Calcareous Fen Management Plan

Minnesota | Water


ISG navigated complex regulatory permitting processes with state and local agencies to develop a first-of-its-kind Calcareous Fen Management Plan (CFMP), demonstrating effective design solutions to protect fragile ecological communities while also meeting industry demands.


Calcareous fens were discovered on a proposed mining site. These rare and distinctive wetlands receive continuous groundwater discharge that is calcium enriched because of contact with bedrock or glacial deposits. A protection plan was needed to preserve this invaluable part of Minnesota's rich natural heritage while meeting the landowner’s operational goals.


Minnesota’s fourth Calcareous Fen Management Plan (CFMP), developed by ISG for a mining client, was approved by the Minnesota Department of Natural Resources (DNR) in cooperation with several state and local agencies. Calcareous fens require a stable groundwater level to maintain their ecological integrity. Therefore, a key component of the CFMP was to prevent water table fluctuations that occur with standard mining practices. ISG civil engineers took a fresh and original approach to this challenge by designing a 460 x 14 foot infiltration trench system that would hold the groundwater levels steady.

ISG Environmental Services staff also conducted testing at an alternate simulation site as part of a case study and pre-mining field test. Research data was collected for one year to measure the trench’s ability to maintain the groundwater level and chemistry necessary to support a calcareous fen. Upon successful completion of the study, the trench was constructed at the intended location along the Minnesota River in southern Minnesota and now provides adequate water supply for the calcareous fen.

The State’s approval of the CFMP included an ongoing monitoring program, and the project has successfully passed all consecutive annual reviews. ISG’s Environmental team continues to monitor this sensitive ecosystem annually, with reviews for several parameters, including water and peat levels, water chemistry, native plant species, and inspections for potential invasive species.

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