STATE OF MINNESOTA COUNTY ATLAS SERIES DEPARTMENT OF NATURAL RESOURCES ATLAS C–11, PART B, PLATE 7 OF 10 DIVISION OF WATERS Bedrock Hydrogeology

92°45' R 18 W 93°00' R 17 W R 16 W BEDROCK HYDROGEOLOGY CROSS-SECTION EXPLANATION Dsom 56 6 6 1 6 1 1 Recent—Water entered the ground since 1953 (10 or more tritium units). Ogal 92°30' R 15 W R 14 W By Well screen color shows recent water. Odub er 6000 Mixed—Water is a mixture of recent and vintage waters Odub iv Dsom 16 R reek (0.8 to less than 10 tritium units). Well screen color shows mixed water. UDOLPHO 2500 C Moira Campion 7 ot Dsom ek o re 818,000 Ogal Dsom R C ’ Vintage—Water entered the ground before 1953 (less than 0.8 tritium units). 1 PLEASANT y A e 2002 Well screen color shows vintage water. A 1240 r Odub Waltham VALLEY 1260 a Dsom C Dcvl Very old—Water with carbon-14 age greater than 10,000 years before present. 16,000 63 Well screen color shows vintage water. 1 Sargeant T 104 N son 90 in Dsom b Potentiometric Contour Cross-Section Symbols ch o In feet above mean sea level. 1240 n R Waltham a If shown, ground-water age in years, Br Dsom I-90 Contour interval is 20 feet. Arrow 18,000 1220 1220 T 104 N Robinson indicates general direction of ground- estimated by carbon-14 SARGEANT Creek ( ) U.S. 63 ’ A Cedar River A water movement Dsom SV Vintage water shallower than mixed water C Dsom e 1300 1300 Upper Cedar Valley d WALTHAM RACINE Spring associated with stream a 20 Dcvl 218 r 1240 SV Lower Cedar Valley 1 6000 Ground-water flow into the cross section 1200 2500 1200 Spillville-Maquoketa Ground-water flow out of the cross section North 36 31 Racine 1100 SV 1100 R 36 31 56 36 31 36 31 31 iv e r ’ Geologic Units and Aquifers

Elevation B (feet above sea level) 1000 1000 No r B t 6000 h Dsom Sand and gravel deposits Spillville-Maquoketa aquifer R o 1 900 b 6 1 6 1 6 6 1 6 erts ° Elevation LANSING 1 16,000 (feet above sea level) Undifferentiated till Lansing Creek Dcvl 7 Bear 43 45' 43°45' Fork 2 800 Creek 7500 Dsom 18,000 Upper Cedar Valley aquifer Galena Group aquifer Dsom 2 DEXTER Dsom 1220 Brownsdale 700 Chickasaw shale Decorah-Platteville-Glenwood map unit* 1260 Dcvl k Dcvl ee Cr Lower Cedar Valley aquifer St. Peter-Prairie du Chien-Jordan aquifer Dsom ear ek GRAND B Odub Wolf Cre Dclc MEADOW *The and both act as confining units, but the intervening outh Fork S eek Platteville Formation is a thin aquifer. Combined, these units are treated as a confining unit. Ramsey 9000 er Cr T 103 N Mill Pond 1200 De T 103 N Dsom Grand Dexter 1280 Ogal Dcvu 16 Meadow 16 RED ROCK I-90 Racine Characterization of Bedrock Hydrogeology 35,000 Brownsdale k 16 e 20 Roberts Creek ( ) ’ e Dcvu Dclc ’ B Lansing B This plate displays the Mower County aquifer system in map and cross-section Mu r C r phy C Cedar River ( ) views. This presentation provides practical information about the hydrogeology in C 1200 C 1300 re 1300 e the county, which is crucial to understanding ground-water supply and management k 1240 FRANKFORD ins issues. The information also was essential to the development of the pollution b 1320 Dcvl b 1200 1200 o Dcvl Dsom sensitivity map on Plate 9. Concepts that require more detailed explanation are D 1300 7500 Dclp Maple View 1240 discussed on Plate 8 and in the Technical Appendix. 1100 6000 1220 8 1100 The interpretation of the bedrock hydrogeology was modified from a historical Dsom 36 31 14 one-aquifer system to a sequence of several aquifers and confining units. This 31 31 36 31 36

