OTHELLO - A year-long rehabilitation project lowered fluoride levels in one of Othello's municipal wells although the amounts still exceed US Environmental Protection Agency thresholds.
The project - paid for with $309,000 in state and federal grants - plugged the 1,200 foot well at the 900 foot level to block the higher concentrations of fluoride found in the deeper water, according to city engineer Larry Julius and Kevin Lindsey, senior hydrogeologist with GSI Waster Solutions.
They gave city council a rundown of how the project went before council signed off on it's completion earlier this month.
Well water tests performed in 2008 found fluoride levels to be as high as 15 milligrams per liter. Last year levels hovered around 5 mpl, Julius said; adding tests done since the project's completion have revealed levels of around 4.3 mpl.
The EPA requires cities to take action when levels exceed 4 milligrams per liter, an amount the agency says can increase the risk of bone fracture in adults and pitted tooth enamel in children.
Recent tests revealed .21 micrograms per liter of a herbicide called DCPA, which is used on annual grasses, broadleaf wheat species and a wide range of vegetable crops, Julius said. In 2008 the well registered nearly double that amount, well above the .1 mpl detection limit imposed by the state Department of Health, but Julius said the agency requires no further investigation at this time.
"We checked with the Department of Health and they weren't too worried about it," Julius said. "They said the city just needs to continue monitoring it."
Whenever a city attempts to bring a well back online they're required to test more frequently for numerous substances, explained Mike Means, water quality manager with the Department of Health. In the case of DCPA, exceeding the .1 mpl detection level is very different than reaching the health advisory level of 70 mpl, he said. The herbicide has been detected in two other Othello water sources besides well six, but also at low levels requiring no action, Means added.
Well six, which was built in the early 1970s, is one of the city's largest, previously pumping up to 3,000 gallons of water per minute, about 36 percent of the city's total water production. While its depth has been reduced, Lindsey said the well can still pump as much as 2,000 gpm, which he and Julius both recommended doing for the next month or so in order to flush out the remaining fluoride-rich water.
Prior to being partially plugged, the well had a "thief zone," which had been moving deeper well water out into higher aquifers, Lindsey explained.
"When the pump is on its pulling that water back in," he said. "So we've turned off most of the uphill flow, but we've got forty odd years of fluoride rich water out in the immediately surrounding hydrogeologic environment ... We're developing out some of that old water and pulling in shallow, cleaner water that can now take over more production and chemistry of the hole."
Council members all agreed the well should be run continually for a month or more with daily monitoring of fluoride levels.
"Now is the time to flip the switch and get us going 1,000 gallons a minute and see what happens," Councilman Marc Spohr said.
Another way to bring fluoride levels down in the short term might be to operate the well in a "sweet spot," experimenting with a lower production rate to draw shallower water, Julius said. He also noted the city has been granted permission to "comingle" water drawn from well six with water drawn from other wells to further dilute fluoride levels.
"There will be tweaking that public works will look at going forward," he said. "The Department of Health still looks at this well as a backup well because fluoride levels are still high. The best way to get it from standby to permanent is to consistently and reliably be below that 4 milligrams per liter mark."
Julius cautioned the EPA is considering changing the threshold level to between 1 and 2 mpl.
"If that's the case there are a lot of entities around this state that are going to be scrambling because their natural fluoride levels are greater than two but less than four," he said.