• 62 questions

Waste Water Exam Grade 1 Practice Test

Our own questions in the four content areas of the Class I outline, each naming the page it came from.

Which part of a centrifugal pump throws the water outward?

Pick an answer, then press Check answer. Then you see Correct or Not quite, with the reason. Keys: A to D pick, Enter checks.

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Exam mode: 50 questions, 90 minutes, 35 right to pass (70%).

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Unofficial practice questions, not affiliated with Water Professionals International (formerly ABC). Bank checked October 11, 2026.

The real exam, as its owner describes it

Questions
100
To pass
70 of 100 right (70%)
Time limit
180 minutes
Content areas
Equipment Evaluation, Maintenance and Operation 39 questions, Treatment Process Evaluation and Adjustment 38, Laboratory Analysis 10, Security, Safety and Admin
Calculations
About 10 percent of the Class I exam, in US and metric units. A formula and conversion table is given with the exam.
Unscored questions
Up to 10 extra pre-test questions may be mixed in. They are not marked out and do not count toward the score.
Format
Multiple choice with four options, closed book. Programmable calculators are not allowed.
Time and pass mark
Three hours and 70 percent are what the exam owner states for its own certification. A state or province that uses the exam sets its own.
Other editions
Certification programs also give earlier editions of the standardized exam, and customized exams. Your certifying authority can say which it uses.

Checked October 11, 2026 against Water Professionals International's Need-to-Know Criteria for the Class I exam and its certification pages. Rules change, so confirm with the agency itself before your test.

The exam owner's Need-to-Know Criteria

Next step Water treatment operator practice testWater and wastewater operator math

All 62 questions

Equipment Evaluation, Maintenance and Operation 23

  • A centrifugal pump sits above the wet well and has drained. What must be done before it is started? Pennsylvania DEP wastewater operator training, Module 9: Basics of Pumps and Hydraulics, Unit 4 key points, page 4-18
  • A grit channel has not been cleaned for weeks. What happens as grit builds up in it? Pennsylvania DEP wastewater operator training, Module 1: Introduction to Wastewater Treatment (revised 2016), Unit 3, Grit Removal, page 3-7
  • A magnetic flow meter on a force main reads correctly only when the pipe is: Pennsylvania DEP wastewater operator training, Module 1: Introduction to Wastewater Treatment (revised 2016), Unit 3, Flow Metering, page 3-10
  • A progressing cavity pump moves thick sludge well. Which condition must it never run in? Pennsylvania DEP wastewater operator training, Module 9: Basics of Pumps and Hydraulics, Unit 4, page 4-14
  • About what flow velocity is held in a grit channel so that grit settles but lighter organic solids move on? Pennsylvania DEP wastewater operator training, Module 4: Fundamentals of Wastewater Treatment (revised 2016), Unit 1, page 1-5
Show all 62 questions (57 more)

