California Water Distribution Operator Exam: all 229 questions with answers

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

• Disinfection31 questions
• Distribution System Design and Hydraulics35 questions
• Equipment Operation, Maintenance and Inspections35 questions
• Drinking Water Regulations, Management and Safety31 questions
• Water Mains and Piping36 questions
• Water Quality and Water Sources25 questions
• Distribution Math36 questions

Disinfection

• 1001Why is a new or repaired water main disinfected before it is placed in service?
• 1002Under the AWWA C651 continuous-feed method, what is the minimum chlorine concentration in the new main at the start of the contact period?
• 1003Under the AWWA C651 slug method, which dose and contact time apply?
• 1004After the 24-hour contact period of the continuous-feed method, what free chlorine residual must remain in the main?
• 1005Why should a new main be flushed before the disinfectant is added?
• 1006Heavily chlorinated water flushed from a main must be dechlorinated before it reaches a storm drain or creek. Which chemical is commonly used?
• 1007Approximately what percentage of available chlorine does calcium hypochlorite (HTH) contain?
• 1008Which form of chlorine is 100 percent available chlorine?
• 1009A chlorine dose of 3.0 mg/L produces a free chlorine residual of 0.8 mg/L after the contact time. What is the chlorine demand?
• 1010Which substances commonly create chlorine demand in a distribution system?
• 1011The total chlorine residual equals which combination?
• 1012Which test is most often used by operators in the field to measure chlorine residual?
• 1013A sudden drop of chlorine residual at a dead-end hydrant most likely points to what?
• 1014Before a newly disinfected main is placed in service, what must the bacteriological samples show?
• 1015Which standard covers the disinfection of new and repaired water mains?
• 1016A well is most likely to need disinfection in which situation?
• 1017Which of the following is a common source of contamination of a water storage reservoir?
• 1018Chlorine gas is heavier than air. Where should an operator expect leaking gas to collect?
• 1019At which pH is free chlorine the most effective disinfectant?
• 1020Which form of free chlorine is the stronger disinfectant?
• 1021What chlorine to ammonia-nitrogen ratio, by weight, is typically targeted when making chloramines?
• 1022Which is an advantage of using chloramines instead of free chlorine in a distribution system?
• 1023Which problem is specific to chloraminated distribution systems?
• 1024Water that will be used for kidney dialysis or fish tanks needs special treatment when the system uses chloramines. Why?
• 1025On the chlorine dose curve, what is the breakpoint?
• 1026In a breakpoint chlorination curve, what makes up the residual after the breakpoint is passed?
• 1027What is the main cause of disinfection byproducts such as trihalomethanes in a distribution system?
• 1028Which AWWA standard covers disinfection of water storage facilities?
• 1029Which AWWA standard covers disinfection of wells?
• 1030Under 22 CCR 64580, what must be true of the bacteriological samples from a new water main before it is placed into service?
• 1031Which AWWA standard does 22 CCR 64582 require for disinfecting and bacteriological sampling of a distribution reservoir that was taken out of service for repair or inspection?

Distribution System Design and Hydraulics

• 2001What is backflow?
• 2002Back-siphonage occurs when which condition exists in the supply piping?
• 2003Back-pressure backflow occurs when:
• 2004Which backflow prevention method provides the highest level of protection?
• 2005Under the State Water Board's Cross-Connection Control Policy Handbook, what is the minimum vertical air-gap separation between the supply outlet and the flood level of the receiving vessel?
• 2006Which assembly is generally required to protect the public water supply from a high-hazard cross-connection that may see back-pressure?
• 2007A garden hose submerged in a bucket of fertilizer solution and connected to a hose bib is an example of what?
• 2008How often must testable backflow prevention assemblies be tested in California?
• 2009What is the water hammer?
• 2010Which operating practice helps reduce water hammer?
• 2011A pressure gauge reading is 0 psi at a customer's tap that normally has 60 psi. What should the operator check first?
• 2012In a gridded or looped distribution system, how is the water supplied to a given point?
• 2013What is the main disadvantage of a dead-end main?
• 2014Which type of pipe carries water from the source or treatment plant to the distribution system with few or no service connections?
• 2015How does a trunk main differ from a transmission main?
• 2016How are pressure and elevation related in a distribution system?
• 2017What is static pressure?
• 2018During a hydrant flow test, what does the residual pressure represent?
• 2019Which term describes the highest rate of water use during a single hour of the day?
• 2020What does per-capita demand measure?
• 2021Higher friction in a pipe causes which result?
• 2022What is cavitation in a pump?
• 2023Which sign usually indicates that a pump is cavitating?
• 2024Which type of storage facility sits on high ground and floats on the system to even out pressure and demand?
• 2025What are the main purposes of distribution system storage?
• 2026Which action should be done when a storage tank is drained for cleaning?
• 2027How is a map scale of 1 inch = 200 feet used?
• 2028What is the main purpose of a service line record such as a tap card?
• 2029Which material is commonly used for a corporation stop at the main tap?
• 2030What does a pressure reducing valve (PRV) do in a distribution system?
• 2031How is the surface area of a valve face calculated when thrust force is needed?
• 2032Which action increases the velocity of water in a pipe if the flow rate stays the same?
• 2033What relationship exists between water velocity and pressure in a pipe at a constant flow rate?
• 2034What is the pressure at the bottom of a tank filled with 46.2 feet of water?
• 2035A pressure gauge on a hydrant reads 80 psi. What is the matching head, in feet?

