Free Practice Questions for Engineer Water Pollution Environmental

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Exam pass rate: Written examination about 29%; practical examination about 36% (HRD Korea statistics for the most recent full year)

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Key Facts: Engineer Water Pollution Environmental Exam

80 Items

Written examination questions since 2025 (20 items x 4 subjects)

HRD Korea / Q-Net 출제기준

120 Mins

Total written testing time (30 minutes per subject)

Q-Net examination guide

KRW 19,400

Written examination registration fee

HRD Korea fee schedule

KRW 22,600

Practical examination (수질오염방지 실무) fee

HRD Korea fee schedule

60 Points

Overall pass mark, with at least 40 points required in every subject

National Technical Qualifications Act

80 MCQs

Questions in this independent English-language study bank

OpenExamPrep practice bank

Administered by HRD Korea (한국산업인력공단 / Q-Net) under the Ministry of Environment, the Engineer Water Pollution Environmental (수질환경기사) written examination is 80 four-option multiple-choice questions across 4 subjects in 120 minutes, with at least 40 points required in every subject and 60 points overall. Written fee KRW 19,400; practical fee KRW 22,600. This 80-question bank is an independent English-language MCQ study adaptation by OpenExamPrep — not an official translation or format simulation — built to the subject list that took effect on 1 January 2025.

Sample Engineer Water Pollution Environmental Practice Questions

Try these sample questions to review concepts for the Engineer Water Pollution Environmental exam. Each question includes a detailed explanation. Start the interactive quiz above for the full 80+ question experience with AI tutoring.

1A wastewater sample has a 5-day biochemical oxygen demand (BOD5) of 150 mg/L at 20°C. Assuming the carbonaceous deoxygenation follows first-order reaction kinetics with a base-10 reaction rate constant k1 of 0.10 day^-1, what is the ultimate biochemical oxygen demand (Lo) of this wastewater?

A.185 mg/L

B.220 mg/L

C.280 mg/L

D.315 mg/L

Explanation: Under first-order BOD kinetics using common logarithm (base 10), the relationship between BOD at time t and ultimate BOD (Lo) is given by BODt = Lo * (1 - 10^(-k1 * t)). Substituting t = 5 days, k1 = 0.10 day^-1, and BOD5 = 150 mg/L: 150 = Lo * (1 - 10^(-0.10 * 5)) = Lo * (1 - 10^(-0.50)). Since 10^(-0.50) = 1 / sqrt(10) ≈ 0.3162, we have (1 - 0.3162) = 0.6838. Therefore, Lo = 150 / 0.6838 ≈ 219.36 mg/L, which rounds to 220 mg/L.

2The base-10 BOD deoxygenation rate constant (탈산소계수 k1) of a municipal river is determined to be 0.10 day^-1 at standard temperature (20°C). Using the modified Streeter-Phelps temperature coefficient theta (θ) = 1.047, what is the deoxygenation rate constant at 25°C?

A.0.105 day^-1

B.0.126 day^-1

C.0.148 day^-1

D.0.172 day^-1

Explanation: The temperature dependence of the biochemical deoxygenation rate constant is modeled by the modified Arrhenius equation: k_T = k_20 * θ^(T - 20). Here, T = 25°C, k_20 = 0.10 day^-1, and θ = 1.047. Thus, k_25 = 0.10 * (1.047)^(25 - 20) = 0.10 * (1.047)^5. Calculating (1.047)^5: 1.047^2 ≈ 1.0962, 1.047^4 ≈ 1.2017, and 1.2017 * 1.047 ≈ 1.2582. Therefore, k_25 = 0.10 * 1.2582 ≈ 0.126 day^-1.

3In the Streeter-Phelps dissolved oxygen sag analysis for a river, what does Fair's self-purification constant (자가정화계수 f = k2 / k1) signify regarding aquatic assimilation capacity?

A.When f > 1.0, microbial deoxygenation outpaces atmospheric reaeration, leading to prolonged septic conditions and complete oxygen depletion.

