BEDROCK HYDROGEOLOGY...Bedrock Hydrogeology GEOLOGIC ATLAS OF CARVER COUNTY, MINNESOTA Prepared and...
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Y E L B I S Y T N U O C N I P E N N E H Y T N U O C N I P E N N E H Y T N U O C D O E L C M Y T N U O C D O E L C M Y T N U O C T T O C S Y T N U O C SCOTT COUNTY T. 117 N. R. 24 W. R. 23 W. T. 116 N. T. 115 N. T. 114 N. R. 24 W. R. 25 W. T. 114 N. R. 26 W. T. 115 N. T. 116 N. T. 117 N. R. 26 W. R. 25 W. 44°45' N. 93°45' W. 93°45' W. 94°00' W. 94°00' W. 44°45' N. Lake Oak Mud Lake Swede Lake Buck Lake Waconia Lake Hydes Lake Rice Lake Eagle Lake Rutz Lake Lippert Lake Tiger Lake Brand Lake Barnes Lake Young America Lake Maria Lake Winkler Lake Parley Lake Lunsten Lake Lake Pierson Lake Reitz Lake Riley Lake Miller Lake Long Lake Kelly Lake Wassermann Lake Hazeltine Lake Lake Goose Lake Auburn Zumbra Lake Lake Lake Ann Lake Lotus Bavaria Minnewashta Lake Burandt r e v i R r e v i R h t u o S w o r C k e e r C k e e r C s n e v e B s n e v e B a k s a h C k e e r C k e e r C r e v l i S f f u l B k r o F a t o s e n n i M Waconia Watertown Mayer New Germany Hamburg Norwood Young America Cologne Victoria Chanhassen Chaska Carver r e v r a C k e e r C r e v r a C k e e r C k e e r C Benton 212 212 7 25 25 5 5 284 101 41 25 5 SIBLEY COUNTY WRIGHT COUNTY WRIGHT COUNTY Y E L B I S Y T N U O C N I P E N N E H Y T N U O C N I P E N N E H Y T N U O C D O E L C M Y T N U O C D O E L C M Y T N U O C T T O C S Y T N U O C SCOTT COUNTY T. 117 N. R. 24 W. R. 23 W. T. 116 N. T. 115 N. T. 114 N. R. 24 W. R. 25 W. T. 114 N. R. 26 W. T. 115 N. T. 116 N. T. 117 N. R. 26 W. R. 25 W. 44°45' N. 93°45' W. 93°45' W. 94°00' W. 94°00' W. 44°45' N. Lake Oak Mud Lake Swede Lake Buck Lake Waconia Lake Hydes Lake Rice Lake Eagle Lake Rutz Lake Lippert Lake Tiger Lake Brand Lake Barnes Lake Young America Lake Maria Lake Winkler Lake Parley Lake Lunsten Lake Lake Pierson Lake Reitz Lake Riley Lake Miller Lake Long Lake Kelly Lake Wassermann Lake Hazeltine Lake Lake Goose Lake Auburn Zumbra Lake Lake Lake Ann Lake Lotus Bavaria Minnewashta Lake Burandt r e v i R r e v i R h t u o S w o r C k e e r C k e e r C s n e v e B s n e v e B a k s a h C k e e r C k e e r C r e v l i S f f u l B k r o F a t o s e n n i M Waconia Watertown Mayer New Germany Hamburg Norwood Young America Cologne Victoria Chanhassen Chaska Carver r e v r a C k e e r C r e v r a C k e e r C k e e r C Benton 212 212 7 25 25 5 5 284 101 41 25 5 SIBLEY COUNTY WRIGHT COUNTY WRIGHT COUNTY Y E L B I S Y T N U O C N I P E N N E H Y T N U O C N I P E N N E H Y T N U O C D O E L C M Y T N U O C D O E L C M Y T N U O C T T O C S Y T N U O C SCOTT COUNTY T. 117 N. R. 24 W. R. 23 W. T. 116 N. T. 115 N. T. 114 N. R. 24 W. R. 25 W. T. 114 N. R. 26 W. T. 115 N. T. 116 N. T. 117 N. R. 26 W. R. 25 W. 44°45' N. 93°45' W. 93°45' W. 94°00' W. 94°00' W. 44°45' N. Lake Oak Mud Lake Swede Lake Buck Lake Waconia Lake Hydes Lake Rice Lake Eagle Lake Rutz Lake Lippert Lake Tiger Lake Brand Lake Barnes Lake Young America Lake Maria Lake Winkler Lake Parley Lake Lunsten Lake Lake Pierson Lake Reitz Lake Riley Lake Miller Lake Long Lake Kelly Lake Wassermann Lake Hazeltine Lake Lake Goose Lake Auburn Zumbra Lake Lake Lake Ann Lake Lotus Bavaria Minnewashta Lake Burandt r e v i R r e v i R h t u o S w o r C k e e r C k e e r C s n e v e B s n e v e B a k s a h C k e e r C k e e r C r e v l i S f f u l B k r o F a t o s e n n i M Waconia Watertown Mayer New Germany Hamburg Norwood Young America Cologne Victoria Chanhassen Chaska Carver r e v r a C k e e r C r e v r a C k e e r C k e e r C Benton 212 212 7 25 25 5 5 284 101 41 25 5 SIBLEY COUNTY WRIGHT COUNTY WRIGHT COUNTY T. 117 N. T. 116 N. T. 115 N. R. 26 W. R. 25 W. R. 24 W. R. 23 W. 212 7 Norwood Young America Waconia Chaska Watertown 25 5 5 41 284 T. 117 N. T. 116 N. T. 115 N. R. 26 W. R. 25 W. R. 24 W. R. 23 W. 212 7 Norwood Young America Waconia Chaska Watertown 25 5 5 41 284 Lake Zumbra E F D G C B A A’ B’ C’ D’ G’ E’ F’ E F D G C B A A’ B’ C’ D’ G’ E’ F’ E F D G C B A A’ B’ C’ D’ G’ E’ F’ E F D G C B A A’ B’ C’ D’ G’ E’ F’ E F D G C B A A’ B’ C’ D’ G’ E’ F’ 900 850 800 750 700 D D U U D U D D U D U D U D U D U D U D U DU D U D D U D U U 925 900 875 850 825 800 775 750 725 D D U U D U D D U D U D U D U D U D U D U DU D U D D U D U U 925 875 850 850 825 800 775 750 900 D D U U D U D D U D U D U D U D U D U D U DU D U D D U D U U 111 64.1 34.1 22.3 18.9 11.5 20,000 2000 20,000 5000 6000 65.4 33.6 7000 900 2000 8.7 6.1 8.8 5.3 7 7 8.16 8.39 4000 8000 13.6 10003 10002 Upper Tunnel City - Wonewoc Upper Tunnel City - Wonewoc Upper Tunnel City - Wonewoc Upper Tunnel City - Wonewoc Prairie du Chien - Jordan Unnamed Unnamed Unnamed Unnamed STATE OF MINNESOTA DEPARTMENT OF NATURAL RESOURCES DIVISION OF ECOLOGICAL AND WATER RESOURCES COUNTY ATLAS SERIES CARVER COUNTY ATLAS C-21, PART B, PLATE 8 of 9 Bedrock Hydrogeology GEOLOGIC ATLAS OF CARVER COUNTY, MINNESOTA Prepared and Published with the Support of the MINNESOTA ENVIRONMENT AND NATURAL RESOURCES TRUST FUND and the CLEAN WATER FUND This map was compiled and generated using geographic information systems (GIS) technology. Digital data products, including chemistry and geophysical data, are available from DNR Ecological and Water Resources at http://www.dnr.state.mn.us/waters. This map was prepared from publicly available information only. Every reasonable effort has been made to ensure the accuracy of the factual data on which this map interpretation is based. However, the Department of Natural Resources does not warrant the accuracy, completeness, or any implied uses of these data. Users may wish to verify critical information; sources include both the references here and information on file in the offices of the Minnesota Geological Survey and the Minnesota Department of Natural Resources. Every effort has been made to ensure the interpretation shown conforms to sound geologic and cartographic principles. This map should not be used to establish legal title, boundaries, or locations of improvements. Base modified from Minnesota Geological Survey, Carver County Geologic Atlas, Part A, 2009. Project data compiled from 2010 to 2012 at a scale of 1:100,000 to 1:300,000. Universal Transverse Mercator projection, grid zone 15, 1983 North American datum. Vertical datum is mean sea level. GIS and cartography by Todd Petersen, Shana Pascal, and Greg Massaro. Edited by Neil Cunningham. The DNR Information Center Twin Cities: (651) 296-6157 Minnesota toll free: 1-888-646-6367 DNR web site: http://www.mndnr.gov This information is available in alternative format on request. Equal opportunity to participate in and benefit from programs of the Minnesota Department of Natural Resources is available regardless of race, color, national origin, sex, sexual orientation, marital status, status with regard to public assistance, age, or disability. Discrimination inquiries should be sent to Minnesota DNR, 500 Lafayette Road, St. Paul, MN 55155-4031, or the Equal Opportunity Office, Department of the Interior, Washington, DC 20240. © 2014 State of Minnesota, Department of Natural Resources and the Regents of the University of Minnesota. BEDROCK HYDROGEOLOGY By Todd A. Petersen 2014 Low: 537 High: 833 Elevation of the top of the Prairie du Chien aquifer where it is present, and the top of the Jordan aquifer elsewhere. (feet above mean sea level) Elevation of the top of the Mt. Simon aquifer. (feet above mean sea level) Low: 140 High: 654 INTRODUCTION This plate describes the distribution of bedrock aquifers, groundwater flow, aquifer properties, and the connection between groundwater and surface water. The most used aquifers in Carver County are the Prairie du Chien, Jordan, Upper Tunnel City, Wonewoc, and Mt. Simon aquifers. In most of the county, the groundwater in these bedrock aquifers has very long residence times, typically thousands of years. However, recent tritium-age groundwater was sampled from both the Jordan