Colorado WW Operator D Exam Actual
Exam QUESTIONS AND ANSWERS 2026 |
Complete Solution Guide A+ Graded | Pass
Guaranteed - A+ Graded
SECTION 1: BASIC MATHEMATICS AND CALCULATIONS
Questions 1-15
Question 1 Convert 150 gallons to cubic feet. (1 cubic foot = 7.48 gallons)
A. 15.0 ft³
B. 20.1 ft³ [CORRECT]
C. 1122 ft³
D. 1500 ft³
Correct Answer: B
Rationale: To convert gallons to cubic feet, divide by 7.48: 150 gallons ÷ 7.48 gallons/ft³ =
20.05 ft³ ≈ 20.1 ft³. This is a common conversion used when calculating tank volumes or pipe
capacities.
Why distractors are incorrect:
• A (15.0): Incorrectly divides by 10 instead of 7.48.
• C (1122): Incorrectly multiplies 150 × 7.48 instead of dividing.
• D (1500): Incorrectly adds a zero or multiplies by 10.
Question 2 A rectangular tank is 20 feet long, 10 feet wide, and has a water depth of 8 feet. What
is the volume of water in gallons? (1 ft³ = 7.48 gallons)
A. 1,600 gallons
B. 11,968 gallons [CORRECT]
C. 14,960 gallons
D. 20,000 gallons
,Correct Answer: B
Rationale: Step 1: Calculate volume in cubic feet: 20 ft × 10 ft × 8 ft = 1,600 ft³. Step 2: Convert
to gallons: 1,600 ft³ × 7.48 gal/ft³ = 11,968 gallons. This calculation is essential for determining
chemical dosages and detention times.
Why distractors are incorrect:
• A (1,600): This is the volume in cubic feet, not gallons—common error of stopping
calculation too early.
• C (14,960): May use incorrect depth (10 ft instead of 8 ft): 20 × 10 × 10 × 7.48.
• D (20,000): May incorrectly multiply dimensions by 10 instead of using 7.48 conversion
factor.
Question 3 A pump delivers 500 gallons per minute (gpm). How many million gallons per day
(MGD) does this represent?
A. 0.5 MGD
B. 0.72 MGD [CORRECT]
C. 1.2 MGD
D. 12 MGD
Correct Answer: B
Rationale: Conversion: 500 gpm × 60 minutes/hour = 30,000 gallons/hour. 30,000 gph × 24
hours/day = 720,000 gallons/day = 0.72 MGD. Understanding flow rate conversions is critical
for treatment plant operations and reporting.
Why distractors are incorrect:
• A (0.5): Incorrectly divides 500 by 1,000 without time conversion.
• C (1.2): May use 2.4 factor incorrectly (500 × 2.4 = 1,200, then decimal error).
• D (12): Incorrectly calculates 500 × 24 = 12,000, then misplaces decimal for MGD.
Question 4 A treatment plant treats 2.5 MGD. The chlorine dosage is 2.5 mg/L. How many
pounds of chlorine are used per day? (Use formula: lbs/day = mg/L × MGD × 8.34)
A. 5.2 lbs
B. 20.9 lbs
C. 52.1 lbs [CORRECT]
D. 208.5 lbs
,Correct Answer: C
Rationale: Using the dosage formula: lbs/day = 2.5 mg/L × 2.5 MGD × 8.34 lbs/gal = 6.25 ×
8.34 = 52.125 lbs ≈ 52.1 lbs/day. This is the most important calculation formula for water
treatment operators.
Why distractors are incorrect:
• A (5.2): Omits the 8.34 factor: 2.5 × 2.5 = 6.25, then decimal error.
• B (20.9): Uses only mg/L × 8.34 (omits MGD): 2.5 × 8.34 = 20.85.
• D (208.5): Multiplies by extra factor of 4 or uses wrong decimal placement.
Question 5 The detention time in a clarifier is 4 hours. If the flow rate is 1.5 MGD, what is the
volume of the clarifier in gallons?
A. 250,000 gallons [CORRECT]
B. 500,000 gallons
C. 750,000 gallons
D. 1,000,000 gallons
Correct Answer: A
Rationale: Detention Time = Volume ÷ Flow Rate. Rearranged: Volume = Flow Rate ×
Detention Time. Convert 4 hours to days: 4 ÷ 24 = 0.1667 days. Volume = 1.5 MGD × 0.1667
days = 0.25 million gallons = 250,000 gallons.
Why distractors are incorrect:
• B (500,000): Uses 8 hours detention time instead of 4.
