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Illinois Environmental Protection Agency (IEPA) operator
certification exam 2025 Questions and Correct Answers
(Verified Answers) Plus Rationales
It covers topics relevant to water and wastewater operators in Illinois, including regulations, process control, safety, math, and sampling.
- What is the primary purpose of a sedimentation basin in water treatment? A. Disinfection B. Removal of suspended solids C. Removal of dissolved gases D. Reduction of hardness Sedimentation allows particles to settle out of water by gravity, removing suspended solids.
- What is the typical detention time for a primary clarifier? A. 15 minutes B. 1 hour C. 2 hours D. 6 hours A detention time of around 2 hours is standard for primary clarification to allow solids to settle.
- Chlorine residual is most commonly measured using which method?
A. Spectrophotometry B. Ion exchange C. DPD colorimetric method D. UV absorbance The DPD (N,N-diethyl-p-phenylenediamine) method is widely used for measuring chlorine residual.
- Which component removes fine particles following sedimentation? A. Filtration B. Screening C. Coagulation D. Grit removal Filters remove fine particulate matter that was not settled in earlier processes.
- What is the standard pH range for optimal coagulation? A. 3.5–4. B. 5.5–7. C. 8.0–9. D. 10.0–11. Most coagulants work effectively within a pH of 5.5 to 7.5.
- What is a typical free chlorine residual required in a water distribution system? A. 0.05 mg/L B. 0.1 mg/L C. 0.2 mg/L D. 1.5 mg/L
C. Carbon dioxide D. Sulfate Chloramines are often used to maintain residual disinfectant levels in distribution. 11.What does BOD measure? A. Chemical content B. Biodegradable organic matter C. Pathogens D. Chlorine demand BOD (Biochemical Oxygen Demand) indicates the amount of biodegradable material present. 12.The IEPA requires water systems to submit what type of report annually? A. Permit-to-operate B. MSDS report C. Emergency action plan D. Consumer Confidence Report The CCR informs consumers about water quality and any violations. 13.What is the standard for total coliform in drinking water? A. 0 per 100 mL B. 1 per 100 mL C. 5 per 100 mL D. 10 per 100 mL Any detection of coliform bacteria is a violation in a routine sample.
14.What is the maximum contaminant level (MCL) for nitrate in drinking water? A. 1 mg/L B. 5 mg/L C. 10 mg/L D. 15 mg/L The MCL for nitrate is 10 mg/L to protect against methemoglobinemia ("blue baby syndrome"). 15.Which agency certifies drinking water operators in Illinois? A. OSHA B. Illinois Environmental Protection Agency (IEPA) C. U.S. EPA D. CDC IEPA oversees operator certification and compliance. 16.What PPE is typically required when handling chlorine gas? A. Respirator and chemical-resistant gloves B. Hard hat and ear plugs C. Face shield and apron D. Safety vest Chlorine gas is toxic; proper PPE includes a respirator and gloves. 17.Which of the following chemicals is a coagulant? A. Lime B. Aluminum sulfate
A. Destroy pathogenic microorganisms B. Remove solids C. Reduce hardness D. Adjust pH Disinfection inactivates harmful pathogens in the water. 22.Which method is used to determine total suspended solids (TSS)? A. pH test B. Gravimetric analysis C. Turbidimeter D. Chlorine titration TSS is measured by filtering, drying, and weighing solids. 23.What is the purpose of a weir in a clarifier? A. Control sludge thickness B. Increase mixing C. Ensure even flow distribution D. Add chemicals Weirs help distribute flow evenly across the clarifier’s surface. 24.A positive coliform test requires: A. Retesting within a week B. Immediate public notification and repeat testing C. System shutdown D. Sample dilution Immediate action is required for positive coliform samples per IEPA rules.
25.What is the purpose of a jar test? A. Determine optimal coagulant dosage B. Measure chlorine demand C. Test BOD D. Determine flow rate Jar testing helps optimize coagulation and flocculation treatment. 26.Which of the following best describes cross-connection? A. Two pipes of the same type joined together B. A backup power line C. A connection between potable and non-potable water systems D. A double-check valve A cross-connection can allow contaminants to enter the potable water system, creating a health hazard. 27.What is the primary concern if pressure in the distribution system drops below 20 psi? A. Pump cavitation B. Water hammer C. Contamination through backflow D. Over-chlorination Low pressure can allow back-siphonage or backflow, potentially contaminating the water supply.
A. Lime B. Alum C. Fluoride D. Sulfur dioxide Sulfur dioxide is commonly used to remove residual chlorine from treated water. 32.If the pH of water is too low, it may: A. Increase hardness B. Corrode pipes C. Improve taste D. Reduce chlorine demand Acidic water can corrode metal pipes and plumbing systems. 33.What is the purpose of fluoride addition in drinking water? A. Control corrosion B. Disinfect C. Prevent tooth decay D. Remove iron Fluoride helps strengthen enamel and reduce dental cavities. 34.What is the primary danger of confined spaces in a treatment plant? A. High humidity B. Oxygen deficiency or toxic gases C. Slippery floors D. Loud equipment Confined spaces may have unsafe air quality, requiring testing before entry.