and St. Lawrence aquifers in the Minnesota River valley, where the fine-grained glacial sediment that covers most of the bedrock aquifers in Carver County has been eroded and replaced by surficial sand. POTENTIOMETRIC SURFACES OF MAJOR BEDROCK AQUIFERS The eight bedrock aquifers in Carver County are the Ka (based on the geologic unit shown as PMu on Plate 2, Part A), the St. Peter, the Prairie du Chien, the Jordan, the Upper Tunnel City, the Wonewoc, the Mount Simon, and the Hinckley–Fond du Lac. The sequence of bedrock geologic units, hydrogeologic units, and hydrogeologic properties is shown in Figure 1. The confining units generally have low vertical permeability, but may have relatively high horizontal permeability along bedding fractures. In contrast, the bedrock aquifers have good vertical and horizontal permeability. The St. Peter, Wonewoc, Mt. Simon, and Hinckley aquifers are sandstones in which groundwater moves primarily through intergranular flow. Groundwater in the Prairie du Chien and Upper Tunnel City aquifers moves mainly through fractures. Groundwater in the Jordan aquifer moves through a combination of intergranular and fracture flow. Groundwater flow in the Fond du Lac aquifer is not well studied, but probably comprises both intergranular and fracture flow. Potentiometric surfaces are shown in Figures 2, 3, and 4 for the three major bedrock aquifers in Carver County: the combined Prairie du Chien and Jordan aquifers, the combined Upper Tunnel City and Wonewoc aquifers, and the Mt. Simon aquifer. Synoptic water-level measurements in these three aquifers were collected by the U.S. Geological Survey (USGS) in March and August 2008 (Sanocki and others, 2009). In that study, the USGS considered the Prairie du Chien and Jordan aquifers to be one aquifer and the Upper Tunnel City and Wonewoc aquifers to be one aquifer. The potentiometric surfaces in this report are based on the March 2008 synoptic measurements reported by Sanocki and others (2009), modified by adding additional well data from the County Well Index (CWI) for wells drilled in the year 2000 or later. The Prairie du Chien and Jordan aquifers are shown as a single unit in Figure 2. The blue color represents the elevation of the top surface of the Prairie du Chien aquifer where it is present and the top surface of the Jordan aquifer elsewhere. The potentiometric surface contours are based on combined water levels from both aquifers. These two aquifers are discontinuous because faulting offset the layers, rivers then eroded the area, and finally it was buried by glacial sediment. The Prairie du Chien aquifer is present in about 9 percent of the county and the Jordan aquifer is present in about 32 percent of the county. The potentiometric surface of the combined Prairie du Chien and Jordan aquifers varies from 925 feet above mean sea level in the northwest part of Carver County to 750 feet in southeast Carver County. The groundwater in these aquifers moves from northwest to southeast and eventually discharges to the Minnesota River. The potentiometric surface contours for the combined Upper Tunnel City and Wonewoc aquifers are shown in Figure 3. The blue color represents the elevation of the top of the Upper Tunnel City aquifer where it is present. The Upper Tunnel City aquifer is also discontinuous because of faulting and subsequent erosion. The combined Upper Tunnel City and Wonewoc aquifers are present in approximately 82 percent of the county. The potentiometric surface of the combined aquifers varies from 925 feet above mean sea level in the northwest part of the county to 725 feet above mean sea level in the southeast. The groundwater in these aquifers moves from northwest to southeast and eventually discharges to the Minnesota River. The potentiometric surface contours for the Mt. Simon aquifer are shown in Figure 4. The blue color represents the elevation of the top of the Mt. Simon aquifer. The Mt. Simon aquifer is also discontinuous because of faulting and subsequent erosion. The Mt. Simon aquifer is present across almost all of Carver County because it is stratigraphically deep and only partially eroded. The potentiometric surface of the Mt. Simon aquifer is highest in the northwest part of the county and lowest in the southeast; it varies from 900 feet above mean sea level to 700 feet above mean sea level. The groundwater in the Mt. Simon aquifer moves from northwest to southeast and eventually discharges to the Minnesota River. AQUIFER SPECIFIC CAPACITY AND TRANSMISSIVITY Table 1 shows specific capacity and transmissivity for the mapped Quaternary aquifers on Plate 6 and the bedrock aquifers on this plate. The specific-capacity data were determined from short-term pumping or well-development tests performed when the well was drilled. The pumping-test data for specific capacity were obtained from the CWI for wells with the following conditions: (1) a casing diameter of at least 12 inches, (2) pumped at least 4 hours, (3) the pumping water level was inside the well casing, at least 2 feet above the well screen or open hole. Transmissivity data were calculated from longer term and larger scale aquifer tests that provide a better test of the aquifer properties. Transmissivity data provide more accurate aquifer parameters than specific-capacity values determined at individual wells. As indicated in Table 1, five wells constructed in buried sand and gravel aquifers had specific capacities that ranged from 35 to 111 gallons per minute per foot (gpm/ft) with a combined mean specific capacity of 62 gpm/ft. The 19 bedrock wells tested had specific capacities ranging from 1 to 83 gpm/ft. Wells constructed across the Prairie du Chien and Jordan aquifers had the highest specific capacity of the bedrock aquifers, averaging 50 gpm/ft. Wells constructed across the Upper Tunnel City and Wonewoc aquifers had the lowest specific capacity, averaging 6 gpm/ft. Aquifer tests to determine aquifer transmissivity were conducted using four wells constructed in Quaternary buried sand and gravel aquifers, one well constructed across the Prairie du Chien and Jordan aquifers, and seven wells constructed across the Upper Tunnel City and Wonewoc aquifers. The transmissivity in buried sand and gravel aquifers varied from 89,800 gallons per day per foot (gpd/ft) to 273,000 gpd/ft. The transmissivity of the bedrock aquifers varied from 4,700 to 52,700 gpd/ft. GROUNDWATER LEVEL, PRECIPITATION, AND GROUNDWATER RESIDENCE TIME The Department of Natural Resources, in cooperation with the Carver County Environmental Services Department, actively measures five deep groundwater-level monitoring wells in Carver County. Hydrographs from two groundwater-level monitoring wells constructed in the Jordan aquifer, 10002 and 10003, are shown in Figures 6a and 6b respectively; the map locations of these wells are shown on Figure 2. Hydrographs from the other three wells are not shown because they had an insufficient period of record. Both hydrographs show annual variations in water level of 3 to 5 feet, which are due to seasonal pumping. The average annual water level has varied during the period of record, but has stayed within a few feet of the long-term average. The hydrographs for wells 10002 and 10003 do not show short-term changes in response to annual precipitation changes. This lack of response of groundwater levels in those wells to precipitation changes also means that these deeper aquifers are not quickly recharged by local precipitation. The residence time of groundwater in the Jordan aquifer near these two wells is thousands of years. The City of Mayer well number 2, which is 750 feet southwest of monitoring well 10002 and is also constructed in the Jordan aquifer, had a carbon-14 age of 4000 years. A domestic well, which is 1.5 miles south of monitoring well 10003 and constructed in the Prairie du Chien aquifer, had a carbon-14 age of 8000 years. Groundwater from the underlying Jordan aquifer should have a