Borough crews restored the water treatment plant to full working order last week after an equipment problem prompted a boil-water notice that lasted a little over 72 hours.

It appears a faulty pH probe which measures the water’s hydrogen-ion activity — a key piece of managing the treatment plant chemistry — was producing inaccurate readings on Sunday, July 20.

A lot of the operations at the plant are based on the pH reading, explained Public Works Director Tom Wetor. “If your instrument is off by just a little bit, it can throw off your entire operation.”

The new $23 million plant started operations in March but is still several weeks away from full capacity, Wetor said.

The new plant uses an improved water filtration system which is a little more complicated — and effective — than the old plant’s separation process for removing organic contaminants. “Now we have a water treatment plant entirely based on chemistry,” Wetor said.

Regardless of the faulty meter disputing operations, the heavy rainfall of a couple of weeks ago (about five inches) followed by a dry spell affected the pH level of water in Wrangell’s two hillside reservoirs, he said.

“The more and more we operate this place, the more we know.”

The borough issued a boil-water notice on July 20 as a precaution, when the equipment problems reduced the amount of time that water was in contact with chlorine in the holding tank for disinfection. City Hall also asked the community to conserve water until the problem was fixed.

After installing a new pH probe, resetting equipment and testing it all out, the Public Works crew flushed the system all the way from the airport to the end of the line at 6-Mile — opening up fire hydrants — to ensure that any possible contamination was removed from the lines, Wetor explained.

The plant was up and running with sufficient chlorine contact time on Monday, July 21, but borough officials said they wanted to move cautiously and it took until Wednesday, July 23, to thoroughly flush out the system and verify water quality standards with multiple tests.

The borough lifted the boil-water notice the afternoon of July 23.

At full capacity, the new plant will be able to handle twice the volume of the previous facility. That means not only more clean water for the community’s needs, particularly during the summer when salmon processing plants are operating, but the increased storage capacity will make it less likely for a repeat of the shortened chlorine contact time, Wetor said.

With the lifting of the boil-water notice, officials advised residents to run taps and also flush out their hot water heaters by running them until the water cools and the tank refills.

Residents also were advised to toss out any ice cubes that were made after the boil-water notice was issued on July 20 but before the all-clear signal was issued July 23.

The borough assembly was scheduled to hold a work session on Tuesday, July 29, to better understand what happened at the treatment plant.