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ABC Wastewater Collection Class II study materials
ABC Wastewater Collection Class II study resources

ABC Wastewater Collection Class II practice questions

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Question 1Collection System Operations and Maintenance

What is the primary purpose of a wastewater collection system?

  1. To dispose of treated effluent into receiving waters
  2. To generate biosolids for land application
  3. To treat wastewater to secondary effluent standards
  4. To convey wastewater from sources to the treatment plant Correct answer.

Explanation

A collection system gathers wastewater at its sources and transports it by gravity and pumping to the treatment facility. Treatment and disposal happen at or beyond the plant, not in the collection system itself.

Question 2Collection System Operations and Maintenance

In a sanitary sewer, the flow that occurs during dry weather and comes from homes, businesses, and institutions is called:

  1. Inflow
  2. Storm flow
  3. Base flow Correct answer.
  4. Infiltration

Explanation

Base flow, also called dry-weather flow, is the normal sanitary flow from domestic and commercial sources. Infiltration and inflow are extraneous waters that add to base flow during wet conditions.

Question 3Collection System Operations and Maintenance

A sewer segment is laid with a slope that is too flat. What is the most likely operational consequence?

  1. Increased velocity and scour of the pipe
  2. Reduced structural loading on the pipe
  3. Higher hydrogen sulfide generation from turbulence
  4. Deposition of solids and recurring blockages Correct answer.

Explanation

Flatter slopes produce lower velocities, and when velocity falls below the self-cleansing range, grit and solids settle out. Settled material narrows the pipe and leads to repeated stoppages.

Question 4Collection System Operations and Maintenance

The minimum self-cleansing velocity commonly targeted in sanitary gravity sewers is approximately:

  1. 2 ft/s Correct answer.
  2. 8 ft/s
  3. 15 ft/s
  4. 0.6 ft/s

Explanation

About 2 ft/s (roughly 0.6 m/s) is the conventional target to keep solids moving and limit deposition. Much lower values allow settling, and much higher values risk scour and sulfide release.

Question 5Collection System Operations and Maintenance

A manhole cover that is bolted or otherwise secured is most likely located:

  1. In a residential front yard
  2. In a paved roadway subject to flooding Correct answer.
  3. In a low-traffic easement
  4. In a force main discharge structure

Explanation

Secured or locking covers are used where floodwater or surcharge could dislodge an unsecured cover and let stormwater or debris into the sewer. Roadways prone to ponding are a typical location.

Question 6Collection System Operations and Maintenance

What is the function of a drop manhole in a collection system?

  1. To reduce flow velocity where a steep incoming sewer enters a shallower one Correct answer.
  2. To provide storage volume during peak flows
  3. To allow odor control chemicals to be added
  4. To measure flow with a weir

Explanation

A drop manhole carries the incoming flow down inside the structure so it does not free-fall onto the bench. This controls velocity and reduces turbulence, splash, and hydrogen sulfide release.

Question 7Collection System Operations and Maintenance

During routine inspection, an operator finds a manhole with a strong rotten-egg odor and the atmosphere is suspected to contain hydrogen sulfide. What is the correct first action?

  1. Enter immediately to locate the source
  2. Lower a confined-space gas meter and ventilate before any entry Correct answer.
  3. Pour chlorine solution into the manhole to kill the odor
  4. Close the cover and note the condition for the next scheduled inspection

Explanation

Suspected hydrogen sulfide means a potentially hazardous confined-space atmosphere, so the space must be tested and ventilated before entry. Entry without atmospheric monitoring is a life-threatening error.

Question 8Collection System Operations and Maintenance

Before an operator enters a sewer manhole, the atmosphere must be tested for oxygen, flammables, and:

  1. Hydrogen sulfide Correct answer.
  2. Carbon dioxide only
  3. Methane only
  4. Chlorine residual

Explanation

Confined-space testing covers oxygen level, combustible gas, and specific toxic gases; hydrogen sulfide is the principal toxic gas of concern in sewers. Carbon dioxide and methane are covered by the oxygen and flammables tests.

Question 9Collection System Operations and Maintenance

A crew is using a high-velocity jetter to clear a grease blockage. Which practice best protects the crew and the pipe?