Equipment Evaluation, Maintenance and Operation, continued

  • An operator closes the discharge valve before stopping the pump. For which pump is that a serious mistake while it is still running? Pennsylvania DEP wastewater operator training, Module 9: Basics of Pumps and Hydraulics, Unit 4, page 4-12
  • The differential pressure across a blower is climbing and the blower is running hot. What should be checked first? Pennsylvania DEP wastewater operator training, Module 15: The Activated Sludge Process, Part 1 (revised July 2014), Unit 2, page 2-5
  • How does a comminutor differ from a bar screen? Pennsylvania DEP wastewater operator training, Module 1: Introduction to Wastewater Treatment (revised 2016), Unit 3, Screening and Comminution, page 3-6
  • In a primary clarifier, what removes the grease and scum that float? Pennsylvania DEP wastewater operator training, Module 1: Introduction to Wastewater Treatment (revised 2016), Unit 3, Primary Treatment, page 3-11
  • In general, how many days of treatment chemicals should a plant keep on hand? Pennsylvania DEP wastewater operator training, Module 7: Basics of Chemical Feed Systems, Unit 4 key points, page 4-17
  • One pump is running. A second, identical pump is started in parallel with it. What happens to the flow? Pennsylvania DEP wastewater operator training, Module 9: Basics of Pumps and Hydraulics, Unit 4, Pump Curve Characteristics, page 4-9
  • Sludge on a belt filter press is releasing its water poorly. What is usually added ahead of a mechanical dewatering unit to condition the sludge? Pennsylvania DEP wastewater operator training, Module 6: Solids Handling and Disposal, Unit 4 key points, page 4-13
  • What does a bar screen at the head of the plant take out of the flow? Pennsylvania DEP wastewater operator training, Module 1: Introduction to Wastewater Treatment (revised 2016), Unit 3, Screening and Comminution, page 3-6
  • What is the job of the packing on a centrifugal pump? Pennsylvania DEP wastewater operator training, Module 9: Basics of Pumps and Hydraulics, Unit 4, Basic Components, page 4-5
  • What routine care does a UV disinfection unit need? Pennsylvania DEP wastewater operator training, Module 5: Disinfection and Chlorination (revised 2016), Unit 6, page 6-7
  • What sets off cavitation in a pump that is working on a suction lift? Pennsylvania DEP wastewater operator training, Module 9: Basics of Pumps and Hydraulics, Unit 4, page 4-10
  • Which device measures flow in an open channel from the depth of the water passing through it? Pennsylvania DEP wastewater operator training, Module 1: Introduction to Wastewater Treatment (revised 2016), Unit 3, Flow Metering, page 3-9
  • Which diffusers dissolve oxygen most efficiently, and at what cost? Pennsylvania DEP wastewater operator training, Module 15: The Activated Sludge Process, Part 1 (revised July 2014), Unit 2 key points, page 2-16
  • Which flow meter is the one more likely to clog on wastewater? Pennsylvania DEP wastewater operator training, Module 9: Basics of Pumps and Hydraulics, Unit 3 key points, page 3-8
  • Which part of a centrifugal pump throws the water outward? Pennsylvania DEP wastewater operator training, Module 9: Basics of Pumps and Hydraulics, Unit 4, Basic Components, page 4-5
  • Which three parts make up a trickling filter? Pennsylvania DEP wastewater operator training, Module 20: Trickling Filters (revised 2016), Unit 1 key points, page 1-44
  • Which way of dewatering sludge uses no mechanical energy? Pennsylvania DEP wastewater operator training, Module 1: Introduction to Wastewater Treatment (revised 2016), Unit 3, Dewatering Technologies, page 3-25
  • Why is grit removed early in the plant? Pennsylvania DEP wastewater operator training, Module 1: Introduction to Wastewater Treatment (revised 2016), Unit 3, Grit Removal, page 3-7

