As shown below, fluoride was at normal levels in drinking water sampled from pipes outside the Jones Ferry Road Water Treatment Plant (WTP) immediately following the shutdown of the plant at 3:22 PM on February 2, 2017 due to the accidental fluoride overfeed.
No water with elevated level of fluoride was pumped into the pipes serving our customers (the water distribution system). All water with elevated fluoride levels was contained on-site at the WTP.
The US Public Health Service’s recommended fluoride level is 0.7 parts per million (ppm). This level has been OWASA’s target fluoride level since 2012. By Federal and State regulations, the maximum limit for fluoride in distribution water systems is 4.0 ppm. Fluoride is also regulated with a secondary maximum limit of 2.0 ppm in distribution water systems; if levels were above this secondary limit, a utility would be required to notify their customers.
Prior to the fluoride overfeed on the morning of February 2, 2017, OWASA laboratory staff collected water samples both at the WTP and from sites within our service area as part of our routine distribution system sampling. The level of fluoride in these samples ranged from 0.62 to 0.67 ppm.
The fluoride overfeed was discovered at 3:00 PM that afternoon. At 3:10 PM laboratory staff collected a sample of drinking water from a location just before the water enters the pipes serving our customers. The fluoride level at this location was 0.68 ppm, which is within the normal range of OWASA drinking water; fluoride levels in 2016 ranged from 0.55 to 0.90 ppm with an average 0.69 ppm.
The WTP was shut down at 3:22 PM to contain the over-fluoridated water within the facility. As an added precaution, laboratory staff collected samples of drinking water at sites bracketing the WTP from 3:47 to 3:59 PM. These sites were selected because they are served by water pipes directly leaving the WTP. Fluoride levels in these samples were all 0.64 ppm, also within the normal range of OWASA drinking water.
The 1.5-million-gallon tank that contained the water with elevated fluoride levels at the WTP has heavy-duty curtains that force the water to follow a set path (shown in the figure below). There are three hatches where samples can be collected as water flows through this path. Beginning at 4:10 PM, two samples were collected from each of the three hatches, from the surface of the water and approximately mid-depth of the water. These sites are located further away from where treated drinking water leaves the WTP than the samples collected at 9:00 AM and 3:10 PM. At the time samples were collected from this tank, the WTP was shut down, no water was flowing through this tank, and all water in the tank was contained. As is shown in the graphic below, water above the secondary maximum limit (2.0 ppm) had not yet reached the point where water is pumped out of the tank into the drinking water piping system.