B.Fair's constant is independent of river depth and velocity and depends exclusively on the biological species present in the benthic sediment.

C.A high f value indicates an anaerobic stagnant swamp where reaeration is virtually zero and deoxygenation is maximized.

D.When f > 1.0, atmospheric reaeration occurs faster than microbial deoxygenation, resulting in rapid dissolved oxygen recovery and a reduced critical oxygen deficit (Dc).

Explanation: Fair's self-purification constant f is defined as the ratio of the atmospheric reaeration coefficient (k2) to the deoxygenation coefficient (k1), i.e., f = k2 / k1. When f > 1.0 (typically 2.0 to 5.0 in swift shallow streams), reaeration supplies dissolved oxygen faster than heterotrophic bacteria consume it, leading to a shallower critical deficit (Dc), shorter critical time (tc), and rapid aquatic recovery. In stagnant sluggish waters, f may drop below 1.5, indicating slow recovery.

4A river receives treated wastewater effluent. At the confluence point, the initial dissolved oxygen deficit is negligible (D0 ≈ 0 mg/L), the ultimate BOD (Lo) of the mixture is 30.0 mg/L, the base-10 deoxygenation coefficient k1 is 0.10 day^-1, and the base-10 reaeration coefficient k2 is 0.20 day^-1 (f = 2.0). If the critical travel time (tc) to the DO sag point is 1.505 days, what is the critical dissolved oxygen deficit (Dc)?

A.5.20 mg/L

B.7.50 mg/L

C.10.60 mg/L

D.15.00 mg/L

Explanation: In the Streeter-Phelps model with D0 = 0, the critical deficit is given by Dc = (k1 / k2) * Lo * 10^(-k1 * tc) or Lo * f^(-f / (f - 1)). Using the rate equation: Dc = (0.10 / 0.20) * 30.0 * 10^(-0.10 * 1.505) = 0.5 * 30.0 * 10^(-0.1505). Since 10^(-0.1505) ≈ 0.7071 (since 10^0.1505 ≈ 1.414 = sqrt(2)), Dc = 15.0 * 0.7071 ≈ 10.60 mg/L.

5In Whipple's four zones of stream self-purification (하천의 자정작용 4지대), which of the following biological and chemical characteristics is uniquely associated with the Zone of Active Decomposition (활성분해지대)?

A.Dissolved oxygen drops near or to zero, anaerobic decomposition generates H2S and CH4, and Tubifex worms and Chironomus larvae predominate.

B.Dissolved oxygen reaches 100% saturation, water becomes crystal clear, and game fish like trout and salmon reproduce.

C.BOD reaches its absolute maximum level while dissolved oxygen remains at 90% of saturation due to immediate reaeration.

D.Mineralized nitrates and phosphates reach zero as all aquatic plant life is completely eliminated by heavy metal poisoning.

Explanation: Whipple classified river self-purification into four zones: (1) Zone of Degradation (분해지대), (2) Zone of Active Decomposition (활성분해지대), (3) Zone of Recovery (회복지대), and (4) Clean Water Zone (정수지대). In the Zone of Active Decomposition, organic pollution is so intense that microbial respiration exhausts DO to zero or near zero. Anaerobic processes produce foul gases (H2S, CH4, NH3), benthic sludge turns black, fish vanish, and polysaprobic indicator organisms such as Tubifex worms (실지렁이) and Chironomus larvae (깔따구) proliferate.

6What is the Theoretical Oxygen Demand (ThOD, 이론적 산소요구량) of an industrial wastewater solution containing 92 mg/L of ethanol (C2H5OH, molecular weight = 46 g/mol), assuming complete oxidation to CO2 and H2O?

A.96 mg/L

B.144 mg/L

C.192 mg/L

D.288 mg/L

Explanation: The stoichiometric oxidation of ethanol is C2H5OH + 3 O2 -> 2 CO2 + 3 H2O. One mole of ethanol (46 g) consumes 3 moles of oxygen (3 x 32 = 96 g O2), so the mass ratio is 96 / 46 = 2.087 g O2 per g ethanol. A concentration of 92 mg/L is exactly 2 mmol/L of ethanol, which therefore demands 2 x 96 = 192 mg/L of oxygen. Equivalently, ThOD = 92 mg/L x (96 / 46) = 192 mg/L.

