Gun Club Lake Fen was a large fen complex situated near the eastern edge of the floodplain in the Minnesota River Valley until it was divided in 1985 by the construction of Interstate Highway 494 (I-494) (Dakota County SWCD, 2018). Gun Club Lake North Fen, also known as Quarry Island Fen, is on the north side of I-494, whereas Gun Club Lake South Fen, also known as Fort Snelling Fen, is on the south side of I-494. Both parts of the fen are located along the Union Pacific (UP) railway within Fort Snelling State Park and the City of Eagan in Dakota County. The area surrounding the fen receives special protection as one of the high-value resource areas managed by the Lower Minnesota River Watershed District (LMRWD). The northern part has received some study and data collection, while the southern portion has been studied more extensively and has a greater number of monitoring wells. To the extent possible, this summary discusses the fen as a single entity, although most of the information is focused on the southern part of the fen. Much of the information in this presentation is contained in the report titled Fens Sustainability Gaps Analysis for Carver, Dakota, and Scott Counties, Minnesota (Young Environmental, 2021).

Most of the area surrounding Gun Club Lake Fen is favorable fen habitat. It is labeled in the adjacent illustration as “Estimated Fen Extent.” If conditions are suitable, the fen and its distinctive plant life might expand to this greater area, but it is not known whether the fen was ever that large.

Hydrology and Hydrogeology

The fen is supplied with upwelling groundwater that is most likely recharged from nearby uplands to the east (Young Environmental, 2021). Impervious surfaces in the upland urban areas may redirect rainfall away rather than allowing it to infiltrate into the ground to replenish the groundwater supply. There are a few ponds and other areas that might capture runoff and improve fen groundwater supply.

Uncontrolled runoff can be detrimental to the fen. Records from an unidentified observer on March 12, 2003, described “a ditch excavated across the fen with a spring found.” The observation also described “a pronounced ice dome that is not from the spring; it is from the stormwater problem,” indicating disturbance of the fen based on information received from the MNDNR. Undated photographs show severe erosion through the peat layer because of excess stormwater discharge through the fen (Young Environmental, 2021). Accidentally or intentionally creating a ditch through the fen will drain it, drying out the fen vegetation and its peat layer, which will change the hydrology and the ecosystem.

Monitoring wells are installed in both the north and south parts of the fen. Two groundwater monitoring wells are north of I-494, and thirteen groundwater monitoring wells are south of I-494. They range in depth from 5 to 80 feet (Young Environmental, 2021). The LMRWD funds monitoring activities by the Dakota County Soil and Water Conservation District (SWCD), which routinely measures water levels in selected wells, compiles the data, and supplies them to the LMRWD. The MNDNR also measures water levels in selected wells and uploads their data to the Cooperative 

Groundwater Monitoring (CGM) network (MNDNR, 2022). Groundwater levels are normalized to mean sea level (MSL) elevation (NOAA, 2018), allowing comparison of groundwater elevations among wells.

Groundwater elevations from aligned wells south of I-494 measured on November 7, 2013, were used to produce the adjacent cross-section graphic, which is an illustration from Burns and McDonnell (2015). Groundwater elevation contours show that deep groundwater is consistently pushing toward the surface. Many of the wells, particularly the deeper ones, have groundwater elevations so high that water flows out of their tops. It is challenging to measure the groundwater elevation in an overflowing well. If there is water in the above-ground section of a well during the winter months, the water in the standing pipe can freeze, preventing measurements of winter water levels.

Groundwater elevations and well information were downloaded from the CGM website for a few selected wells that are actively monitored. Specifically, a cluster of four wells south of I-494 that are exposed to the underlying aquifer at specific depths were chosen for this presentation.

The adjacent graph shows the groundwater elevations at each of the four wells. Gaps in the data lines are usually the result of unsuccessful groundwater-level measurements because of water frozen in the above-ground part of the well during late winter. The groundwater elevations for the deeper wells are higher than for the shallower wells, confirming that pressure from beneath is causing the upward flow of groundwater. A trend of increasing groundwater elevations in the deeper wells is also noticeable, with levels rising from less than 728 feet above MSL before 2010 to about 729 feet MSL in recent years. This suggests improvement in the sustained flow of groundwater to supply water needed by the fen. Groundwater elevations in the shallow well remained relatively constant—near or less than 727 feet MSL, which may be the level of the fen surface.