Equipment Operation, Maintenance and Inspections

• 3001Which valve is normally used to isolate a section of main and is operated fully open or fully closed?
• 3002What is the purpose of a check valve on a pump discharge?
• 3003Where is an air release valve normally installed?
• 3004Which valve type takes many turns of the operator to close, which helps limit water hammer?
• 3005What is a valve exercising program?
• 3006A valve box is found paved over after a street resurfacing. What should the operator do?
• 3007Which meter type is most common for single-family residential service?
• 3008Why is it important to choose the correct meter size for a customer?
• 3009A compound meter is used for which type of service?
• 3010What is the main difference between a dry-barrel and a wet-barrel hydrant?
• 3011After shutting off a dry-barrel hydrant, how can an operator confirm the barrel is draining?
• 3012Why are thrust blocks installed on a water main?
• 3013How should a hydrant be operated during flushing to limit surges?
• 3015How is the feed rate of a chemical metering pump typically adjusted?
• 3016How is a chemical feed pump calibrated using a graduated cylinder?
• 3017A chemical feed pump runs but delivers no chemical. Which is a likely cause?
• 3018What is the purpose of a sacrificial anode in cathodic protection?
• 3019What does a corrosion cell need besides an anode and a cathode?
• 3020What is the purpose of SCADA in a water system?
• 3021A SCADA tank level transmitter outputs 4 to 20 mA. What does 4 mA normally represent?
• 3022Which pump type is most common for booster stations in water distribution?
• 3023What happens in a centrifugal pump when the discharge valve is shut with the pump still running?
• 3024Which condition indicates abnormal pump operation?
• 3025How much leakage should a packed centrifugal pump gland normally show?
• 3026What must be done before working on an electric motor or pump?
• 3027What should be checked before starting a standby generator for a routine test?
• 3028Why must a standby generator never be connected to a building panel without a transfer switch?
• 3029What routine attention do in-line chlorine analyzers need?
• 3030What is proper backfill practice around a newly installed pipe?
• 3031What is the purpose of pipe bedding?
• 3032Which finding during inspection shows that a pipe is damaged and should not be installed?
• 3033How can thrust be resisted where a concrete block is not practical?
• 3034What does a sanitary seal on a well do?
• 3035What is the purpose of a tank overflow pipe?
• 3036Which security measure is commonly used for storage facilities?

Drinking Water Regulations, Management and Safety

• 4001What is the main purpose of the Safe Drinking Water Act (SDWA)?
• 4002What is a maximum contaminant level (MCL)?
• 4003How do primary and secondary MCLs differ?
• 4004What is the maximum residual disinfectant level (MRDL) for chlorine in the federal rule?
• 4005What is the federal MCL for total trihalomethanes (TTHM)?
• 4006What is the MCL for nitrate as nitrogen?
• 4007Under public notification rules, which event is an acute violation requiring notice within 24 hours?
• 4008How quickly must Tier 2 public notice be given after a violation, in general?
• 4009What document identifies the locations where routine total coliform samples are collected?
• 4010After a routine total coliform positive sample, how many repeat samples are generally collected under the revised total coliform rule?
• 4011What do the regulations require operators to do after a positive E. coli result?
• 4012What is the federal lead action level?
• 4013What is the federal action level for copper at the tap?
• 4014How is a standard lead and copper tap sample collected?
• 4015Where are Stage 2 disinfection byproduct samples generally collected?
• 4016How long after passing the exam can an applicant submit the certification application in California?
• 4017What is the education requirement for taking the D1 exam in California?
• 4018What additional qualification does D2 require for the exam, beyond a high school diploma or GED?
• 4019At what trench depth does Cal/OSHA generally require a protective system such as shoring, sloping or a trench box?
• 4020What is the role of the competent person at an excavation?
• 4021In a trench 4 feet or deeper, how close must a ladder or other exit be to workers?
• 4022How far from the edge of an excavation should spoil piles and equipment be kept?
• 4023What oxygen concentration range is considered safe to enter a confined space?
• 4024Which is an example of a permit-required confined space hazard for water workers?
• 4025What is the purpose of a Safety Data Sheet (SDS)?
• 4026What does California's Injury and Illness Prevention Program (IIPP) require?
• 4027Before digging in California, an operator should contact Underground Service Alert (811). How much notice is typically required?
• 4028Which traffic control practice protects workers at a street excavation?
• 4029Which activity is part of the preventive maintenance program?
• 4030Which of the following should be included in a water system's emergency response plan?
• 4031Why is record keeping of a fire hydrant testing program important?