similarly long residence time. In the Minnesota River valley in southeastern Carver County, recent tritium-age groundwater samples were collected from two bedrock wells; one well is constructed in the Jordan aquifer and the other is constructed in the St. Lawrence Formation. In the broad valley of the Minnesota River and in the surrounding bluffs, these shallow bedrock aquifers are overlain by the surficial sand aquifer. Unlike other areas in the county where fine-grained glacial sediment is at the land surface, precipitation rapidly infiltrates through the surficial sand aquifer to deeper aquifers. STABLE ISOTOPE ANALYSIS OF GROUNDWATER AND SURFACE WATER Isotopic chemical changes as water moves from precipitation to surface water and groundwater are complex but can be reconstructed to help determine whether groundwater was recharged directly from precipitation, lake water, or a mixture of the two. Stable isotopes of hydrogen and oxygen were analyzed for 79 groundwater samples from wells and one lake-water sample from Lake Zumbra. Common hydrogen has only one proton; its stable isotope, deuterium (hydrogen-2 or 2 H), has one proton and one neutron. Because of this difference, deuterium has approximately twice the mass of common hydrogen. Oxygen-16 ( 16 O) contains eight protons and eight neutrons, and its stable isotope, oxygen-18 ( 18 O), contains 8 protons and 10 neutrons; thus, oxygen-18 has slightly more mass than oxygen-16. This mass difference causes the stable isotopes of hydrogen and oxygen to fractionate or separate during evaporation (Ekman and Alexander, 2002). The lighter isotopes will evaporate more easily than the heavier isotopes. Because lake water is exposed to the atmosphere, evaporation causes significant fractionation of the stable isotopes of hydrogen and oxygen; as a result, lake water contains more of the heavier isotopes than are found in precipitation. Groundwater is more isolated from the atmosphere, however, so negligible fractionation occurs. Figure 7 is a plot of the stable isotopes of hydrogen and oxygen in sampled groundwater and sampled lake water. The value on the x-axis represents the ratio of oxygen-18 to oxygen-16 in the sample divided by the same ratio in a standard. The value on the y-axis represents the ratio of deuterium to hydrogen in the sample divided by the same ratio in a standard. Values to the left on the x-axis or to the bottom on the y-axis indicate relatively more of the lighter isotope, while values to the right or to the top indicate more of the heavier isotope. Regional background precipitation values for the stable isotopes of hydrogen and oxygen generally plot along a trend called the meteoric water line shown in Figure 7 (IAEA/WMO, 2002). The stable isotope values of the water samples from Lake Zumbra and some of the groundwater samples plot on a slightly lower slope than the meteoric water line, which indicates that the water has undergone some fractionation during evaporation. This evaporative trend crosses the meteoric water line at the average value for precipitation in the county. The slope of the evaporative trend and the location where it meets the meteoric water line depend on the local climate, primarily the average temperature and humidity (Kendall and Doctor, 2003). The groundwater samples that plot on the evaporative trend line away from the meteoric water line have undergone some evaporative fractionation, which means that part of this groundwater was recharged from lake water. These samples are shown in Figure 7 as symbols with colors indicating an evaporative isotopic signature. The locations of these wells are shown in Figure 8 as large well symbols. Groundwater samples that were recharged directly from precipitation plot on the meteoric water line. These samples are plotted on Figure 7 as small gray symbols and the well locations are shown in Figure 8 as small symbols. Groundwater flow paths cannot be determined by hydrologic data or isotopes alone. Water may take a complex path through the watershed, part on the surface and part in the subsurface. The mingling of groundwater and surface water is most clearly seen by the continuum of values of stable isotope samples along the evaporative trend line. Recharge from surface water forms an important component of groundwater in northeastern Carver County, where there are many lakes, and in southeastern Carver County, near the Minnesota River valley. Recharge to groundwater by surface water is not common elsewhere in the county where groundwater is more typically recharged by direct infiltration of precipitation to the subsurface. REFERENCES CITED Ekman, J. and Alexander, S., 2002, Technical appendix to Part B, Regional Hydrogeologic Assessment, Otter Tail area, west-central Minnesota: Regional Hydrogeologic Assessment Series RHA–5, Minnesota Department of Natural Resources, St. Paul, 13 p. IAEA/WMO, 2002, Global network of isotopes in precipitation: The GNIP Database, available at URL: http://www.iaea.org/water. Kendall, C. and Doctor, D., 2003, Stable isotope applications in Hydrologic studies, Holland, H.D. and Turekian, K.K., editors, chap. 11 of v. 5, Surface and ground water, weathering, and soils, in Treatise on geochemistry: Amsterdam, The Netherlands, Elsevier, Inc., p. 319–364. Sanocki, C.A., Langer, S.K., and Menard, J.C., 2009, Potentiometric Surfaces and Changes in Groundwater Levels in Selected Bedrock Aquifers in the Twin Cities Metropolitan Area, March-August 2008 and 1988-2008: U.S. Geological Survey Scientific Investigations Report 2009-5226, 67 p. ACKNOWLEDGEMENTS I received much help from my colleagues at DNR. Jan Falteisek provided assistance and guidance throughout the project. Shana Pascal, Greg Massaro, and Neil Cunningham made the plates more understandable through their GIS, layout, and editing. Joe Enfield of Carver County Environmental Services provided many years of historical groundwater chemistry data. Jim Berg provided geologic insight and data from his “South-Central Minnesota Groundwater Monitoring of the Mt. Simon Aquifer” report that was funded by the Minnesota Environment and Natural Resources Trust Fund. John Barry reviewed the final report. Thanks are due also to my colleagues at other agencies who provided excellent suggestions during peer review: Bob Tipping and Barb Lusardi of the Minnesota Geological Survey; Rich Soule of the Minnesota Department of Health; and Madeline Seveland of Carver County Water Management Department. I would like to thank Scott Alexander of the University of Minnesota, Department of Earth Sciences for collecting the carbon-14 water samples for analysis and interpreting the results. Elevation of the top of the Upper Tunnel City aquifer. (feet above mean sea level) Low: 403 High: 833 Water use reported by DNR groundwater appropriation permit holders for 2010 (millions of gallons per year) > 100 to 150 > 150 0 to 20 50 to 100 20 to 50 > > FIGURE 4. Potentiometric surface elevation contours of the Mt. Simon aquifer. Contour interval: 50 feet. The location of wells constructed in the Mt. Simon aquifer that were sampled for chemistry and isotope analysis are shown. The location of wells and reported water use by DNR groundwater appropriation permit holders are also shown. FIGURE 5. Locations of aquifer tests described in Table 1. FIGURE 3. Potentiometric surface elevation contours of the combined Upper Tunnel City and Wonewoc aquifers. Dotted lines connect contours across areas where aquifer is not present. Contour interval: 25 feet. The location of wells constructed in the Upper Tunnel City and Wone- woc aquifers that were sampled for chemistry and isotope analysis are shown. The location of wells and reported water use by DNR groundwater appropriation permit holders are also shown. FIGURE 2. Potentiometric surface elevation contours of the combined Prairie du Chien and Jordan aquifers. Dotted lines connect contours across areas where aquifer is not present. Contour interval: 25 