Groundwater Atlas User Guide - Minnesota Department of ...Groundwater Atlas User Guide, March 2019 1 Groundwater Atlas User Guide Introduction This is a guide for the County Geologic

Groundwater Atlas User GuideFor the County Atlas Series - Part B

St. PaulMarch 2019

mndnr.gov/groundwatermapping

Report Contents

County Atlas Program ............................................................................. d

Introduction .............................................................................................1

Geology and physical hydrogeology ........................................................2

Water chemistry ......................................................................................6

Pollution sensitivity .................................................................................8

Hydrogeologic cross sections ................................................................10

Aquifer characteristics and groundwater use ........................................12

Navigating an atlas ................................................................................13

By Ruth C. MacDonald

Editor, County Geologic Atlas Program

March 2019

County Atlas Program

A Minnesota County Atlas (CGA) provides information about the geology and groundwater resources of a county, including the groundwater quality, quantity, and sensitivity to pollution.

Maps and reports are available in print or online as geographic information system (GIS) files or PDFs. Most are available in two parts (since 1992), and are created in sequence: geology in Part A, followed by groundwater in Part B.

How is an atlas used?The atlas provides information for understanding county resources and for making informed decisions on land-use and water resources. The following are a few examples.

• Identify aquifers for water supply planning and well construction.

• Develop county plans for long-term stable water supplies.

• Prepare plans for wellhead protection and well abandonment.

• Understand groundwater movement and interaction with surface water.

• Identify pollution sensitivity of aquifers and protect critical groundwater recharge areas.

• Construct septic systems, landfills, industrial sites, and feedlots.

• Identify valuable natural resources and plan for their use or protection.

How is a county studied?Geology: Part A

County staff meet with the Minnesota Geological Survey (MGS) and request the preparation of an atlas. Counties must be ready to provide in-kind support.

Geologists from the MGS investigate the properties and distribution of earth materials beneath the land surface using existing databases, field sampling, and laboratory analysis. Subsurface information is obtained from geophysical studies and rock and sediment sampling from outcrops and drill holes.

The information is used to produce maps of the geology, geologic layering, sand distribution, bedrock surface, and depth to bedrock.

Groundwater: Part B

After Part A is complete, hydrologists from the Minnesota Department of Natural Resources (DNR) study the groundwater resources of the county. A network of wells in the most commonly used aquifers is selected and sampled for chemistry and measured for water levels.

The completed groundwater atlas includes maps and reports identifying the direction of groundwater flow, aquifer properties, groundwater chemistry, the residence time (age) of the groundwater, and pollution sensitivity of individual aquifers.

Atlases can address special conditions upon request. Previous studies have included geologic resources, lake-groundwater interaction, sinkholes, and springs.

How is the work funded?The program is supported by the following:

• The DNR Ecological and Water Resources budget as appropriated by the legislature.

• The Minnesota Environment and Natural Resources Trust Fund.

• The Clean Water Fund of the Clean Water, Land and Legacy Amendment.

• County contributions of in-kind service to the project.• Other sources that support geologic mapping at

the MGS.

ResourcesFor existing atlases, studies, user guides, and more information consult the following:

Geology - Part AMinnesota Geological Survey(612) 626-2969mngs.umn.edu/county_atlas/countyatlas.htm

Groundwater - Part BMinnesota Department of Natural Resources(651) 296-4800mndnr.gov/groundwatermapping

Groundwater Atlas User Guide, March 2019

1

Groundwater Atlas User Guide Introduction

This is a guide for the County Geologic Atlas - Part B, which describes the groundwater characteristics of a county. The information is intended for those who use groundwater or make decisions on land-use and water resources. The purpose is to help the reader use the atlases more effectively. This initial page summarizes the information incorporated into the atlases. The pages that follow go into more detail about reading the maps and interpreting the reports.

Geology and physical hydrogeology describes the layering of the geologic units and aquifers (stratigraphy and hydrostratigraphy). Additional topics include potential recharge sources and the direction of groundwater flow.

Aquifers hold enough groundwater for pumping for practical use. The water is held in the spaces (pores) between grains of sediment, in bedrock fractures, or in limestone conduits.

• Surficial or water-table aquifers are unconfined and readily affected by surface activity.

• Buried aquifers are confined between aquitards.

Aquitards or confining layers impede water movement because the pore space connections are too limited to transmit much water. They are made up of fine-grained sediment, shale, siltstone, massive limestone, or hard crystalline rock. Aquifers that are protected by aquitards are better protected from contamination but receive slower recharge.

Flow direction is important for predicting the recharge to wells, lakes, and rivers, as well as the direction contamination could flow. Groundwater in aquifers flows from areas of high pressure to low pressure.

Water chemistry provides clues about the path the water has traveled, aquifer connections, possible sources of human contamination, and groundwater quality. All water starts as precipitation. Select chemicals are dissolved out of sediment on the way to an aquifer, giving clues about the material the groundwater traveled through. Other chemicals that travel from the surface unchanged can indicate sensitivity to contamination.

Groundwater flows into aquifers as recharge and out as discharge. Groundwater discharge can feed lakes, streams, and wetlands and is part of the reason surface water bodies don't dry up between rains. Groundwater recharge from lakes or open wetlands can have important implications for quantity and quality in "leaky" aquifers and lakes.

Connections can be identified from the effect of surface evaporation on the elements of water molecules.

Residence time is a measure of how long groundwater has remained in an aquifer. Water that arrived long ago indicates slow travel time. Longer residence time can indicate that modern contaminants will not reach the aquifer for a long time, but also that the recharge is slow and that this clean and limited resource should be managed wisely. Residence times are measured from the 1950s to thousands of years.

Areas of health concern for groundwater consumption can be identified by the presence of elevated levels of select chemicals in the well-water samples.

