California Wastewater Operator Exam: all 234 questions with answers

Each question leads to its own page with the answers and the solution.

• Safety and Hazards26 questions
• Sampling, Laboratory Analysis and Wastewater Characteristics30 questions
• Preliminary and Primary Treatment23 questions
• Secondary Treatment (Activated Sludge, Trickling Filters, RBC)31 questions
• Stabilization Ponds16 questions
• Sludge Digestion and Solids Handling23 questions
• Disinfection and Dechlorination20 questions
• Regulations, Classification and Operator Certification29 questions
• Process Math and Unit Conversions36 questions

Safety and Hazards

• 1001Hydrogen sulfide (H2S) is especially dangerous to operators because, at higher concentrations, it
• 1002Which gas is heavier than air and tends to collect in manholes and wet wells?
• 1003What must be done before an employee enters a permit-required confined space such as a wet well?
• 1004What is the minimum safe oxygen concentration in the air of a confined space before entry?
• 1005Which instrument reading means a confined space has a flammable atmosphere hazard?
• 1006Which is the purpose of a lockout/tagout procedure?
• 1007During lockout/tagout, who may remove a lock that was placed on a motor control center?
• 1008Chlorine gas leaks are best approached by an operator who is
• 1009What should be done first when an employee is found unconscious in a manhole?
• 1010Which type of fire extinguisher is rated for energized electrical equipment?
• 1011Under hazard communication (right-to-know) rules, a Safety Data Sheet (SDS) provides
• 1012Which personal protective equipment is most appropriate for a worker collecting a raw sewage sample?
• 1013Which immunization is typically recommended for wastewater workers because of their exposure to sewage?
• 1014What is the main hazard of working near open channels and clarifiers?
• 1015Methane produced in an anaerobic digester is dangerous mainly because it is
• 1016Digester gas piping and gas-handling equipment should be protected by
• 1017The fire triangle consists of
• 1018What does a chlorine ton container's fusible plug do?
• 1019How should a wastewater operator test for a chlorine gas leak at a connection?
• 1020What is the first step in the safe response to a small acid spill on the floor?
• 1021Which action is required before a pump or machine can be repaired while it is connected to a piping system with stored pressure?
• 1022A noise survey shows an operator is exposed to 90 decibels over an 8-hour shift. The best control is
• 1023Lifting heavy objects safely means
• 1024Which situation requires an immediate evacuation by employees?
• 1025A written safety program for a plant is most effective when it includes
• 1026A person who is exposed to raw sewage and then eats lunch without washing is at risk mainly of

Sampling, Laboratory Analysis and Wastewater Characteristics

• 2001A composite sample is made by
• 2002Which test should be run on a grab sample rather than a composite sample?
• 2003A pH of 7.0 is
• 2004If the pH of a sample drops from 7 to 5, the hydrogen ion concentration has
• 2005The five-day BOD test measures
• 2006At what temperature is a standard BOD test incubated?
• 2007How should a BOD sample be preserved if it cannot be analyzed immediately?
• 2008Total suspended solids (TSS) are determined by
• 2009Volatile solids are the portion of solids that
• 2010Settleable solids are measured with
• 2011Which of the following is a typical value for untreated domestic wastewater BOD?
• 2012Typical secondary effluent limits for BOD and TSS under federal secondary treatment standards are
• 2013The dissolved oxygen level in an aeration tank is commonly maintained at
• 2014Chlorine residual in a sample must be measured
• 2015A sample bottle for bacteriological analysis of chlorinated effluent should contain
• 2016Which group of bacteria is the traditional indicator of fecal contamination?
• 2017Which statement about sample bottles is correct?
• 2018The proper location for collecting a sample of plant influent is
• 2019Which in-plant stream is a recycle flow that can raise influent BOD and ammonia when returned untreated?
• 2020Which analysis shows how much organic matter is converted to carbon dioxide and water regardless of biological action?
• 2021Alkalinity in wastewater is important because it
• 2022Nitrification in an activated sludge plant consumes about how much alkalinity per mg/L of ammonia nitrogen oxidized?
• 2023Wastewater that smells like rotten eggs and is black in color is most likely
• 2024What is the most common reason for taking a split sample?
• 2025Which quality control practice best shows whether a laboratory test method is working correctly?
• 2026Turbidity is a measurement of
• 2027Which flow measurement device is a common choice for open channel flow in a treatment plant?
• 2028A sludge sample is found to be 4 percent solids. What is the approximate concentration in mg/L?
• 2029Which is a characteristic of typical domestic wastewater?
• 2030In a laboratory, the best way to dilute concentrated acid is to