35.Which of the following requires a confined space entry permit? A. Mechanical room B. Laboratory C. Underground wet well D. Chemical storage shed Wet wells are considered permit-required confined spaces due to limited entry and hazardous atmosphere risk. 36.What is the most common cause of pump cavitation? A. Too much voltage B. Insufficient suction head C. High chlorine levels D. Poorly lubricated bearings Cavitation occurs when pressure drops below vapor pressure, causing vapor bubbles and damage. 37.When sampling for lead and copper, where should samples be collected? A. From the water main B. From a hydrant C. From the treatment plant D. From the customer's tap Samples are taken from household taps because the concern is corrosion from plumbing. 38.What laboratory test is most commonly used to assess treatment plant efficiency?
42.Why are volatile organic compounds (VOCs) regulated in drinking water? A. They can be toxic and carcinogenic B. They are nutrients for bacteria C. They reduce dissolved oxygen D. They are odorless and harmless VOCs can pose serious health risks and must be monitored. 43.What is the function of a check valve? A. Regulates flow rate B. Mixes chemicals C. Measures flow D. Prevents backflow A check valve allows flow in one direction, preventing reverse flow contamination. 44.Which best describes flocculation? A. Removal of dissolved gases B. Gentle mixing to form larger particles C. High-speed mixing D. pH adjustment Flocculation gently stirs the water to form larger flocs from smaller particles. 45.What is the typical temperature range for accurate BOD testing? A. 5°C B. 20°C C. 37°C
D. 100°C
BOD tests are incubated at 20°C for 5 days according to standard methods. 46.What is the maximum allowable limit for arsenic in drinking water under the Safe Drinking Water Act? A. 1 μg/L B. 10 μg/L C. 50 μg/L D. 100 μg/L The U.S. EPA MCL for arsenic is 10 μg/L. 47.How often must chlorine residual be tested in a community water system? A. Once per week B. Daily or more, depending on system size C. Monthly D. Quarterly IEPA requires regular testing, typically daily or per sampling schedule, depending on population. 48.What is used to remove manganese and iron? A. Oxidation and filtration B. Coagulation and flocculation C. Sedimentation only D. UV disinfection Oxidation with chlorine or potassium permanganate followed by filtration removes iron and manganese.
A. Coagulation B. Sedimentation C. Filtration D. Disinfection Coagulation destabilizes particles for removal in subsequent processes. 53.What is the main concern when chlorine gas leaks in a confined space? A. Low light levels B. Asphyxiation or chemical burns C. Slippery floors D. Heat buildup Chlorine gas is highly toxic and can displace oxygen, causing respiratory failure. 54.What is the purpose of a clearwell? A. Aeration B. Sludge digestion C. Contact time for disinfection D. Sand removal Clearwells provide the necessary time for disinfectants like chlorine to inactivate pathogens. 55.Which measurement unit is most commonly used for turbidity? A. mg/L B. mL/L C. NTU D. μg/L Nephelometric Turbidity Units (NTU) are used with turbidity meters.
56.What chemical is commonly used for pH adjustment in water treatment? A. Fluoride B. Sodium hydroxide C. Chlorine D. Potassium permanganate Sodium hydroxide (caustic soda) raises pH by neutralizing acids. 57.How should chlorine cylinders be stored? A. Vertically, valve up B. Horizontally, secured and ventilated C. Next to heat sources D. Submerged in water Chlorine gas cylinders are stored horizontally and must be secured in a ventilated space. 58.What is the IEPA’s limit for turbidity in filtered drinking water (95% of samples per month)? A. 5 NTU B. 1.0 NTU C. 0.3 NTU D. 0.1 NTU IEPA and EPA require turbidity of ≤0.3 NTU in 95% of monthly samples for compliance. 59.What is a breakpoint in chlorination?
D. 90 minutes From EPA CT tables, at 1 mg/L, 60 min of contact time is typically needed at 10°C for 4-log virus inactivation. 63.Which valve is best for throttling flow? A. Check valve B. Gate valve C. Globe valve D. Butterfly valve Globe valves allow for precise flow regulation. 64.What is head loss? A. Total height of the tank B. Pressure loss due to friction in pipes or filters C. Velocity head D. Overflow level Head loss is the energy loss in a system caused by friction or obstructions. 65.What is a typical filter media used in water treatment? A. Sand and anthracite B. Activated carbon only C. Zeolite D. Gravel only Dual media filters commonly use sand and anthracite to improve efficiency. 66.The IEPA requires public notification within how long for a Tier 1 (acute) violation?
A. 24 hours B. 48 hours C. 7 days D. 30 days Tier 1 violations (e.g., total coliforms, nitrates) require 24-hour public notification. 67.What does a fluoride overfeed most directly affect? A. Dental health and skeletal safety B. Turbidity C. pH D. Iron levels Too much fluoride can cause fluorosis or skeletal issues. 68.When performing jar testing, what is adjusted to form floc? A. Coagulant dose and pH B. Chlorine dose and turbidity C. Flow rate and temperature D. Filter run time Jar testing optimizes coagulant dosage and pH to maximize floc formation. 69.What is the typical detention time for a flocculation basin? A. 15 minutes B. 30 seconds C. 30–45 minutes D. 3 hours
