Age of water

A map of Little Falls' water system shows, by color, the average age of the water being consumed in different parts of the city. Blue represents the freshest water, while red is the oldest.

An analysis of Little Falls’ water system is giving city officials better insight into how to improve it.

Short Elliott Hendrickson recently completed the analysis in response to complaints the city had received about pressure surges in the southeast part of town. Tuesday, Public Works Director Greg Kimman reported their findings to the Little Falls City Council, along with possible solutions to issues they found.

The city’s water system works on two zones; one low and one high. The water treatment plant near City Hall pumps water into the low zone, which is the water tower on the west side of town near Pine Grove Zoo. When the water tower on the east side of town near Walmart — the high zone — calls for water, it pulls from the low zone.

“So, those two are separated, but everything pulls through the low zone up to the high zone,” Kimman said.

Kimman said it was about a year and a half or two years ago that the city received complaints about pressure spikes in the area of the Little Falls Golf Course. As part of the analysis, monitoring stations were installed in each of the four quadrants of towns for one week to track the pressure. Initial checks showed that when the high-service pump at the treatment plant turned on and off, spikes were occurring down the line.

At the monitoring station closest to the water treatment plant, the pressure remained consistent, with no major spikes. The second-closest station to the plant, in the low pressure zone, showed one small spike, but it was still relatively consistent. Kimman explained that the water towers also act as a buffer between pressure surges because they give the water a place to bounce.

As the water gets further away from the treatment plant and the towers, the more pronounced the spikes get. The largest spikes and the most often they occurred was at a monitoring station near Thomas Drive on the far south end of town.

“We wanted to find out, well, what are some of the things that we can do to eliminate those spikes?” Kimman said.

He pointed out that there are no places where the water lines cross the Mississippi River near where the Thomas Drive monitoring station was placed. The two places the lines currently cross the river are the trestle bridge near City Hall and on the Memorial Bridge on Broadway Avenue/Highway 27.

There are also a lot of dead lines going into the south side of town that end and do not connect to any more piping.

“What happens when you have a dead end is, when there’s a pressure surge, it comes to the end, it hits it, and then it comes back,” Kimman said. “So, you start to get a little bit of that water hammering. That’s why you see these water spikes the way that they are.”

As a result, the city is examining if adding another connection further south would help resolve some of those surging issues.

Another issue found in the system was the average age of the water being consumed in some parts of town. A color coded map showed areas of blue where water was being consumed within a day of being pumped, green where it was consumed within seven days, orange where it was 12 - 13 days between pumping and consumption and red where it was 14 or more days from the time the water was leaving the treatment plant until it was being used.

The water being consumed near the treatment plant and much of the southeast portion of town was coded as blue, the freshest on the map. However, more reds and oranges can be found immediately near both towers, as well as in the southwest and northern parts of town.

In searching for the cause of that, Kimman said it may be caused by how the towers are operated. The city typically likes to keep those towers at a constant level so that pressure remains consistent. But, by keeping it at the same level, the tank never has an opportunity to drop and refill with fresh water.

“So, by keeping it at that, whatever we put into the pipe system is being consumed — the folks closest to the treatment facility get the fresh water, and as you get farther out toward the water tower, that’s when it’s the older water,” Kimman said.

One of the solutions the city is exploring is to allow the levels in the towers to fluctuate up and down more frequently. That would likely help with keeping fresher water pumping through the system.

When asked by Council Member Frank Gosiak, Kimman said that would cause a slight, but practically unnoticeable drop in pressure. Currently, he said the pressure is about 70 pounds per square inch (PSI). Allowing it to fluctuate in the towers might let it drop as low as 60 PSI.

“You really wouldn’t notice that change at your house,” Kimman said.

One issue with that, however, is that the Little Falls Fire Department will have to remain in contact with the city because, with the tanks kept as they are currently, it always has the maximum amount of pressure while trying to fight fires. If the levels are allowed to fluctuate, the city will have to start the pumps to ensure it has the most possible pressure.

“We’ll never be in danger of necessarily running out of water, because we’ve got a million gallons of water sitting in the ground to pump into the system,” Kimman said. “It’s just that they won’t have two million gallons, one on each side, readily available. If they have a bad fire, they’re definitely going to have to give us a call so we can make sure there’s enough pressure there.”

Another map showed how the age of the water pumping through the system would likely look if another river crossing was added on the south side of town. While there was still older water being used in the Riverwood area on the north side of the town, fresher water was being used on the south and southwest sides of town.

“It’s also going to have the other benefit of reducing that pressure spike, because we notice farther away from the towers, when you have that spike, it didn’t have anywhere for the pressure to go,” Kimman said. “In this instance, when we put that connection in, that pressure will be able to go around and eventually get back to the water tower to have that buffer so we don’t see those spikes.”

In order to alleviate the issue on the north end of town, SEH suggested coming up with a flushing system that would pump about 50 gallons of water per minute in that area.

One solution to do that while still benefiting the city was to use the splash pad at Twitchel Park.

“I don’t know if it would necessarily use that 50 gallons per minute, but it’s definitely something that would have a benefit to using that water to be able to bring that fresh water up into that area,” Kimman said.

He said those are options that are being explored for the next couple of years. Funding for upgrades to the water system is already allocated within the city’s capital improvement plan.

Looking longer term, Kimman said the city would also like to add a second new crossing to create redundancy in the system. As it is now, there is only one line feeding everything north of Highway 10. If that line were to break, every customer in that area would be without water until that was fixed.

Infrastructure projects on Lindbergh Drive and Thomas Drive show the city was already prepared to add more lines for redundancy, eventually.

“They’ve got a stub, so they were planning this for quite some time,” Kimman said. “It makes sense in terms of redundancy, it makes sense for growth, it makes sense for pressure, it makes sense for age of the water.”

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