Pollution sensitivity of an aquifer is estimated based on the time it takes water to flow through various types and thicknesses of soils and geologic materials. Pollutants are assumed to travel with water at the same rate. Sensitivity ratings and water chemistry are compared to interpret flow paths.

Groundwater conditions are an interpretation of how water entered an aquifer, flowed through, discharged, and if it interacted with a lake or other surface water body. Conditions include aquifers that connect because the confining layers are thin or incomplete, the groundwater discharges to surface water, the flow is lateral, or the flow is redirected by nearby high-capacity pumping.

Hydrogeologic cross sections bring together the elements of the atlas in vertical slices of the county. They show the extent of aquifers and aquitards, water chemistry, residence time, groundwater conditions, flow directions, and areas of important recharge and discharge.

Aquifer characteristics and groundwater use summarize the capacity of aquifers to provide water and how the water is used. These data help with planning for well installations to meet a given use.

Navigating an atlas guides the user through questions typically asked about groundwater issues and indicates where to find the information in the atlases.


2

Geology and physical hydrogeologyOver the millennia ancient seas, lakes, and glaciers deposited layers of sediment with varied compositions and textures. Volcanic activity laid down lava. Tectonic forces buried, compressed, and heated layers transforming them into different types of rocks. The geologic characteristics of the sediment and bedrock define the physical properites of the aquifers and aquitards.

The information helps estimate aquifer productivity, the degree of protection from pollution, where the water came from, where it is headed, interaction with the surface and other water sources, and chemical changes that have occurred as the water dissolved material in its path.

Aquifers

Aquifers hold water in the pore spaces between sediment grains or in cracks and crevices. More productive aquifers have higher porosity (volume of pores) and permeability (connectedness of pores). The space is increased by coarser grains like sand and gravel or by greater fracturing from ancient weathering.

Aquitard

Bedrock aquifer

Buried sand and gravel aquifer

Aquitard

Water-table aquiferWater tableUnsaturated zone

Aquitard

Bedrock aquifer


Aquitard


Surficial or water table aquifers (unconfined) are typically the first water sources encountered beneath the land surface and have minimal protection from the surface. They are readily affected by surface events and therefore fluctuate with surface conditions (i.e., precipitation and evaporation).

Buried or confined aquifers are confined between aquitards. Pressure is created from both confinement and from water moving in from higher elevations in the aquifer. This causes groundwater to flow in the direction of decreasing pressure. The two types of buried aquifers detailed on subsequent pages are 1) buried sand and gravel and 2) bedrock.

Aquitards/confining layers

Aquitards have the opposite composition from aquifers and may protect the aquifers between them. Aquitards are generally composed of finer material (silt and clay) that limits pore size and connection, but can include a wide range of sediment and rock types.

How protective an aquitard is depends not only on its texture but also on its continuity and thickness. Aquitards will leak if they are discontinuous, thin, contain a coarser texture, or have heavy fracturing. More details are found in the sections on aquifer types.

Aquitards that provide good protection against surface pollution cause the aquifers below to recharge slowly. This must be taken into consideration for future groundwater availability.

AquitardBedrock aquifer


Aquitard



3Surficial aquifers: the water table

The unsaturated zone is the area near the land surface where the pore spaces are filled with air.

The water table is the depth at which the ground is saturated. The water table forms the upper boundary of the water-table aquifer.

The water table generally follows the surface topography. Flow is typically from local highs to river tributaries, lakes, and wetlands. The lack of confining layers above it generally makes for rapid recharge and higher pollution sensitivity.

The water table fluctuates with precipitation and local water use so the figures presented in the atlases are only estimates based on the combined available data.

• Water-table elevation is estimated from well-water levels, surface-water elevations, and depth to wet soil conditions.

• Depth to water table is derived by subtracting the water-table elevation from the land-surface elevation.

1 0 1 2 3 4 5 MILES

SCALE 1:375 000

1 0 1 2 3 4 5 6 7 KILOMETERS

Water-table elevation (feet)

>1480–1520

>1440–1480

>1400–1440

>1360–1400

>1320–1360

>1280–1320

>1240–1280

>1200–1240

>1160–1200

>1120–1160

>1080–1120

>1040–1080

>1000–1140

>960–1000

>920–960

>880–920

>840–880

Groundwater flow direction

1 0 1 2 3 4 5 MILES

SCALE 1:375 000

1 0 1 2 3 4 5 6 7 KILOMETERS

Water-table elevation (feet)

>1480–1520

>1440–1480

>1400–1440

>1360–1400

>1320–1360

>1280–1320

>1240–1280

>1200–1240

>1160–1200

>1120–1160

>1080–1120

>1040–1080

>1000–1140

>960–1000

>920–960

>880–920

>840–880


1 0 1 2 3 4 5 MILES

SCALE 1:375 000

1 0 1 2 3 4 5 6 7 KILOMETERS

Depth to water table (feet)

>30

>20–30

>10–20

0–10

Symbols and labelsLine of cross section (Part B)BB ’

Body of water

0–10

>10–20

>20–30

>30–40

>40

Depth of selected lakes (feet)

1 0 1 2 3 4 5 MILES

SCALE 1:375 000

1 0 1 2 3 4 5 6 7 KILOMETERS

Depth to water table (feet)

>30

>20–30

>10–20

0–10

Symbols and labelsLine of cross section (Part B)BB ’

Body of water

0–10

>10–20

>20–30

>30–40

>40

Depth of selected lakes (feet)


4Buried sand and gravel aquifers

Beneath the surface deposits are alternating layers of older deposits. The stratigraphic column correlates these geologic unit names the Part A atlas with the hydrogeologic names from Part B and indicates the labels used on the maps. The layers are shown on the cross section plates as follows:

• Aquifers are indicated with patterns.

