• 65 questions

Waste Water Conversion Practice Test

Unit conversions first, then volumes, flow, detention time, dosage and lab math, with every answer worked.

How many gallons are in 3 cubic feet of water?

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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Unofficial practice questions, not affiliated with any state operator certification program or exam owner. Bank checked October 11, 2026.

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All 65 questions

Unit conversions 13

  • A channel carries 2 cubic feet per second. What is that in gallons per minute? Worked arithmetic. Formula: Pennsylvania DEP operator training, Module 28: Basic Math, Appendix 3, Flow, page A-3
  • A lagoon covers 3 acres. What is its surface area in square feet? Worked arithmetic. Formula: Pennsylvania DEP operator training, Module 28: Basic Math, Appendix 1, page A-1
  • A plant treats 2.5 MGD. What is that in gallons per minute, using 1 MGD = 694 gpm? Worked arithmetic. Formula: Pennsylvania DEP operator training, Module 28: Basic Math, Appendix 1, page A-1
  • A pump delivers 350 gallons per minute around the clock. What is that in MGD? Worked arithmetic. Formula: Pennsylvania DEP operator training, Module 28: Basic Math, Appendix 3, Flow, page A-3
  • A sludge is 2 percent solids. What is that in mg/L? Worked arithmetic. Formula: Pennsylvania DEP operator training, Module 28: Basic Math, Appendix 1, page A-1
  • A tank holds 15,000 gallons. What is its volume in cubic feet? Worked arithmetic. Formula: Pennsylvania DEP operator training, Module 28: Basic Math, Appendix 1, page A-1
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Unit conversions, continued

  • A truck hauls away 5 cubic yards of grit. How many cubic feet is that? Worked arithmetic. Formula: Pennsylvania DEP operator training, Module 28: Basic Math, Appendix 1, page A-1
  • How many gallons are in 3 cubic feet of water? Worked arithmetic. Formula: Pennsylvania DEP operator training, Module 28: Basic Math, Appendix 1, page A-1
  • How many liters are in 10 gallons? Worked arithmetic. Formula: Pennsylvania DEP operator training, Module 28: Basic Math, Appendix 1, page A-1
  • How much do 500 gallons of water weigh? Worked arithmetic. Formula: Pennsylvania DEP operator training, Module 28: Basic Math, Appendix 1, page A-1
  • Water hardness is reported as 5 grains per gallon. What is that in mg/L? Worked arithmetic. Formula: Pennsylvania DEP operator training, Module 28: Basic Math, Appendix 1, page A-1
  • What is 1.2 MGD in cubic feet per second? Worked arithmetic. Formula: Pennsylvania DEP operator training, Module 28: Basic Math, Appendix 1, page A-1
  • What is 40 psi in feet of head? Worked arithmetic. Formula: Pennsylvania DEP operator training, Module 28: Basic Math, Appendix 1, page A-1

Area and volume 8

  • A circular clarifier is 50 ft in diameter. What is its surface area? Worked arithmetic. Formula: Pennsylvania DEP operator training, Module 28: Basic Math, Unit 2, Area, page 2-5
  • A circular tank is 20 ft in diameter and the water is 12 ft deep. How many gallons does it hold? Worked arithmetic. Formula: Pennsylvania DEP operator training, Module 28: Basic Math, Unit 2, Volume, page 2-13
  • A lagoon covers 2 acres and is 4 ft deep. About how many million gallons does it hold? Worked arithmetic. Formula: Pennsylvania DEP operator training, Module 28: Basic Math, Unit 2, Volume, page 2-9, and Appendix 1
  • A rectangular basin is 40 ft long and 15 ft wide. What is its surface area? Worked arithmetic. Formula: Pennsylvania DEP operator training, Module 28: Basic Math, Unit 2, Area, page 2-2
  • A rectangular tank is 30 ft long, 12 ft wide and 8 ft deep. How many gallons does it hold? Worked arithmetic. Formula: Pennsylvania DEP operator training, Module 28: Basic Math, Unit 2, Volume, page 2-9
  • A trench is 3 ft wide, 5 ft deep and 200 ft long. How many cubic yards of soil come out? Worked arithmetic. Formula: Pennsylvania DEP operator training, Module 28: Basic Math, Unit 2, Volume, page 2-9, and Appendix 1
  • How many gallons does 500 ft of 8-inch pipe hold? Worked arithmetic. Formula: Pennsylvania DEP operator training, Module 28: Basic Math, Unit 2, Volume, page 2-13
  • How many gallons does 1,000 ft of 12-inch water main hold? Worked arithmetic. Formula: Pennsylvania DEP operator training, Module 28: Basic Math, Unit 2, Volume, page 2-13