7In environmental water quality analysis, why does the potassium dichromate method (COD-Cr) typically yield significantly higher oxidation values than the acidic potassium permanganate method (COD-Mn) for industrial wastewater?

A.Potassium dichromate in strong sulfuric acid at 150°C with silver sulfate catalyst oxidizes straight-chain aliphatic hydrocarbons, branched organic acids, and sugars to near 90–95% completion, whereas permanganate only oxidizes 50–60% of organic compounds.

B.Potassium permanganate has a higher standard oxidation-reduction potential than potassium dichromate, but its reaction is stopped prematurely after 5 minutes.

C.Potassium dichromate oxidizes ammonia nitrogen to nitrate, which increases the measured COD value substantially.

D.Potassium permanganate is consumed exclusively by dissolved oxygen rather than organic carbon compounds.

Explanation: Potassium dichromate (K2Cr2O7) in strong boiling sulfuric acid with silver sulfate (Ag2SO4) catalyst provides an aggressive oxidizing environment that oxidizes approximately 90–95% of theoretical oxygen demand, including straight-chain aliphatic compounds, volatile fatty acids, and complex carbohydrates. In contrast, the acidic potassium permanganate method (COD-Mn) at 100°C achieves only 50–60% oxidation efficiency and fails to oxidize straight-chain fatty acids (such as acetic acid) and aromatic hydrocarbons.

8During seasonal thermal stratification in a deep temperate lake, at what water temperature is water density maximized, and during which seasons does lake turnover (전도현상) typically occur?

A.Density is maximized at 0°C; turnover occurs in mid-summer and mid-winter.

B.Density is maximized at 3.98°C; turnover occurs in spring and autumn.

C.Density is maximized at 10.0°C; turnover occurs exclusively during spring snowmelt.

D.Density is maximized at 25.0°C; turnover occurs when wind speed drops to zero.

Explanation: Pure water reaches its maximum density at approximately 3.98°C (commonly rounded to 4°C). In dimictic lakes of temperate regions (such as South Korea), thermal stratification forms in summer (warm light epilimnion above cold dense hypolimnion separated by the metalimnion/thermocline) and inverse stratification forms in winter under ice. Turnover (전도현상) occurs in spring and autumn when surface waters reach ~4°C, destroying thermal density gradients and allowing wind action to mix the entire water column completely.

9According to Carlson's Trophic State Index (TSI, 칼슨 영양상태지수), what trophic classification is assigned to a lake with a TSI value of 55, and what is the primary visual indicator of this condition?

A.Oligotrophic (빈영양호); Secchi depth exceeds 8 meters with pristine water clarity.

B.Mesotrophic (중영양호); balanced nutrient levels with low seasonal diatom growth.

C.Eutrophic (부영양호); elevated algae and chlorophyll-a concentrations with reduced Secchi depth transparency.

D.Hypertrophic (과영양호); complete fish kill with zero light penetration beyond 5 centimeters.

Explanation: Carlson's Trophic State Index (TSI) classifies lakes based on Secchi depth (SD), Chlorophyll-a (Chl-a), and Total Phosphorus (T-P). The standard scale is: TSI < 40 = Oligotrophic (빈영양호), TSI 40–50 = Mesotrophic (중영양호), TSI 50–70 = Eutrophic (부영양호), and TSI > 70 = Hypertrophic (과영양호). A TSI value of 55 places the lake in the Eutrophic category, characterized by substantial algal blooms, elevated chlorophyll-a, and reduced water transparency.

10In the biological nitrification of ammonia nitrogen (NH4+-N) to nitrate nitrogen (NO3--N), what is the stoichiometric mass of oxygen consumed and alkalinity destroyed per 1.0 g of NH4+-N oxidized?