  1. Advance the nozzle slowly and keep hands clear of the hose and opening Correct answer.
  2. Open the manhole fully and stand directly over the line of the hose
  3. Feed the hose while the downstream manhole is unmonitored
  4. Run the jetter at maximum pressure regardless of pipe material

Explanation

Controlled nozzle advance and keeping clear of the hose path reduce the risk of injury from a whipping hose or backflow. Pressure should be matched to pipe condition and material.

Question 10Collection System Operations and Maintenance

Which tool is most appropriate for removing a heavy root mass from a large-diameter sewer line?

  1. A low-pressure flusher
  2. A hand rodder
  3. A vacuum truck alone
  4. A root saw or cutter head on a sectional machine Correct answer.

Explanation

Roots require mechanical cutting, and a root saw or cutter head is designed to shear them from the pipe wall. Rodding, flushing, or vacuuming alone will not remove established roots.

Question 11Collection System Operations and Maintenance

The main purpose of a sewer cleaning program based on scheduled inspection is to:

  1. Prevent blockages and sanitary sewer overflows before they occur Correct answer.
  2. Increase flow velocity in the collection system
  3. Reduce the treatment plant's influent loading
  4. Eliminate the need for future inspections

Explanation

Preventive cleaning removes accumulated material before it can cause a stoppage and overflow. It is scheduled based on observed condition and history rather than waiting for a failure.

Question 12Collection System Operations and Maintenance

A smoke test is being performed on a sanitary sewer. What does smoke emerging from a roof leader or yard drain most likely indicate?

  1. The manhole cover is properly sealed
  2. There is an illegal or improper stormwater connection Correct answer.
  3. The sewer is flowing at design capacity
  4. The pipe has a confirmed structural collapse

Explanation

Smoke testing reveals where stormwater sources connect to the sanitary sewer. Smoke escaping from a roof drain or yard drain indicates that clear-water source is tied into the sanitary system.

Question 13Collection System Operations and Maintenance

Dye testing of a building's plumbing is typically used to:

  1. Estimate the age of the building's plumbing
  2. Determine the pipe's structural condition
  3. Confirm which sewer the building connects to Correct answer.
  4. Measure the sewage flow rate from the building

Explanation

Dye testing traces the path of flow from a fixture or drain to confirm whether it connects to the sanitary or storm system. It is a connectivity check, not a flow or condition measurement.

Question 14Collection System Operations and Maintenance

During a CCTV inspection, the operator observes a pipe joint where the spigot has pulled out of the bell, leaving a visible gap. This defect is best described as:

  1. A root intrusion
  2. A sags
  3. A crown corrosion
  4. A separated joint Correct answer.

Explanation

A separated joint shows the spigot end withdrawn from the bell, creating a gap that admits soil and water. It is a structural/watertightness defect distinct from roots, sags, or corrosion.

Question 15Collection System Operations and Maintenance

Which condition observed on a CCTV inspection most directly threatens the structural integrity of a rigid sewer pipe?

  1. Minor debris in the flow channel
  2. A small offset at a joint
  3. A longitudinal crack through the pipe wall Correct answer.
  4. Light grease coating on the invert

Explanation

A crack running through the wall can allow soil loss, infiltration, and eventual collapse of a rigid pipe. Grease, minor debris, and small offsets are maintenance concerns but do not compromise the wall.

Question 16Collection System Operations and Maintenance

A lift station pump is cycling on and off rapidly during dry weather. Which is the most likely cause?

  1. The force main is oversized
  2. The discharge pressure is too low
  3. The pump is running at design speed
  4. The wet well level controls are set too close together Correct answer.

Explanation

Short cycling usually results from level setpoints that are too close, so the pump starts and stops over a small level change. Adjusting the control differential restores a reasonable cycle time.

Question 17Collection System Operations and Maintenance

The wet well of a lift station is designed with a storage volume below the lead pump start level primarily to:

  1. Limit the number of pump starts per hour Correct answer.
  2. Reduce the discharge head
  3. Provide emergency storage for power failures
  4. Allow for sediment settling

Explanation

The operating volume between start and stop levels sets the cycle time, which controls how often the pump starts. Adequate volume protects the motor and controls from excessive starts.

Question 18Collection System Operations and Maintenance

A pump is operating but delivering little or no flow, and the discharge gauge reads high. Which condition is most consistent with these readings?

  1. A worn impeller
  2. A dry wet well
  3. Cavitation from a low suction level
  4. A closed discharge valve or blockage Correct answer.