Water Mains and Piping

• 5001Which of these pipe materials is used for gravity sewers rather than pressurized water mains?
• 5002What is a main advantage of ductile iron pipe?
• 5003Why is polyethylene encasement used on ductile iron pipe?
• 5004Which pipe material resists corrosion but can become brittle in sunlight and must be stored out of UV exposure?
• 5005Why must asbestos-cement (AC) pipe be cut with wet methods or hand tools?
• 5006Which pipes are likely to have lead solder or lead goosenecks in older service lines?
• 5007Which is the main reason to keep mains and service lines of dissimilar metals separated by dielectric fittings?
• 5008What is the purpose of flushing a main?
• 5009Who should be notified before a planned flushing program?
• 5010What is a typical sign of a main break?
• 5011Which method is used to locate a buried metallic pipe?
• 5012What is the purpose of a tracer wire installed with plastic pipe?
• 5013How is a temporary service set up during a main repair?
• 5014Which practice prevents contamination of a pipe being installed?
• 5015What is the correct way to lower a heavy pipe section into a trench?
• 5016What should be done with wet or unstable soil at the bottom of a trench before laying pipe?
• 5017Which equipment is used to compact backfill in layers?
• 5018What does a tapping machine do?
• 5019Which factor determines the tap size relative to the main?
• 5020What is the purpose of a corporation stop?
• 5021Where is a curb stop usually located?
• 5022Why should a new service line be flushed before the meter is installed?
• 5023Which pipe fitting changes a line's direction?
• 5024Which fitting would be used to connect two pipes of different diameters?
• 5025Which kind of joint allows a pipeline to deflect slightly and absorb ground movement?
• 5026What is the C-factor (Hazen-Williams coefficient) a measure of?
• 5027Which C-factor best fits new PVC pipe?
• 5028What causes tuberculation inside iron pipe?
• 5029Which effect results from heavy tuberculation?
• 5030Which method can clean a main by pushing a foam swab through it?
• 5031How is a leak in a buried main commonly pinpointed?
• 5032Which factor makes leak detection by sound more difficult?
• 5033What is the purpose of a thrust block's size calculation?
• 5034Under 22 CCR 64570, which AWWA standard applies to the installation of newly installed ductile iron water mains?
• 5035Which soil type is the most difficult for trench stability?
• 5036What is the purpose of dewatering in a trench?

Water Quality and Water Sources

• 6001What are pathogenic organisms?
• 6002Why are coliform bacteria tested for in drinking water?
• 6003A positive E. coli result in a drinking water sample indicates what?
• 6004What does a presumptive coliform test result tell you?
• 6005Why do bacteriological sample bottles contain sodium thiosulfate?
• 6006Which sampling technique helps avoid contaminating a coliform sample?
• 6007What is the maximum holding time for a total coliform sample before analysis?
• 6008What does a heterotrophic plate count (HPC) indicate?
• 6009High turbidity in a distribution system is most likely caused by what?
• 6010What is the normal pH range of drinking water in the secondary standards?
• 6011What effect does a low pH have on distribution pipes?
• 6012What is a common effect of very hard water in a distribution system?
• 6013What health risk is associated with high nitrate in drinking water?
• 6014What does the term conductivity measure?
• 6015What is the hydrologic cycle?
• 6016What is the static water level in a well?
• 6017What is the cone of depression around a pumping well?
• 6018Which of these is a potential groundwater contamination source near a well?
• 6019What is a sanitary survey?
• 6020Why are Giardia and Cryptosporidium difficult to control with chlorine alone?
• 6021Which disease is caused by a waterborne protozoan?
• 6022A customer reports a rotten-egg odor from the hot water tap only. What is a likely cause?
• 6023Which customer complaint is most often caused by iron corrosion products stirred up by a flow change?
• 6024What is the purpose of unidirectional flushing?
• 6025Under 22 CCR 64575, what is the minimum flushing velocity that must be maintained in a main?