Flow and velocity 8

  • A 12-inch pipe flowing full carries 1.57 cubic feet per second. What is the velocity? Worked arithmetic. Formula: Pennsylvania DEP operator training, Module 28: Basic Math, Appendix 3, Velocity, page A-3
  • A channel is 2 ft wide and the water is 1.5 ft deep, moving at 1.2 ft/sec. What is the flow? Worked arithmetic. Formula: Pennsylvania DEP operator training, Module 28: Basic Math, Appendix 3, Velocity, page A-3
  • A float travels 30 ft down a channel in 20 seconds. What is the velocity? Worked arithmetic. Formula: Pennsylvania DEP operator training, Module 28: Basic Math, Appendix 3, Velocity, page A-3
  • A flow of 3.6 cubic feet per second is how many gallons per minute? Worked arithmetic. Formula: Pennsylvania DEP operator training, Module 28: Basic Math, Appendix 3, Flow, page A-3
  • A pump fills a 30,000 gallon tank at 250 gallons per minute. How long does it take? Worked arithmetic. Formula: Pennsylvania DEP operator training, Module 28: Basic Math, Appendix 3, Flow, page A-3
  • A system produces 1.5 MGD for 12,000 people. What is the use per person per day? Worked arithmetic. Formula: California State Water Resources Control Board, Exam Conversion Sheet, gallons per capita per day
  • Daily flows for five days were 0.8, 1.0, 1.2, 0.9 and 1.1 MGD. What was the average daily flow? Worked arithmetic. Formula: Pennsylvania DEP operator training, Module 28: Basic Math, Appendix 3, Flow, page A-7
  • With the inflow shut off, a pump lowers a wet well that is 8 ft by 6 ft by 2 ft in 4 minutes. What is the pumping rate? Worked arithmetic. Formula: Pennsylvania DEP operator training, Module 28: Basic Math, Unit 2, Volume, page 2-9

Detention time and loading rates 8

  • A 60,000 gallon tank receives 500 gallons per minute. What is the detention time? Worked arithmetic. Formula: Pennsylvania DEP operator training, Module 28: Basic Math, Appendix 3, Sedimentation Tanks and Clarifiers, page A-4
  • A chlorine contact tank is 40 ft by 10 ft by 6 ft. The flow is 0.8 MGD. What is the detention time? Worked arithmetic. Formula: Pennsylvania DEP operator training, Module 28: Basic Math, Appendix 3, Sedimentation Tanks and Clarifiers, page A-4
  • A circular clarifier is 40 ft in diameter and 10 ft deep. The flow is 1.2 MGD. What is the detention time? Worked arithmetic. Formula: Pennsylvania DEP operator training, Module 28: Basic Math, Appendix 3, Sedimentation Tanks and Clarifiers, page A-4
  • A clarifier 50 ft in diameter receives 1.5 MGD. What is the surface loading rate? Worked arithmetic. Formula: Pennsylvania DEP operator training, Module 28: Basic Math, Appendix 3, Sedimentation Tanks and Clarifiers, page A-4
  • A clarifier has 157 ft of weir and receives 1.5 MGD. What is the weir overflow rate? Worked arithmetic. Formula: Pennsylvania DEP operator training, Module 28: Basic Math, Appendix 3, Sedimentation Tanks and Clarifiers, page A-4
  • A clarifier holds 90,000 gallons and the flow is 0.72 MGD. What is the detention time? Worked arithmetic. Formula: Pennsylvania DEP operator training, Module 28: Basic Math, Appendix 3, Sedimentation Tanks and Clarifiers, page A-4
  • A treatment pond holds 5 million gallons and receives 0.1 MGD. What is the detention time? Worked arithmetic. Formula: Pennsylvania DEP operator training, Module 28: Basic Math, Appendix 3, Sedimentation Tanks and Clarifiers, page A-4
  • An aeration basin holds 0.25 million gallons and the flow is 1.0 MGD. What is the detention time? Worked arithmetic. Formula: Pennsylvania DEP operator training, Module 28: Basic Math, Appendix 3, Sedimentation Tanks and Clarifiers, page A-4