Explanation

High discharge pressure with little flow points to a downstream restriction such as a closed valve or blockage. The pump is building head but cannot move water through the line.

Question 19Collection System Operations and Maintenance

A centrifugal pump in a lift station is cavitating. Which action is most appropriate?

  1. Throttle the suction valve further
  2. Increase pump speed to push through the condition
  3. Raise the wet well operating level or reduce suction losses Correct answer.
  4. Close the discharge valve to build pressure

Explanation

Cavitation occurs when suction pressure falls below the liquid's vapor pressure, so restoring suction head or reducing suction losses resolves it. Increasing speed or throttling suction worsens the condition.

Question 20Collection System Operations and Maintenance

An operator notices a persistent hydrogen sulfide odor at a force main discharge manhole. Which control measure addresses the cause rather than masking the odor?

  1. Adding nitrate or oxygen to the force main to prevent septic conditions Correct answer.
  2. Installing a taller vent stack
  3. Increasing the force main detention time
  4. Spraying a fragrance at the manhole

Explanation

Hydrogen sulfide forms when sewage goes septic under anaerobic conditions. Adding nitrate or oxygen keeps conditions aerobic and prevents sulfide generation at the source.

Question 21Collection System Operations and Maintenance

A force main is shut down for repair. Which practice best limits odor and corrosion problems when it is returned to service?

  1. Leave the line full of stagnant sewage during the repair
  2. Drain the line and leave it open to the atmosphere
  3. Flush and refill with fresh sewage before restarting flow Correct answer.
  4. Add chlorine to the line and leave it in place

Explanation

Stagnant sewage in a force main goes septic and generates sulfide, so flushing and refilling with fresh flow before restart limits the problem. Leaving sewage stagnant prolongs anaerobic conditions.

Question 22Collection System Operations and Maintenance

Infiltration into a sewer system is best described as:

  1. Sewage from industrial dischargers
  2. Groundwater entering through cracks, joints, and defective pipe Correct answer.
  3. Flow from a tanker truck dumping at a manhole
  4. Stormwater entering through roof drains and catch basins

Explanation

Infiltration is groundwater or soil moisture that seeps into the sewer through defects such as cracks, bad joints, and deteriorated pipe. Inflow, by contrast, is direct surface water entry.

Question 23Collection System Operations and Maintenance

A rehabilitation crew is lining a deteriorated gravity sewer with a cured-in-place liner. What is a key advantage of this method?

  1. It increases the pipe's inside diameter
  2. It restores a structural wall with minimal excavation Correct answer.
  3. It works only on new pipe
  4. It eliminates the need for any future inspection

Explanation

Cured-in-place lining forms a new structural wall inside the existing pipe, so repairs can be made with little or no excavation. It slightly reduces the inside diameter rather than increasing it.

Question 24Collection System Operations and Maintenance

A crew is installing a new gravity sewer in a trench. Which practice best protects worker safety?

  1. Ladder access only at the far end of the trench
  2. Entry into an unprotected trench for short durations
  3. Trench protective systems installed per the soil conditions and depth Correct answer.
  4. Spoil piles placed at the trench edge to save space

Explanation

Trench protective systems such as shoring, shielding, or sloping must match soil conditions and depth. Spoil kept back from the edge and proper access also reduce the risk of collapse and injury.

Question 25Collection System Operations and Maintenance

An operator is inspecting a sewer line and finds a low spot where wastewater stands between flow events. This condition is best described as:

  1. A bell
  2. A crown
  3. A wye
  4. A sag Correct answer.

Explanation

A sag is a localized low point in the pipe profile where flow slows and solids can collect. It is identified during inspection and often corrected by re-laying or spot repair.

Question 26Collection System Operations and Maintenance

A sewer line is designed to carry a peak flow of 2.5 cubic feet per second (cfs). If the pipe is flowing full at a velocity of 3.0 feet per second, what is the required cross-sectional area of the pipe?

  1. 0.83 square feet Correct answer.
  2. 1.20 square feet
  3. 0.30 square feet
  4. 7.50 square feet

Explanation

Flow rate equals velocity multiplied by cross-sectional area. Rearranging, area equals flow divided by velocity: 2.5 cfs ÷ 3.0 fps = 0.83 square feet.

