WASTEWATER D LICENSE EXAM
2025/2026 QUESTIONS AND ANSWERS
100% PASS
How many PPB equals one PPM? - ANS One thousand parts per billion equals one part per
million
If the bubbler system air supply line at the wet well is clogged, what will this cause the pump to
do? - ANS Pressure build up in the supply line would signal more water column then there
really was, causing the pump to run longer than necessary, possibly not kick off and run
continually
If the bubbler system air supply line at the wet well has a hole in it above the water level, what
will this cause the pump to do? - ANS It would cause a low pressure reading showing a lower
water level then there really is, or possible not even kicking on the pump
What is the best way to keep within the operating budget? - ANS keep list of purchases and
expenses to date during fiscal year
comparisons should be made with budget allocations to avoid excess purchases
review purchases monthly and compare to budget
1 @COPYRIGHT 2025/2026 ALLRIGHTS RESERVED
,If a diaphragm pump has 2 check valves open, what will the pump do? - ANS It would not
pump properly because 1 check valve should be shut while the other is open
A suction lift pump on the inlet side normally reads 2in of mercury on the psi vacuum gauge but
not reads 3in of mercury. What is the problem with the pump? - ANS A higher vacuum than
normal may indicate a partially plugged or restricted suction line.
A lower vacuum may indicate a higher wet well level or a worn pump impeller or wearing rings.
One mg per L equals how many pounds per 1 MG? - ANS 8.34
What is the proper way to put packing in a pump? - ANS cut the packing rope about 45
degree angle, place around shaft, be sure to offset/stagger the next joint from the previous
How many drips of water should you have coming out of a packing seal? - ANS no drip on a
mechanical seal
How many drips of water should you have coming out of a packing seal? 2 - ANS what the
operation and maintenance manual recommends
A one horsepower motor that runs on 110 volts using 10 amps has what efficiency? -
ANS most motors run from 80-95% efficiency
A motor that has 440 volt supply is usually what phase of power? - ANS 3 phase
NPDES - ANS National Pollutant Discharge Elimination System
2 @COPYRIGHT 2025/2026 ALLRIGHTS RESERVED
,the regulatory agency document issued by either a federal or state agency which is designed to
control all discharges of pollutants from point sources into US waterways - ANS NPDES
permit
What is the name of our operating permit? - ANS NPDES
What is the best way to promote safety in the workplace? - ANS the supervisor needs to be
safe and promote safety in such a manner to get the employees involved
What is normally used to raise the pH in sludge? - ANS lime
What is the common device used to measure the effluent of a lagoon? - ANS v notch weir
What concentration of H2S is unsafe to humans? - ANS death in a few minutes at 0.2%.
Paralyzes respiratory center
What is the minimum O2 concentration that is safe for workers to enter a manhole? - ANS If
O2 is less than 19.5%, do not enter space without respiratory protection. Normal air contains
20.93% of O2.
Normal air contains ______% of O2 - ANS 19.5%
What knob is turned to control the usage of chlorine applied? - ANS rotameter
Can you store BOD at 4C for 48 hours? - ANS yes
What is the minimum velocity of the water flow for a grit chamber and the maximum flow? -
ANS 1.0 feet per second minimum
1.5 feet per second optimum
3 @COPYRIGHT 2025/2026 ALLRIGHTS RESERVED
, 2.0 feet per second maximum
How many mg/L equals one grain per gallon? - ANS 17.1 mg/L
Dissolved oxygen increases when the temperature __________ - ANS decreases
You can tell if a clarifier scraper arm is working by what means? - ANS the simplest is to
visual check to see if the scum scraper arm is moving properly
check into foam
If the sludge is thick or thin, then what does this tell you about the sludge scraper? -
ANS possible answer is the flights are damaged or the speed of the scrapers(flights) need to
be increased if sludge is too thick
or slowed down if the sludge is too thin
aging and maturing of a body of water - ANS eutrophication
eutrophication - ANS aging and maturing of a body of water
If the effluent from a treatment facility contained 5mg/L of BOD, what effect would this have
on the receiving stream? - ANS little effect
If you are doing a test and add one drop of chemical at a time, what is this method called? -
ANS titration
4 @COPYRIGHT 2025/2026 ALLRIGHTS RESERVED
2025/2026 QUESTIONS AND ANSWERS
100% PASS
How many PPB equals one PPM? - ANS One thousand parts per billion equals one part per
million
If the bubbler system air supply line at the wet well is clogged, what will this cause the pump to
do? - ANS Pressure build up in the supply line would signal more water column then there
really was, causing the pump to run longer than necessary, possibly not kick off and run
continually
If the bubbler system air supply line at the wet well has a hole in it above the water level, what
will this cause the pump to do? - ANS It would cause a low pressure reading showing a lower
water level then there really is, or possible not even kicking on the pump
What is the best way to keep within the operating budget? - ANS keep list of purchases and
expenses to date during fiscal year
comparisons should be made with budget allocations to avoid excess purchases
review purchases monthly and compare to budget
1 @COPYRIGHT 2025/2026 ALLRIGHTS RESERVED
,If a diaphragm pump has 2 check valves open, what will the pump do? - ANS It would not
pump properly because 1 check valve should be shut while the other is open
A suction lift pump on the inlet side normally reads 2in of mercury on the psi vacuum gauge but
not reads 3in of mercury. What is the problem with the pump? - ANS A higher vacuum than
normal may indicate a partially plugged or restricted suction line.