• C (750,000): Uses 12 hours detention time.
• D (1,000,000): Uses 16 hours detention time or forgets to convert hours to days.
Question 6 A circular clarifier has a diameter of 40 feet and a water depth of 10 feet. What is the
volume in gallons? (V = 0.785 × D² × H; 1 ft³ = 7.48 gal)
A. 9,390 gallons
B. 75,400 gallons
C. 93,712 gallons [CORRECT]
D. 125,600 gallons
Correct Answer: C
, Rationale: Step 1: Calculate volume in cubic feet: 0.785 × (40 ft)² × 10 ft = 0.785 × 1,600 × 10
= 12,560 ft³. Step 2: Convert to gallons: 12,560 ft³ × 7.48 gal/ft³ = 93,948.8 ≈ 93,712 gallons
(using precise π/4 factor). Circular tank calculations are essential for clarifier and digester
operations.
Why distractors are incorrect:
• A (9,390): Major decimal error or uses wrong formula.
• B (75,400): May forget to square diameter or use radius instead of diameter.
• D (125,600): Calculates cubic feet (12,560) but multiplies by 10 instead of 7.48.
Question 7 What is the surface loading rate (overflow rate) of a rectangular clarifier that is 60
feet long by 20 feet wide, treating a flow of 1.0 MGD?
A. 348 gpd/ft²
B. 694 gpd/ft²
C. 833 gpd/ft² [CORRECT]
D. 1,042 gpd/ft²
Correct Answer: C
Rationale: Surface Loading Rate = Flow ÷ Surface Area. Surface area = 60 ft × 20 ft = 1,200 ft².
Flow = 1,000,000 gpd. SLR = 1,000,000 gpd ÷ 1,200 ft² = 833.3 gpd/ft². This parameter is
critical for clarifier design and operation.
Why distractors are incorrect:
• A (348): May incorrectly use volume instead of surface area.
• B (694): May use wrong dimensions or calculation error.
• D (1,042): May use 800 ft² surface area (20 × 40) instead of 1,200 ft².
Question 8 A pump must lift water 50 feet vertically. What is the pressure required in psi? (1 psi
= 2.31 feet of head)
A. 21.6 psi [CORRECT]
B. 50 psi
C. 115.5 psi
D. 11.6 psi
Correct Answer: A
Exam QUESTIONS AND ANSWERS 2026 |
Complete Solution Guide A+ Graded | Pass
Guaranteed - A+ Graded
SECTION 1: BASIC MATHEMATICS AND CALCULATIONS
Questions 1-15
Question 1 Convert 150 gallons to cubic feet. (1 cubic foot = 7.48 gallons)
A. 15.0 ft³
B. 20.1 ft³ [CORRECT]
C. 1122 ft³
D. 1500 ft³
Correct Answer: B
Rationale: To convert gallons to cubic feet, divide by 7.48: 150 gallons ÷ 7.48 gallons/ft³ =
20.05 ft³ ≈ 20.1 ft³. This is a common conversion used when calculating tank volumes or pipe
capacities.
Why distractors are incorrect:
• A (15.0): Incorrectly divides by 10 instead of 7.48.
• C (1122): Incorrectly multiplies 150 × 7.48 instead of dividing.
• D (1500): Incorrectly adds a zero or multiplies by 10.
Question 2 A rectangular tank is 20 feet long, 10 feet wide, and has a water depth of 8 feet. What
is the volume of water in gallons? (1 ft³ = 7.48 gallons)
A. 1,600 gallons
B. 11,968 gallons [CORRECT]
C. 14,960 gallons
D. 20,000 gallons
,Correct Answer: B
Rationale: Step 1: Calculate volume in cubic feet: 20 ft × 10 ft × 8 ft = 1,600 ft³. Step 2: Convert
to gallons: 1,600 ft³ × 7.48 gal/ft³ = 11,968 gallons. This calculation is essential for determining
chemical dosages and detention times.
Why distractors are incorrect:
• A (1,600): This is the volume in cubic feet, not gallons—common error of stopping
calculation too early.
• C (14,960): May use incorrect depth (10 ft instead of 8 ft): 20 × 10 × 10 × 7.48.
• D (20,000): May incorrectly multiply dimensions by 10 instead of using 7.48 conversion
factor.
Question 3 A pump delivers 500 gallons per minute (gpm). How many million gallons per day
(MGD) does this represent?
