked out, and closing a valve alone does not remove that hazard.

Question 28Collection System Operation and Maintenance

A gravity main must be taken out of service for repair while flow continues. The bypass pump should be sized to:

  1. Carry only the sanitary flow from upstream homes
  2. Handle the peak flow reaching the section Correct answer.
  3. Match only the average daily dry-weather flow
  4. Run at the highest pressure the pump can produce

Explanation

Bypass capacity must be based on the maximum flow that can reach the work section during the repair, including peak wet-weather flow and inflow. Sizing to average or sanitary-only flow can lead to overflows.

Question 29Collection System Operation and Maintenance

Smoke testing of a sanitary sewer is primarily used to:

  1. Determine the slope of the sewer main
  2. Remove grease and roots from the pipe
  3. Find inflow and infiltration sources Correct answer.
  4. Measure dry-weather flow in the sewer line

Explanation

Smoke testing reveals illegal connections and defects by showing where smoke escapes from the sewer system. It is not a cleaning method and does not measure flow or slope.

Question 30Collection System Operation and Maintenance

A dye test at a residential foundation drain is used to determine whether:

  1. The flow meter is calibrated correctly
  2. The drain is tied to the sewer Correct answer.
  3. The pipe contains infiltrating groundwater
  4. The sewer has adequate slope for flow

Explanation

Dye is placed in a foundation drain, roof drain, or other suspected source and observed in the sanitary sewer. If dye appears, a direct connection is confirmed.

Question 31Collection System Operation and Maintenance

The most effective way to reduce grease blockages in a collection system is to:

  1. Add chlorine tablets to the gravity sewer
  2. Require grease interceptors at food businesses Correct answer.
  3. Flush the lines with larger volumes of water
  4. Increase the slope of the collection main

Explanation

Keeping grease out of the sewer at the source is the primary control strategy. Grease interceptors at food service establishments remove fats, oils, and grease before they reach the collection system.

Question 32Collection System Operation and Maintenance

Foaming root control applied inside a sewer line works mainly to:

  1. Dissolve concrete around the pipe joints
  2. Neutralize hydrogen sulfide in the line
  3. Lubricate the pipe to increase velocity
  4. Kill roots and inhibit regrowth Correct answer.

Explanation

Root-control foam places a contact herbicide against roots and pipe surfaces where roots enter. It kills the roots and can inhibit new growth for a period, but follow-up cleaning may still be needed.

Question 33Collection System Operation and Maintenance

Concrete gravity sewers above the waterline often corrode because hydrogen sulfide is converted to:

  1. Methane gas
  2. Sulfuric acid Correct answer.
  3. Nitric acid
  4. Carbon monoxide

Explanation

Hydrogen sulfide in the sewer atmosphere is oxidized by bacteria on moist concrete surfaces to sulfuric acid. The acid attacks concrete and metal above the flow line, where condensation occurs.

Question 34Collection System Operation and Maintenance

A lift station pump is leaking steadily from the seal area while running. The operator should:

  1. Ignore the leak because seal leakage is normal
  2. Add grease to the wet well to lubricate the seal
  3. Schedule the pump for seal repair Correct answer.
  4. Tighten the packing until the leak stops completely

Explanation

A steady leak at a mechanical seal indicates wear or damage and should be repaired before it worsens. Packing is different and is normally allowed a slight drip, but a mechanical seal should not leak steadily.

Question 35Collection System Operation and Maintenance

Rags and stringy material wrap around a pump impeller. The most likely result is:

  1. Cleaner discharge and lower odor
  2. Reduced capacity and vibration Correct answer.
  3. Lower wet well level and longer run time
  4. Higher discharge pressure and lower current

Explanation

Material wrapped around an impeller unbalances the rotating assembly and blocks flow passages. This typically reduces capacity and causes vibration, and it can eventually overload the motor.

Question 36Collection System Operation and Maintenance

The check valve on a lift station discharge has failed open. What condition does this allow?

  1. Air binding in the wet well
  2. A completely blocked discharge line
  3. Backflow through the idle pump Correct answer.
  4. Loss of pump prime on a submersible pump

Explanation

A check valve prevents flow from reversing through a pump when it stops. If it fails open, water from the force main can run backward through the idle pump and back into the wet well.

Question 37Collection System Operation and Maintenance

Periodic exercising of gate valves in a collection system is done mainly to:

  1. Prevent valves from seizing Correct answer.
  2. Measure the volume of sewage conveyed
  3. Reduce hydrogen sulfide in the sewer
  4. Increase the flow capacity of the main

Explanation

Valves that are never operated can corrode, scale, or become obstructed and then fail when needed. Exercising confirms that the valve moves freely and remains operable.

Question 38Collection System Operation and Maintenance

Grease and grit accumulate in a lift station wet well. If not removed, the most likely consequence is:

  1. Pump clogging and lost storage capacity Correct answer.
  2. Higher dissolved oxygen in the wastewater
  3. Increased sewer slope and higher velocity
  4. Lower hydrogen sulfide production

Explanation

Solids and grease reduce the usable volume of the wet well and can be drawn into the pumps. This can clog impellers and cause frequent pump problems and odors.

