Canton Area Dye Tracing- Canton Stormwater Estavelle and Highway Runoff Receptor Sinkholes, Fillmore County, MN Dye Trace Report Tracing Conducted April 1993 Report Created June 2020 Green, Jeffrey A.1, Alexander, E. Calvin, Jr.2, Alexander, Scott C.2, Barry, John.D.1 1 Minnesota Department of Natural Resources [email protected], [email protected] 2University of Minnesota Department of Earth and Environmental Sciences [email protected], [email protected] Funding for this project is provided by the Minnesota Environment and Natural Resources Trust Fund Introduction This report presents the findings of dye tracing that was conducted in 1993 as part of the Fillmore County Geologic Atlas Springshed plate mapping. Three traces in and near Canton, Minnesota are described in this report. Canton is an active karst area with many sinkholes and springs (Figure 1). The tracing was done in cooperation with the Fillmore County Soil and Water Conservation District. Collaboration between the Minnesota Department of Natural Resources, University of Minnesota Department of Earth and Environmental Sciences, Minnesota Department of Agriculture, and Soil & Water Conservation Districts (SWCD) has led to many dye tracing investigations in southeastern Minnesota. The results of these investigations are available through an online Minnesota Groundwater Tracing Database application developed by the Minnesota Department of Natural Resources. The application allows users to view the content in the figures below at different scales and to access data associated with this and other trace investigations. Dye tracing and spring chemistry are used to understand groundwater recharge characteristics, groundwater flow direction and velocity, and to assist in determining the size and areal extent of the groundwater springsheds that supply perennial groundwater discharge to springs. 2 Figure 1. Location map and karst features of the Canton, MN study area. Geology base map unit colors and symbols correspond with colors and symbols used in the formation column of Figure 2. 3 Area Geology and Hydrogeology Underlying the relatively thin veneer of unconsolidated sediments, glacial till, loess, sand, and colluvium in Fillmore County, is a thick stack of Paleozoic bedrock units that range from middle Ordovician to Cambrian in age (Mossler, 1995). Ordovician rocks are generally dominated by carbonates, whereas the Cambrian rocks are generally siliciclastic. A generalized stratigraphic column (Figure 2) shows lithostratigraphic and generalized hydrostratigraphic properties (modified from Runkel and others, 2013). Hydrostratigraphic attributes have been generalized into either aquifer or aquitard based on their relative permeability. Layers assigned as aquifers are permeable and easily transmit water through porous media, fractures or conduits. Layers assigned as aquitards have lower permeability that vertically retards flow, hydraulically separating aquifer layers. However, layers designated as aquitards may contain high permeability bedding plane partings conductive enough to yield large quantities of water In southeast Minnesota, springs and groundwater seepage frequently occurs at the toe of bluff slopes and at specific hydrostratigraphic intervals. Common intervals include near the geologic contact of the Maquoketa-Dubuque, Dubuque-Stewartville, Stewartville-Prosser, Prosser-Cummingsville, Decorah-Platteville, St. Peter-Shakopee, Shakopee- Oneota, and Jordan-St. Lawrence (Steenberg and Runkel, 2018). A hydrogeologic framework that describes prominent karst systems for southeastern Minnesota (Runkel and others, 2013) is based largely on the work of (Alexander and Lively 1995), (Alexander and others, 1996), and (Green and others, 1997, 2002). The systems described in this framework include the Devonian Cedar Valley, the lower Devonian-Upper Ordovician Spillville-Galena, the Upper Ordovician Platteville Formation, and the Lower Ordovician Figure 2. Geologic and hydrogeologic attributes of Paleozoic Prairie du Chien Group. The dye tracing presented in rocks in southeastern Minnesota. Modified from Runkel and this report occurred in the Galena Group of the others, 2013. Galena-Spillville karst, where groundwater time of travel can be as high as 1-3 miles/day (Green and others, 2014). 