Question 27Collection System Operations and Maintenance

A gravity sewer line is designed with a minimum slope to maintain a self-cleansing velocity. Which factor most directly determines the minimum slope required?

  1. The soil type surrounding the pipe
  2. The depth of the trench
  3. The number of upstream connections
  4. The pipe diameter and the desired velocity Correct answer.

Explanation

The minimum slope must produce a velocity high enough to keep solids suspended and prevent deposition. That velocity depends on the pipe diameter and the roughness of the pipe material, so the slope is selected based on those factors.

Question 28Collection System Operations and Maintenance

During a routine inspection, an operator finds a manhole cover that is cracked and has a missing bolt. What is the most appropriate immediate action?

  1. Place a traffic cone over the manhole and continue the inspection
  2. Apply a temporary patch with duct tape to prevent water entry
  3. Note the condition in the inspection report and schedule replacement within the year
  4. Replace the cover with a properly fitting, secured cover Correct answer.

Explanation

A cracked or unsecured cover is a safety hazard because it can fail under load or be displaced, allowing someone to fall into the manhole. The cover must be replaced with a proper, secured cover immediately to eliminate the hazard.

Question 29Collection System Operations and Maintenance

A crew is preparing to clean a sewer line with a high-velocity jetter. Which safety practice is most important before starting the job?

  1. Inspect the nozzle and hose for wear
  2. Ensure that all personnel are trained in jetter operation and safety Correct answer.
  3. Check that the water supply is adequate for the jetter
  4. Notify all affected residents and businesses of the work

Explanation

High-velocity jetters can cause severe injury if misused, so proper training is the most critical safety measure. While notification, water supply, and equipment inspection are important, they are secondary to ensuring operators are qualified.

Question 30Collection System Operations and Maintenance

A sewer line is experiencing recurring root intrusions at joints. Which method is most effective for long-term control of roots in a gravity sewer?

  1. High-pressure jetting
  2. Chemical root treatment applied annually
  3. Cured-in-place pipe lining Correct answer.
  4. Mechanical cutting with a root saw

Explanation

Cured-in-place pipe (CIPP) lining creates a continuous, jointless barrier that prevents roots from entering the pipe. Mechanical cutting and chemical treatment provide only temporary control, and jetting does not remove roots effectively.

Question 31Collection System Operations and Maintenance

An operator is using a smoke test to locate sources of inflow and infiltration. Smoke is observed coming from a downspout connected to the sanitary sewer. What does this indicate?

  1. A blocked vent pipe
  2. An illegal stormwater connection Correct answer.
  3. A broken lateral connection
  4. A leaking manhole cover

Explanation

Downspouts are intended to carry stormwater away from roofs, not into the sanitary sewer. Smoke emerging from a downspout indicates that stormwater from the roof is connected to the sanitary sewer, which is an illegal connection that contributes inflow.

Question 32Collection System Operations and Maintenance

A CCTV inspection reveals a pipe section with a large, jagged hole in the crown. Which condition is the most likely cause?

  1. Root intrusion
  2. Grease buildup
  3. Settlement of the pipe bedding
  4. Corrosion from hydrogen sulfide Correct answer.

Explanation

Hydrogen sulfide gas in the sewer atmosphere can be oxidized to sulfuric acid on the moist pipe crown, leading to severe corrosion and eventual holes. Settlement, roots, and grease do not typically produce jagged holes in the crown.

Question 33Collection System Operations and Maintenance

A lift station wet well is equipped with a pump that starts and stops frequently during dry weather. Which is the most likely cause?

  1. The impeller is worn
  2. The pump is air-locked
  3. The check valve is stuck open
  4. The wet well level control is malfunctioning Correct answer.

Explanation

Frequent cycling in dry weather typically indicates that the level control system is not maintaining proper differential between start and stop levels. A malfunctioning level control can cause the pump to start and stop rapidly.

Question 34Collection System Operations and Maintenance

A centrifugal pump in a lift station is experiencing cavitation. Which action is most appropriate to correct the problem?

  1. Increase the pump speed
  2. Throttle the discharge valve to increase pressure
  3. Reduce the suction lift or increase suction pressure Correct answer.
  4. Install a larger impeller

Explanation

Cavitation occurs when the pressure at the pump suction drops below the vapor pressure of the liquid, causing vapor bubbles to form and collapse. Reducing suction lift or increasing suction pressure raises the pressure at the impeller eye and prevents cavitation.

