Posted on November 6, 2024
The City of Bloomington is trying to figure out how it will meet future demands for drinking water. Bloomington gets its water from two lakes north of the Twin Cities, Lakes Bloomington and Evergreen.
There’s no problem with capacity right now, but that won’t always be true.
“Well, we’re growing and that creates an increase in the need for capacity, so, we’re looking at our options,” said Deputy City Manager Sue McLaughlin.
Last year, the city used an average of 11.1 million gallons of water per day. Back in 2010, the city’s whopping 480-page Water Supply Plan projected the safe yield of the reservoirs in 2030 at 13.3 million gallons per day. “Safe yield” is the estimated natural recharge rate from the watershed that drains into the two lakes. The minimum safe yield is generally 100% of average daily use.
With a couple million gallons per day to spare, no, problem, right?
Bloomington water use has risen each year since 2015.
It’s tighter than you might think.
“The desired performance measure for safe yield is 125% of the projected average demand,” said the report.
And at 119%, the city already is below that target. Again, not a crisis right now.
Historic water use went down in Bloomington from 2005 to 2016. Most cities had the same trend because homes and businesses were changing over to water-efficient plumbing fixtures. That toilet and shower head swap-out is largely over and the city said since 2015 average daily water production has returned to an upward trend.
2010 simulated safe yield and reservoir sedimentation projections in the Bloomington Water Supply Plan.
Eventually, the city will need more water than it has available now.
So where can Bloomington get more water? About a decade ago, there was an effort to reach a deal with small towns west of Bloomington like Danvers and Stanford to create a regional water authority with a new well field drilled into the Mahomet Aquifer north of Minier. That didn’t go anywhere because the potential partners couldn’t agree on how to share both the water and the substantial cost to build a treatment plant near the wells.
Bloomington does have a couple of wells, as well as the lakes. McLaughlin said those are not a long-term answer to the need for more H2O, though.
“There are certain chemicals in the water that need to be treated and the output of those wells is very low in comparison to what it would take to treat them, she said. “So right now, they’re just not being used.”
The city did raise the spillway for the Evergreen Lake Reservoir in 1995, adding more than 1.2 billion gallons of capacity.
The Bloomington Water Supply Plan estimated a loss of close to 500,000 gallons of reservoir capacity per decade from sedimentation.
Climate change forecasts suggest droughts may become more frequent and more severe just as high rainfall events have done. If there’s a drought, Bloomington’s narrow margin of capacity above safe yield could mean mandatory water conservation measures would go into effect sooner than they would if there were more space in the lakes.
Even without any water trickling into the lakes from the watershed at all, it would still take a while for Bloomington to suck out all the water — 1-2 years, according to that report.
The city has tried to address the emergency issue. In 1992, Bloomington built a pumping station to draw water from the Mackinaw River in emergencies. The state has strict conditions on when and how much the city can pump.
Adding to the pressure of the forecast of increased use by thirsty residents is the fact that the capacity of the lakes is shrinking.
“While demands are increasing, storage is slowly decreasing, calculations and measurements confirm that both Lake Bloomington and Evergreen Lake have high sedimentation rates,” said the 2010 plan.
The city water plan estimated the lakes are losing close to a 500,000 gallons of space per decade.
“We’re looking at our options,” McLaughlin said. “What is the best option? And obviously we already draw our source from Evergreen and Bloomington, so it would make the most sense to dredge since they’ve never been dredged.”
How much would that cost?
“We are actually actively studying the costs to dredge both Lake Evergreen and Lake Bloomington,” she said.
McLaughlin said the study may take six to nine months and the city council wouldn’t get the issue and options to discuss until the next budget year.
Lake Bloomington was built in 1929 and Lake Evergreen in the late 1960s with service beginning in 1972. The city formed both lakes, five miles apart, by taking water from Money Creek and Six Mile Creek which are tributaries of the Mackinaw River.