• Aquitards are indicated with shades of gray.

mls

sct

scs

hbt

nts

nt

ms

mt

pws

prt

prs

zus

pu

psu

cg

ct

cg1

ct1

hs

hwt

mlt

pwt

surficial sand and gravel

Heiberg (loam till)

sand and gravel

Villard/Twin Cities (loam till)

sand and gravel

Moland (sandy loam till)

sand and gravel

St. Croix (sandy loam till)

sand and gravel

Emerald (sandy loam till)

sand and gravel

Hewitt (sandy loam till)

sand and gravel

Sauk Centre (loam till)

sand and gravel

Meyer Lake (loam till)

sand and gravel

St. Francis (loam till)

sand and gravel

W sequence (loam till)

sand and gravel*

sediment*

basal sand and gravel*

hbt

nt

ms

mt

cg

ct

cg1

ct1

hs

hwt

scs

sct

mls

mlt

prs

prt

pws

pwt

psu

pu

zus

Percent sand in aquitard

>60%

>50% and ≤60%

>40% and ≤50%

>30% and ≤40%

≤30%

Part A Part Bha wmt

nhsnts

*undifferentiated

Hydraulic conductivity is indicated by shades of gray. Lighter shades represent higher sand content and greater ease with which water can move through the pore spaces or fractures.

mls

sct

scs

hbt

nts

nt

ms

mt

pws

prt

prs

zus

pu

psu

cg

ct

cg1

ct1

hs

hwt

mlt

pwt

surficial sand and gravel

Heiberg (loam till)

sand and gravel

Villard/Twin Cities (loam till)

sand and gravel

Moland (sandy loam till)

sand and gravel

St. Croix (sandy loam till)

sand and gravel

Emerald (sandy loam till)

sand and gravel

Hewitt (sandy loam till)

sand and gravel

Sauk Centre (loam till)

sand and gravel

Meyer Lake (loam till)

sand and gravel

St. Francis (loam till)

sand and gravel

W sequence (loam till)

sand and gravel*

sediment*

basal sand and gravel*

hbt

nt

ms

mt

cg

ct

cg1

ct1

hs

hwt

scs

sct

mls

mlt

prs

prt

pws

pwt

psu

pu

zus

Percent sand in aquitard

>60%

>50% and ≤60%

>40% and ≤50%

>30% and ≤40%

≤30%

Part A Part Bha wmt

nhsnts

*undifferentiated

Bedrock aquifersBedrock aquifers transmit water through pores, fractures, or conduits. Aquitards restrict flow, but could still yield enough water for domestic well use through bedding plane fractures caused by ancient weathering processes when they were at the surface.

The bedrock layer is named in the caption on the maps.

On the cross section plates the bedrock layers are shown similar to sand and gravel:

• Aquifers in are indicated with patterns.

• Aquitards are indicated with shades of green.

1050

106034

9.6

7.41.2

9.8

2000

_e

ss

ct

mt

ms

cg

cg

cg

ms

ss

_w

pu

pu

Rive

r

1090 –

1080 –

1070 –

1060 –

1050 –

1040 –

1030 –

1020 –

1010 –

1000 –

990 –

980 –

Elev

ation

(fee

t)

ss

Aquifers and aquitards grouped by stratigraphy

Quaternary unconsolidated sediment

Aquitard shades of gray indicate sand content and hydraulic conductivity.

Surficial sand and gravel

Buried aquifers (patterns) and aquitards (grays)

Geologic unit code Percent sand

Bedrock

Wonewoc

Eau Claire Formation_e

_w

ct

mt

>60%

>30% and ≤40%

Symbols and labels

Tritium ageDarker color in small vertical rectangle (well screen symbol) indicates tritium age of water sampled in well. Lighter color indicates interpreted age of water in aquifer.

Mixed: water is a mixture of recent and vintage waters.

Vintage: water entered the ground before 1953

Recent: water entered the ground since about 1953.

Background color indicates interpreted tritium age of aquifer.

Aquifers are indicated by patterns, pattern color indicates interpreted tritium age.Aquitards are indicated by solid color.

ct

ms

mt

cg

pu

General groundwater flow direction

Approximate equipotential contour; contour interval 10 feet

1060

Chloride: if shown, concentration is ≥5 ppm.9.8

Nitrate: if shown, concentration is ≥1 ppm.1.2

Carbon-14 (14C): if shown, estimated groundwater residence time in years.

2000

A bedrock stratigraphic column is often included that categorizes bedrock aquifers and aquitards based on their relative permeability.

Low

er to

Upp

er

Cret

aceo

usU

pper

Cr

etac

eous

Syst

em-

Serie

s

MES

OZO

ICER

APR

ECAM

BRIA

NPA

LEO

ZOIC

Upp

er C

ambr

ian

Mid

dle

Cam

bria

nM

ESO

PRO

TERO

ZOIC

Relatively high intergranular permeability with high permeability fractures

Jordan Sandstone Jordan aquifer

St. Lawrence Formation

Lone RockFormation

Mazomanie Formation Relatively low to moderate

intergranular permeability with high permeability fractures

Generally low permeability




Moderate intergranular permeability

Wonewoc Sandstone Wonewoc aquifer

aquitard

aquitard

aquitard

aquitard

Eau Claire Formation

Mt. Simon Sandstone

Mt. Simon aquifer

Moderate intergranular permeability

Low intergranular permeability. Mudstone and siltstone interlayered with thin sandstone. Low yielding aquifer.

Low to moderate intergranular permeability. Thin sandstones are interlayered with siltstone and claystone. Probably low yielding aquifer.