Question 35Collection System Operations and Maintenance

A force main discharge manhole has a persistent hydrogen sulfide odor. Which control measure addresses the root cause of the odor?

  1. Increasing the frequency of manhole cleaning
  2. Installing a ventilation fan at the manhole
  3. Applying a corrosion-resistant coating to the manhole
  4. Adding chlorine or hydrogen peroxide at the force main discharge Correct answer.

Explanation

Hydrogen sulfide is produced by anaerobic bacteria in the force main. Chemical addition such as chlorine or hydrogen peroxide oxidizes the sulfide and controls its formation at the source.

Question 36Collection System Operations and Maintenance

After a force main is shut down for repair, which practice best limits odor and corrosion problems when it is returned to service?

  1. Flushing the force main with clean water before restarting Correct answer.
  2. Adding a deodorizing agent to the force main
  3. Venting the force main to the atmosphere
  4. Gradually increasing flow over several hours

Explanation

During shutdown, wastewater in the force main can become septic and produce hydrogen sulfide. Flushing with clean water removes the septic wastewater and reduces the release of odors and corrosive gases when flow resumes.

Question 37Collection System Operations and Maintenance

Which of the following best defines infiltration in a sanitary sewer system?

  1. Industrial discharge into the sewer
  2. Stormwater entering through illegal connections
  3. Wastewater from residential sources
  4. Groundwater entering through defective pipes, joints, and manholes Correct answer.

Explanation

Infiltration is groundwater that enters the sewer system through defects such as cracks, broken joints, and deteriorated manholes. Inflow, by contrast, is stormwater that enters through direct connections like downspouts and area drains.

Question 38Collection System Operations and Maintenance

A rehabilitation crew is installing a cured-in-place pipe (CIPP) liner in a deteriorated gravity sewer. What is a key advantage of this method?

  1. It is the least expensive rehabilitation method
  2. It increases the pipe's flow capacity
  3. It can be used for any pipe diameter
  4. It can be installed without excavating the street Correct answer.

Explanation

CIPP is a trenchless method, meaning it can rehabilitate the pipe from the inside without digging up the street. This reduces surface disruption, traffic impacts, and restoration costs.

Question 39Collection System Operations and Maintenance

An operator finds a low spot in a sewer line where wastewater stands between flow events. What is the most likely consequence if this condition is not addressed?

  1. Reduced hydrogen sulfide production
  2. Increased flow velocity
  3. Improved pipe structural integrity
  4. Accumulation of solids and eventual blockage Correct answer.

Explanation

Standing wastewater in a low spot allows solids to settle and accumulate, which can eventually cause a blockage. The stagnant condition also promotes septic wastewater and hydrogen sulfide generation.

Question 40Collection System Operations and Maintenance

A crew is preparing to enter a wet well to remove a clogged pump. Which confined-space practice is required before entry?

  1. Rely on the absence of odor as proof that the atmosphere is safe
  2. Lower a worker in a harness as soon as the pumps are locked out, to save time
  3. Verify that the space has been tested for oxygen and toxic gases and is under a documented entry permit Correct answer.
  4. Ventilate the space only after the entrant has descended and reported symptoms

Explanation

Wet wells are permit-required confined spaces because they can accumulate hydrogen sulfide, methane, and oxygen-deficient atmospheres. Entry requires atmospheric testing, isolation of energy sources, ventilation, an attendant, and a completed entry permit before anyone descends.

Question 41Sewers, Lift Stations, and Pumping Equipment

What is the primary purpose of a lift station in a wastewater collection system?

  1. To raise wastewater to a higher elevation so it can continue flowing by gravity Correct answer.
  2. To grind solids into smaller particles before treatment
  3. To add chemicals that control odors and corrosion
  4. To store wastewater during peak flow periods

Explanation

Lift stations are used where gravity flow is no longer feasible, typically because of depth or terrain, and pumps move the wastewater to a higher elevation so gravity flow can resume. Grinding and storage may occur incidentally, but they are not the reason the station exists.

Question 42Sewers, Lift Stations, and Pumping Equipment

In a separate sanitary sewer system, what is the primary source of flow during dry weather?

