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Water Treatment Plant Operator Test Questions > THMs (Trihalomethanes) > Flashcards

THMs (Trihalomethanes) Flashcards

1
Q

What is the disadvantage of pre-chlorination?

A

THM formation

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2
Q

What is the PMCL for THM?

A

0.08 mg / L

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3
Q

THMs are formed when chlorine interacts with what substances in the water?

A

Naturally occurring volatile organic precursors

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4
Q

When must a water system serving 10,000 or fewer customers test for THMs?

A

Annually

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5
Q

If THMs are formed during pre-chlorination, what should you do?

A

Stop pre-chlorination

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6
Q

How long can you hold a THM sample before analysis?

A

14 days

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7
Q

What is the minimum amount of sample needed for analysis?

A

25 mL

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8
Q

What color bottle is used to gather THM samples?

A

Amber

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9
Q

A WTP required to test once annually for THMs, fails to meet MCL for THMs. What action must they take?

A

Immediately begin quarterly sampling

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10
Q

How are THMs results entered on the MOR?

A

Annual running average

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11
Q

Where should a system that tests annually take THM samples?

A

At a site that is representative of the longest resident time

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12
Q

What is the best method to remove THM’s after they are formed?

A

Air stripping

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13
Q

What is the most common alternate disinfectant used to avoid forming THMs?

A

Chloramines

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14
Q

What is the sampling process for a system serving more than 10,000 customers?

A

Four, quarterly

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15
Q

What other analysis is taken at the same time as the THMs?

A

HAA5 and C1² residual

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16
Q

What is the MCL for HAA 5?

A

60 PPB

17
Q

Which of the following is the best way to avoid forming THMs?

A

Remove precursors before chlorination

18
Q

Which of the following are optimal conditions for forming THMs ?

A

Higher temperature, higher pH, higher dosage, longer detention time

19
Q

Higher temperature and/ or higher pH can cause which other following events regarding THMs?

A

More THMs

20
Q

What is sampling protocol for a system taking four samples quarterly?

A

25% of samples must be taken at longest residence time site

21
Q

When does a system testing annually for THMs take the sample?

A

Third quarter

22
Q

If the sum of THMs for the first 3 quarters is greater than 320 ppb, what does that indicate?

A

System is immediately out of compliance

23
Q

What problem do bubbles cause with THM analysis?

A

False readings

24
Q

What do you do if there are bubbles in THM sample?

A

Put the cap on, tap the side of the sample jar, discard if bubbles are large

25
Q

What is the disadvantage of lime softening?

A

THM formation

Water Treatment Plant Operator Test Questions (16 decks)

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