Ka aquitardUnnamed unit(Ka)

Kd aquiferDakota Formation (Kd)

Tunn

el C

ity G

roup Upper

Tunnel City aquifer

Hinckley Sandstone, Fond du Lac and

Solor Church formations

Mesoproterozoic aquifers

Moderate intergranularpermeability

Geologic UnitHydrogeologic

UnitHydrogeologic Unit Properties

Generalized high permeability bedding fracture


5Groundwater flow: potentiometric surfaces

The direction of groundwater flow is shown with potentiometric surface maps. In confined aquifers, pressure causes water in a well to rise above the aquifer. These levels are measured, posted on a map, and equal values are connected to create a contour map of the potentiometric surface for each aquifer.

The resulting maps show aquifer elevations like topographic maps show land-surface. Groundwater flows perpendicular to the contours as it moves from higher to lower potentiometric elevations (see arrows).

This represents the potential energy available to move groundwater: from days to weeks for shallower aquifers or centuries to millennia in deeper aquifers.

Higher elevations can indicate important recharge areas. Low elevations are typically discharge areas like River valleys. Discharge to rivers creates convergent flow toward rivers.

On the hydrogeologic cross section plates flow is indicated by the equipotential contour. Flow direction is shown with arrows on all maps

1050

106034

9.6

7.41.2

9.8

2000

Becrock aquitard 1

Surficial sand aquifer

Aquitard 1

Aquitard 2

Aquifer 1

Aquifer 2

Aquifer 2

cg

Aquifer 1

ss

Bedrock aquifer 1

Undifferentiated sediment

Und. sediment

Rive

r

1090 –

1080 –

1070 –

1060 –

1050 –

1040 –

1030 –

1020 –

1010 –

1000 –

990 –

980 –

Elev

ation

(fee

t)





Buried aquifers (patterns) and aquitards (grays). Shades of gray indicate hydraulic conductivity.

Bedrock

Aquifer

Aquitard_e

_w

Symbols and labels







Aquitard 1 (>60% sand)

Aquifer 1

Aquitard 2 (>30% and ≤40% sand)

Aquifer 2

undifferentiated sediment



1060




2000

1000

1040

1200

1080

1160

960

1200

1320

1280

920

1160880

1120

1240

Symbols and labelsGroundwater flow directionPotentiometric surface contour960

Potentiometric surface elevation (feet)

Aquifer not present

>840–920

>920–1000

>1000–1080

>1080–1160

>1160–1240

>1240–1320

>1320–1400

1000

1040

1200

1080

1160

960

1200

1320

1280

920

11608801120

1240



Aquifer not present

>840–920

>920–1000

>1000–1080

>1080–1160

>1160–1240

>1240–1320

>1320–1400

1000

1040

1200

1080

1160

960

1200

1320

1280

920

1160880

1120

1240



Aquifer not present

>840–920

>920–1000

>1000–1080

>1080–1160

>1160–1240

>1240–1320

>1320–1400


6

Water chemistryDissolved elements and compounds in groundwater provide information about the groundwater path: where the water came from, what it flowed through, when it arrived, and how long it remained. This information can be used to answer questions about how quickly an aquifer recharges, its source, its sensitivity to pollution, its interaction with other water bodies or wells, and well-water potability.

Samples are collected from wells in aquifers most important for domestic and community water supply. An ideal well-sampling network is evenly distributed across the county, includes populated areas, and targets surface water and groundwater interaction around lakes and larger rivers.

Recharge sourcesAquifer connections with lakes or other open water bodies (such as wetlands) have implications for groundwater recharge and cross-contamination. Groundwater keeps water bodies from drying up between rains, and surface contamination can reach groundwater through lakes, rivers, and wetlands.

Recharge from surface water can be determined by measuring the effect of evaporation on hydrogen and oxygen isotopes. In open water, lighter isotopes tend to evaporate more readily into the atmosphere, leaving behind a heavier signature in the water body. If it moves into the groundwater, the concentrations can be measured to determine its signature.

• A meteoric signature indicates that precipitation infiltrated directly into the ground before reaching the aquifer, without having a chance to evaporate.

• An evaporative signature indicates precipitation spent time in open water and experienced evaporation before reaching the aquifer, indicating a connection with a lake or other open water body.

The atlases may indicate evaporative signatures in the text in the text, on a graph, and on other maps and cross sections as appropriate. Look for indications in the legend.

Residence time indicatorsResidence time is a measure of how long groundwater has remained in an aquifer. This has the usual double-edged implications. Long residence time suggests that contaminants won't reach an aquifer for a long time in the future, but the recharge is likely slow and this clean resource is not renewable for many lifetimes.

Residence time is estimated from concentrations of tritium and carbon-14 isotopes. Times range from the 1950s to thousands of years.

• Recent tritium-age is represented with magenta or pink coloring of aquifer symbols and patterns. It represents short residence time suggesting high recharge rates, short travel paths, and higher sensitivity to pollution.

• Vintage tritium-age is represented with blue coloring of aquifer symbols and patterns. It represents long residence time suggesting low recharge rates, long travel paths, and low pollution sensitivity.

Select vintage wells may also contain a numeric value indicating a carbon-14 date of hundreds to thousands of years.

• Mixed tritium age suggests possible connections between aquifers with recent and vintage tritium ages.

Chemicals of concernSelect chemicals can indicate areas where groundwater consumption could harm human health. Some are introduced at the surface by humans and are used as indicators of an aquifer's sensitivity to pollution, such as chloride and nitrate. Others can occur naturally from the geologic materials, such as arsenic and manganese.

The maps list color-coded numeric values near each well for elevated levels of chemicals of concern. The atlases use guidelines from the U.S. Environmental Protection Agency and the Minnesota Department of Health.