A.1.00 g O2 consumed and 3.57 g CaCO3 alkalinity destroyed

B.2.86 g O2 consumed and 5.14 g CaCO3 alkalinity destroyed

C.4.57 g O2 consumed and 7.14 g CaCO3 alkalinity destroyed

D.6.25 g O2 consumed and 9.42 g CaCO3 alkalinity destroyed

Explanation: Nitrification occurs in two sequential steps: (1) Nitrosomonas: 2 NH4+ + 3 O2 -> 2 NO2- + 4 H+ + 2 H2O (3.43 g O2 / g N), and (2) Nitrobacter: 2 NO2- + O2 -> 2 NO3- (1.14 g O2 / g N). Total oxygen demand is 3.43 + 1.14 = 4.57 g O2 per g NH4+-N oxidized. The overall reaction produces 2 moles of H+ per mole of NH4+ oxidized (NH4+ + 2 O2 -> NO3- + H2O + 2 H+). Neutralizing 2 moles of H+ requires 1 mole of CaCO3 (100 g) per mole of N (14 g), which equals 100 / 14 = 7.14 g CaCO3 alkalinity destroyed per g NH4+-N oxidized.

About the Engineer Water Pollution Environmental Exam

The Engineer Water Pollution Environmental (수질환경기사) qualification is South Korea's Engineer-grade national technical credential for wastewater treatment designers, water quality specialists and industrial environmental managers. Established under the National Technical Qualifications Act (국가기술자격법) and administered by HRD Korea (한국산업인력공단) under the Ministry of Environment (환경부), it is the qualification that Table 17 of the Enforcement Decree of the Water Environment Conservation Act requires a Type 1 workplace to appoint as its Environmental Engineer (수질환경기술인). Since 1 January 2025 the written paper has covered four subjects rather than five, 수질환경관계법규 having ceased to be a standalone subject. This practice material is an independent English-language MCQ study adaptation by OpenExamPrep, not an official translation or format simulation. It provides 80 questions that keep the official Korean engineering and statutory terms in parentheses — such as (수질오염개론), (상하수도계획), (수질오염방지기술), (수질오염공정시험기준) and (물환경보전법).

Exam sponsor: Human Resources Development Service of Korea (한국산업인력공단 / Q-Net) under the Ministry of Environment (환경부). The requirements and fees below concern the certification or admission exam, separate from our free practice resources.

Assessment

Written examination (필기): four 20-item subjects sat together over 120 minutes, 30 minutes per subject — Subject 1: Water Pollution Introduction (수질오염개론, 20 items); Subject 2: Water and Sewerage Planning (상하수도계획, 20 items); Subject 3: Water Pollution Prevention Technology (수질오염방지기술, 20 items); Subject 4: Standard Test Methods for Water Pollution (수질오염공정시험기준, 20 items). Candidates must score at least 40 points in every subject to avoid subject failure (과락) and at least 60 points overall. Practical examination (실기): 수질오염방지 실무, a written-answer paper of 3 hours marked out of 100, with 60 points required to pass.

Time Limit

120 minutes (2 hours) for the written examination; 3 hours for the written-answer practical

Passing Score

At least 40 points in each subject and an overall average of at least 60 points (60% aggregate)

Exam / Certification Fees

KRW 19,400 (written examination / 필기시험); KRW 22,600 (practical examination / 실기시험)

Exam sponsor website

Reported exam pass rate: Written examination about 29%; practical examination about 36% (HRD Korea statistics for the most recent full year). HRD Korea's published statistics put the written pass rate near 29% and the practical pass rate near 36%, making this one of the harder Engineer-grade environmental papers. The written paper mixes reaction kinetics, open-channel and pipe hydraulics, reactor mass balances and analytical protocols, and the practical paper is written-answer rather than multiple choice. This describes exam candidates, not OpenExamPrep users or results from using our resources. Exam sponsor website

Fees, eligibility, and exam policies can change. Confirm them with the exam sponsor before applying or paying.