Question 39Collection System Operation and Maintenance

A V-notch weir measures flow by relating flow rate to:

  1. The depth of water above the notch Correct answer.
  2. The pressure inside the pipe
  3. The slope of the channel bottom
  4. The velocity of flow through the pipe

Explanation

For a V-notch weir, flow is calculated from the head, or depth of water, upstream of the notch. The relationship is established by the weir geometry and calibration.

Question 40Collection System Operation and Maintenance

When setting up a work zone on a public street, the first consideration should be:

  1. Protect workers and traffic with signs and devices Correct answer.
  2. Use the loudest equipment to warn drivers
  3. Park the truck as close to the manhole as possible
  4. Finish the work quickly to reduce exposure time

Explanation

Traffic control must be established before work begins so that workers and the public are protected. Proper signs, cones, barricades, and high-visibility clothing are part of that setup.

Question 41Collection System Operation and Maintenance

Before excavating for a sewer repair, the crew should:

  1. Assume utilities are deeper than the sewer
  2. Use hand tools only for the entire excavation
  3. Call the one-call utility locate service Correct answer.
  4. Begin digging until utilities are uncovered

Explanation

Underground utilities must be located and marked before excavation to prevent damage and injury. The one-call service coordinates locating of gas, electric, water, and other buried lines.

Question 42Collection System Operation and Maintenance

A trench in unstable soil must be shored or sloped because:

  1. It protects workers from cave-ins Correct answer.
  2. It speeds up the backfill process
  3. It improves flow through the new pipe
  4. It reduces groundwater infiltration

Explanation

Trench protective systems are required to prevent soil from collapsing onto workers. Shoring, sloping, or shielding addresses the cave-in hazard, not pipeline performance.

Question 43Collection System Operation and Maintenance

A missing or damaged manhole cover should be:

  1. Paint the frame bright orange
  2. Replace or barricade it immediately Correct answer.
  3. Cover it with a sheet of plywood
  4. Left open so flow can be observed

Explanation

An open manhole is a serious fall and traffic hazard and can allow debris or stormwater to enter the sewer. It should be barricaded immediately and the cover replaced or repaired.

Question 44Collection System Operation and Maintenance

During a heavy rain, a sewer flow meter shows a sharp increase within minutes. This most likely indicates:

  1. Direct stormwater inflow Correct answer.
  2. Delayed infiltration through pipe joints
  3. Normal dry-weather wastewater flow
  4. Groundwater seepage into the sewer

Explanation

A rapid rise soon after rainfall is characteristic of direct inflow, such as roof drains, sump pumps, or storm connections. Infiltration tends to respond more slowly as groundwater moves through the soil.

Question 45Collection System Operation and Maintenance

Infiltration in a sanitary sewer is best described as:

  1. Wastewater discharged from homes
  2. Industrial flow from permitted users
  3. Groundwater entering through defects Correct answer.
  4. Storm water from direct roof connections

Explanation

Infiltration is groundwater that enters the sewer through cracks, joints, and other defects. It is different from inflow, which enters directly from stormwater sources.

Question 46Collection System Operation and Maintenance

A leaking joint in a gravity sewer is often repaired by:

  1. Adding chlorine to the upstream manhole
  2. Jetting the line at high pressure
  3. Chemical grouting of the joint Correct answer.
  4. Increasing flow velocity in the line

Explanation

Chemical grouting seals the joint by filling voids and stopping groundwater entry. It is a common trenchless repair for leaking joints that are structurally sound.

Question 47Collection System Operation and Maintenance

In a gravity sewer, adding ferrous chloride is used mainly to:

  1. Raise the pH of the wastewater
  2. Precipitate sulfide and reduce odor Correct answer.
  3. Increase dissolved oxygen in the flow
  4. Kill roots at pipe joints

Explanation

Ferrous chloride reacts with dissolved sulfide to form insoluble compounds, reducing hydrogen sulfide release and odor. It is a chemical odor-control method, not a root killer or aeration method.

Question 48Collection System Operation and Maintenance

A portable gas detector used for confined space entry should be:

  1. Stored inside the wet well between shifts
  2. Calibrated and bump-tested before use Correct answer.
  3. Used only after the worker has entered
  4. Shared without cleaning between users

Explanation

Gas detectors must be calibrated and bump-tested to confirm they respond correctly to test gas. A detector that is out of calibration can give a false safe reading.

Question 49Collection System Operation and Maintenance

If a worker collapses inside a manhole, the attendant should:

  1. Enter immediately to pull the worker out
  2. Lower a rope and wait for the worker
  3. Ventilate the space and enter alone
  4. Call for trained rescue help Correct answer.

Explanation

Untrained rescue entry can create multiple victims because the atmosphere may be immediately dangerous. The attendant should summon trained confined-space rescue and follow the rescue plan while maintaining contact.

Question 50Collection System Operation and Maintenance

A lift station has two pumps that alternate. The purpose of alternating lead pump is to:

  1. Equalize wear and runtime Correct answer.
  2. Prevent odors in the wet well
  3. Reduce the wet well operating level
  4. Increase the total station capacity

Explanation

Alternating the lead pump distributes operating hours and starts among pumps. This helps equalize wear and reduces the chance that one pump sits idle for long periods.