7

1050

106034

9.6

7.41.2

9.8

2000

Becrock aquitard 1


Aquitard 1

Aquitard 2

Aquifer 1

Aquifer 2

Aquifer 2

cg

Aquifer 1

ss

Bedrock aquifer 1


Und. sediment

Rive

r

1090 –

1080 –

1070 –

1060 –

1050 –

1040 –

1030 –

1020 –

1010 –

1000 –

990 –

980 –

Elev

ation

(fee

t)






Bedrock

Aquifer

Aquitard_e

_w

Symbols and labels








Aquifer 1


Aquifer 2




1060




2000

Chloride: if shown, concentration ≥5 ppm.9.8

Symbols and labels


Mixed VintageRecent


Bedrock

Aquifer Interpreted tritium age is indicated by pattern color.

AquiferInterpreted tritium age is indicated by background color.

1.02

1.15

1.39

1.7

17.7

3.01

4

3.8

8

7

6

2.3

2.42

2

24.4

2.85

5.9

22.2

52

17.4

20

16

6.2

6.54.3

6

11.5

17

16

24

30

31

37

6.3

12.8

9

12

6

24

97

55

24.3

40

35

50

50

20.7

73

54

45

31

53

27.1

35

49

36

<5

<5

<511

49

20

32

49

13.6

28

21

41

33

22.4

46

3.1

15.7

3.8

25

30

11

12

30

14.8

9

9.810

67

11

2615.1

21.9

10.7

19

15.9

26.7

24.4

26.6

16.5

35 5.9

18

17

53

4.53.7

5017

120

149

229

109

238

280

119

103

360

131

100

310

234

120

120

274

220

103

150

284

950

262

146

177

126

142

153

276

156

520

480

440

101

140

210

230

120

186

290

306

150

480

120

220

700

150

166

102

250

180

109

124

390

200

150

320

294

690

490

490

430

103

160

200

154

940

350

100

181

180

104

450

130

167

258

130

285

106

136

111

470

256

126

340

109

285420

320

600

302510

1290

630

420

410350

610

288

<100

2500

14,000

20,000

<100

6000

15,000

35,000

9000

40,000

30,000<100

7.6+

8.9+

23.1+

10.6+

62*

16.6*

8.6*

10.1*

6.8*

11*

38*

43*

6.5*

18.2*

35*

6.8*

7.3*

20.4*

13.2*

22.1*

10.3*

23.8*

7.1*

15.1*

20.9*

28.6*

8.4*

5.2*

35*

25.1*

27.3*

8.3*

70*

49*

25.9*

10.7*

18.7*

7.4*

18.6*

5.8*

5.3*

28.3*

12.1*

53*

63*

14.7*

31.3*

7.8*

6.3*

15.4*

19*

8.5*

20.7*

22.2*

38*

12.7*

5.1*

98*

15.7*

16.3*

25.2*

13*

36*

11.7*

6.8*

15.4*

63*

6.3*

15.8*

15.1*7.9*

5.8*

52*

9.4*

5.9*

5*

11.3

5.4

198

93

5.9

19.4

5

142

177

60

8.936

62

23.9

33

10.3

11.5

12.4

17.5

21.2

MAP EXPLANATION

dg/br

rlf

h3/h4

Surficial and buried sand aquifer or aquifer group

Symbol color indicates tritium age of water sample.

Symbols for water samples and aquifers

ot/nv

Chemistry labels

23.9

26.7

8000180

Chloride

Arsenic

Manganese

Carbon-14 (14C)

Sulfate288

Mixed VintageRecent

Tritium age

1 0 1 2 3 4 5 MILES

1 0 1 2 4 5 KILOMETERS3

SCALE 1:100 000

1.02

1.15

1.39

1.7

17.7

3.01

4

3.8

8

7

6

2.3

2.42

2

24.4

2.85

5.9

22.2

52

17.4

20

16

6.2

6.54.3

6

11.5

17

16

24

30

31

37

6.3

12.8

9

12

6

24

97

55

24.3

40

35

50

50

20.7

73

54

45

31

53

27.1

35

49

36

<5

<5

<511

49

20

32

49

13.6

28

21

41

33

22.4

46

3.1

15.7

3.8

25

30

11

12

30

14.8

9

9.810

67

11

2615.1

21.9

10.7

19

15.9

26.7

24.4

26.6

16.5

35 5.9

18

17

53

4.53.7

5017

120

149

229

109

238

280

119

103

360

131

100

310

234

120

120

274

220

103

150

284

950

262

146

177

126

142

153

276

156

520

480

440

101

140

210

230

120

186

290

306

150

480

120

220

700

150

166

102

250

180

109

124

390

200

150

320

294

690

490

490

430

103

160

200

154

940

350

100

181

180

104

450

130

167

258

130

285

106

136

111

470

256

126

340

109

285420

320

600

302510

1290

630

420

410350

610

288

<100

2500

14,000

20,000

<100

6000

15,000

35,000

9000

40,000

30,000<100

7.6+

8.9+

23.1+

10.6+

62*

16.6*

8.6*

10.1*

6.8*

11*

38*

43*

6.5*

18.2*

35*

6.8*

7.3*

20.4*

13.2*

22.1*

10.3*

23.8*

7.1*

15.1*

20.9*

28.6*

8.4*

5.2*

35*

25.1*

27.3*

8.3*

70*

49*

25.9*

10.7*

18.7*

7.4*

18.6*

5.8*

5.3*

28.3*

12.1*

53*

63*

14.7*

31.3*

7.8*

6.3*

15.4*

19*

8.5*

20.7*

22.2*

38*

12.7*

5.1*

98*

15.7*

16.3*

25.2*

13*

36*

11.7*

6.8*

15.4*

63*

6.3*

15.8*

15.1*7.9*

5.8*

52*

9.4*

5.9*

5*

11.3

5.4

198

93

5.9

19.4

5

142

177

60

8.936

62

23.9

33

10.3

11.5

12.4

17.5

21.2

MAP EXPLANATION

dg/br

rlf

h3/h4

Surficial and buried sand aquifer or aquifer group

Symbol color indicates tritium age of water sample.