Preliminary and Primary Treatment

• 3001Under the California operator certification regulations, preliminary treatment is a process that
• 3002Primary treatment is a process that
• 3003The main purpose of a bar screen is to
• 3004The typical approach velocity in the channel ahead of a mechanically cleaned bar screen is about
• 3005What is the purpose of a grit chamber?
• 3006The velocity in a horizontal-flow grit channel is normally controlled at about
• 3007If a grit chamber velocity is too low, the result will most likely be
• 3008A comminutor or grinder is used to
• 3009The most common cause of odors from a preliminary treatment area is
• 3010How should screenings from a bar screen be handled?
• 3011The main function of a primary clarifier is to
• 3012The typical detention time in a primary clarifier is
• 3013Which problem is most likely to result from leaving sludge in a primary clarifier too long?
• 3014A primary clarifier's overflow rate is calculated by dividing
• 3015If the flow to a clarifier increases and nothing else changes, the surface overflow rate will
• 3016Scum collected from a primary clarifier is normally sent to
• 3017Which is the best indicator that a primary clarifier is being operated properly?
• 3018Pumping primary sludge too infrequently will most likely cause
• 3019A flow equalization basin is used to
• 3020Which action helps protect pumps from damage caused by rags?
• 3021Which of the following is a routine maintenance task for a primary clarifier drive mechanism?
• 3022State design criteria based on the Ten States Standards commonly recommend a primary clarifier weir loading rate in which range?
• 3023Wastewater lift stations are usually equipped with a high-level alarm to

Secondary Treatment (Activated Sludge, Trickling Filters, RBC)

• 4001In the activated sludge process, the activated sludge is
• 4002The purpose of returning activated sludge (RAS) from the secondary clarifier to the aeration tank is to
• 4003The purpose of wasting activated sludge (WAS) is to
• 4004If the operator wastes more sludge from an activated sludge system, the mean cell residence time (MCRT) will
• 4005Which F/M ratio range is typical for a conventional activated sludge plant?
• 4006A very low F/M ratio in an activated sludge plant tends to produce
• 4007Which sludge condition is typically seen with a high F/M ratio?
• 4008A sludge volume index (SVI) of 80 mL/g indicates
• 4009Filamentous bulking is often related to
• 4010Which microscopic organism is commonly found in a healthy, well-settling activated sludge with moderate sludge age?
• 4011Rotifers in large numbers in the aeration tank suggest
• 4012The best location to measure the settleability of mixed liquor with a 30-minute test is
• 4013Foam that is thick, brown, and greasy on an aeration tank is often caused by
• 4014White, billowy foam on an aeration tank is most often a sign of
• 4015Nitrification is the biological conversion of
• 4016Denitrification occurs when
• 4017Rising sludge or floating clumps in a secondary clarifier on a hot day is often caused by
• 4018A trickling filter is a
• 4019Sloughing in a trickling filter refers to
• 4020Which problem often occurs in trickling filters when the hydraulic loading is too low?
• 4021The purpose of recirculation in a trickling filter plant is to
• 4022A rotating biological contactor (RBC) is a
• 4023The purpose of the secondary clarifier is to
• 4024A sludge blanket that is rising too high in a secondary clarifier should be corrected by
• 4025Which is a sign of toxic shock to an activated sludge system?
• 4026Extended aeration plants typically operate with
• 4027A sequencing batch reactor (SBR) carries out its treatment steps
• 4028When dissolved oxygen in an aeration tank is too low, the most likely result is
• 4029Which of the following is true about return activated sludge concentration compared to mixed liquor?
• 4030Which factor most affects the oxygen transfer in a diffused aeration system?
• 4031Suspended-growth treatment is best described as

Stabilization Ponds

• 5001Under 23 CCR 3671, a conventional treatment pond is a pond in which
• 5002A modified treatment pond, by regulatory definition, is a pond in which
• 5003In a facultative pond, oxygen near the surface comes mainly from
• 5004A facultative pond has an aerobic upper layer and
• 5005Dissolved oxygen in a pond is usually highest
• 5006The pH of a healthy pond during the day is usually
• 5007A pond that turns from green to gray or black and develops strong odors has most likely
• 5008A pond that is pink or red in color is often due to
• 5009Which is a common method to control emergent vegetation on pond dikes?
• 5010Which animal activity may seriously damage pond dikes?
• 5011The organic loading rate of a pond is typically expressed as
• 5012What is the typical total detention time in a pond system for facultative treatment?
• 5013Pond effluent often has high suspended solids because of
• 5014Which action can reduce short-circuiting in a pond?
• 5015Ponds in a series are used so that
• 5016The best way to deal with a pond that is anaerobic and odorous is to

