TCEQ Wastewater Class D
License Exam Practice Guide
Questions and Answers with Rationales| Latest Update
,Basic Math & Conversions
Question 1
How many gallons are in one cubic foot of water?
A. 5.61 gallons
B. 7.48 gallons
C. 8.34 gallons
D. 62.4 gallons
Correct Answer: B
Rationale: One cubic foot of water contains 7.48 gallons. This constant is
used constantly to convert tank volumes calculated in cubic feet into gallons.
Question 2
What is the weight of one gallon of water?
A. 7.48 lbs
B. 8.34 lbs
C. 62.4 lbs
D. 1.0 lbs
Correct Answer: B
Rationale: One gallon of water weighs 8.34 pounds. This value is essential
for chemical feed and loading calculations (lbs = MGD x mg/L x 8.34).
,Question 3
A rectangular tank is 20 ft long, 10 ft wide, and 8 ft deep. What is its
volume in gallons?
A. 1,600 gallons
B. 11,968 gallons
C. 1,600 cubic feet
D. 13,344 gallons
Correct Answer: B
Rationale: Volume = 20 x 10 x 8 = 1,600 cubic feet. Convert to gallons:
1,600 x 7.48 = 11,968 gallons.
Question 4
Using the formula lbs/day = MGD x mg/L x 8.34, what is the chlorine
dose in lbs/day for a flow of 2.0 MGD at a dose of 5 mg/L?
A. 8.34 lbs/day
B. 41.7 lbs/day
C. 83.4 lbs/day
D. 16.68 lbs/day
Correct Answer: C
Rationale: lbs/day = 2.0 MGD x 5 mg/L x 8.34 = 83.4 lbs/day. Always
multiply flow (MGD) by concentration (mg/L) by the constant 8.34 to get
pounds per day.
, Question 5
Convert a flow of 500 gallons per minute (gpm) to million gallons per
day (MGD).
A. 0.072 MGD
B. 0.72 MGD
C. 7.2 MGD
D. 72 MGD
Correct Answer: B
Rationale: 500 gpm x 1,440 minutes/day = 720,000 gallons/day = 0.72
MGD. Multiply gpm by 1,440 (minutes in a day), then divide by 1,000,000.
Question 6
What is the detention time in hours for a 100,000-gallon tank receiving a
flow of 200,000 gallons per day?
A. 0.5 hours
B. 2 hours
C. 12 hours
D. 24 hours
Correct Answer: C
Rationale: Detention time = Volume / Flow = 100,000 gal / 200,000 gal/day
= 0.5 day = 0.5 x 24 hours = 12 hours.
License Exam Practice Guide
Questions and Answers with Rationales| Latest Update
,Basic Math & Conversions
Question 1
How many gallons are in one cubic foot of water?
A. 5.61 gallons
B. 7.48 gallons
C. 8.34 gallons
D. 62.4 gallons
Correct Answer: B
Rationale: One cubic foot of water contains 7.48 gallons. This constant is
used constantly to convert tank volumes calculated in cubic feet into gallons.
Question 2
What is the weight of one gallon of water?
A. 7.48 lbs
B. 8.34 lbs
C. 62.4 lbs
D. 1.0 lbs
Correct Answer: B
Rationale: One gallon of water weighs 8.34 pounds. This value is essential
for chemical feed and loading calculations (lbs = MGD x mg/L x 8.34).
,Question 3
A rectangular tank is 20 ft long, 10 ft wide, and 8 ft deep. What is its
volume in gallons?
A. 1,600 gallons
B. 11,968 gallons
C. 1,600 cubic feet
D. 13,344 gallons
Correct Answer: B
Rationale: Volume = 20 x 10 x 8 = 1,600 cubic feet. Convert to gallons:
1,600 x 7.48 = 11,968 gallons.
Question 4
Using the formula lbs/day = MGD x mg/L x 8.34, what is the chlorine
dose in lbs/day for a flow of 2.0 MGD at a dose of 5 mg/L?
A. 8.34 lbs/day
B. 41.7 lbs/day
C. 83.4 lbs/day
D. 16.68 lbs/day
Correct Answer: C
Rationale: lbs/day = 2.0 MGD x 5 mg/L x 8.34 = 83.4 lbs/day. Always
multiply flow (MGD) by concentration (mg/L) by the constant 8.34 to get
pounds per day.
, Question 5
Convert a flow of 500 gallons per minute (gpm) to million gallons per
day (MGD).
A. 0.072 MGD
B. 0.72 MGD
C. 7.2 MGD
D. 72 MGD
Correct Answer: B
Rationale: 500 gpm x 1,440 minutes/day = 720,000 gallons/day = 0.72
MGD. Multiply gpm by 1,440 (minutes in a day), then divide by 1,000,000.
Question 6
What is the detention time in hours for a 100,000-gallon tank receiving a
flow of 200,000 gallons per day?
A. 0.5 hours
B. 2 hours
C. 12 hours
D. 24 hours
Correct Answer: C
Rationale: Detention time = Volume / Flow = 100,000 gal / 200,000 gal/day
= 0.5 day = 0.5 x 24 hours = 12 hours.