Symbols for water samples and aquifers

ot/nv

Chemistry labels

23.9

26.7

8000180

Chloride

Arsenic

Manganese

Carbon-14 (14C)

Sulfate288

Mixed VintageRecent

Tritium age

1 0 1 2 3 4 5 MILES

1 0 1 2 4 5 KILOMETERS3

SCALE 1:100 000


8

Pollution sensitivityPollution sensitivity methods assume that contaminants travel with water unchanged as they move through the soil and underlying sediment to an aquifer. Two models are used based on the different properties of the aquifer materials: 1) near-surface materials and 2) buried sand and gravel and bedrock surface.

Near-surface materialsThis method estimates the time it takes for water to infiltrate the land surface and reach the water table. The water table is assumed to be 10 feet below land surface: 0–3 feet is assumed to be soil, 3–10 feet is assumed to be surficial geological material.

The transmission rate varies depending on the texture. Coarse-grained materials have faster transmission rates than fine-grained materials. The time of travel varies from hours to approximately a year.

• High sensitivity ratings have relatively short travel times (hours to a week).

• Low or very low ratings have longer travel times (weeks to a year).

• Ultra-low ratings have travel times of more than a year.

Buried sand and gravel aquifers and bedrock surface

Farther below, buried aquifers have estimated vertical travel times that can vary from hours to thousands of years. The pollution sensitivity of these aquifers and recharge characteristics are evaluated by the following.

1. Calculating the cumulative thickness of the protective fine-grained sediment above each buried sand aquifer and the top of bedrock

2. Comparing the pollution sensitivity maps with other groundwater chemistry results such as residence time and the presence of surface contaminants

3. Determining the groundwater conditions for flow and aquifer connections

1. Cumulative till thickness (protective layering)

The thicker the layer of fine-grained (till) sediment overlying an aquifer, the longer it takes for water to move through it. The more of these layers above an aquifer, the greater the protection. GIS software first calculates cumulative thickness of the sediment layers in the county for the following ratings.

• Thicknesses of 10 feet or less were rated very high• Thicknesses greater than 40 feet were rated very low. • Intermediate ratings and thicknesses are indicated on

the maps.

3. Groundwater Chemistry

Higher sensitivity is associated with the following results.

• Tritium age is recent.

• Nitrate is elevated and anthropogenic (human caused) if concentrations are greater than or equal to 1 ppm (part per million).

• Chloride is elevated if concentrations are greater than or equal to 5 ppm. It is anthropogenic if chloride/bromide ratios are greater than 250.

Tritium age is indicated by the color of the well symbol. Chemical values are listed near the well symbols.

2. Groundwater conditions

The pollution sensitivity model assumes only vertical flow, but in natural systems the flow is vertical, lateral, and even upward in discharge areas. The following conditions can help explain pollution sensitivity and chemistry results.

The first three conditions match the assumptions of the sensitivity model. The others are possible explanations of unique conditions and chemical results. A hypothetical example is found in the next section.

Water from the surface moves through a thin layer of overlying fine-grained material to an underlying aquifer.

Groundwater moves from an overlying surficial aquifer to a buried aquifer.

Groundwater moves from an overlying buried aquifer to an underlying buried aquifer.

Groundwater flows laterally.

U Groundwater flowpath is unknown.

Groundwater discharges to a surface-water body.


9

1.4

1.1

16.4

60.5

10.4

17.4

8.17

15.6

61.4

2000

10,000

1000

8000

Pollution sensitivity of near-surface materials

Very High: hours to months

High: weeks to years

Moderate: years to decades

Low: decades to a century

Very Low: a century or more

Estimated vertical travel time.

Symbol color indicates tritium age of water sample.Tritium age

Mixed

Vintage

Recent

10.3 Chloride: if shown, concentration is ≥5 ppm.

Nitrate: if shown, concentration is ≥1 ppm.

Symbols and labels


Carbon-14 (14C): residence time in years.15,000

1.39

High: hours to a week

Moderate: a week to weeks

Low: weeks to months

Very low: months to a year

Estimated vertical travel time through near-surface materials

Groundwater conditionsWater from the surface moves through a thin layer of overlying fine-grained material to an underlying aquifer.Groundwater moves from an overlying surficial aquifer to a buried aquifer. .Groundwater flows laterally.Groundwater discharges to a surface-water body.

Pollution sensitivity of the bedrock surface


10

Hydrogeologic cross sectionsCross sections add the vertical dimension and illustrate aquifer connections more clearly. The location of each cross section line is indicated on all the maps for the county. Most of the elements previously discussed in this atlas are included on these plates. The following is a recap:

• Aquifers are labeled by pattern.

• Aquitards are indicated by solid color. The shade of gray for the Quaternary aquitards indicates the sand content and relative hydraulic conductivity, or the ability to transmit water.

• Residence time is indicated in the aquifer as follows.

Tritium-age color: • In the sediment aquifer background • In the bedrock aquifer pattern• In the well symbol

Carbon-14 age• Value in years listed near the well symbol

Longer residence times generally mean slower recharge and lower pollution sensitivity.

• Elevated chemical concentrations list color-coded values near each well symbol. Their presence can indicate either faster recharge and higher pollution sensitivity, or a naturally elevated situation.

• Groundwater flow is perpendicular to the equipotential lines, in the direction of decreasing pressure. Equipotential lines show where the pressure head of groundwater is the same.

• Recharge and discharge areas indicate important areas of connection and possible convergent flow.

• Groundwater conditions are indicated by a circled number or letter, and indicate types of groundwater connections and type of flow (vertical or lateral).

