Water treatment plant nearing completion: a look inside

After seven years of planning and almost 18 months of construction, Wrangell's state-of-the-art water treatment plant is in the final phases. The $23 million project not only modernizes Wrangell's system but ensures the town is better prepared for future dry spells.

The plant will likely go fully online this spring.

The current plant started operations in 1999, and many of its pieces are being repurposed into the new plant just next door. While the current plant initially relies on an electrical current to break apart the organic matter in the water, the new plant purifies water through a dissolved air flotation (DAF) system.

On Feb. 7, Public Works Director Tom Wetor and Water Treatment Lead Operator Andrew Scrambler hosted the Sentinel for a behind-the-scenes tour of the new facility and explained every step in the water filtration process.

The hillside runoff enters the plant through a pipe that leads from the reservoirs just up the hill. Almost immediately, sensors measure several parameters within the water, including pH (acidity) levels and the amount of organic matter. Wetor noted that these numbers fluctuate, and Wrangell tends to see higher-quality water in February and March and lower-quality water in September.

The results from the data inform plan operators how they need to treat the water. They then add the appropriate amount of a liquid coagulant. The coagulant and the "raw" water are then combined in the first step of the treatment process: the static mixer.

In the static mixer, the coagulant attaches itself to organic matter in the water. Though the coagulant is a chemical compound (it includes chlorine), it is 100% safe to drink, and Wetor added that everything in the plant complies with the standards of all relevant regulatory agencies.

"We are using as few chemicals as possible," he said.

After the coagulant combines with the organic matter, thus separating it from the water, the water is split into one of three units, called DAF trains. On days where there is a high demand for water, Wetor and Scrambler may operate two or three of the trains, but on most days, they will only need to operate just one.

The DAF trains are further split into essentially three giant tanks. The water slowly flows from one tank to the next, with each serving a different purpose in the purification process. The first tank has what looks like an upside-down ceiling fan on its floor, and it continues to mix the coagulant with the water.

After the water moves into the second of the three enormous metal tanks, it is injected with air from several nozzles at the bottom of the tank. By this point, the coagulant and the organic matter have adequately separated from the water compounds, forming a foamy white substance called floc. The air injection helps raise the floc to the top of the tank in a process called flocculation.

While the tank may look a bit grimy at this point, that's only because the floc is covering up the mostly clarified water that lies just beneath. In the third tank, a paddle scrapes the "floc bed" off the top, leaving just clean water remaining.

If the DAF train is a wide brush, the next step is a fine-toothed comb. The water then moves to one of six filters, which filters the water through silica sand and mineral coal beds.

"The DAF is going to get a big majority of the (organic) items out of the water," Wetor said, "and whatever's left is getting filtered out through these filter beds."

Cleaning the filtration beds can be a bit of a pain, though, something that the new plant is already much better able to handle than the existing one. The way you clean them is by running water in the opposite direction through the filtration beds. This is called backwash, and while it only needs to occur once a week or so (depending on demand), the new plant offers an incredible upgrade to this process.

For starters, instead of having to adhere to a predefined backwash schedule, the plant's sensors can detect when a backwash is needed. Also, because there are six filtration beds, plant operators can keep running water through different filters while the filter in need of a backwash is cleaned.

The new backwash system is also more efficient, using just 10% of the water that the current plant uses, according to Wetor.

Censors at nearly every step of the process ensure that the plant maintains water quality standards set by the federal government. And when the water leaves the plant, it is stored in a nearby tank for a short amount of time before it heads into town.

Though the initial timeline projected the new plant will go live in June, it appears that things are a tad ahead of schedule. Though there is no official opening day set, the Public Works Department has begun giving tours to borough assembly members. Eventually, they will give tours to members of the public as the plant becomes operational.

The department will briefly operate both the old and new plants simultaneously while staff phases in the new facility to full capacity.

Wetor and Scrambler both noted that they would love to collaborate with the school district and maybe provide tours to science classes sometime in the future.

"We're really excited," Wetor said. "It's one of the biggest projects Wrangell has ever done."

It's also one of the most expensive. Nearly $16 million in state and federal grants covered almost two-thirds of the project's $23 million price tag. The borough borrowed $6.5 million in long-term federal loans. With all the federal and state help, the borough needed to kick in just $119,000 of its own money for construction.