Official sources

Our practice resources: topics covered

We aim to reflect publicly available exam outlines and topic information in our study resources. Coverage, format, and difficulty may differ from the actual exam, and we cannot guarantee that every detail is accurate or current. Confirm exam requirements, fees, and policies with the official exam sponsor.

25%

Water Pollution Introduction (수질오염개론)

First-order BOD kinetics and temperature correction, ultimate BOD, theoretical oxygen demand, COD-Mn versus COD-Cr and TOC, Streeter-Phelps dissolved oxygen sag and Fair's self-purification constant, Whipple's self-purification zones, lake thermal stratification and turnover, Carlson's trophic state index and Vollenweider phosphorus loading, nitrification and denitrification stoichiometry, sediment phosphorus release, carbonate equilibrium, Henry's law and dissolved oxygen saturation, aquatic toxicology and bioconcentration, river mixing mass balance, Darcy's law for groundwater, and the statutory residue folded into this subject from 2025 — workplace size classes, environmental engineer appointment standards and ambient river water quality grades under the Water Environment Conservation Act (물환경보전법).

25%

Water and Sewerage Planning (상하수도계획)

Population forecasting methods, planned daily average, daily maximum and hourly maximum supply and what each sizes, service reservoir storage, intake structures and infiltration galleries, Hazen-Williams head loss, Hardy Cross network balancing, water hammer protection, pump specific speed, pump power and cavitation/NPSH, separate versus combined sewer systems, sewer self-cleansing and maximum velocities, Manning's formula, the Rational Method for stormwater, inverted siphons, manhole spacing, rapid mixing and flocculation design, slow versus rapid sand filtration, and Marston's buried-pipe earth load.

25%

Water Pollution Prevention Technology (수질오염방지기술)

Grit chambers, coagulation and the Camp-Stein velocity gradient, alum alkalinity stoichiometry, surface overflow rate and discrete-particle removal, dissolved air flotation, Carman-Kozeny filter head loss, Langmuir and Freundlich adsorption, activated sludge F/M ratio, mean cell residence time and sludge volume index, filamentous bulking, rising sludge and biological foaming, rotating biological contactors, membrane bioreactors, A2O and MLE biological nutrient removal, anaerobic digestion and methane yield, and sludge conditioning and dewatering.

25%

Standard Test Methods for Water Pollution (수질오염공정시험기준)

Sample preservation by analyte, the Winkler azide dissolved oxygen method and its calculation, BOD incubation protocol, seeded dilution BOD calculation and glucose-glutamic acid quality control, acidic and alkaline permanganate COD, dichromate COD with mercuric sulfate and ferroin, gravimetric suspended solids, total nitrogen by UV absorbance with 220/275 nm correction, total phosphorus by ascorbic acid molybdenum blue, ammonia by the indophenol method, flame and cold-vapour atomic absorption, hydride generation, ICP-OES, matrix spike recovery, method detection limit and limit of quantitation, and purge-and-trap GC/MS for volatile organics.

Preparing for the Engineer Water Pollution Environmental Exam

What You Need to Know

Passing score: At least 40 points in each subject and an overall average of at least 60 points (60% aggregate)
Assessment: Written examination (필기): four 20-item subjects sat together over 120 minutes, 30 minutes per subject — Subject 1: Water Pollution Introduction (수질오염개론, 20 items); Subject 2: Water and Sewerage Planning (상하수도계획, 20 items); Subject 3: Water Pollution Prevention Technology (수질오염방지기술, 20 items); Subject 4: Standard Test Methods for Water Pollution (수질오염공정시험기준, 20 items). Candidates must score at least 40 points in every subject to avoid subject failure (과락) and at least 60 points overall. Practical examination (실기): 수질오염방지 실무, a written-answer paper of 3 hours marked out of 100, with 60 points required to pass.
Time limit: 120 minutes (2 hours) for the written examination; 3 hours for the written-answer practical
Exam / certification fees: KRW 19,400 (written examination / 필기시험); KRW 22,600 (practical examination / 실기시험) Official sources

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Engineer Water Pollution Environmental: Suggested Study Strategy

1Get fluent with the kinetics in 수질오염개론: first-order BOD with base-10 rate constants, Arrhenius temperature correction, and the Streeter-Phelps critical deficit. These reappear every sitting and are quick marks once the algebra is automatic.

