To the Editor:
This letter is in response to a letter to the editor written by Henry Roehler of Fairmont, in regard to Fairmont's drinking water. I was surprised at how Mr. Roehler presented information I provided to him, and feel I was unfairly misquoted in his letter. What follows is my original reply to Mr. Roehler:
Dr. Mr. Roehler:
Currently there is no requirement for the testing of cyanotoxins in drinking water and it may not be required for a long time unless USEPA sees the need to regulate with sufficient supporting data and cost benefit analysis.
Fortunately the Safe Drinking Water Act Surface Water Treatment Rules require all Surface Water Systems to use multiple barrier treatment approach to treat, remove and protect against chemical and microbial contamination. In Minnesota, all surface water systems are required to use coagulation, (the majority of them also with flocculation and sedimentation), filtration, and provide sufficient chlorine contact time to ensure effective disinfection. Water that flows through the entire treatment train and meets the disinfection requirement and water quality standards is deemed to have 99.9% of Giardia and Cryptosporidium and 99.99% of viruses removed from it. It also means between 99 and 99.9% of the "intact" blue-green algae are also removed by reason of size exclusion.
I won't worry much about cyanotoxins in Fairmont's drinking water because of the treatment processes used and the location of Fairmont's raw water intake.
Cyanobacteria/blue-green algae typically populated on the top layer of surface water and carry a distinct greenish color, particularly in warm, shallow, surface waters.
Fairmont's water intake goes out 250 feet into the Budd Lake and more than 20 feet below the surface; from visual examination, blue-green algae don't seem to be a problem.
Besides, Fairmont water treatment plant uses strong oxidants like chlorine dioxide and chlorine; both have shown to be effective in destroying/removing the cyanotoxins.
A big challenge for all surface water systems is the treatment for Taste & Odor and addressing T & O concerns/complaints to their consumers.
Almost all T & O problems/complaints in Minnesota are associated with two of the most commonly occurring chemicals - Geosmin and 2-Methylisoborneol (2-MIB). They attributed to the unpleasant taste and odor characteristics of drinking water. These compounds are formed intracellularly in blue green algae and actinobacteria released upon cell destruction. They can be in extremely low concentrations but detectable to human nose at or below 10 ng/L (ppt).
So, rather than testing for cyanotoxins, many surface water systems routinely test for Geosmin and MIB to adjust their treatment chemicals such as powdered activated carbon, ozone, chlorine dioxide, and/or potassium permanganese, to address potential T & O issues/complaints. The St. Paul Regional Water Services in 2007-2008 rebuilt all its filters and replaced the media with the granular activated carbon (GAC) media to remove contaminants and polish off reminding Geosmin and MIB to concentrations below detectable threshold by the human nose, and from what I know about Fairmont's new water plant that is under construction, GAC filters will also be used to address the T & O concerns.
I hope this answers your questions; please feel free to contact me if you have further questions.
Lih-in W. Rezania,
public health engineer
Drinking Water Protection Section
Environmental Health Division