Pounds formula and dosage 13

  • A 100,000 gallon tank is to be disinfected at 50 mg/L with 65 percent calcium hypochlorite. How much product is needed? Worked arithmetic. Formula: California State Water Resources Control Board, Exam Conversion Sheet, chlorination, HTH solid
  • A chlorinator feeds 40 lb/day into a flow of 1.6 MGD. What is the dose? Worked arithmetic. Formula: Pennsylvania DEP operator training, Module 28: Basic Math, Unit 3, page 3-9
  • A feed pump can deliver 120 gallons per day at full stroke. The process needs 30 gallons per day. What is the setting? Worked arithmetic. Formula: Pennsylvania DEP operator training, Module 28: Basic Math, Appendix 3, Chemical Feeder Setting, page A-6
  • A flow of 2 MGD is dosed with 3 mg/L of chlorine. How many pounds of chlorine are fed each day? Worked arithmetic. Formula: Pennsylvania DEP operator training, Module 28: Basic Math, Unit 3, page 3-8
  • A job needs 10 lb of chlorine. How many pounds of 65 percent calcium hypochlorite supply it? Worked arithmetic. Formula: California State Water Resources Control Board, Exam Conversion Sheet, chlorination, HTH solid
  • A liquid chemical has a specific gravity of 1.17 and is 12.5 percent active. What is its active strength? Worked arithmetic. Formula: Pennsylvania DEP operator training, Module 28: Basic Math, Unit 3, page 3-3
  • A plant needs 16.7 lb/day of chlorine from a hypochlorite solution with 1.22 lb of chlorine per gallon. How many gallons a day? Worked arithmetic. Formula: Pennsylvania DEP operator training, Module 28: Basic Math, Appendix 3, Chemical Feeder Setting, page A-6
  • A trickling filter receives 600 lb of BOD a day on 20,000 cubic feet of media. What is the organic loading? Worked arithmetic. Formula: Pennsylvania DEP operator training, Module 28: Basic Math, Appendix 3, Trickling Filters, page A-4
  • A truck takes 5,000 gallons of sludge at 4 percent solids. How many pounds of dry solids is that? Worked arithmetic. Formula: Pennsylvania DEP operator training, Module 28: Basic Math, Appendix 3, Dry Sludge, page A-6
  • A water plant treats 3 MGD with an alum dose of 20 mg/L. How much alum is fed each day? Worked arithmetic. Formula: Pennsylvania DEP operator training, Module 28: Basic Math, Unit 3, page 3-8
  • An aeration tank holds 0.3 MG at a mixed liquor suspended solids level of 2,500 mg/L. What weight of solids, in pounds, does the tank hold? Worked arithmetic. Formula: Pennsylvania DEP operator training, Module 28: Basic Math, Appendix 3, Activated Sludge, page A-5
  • The chlorine dose is 5.0 mg/L and the residual is 0.8 mg/L. What is the chlorine demand? Worked arithmetic. Formula: Pennsylvania DEP operator training, Module 28: Basic Math, Appendix 3, Chlorine Calculations, page A-5
  • Influent flow is 0.75 MGD with 240 mg/L of suspended solids. What is the solids loading? Worked arithmetic. Formula: Pennsylvania DEP operator training, Module 28: Basic Math, Unit 3, page 3-2

Pressure and head 6

  • A gauge at the base of a standpipe reads 52 psi. How high is the water above the gauge? Worked arithmetic. Formula: Pennsylvania DEP operator training, Module 28: Basic Math, Appendix 1, page A-1
  • A pump delivers 10 water horsepower and is 80 percent efficient. What brake horsepower does it need? Worked arithmetic. Formula: Pennsylvania DEP operator training, Module 9: Basics of Pumps and Hydraulics, Unit 4, page 4-3
  • A pump has 5 psi on its suction gauge and 65 psi on its discharge gauge. What head is the pump adding? Worked arithmetic. Formula: Pennsylvania DEP operator training, Module 28: Basic Math, Appendix 1, page A-1
  • A pump moves 500 gpm against a head of 80 ft. What is the water horsepower? Worked arithmetic. Formula: Pennsylvania DEP operator training, Module 9: Basics of Pumps and Hydraulics, Unit 4, page 4-3
  • A tank overflows at elevation 520 ft. A hydrant sits at elevation 400 ft. What is the static pressure at the hydrant when the tank is full? Worked arithmetic. Formula: Pennsylvania DEP operator training, Module 28: Basic Math, Appendix 1, page A-1
  • The water level in a tank is 60 ft above a pressure gauge. What does the gauge read? Worked arithmetic. Formula: Pennsylvania DEP operator training, Module 28: Basic Math, Appendix 1, page A-1