Sludge Digestion and Solids Handling

• 6001The main purpose of anaerobic sludge digestion is to
• 6002The typical operating temperature of a mesophilic digester is
• 6003The two groups of bacteria in anaerobic digestion are
• 6004Which condition is the most likely sign of an upset digester?
• 6005A steadily rising volatile acids to alkalinity ratio in an anaerobic digester is mainly a warning of
• 6006A digester that is sour can be corrected by
• 6007Digester gas is normally composed of about
• 6008How should sludge be fed to a digester to keep it stable?
• 6009Under 40 CFR Part 503 Appendix B, anaerobic digestion counts as a Process to Significantly Reduce Pathogens at 35 to 55 degrees C when the mean cell residence time is at least
• 6010Percent volatile solids reduction in a digester is a measure of
• 6011Digester supernatant is returned to the plant headworks. This practice can cause
• 6012Sludge drying beds work by
• 6013Which weather condition will interfere with the use of sludge drying beds?
• 6014A belt filter press is used to
• 6015Polymer is added to sludge before dewatering to
• 6016Gravity thickening of primary sludge is mainly used to
• 6017Waste activated sludge is often thickened by
• 6018What is the best way to prevent odors when handling dewatered sludge?
• 6019The land application of biosolids is regulated mainly to protect
• 6020Class B biosolids must meet requirements for
• 6021Digester mixing is important because it
• 6022The safe way to inspect a digester gas safety device such as a pressure relief valve is
• 6023Scum accumulation in a digester can be reduced by

Disinfection and Dechlorination

• 7001In California operator certification regulations, disinfection includes
• 7002The chemical commonly used for dechlorination is
• 7003What is chlorine demand?
• 7004Chlorine residual is
• 7005Combined chlorine residual is formed when chlorine reacts with
• 7006Compared with free chlorine, combined chlorine residual is
• 7007Which factor does NOT improve chlorine disinfection?
• 7008A chlorine contact tank is designed to provide
• 7009For disinfected tertiary recycled water, California Title 22 requires a chlorine disinfection process to provide a CT of at least 450 mg-min/L and a modal contact time of at least
• 7010How is chlorine gas supplied to treatment plants?
• 7011Sodium hypochlorite is
• 7012Ultraviolet (UV) disinfection works by
• 7013Which water quality factor most strongly reduces the effectiveness of UV disinfection?
• 7014Which test is used to monitor whether a UV system is delivering a proper dose?
• 7015Which regulatory action may result if chlorine residual in a discharge exceeds the permit limit?
• 7016The best way to confirm that sulfur dioxide is not over-applied in dechlorination is to
• 7017Which action is part of safely changing a chlorine cylinder?
• 7018Breakpoint chlorination refers to
• 7019Why are chlorine cylinders stored upright and secured?
• 7020A chlorine residual in the effluent that suddenly drops while the dose stays the same most likely means

Regulations, Classification and Operator Certification

• 8001Which agency administers wastewater treatment plant operator certification in California?
• 8002A wastewater treatment plant with a primary process and a design flow of 0.8 MGD is classified as
• 8003A conventional treatment pond is classified as
• 8004An activated sludge plant with a design flow of 3.0 MGD is classified as
• 8005A biofiltration (trickling filter) plant with a design flow of 0.9 MGD is classified as
• 8006A primary treatment plant with a design flow of 3 MGD is classified as
• 8007What minimum grade must the chief plant operator hold at a Class II wastewater treatment plant?
• 8008What minimum grade must the designated operator-in-charge hold at a Class III wastewater treatment plant?
• 8009An operator-in-training must work
• 8010An operator-in-training certificate is valid for
• 8011Passing examination results for a wastewater operator exam are valid for
• 8012An operator certificate may be renewed repeatedly for periods of
• 8013Which education is required to apply for the Grade I exam and certificate?
• 8014What is the experience requirement for Grade II certification under path 1?
• 8015One semester college course of three units equals how many educational points?
• 8016Operations experience in an industrial or manufacturing facility is
• 8017Under the California wastewater operator certification regulations, which fees are refundable?
• 8018The designated operator-in-charge is appointed by
• 8019Lone operator approval by the Office of Operator Certification is valid for
• 8020What must a plant owner show to get approval to use a lone operator?
• 8021Wastewater operator exam questions are
• 8022The federal law that regulates discharges of pollutants to waters of the United States is the
• 8023An NPDES permit is issued to
• 8024In California, waste discharge requirements for wastewater plants are issued mainly by
• 8025A discharge monitoring report (DMR) or self-monitoring report is used to
• 8026When a sanitary sewer overflow occurs, the operator should
• 8027Pretreatment programs for industrial users are meant to
• 8028The most important reason for keeping accurate operating records is to
• 8029A basic supervision responsibility of a Grade II operator includes