feet. The location of wells constructed in the Prairie du Chien and Jordan aquifers that were sampled for chemistry and isotope analysis are shown. The location of wells and reported water use by DNR groundwater appropriation permit holders are also shown. Aquifer TABLE 1. Specific capacity from well development tests and transmissivity from aquifer tests for selected large-capacity wells. [gpm/ft, gallons per minute per foot; gpd/ft, gallons per day per foot; dash marks (--), no data available] Mean Minimum Maximum No. of Tests Well Diameter (inches) Buried sand and gravel Bedrock sdv sr sb sg sx su Unnamed Prairie du Chien–Jordan 4 Jordan -- -- -- -- 74 69 47 50 16 -- -- -- -- 38 69 35 15 14 -- -- -- -- 111 69 60 83 17 -- -- -- -- 2 1 2 4 2 -- -- -- -- 12–14 14 18 12–18 16–24 FIGURE 1. Sequence of bedrock geologic units and hydrogeologic units in Carver County. The Ka geologic unit is shown in Part A as PMu. EXPLANATION Aquifer Confining unit, generally low permeability Low to moderate permeability aquifer; thin sandstones interbedded with siltstone and claystone High permeability bedding fracture Relatively high intergranu- lar permeability with high permeability fractures. Jordan Sandstone Jordan aquifer St. Lawrence Formation Lone Rock Formation Relatively low intergranular permeability with high permeability bedding fractures. Confining unit. Moderate intergranular permeability. Wonewoc Sandstone Wonewoc aquifer Eau Claire Formation Confining unit. Mt. Simon Sandstone Mt. Simon aquifer Moderate intergranular permeability. Low to moderate intergranular permeability. Thin sandstones are interlayered with siltstone and claystone. Probably low yielding aquifer. Ka aquifer Unnamed Unit (Ka) Confining unit. Tunnel City Group Upper Tunnel City aquifer Confining unit. Hinckley Sandstone and Fond du Lac Formation Hinckley/Fond du Lac aquifer Moderate intergranular permeability Geologic Unit Hydrogeologic Unit Hydrogeologic Unit Properties St. Peter Sandstone Undivided St. Peter aquifer Moderate intergranular permeability. Relatively low intergranular permeability with high permeability fractures. Confining unit. Prairie du Chien Group Prairie du Chien aquifer FIGURE 6. Comparison of hydrographs of two DNR groundwater-level monitoring wells to 1970–2011 precipitation. The hydrograph of DNR Jordan aquifer monitoring well 10002 is shown in Figure 6a. The hydrograph of DNR Jordan aquifer monitoring well 10003 is shown in Figure 6b. A chart of precipitation at Chaska is shown in Figure 6c. The elevation of water levels in these two wells are not directly influenced by short-term trends in local precipitation. The location of these two monitoring wells is shown on Figure 2. Aquifer test locations: label indicates aquifer Upper Tunnel City–Wonewoc FIGURE 8. Location of wells sampled for chemistry and isotope analysis. Groundwater samples with evaporative signatures are shown with larger symbols; they are clustered in northeastern Carver County near lakes or in southeastern Carver County near the Minnesota River. Tritium age Symbol color indicates tritium age of water sampled in well. Well Diameter (inches) Mean Minimum Maximum No. of Tests -- -- -- -- -- -- 6–12 20 -- -- -- -- -- -- -- 175,500 52,700 -- -- -- -- -- -- -- 89,800 52,700 -- -- -- -- -- -- -- 273,000 52,700 -- -- -- -- -- -- -- 4 1 -- 6–16 -- 11,600 -- 4,700 -- 35,200 -- 7 -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- Upper Tunnel City–Wonewoc 4 Upper Tunnel City–Mt.Simon 4 6 10 1 10 12 10 3 1 12–18 12 Wonewoc–Mt.Simon 4 11 9 13 2 16 Mt. Simon 16 9 7 5 26 12 4 3 12–18 12–16 Mt. Simon–Fond du Lac 4 Specific Capacity (gpm/ft) 1 Transmissivity from Aquifer Test (gpd/ft) 2,3 1 Data adapted from the County Well Index. 2 See Figure 5 for locations of aquifer tests. 3 Data adapted from a compilation of aquifer test data from Minnesota Department of Natural Resources, Minnesota Department of Health, and the U. S. Geological Survey. 4 Well constructed across more than one aquifer. Potentiometric surface elevation contour 875 If shown, arsenic concentration equals or exceeds 5 parts per billion 30.6 If shown, chloride concentration equals or exceeds 5 parts per million 9.73 If shown, nitrate-nitrogen concentration equals or exceeds 3 parts per million 8.39 If shown, groundwater residence time in years, estimated by carbon-14 ( 14 C) isotope analysis 7000 If shown on well symbol, arsenic not sampled Map symbols and labels Map symbols and labels Static water level data from March 2008 synoptic Static water level data 10002 DNR groundwater level monitoring well. Label is well number Line of cross section Body of water -90 δ 18 O (‰) -13 -7 -1 δ 2 H (‰) -70 -80 -60 -30 -20 -50 -40 North American meteoric water line Lake Zumbra Evaporative trend maximum FIGURE 7. Graph of stable isotopes of oxygen and hydrogen from sampled groundwater and lake water in Carver County compared to the North Ameri- can meteoric water line. The colored well symbols indicate water samples that were affected by evaporation prior to moving into groundwater. The Lake Zumbra sample was highly fractionated by evaporation. The regression line of these samples shows the evaporative fractionation trend in Carver County. The groundwater samples shown by gray symbols represent groundwater directly recharged by precipitation. The dashed “2σ” lines show the statistical variation of stable isotope precipitation values used to derive the North American mete- oric water line (IAEA/WMO, 2002). Explanation Isotopic Signature Meteoric Evaporative-Southeastern Carver County Evaporative-Lake Zumbra Evaporative-Northeastern Carver County Wells Lake LOCATION DIAGRAM MAP EXPLANATION Figure 8 MAP EXPLANATION Figures 2–4 Sampled well and aquifer symbols Upper Tunnel City Wonewoc Mt. Simon and Fond du Lac Bedrock aquifers Prairie du Chien Jordan Tritium age Symbol color indicates tritium age of water sampled in well. Recent—Water entered the ground since about 1953 (8 to 15 tritium units [TU]). Mixed—Water is a mixture of recent and vintage waters (greater than 1 TU to less than 8 TU). Vintage—Water entered the ground before 1953 (less than or equal to 1 TU). Well not sampled for tritium. Sampled well and aquifer symbols su sg sx sr Buried sand and gravel aquifers Bedrock aquifers Upper Tunnel City Wonewoc Mt. Simon or Fond du Lac Prairie du Chien Jordan St. Lawrence and St. Lawrence– Upper Tunnel City Recent—Water entered the ground since about 1953 (8 to 15 tritium units [TU]). Mixed—Water is a mixture of recent and vintage waters (greater than 1 TU to less than 8 TU). Vintage—Water entered the ground before 1953 (less than or equal to 1 TU). Well not sampled for tritium. Static Water Elevation (feet above mean sea level) 925 920 915 930 935 6a. Explanation—monitoring well 10002, Jordan aquifer, 191 feet deep Water elevation Average water elevation over period of record (924.3 feet) Land surface elevation at monitoring well (feet) 956.6 Year 1970 1975 1980 1985 1990 1995 2000 2005 2010 2015 Static Water Elevation (feet above mean sea level) 905 900 895 910 915 Year 1970 1975 1980 1985 1990 1995 2000 2005 2010 2015 Annual Precipitation (inches) 1970 1975 1980 1985 1990 1995 2000 2005 2010 Year 0 5 10 15 20 25 30 35 40 45 1981-2010 30-year normal precipitation (31.85 inches) 6c. 6b. Explanation—monitoring well 10003, Jordan aquifer, 292 feet deep Water elevation Average water elevation over period of record (907.8 feet) Land surface elevation at monitoring well (feet) 993.8 Lake sampled for isotopes Line of cross section Body of water MAP EXPLANATION Trace of fault; letters indicate relative vertical displacement: U, up; D, down 1 0 1 2 3 4 5 MILES SCALE 1:200 000 1 0 1 2 4 5 6 7 8 3 9 KILOMETERS COMPILATION SCALE 1:100 000 1 0 1 2 3 4 SCALE 1:300 000 1012 45678 3 9 KILOMETERS 5 MILES 1 0 1 2 3 4 SCALE 1:300 000 1012 45678 3 9 KILOMETERS 5 MILES
Transcript of BEDROCK HYDROGEOLOGY...Bedrock Hydrogeology GEOLOGIC ATLAS OF CARVER COUNTY, MINNESOTA Prepared and...