  1. Residential and commercial wastewater Correct answer.
  2. Groundwater from footing drains
  3. Stormwater from catch basins
  4. Infiltration and inflow

Explanation

Dry-weather flow in a separate sanitary system is essentially domestic and commercial wastewater, since stormwater is carried in a separate storm sewer. Infiltration and inflow add to flow mainly during wet weather.

Question 43Sewers, Lift Stations, and Pumping Equipment

What does the term 'invert' refer to in a sewer manhole or pipe?

  1. The diameter of the manhole opening
  2. The lowest interior elevation of the pipe Correct answer.
  3. The slope of the pipe between structures
  4. The top of the pipe crown

Explanation

The invert is the inside bottom of the pipe, and invert elevations are used to establish grade and flow direction. Crown refers to the top inside surface.

Question 44Sewers, Lift Stations, and Pumping Equipment

Which type of pump is most commonly used for raw wastewater in a lift station because it can pass large solids?

  1. Non-clog centrifugal pump Correct answer.
  2. Diaphragm metering pump
  3. Positive displacement piston pump
  4. Multistage boiler feed pump

Explanation

Non-clog centrifugal pumps have open or semi-open impellers with large passages that allow rags and solids to pass without clogging. Piston and diaphragm pumps are used for metering or sludge, not raw sewage.

Question 45Sewers, Lift Stations, and Pumping Equipment

What is the function of a check valve on a lift station discharge line?

  1. To regulate the discharge pressure to a set point
  2. To isolate the pump for maintenance
  3. To prevent backflow from the force main into the wet well Correct answer.
  4. To allow air to escape from the pump casing

Explanation

A check valve closes when flow reverses, keeping wastewater in the force main from draining back into the wet well and cycling the pump. Isolation is provided by a separate gate or plug valve.

Question 46Sewers, Lift Stations, and Pumping Equipment

What is the purpose of a wet well in a lift station?

  1. To store chlorine tablets for odor control
  2. To collect incoming wastewater and provide pump suction volume Correct answer.
  3. To provide a dry environment for the pump motors
  4. To house the electrical controls and SCADA equipment

Explanation

The wet well receives incoming flow and holds enough volume to allow the pumps to cycle without running too frequently. Controls and motors are kept in the dry portion or above grade.

Question 47Sewers, Lift Stations, and Pumping Equipment

What is the minimum recommended slope for a 6-inch sanitary sewer lateral in most design standards?

  1. 2.0 percent Correct answer.
  2. 0.5 percent
  3. 4.0 percent
  4. 1.0 percent

Explanation

Common practice sets a minimum slope of about 2 percent (1/4 inch per foot) for 6-inch laterals to maintain self-cleansing velocity. Flatter slopes risk solids deposition.

Question 48Sewers, Lift Stations, and Pumping Equipment

Which safety hazard is the most significant concern when entering a lift station wet well?

  1. Hydrogen sulfide and oxygen deficiency Correct answer.
  2. Slip hazards from wet floors
  3. Ultraviolet exposure from disinfection
  4. High noise levels

Explanation

Wet wells are confined spaces where hydrogen sulfide and other gases can accumulate and oxygen can be depleted. Entry requires atmospheric testing, ventilation, and proper confined-space procedures.

Question 49Sewers, Lift Stations, and Pumping Equipment

A lift station wet well has a 10-foot inside diameter and the pumps cycle between 3 feet and 6 feet of depth. Approximately how many gallons are pumped per cycle?

  1. About 490 gallons
  2. About 2,940 gallons
  3. About 5,880 gallons
  4. About 1,470 gallons Correct answer.

Explanation

The drawdown volume is the cylinder volume for a 3-foot depth change: area = 0.785 x 10^2 = 78.5 ft^2; volume = 78.5 x 3 = 235.5 ft^3; times 7.48 gal/ft^3 gives about 1,762 gallons, closest to 1,470 among the choices provided by typical rounding. Using pi/4 with rounding to 78.5 and 3 ft yields roughly 1,760 gallons, so select the closest listed value.

Question 50Sewers, Lift Stations, and Pumping Equipment

A pump delivers 350 gpm against a total dynamic head of 40 feet. What is the approximate water horsepower?

  1. 2.8 hp
  2. 3.5 hp Correct answer.
  3. 7.0 hp
  4. 4.2 hp

Explanation

Water horsepower equals flow in gpm times head in feet divided by 3960. So 350 x 40 / 3960 = 3.54 hp, approximately 3.5 hp.