Every spring and fall, the City of Monticello alerts residents that we will be flushing the water hydrants around town, and that it may cause some yellowish to brownish discoloration of water in homes near areas being flushed. Our staff sat down to answer one of our favorite questions, “Water they doing to the hydrants?” (Sorry, we couldn’t help ourselves).
Why do we have to clean the water system?
Brian Rousselow is a W&S Technician for the City’s Water & Sewer department, and Mat Stang is the Utilities Superintendent for the department, which falls under the City’s Public Works umbrella.
The Water Department completes hydrant flushing once in the spring and once in the fall. The process of periodically flushing fire hydrants is an important preventive maintenance activity in the city.
“The flushing action causes an increase in flow rate that scours or scrubs the inside of the water main helping to remove naturally occurring debris and sediment from the pipe,” explains Stang.
Rousselow notes this action is necessary because, “Water always takes the path of least resistance. The water will go down the center of the water main, while stagnant water allows minerals to settle and build up over time.”
Now time for our super simple science refresher: Stagnant areas in the water system allow the naturally dissolved minerals like iron and manganese to oxidize. The oxidation of these minerals causes them to change from colorless and dissolved to colored and solid: dark orange from the iron, black from the manganese. The minerals (once solidified) come out of suspension and settle in the pipe, building up on the bottom of the pipe over time. For those of us who don’t remember our high school science classes – suspension is when small pieces of a solid, in this case the natural minerals in the water, are mixed in the water, but are no longer dissolved. For example: sand in water. If there’s a wave, it will mix together, but if it’s stagnant, or not moving, the sand will fall or settle (because of gravity).
Keep in mind, the sediment isn’t toxic, it is made up of naturally occurring minerals in the ground, specifically iron and manganese, because we don’t have a water treatment facility (*yet, learn more about our proposed Water Treatment Facility Project here).
Rousselow explains the water system with the following analogy: think of the City’s water system like that of the human body. The water towers are your heart, the water mains are like your veins.
“You want fresh or clean blood coming from your heart, that main source. So that’s why we start with cleaning the water towers, then start flushing the hydrants. Water fills in the towers, then drains from the towers to the rest of the system. The water gets stagnant in the towers too, and the tower is where all the water is being pulled from, so we want to get that cleaned then start feeding that clean water out into the system,” says Rousselow.
City staff cleans and inspects both of the City’s water towers each year before the flushing starts. There is also an underground water storage reservoir that the water department cleans and inspects bi-yearly.
Do you “flush” every hydrant in the City?
The short answer is no. If we go back to the heart and veins analogy, the water mains are like your veins, they branch out across the city. We use the water hydrants to access those “veins” and flush out the “old water” so the new, “fresh” water from the freshly cleaned water system can spread throughout the City.
“A lot of people always think, ‘Oh you’re flushing random hydrants.’ When really, we’re not. We’re flushing water mains and utilizing hydrants to do that. So, we’re not actually flushing every individual hydrant in the city,” explains Rousselow.
What is used to clean the water towers?
Once the Water Department drains the tower, they perform maintenance and inspections. What’s left is a layer of sediment on the bottom of the tower.
From there we just add water! Staff use water to rinse the sediment out of the water towers into the stormwater system, so it doesn't go into the drinking water.
After the tower is cleaned, it’s refilled with drinking water. The tower is sampled to ensure that it was disinfected properly before being brought back online.
The City’s potable (drinking) water system is tested regularly (15 samples monthly), but the additional testing is incorporated during the cleaning process as an additional precaution.
Where does the water in water towers come from?
The City’s water is sourced from five wells connected to an aquifer several hundred feet below (wells range from 148 to 310 feet deep). Because the City does not have a Water Treatment Facility at this time, our water is treated regularly at each well site. From there, using a pump station, it is pulled into the water towers and the underground reservoir. Two wells pump into the Reservoir and three wells pump directly into towers.
Fun fact: gravity and the elevation of water in the tower creates the pressure inside your home, the water is pulled down into the potable water system by natural gravity (0.433 PSI per foot of water elevation).
Water levels are another key factor to maintaining a healthy water system. Levels in each water tower and in the aquifer are monitored regularly to ensure that our drinking water supply is maintained. That’s why precautions are taken, like the City’s seasonal watering restrictions.
“The reservoir acts as extra storage that we can provide, especially in the summertime, when people are using so much water for irrigation,” said Rousselow.
Monticello has a permanent odd/even watering schedule from June 1 through September 30 every year. To learn more about the City’s Water & Sewer Department, visit our website: https://www.monticellomn.gov/201