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TTOCS YTNUOC
SCOTTCOUNTY
T. 117 N.
R. 24 W. R. 23 W.
T. 116 N.
T. 115 N.
T. 114 N.
R. 24 W.R. 25 W.
T. 114 N.
R. 26 W.
T. 115 N.
T. 116 N.
T. 117 N.
R. 26 W. R. 25 W.
44°45' N.
93°45' W.
93°45' W.
94°00' W.
94°00' W.
44°45' N.
LakeOak
MudLake
SwedeLake
BuckLake
WaconiaLake
HydesLake
RiceLake
EagleLake
RutzLake
LippertLake
TigerLake
BrandLake
BarnesLake
YoungAmericaLake
MariaLake
WinklerLake
ParleyLake
LunstenLake
LakePiersonLake
ReitzLake
RileyLake
MillerLake
LongLake
KellyLake
WassermannLake
HazeltineLake
LakeGoose
LakeAuburn
ZumbraLake
Lake
LakeAnn
LakeLotus
Bavaria
Minnewashta
LakeBurandt
reviR
reviR
htuoS
worC
keerC
keer
C
sneveB
sneveB
aksahC keerC
keerCrevli
S
ffulB
kroF
atosenniM
Waconia
Watertown
MayerNew
Germany
Hamburg
Norwood
YoungAmerica
Cologne
Victoria
Chanhassen
Chaska
Carver
revraC
keerC
revr
aC
keerC
keerC
Benton212
212
7
25
25
5
5
284101
41
25
5
SIBLEY
COUNTY
WRIGHTCOUNTY
WRIGHTCOUNTY
YEL
BIS
YT
NU
OC
NIP
EN
NE
HY
TN
UO
C
NIP
EN
NE
HY
TN
UO
C
DO
ELC
MY
TN
UO
CD
OEL
CM
YT
NU
OC
TTOCS YTNUOC
SCOTTCOUNTY
T. 117 N.
R. 24 W. R. 23 W.
T. 116 N.
T. 115 N.
T. 114 N.
R. 24 W.R. 25 W.
T. 114 N.
R. 26 W.
T. 115 N.
T. 116 N.
T. 117 N.
R. 26 W. R. 25 W.
44°45' N.
93°45' W.
93°45' W.
94°00' W.
94°00' W.
44°45' N.
LakeOak
MudLake
SwedeLake
BuckLake
WaconiaLake
HydesLake
RiceLake
EagleLake
RutzLake
LippertLake
TigerLake
BrandLake
BarnesLake
YoungAmericaLake
MariaLake
WinklerLake
ParleyLake
LunstenLake
LakePiersonLake
ReitzLake
RileyLake
MillerLake
LongLake
KellyLake
WassermannLake
HazeltineLake
LakeGoose
LakeAuburn
ZumbraLake
Lake
LakeAnn
LakeLotus
Bavaria
Minnewashta
LakeBurandt
reviR
reviR
htuoS
worC
keerC
keer
C
sneveB
sneveB
aksahC keerC
keerCrevli
S
ffulB
kroF
atosenniM
Waconia
Watertown
MayerNew
Germany
Hamburg
Norwood
YoungAmerica
Cologne
Victoria
Chanhassen
Chaska
Carver
revraC
keerC
revr
aC
keerC
keerC
Benton212
212
7
25
25
5
5
284101
41
25
5
SIBLEY
COUNTY
WRIGHTCOUNTY
WRIGHTCOUNTY
YEL
BIS
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NE
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DO
ELC
MY
TN
UO
CD
OEL
CM
YT
NU
OC
TTOCS YTNUOC
SCOTTCOUNTY
T. 117 N.
R. 24 W. R. 23 W.
T. 116 N.
T. 115 N.
T. 114 N.
R. 24 W.R. 25 W.
T. 114 N.
R. 26 W.
T. 115 N.
T. 116 N.
T. 117 N.
R. 26 W. R. 25 W.
44°45' N.
93°45' W.
93°45' W.
94°00' W.
94°00' W.
44°45' N.
LakeOak
MudLake
SwedeLake
BuckLake
WaconiaLake
HydesLake
RiceLake
EagleLake
RutzLake
LippertLake
TigerLake
BrandLake
BarnesLake
YoungAmericaLake
MariaLake
WinklerLake
ParleyLake
LunstenLake
LakePiersonLake
ReitzLake
RileyLake
MillerLake
LongLake
KellyLake
WassermannLake
HazeltineLake
LakeGoose
LakeAuburn
ZumbraLake
Lake
LakeAnn
LakeLotus
Bavaria
Minnewashta
LakeBurandt
reviR
reviR
htuoS
worC
keerC
keer
C
sneveB
sneveB
aksahC keerC
keerCrevli
S
ffulB
kroF
atosenniM
Waconia
Watertown
MayerNew
Germany
Hamburg
Norwood
YoungAmerica
Cologne
Victoria
Chanhassen
Chaska
Carver
revraC
keerC
revr
aC
keerC
keerC
Benton212
212
7
25
25
5
5
284101
41
25
5
SIBLEY
COUNTY
WRIGHTCOUNTY
WRIGHTCOUNTY
T. 117 N.
T. 116 N.
T. 115 N.
R. 26 W. R. 25 W.
R. 24 W. R. 23 W.
212
7
NorwoodYoung America
Waconia
Chaska
Watertown
25
5
5
41
284
T. 117 N.
T. 116 N.
T. 115 N.
R. 26 W. R. 25 W.
R. 24 W. R. 23 W.
212
7
NorwoodYoung America
Waconia
Chaska
Watertown
25
5
5
41
284
LakeZumbra
E
F
D
G
C
B
A A’
B’
C’
D’
G’
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F
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B
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D’
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D’
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900
850
800
750
700
D
D
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DDU
D U DU DU
DU
DU
DU
D U
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900
875
850
825
800
775
750
725
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D U
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64.1
34.1
22.3
18.9
11.5
20,000
2000
20,000
5000
6000
65.4
33.6
7000
900
2000
8.7
6.1
8.8
5.3
7
7
8.168.39
4000
8000 13.6
10003
10002
Upper Tunnel City - Wonewoc
Upper Tunnel City - Wonewoc
Upper Tunnel City - Wonewoc
Upper Tunnel City - Wonewoc
Prairie du Chien - Jordan
UnnamedUnnamed
Unnamed
Unnamed
STATE OF MINNESOTADEPARTMENT OF NATURAL RESOURCESDIVISION OF ECOLOGICAL AND WATER RESOURCES
COUNTY ATLAS SERIESCARVER COUNTY
ATLAS C-21, PART B, PLATE 8 of 9Bedrock Hydrogeology
GEOLOGIC ATLAS OF CARVER COUNTY, MINNESOTA
Prepared and Published with the Support of the MINNESOTA ENVIRONMENT AND NATURAL RESOURCES TRUST FUND and the CLEAN WATER FUND
This map was compiled and generated using geographic information systems (GIS) technology. Digital data products, including chemistry and geophysical data, are available from DNR Ecological and Water Resources at http://www.dnr.state.mn.us/waters.This map was prepared from publicly available information only. Every reasonable effort has been made to ensure the accuracy of the factual data on which this map interpretation is based. However, the Department of Natural Resources does not warrant the accuracy, completeness, or any implied uses of these data. Users may wish to verify critical information; sources include both the references here and information on file in the offices of the Minnesota Geological Survey and the Minnesota Department of Natural Resources. Every effort has been made to ensure the interpretation shown conforms to sound geologic and cartographic principles. This map should not be used to establish legal title, boundaries, or locations of improvements.Base modified from Minnesota Geological Survey, Carver County Geologic Atlas, Part A, 2009.Project data compiled from 2010 to 2012 at a scale of 1:100,000 to 1:300,000. Universal Transverse Mercator projection, grid zone 15, 1983 North American datum. Vertical datum is mean sea level.GIS and cartography by Todd Petersen, Shana Pascal, and Greg Massaro. Edited by Neil Cunningham.
