The City of Ithaca had a chlorine dioxide residual reading greater than the maximum residual level (MRDL) of 0.80 mg/l on Feb. 5.
Any readings over this limit will trigger samples to be taken in the distribution system the next day. But the high reading was not reported by staff and wasn’t caught on the daily sheets until Feb. 7, according to a press release from the City of Ithaca. As a result, no follow up samples were taken, Chief Operator Charles Baker said, until they caught the high reading.
Ithaca uses chlorine dioxide to help lower natural organics in the source water which lowers disinfection by-products that are produced. It also helps with any taste and odor problems, though it can produce a variety of its own. The City’s water plant monitors the MRDL for chlorine dioxide at the entry point of the distribution system at different times of the day.
On Feb. 5, a sample was taken at 4 p.m. that was 1.58 mg/l, which is over the allowable limit. Since it wasn't reported, no specific follow-up samples were taken during the day, but two other regularly-scheduled samples taken during the day were shown to be less than 0.45 mg/l. Both the in-plant samples taken on Feb. 4 and 6 were less than 0.25 mg/l. The city will be taking additional samples in the distribution system this week, and Baker said his staff will be reviewing its standard operating procedures to ensure all staff members know when notifications have to be made. Baker further said that New York State takes care of notifying the Environmental Protection Agency, and that there isn't much further action to be taken besides reviewing procedure.
Because of this monitoring violation, the city cannot prove whether or not the distribution system was compromised and must provide the EPA required “Standard Health Effects Language," even though it may not be specific to what actually occurred, according to the city's press release. This language is as follows and it refers to a distribution 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.”
At this time, the city does not feel there is any reason for concern since the numbers have been within limits on a regular basis leaving the water plant and into the distribution system.
"There have been slight ‘blips’ in analysis before but re-checks show a lower number," the press release said. "Normally, this is considered an analysis issue, (i.e., items being used for sampling/analysis not flushed or cleaned well, a wrong sample taken, etc.)"