Bloomington studies dredging of Lakes Bloomington and Lake Evergreen

City of Bloomington trying to figure out how he will satisfy future drinking needs water. Bloomington gets its water from two lakes north of the Twin Cities: Lakes Bloomington and Lake Evergreen. There are no problems with capacity now. This won’t always be true.

“Well, we’re growing and that’s increasing the need for capacity, so we’re looking at our options,” Deputy City Manager Sue McGlaughlin said.

Bloomington water use chart from 1980 to 2025 — Water consumption in Bloomington has increased every year since 2015.

Last year, the city used an average of 11.1 million gallons of water per day. Back in 2010, the city’s colossal 480-page Water supply plan the projected safe reservoir capacity in 2030 is 13.3 million gallons per day. “Safe Exit” is the estimated natural rate of replenishment of water from the watershed draining the two lakes. The minimum safe yield is usually 100% of average daily use. Having a couple million gallons a day on hand is, no, a problem, right?

It’s more difficult than you think.

“The desired performance measure for safe yield is 125% of projected average demand,” the report said.

And at 119% the city is already below this goal. Again, this is not a crisis.

Historical water use in Bloomington decreased from 2005 to 2016. Most cities saw the same trend as homes and businesses switched to water-efficient plumbing fixtures. Replacement of toilets and showerheads has largely been completed, and city officials said average daily water production has returned to an upward trend since 2015.

Graph showing modeling of sedimentation and safe release in Bloomington reservoirs. — The 2010 Bloomington Water Supply Plan modeled safe projections for yields and reservoir sediments.

But eventually the city will need more water than it currently has.

So where can Bloomington get more water? About a decade ago, there was an attempt to reach an agreement with small towns west of Bloomington, such as Danvers and Stanford, to create a regional water authority with a new well field drilled into the Mahomet Aquifer north of Miniere. This came to nothing because potential partners could not agree on how to share the water and the significant costs of building treatment facilities near the wells.

Bloomington has a couple of wells and lakes. However, Sue McGlaughlin said it was not a long-term answer to the need for more H2O.

“There are certain chemicals in the water that need to be treated, and the flow rates of these wells are very low compared to what it would take to treat them,” McGlaughlin said. “So right now they’re just not being used.” “

In 1995, the city did raise the spillway for the Evergreen Lake Reservoir. This increased capacity by more than 1.2 billion gallons.

Histogram showing the reduction in storage capacity of Lakes Bloomington and Lake Evergreen as a result of sedimentation modeling. — Bloomington’s water plan estimates the loss of about 500,000 gallons of reservoir capacity per decade due to sediment.

Climate change projections suggest droughts could become more frequent and more severe, as has happened with heavy rainfall. If a drought occurs, Bloomington’s tight capacity margin above safe production levels could mean mandatory water conservation measures would take effect sooner than if there was more room in the lakes. According to this report, even if no water flows into the lakes from the watershed at all, it would still take Bloomington some time to suck all the water out—1-2 years.

City officials tried to solve the emergency problem. In 1992, Bloomington built a pumping station to draw water from the Mackinac River in emergencies. The state has strict conditions on when and how much the city can pump.

Compounding the pressure to forecast increased consumption by thirsty residents is the fact that lake capacity is shrinking.

“Although demands are increasing and storage volumes are slowly decreasing, calculations and measurements confirm that both Lake Bloomington and Lake Evergreen have high sedimentation rates,” the 2010 plan states.

The lakes lose about 500,000 gallons of space per decade, according to the city’s water plan.

Map of Lake Bloomington and Lake Evergreen, bodies of water in the city of Bloomington located approximately five miles apart. — Lake Bloomington was built in 1929 and Lake Evergreen in the late 1960s, and began operating in 1972. The city created both lakes, located five miles apart, by drawing water from Money Creek and Six Mile Creek, which are tributaries of the Mackinac River.

“We are looking at our options,” McLaughlin said. “Which option is best? And obviously we already draw from Evergreen and Bloomington, so it would make more sense to dredge it since it was never dredged.”

How much will it cost?

“We’re actually actively looking at the cost of dredging Lake Evergreen and Lake Bloomington,” McLaughlin said.

McGlaughlin said the study could take six to nine months and the City Council won’t be able to discuss the issue and options until the next budget year.