Laboratory math 9

  • A 50 g sample of wet sludge dries to 2 g. What is the percent solids? Worked arithmetic. Formula: Pennsylvania DEP operator training, Module 12: Laboratory Overview, Unit 4, pages 4-4 and 4-5
  • A 100 mL sample is filtered and the dried filter gains 0.0180 g. What is the total suspended solids result? Worked arithmetic. Formula: Pennsylvania DEP operator training, Module 12: Laboratory Overview, Unit 4, page 4-4
  • A BOD bottle starts at 8.2 mg/L of dissolved oxygen and ends at 4.0 mg/L. The sample was diluted 30 times. What is the BOD? Worked arithmetic. Formula: Pennsylvania DEP operator training, Module 12: Laboratory Overview, Unit 4, page 4-11
  • A BOD incubator is set to 20 °C. What is that in degrees Fahrenheit? Worked arithmetic. Formula: California State Water Resources Control Board, Exam Conversion Sheet, temperature
  • Dried sludge solids weigh 5.0 g. After burning in the furnace 1.5 g of ash is left. What percent of the solids was volatile? Worked arithmetic. Formula: Pennsylvania DEP operator training, Module 12: Laboratory Overview, Unit 4, pages 4-4 and 4-5
  • How many mL of a 100 mg/L stock solution make 500 mL of a 10 mg/L standard? Worked arithmetic. Formula: California State Water Resources Control Board, Exam Conversion Sheet, dilution and blending
  • In a jar test, 1 mL of a 10,000 mg/L alum solution is added to a 1,000 mL jar. What dose does the jar receive? Worked arithmetic. Formula: California State Water Resources Control Board, Exam Conversion Sheet, dilution and blending
  • Influent BOD is 250 mg/L and effluent BOD is 20 mg/L. What is the removal efficiency? Worked arithmetic. Formula: Pennsylvania DEP operator training, Module 28: Basic Math, Unit 3, page 3-15
  • Mixed liquor settles to 25 percent of its volume in 30 minutes. The MLSS is 2,500 mg/L. What is the sludge volume index? Worked arithmetic. Formula: Pennsylvania DEP operator training, Module 28: Basic Math, Appendix 3, Activated Sludge, page A-5

How this list was compiled: Our own arithmetic questions for water and wastewater operator certification exams. The conversion factors and formulas are the ones in Module 28: Basic Math, Module 9: Basics of Pumps and Hydraulics and Module 12: Laboratory Overview of the Pennsylvania Department of Environmental Protection's operator certification training (https://files.dep.state.pa.us/Water/BSDW/OperatorCertification/TrainingModules/) and on the Exam Conversion Sheet of the California State Water Resources Control Board, all read on 2026-10-11. Each question names the page of its formula. Licence: Own work. Every question, its numbers, its answer choices and its worked answer were written for this site. Nothing is taken from an exam, from a formula sheet's sample problems, from the training workbooks' own exercises, or from another practice test.

How it works

This wastewater conversion practice test covers the arithmetic on water and wastewater operator exams, starting with unit conversions. It is unofficial and not affiliated with, endorsed by or sponsored by any state certification program or exam owner.

Read the full guide

Three numbers to know

Most answers turn on three factors: 7.48 gallons in a cubic foot, 8.34 pounds in a gallon of water and 2.31 feet of water in one psi.

One page for water and wastewater

A wastewater math practice test and a water treatment math practice test share most of their arithmetic. The drinking water side leans on chlorine dose and pressure, the wastewater side on loading, detention time and solids.

Lab math

The last group is wastewater lab analyst practice test math: suspended solids from filter weights, BOD from a dilution, percent removal, making a standard.

  • Write the units beside every number and cancel them. If the units left over are wrong, so is the answer.
  • Change inches to feet before you square a pipe diameter. Skip that step and the answer comes out 144 times too large.

Questions and answers

What math is on a wastewater operator math practice test?

Unit conversions, areas and volumes of tanks and pipes, flow and velocity, detention time, loading rates, the pounds formula for chemical feed and solids, pressure and head, and laboratory arithmetic. This page has a group for each.

Is this a free water treatment math study guide?

It works as one. Every answer is worked step by step and names the page of a free public math module that holds its formula, so a miss points to what to read.

What is the pounds formula?

Pounds per day = flow in million gallons per day x concentration in mg/L x 8.34. It turns a concentration into a loading, or a dose into a chemical feed rate. Divide pounds by flow x 8.34 to get a dose back.

Do operator exams give a formula sheet?

The standardized exams of Water Professionals International come with a formula and conversion table, and California hands out its own sheet. Ask your certification program what it provides and which calculator it allows.

Are the answers in US or metric units?

US units: gallons, cubic feet, pounds, psi and MGD. The standardized exam prints its calculations in both US and metric units, so check which your exam uses.

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