Treatment Process Evaluation and Adjustment 25

  • A plant flow of 1.2 MGD is to be dosed with 6 mg/L of chlorine. How many pounds of chlorine are needed each day? Worked arithmetic; formula in Pennsylvania DEP operator training, Module 28: Basic Math, page 3-8
  • A plant treats 0.5 MGD of wastewater with a BOD of 200 mg/L. What is the BOD loading? Worked arithmetic; formula in Pennsylvania DEP operator training, Module 28: Basic Math, page 3-2
  • A pond gives off a rotten egg odor. What does that point to? Pennsylvania DEP wastewater operator training, Module 19: Treatment Ponds and Lagoons, Unit 3 key points, page 3-11
  • A primary clarifier is 60 ft long, 20 ft wide and 10 ft deep. The flow is 900,000 gallons per day. What is the detention time? Worked arithmetic; formula in Pennsylvania DEP operator training, Module 28: Basic Math, page 2-13 (volume) and Appendix 1
  • An operator doubles the return activated sludge rate. What is the risk? Pennsylvania DEP wastewater operator training, Module 15: The Activated Sludge Process, Part 1 (revised July 2014), Unit 1, page 1-7
  • Below about what wastewater temperature does biological activity fall off sharply? Pennsylvania DEP wastewater operator training, Module 15: The Activated Sludge Process, Part 1 (revised July 2014), Unit 1, page 1-13
  • The chlorine dose is 8.0 mg/L and the residual after the contact tank is 1.5 mg/L. What is the chlorine demand? Pennsylvania DEP wastewater operator training, Module 5: Disinfection and Chlorination (revised 2016), Unit 1, page 1-9
  • Dissolved oxygen in the aeration tank has been low for days. Which organisms does that favor? Pennsylvania DEP wastewater operator training, Module 15: The Activated Sludge Process, Part 1 (revised July 2014), Unit 1, Dissolved Oxygen Levels, page 1-14
  • During aerobic digestion the sludge mass goes down. Why? Pennsylvania DEP wastewater operator training, Module 6: Solids Handling and Disposal, Unit 3, page 3-4
  • In the activated sludge process, why is settled sludge returned from the secondary clarifier to the aeration tank? Pennsylvania DEP wastewater operator training, Module 15: The Activated Sludge Process, Part 1 (revised July 2014), Unit 1 key points, page 1-16
  • Influent suspended solids are 220 mg/L and effluent suspended solids are 22 mg/L. What is the removal efficiency? Worked arithmetic; formula in Pennsylvania DEP operator training, Module 28: Basic Math, page 3-15
  • The sludge pumped from the primary clarifier is thin and watery. What does that suggest? Pennsylvania DEP wastewater operator training, Module 1: Introduction to Wastewater Treatment (revised 2016), Unit 3, Primary Treatment, page 3-11
  • Under the federal secondary treatment rule, what is the highest 30-day average BOD5 an effluent may have? 40 CFR 133.102, paragraph (a)
  • What dissolved oxygen level is the usual goal in an aeration tank? Pennsylvania DEP wastewater operator training, Module 15: The Activated Sludge Process, Part 1 (revised July 2014), Unit 1, Dissolved Oxygen Levels, page 1-14
  • What effluent pH range does the federal secondary treatment rule set? 40 CFR 133.102, paragraph (c)
  • What happens to the solids that settle to the bottom of a facultative pond? Pennsylvania DEP wastewater operator training, Module 1: Introduction to Wastewater Treatment (revised 2016), Unit 3, Waste Treatment Ponds, page 3-17
  • What is recirculation on a trickling filter? Pennsylvania DEP wastewater operator training, Module 20: Trickling Filters (revised 2016), Unit 1, Benefits of Recirculation, page 1-39
  • What is secondary treatment meant to remove? Pennsylvania DEP wastewater operator training, Module 1: Introduction to Wastewater Treatment (revised 2016), Unit 3, Secondary Treatment, page 3-12
  • What is the usual detention time in a primary clarifier? Pennsylvania DEP wastewater operator training, Module 4: Fundamentals of Wastewater Treatment (revised 2016), Unit 2, page 2-4
  • What kind of process is primary treatment? Pennsylvania DEP wastewater operator training, Module 1: Introduction to Wastewater Treatment (revised 2016), Unit 3, Primary Treatment, page 3-11
  • Where does the oxygen in the upper layer of a facultative pond come from? Pennsylvania DEP wastewater operator training, Module 1: Introduction to Wastewater Treatment (revised 2016), Unit 3, Waste Treatment Ponds, page 3-17
  • Which condition does denitrification need? Pennsylvania DEP wastewater operator training, Module 1: Introduction to Wastewater Treatment (revised 2016), Unit 3, Nitrogen Removal, page 3-21
  • Which is true of ultraviolet disinfection? Pennsylvania DEP wastewater operator training, Module 1: Introduction to Wastewater Treatment (revised 2016), Unit 3, Disinfection, page 3-22
  • Which kind of activated sludge plant makes the least sludge and often nitrifies? Pennsylvania DEP wastewater operator training, Module 15: The Activated Sludge Process, Part 1 (revised July 2014), Unit 1, pages 1-12 and 1-13
  • Why is effluent dechlorinated before it reaches the stream? Pennsylvania DEP wastewater operator training, Module 5: Disinfection and Chlorination (revised 2016), Unit 5 key points, page 5-6

Laboratory Analysis 6

  • A 50 mL sample is filtered. The dry filter weighed 0.1250 g before and 0.1305 g after. What is the total suspended solids result? Pennsylvania DEP wastewater operator training, Module 12: Laboratory Overview, Unit 4, page 4-4
  • At what temperature is the filter dried in the total suspended solids test? Pennsylvania DEP wastewater operator training, Module 12: Laboratory Overview, Unit 4, page 4-4
  • How is a BOD sample incubated? Pennsylvania DEP wastewater operator training, Module 12: Laboratory Overview, Unit 4, page 4-11
  • How soon must an effluent sample be tested for pH or total chlorine residual? 40 CFR 136.3, Table II, hydrogen ion (pH) and chlorine, total residual
  • What is the longest a BOD sample may be held before the test is started, and how is it kept? 40 CFR 136.3, Table II, biochemical oxygen demand
  • Which test should be run on a grab sample and not on a composite? Pennsylvania DEP wastewater operator training, Module 12: Laboratory Overview, Unit 3, page 3-3