The DNR Information Center
Twin Cities: (651) 296-6157Minnesota toll free: 1-888-646-6367DNR web site: http://www.mndnr.gov
This information is available in alternative format on request.
Equal opportunity to participate in and benefit from programs of the Minnesota Department of Natural Resources is available regardless of race, color, national origin, sex, sexual orientation, marital status, status with regard to public assistance, age, or disability. Discrimination inquiries should be sent to Minnesota DNR, 500 Lafayette Road, St. Paul, MN 55155-4031, or the Equal Opportunity Office, Department of the Interior, Washington, DC 20240.
© 2014 State of Minnesota,Department of Natural Resources and theRegents of the University of Minnesota.
BEDROCK HYDROGEOLOGY
By Todd A. Petersen
2014
Low: 537
High: 833
Elevation of the top of the Prairie du Chien aquifer where it is present, and the top of the Jordan aquifer elsewhere.(feet above mean sea level)
Elevation of the top of the Mt. Simon aquifer. (feet above mean sea level)
Low: 140
High: 654
INTRODUCTION
This plate describes the distribution of bedrock aquifers, groundwater flow, aquifer properties, and the connection between groundwater and surface water. The most used aquifers in Carver County are the Prairie du Chien, Jordan, Upper Tunnel City, Wonewoc, and Mt. Simon aquifers. In most of the county, the groundwater in these bedrock aquifers has very long residence times, typically thousands of years. However, recent tritium-age groundwater was sampled from both the Jordan and St. Lawrence aquifers in the Minnesota River valley, where the fine-grained glacial sediment that covers most of the bedrock aquifers in Carver County has been eroded and replaced by surficial sand.
POTENTIOMETRIC SURFACES OF MAJOR BEDROCK AQUIFERS
The eight bedrock aquifers in Carver County are the Ka (based on the geologic unit shown as PMu on Plate 2, Part A), the St. Peter, the Prairie du Chien, the Jordan, the Upper Tunnel City, the Wonewoc, the Mount Simon, and the Hinckley–Fond du Lac. The sequence of bedrock geologic units, hydrogeologic units, and hydrogeologic properties is shown in Figure 1. The confining units generally have low vertical permeability, but may have relatively high horizontal permeability along bedding fractures. In contrast, the bedrock aquifers have good vertical and horizontal permeability. The St. Peter, Wonewoc, Mt. Simon, and Hinckley aquifers are sandstones in which groundwater moves primarily through intergranular flow. Groundwater in the Prairie du Chien and Upper Tunnel City aquifers moves mainly through fractures. Groundwater in the Jordan aquifer moves through a combination of intergranular and fracture flow. Groundwater flow in the Fond du Lac aquifer is not well studied, but probably comprises both intergranular and fracture flow.
Potentiometric surfaces are shown in Figures 2, 3, and 4 for the three major bedrock aquifers in Carver County: the combined Prairie du Chien and Jordan aquifers, the combined Upper Tunnel City and Wonewoc aquifers, and the Mt. Simon aquifer. Synoptic water-level measurements in these three aquifers were collected by the U.S. Geological Survey (USGS) in March and August 2008 (Sanocki and others, 2009). In that study, the USGS considered the Prairie du Chien and Jordan aquifers to be one aquifer and the Upper Tunnel City and Wonewoc aquifers to be one aquifer. The potentiometric surfaces in this report are based on the March 2008 synoptic measurements reported by Sanocki and others (2009), modified by adding additional well data from the County Well Index (CWI) for wells drilled in the year 2000 or later.
The Prairie du Chien and Jordan aquifers are shown as a single unit in Figure 2. The blue color represents the elevation of the top surface of the Prairie du Chien aquifer where it is present and the top surface of the Jordan aquifer elsewhere. The potentiometric surface contours are based on combined water levels from both aquifers. These two aquifers are discontinuous because faulting offset the layers, rivers then eroded the area, and finally it was buried by glacial sediment. The Prairie du Chien aquifer is present in about 9 percent of the county and the Jordan aquifer is present in about 32 percent of the county. The potentiometric surface of the combined Prairie du Chien and Jordan aquifers varies from 925 feet above mean sea level in the northwest part of Carver County to 750 feet in southeast Carver County. The groundwater in these aquifers moves from northwest to southeast and eventually discharges to the Minnesota River.
The potentiometric surface contours for the combined Upper Tunnel City and Wonewoc aquifers are shown in Figure 3. The blue color represents the elevation of the top of the Upper Tunnel City aquifer where it is present. The Upper Tunnel City aquifer is also discontinuous because of faulting and subsequent erosion. The combined Upper Tunnel City and Wonewoc aquifers are present in approximately 82 percent of the county. The potentiometric surface of the combined aquifers varies from 925 feet above mean sea level in the northwest part of the county to 725 feet above mean sea level in the southeast. The groundwater in these aquifers moves from northwest to southeast and eventually discharges to the Minnesota River.
The potentiometric surface contours for the Mt. Simon aquifer are shown in Figure 4. The blue color represents the elevation of the top of the Mt. Simon aquifer. The Mt. Simon aquifer is also discontinuous because of faulting and subsequent erosion. The Mt. Simon aquifer is present across almost all of Carver County because it is stratigraphically deep and only partially eroded. The potentiometric surface of the Mt. Simon aquifer is highest in the northwest part of the county and lowest in the southeast; it varies from 900 feet above mean sea level to 700 feet above mean sea level. The groundwater in the Mt. Simon aquifer moves from northwest to southeast and eventually discharges to the Minnesota River.
AQUIFER SPECIFIC CAPACITY AND TRANSMISSIVITY
Table 1 shows specific capacity and transmissivity for the mapped Quaternary aquifers on Plate 6 and the bedrock aquifers on this plate. The specific-capacity data were determined from short-term pumping or well-development tests performed when the well was drilled. The pumping-test data for specific capacity were obtained from the CWI for wells with the following conditions: (1) a casing diameter of at least 12 inches, (2) pumped at least 4 hours, (3) the pumping water level was inside the well casing, at least 2 feet above the well screen or open hole. Transmissivity data were calculated from longer term and larger scale aquifer tests that provide a
better test of the aquifer properties. Transmissivity data provide more accurate aquifer parameters than specific-capacity values determined at individual wells.
As indicated in Table 1, five wells constructed in buried sand and gravel aquifers had specific capacities that ranged from 35 to 111 gallons per minute per foot (gpm/ft) with a combined mean specific capacity of 62 gpm/ft. The 19 bedrock wells tested had specific capacities ranging from 1 to 83 gpm/ft. Wells constructed across the Prairie du Chien and Jordan aquifers had the highest specific capacity of the bedrock aquifers, averaging 50 gpm/ft. Wells constructed across the Upper Tunnel City and Wonewoc aquifers had the lowest specific capacity, averaging 6 gpm/ft.
Aquifer tests to determine aquifer transmissivity were conducted using four wells constructed in Quaternary buried sand and gravel aquifers, one well constructed across the Prairie du Chien and Jordan aquifers, and seven wells constructed across the Upper Tunnel City and Wonewoc aquifers. The transmissivity in buried sand and gravel aquifers varied from 89,800 gallons per day per foot (gpd/ft) to 273,000 gpd/ft. The transmissivity of the bedrock aquifers varied from 4,700 to 52,700 gpd/ft.
GROUNDWATER LEVEL, PRECIPITATION, AND GROUNDWATER RESIDENCE TIME
The Department of Natural Resources, in cooperation with the Carver County Environmental Services Department, actively measures five deep groundwater-level monitoring wells in Carver County. Hydrographs from two groundwater-level monitoring wells constructed in the Jordan aquifer, 10002 and 10003, are shown in Figures 6a and 6b respectively; the map locations of these wells are shown on Figure 2. Hydrographs from the other three wells are not shown because they had an insufficient period of record. Both hydrographs show annual variations in water level of 3 to 5 feet, which are due to seasonal pumping. The average annual water level has varied during the period of record, but has stayed within a few feet of the long-term average. The hydrographs for wells 10002 and 10003 do not show short-term changes in response to annual precipitation changes. This lack of response of groundwater levels in those wells to precipitation changes also means that these deeper aquifers are not quickly recharged by local precipitation. The residence time of groundwater in the Jordan aquifer near these two wells is thousands of years. The City of Mayer well number 2, which is 750 feet southwest of monitoring well 10002 and is also constructed in the Jordan aquifer, had a carbon-14 age of 4000 years. A domestic well, which is 1.5 miles south of monitoring well 10003 and constructed in the Prairie du Chien aquifer, had a carbon-14 age of 8000 years. Groundwater from the underlying Jordan aquifer should have a similarly long residence time.