Process Math and Unit Conversions

• 9001A plant receives 2.5 MGD with an influent BOD of 220 mg/L. How many pounds of BOD enter the plant per day?
• 9002A plant treats 1.8 MGD. Influent TSS is 250 mg/L and effluent TSS is 20 mg/L. How many pounds of TSS are removed per day?
• 9003Influent BOD is 210 mg/L and effluent BOD is 18 mg/L. What is the percent removal?
• 9004A rectangular tank is 60 ft long, 20 ft wide, and 10 ft deep. Flow is 1.5 MGD. What is the detention time in hours?
• 9005A circular clarifier has a diameter of 50 ft and receives 1.2 MGD. What is the surface overflow rate?
• 9006A circular clarifier, 60 ft in diameter, has a weir around its circumference. Flow is 1.5 MGD. What is the weir overflow rate?
• 9007The chlorine dose is 8 mg/L and the flow is 3 MGD. How many pounds of chlorine are needed per day?
• 9008A chlorine dosage of 9.0 mg/L produces a residual of 1.5 mg/L after contact. What is the chlorine demand?
• 9009A wet well is 10 ft by 12 ft. The pump lowers the water level by 2.5 ft in 5 minutes. What is the pumping rate?
• 9010A sludge sample contains 5,000 mg/L of solids. What is this in percent solids?
• 9011Sludge is 3.2 percent solids. What is the concentration in mg/L?
• 9012A flow of 2.4 MGD is equal to how many gallons per minute?
• 9013A flow of 900 gpm is equal to how many MGD?
• 9014Water flows in a channel 4 ft wide at a depth of 1.5 ft. The flow is 9 cfs. What is the velocity?
• 9015A cylindrical digester has a diameter of 40 ft and a sidewater depth of 25 ft. What is its volume in cubic feet?
• 9016A digester receives 2,200 lbs of volatile solids per day. Its volume is 15,000 ft3. What is the volatile solids loading rate?
• 9017A trickling filter receives 0.8 MGD with 150 mg/L BOD. Its media volume is 40,000 ft3. What is the organic loading in lbs BOD/day/1,000 ft3?
• 9018A trickling filter has a surface area of 7,850 ft2 and receives 1.0 MGD. What is the hydraulic loading rate?
• 9019A pond receives 0.3 MGD with a BOD of 180 mg/L. The pond surface area is 12 acres. What is the organic loading rate in lbs BOD/acre/day?
• 9020A pond is 5 acres in area with an average depth of 4 ft. Flow is 0.25 MGD. What is the detention time in days? (1 acre-ft = 325,851 gal)
• 9021A sludge pump runs 15 minutes each hour at 40 gpm. The sludge is 5 percent solids. How many pounds of solids are pumped per day? (Assume 8.34 lbs/gal)
• 9022An aeration tank holds 1.2 MG and the MLSS is 2,800 mg/L. How many pounds of MLSS are in the tank?
• 9023Flow is 2.0 MGD, primary effluent BOD is 200 mg/L, the aeration tank is 0.8 MG, and MLVSS is 2,100 mg/L. What is the F/M ratio?
• 9024The 30-minute settled volume is 280 mL/L and the MLSS is 2,800 mg/L. What is the sludge volume index?
• 9025A 1-liter sample of mixed liquor settles to 250 mL in 30 minutes. The MLSS is 2,000 mg/L. What is the sludge volume index (SVI)?
• 9026An activated sludge system has 37,530 lbs of solids in the aeration tank and 6,000 lbs in the clarifier. Solids leaving per day are 3,336 lbs in the waste sludge and 167 lbs in the effluent. What is the MCRT?
• 9027Waste activated sludge is pumped at 0.04 MGD with a concentration of 7,500 mg/L. How many pounds per day are wasted?
• 9028The return activated sludge flow is 1.2 MGD and the influent flow is 3.0 MGD. What is the return rate as a percent of influent flow?
• 9029Influent ammonia nitrogen is 28 mg/L and effluent ammonia nitrogen is 2 mg/L at a flow of 1.5 MGD. How many pounds of ammonia nitrogen are removed per day?
• 9030A lab measures a sample temperature of 77 degrees Fahrenheit. What is this in degrees Celsius?
• 9031The water depth in a tank is 18 ft. What is the pressure at the bottom? (1 ft of water = 0.43 psi)
• 9032A pump delivers 500 gpm against a total dynamic head of 60 ft. Pump efficiency is 70 percent. What is the brake horsepower? (1 hp = 3,960 gpm-ft)
• 9033A circular clarifier has a diameter of 60 ft and a water depth of 12 ft. The flow is 2.0 MGD. What is the detention time in hours?
• 9034A 50 gram wet sludge sample leaves 2.5 grams of dry solids after drying. What is the percent solids?
• 9035A flow of 3 cfs is equal to how many MGD? (1 MGD = 1.547 cfs)
• 9036A plant feeds 12.5 percent sodium hypochlorite (about 1.04 lbs of available chlorine per gallon) to dose 4 mg/L at 1.5 MGD. How many gallons of solution are needed per day?