Well 12 Shut Down: The Details

Here’s the details of the problems with Well 12:

Low chlorine prompts shutdown of Unit Well 12; leads to discovery of
fluoride pump failure

Unit Well 12 was taken out of service this morning due to a low chlorine
level observed at the well. Water Utility staff repaired the
chlorinator, then drained and refilled the 150,000-gallon reservoir.
During the repairs, staff observed that fluoride usage during the
preceding 24-hour period was higher than normal. About 25 gallons of
fluoride had been used compared to the normal 6-7 gallons per 24-hour
period. A malfunctioning anti-siphon valve on the fluoride feed system
is believed to be responsible for the high fluoride usage.

Unit Well 12 operated for 45 minutes this morning before it was taken
out of service. While out of service, the fluoride overfeed was
determined. It is believed that most if not all of the high fluoride
water was discharged into the sanitary sewer when the un-chlorinated
water was drained from the reservoir. As a precaution, water samples
were collected at six distribution system locations upon discovery of
the potential for high fluoride in the water distribution system. All
samples tested at or below 2.0 mg/L fluoride, with the majority testing
between 1.0 – 1.3 mg/L. Samples were collected at public buildings
including schools, libraries, a fire station, seasonal well, and
convenient store.

The fluoride feed pump and anti-siphon valve have been replaced, the
chlorinator repaired, and the well was placed back into service around
4:30 p.m. Water Utility staff continue to monitor the chlorine and
fluoride levels at the well to confirm that they are within range and
that the pumps and chemical feed systems are operating correctly.

Unit Well 12 is located on the near west side and generally serves the
area between Whitney Way and Lake Wingra, south of Regent Street and
north of Raymond Road.

Chlorine is added to the water to kill bacteria and disinfect viruses
that may be present in the groundwater. The target chlorine level for
water leaving the well is 0.3 mg/L. Madison Water Utility standard
operating procedures require that a well be taken out of service when
the chlorine level at the well drops below 0.15 mg/L.

Fluoride is added to drinking water to promote dental health. The
target level is 1.1 mg/L.

Please contact the Water Utility at 266-4665 if you have any questions
or concerns.