In the Minnesota River valley in southeastern Carver County, recent tritium-age groundwater samples were collected from two bedrock wells; one well is constructed in the Jordan aquifer and the other is constructed in the St. Lawrence Formation. In the broad valley of the Minnesota River and in the surrounding bluffs, these shallow bedrock aquifers are overlain by the surficial sand aquifer. Unlike other areas in the county where fine-grained glacial sediment is at the land surface, precipitation rapidly infiltrates through the surficial sand aquifer to deeper aquifers.
STABLE ISOTOPE ANALYSIS OF GROUNDWATER AND SURFACE WATER
Isotopic chemical changes as water moves from precipitation to surface water and groundwater are complex but can be reconstructed to help determine whether groundwater was recharged directly from precipitation, lake water, or a mixture of the two. Stable isotopes of hydrogen and oxygen were analyzed for 79 groundwater samples from wells and one lake-water sample from Lake Zumbra.
Common hydrogen has only one proton; its stable isotope, deuterium (hydrogen-2 or 2H), has one proton and one neutron. Because of this difference, deuterium has approximately twice the mass of common hydrogen. Oxygen-16 (16O) contains eight protons and eight neutrons, and its stable isotope, oxygen-18 (18O), contains 8 protons and 10 neutrons; thus, oxygen-18 has slightly more mass than oxygen-16. This mass difference causes the stable isotopes of hydrogen and oxygen to fractionate or separate during evaporation (Ekman and Alexander, 2002). The lighter isotopes will evaporate more easily than the heavier isotopes. Because lake water is exposed to the atmosphere, evaporation causes significant fractionation of the stable isotopes of hydrogen and oxygen; as a result, lake water contains more of the heavier isotopes than are found in precipitation. Groundwater is more isolated from the atmosphere, however, so negligible fractionation occurs.
Figure 7 is a plot of the stable isotopes of hydrogen and oxygen in sampled groundwater and sampled lake water. The value on the x-axis represents the ratio of oxygen-18 to oxygen-16 in the sample divided by the same ratio in a standard. The value on the y-axis represents the ratio of deuterium to hydrogen in the sample divided by the same ratio in a standard. Values to the left on the x-axis or to the bottom on the y-axis indicate relatively more of the lighter isotope, while values to the right or to the top indicate more of the heavier isotope.
Regional background precipitation values for the stable isotopes of hydrogen and oxygen generally plot along a trend called the meteoric water line shown in Figure 7 (IAEA/WMO, 2002). The stable isotope values of the water samples from Lake Zumbra and some of the
groundwater samples plot on a slightly lower slope than the meteoric water line, which indicates that the water has undergone some fractionation during evaporation. This evaporative trend crosses the meteoric water line at the average value for precipitation in the county. The slope of the evaporative trend and the location where it meets the meteoric water line depend on the local climate, primarily the average temperature and humidity (Kendall and Doctor, 2003).
The groundwater samples that plot on the evaporative trend line away from the meteoric water line have undergone some evaporative fractionation, which means that part of this groundwater was recharged from lake water. These samples are shown in Figure 7 as symbols with colors indicating an evaporative isotopic signature. The locations of these wells are shown in Figure 8 as large well symbols. Groundwater samples that were recharged directly from precipitation plot on the meteoric water line. These samples are plotted on Figure 7 as small gray symbols and the well locations are shown in Figure 8 as small symbols.
Groundwater flow paths cannot be determined by hydrologic data or isotopes alone. Water may take a complex path through the watershed, part on the surface and part in the subsurface. The mingling of groundwater and surface water is most clearly seen by the continuum of values of stable isotope samples along the evaporative trend line. Recharge from surface water forms an important component of groundwater in northeastern Carver County, where there are many lakes, and in southeastern Carver County, near the Minnesota River valley. Recharge to groundwater by surface water is not common elsewhere in the county where groundwater is more typically recharged by direct infiltration of precipitation to the subsurface.
REFERENCES CITED
Ekman, J. and Alexander, S., 2002, Technical appendix to Part B, Regional Hydrogeologic Assessment, Otter Tail area, west-central Minnesota: Regional Hydrogeologic Assessment Series RHA–5, Minnesota Department of Natural Resources, St. Paul, 13 p.
IAEA/WMO, 2002, Global network of isotopes in precipitation: The GNIP Database, available at URL: http://www.iaea.org/water.
Kendall, C. and Doctor, D., 2003, Stable isotope applications in Hydrologic studies, Holland, H.D. and Turekian, K.K., editors, chap. 11 of v. 5, Surface and ground water, weathering, and soils, in Treatise on geochemistry: Amsterdam, The Netherlands, Elsevier, Inc., p. 319–364.
Sanocki, C.A., Langer, S.K., and Menard, J.C., 2009, Potentiometric Surfaces and Changes in Groundwater Levels in Selected Bedrock Aquifers in the Twin Cities Metropolitan Area, March-August 2008 and 1988-2008: U.S. Geological Survey Scientific Investigations Report 2009-5226, 67 p.
ACKNOWLEDGEMENTS
I received much help from my colleagues at DNR. Jan Falteisek provided assistance and guidance throughout the project. Shana Pascal, Greg Massaro, and Neil Cunningham made the plates more understandable through their GIS, layout, and editing. Joe Enfield of Carver County Environmental Services provided many years of historical groundwater chemistry data. Jim Berg provided geologic insight and data from his “South-Central Minnesota Groundwater Monitoring of the Mt. Simon Aquifer” report that was funded by the Minnesota Environment and Natural Resources Trust Fund. John Barry reviewed the final report. Thanks are due also to my colleagues at other agencies who provided excellent suggestions during peer review: Bob Tipping and Barb Lusardi of the Minnesota Geological Survey; Rich Soule of the Minnesota Department of Health; and Madeline Seveland of Carver County Water Management Department. I would like to thank Scott Alexander of the University of Minnesota, Department of Earth Sciences for collecting the carbon-14 water samples for analysis and interpreting the results.
Elevation of the top of the Upper Tunnel City aquifer.(feet above mean sea level)
Low: 403
High: 833
Water use reported by DNR groundwater appropriation permit holders for 2010 (millions of gallons per year)
> 100 to 150
> 150
0 to 20
50 to 10020 to 50
>>
FIGURE 4. Potentiometric surface elevation contours of the Mt. Simon aquifer. Contour interval: 50 feet. The location of wells constructed in the Mt. Simon aquifer that were sampled for chemistry and isotope analysis are shown. The location of wells and reported water use by DNR groundwater appropriation permit holders are also shown.
FIGURE 5. Locations of aquifer tests described in Table 1.
FIGURE 3. Potentiometric surface elevation contours of the combined Upper Tunnel City and Wonewoc aquifers. Dotted lines connect contours across areas where aquifer is not present. Contour interval: 25 feet. The location of wells constructed in the Upper Tunnel City and Wone-woc aquifers that were sampled for chemistry and isotope analysis are shown. The location of wells and reported water use by DNR groundwater appropriation permit holders are also shown.
FIGURE 2. Potentiometric surface elevation contours of the combined Prairie du Chien and Jordan aquifers. Dotted lines connect contours across areas where aquifer is not present. Contour interval: 25 feet. The location of wells constructed in the Prairie du Chien and Jordan aquifers that were sampled for chemistry and isotope analysis are shown. The location of wells and reported water use by DNR groundwater appropriation permit holders are also shown.