2Learn which design flow sizes which structure in 상하수도계획: planned daily maximum supply sizes intake, transmission and treatment; planned hourly maximum sizes distribution mains and service reservoirs; planned daily average is for budgeting. Examiners test the mapping, not the arithmetic.

3Practise the activated-sludge index calculations in 수질오염방지기술 until they are one-step: F/M = QS0/VX, MCRT = VX divided by total daily solids loss, SVI = SV30 in mL/L times 1,000 divided by MLSS, and Xr ≈ 10⁶/SVI.

4In 수질오염공정시험기준, pair each analyte with its preservation, its reagent and its wavelength: nitric acid to pH < 2 for metals, sodium azide for the Winkler test, 220 nm minus twice 275 nm for total nitrogen, 880 nm molybdenum blue for total phosphorus, and sodium nitroprusside as the indophenol catalyst.

5Do not abandon the statutory numbers just because 수질환경관계법규 lost its own paper: workplace size classes (2,000 / 700 / 200 / 50 m³/day), Environmental Engineer standards under Table 17, and the Grade Ia river standards (BOD ≤ 1.0, TOC ≤ 2.0, DO ≥ 7.5 mg/L) are still examined inside 수질오염개론.

Frequently Asked Questions

What is the Engineer Water Pollution Environmental (수질환경기사) qualification?

It is an Engineer-grade national technical qualification established under South Korea's National Technical Qualifications Act (국가기술자격법) and administered by HRD Korea (한국산업인력공단 / Q-Net) under the Ministry of Environment (환경부). Holders design and operate water and wastewater treatment facilities, and the qualification satisfies the statutory appointment of an Environmental Engineer (수질환경기술인) at a Type 1 workplace.

What is the structure, timing and passing standard of the written examination?

Since 1 January 2025 the written examination has been 80 four-option multiple-choice questions across 4 subjects, 20 questions each, in a single 120-minute CBT session: (1) Water Pollution Introduction (수질오염개론), (2) Water and Sewerage Planning (상하수도계획), (3) Water Pollution Prevention Technology (수질오염방지기술), and (4) Standard Test Methods for Water Pollution (수질오염공정시험기준). Candidates must score at least 40 points in every subject to avoid 과락 and at least 60 points overall.

What changed in the 2025 examination standard?

Under the amended 출제기준 effective 1 January 2025, 수질환경관계법규 was removed as a standalone fifth subject. The written paper fell from five subjects and 100 questions to four subjects and 80 questions, and from 150 to 120 minutes. A small residue of statutory material — workplace size classes, environmental engineer appointment standards, effluent and ambient standards — is still examined inside 수질오염개론.

What fees apply?

The written examination fee is KRW 19,400. After passing the written examination the practical examination (실기시험, 수질오염방지 실무) fee is KRW 22,600.

How long does a written pass stay valid?

A written examination pass is valid for two years from the date the written result is announced. During that period the candidate is exempt from the written paper and may register directly for the practical examination.

How are wastewater discharging workplaces classified, and who must they appoint?

Table 13 of the Enforcement Decree of the Water Environment Conservation Act classifies workplaces by daily wastewater discharge: Type 1 at 2,000 m³/day or more, Type 2 at 700 to under 2,000, Type 3 at 200 to under 700, Type 4 at 50 to under 200 and Type 5 below 50. Table 17 then sets the Environmental Engineer standard: Type 1 requires at least one 수질환경기사, Type 2 at least one 수질환경산업기사, and Type 3 수질환경산업기사, 환경기능사 or a person with three or more years of direct water-field environmental work.

Is this practice bank an official examination paper?

No. The official examination is administered in Korean. This bank is an independent English-language MCQ study adaptation by OpenExamPrep — not an official translation, a format simulation, or a substitute for the written-answer practical examination.