PAISLEY, Ore. – When a problem with a valve in Paisley, Oregon’s new treatment plant lead to high levels of arsenic, experts from the Oregon Association of Water Utilities helped locate the problem and bring the drinking water back into compliance.
Paisley had a history of arsenic levels that exceeded the regulated Maximum Contaminant Levels. To bring the arsenic levels within the MCL, the utility had installed an arsenic treatment facility, but it wasn’t performing as expected.
“They put the plant on-line and met the MCL for a couple of weeks, but it never got it low enough again,” explained Heath Cokeley, an OAWU Circuit Rider.
The new pressure vessel filtration system adds iron to the water and then runs water through a system of pressurized metal containers lined with layers of filtration media.
“Arsenic is extremely small, it’s very difficult to filter out,” Cokeley said. “So, we like to attach it to something to like iron and filter the larger molecule.”
Cokeley examined the plant and relevant design and specification documents. He compared those to plant logs and information from Duane Young, the Paisley System Operations Specialist. He determined an improper valve was creating problems later in the process.
“The levels were very inconsistent and they were losing filter media, which was a strong indication it was a valve,” Cokeley said.
The issues occurred during the plant’s backwash cycle. All filtration systems have a backwash cycle that flushes the filters and prevents them from becoming saturated. Too much flow during this cycle would wash out filter material and degrade its quality, while too little would allow the filter to become saturated and unable to remove further contaminates. This series of flow problems was traced to a single valve.
“A lower quality valve, something more suited to irrigation, was installed and it was a gate-style valve,” Cokeley said. “The problem is that gate valves can open and close under pressure.”
Cokeley suspected that the inconsistencies were caused by the gate valve opening too much or too little during operation. The Circuit Rider assisted in replacing the valve with a higher-quality, butterfly valve. Cokeley and OAWU Training Specialist Scott Berry helped train the staff on the plant operations with the new, appropriate valve.
“We had to go back to the drawing board and do the math on the appropriate chemical dosing,” Cokeley said.
The plant has been performing well since the assistance, with the drinking water testing below the MCL and, at times, well below the required limits.