Madeline Gotkowitz Hydrogeologist

Groundwater Conditions in Carbonate Bedrock Areas, Southwest Wisconsin

NR 151 Technical Advisory Committee December 13, 2016

Outline

• Southwest Wisconsin Hydrogeology • Pathogen transport in fractured rock • groundwater quality

Karst is a type of landscape

• Formed when soluble rocks, such as limestone and dolomite, dissolve

• Dissolution occurs because percolating rainwater is slightly acidic, pH about 5.7

• Spectacular, well-developed karst systems feature large caves and sinkholes (Kentucky, New Mexico, Cave of the Mounds)

• Wisconsin’s karst features are relatively muted, with small sinkholes, enlarged fracture networks and conduits

20% of U.S. land surface is karst

Weary and Doctor, 2014

crystalline rock

sandstone

carbonate

Carbonate rocks Silurian

Sinnipee

Prairie du Chien

sandstone

Mount Simon sandstone

Sinnipee

Wisconsin River Valley

Sinnipee dolomite

Galena

sandstone

St. Peter sandstone

Prairie du Chien dolomite

Cross section of geologic strata in Driftless Area

Galena dolomite

Bedding plane fractures, Iowa County

Horizontal

Vertical

Platteville Fm, Hwy 151 Lafayette County

southwest

northeast

Near Cave of the Mounds, Dane County

Easy to see…

Or not so easy to see…

Sinnipee dolomite, Iowa County

Lafayette County Fracture traces in field

• Cause acute illness • Survival depends on

temperature, moisture, and absence of UV light

• Present in large numbers in human and animal waste

• Septic systems, sewer systems, and manure

• Remain infectious on the order of 10s of months in groundwater

Pathogens: bacteria, protozoa and viruses

Bacteria: Campylobacter, Salmonella, E. coli O157:H7,

Aeromonas

Pathogen transport

Particulates and common diameters: (1 micron = 1 millionth of a meter)

Human hair (~50-100 um) Rock fracture (1 – 1,000s um)

Colloids (<0.2 um) Bacteria (~.2 – 20 um) Viruses (~0.005 um)

Porous media: slows groundwater transport, filters pathogens, dilutes dissolved contaminants (e.g. nitrate)

Fractures: rapid transport, no filtration or contaminant decay

Pore spaces filled with water

Dodgeville Fleet Farm

Bacteria, private residential wells

Well water quality viewer, Center for Watershed Science and Education, UW Extension; Accessed 12/9/2016

Well water quality viewer, Center for Watershed Science and Education, UW Extension; Accessed 12/9/2016

27% 34 of 126

27% 351 of 958

16% 5 of 31

19% 33 of 171 35%

40 of 115

41% 128 of 312

23% 253 of 1,087

32% 37 of 114

20% 106 of 536

14% 332 of 2,381

20% 229 of 1,167

11% 42 of 374

19% 100 of 525

28% 101 of 355

21% 553 of 2681

17% 16 of 96

22% 22 of 102

Summary • Karst is a landscape typified by large openings in

carbonate bedrock • Wisconsin geology is not uniform: karst forms a

V-shaped band across the state • Groundwater in carbonate rock with thin soil

cover is very vulnerable to contamination because of rapid flow pathways from the land surface

• Southwest Wisconsin has ridge and valley topography with thin soil on uplands

Summary

• Sinnipee and Platteville formations are highly fractured and karst features are common

• The layered geology leads to perched groundwater in some areas

• 15 to 40% of tested private residential wells are positive for coliform bacteria (an indicator bacteria)

sandstone

shale

dolomite

Water levels respond to precipitation.

Galena aquifer Mt Simon aquifer

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Prairie du Chein Dolomite underlain by Cambrian sandstone and siltstone layers(up to 1,000 feet thick in this area)

WELL CONSTRUCTION IN IOWA COUNTY UPLANDS

Soil and clay

Galena Dolomite

Decorah Shale

Platteville Dolomite

St. Peter Sandstone

regional water table

YF365new well

UG327old well

Septictank

perched water table

Karst landscapes are characterized by sinkholes, caves, and underground drainage

Runkel, et al., 2003

In Wisconsin, fracture networks are the predominant expression of karst

Well design and construction support groundwater quality in deep aquifers.