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City of Ithaca News

Posted on: February 10, 2020

Important Information About Your Water System


On February 5th, 2020 the City of Ithaca had a chlorine dioxide residual reading of greater than the MAXIMUM RESIDUAL LEVEL (MRDL) of 0.80 mg/l.  Any readings, confirmed over this limit, trigger samples to be taken in the distribution system the next day. The high reading was not reported by staff and was not caught on the daily sheets until reviewed on the 7th.  As a result, no follow up samples were taken. This has triggered this notification.

The City uses chlorine dioxide to help lower natural organics in the source water, to lower disinfection byproducts produced, and to help with any taste and odor problems (yet it can produce a variety of its own). The City water plant monitors for chlorine dioxide residual at the entry point to the distribution system at set intervals during the day.  It is only required that a daily be taken at the entry point into the distribution system.  On the 5th a sample taken at 4 pm was 1.58 mg/l.  Our other two samples taken during the day were less than 0.45 mg/l.  The in plant samples taken on the 4th and 6th were less than 0.25 mg/l.  We will be taking follow up samples in the distribution system this week.

Due to this monitoring violation, we cannot prove that the distribution system was not compromised and as such must provide the EPA required “Standard Health Effects Language”, even though it may not be specific to what actually occurred.  This language is as follows (and refers to a dist. system violation):

Some infants and young children who drink water containing chlorine dioxide in excess of the MRDL could experience nervous system effects.  Similar effects may occur in fetuses of pregnant women who drink water containing chlorine dioxide in excess of the MRDL.  Some people may experience anemia.

We do not feel that there is any reason for concern.  Our numbers have been within limits, on a regular basis leaving the water plant and into the distribution system.  We do not think that has changed.  We have had “blips” in analysis before, but re-checks show a lower number.  This is normally an analysis issues (i.e., items being used for sampling/analysis not flushed or cleaned well, wrong sample taken, etc.) 

Please share this information with all the other people who drink this water, especially those who may not have received this notice directly (for example, people in apartments, nursing homes, schools, and businesses).  You can do this by putting this notice in a public place or distributing copies by hand or mail.

For more information you can contact Charles Baker, Chief Operator, at 273-4680, or

This notice is being provided by the City of Ithaca, Water Treatment Plant, Water & Sewer Division, Dept. of Public Works.

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