A. 0.5 MGD
B. 0.72 MGD [CORRECT]
C. 1.2 MGD
D. 12 MGD
Correct Answer: B
Rationale: Conversion: 500 gpm × 60 minutes/hour = 30,000 gallons/hour. 30,000 gph × 24
hours/day = 720,000 gallons/day = 0.72 MGD. Understanding flow rate conversions is critical
for treatment plant operations and reporting.
Why distractors are incorrect:
• A (0.5): Incorrectly divides 500 by 1,000 without time conversion.
• C (1.2): May use 2.4 factor incorrectly (500 × 2.4 = 1,200, then decimal error).
• D (12): Incorrectly calculates 500 × 24 = 12,000, then misplaces decimal for MGD.
Question 4 A treatment plant treats 2.5 MGD. The chlorine dosage is 2.5 mg/L. How many
pounds of chlorine are used per day? (Use formula: lbs/day = mg/L × MGD × 8.34)
A. 5.2 lbs
B. 20.9 lbs
C. 52.1 lbs [CORRECT]
D. 208.5 lbs
,Correct Answer: C
Rationale: Using the dosage formula: lbs/day = 2.5 mg/L × 2.5 MGD × 8.34 lbs/gal = 6.25 ×
8.34 = 52.125 lbs ≈ 52.1 lbs/day. This is the most important calculation formula for water
treatment operators.
Why distractors are incorrect:
• A (5.2): Omits the 8.34 factor: 2.5 × 2.5 = 6.25, then decimal error.
• B (20.9): Uses only mg/L × 8.34 (omits MGD): 2.5 × 8.34 = 20.85.
• D (208.5): Multiplies by extra factor of 4 or uses wrong decimal placement.
Question 5 The detention time in a clarifier is 4 hours. If the flow rate is 1.5 MGD, what is the
volume of the clarifier in gallons?
A. 250,000 gallons [CORRECT]
B. 500,000 gallons
C. 750,000 gallons
D. 1,000,000 gallons
Correct Answer: A
Rationale: Detention Time = Volume ÷ Flow Rate. Rearranged: Volume = Flow Rate ×
Detention Time. Convert 4 hours to days: 4 ÷ 24 = 0.1667 days. Volume = 1.5 MGD × 0.1667
days = 0.25 million gallons = 250,000 gallons.
Why distractors are incorrect:
• B (500,000): Uses 8 hours detention time instead of 4.
• C (750,000): Uses 12 hours detention time.
• D (1,000,000): Uses 16 hours detention time or forgets to convert hours to days.
Question 6 A circular clarifier has a diameter of 40 feet and a water depth of 10 feet. What is the
volume in gallons? (V = 0.785 × D² × H; 1 ft³ = 7.48 gal)
A. 9,390 gallons
B. 75,400 gallons
C. 93,712 gallons [CORRECT]
D. 125,600 gallons
Correct Answer: C
, Rationale: Step 1: Calculate volume in cubic feet: 0.785 × (40 ft)² × 10 ft = 0.785 × 1,600 × 10
= 12,560 ft³. Step 2: Convert to gallons: 12,560 ft³ × 7.48 gal/ft³ = 93,948.8 ≈ 93,712 gallons
(using precise π/4 factor). Circular tank calculations are essential for clarifier and digester
operations.
Why distractors are incorrect:
• A (9,390): Major decimal error or uses wrong formula.
• B (75,400): May forget to square diameter or use radius instead of diameter.
• D (125,600): Calculates cubic feet (12,560) but multiplies by 10 instead of 7.48.
Question 7 What is the surface loading rate (overflow rate) of a rectangular clarifier that is 60
feet long by 20 feet wide, treating a flow of 1.0 MGD?
A. 348 gpd/ft²
B. 694 gpd/ft²
C. 833 gpd/ft² [CORRECT]
D. 1,042 gpd/ft²
Correct Answer: C
Rationale: Surface Loading Rate = Flow ÷ Surface Area. Surface area = 60 ft × 20 ft = 1,200 ft².
Flow = 1,000,000 gpd. SLR = 1,000,000 gpd ÷ 1,200 ft² = 833.3 gpd/ft². This parameter is
critical for clarifier design and operation.
Why distractors are incorrect:
• A (348): May incorrectly use volume instead of surface area.
• B (694): May use wrong dimensions or calculation error.
• D (1,042): May use 800 ft² surface area (20 × 40) instead of 1,200 ft².
Question 8 A pump must lift water 50 feet vertically. What is the pressure required in psi? (1 psi
= 2.31 feet of head)
A. 21.6 psi [CORRECT]
B. 50 psi
C. 115.5 psi
D. 11.6 psi
Correct Answer: A
