THMs (Trihalomethanes) Flashcards
What is the disadvantage of pre-chlorination?
THM formation
What is the PMCL for THM?
0.08 mg / L
THMs are formed when chlorine interacts with what substances in the water?
Naturally occurring volatile organic precursors
When must a water system serving 10,000 or fewer customers test for THMs?
Annually
If THMs are formed during pre-chlorination, what should you do?
Stop pre-chlorination
How long can you hold a THM sample before analysis?
14 days
What is the minimum amount of sample needed for analysis?
25 mL
What color bottle is used to gather THM samples?
Amber
A WTP required to test once annually for THMs, fails to meet MCL for THMs. What action must they take?
Immediately begin quarterly sampling
How are THMs results entered on the MOR?
Annual running average
Where should a system that tests annually take THM samples?
At a site that is representative of the longest resident time
What is the best method to remove THM’s after they are formed?
Air stripping
What is the most common alternate disinfectant used to avoid forming THMs?
Chloramines
What is the sampling process for a system serving more than 10,000 customers?
Four, quarterly
What other analysis is taken at the same time as the THMs?
HAA5 and C1² residual
What is the MCL for HAA 5?
60 PPB
Which of the following is the best way to avoid forming THMs?
Remove precursors before chlorination
Which of the following are optimal conditions for forming THMs ?
Higher temperature, higher pH, higher dosage, longer detention time
Higher temperature and/ or higher pH can cause which other following events regarding THMs?
More THMs
What is sampling protocol for a system taking four samples quarterly?
25% of samples must be taken at longest residence time site
When does a system testing annually for THMs take the sample?
Third quarter
If the sum of THMs for the first 3 quarters is greater than 320 ppb, what does that indicate?
System is immediately out of compliance
What problem do bubbles cause with THM analysis?
False readings
What do you do if there are bubbles in THM sample?
Put the cap on, tap the side of the sample jar, discard if bubbles are large
What is the disadvantage of lime softening?
THM formation