36 Elevation 31 (feet above sea level) 1000 1000 approach has been used by hydrogeologists in Iowa and Minnesota (see Plate 2, Part Dclc 1340 A). The presence of regional shale confining units provides protection from surface 1300 Elkton1280 900 contamination in areas with limited, low-permeability glacial cover. Mapping the 3000 Dclc 16 90 Dcvu 1260 1 shallow confining units at a countywide scale provides an opportunity to avoid 6 1 6 Elevation 1 6 1 6 1 (feet above sea level) 6 800 drilling unnecessarily deep wells for drinking water supply. Regulators who know 90 ek re 6000 the location of the regional shale units can target aquifers that may be hydrologically r C er ee iv protected from surface contamination. This can reduce drilling costs for municipalities Dclc Dcvl D R 700 3 Dcvu and residents who depend on ground water for drinking water, irrigation, and industry.

Root The bedrock aquifers, confining units, and major mapped faults in the county 28,000 Dclc Dcvu 3 D’ are shown on the map, and a pattern overlies the area where till thickness is greater D Dclc 56 Branch than 75 feet. deposits are thin and discontinuous; they are not shown on Austin Dcvu I-90 Grand the map or cross sections. The potentiometric surfaces for the three uppermost 7 Dexter Meadow O 1240 South aquifers are shown with 20-foot contours of different colors, as well as the locations r c 3 h 105 CLAYTON T 102 N of wells used to develop the potentiometric contours. The locations of wells sampled a r ’ T 102 N d C for geochemistry and for residence time information from tritium and carbon-14 age

Dcvl C AUSTIN 1200 Dcvu C

r Maple View

e MARSHALL dating are also displayed. The cross sections show the arrangement of aquifers and

e BENNINGTON 1300 1300 k Cedar River ( ) confining units at depth and colored residence time interpretations based on the age- Dcvu 3 dating results from the sampled wells. All sampled wells have been projected onto 1200 SV 1200 Dcvl SV the closest cross section. No well is more than 2 miles from a cross section. See Dclc 43,000 Dcvu Dcvu 9000 Plate 8 for a description of radiometric dating of ground water. 4 1100 SV 1100 The map shows potentiometric contours of the Upper Cedar Valley, Lower er v r Varco Rose i 1320 ve Cedar Valley, and Spillville-Maquoketa aquifers. The small data points showing the r 4 4 R 9000 i e WINDOM Creek a R 1000 iv 1180 1000 well locations used to develop these surfaces are displayed in colors corresponding R R w a o o w s Creek I o Dcvu e r I to the contours. There are few locations where wells from shallower and deeper e p 36 900 Elevation 900 36 31 Dcvu (feet above sea level) aquifers are close enough to one another to be used as nests for a point-by-point Dsom 218 36 36 31 p 31 ar 31 31 U d 36 Dclc comparison of water-level information from different aquifers. Enough data points e ’

Elevation C E (feet above sea level) 800 800 exist, however, to show that the potentiometric surface of each aquifer is different.

E 1200 56 7 Dcvl The potentiometric differences between the Upper Cedar Valley and the Lower Cedar

Dclc nch 6 1

1 6 1 a 1 e 700 Valley aquifers are subtle in the southeastern part of the county. Greater differences

6 1 6 6 r tl it B L appear in the center of cross-section E–E’. The difference between the potentiometric h Adams t r 1320 600 surfaces of the Lower Cedar Valley and the Spillville-Maquoketa is most obvious o 8000 N in the center of the map and in the center of cross-section C–C’. Generally, ground Dclc Tritium units: less than 0.8 Dclc 5 35,000 Casing depth: 930 feet water flows from east-central Mower County to the south and west in the Upper and 1160 Taopi Depth completed: 1035 feet LE ROY 11 Lower Cedar Valley aquifers. In the northeast, ground water in the Spillville- 5 Maquoketa aquifer flows from the center of the county to the north. In the northwest, 7 Dsom ground water in the Spillville-Maquoketa aquifer flows south through potentiometric U 1200 1260 1300 p Dcvu p Elkton troughs toward the Cedar River discharge area. Generally, potentiometric differences er 1300 Root Dcvu River are smallest at the Cedar and Little Iowa rivers, which are regional discharge areas. Little 1280 Austin 1180 5 1280 T 101 N ’ Recent ground water was found in samples from 12 wells based on tritium LYLE 5 NEVADA D T 101 N Cedar dating. Nine of the wells with samples of recent water have till cover less than 75 1180 Dcvu D