A lower vacuum may indicate a higher wet well level or a worn pump impeller or wearing rings.
One mg per L equals how many pounds per 1 MG? - ANS 8.34
What is the proper way to put packing in a pump? - ANS cut the packing rope about 45
degree angle, place around shaft, be sure to offset/stagger the next joint from the previous
How many drips of water should you have coming out of a packing seal? - ANS no drip on a
mechanical seal
How many drips of water should you have coming out of a packing seal? 2 - ANS what the
operation and maintenance manual recommends
A one horsepower motor that runs on 110 volts using 10 amps has what efficiency? -
ANS most motors run from 80-95% efficiency
A motor that has 440 volt supply is usually what phase of power? - ANS 3 phase
NPDES - ANS National Pollutant Discharge Elimination System
2 @COPYRIGHT 2025/2026 ALLRIGHTS RESERVED
,the regulatory agency document issued by either a federal or state agency which is designed to
control all discharges of pollutants from point sources into US waterways - ANS NPDES
permit
What is the name of our operating permit? - ANS NPDES
What is the best way to promote safety in the workplace? - ANS the supervisor needs to be
safe and promote safety in such a manner to get the employees involved
What is normally used to raise the pH in sludge? - ANS lime
What is the common device used to measure the effluent of a lagoon? - ANS v notch weir
What concentration of H2S is unsafe to humans? - ANS death in a few minutes at 0.2%.
Paralyzes respiratory center
What is the minimum O2 concentration that is safe for workers to enter a manhole? - ANS If
O2 is less than 19.5%, do not enter space without respiratory protection. Normal air contains
20.93% of O2.
Normal air contains ______% of O2 - ANS 19.5%
What knob is turned to control the usage of chlorine applied? - ANS rotameter
Can you store BOD at 4C for 48 hours? - ANS yes
What is the minimum velocity of the water flow for a grit chamber and the maximum flow? -
ANS 1.0 feet per second minimum
1.5 feet per second optimum
3 @COPYRIGHT 2025/2026 ALLRIGHTS RESERVED
, 2.0 feet per second maximum
How many mg/L equals one grain per gallon? - ANS 17.1 mg/L
Dissolved oxygen increases when the temperature __________ - ANS decreases
You can tell if a clarifier scraper arm is working by what means? - ANS the simplest is to
visual check to see if the scum scraper arm is moving properly
check into foam
If the sludge is thick or thin, then what does this tell you about the sludge scraper? -
ANS possible answer is the flights are damaged or the speed of the scrapers(flights) need to
be increased if sludge is too thick
or slowed down if the sludge is too thin
aging and maturing of a body of water - ANS eutrophication
eutrophication - ANS aging and maturing of a body of water
If the effluent from a treatment facility contained 5mg/L of BOD, what effect would this have
on the receiving stream? - ANS little effect
If you are doing a test and add one drop of chemical at a time, what is this method called? -
ANS titration
4 @COPYRIGHT 2025/2026 ALLRIGHTS RESERVED