Distribution Math

• 7001How many gallons does a 500-foot section of 12-inch water main hold?
• 7002How many gallons are needed to fill 1,000 feet of 8-inch main?
• 7003A rectangular tank is 20 feet long, 10 feet wide and holds water 8 feet deep. What is its volume?
• 7004A cylindrical storage tank is 30 feet in diameter and holds water 20 feet deep. About how many gallons does it hold?
• 7005A trench is 200 feet long, 3 feet wide and 5 feet deep. How many cubic yards of soil are excavated?
• 7006How many pounds of pure chlorine are needed to dose a 2,000-foot, 8-inch main to 25 mg/L?
• 7007How many pounds of chlorine gas are needed to dose 0.25 million gallons of water to 2.0 mg/L?
• 7008How many pounds of 65 percent calcium hypochlorite are needed to dose 0.5 MG of water to 3.0 mg/L?
• 7009How many gallons of 12.5 percent liquid hypochlorite (assume 8.34 lb per gallon) are needed to dose 1.0 MG of water to 2.0 mg/L?
• 7010A water sample has a chlorine demand of 1.8 mg/L and the operator wants a free chlorine residual of 0.5 mg/L. What dose is required?
• 7011Water flows at 3 feet per second in a 12-inch pipe. What is the flow in gallons per minute?
• 7012A tank water level is 92.4 feet above a pressure gauge. What gauge pressure is shown?
• 7013A pressure gauge reads 65 psi. What is the equivalent head in feet?
• 7014A pump delivers 350 gallons per minute. How many gallons does it deliver in one day?
• 7015A system uses 1.44 million gallons per day (MGD). What is the average flow in gpm?
• 7016A well with an 8-inch casing has 120 feet of water standing in it. About how many gallons of water are in the casing?
• 7017The static water level in a well is 45 feet and the pumping level is 72 feet. What is the drawdown?
• 7018What is the cross-sectional area of an 18-inch pipe, in square feet?
• 7019A 12-inch valve is closed against 60 psi. What is the total force on the valve face?
• 7020A 50,000 gallon tank is filled at 250 gpm. How long will it take to fill an empty tank?
• 7021A meter reads 482,500 gallons on May 1 and 497,200 gallons on May 15. What is the average daily use over those 14 days?
• 7022What is the velocity in a 12-inch pipe that carries 1.0 MGD? (1 MGD = 1.55 cfs)
• 7023What is the capacity of an 8-inch pipe flowing at 4 feet per second, in gallons per minute?
• 7024A cylindrical tank is 40 feet in diameter and 25 feet high. What is the area of the interior side wall to be sprayed with disinfectant?
• 7025The thrust on a bend is 12,000 pounds and the soil can bear 2,000 pounds per square foot. What bearing area is needed on the thrust block?
• 7026Water contains 0.5 mg/L of ammonia-nitrogen. How much chlorine is needed to reach a 4:1 chlorine to ammonia-nitrogen ratio?
• 7027A pressure gauge on a well discharge reads 18 psi at ground level, with the pump off and a closed valve. How many feet of water is above the gauge?
• 7028On a system map, 1 inch equals 400 feet. A main measures 3.5 inches on the map. What is the actual length?
• 7029A 120,000 gallon tank has 200 gpm flowing in and 700 gpm flowing out. How many hours until the full tank is empty?
• 7030A chemical feed pump delivers 120 mL per minute. How many gallons per day is this?
• 7031How many pounds of chlorine are needed to raise 2.4 MG of water by 1.5 mg/L?
• 7032How many mg/L are in a 0.5 percent chlorine solution?
• 7033A trench is 150 feet long, 3 feet wide and 6 feet deep. A 12-inch pipe 150 feet long is laid in it. What is the trench volume in cubic yards?
• 7034A system uses 25 pounds of chlorine per day at $0.90 per pound. What is the daily chemical cost?
• 7035How many gallons are in 300 feet of 6-inch service main?
• 7036A reservoir surface measures 40 feet by 20 feet. How many gallons are held by each foot of depth?