1200 Dcvu LODI River ( ) U.S. 218 Dcvl 1240 Dcvu Cedar 56 feet thick. For most of the central and northeastern parts of the county, ground water 1220 Dcvu Dcvu 1300 1300 Dcvu 105 Iowa 14 gets progressively older with depth. This is a typical way for water to infiltrate from Dcvu ’ 6000 the land surface into the bedrock aquifers. However, there are areas shown on cross- F 1200 1200 R iver sections A–A’ and C–C’ where samples of vintage waters were found shallower F W Dclc o 3000 o than the samples of mixed waters in deeper nearby wells. In southwest and southeast d 1100 1100 b R 1280 ur Dcvu 1260 y iv Mower County, the distribution of recent, mixed, and vintage samples on the cross C O r er eek t ter 6 e 6 sections is different from the rest of the county. Recent and mixed waters are found r e Elevation 6 C k 1260 1000 1000 (feet above sea level) at great depths. Recent and mixed waters found at depth indicate focused recharge. Dcvu Le Roy 7500 10,000 Faulting and sinkholes are also found in the western portion of C–C’ and D–D’ Lyle 900 31 36 7 36 31 36 31 36 and the eastern portion of E–E’ and F–F’. The presence of faulting and karst features 31 31 Dclc Elevation (feet above sea level) may be a factor in focused recharge. These residence time patterns are discussed in 36 43°30' 800 43°30' R 14 W ° more detail on Plate 8. ° R 15 W 92 30' 93°00' R 18 W R 17 W R 16 W 92 45' Mower County has an abundant supply of high-quality drinking water in the 700 bedrock aquifers found throughout the county. Ground water in the two uppermost Digital base map composite: 28,000 bedrock aquifers flows from the east-central part of the county to the south and west. Roads and county boundaries—Minnesota Department of Transportation GIS Statewide Base MULTIAQUIFER SYSTEM IN AND Map (source scale 1:24,000) SCALE 1:100 000 In the northeast, ground water in the Spillville-Maquoketa aquifer flows from the UPPER BEDROCK IN MOWER COUNTY Hydrologic features—U.S. Geological Survey Digital Line Graphs (source scale 1:100,000) 1 0 1 2 3 4 5 MILES center of the county generally to the north. Results of age dating show that till thicker Digital base map annotation—Minnesota Geological Survey. Most of the previous hydrogeologic studies in Mower County describe a single, thick bedrock aquifer underlying the county. This study Upper than 75 feet can restrict infiltration from the land surface to the bedrock aquifers. Adams Iowa River ( ) The faults and karst features in the west and southeast may contribute to the focused Project data compiled from 1997 to 2001 at the scale of 1:100,000. Universal Transverse presents the Devonian and upper Ordovician bedrock as a sequence of carbonate aquifers separated by shale units. Hydrogeologists in Iowa Rose ’ Mercator projection, grid zone 15, 1983 North American datum. Vertical datum is mean sea 1 0 1 2 3 4 5 6 7 8 KILOMETERS (Libra and Hallberg, 1985) first classified the rocks as regionally extensive carbonate and shale units that compose a regional system of Creek E recharge of the bedrock aquifers from the land surface. level. aquifers and confining units. John Mossler used this approach to classify the stratigraphy of these carbonates and shales on Plate 2, Part A. U.S. 218 GIS data and metadata available through the DNR Waters website: http://www.dnr.state.mn.us/waters Green and others (1997) also described these rock units as aquifers and confining units similar to those in Iowa. Pump test data and residence E Cedar River 1300 REFERENCES CITED time information in this study supported this approach to characterizing the carbonate and shale units. This approach also has practical 9000 benefits. With approval from the Minnesota Department of Health, wells may be completed in some shallow carbonate units beneath regional 1200 1200 Green, J. A., Mossler, J. H., Alexander, S. C., and Alexander, E. C., Jr., 1997, Karst hydrogeology of Le Roy Township, Mower County, Minnesota: Minnesota MAP EXPLANATION Uppermost Bedrock Aquifers and Confining Units shale units. This change would reduce required depths of well completion by 300 feet to 500 feet and reduce construction costs by several thousand dollars per well. 1100 1100 Geological Survey Open-File Report 97-2, 2 pls., scale 1:24,000. Aquifer or The information below includes the rock unit name, aquifer symbol (where applicable, boldface in parentheses), bedrock symbol (in Libra, R. D., and Hallberg, G. R., 1985, Hydrogeologic observations from multiple Well Symbols Symbol confining unit parentheses), and details about the rock units. A geologic column and more information about these aquifers are in the Technical Appendix. 1000 1000 core holes and piezometers in the Devonian carbonate aquifers in Floyd and

