Mining the riverbed? An unusual proposal being considered in Cottage Grove
The expanding sand and gravel mine would create a pit in the river across from Spring Lake Park Reserve near Grey Cloud Island.
A well-known mining company is pushing an unusual proposal in Cottage Grove: a mining operation directly in the riverbed.
Holcim (formerly Aggregate Industries), which operates several aggregate (sand and gravel) mines in the Twin Cities area, is seeking permission to expand its existing Lower Grey Cloud Island mine. The company wants to shift operations into the Mississippi River and mine the riverbed.
We have some concerns about this plan's potential impact on the river.
The city of Cottage Grove is hosting a public meeting to share more information about this proposed project on Thursday, Dec. 19, from 6-8 p.m. at the Hero Center (10125 85th St S). FMR staff will be at the meeting.
In addition, a draft Environmental Impact Statement (EIS) has been released for public review through Jan. 17, 2025. The EIS is an early step in what could be a lengthy review and permitting process.
Keep reading to learn more about the proposal, possible impacts to the river and how to weigh in.
The proposed project
Holcim's existing mining operation covers most of Lower Grey Cloud Island. There is currently a large inland mine pit there. Holcim says this pit will run out of new material within the next few years. If Holcim can't expand into adjoining areas, its mine would shut down.
The proposed expansion site is about 260 acres in size. Within this area, Holcim would mine the river bottom to a depth of about 200 feet in sections over 20-25 years. Leftover material would be used to backfill the newly created mine pit, but only to about 100 feet. This would leave a deep mine pit in the river bottom. The surrounding area is mostly shallow — no deeper than 25 feet.
Mining in a river bottom is rare; there may not be any other such project in Minnesota.
The state usually owns riverbeds, but this site is privately owned because it didn't actually used to be underwater. The construction of Lock and Dam 2 downstream in 1930 increased the water level and submerged this upland site.
It's an unusual situation that is being closely reviewed by the Minnesota Department of Natural Resources (DNR).
Possible impacts to the river
We have concerns about this proposed project's impacts on the Mississippi River. Some of the most significant impacts could be to the plant and animal species at the site, including some endangered species. Mussels have been identified as particularly at risk of harm.
The proposed mine would also have recreational and scenic impacts. To reduce water flow into the mine pit, a low earthen berm would be constructed between some of the existing islands. The berm would be approximately 1,500 feet long and 100 feet wide at the crest. This berm, in addition to the needed mining equipment, would be visible from the surrounding area, including Spring Lake Park Reserve. Impacts from the existing mine, such as noise, would continue for the next 20-25 years as the new area is mined.
We're also concerned that Holcim's proposal has a very narrow goal: to extend the life of its existing mine site, barge network and distribution systems, and to do so at the lowest cost to the company.
The Twin Cities does need continued supply of aggregate material for construction projects — but there is more than one way to meet that need. A riverbed mine might be the best option for this multinational company's bottom line, but it may not be the best solution for our community or the river and its many plants and animals.
The proposal would see Holcim shift its mining operations into the riverbed, along the southeastern edge of its current, on-land work. (Image from City of Cottage Grove public documents.)
Lengthy process ahead
The EIS is only an advisory document to guide future decision-making about the project. It provides information about anticipated project impacts and opportunities to avoid, minimize or mitigate those impacts. It is not a permit, nor is it an approval document.
The city of Cottage Grove is responsible for deciding whether the EIS is "adequate," meaning that it meets the state's required level of thoroughness. Should the city approve the EIS, there are still many more steps before the project could actually begin.
This is a complex project that will require Holcim to obtain permits from the city, the DNR, the U.S. Army Corps of Engineers and other agencies. Because Grey Cloud Island is important to Dakota people, we expect thorough tribal consultation before any permits could be issued.
It's a lengthy process, and we aren't sure this proposed mine will be able to meet the permitting requirements it needs to address next. The environmental impacts may be too severe.
How to comment on the EIS
You may submit comments on the draft EIS to Emily Schmitz at eis@cottagegrovemn.gov through Jan. 17, 2025.
If you'd like to submit comments, focus on what may be missing from or incorrect in the EIS. Emphasize facts and specifics. For instance, stating, "I oppose this project," or, "I'm concerned about water quality," isn't detailed enough to be actionable in this particular phase.
An effective comment would focus on a specific environmental impact that concerns you, ideally with an eye toward how the EIS could be amended to address your concern. For instance, you might share that you are aware of specific bird species in the area that don't seem to be accounted for in the draft EIS.
The Minnesota Environmental Quality Board has a helpful guide for writing comments.
It's OK if you don't have any comments to make. An EIS can be very technical and isn't always approachable to the broad public. Future permitting processes may include public input opportunities that are better suited for broader comments about why you do or do not think this project should be allowed.
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