Example of how to read a cross sectionThe hypothetical cross section in the figure gives an example of some groundwater conditions that connect aquifers and affect pollution sensitivity.

Water from the surface moves through a thin layer of overlying fine-grained material to an underlying aquifer.

Recent tritium-age water reached this thinly buried aquifer from the surface, along with anthropogenic chloride (34 ppm) and nitrate (9.6 ppm). This indicates a pollution sensitivity issue.

Groundwater moves from an overlying surficial aquifer to a buried aquifer.

Recent tritium-age water and chloride (9.8 ppm) moved from the Surficial sand aquifer to buried Aquifer 1, because the overlying protective till is thin.

Groundwater moves from an overlying buried aquifer to an underlying buried aquifer.

The two thin overlying till layers allowed mixed tritium-aged water to move from Aquifer 1 to Aquifer 2.

Groundwater flows laterally.

Groundwater flowed laterally through Aquifer 1 to another part of Aquifer 1 through a part of this aquifer that is not visible on the cross section.

U

Tritium concentrations may be artificially elevated by high capacity pumping.

Not shown in figure. The residence time would be less than expected. The pump and aquifer would show different tritium-ages. Flow arrows might converge toward a high-capacity pump.

U Groundwater flowpath is unknown.

Not shown in figure. The condition is labeled unknown when the well sample results do not match the surrounding information and other explanations are not available.

Groundwater discharges to a surface-water body.

The groundwater discharged to the river.


11

1050

106034

9.6

7.41.2

9.8

2000

Becrock aquitard 1


Aquitard 1

Aquitard 2

Aquifer 1

Aquifer 2

Aquifer 2

cg

Aquifer 1

ss

Bedrock aquifer 1


Und. sediment

Rive

r

1090 –

1080 –

1070 –

1060 –

1050 –

1040 –

1030 –

1020 –

1010 –

1000 –

990 –

980 –

Elev

ation

(fee

t)






Bedrock

Aquifer

Aquitard_e

_w

Symbols and labels








Aquifer 1


Aquifer 2




1060




2000


12

Aquifer characteristics and groundwater useAquifer characteristics such as specific capacity and transmissivity are used to describe how well water is transmitted by an aquifer. Larger values of each of these parameters indicate more productive aquifers.

Specific capacity is the pumping rate per unit depth of drawdown, and is determined from short-term pumping or well-development tests performed after a well was drilled.

Transmissivity is an aquifer’s capacity to transmit water. It provides a more accurate representation of the aquifer

properties than specific capacity because it is from longer-term and larger-scale aquifer tests.

Groundwater use is mapped and compiled from water-use appropriation permits from the DNR, required for groundwater users withdrawing more than 10,000 gallons of water per day or 1 million gallons per year.

The values in the atlas are listed in tables by category and show the physical distribution on maps.

Specific capacity and transmissivity of selected wells

Aquifer

Specific capacity (gpm/ft) Transmissivity (ft2/day)

Casing diam. (in.) Mean Min Max Number

of testsCasing

diam. (in.) Mean Min Max

Unconsolidated aquifersblankWater table 8 13 13 13 1 -- -- -- --Unconfined buried sand 10 32 32 32 1 -- -- -- --Confined buried sand 8–20 32 3 102 22 6–20 21,900 5,800 49,200

Bedrock aquifersCretaceous undifferentiated 8 0.3 0.3 0.3 1 -- -- -- --

St. Lawrence–Eau Claire 10 150 150 150 1 -- -- -- --Tunnel City–Wonewoc 12 6 4 8 2 -- -- -- --Tunnel City–Eau Claire 12 5 5 5 1 -- -- -- --Tunnel City–Mt. Simon 10 75 75 75 1 -- -- -- --Wonewoc–Mt. Simon 8 8 8 8 1 -- -- -- --Wonewoc 18 9 7 11 2 -- -- -- --Eau Claire–Mt. Simon 8 20 20 20 1 12 37,500 46,300Mt. Simon 8–24 16 2 26 4 -- -- -- --Mt. Simon–Hinckley 14–20 25 2 57 3 -- -- -- --Mt. Simon–Fond du Lac 12 8 8 8 1 -- -- -- --Hinckley 10 5 5 5 1 -- -- -- --Hinckley–Fond du Lac 12 17 17 17 1 * -- -- --

Specific capacity data adapted from the CWI; gpm/ft, gallons per minute per foot. Transmissivity data are from aquifer test data compiled by the DNR; ft2/day, --, no data.

Reported water use from DNR groundwater permit holders

blank Use category

Aquifer

Num

ber o

f wel

ls

Mun

icip

al/p

ublic

w

ater

supp

ly

Crop

irrig

ation

(a

gric

ultu

ral,

orch

ard,

vi

neya

rd, n

urse

ry)

Golf

cour

se ir

rigati

on

Food

pro

cess

ing

Lake

leve

l m

aint

enan

ce

Live

stoc

k w

ater

ing

Land

scap

ing/

athl

etic

field

s

Wat

er su

pply

(p

rivat

e, ca

mpg

roun

d,

way

side,

rest

are

a)

