LISBON — The events that led to a “do not drink” order issued by Lisbon Water Department Aug. 29 were caused by a monthslong leaky valve on one of the wells at the water plant that worsened over time, causing contaminated backwash water to enter the water system in late August.

Once the contamination was detected, the order was issued as there were concerns of arsenic contamination. That order stayed in place for more than 24 hours while the town awaited expedited water test results, which ultimately determined that there were no elevated levels of arsenic in the water.

The initial cause of the contamination was thought to be from a basin level sensor fail, however an engineering report by Wright-Perce concluded that the issue was mechanical and likely caused by a failed check valve at the plant well, according to Daniel Flaig, Wright-Pierce engineer.

It is possible that the water hardness, which in Lisbon is harder than average, caused mineral buildup on the valve over time preventing it from closing all the way, he said. It got to a point where water in the decant line was flowing backward into the well when the water pump was turned off, causing decant water from one of the tanks to flow back into the well.

Flaig recommended replacing the check valve in the well and to install a second check valve in one of the water lines as a secondary alert in case the issue comes up again — helping staff to understand the specific problem sooner.

The engineering firm went back and looked at stored system data and found that the issue likely started sometime around March, though the changes in water data were very small at that time, he said. But by the time June rolled around an anomaly in the data clearly showed something abnormal was happening.

Though department staff started noticing issues in the data indicating something was wrong in late June, staff did not understand what was causing the data issue but they had been looking into the cause of those data issues when the contamination happened in August, Interim General Manager Shellie Reynolds said.

“Once we started noticing things, I started asking questions,” she said. “It just didn’t occur fast enough to prevent what happened on the 28th,” she said.

Recommendations to address that issue include operator training and a better general awareness of system alarms, Flaig said. The system creates a lot of data from day to day providing a lot of information. The report was positive in that it determined that the water treatment plant was functioning well overall and in good condition.

“I didn’t really find anything, although there’s some routine maintenance that needs to be done, the plant’s in good shape,” he said. “There’s plenty of data there and I think the important part is for operators to understand, have enough awareness of the data and understand what normal data looks like and when they start to see data that doesn’t look right, taking that next step to interpret that data.”

Another concern highlighted in the report is the town’s reliance on only one well drawing water from a large water source, there is another well that can draw from a large water source but it is inactive because of elevated arsenic levels found in a water test last year.

However Flaig said the department should develop a treatment plan for water at that well to remove those elevated levels of arsenic so the town can have a backup source should its primary well go offline — along with monthly arsenic testing at that well to monitor contamination levels.

There were several other recommendations from upgrading the department’s data reporting system to testing water samples as reports of dirty water complaints from customers come in.

Staff are still in the process of developing a plan of action based on the recommendations in the report.

Flaig impressed that even experienced licensed operators encounter situations that they need to seek help to resolve, so it is not uncommon to bring in outside resources to help fix something — encouraging them to do so as issues arise in the future, he said.

“That’s why I say there’s no stupid question,” he said. “… You could be a competent licensed operator but you’re going to run into new situations that you don’t know and you just got to send a message that ‘if you don’t know something you got to bring in other people.’”