4 Dye Tracing Methods Dye tracing is a technique used to characterize the groundwater flow system to determine groundwater flow directions and rates. Traces are designed to establish connections between recharge points (sinkholes and stream sinks) and discharge points (springs and streams). Multiple traces are necessary to delineate the boundaries of a springshed. Dye tracing is accomplished using fluorescent dyes that travel at approximately the same velocity as water and are not lost to chemical or physical processes (conservative tracers). Fluorescent dyes used in tracing are non-toxic, simple to analyze, detectable at very low concentrations, and not naturally present in groundwater. To detect the presence or absence of dye at springs and other monitoring locations, passive charcoal detectors were used. These detectors, often referred to as “bugs”, were deployed prior to introducing dye to determine background levels of fluorescence in the groundwater. After dyes were introduced, the bugs were changed periodically by Minnesota DNR staff until the trace was terminated. The time resolution of the dye arrival at the monitored points is limited to how long the charcoal packets were left in the water before being analyzed. Passive dye detectors were sent to the University of Minnesota, Department of Earth Sciences for analysis. Bugs were analyzed by extracting the dyes with an extract of water, sodium hydroxide and isopropanol. The solution was then analyzed using a Shimadzu scanning spectrofluorophotometer and the resultant dye peaks were analyzed with a non-linear curve-fitting software. Project Area and Trace Background The project area, located in southern Fillmore County, Minnesota, is an active karst landscape where groundwater flow is partially governed by conduits and large solution-enhanced fractures. The trace occurred in an area with abundant sinkholes in and east of Canton, Minnesota (Figure 3). The Canton estavelle is one of the few known in Minnesota. Estavelles are surface karst features that function as a sinkhole except during high runoff events. Under those conditions they discharge groundwater and act as springs. 5 Figure 3. Sampling locations for the April 1993 dye trace. Monitoring site CCS was located approximately 4 miles south of the border at Coldwater Springs State Wildlife Area These dye traces were conducted for the Springshed Mapping plate of the Fillmore County Geologic Atlas Part B. The sinkholes were chosen for their proximity to Highway 52 and their potential to receive highway runoff. 6 The estavelle trace was completed to assist the Fillmore SWCD with remediation work on this feature. The estavelle served as the stormwater runoff receptor for the City of Canton. The dye trace, conducted to prove the estavelle’s connection to local springs, was the first step in the process of diverting stormwater flow from it. The sinkhole designated as MNDOT 1 had been modified to receive runoff from the highway ditch and the surrounding area. This was done by placing a concrete culvert into the sinkhole. There was no outlet for the culvert on the north side of Highway 52. Sinkhole MNDOT 2 had a swale leading into it from the highway ditch. The three sinkholes were receiving springtime snowmelt and rain runoff. The previous day had seen roughly 1.5 inches of rain and 3-5 inches of snow in the area. All three dyes were poured on 4/20/1993; the trace input information is summarized in Table 1. Direct water samples were taken for several days before and after dye input to complement the deployed passive charcoal detectors. Table 1. Summary of pour locations, dye types, and masses. UTMs Input Site Name KFD NAD 83, Zone 15 Date Time Dye Dye and Amount Easting Northing Canton Estavelle Sink 23D7462 MN23:D07462 586,629 4,820,482 20 Apr 1993 14:33 RhWT 260.2 g Rhodamine WT (20 wt. % solution) 133.6 g Uranine MN DOT #1 Sinkhole 23D7516 MN23:0D7516 588,026 4,819,485 20 Apr 1993 14:50 Uran (fluorescein) (powder) 114.9 g Eosine MN DOT #2 Sinkhole 23D7517 MN23:D07517 588,286 4,819,317 20 Apr 1993 15:12 Eos (powder) Trace Results Rhodamine WT from the estavelle trace was detected at spring MN23:A0631 and at sampling point MN23:X054, which was reciving flow from spring MN23:A0420 (Figure 4). The uranine and eosine were detected at spring MN23:A00402 (Table 2). Since we did not have permission to go on to the property where A402 is, we placed multiple bugs in Frego Creek at the township road crossing. The high runoff made it difficult to segregate the sampling to particular springs. A403 provides a particular challenge as the road culvert was built over it and water comes squirting out of the culvert joints. Table 3 contains daily water sample results; these samples give a general idea of groundwater time of travel. The eosine was injected into MNDOT 2 at 1450 on 4/20/1993. It was detected shortly downstream of spring A0402 at 2100. This is slightly more than 6 hours to travel slightly less than 1 mile straight line underground; the uranine and rhodamine WT were detected the following morning which corresponds to a travel time greater than 1 mile per day. These values are consistent with other tracing in the Galena Group bedrock units (Green and others, 2014). The result of