Security, Safety and Administrative Procedures 8

  • A chlorine cylinder is leaking and trained responders can reach it. How should it be turned? Pennsylvania DEP wastewater operator training, Module 5: Disinfection and Chlorination (revised 2016), Unit 3, page 3-12
  • A noncompliance occurs that could put health or the environment in danger. How soon must it be reported orally? 40 CFR 122.41, paragraph (l)(6)
  • A pump is locked out for repair. Who takes the lock off when the job is done? 29 CFR 1910.147, paragraph (e)(3)
  • An entry team tests the air in a wet well before going in. Which oxygen reading means the air is oxygen deficient? 29 CFR 1910.146, paragraph (b), definitions
  • For at least how long does a discharge permit require monitoring records to be kept? 40 CFR 122.41, paragraph (j)(2)
  • In a discharge permit, what is a bypass? 40 CFR 122.41, paragraph (m)(1)
  • In what order is the air in a permit space tested before entry? 29 CFR 1910.146, paragraph (d)(5)(iii)
  • Where must the safety data sheets for the plant's hazardous chemicals be kept? 29 CFR 1910.1200, paragraph (g)(8)

How this list was compiled: Our own questions, in the four content areas and the shares of the Need-to-Know Criteria for the Wastewater Treatment Operator Class I exam (Water Professionals International, 2025, https://gowpi.org/services/2025-need-to-know-criteria). Facts were read in the Wastewater Operator Certification Training workbooks of the Pennsylvania Department of Environmental Protection (https://files.dep.state.pa.us/Water/BSDW/OperatorCertification/TrainingModules/) and in 40 CFR Parts 122, 133 and 136 and 29 CFR Part 1910 on ecfr.gov, all on 2026-10-11. Each question names the page or section it was written from. Licence: Own work. Every question, answer choice and explanation was written for this site from the public sources named on it. Nothing is taken from the exam, from its owner's sample questions or study guides, from the training workbooks' own exercises, or from another practice test.

How it works

This wastewater grade 1 practice test follows the four content areas of the Need-to-Know Criteria for the Wastewater Treatment Operator Class I exam. It is unofficial and not affiliated with, endorsed by or sponsored by Water Professionals International (formerly ABC).

Read the full guide

Grade 1, Class I, Operator 1

States name the entry certificate differently. Where the state gives the standardized exam, a wastewater treatment plant operator Grade I certification practice test, a wastewater operator 1 practice test and a Class I one all mean this outline.

Where the answers come from

Rule questions cite 40 CFR or an OSHA standard by section. Process and equipment questions cite Pennsylvania's public operator training modules by page, because the exam's listed references are commercial textbooks.

  • Learn the pounds formula first: flow in MGD x mg/L x 8.34 gives pounds per day, for loadings and for chemical feed.
  • Keep the secondary treatment numbers together: 30 mg/L as a 30-day average, 45 as a 7-day average, 85 percent removal.

Questions and answers

Is this a wastewater treatment operator 1 practice test for my state?

It follows the standardized Class I outline. Certification programs also give older editions and customized exams, and some states write their own, so ask your certifying authority which exam it uses.

How many questions are on the grade 1 wastewater exam?

The 2025 Need-to-Know Criteria list 100 scored questions and up to 10 unscored pre-test questions. The owner's own pages give four answer choices per question and a three-hour limit.

What score passes the wastewater operator exam?

Water Professionals International asks 70 percent or higher for its own certification. A state or province that uses the exam sets its own pass mark, so ask your certifying authority.

Can I use this as a wastewater grade 1 study guide?

As the practice half of one. Each explanation names a page of a free public training module or a federal rule to read next. A wastewater operator grade 1 study guide from your own state adds its local rules.

Are there wastewater treatment plant operator study guides for Grade I-V here?

This page is Class I only. Classes II to IV keep the same four content areas, with treatment process growing to 40 and then 42 questions and calculations rising from 10 to 16 percent. A state with five grades publishes its own outline.

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