Aquifer
TABLE 1. Specific capacity from well development tests and transmissivity from aquifer tests for selected large-capacity wells. [gpm/ft, gallons per minute per foot; gpd/ft, gallons per day per foot; dash marks (--), no data available]
Mean Minimum Maximum No. of Tests
Well Diameter(inches)
Buried sand and gravel
Bedrock
sdvsrsbsg
sxsu
Unnamed
Prairie du Chien–Jordan4
Jordan
--------7469
47
50
16
--------3869
35
15
14
--------
11169
60
83
17
--------21
2
4
2
--------
12–1414
18
12–18
16–24
FIGURE 1. Sequence of bedrock geologic units and hydrogeologic units in Carver County. The Ka geologic unit is shown in Part A as PMu.
EXPLANATION
Aquifer
Confining unit, generally low permeability
Low to moderate permeability aquifer; thin sandstones interbedded with siltstone and claystone
High permeability bedding fracture
Relatively high intergranu-lar permeability with high permeability fractures. Jordan Sandstone Jordan aquifer
St. Lawrence Formation
Lone RockFormation
Relatively low intergranular permeability with high permeability bedding fractures.
Confining unit.
Moderate intergranular permeability.
Wonewoc Sandstone Wonewoc aquifer
Eau Claire Formation Confining unit.
Mt. Simon Sandstone Mt. Simon aquifer
Moderateintergranular permeability.
Low to moderate intergranular permeability. Thin sandstones are interlayered with siltstone and claystone. Probably low yielding aquifer.
Ka aquiferUnnamed Unit(Ka)
Confining unit.
Tunn
el C
ity G
roup Upper Tunnel
City aquifer
Confining unit.
Hinckley Sandstone and Fond du Lac Formation
Hinckley/Fond du Lac aquifer
Moderate intergranularpermeability
Geologic Unit Hydrogeologic Unit
Hydrogeologic Unit Properties
St. Peter Sandstone
Undivided
St. Peter aquiferModerate intergranular permeability.
Relatively low intergranular permeability with high permeability fractures.
Confining unit.Prai
rie d
u C
hien
G
roup Prairie du Chien
aquifer
FIGURE 6. Comparison of hydrographs of two DNR groundwater-level monitoring wells to 1970–2011 precipitation. The hydrograph of DNR Jordan aquifer monitoring well 10002 is shown in Figure 6a. The hydrograph of DNR Jordan aquifer monitoring well 10003 is shown in Figure 6b. A chart of precipitation at Chaska is shown in Figure 6c. The elevation of water levels in these two wells are not directly influenced by short-term trends in local precipitation. The location of these two monitoring wells is shown on Figure 2.
Aquifer test locations: label indicates aquifer
Upper Tunnel City–Wonewoc FIGURE 8. Location of wells sampled for chemistry and isotope analysis.
Groundwater samples with evaporative signatures are shown with larger symbols; they are clustered in northeastern Carver County near lakes or in southeastern Carver County near the Minnesota River.
Tritium ageSymbol color indicates tritium age of water sampled in well.
WellDiameter(inches)
Mean Minimum Maximum No. of Tests
------------
6–12
20
--
------------
175,500
52,700
--
------------
89,800
52,700
--
------------
273,000
52,700
--
------------4
1
--
6–16
--
11,600
--
4,700
--
35,200
--
7
--
--
----
--
----
--
----
--
----
--
----
Upper Tunnel City–Wonewoc4
Upper Tunnel City–Mt.Simon4
6
10
1
10
12
10
3
1
12–18
12
Wonewoc–Mt.Simon4 11 9 13 216
Mt. Simon 16
9
7
5
26
12
4
3
12–18
12–16Mt. Simon–Fond du Lac4
Specific Capacity (gpm/ft)1 Transmissivity from Aquifer Test (gpd/ft)2,3
1Data adapted from the County Well Index. 2See Figure 5 for locations of aquifer tests.3Data adapted from a compilation of aquifer test data from Minnesota Department of Natural Resources, Minnesota Department of Health, and the U. S. Geological Survey.4Well constructed across more than one aquifer.
Potentiometric surface elevation contour875
If shown, arsenic concentration equals or exceeds 5 parts per billion
30.6
If shown, chloride concentration equals or exceeds 5 parts per million
9.73
If shown, nitrate-nitrogen concentration equals or exceeds 3 parts per million
8.39
If shown, groundwater residence time in years, estimated by carbon-14 (14C) isotope analysis
7000
If shown on well symbol, arsenic not sampled
Map symbols and labels
Map symbols and labels
Static water level data from March 2008 synoptic
Static water level data10002 DNR groundwater level monitoring
well. Label is well number
Line of cross section
Body of water
-90
δ 18O (‰)
-13 -7 -1
δ 2 H
(‰)
-70
-80
-60
-30
-20
-50
-40
North American meteoric water line
Lake Zumbra
Evaporative trend
maximum
FIGURE 7. Graph of stable isotopes of oxygen and hydrogen from sampled groundwater and lake water in Carver County compared to the North Ameri-can meteoric water line. The colored well symbols indicate water samples that were affected by evaporation prior to moving into groundwater. The Lake Zumbra sample was highly fractionated by evaporation. The regression line of these samples shows the evaporative fractionation trend in Carver County. The groundwater samples shown by gray symbols represent groundwater directly recharged by precipitation. The dashed “2σ” lines show the statistical variation of stable isotope precipitation values used to derive the North American mete-oric water line (IAEA/WMO, 2002).
Explanation
Isotopic Signature
Meteoric Evaporative-Southeastern Carver County
Evaporative-Lake Zumbra
Evaporative-Northeastern Carver CountyWells
Lake
LOCATION DIAGRAM
MAP EXPLANATIONFigure 8
MAP EXPLANATIONFigures 2–4
Sampled well and aquifer symbols
Upper Tunnel CityWonewoc
Mt. Simon and Fond du Lac
Bedrock aquifers
Prairie du ChienJordan
Tritium age
Symbol color indicates tritium age of water sampled in well.
Recent—Water entered the ground since about 1953 (8 to 15 tritium units [TU]).Mixed—Water is a mixture of recent and vintage waters (greater than 1 TU to less than 8 TU).
Vintage—Water entered the ground before 1953 (less than or equal to 1 TU).
Well not sampled for tritium.
Sampled well and aquifer symbols
su
sgsx
sr
Buried sand and gravel aquifers
Bedrock aquifersUpper Tunnel CityWonewocMt. Simon orFond du Lac
Prairie du ChienJordan
St. Lawrence and St. Lawrence–Upper Tunnel City
Recent—Water entered the ground since about 1953 (8 to 15 tritium units [TU]).Mixed—Water is a mixture of recent and vintage waters (greater than 1 TU to less than 8 TU).Vintage—Water entered the ground before 1953 (less than or equal to 1 TU).
Well not sampled for tritium.
Stat
ic W
ater
Ele
vatio
n(fe
et a
bove
mea
n se
a le
vel)
925
920
915
930
9356a. Explanation—monitoring well 10002, Jordan aquifer, 191 feet deep
Water elevation
Average water elevation over period of record (924.3 feet)
Land surface elevation at monitoring well (feet)956.6
Year1970 1975 1980 1985 1990 1995 2000 2005 2010 2015
Stat
ic W
ater
Ele
vatio
n(fe
et a
bove
mea
n se
a le
vel)
905
900
895
910
915
Year1970 1975 1980 1985 1990 1995 2000 2005 2010 2015
Ann
ual P
reci
pita
tion
(inch
es)
1970
1975
1980
1985
1990
1995
2000
2005
2010
Year
0
5
10
15
20
25
30
35
40
451981-2010 30-year normal precipitation (31.85 inches)
6c.
6b. Explanation—monitoring well 10003, Jordan aquifer, 292 feet deep
Water elevation
Average water elevation over period of record (907.8 feet)
Land surface elevation at monitoring well (feet)
993.8
Lake sampled for isotopes
Line of cross section
Body of water
MAP EXPLANATION
Trace of fault; letters indicate relative vertical displacement: U, up; D, down
1 0 1 2 3 4 5 MILES
SCALE 1:200 000
1 0 1 2 4 5 6 7 83 9 KILOMETERS
COMPILATION SCALE 1:100 000
1 0 1 2 3 4
SCALE 1:300 000
1 0 1 2 4 5 6 7 83 9 KILOMETERS
5 MILES
1 0 1 2 3 4
SCALE 1:300 000
1 0 1 2 4 5 6 7 83 9 KILOMETERS
5 MILES