Sand

and

gra

vel

was

hing

Quaternary aquifers

Water table 32 185.3 135 15.6 -- -- -- 5.6 2.7 26.1

Buried sand 121 1879.3 255.7 52.4 93.6 -- 42.6 20.4 27.2 --

Bedrock aquifers

Cretaceous 1 4.5 -- -- -- -- -- -- -- --

Upper Paleozoic1 3 -- -- -- -- 55.1 -- -- -- --

Lower Paleozoic2 14 457 30.4 76 -- 3.4 -- 1.3 -- --

Mesoproterozoic3 2 17.7 2.6 -- -- -- -- -- -- --

Multiple4 10 366.3 -- -- -- -- -- 12.8 -- --

Total (mgy) -- 2910.1 423.7 144 93.6 58.5 42.6 40.1 29.9 26.1

Total (percent) -- 77% 11% 4% 2% 2% 1% 1% 1% >1%

Highest annual use by permit 2011–2015

-- 3541.3 748.1 243.1 104.5 69.8 56.6 40.1 36.1 29.9

Data from MPARS; mgy, million gallons per year; dash marks (--) indicate no use in those categories]1. Upper Paleozoic aquifers includes Jordan and Upper Tunnel City 2. Lower Paleozoic aquifers includes Wonewoc and Mt. Simon4. Multiple aquifer wells extract water from more than one Paleozoic or Mesoproterozoic aquifer

Mississippi River

Cro

w

R

iver

Cle

arw

ater

R

iver

Buffalo Lake

North Fork Crow River

South

For

k C

row

Riv

er

101

)24

)55

)25

)25

)55

94

12

94

)

Lake MariaState Park

Howard Lake

Buffalo

Maple Lake

Annandale

South Haven

Rockford

WaverlyCokato

Montrose

Delano

Albertville

Monticello

Clearwater

45°

94°

94°15'

93°45'

45°15'

B

D

A

C

F

E

G

E’

A’

C’

B’

D’

G’

F’

1 0 1 2 3 4

SCALE 1:300 000

1 0 1 2 4 5 6 7 83 9 KILOMETERS

5 MILES

0–15

>15–45

>45–100

>100–200

>200

Groundwater use

Municipal/public water supply

Crop irrigation (agricultural, orchard, vineyard, nursery)

Golf course irrigation

Food processing

Lake level maintenance

Livestock watering

Landscaping/athletic fields

Water supply (private, campground, wayside, rest area)

Sand and gravel washing

Other (heating/cooling, power generation, dust control)

Water use reported by DNR groundwater appropriation permit holders in 2015(millions of gallons per year)

Line of cross section (Part B)

Symbols and labels

BB ’

Body of water


13

Navigating an atlasThe following is a summary of where to find the information for your county and purpose.

Part A Atlas: Geology1. What are the main surficial geologic units?

Consult the surficial geology plate: Find the dominant units on the map and read their descriptions. Are they sandy and course so they hold and transmit water, or fine graIned so they impede water movement?

2. Where are the aquifers?

Consult the sand distribution model plate: find sandy layers with significant extent and thickness.

Part B Atlas: Groundwater3. Are the aquifers sensitive to pollution?

Consult the pollution sensitivity figures and look for large extents with low sensitivity. Look for the following chemical indicators:

• Vintage tritium color in the aquifer symbols symbols.

• Carbon-14 values.

• Lack of elevated values listed for human introduced chemicals like chloride and nitrate.

• Any groundwater conditions that would cause flow to move other than expected?

4. Are the aquifers protected?

Consult the hydrogeologic cross sections.

Look for overlying confining units that are continuous, have low sand content (darker grays), and have greater thickness and depth. This also means the recharge is slow and the resource may not be as renewable.

Also check the same indicators as indicated in #3.

5. Where is the groundwater from; where is it flowing to?

Check the groundwater flow arrows on many of the maps. Note if there are any pollution concerns with the source or flow.

Check the groundwater conditions (circled numbers or letters) for any unique flow patters and other situations that may be affecting the flow, or even redirecting it.

Note connections to surface water, overlying aquifers, and discharge to lakes and rivers. Check the recharge section (stable isotopes) for connections to surface water bodies and consider how the interaction might be affected by surrounding activity.

Note if the groundwater is the recharge for sensitive surface water such as a trout stream or water supply.

For bedrock, look for possible karst conditions and comments specific to your county.

6. Are harmful chemicals present?

Check the chemistry plate, cross sections, and other maps for numeric values near the well symbols. If shown the wells were sampled and they contain elevated values. The values can represent natural or human-caused contamination.

• Chemicals like chloride and nitrate can indicate higher pollution sensitivity and extensive human activity at the surface.

• Chemicals such as arsenic and manganese can indicate a naturally ocurring issue that may necessitate water treatment.

Consult the Minnesota Department of Health for further information.

7. What is the capacity of the chosen aquifers and their use?

Check the section on aquifer characteristics and groundwater use for results from current wells and aquifer tests.

500 Lafayette RoadSt. Paul, MN 55155-4025888-646-6367 or 651-296-6157www.mndnr.gov/waters

This information is available in alternative format on request.The Minnesota DNR prohibits discrimination in its programs and services based on race, color, creed, religion, national origin, sex, public assistance status, age, sexual orientation, or disability. Persons with disabilities may request reasonable modifications to access or participate in DNR programs and services by contacting the DNR ADA Title II Coordinator at [email protected] or 651-296-6157. Discrimination inquiries should be sent to Minnesota DNR, 500 Lafayette Road, St. Paul, MN 55155-4049; or Office of Civil Rights, U.S. Department of the Interior, 1849 C Street NW, Washington, DC 20240.

© 2019, State of Minnesota, Department of Natural Resources and the Regents of the University of Minnesota

Prepared and published with the support of the following:

The Minnesota Environment and Natural Resources Trust Fund as recommended by the Legislative Citizen Commission on Minnesota Resources (LCCMR).

The Clean Water Fund, which receives 33 percent of the sales tax revenue from the Clean Water, Land and Legacy Amendment, approved by voters in November 2008.

https://www.dnr.state.mn.us/waters/index.html

mailto:info.dnr%40state.mn.us?subject=ADA%20Title%20II%20Coordinator

Documents

Groundwater Atlas User Guide - Minnesota Department of ...Groundwater Atlas User Guide, March 2019 1 Groundwater Atlas User Guide Introduction This is a guide for the County Geologic