Wastewater Class 4 Exam Virginia| 100
questions| with complete solutions
In an electrical circuit, the grounding wire is indicated by which color? Correct Answer: Green
According to the Ohms Law, which electrical unit measures pressure? Correct Answer: Volts
According to the Ohms Law, which electrical unit measures resistance? Correct Answer: Ohms
According to the Ohms Law, which electrical unit measures current? Correct Answer: Amps
How do you convert cubic feet to gallons? Correct Answer: Multiply by 7.48
How do you convert gallons to pounds? Correct Answer: Multiply by 8.34
Calculate the SVI of your aeration basin when your 30-minute settleable sample is 360 mL/L and
your average mixed liquor suspended solids concentration is 4000 mg/L. Correct Answer: 90
Solution:
360 x 1,000
------------- = 90
4,000
What is the most widely used dechlorination agent in a conventional chlorine gas plant? Correct
Answer: Sulfur Dioxide
What is the most prominent concern in failing to remove grit from the wastewater? Correct
Answer: Excessive wear and damage on mechanical equipment
What is the chemical formula for Sulfuric Acid? Correct Answer: H2SO4
What is the ideal velocity in a grit channel, in feet per second? Correct Answer: 1 fps
Conventional pump packing should be: Correct Answer: Tightened down to a drip
In a primary clarifier, the expected performance for removing settleable solids is 90-95%
removal. What about the removal of suspended solids? Correct Answer: 50%
When preparing a sample for laboratory analysis that involves acid and water, how should the
sample be poured? Correct Answer: Always pour the acid into the water
You are tasked with recording a manual flow sample in an open channel. Where will you
position yourself, relative to the weir, to record the most accurate measure of flow? Correct
Answer: Behind the weir, 4 times the maximum head of the weir
, Why must a positive displacement pump never be started against a closed discharge valve?
Correct Answer: Excessive pressure may damage the line, the pump, and the motor
A circular tank is 45 feet in diameter and has a depth of 10 feet. What is the detention time in
hours when the flow is 1.42 MGD? Correct Answer: 2 hours
Solution:
0.785 x 45 x 45 x 10 x 7.48 x 24
----------------------------------- = 2.038
1,420,000
What is the most common device for measuring flow in an open channel? Correct Answer: V-
notch weir, then ultrasonic flowmeter.
You need to make an adjustment to your aeration basin, and foam is the only characteristic you
have data on. Over the last few days, the foam has become white, and billowy. What adjustment
do you make? Correct Answer: Decrease WAS
Over the last week, your mixed liquor color has changed from brown, to dark brown, to black.
What adjustment should you make? Correct Answer: Increase WAS
You receive a surge of high flow into your aeration basins, and as a result, you are developing an
increasing, billowy sludge blanket in your secondary settling tanks. What adjustment should you
make? Correct Answer: Increase RAS
Your pond has turned a blue-green color and there are algae blooms on the surface. What
corrective action do you take? Correct Answer: Add sodium Nitrate
At what temperature does the BOD sample need to be preserved at? Correct Answer: At or
below 6 degrees Celsius
How do you detect a chlorine gas leak? Correct Answer: Using a rag soaked in ammonia to
detect white fumes
What is the surface loading rate of a circular tank with a diameter of 50 ft and a flow of 2.4
MGD? Correct Answer: 1,223 gallons per feet squared
Solution:
0.785 x 50 x 50 = 1,962.5
2,400,000
----------- = 1,223
1,962.5
When is the DO the highest in stabilization ponds? Correct Answer: Mid-afternoon
questions| with complete solutions
In an electrical circuit, the grounding wire is indicated by which color? Correct Answer: Green
According to the Ohms Law, which electrical unit measures pressure? Correct Answer: Volts
According to the Ohms Law, which electrical unit measures resistance? Correct Answer: Ohms
According to the Ohms Law, which electrical unit measures current? Correct Answer: Amps
How do you convert cubic feet to gallons? Correct Answer: Multiply by 7.48
How do you convert gallons to pounds? Correct Answer: Multiply by 8.34
Calculate the SVI of your aeration basin when your 30-minute settleable sample is 360 mL/L and
your average mixed liquor suspended solids concentration is 4000 mg/L. Correct Answer: 90
Solution:
360 x 1,000
------------- = 90
4,000
What is the most widely used dechlorination agent in a conventional chlorine gas plant? Correct
Answer: Sulfur Dioxide
What is the most prominent concern in failing to remove grit from the wastewater? Correct
Answer: Excessive wear and damage on mechanical equipment
What is the chemical formula for Sulfuric Acid? Correct Answer: H2SO4
What is the ideal velocity in a grit channel, in feet per second? Correct Answer: 1 fps
Conventional pump packing should be: Correct Answer: Tightened down to a drip
In a primary clarifier, the expected performance for removing settleable solids is 90-95%
removal. What about the removal of suspended solids? Correct Answer: 50%
When preparing a sample for laboratory analysis that involves acid and water, how should the
sample be poured? Correct Answer: Always pour the acid into the water
You are tasked with recording a manual flow sample in an open channel. Where will you
position yourself, relative to the weir, to record the most accurate measure of flow? Correct
Answer: Behind the weir, 4 times the maximum head of the weir
, Why must a positive displacement pump never be started against a closed discharge valve?
Correct Answer: Excessive pressure may damage the line, the pump, and the motor
A circular tank is 45 feet in diameter and has a depth of 10 feet. What is the detention time in
hours when the flow is 1.42 MGD? Correct Answer: 2 hours
Solution:
0.785 x 45 x 45 x 10 x 7.48 x 24
----------------------------------- = 2.038
1,420,000
What is the most common device for measuring flow in an open channel? Correct Answer: V-
notch weir, then ultrasonic flowmeter.
You need to make an adjustment to your aeration basin, and foam is the only characteristic you
have data on. Over the last few days, the foam has become white, and billowy. What adjustment
do you make? Correct Answer: Decrease WAS
Over the last week, your mixed liquor color has changed from brown, to dark brown, to black.
What adjustment should you make? Correct Answer: Increase WAS
You receive a surge of high flow into your aeration basins, and as a result, you are developing an
increasing, billowy sludge blanket in your secondary settling tanks. What adjustment should you
make? Correct Answer: Increase RAS
Your pond has turned a blue-green color and there are algae blooms on the surface. What
corrective action do you take? Correct Answer: Add sodium Nitrate
At what temperature does the BOD sample need to be preserved at? Correct Answer: At or
below 6 degrees Celsius
How do you detect a chlorine gas leak? Correct Answer: Using a rag soaked in ammonia to
detect white fumes
What is the surface loading rate of a circular tank with a diameter of 50 ft and a flow of 2.4
MGD? Correct Answer: 1,223 gallons per feet squared
Solution:
0.785 x 50 x 50 = 1,962.5
2,400,000
----------- = 1,223
1,962.5
When is the DO the highest in stabilization ponds? Correct Answer: Mid-afternoon