Elevation (feet above sea level) Mitchell counties, Iowa: Iowa Geological Survey Open File Report 85-2, Part Upper Cedar Valley Aquifer (Dcvu) (Dcuu and Dcum). The Lithograph City Formation, the Coralville Formation, and the Hinkle Shape indicates aquifer type Greater than 75 feet and Eagle Center Members of the form a shallow bedrock aquifer. The Lithograph City unit contains many joints, 1, p. 1–19. of till cover 900 900 fractures, and bedding planes enlarged by solution resulting in a well-developed conduit network and high permeability (Green and others, 8000 1997). The Coralville unit contains shale beds that may be several feet thick but are discontinuous (Libra and Hallberg, 1985). Most Upper Cedar Valley Upper Cedar Valley aquifer 800 Dcvu permeability in this aquifer is fracture related, with water moving through joints or bedding planes. The lower part of the aquifer has less The DNR Information Center Lower Cedar Valley solution-related permeability than the Lithograph City This aquifer is up to 110 feet thick.

Elevation . (feet above sea level) Twin Cities: (651) 296-6157 Chickasaw shale ( ) This silty shale has low permeability and hydrologically separates the Upper Cedar Valley above from the 700 Spillville-MaquoketaAquifer Aquifer Lithologic Dclc LOCATION DIAGRAM Chickasaw Shale Dclc . DNR Minnesota Toll Free: 1-888-646-6367 name Code code on map Lower Cedar Valley underneath. It has been mapped on Plate 2, Part A, and is clearly shown on the gamma log in the Technical Appendix. Waters Galena Group 600 Telecommunication Device for the Lower Cedar Valley aquifer In western Mower County, buried stream valleys dissect it. This unit is 36 feet to 43 feet thick in southeastern Mower County and 15 feet Quaternary Q Dcvl Hearing Impaired (TDD): (651) 296-5484 St. Peter-Prairie du Chien-Jordan to 20 feet thick in western Mower County. 43,000 Cedar Valley Upper DCVU ( ) The Bassett Member of the Little Cedar Formation forms a thin aquifer (Green and others, 500 TDD Minnesota Toll Free: 1-800-657-3929 Spillville-Maquoketa aquifer Lower Cedar Valley Aquifer (Dcvl) Dclp . CedarDCVL Valley Lower Dsom 1997) and is 40 feet to 70 feet thick. The upper and lower parts of the Pinicon Ridge Formation contain shale and shaly dolostone that may DNR Web Site: http://www.dnr.state.mn.us act as confining units. The Pinicon Ridge Formation is 20 feet to 47 feet thick. These shaly units were not mapped in Part A, and the distribution Upper Iowa Color indicates tritium age River ( ) This information is available in an alternative format on request. Spillville Maquoketa DSOM Dubuque Formation of data for this study is inconclusive regarding the ability of the Pinicon Ridge shales to hydrologically separate the Lower Cedar Valley ’ Odub Le Roy F Recent—WatersSt. Peter-Prairie with tritium concentrations of 10 tritium aquifer from the underlying Spillville-Maquoketa aquifer. However, results from a pump test in Le Roy provide local evidence that the shales This map was compiled and generated using geographic information systems (GIS) units (TU) or more entered the ground water since 1953. Galena Group aquifer from the Pinicon Ridge do separate the Lower Cedar Valley aquifer from the underlying Spillville-Maquoketa aquifer (Green and others, technology. Digital data products are available from DNR Waters. du Chien-Jordan Ogal Lyle 1300 1997). F This map was prepared from publicly available information only. Every reasonable Mixed—WatersGalena with 0.8 to 10 TU are a mixture of recent Cedar River Spillville-Maquoketa Aquifer (Dsom) (Dspl and Omaq). The Spillville and Maquoketa formations form a single aquifer unit in Mower effort has been made to ensure the accuracy of the factual data on which this map and vintage. County. The porosity and permeability in the upper part of the Spillville is due to fractures and in the lower part is due to features (Plate 1200 1200 interpretation is based. However, the Department of Natural Resources does not warrant Potentiometric Contour 2, Part A). The upper part of the Maquoketa has extensive fracturing possibly because of exposure at the surface before the deposition of the accuracy, completeness, or any implied uses of these data. Users may wish to verify Vintage—Waters with less than 0.8 TU entered 1100 1100 critical information; sources include both the references here and information on file in the the ground water before 1953. the overlying . The lower part of the Maquoketa has many thin shale units and grades into the underlying Dubuque Formation, which together hydrologically separate the Spillville-Maquoketa aquifer from the Galena Group aquifer. The Spillville and offices of the Minnesota Geological Survey and the Minnesota Department of Natural 1200 Potentiometric contour of aquifers in feet Resources. Every effort has been made to ensure the interpretation shown conforms to Upper Cedar Valley —Contour interval is Maquoketa formations together are up to 170 feet thick. 1000 10,000 1000 20above feet. mean Dashed sea where level contour is uncertain. ( ) This formation consist of limestone interbedded with thin to medium beds of calcareous shale. It is a 7500 sound geologic and cartographic principles. This map should not be used to establish legal Elevation Well Label Dubuque Formation Odub . (feet above sea level) title, boundaries, or locations of improvements. 1200 Arrow indicates general direction of ground- confining unit that separates the overlying Spillville-Maquoketa aquifer from the underlying Galena aquifer and is 23 feet to 35 feet thick. 900 900 Equal opportunity to participate in and benefit from programs of the Minnesota

Elevation If shown, ground-water age in years, estimated by Lower Cedar Valley water movement. (feet above sea level) 30,000 Galena Group Aquifer (Ogal) (Ogal). The Galena Group, which is an important regional aquifer, comprises the Stewartville Formation, Department of Natural Resources is available to all individuals regardless of race, color, carbon-14 SCALE 1:146 000 1200 Prosser Limestone, and . The Stewartville and Prosser both have more well-developed porosity and permeability 800 national origin, sex, sexual orientation, marital status, status with regard to public assistance, Spillville-Maquoketa than the Cummingsville and form an aquifer. The greatest permeability of the group occurs where the aquifer is near the surface and has age, or disability. Discrimination inquiries should be sent to Minnesota DNR, 500 Lafayette Tritium units: 1 1 0 1 2 3 4 5 MILES well-developed karst features. Total thickness of this group is 200 feet to 205 feet. Casing depth: 695 feet Road, St. Paul, MN 55155-4031; or the Equal Opportunity Office, Department of the Interior, Decorah Shale–Platteville Formation–Glenwood Formation (Odpg). These three formations are treated collectively because they Depth completed: 911 feet Washington, DC 20240. Map Symbols Upper Cedar Valley Wells measured for static water level are found between two extensive regional aquifers. Only the Decorah Shale and Glenwood Formation have predictable low-permeability 0 2 4 6 8 KILOMETERS Fault line characteristics. They effectively separate the Galena Group aquifer from the underlying St. Peter Sandstone and have a combined thickness ©2002 State of Minnesota, Lower Cedar Valley of 45 feet to 50 feet. The Platteville Formation is a thin limestone aquifer (30 feet thick) between the Decorah Shale and the Glenwood VERTICAL EXAGGERATION X 40 Department of Natural Resources, and the Spring Formation. Although it is not heavily used for water supply, the Glenwood Formation can transport large quantities of water. Regents of the University of Minnesota TM Spillville-Maquoketa GEOLOGIC ATLAS OF MOWER COUNTY, MINNESOTA