Paleozoic Karst Aquifers in the Mid-Continent

Topics• Overview

• Conceptual model

• Aquifer Properties

• Dynamics

• Water quality

• Karst Geomorphology

• Modeling difficulties

Paleozoic carbonates in mid-continent

Edwards

Floridan

Roswell

Wisconsin arch

Ozark plateau

Finlay archCincinnati archLexington domeNashville dome

Illin

ois

basi

n

Mic

higa

n b

asin

Mis

siss

ippi

em

baym

ent

Biscayne Aquifer (Pleistocene)

Floridan Aquifer (Tertiary)

Edwards Aquifer (Cretaceous)

Permian (Roswell in NM and Blaine in TX)

Mississippian

Silurian

Cambrian-Ordovician (Nashville and Lexington, Ozarks, Arbuckle Mtns in OK)

Paleozoic Karst in the Appalachians

Conceptual Models

Mechanism for cave development

Flow through small fractures,

diffuse flow, similar to

porous media

Conduit development and migration of the water table

Conceptual model for Paleozoic Karst Aquifer, Based on Mammoth Cave Area, KY Topo

divideWatershed divide

Erosion of base level stream causing multiple levels of caves. Based on Mammoth Cave area

Properties

• Intact Limestone: Low K and S

• Karstified LS: High K, Low S

• Epikarst (surface): Low K, High S

Hydraulic diffusivity: T/S

Water level response to rainfallLarge Kb/S = fast response (rise and fall)

Small Sy = large magnitude

Water level in well

and local rainfall, Ozark Plateau

Well in Big Clifty Sandstone

Well in St. Louis LS

Rainfall in Mammoth Cave Area

Water Quality

Depth to saline ground water

Vulnerability of Karst Aquifers to Contamination

1. Sinkholes funnel surface contamination into cave conduits.

2. Rapid transport in caves (km+/day) moves contaminants away from source

3. Thin soils provide minor sorption/retention

4. Turbulent flow transports clay. Increase tubidity and contaminants sorbed to clay

Important Hydro-Geomorphic Features in Karst Aquifers

1. Sinkholes: Recharge, ground stability

2. Estevelles: Recharge and discharge

3. Vertical fractures w/dissolution: Recharge/discharge

4. Epikarst: Storage

5. Solution channels: water pathways; high velocity flow

6. Springs: Focused discharge

Porosity

Sinkholes and Estevelles

http://caveandkarst.wku.edu/dishman.htm

Sinkhole collapse related to hydrogeology

Flooding caused by sinkholes

                                                                                          

.

Sinkhole risk evaluation. Controlled largely by underlying formation. Mississippian produces most sinkholes

Springs

First-order spring. Discharge > 100 cfs

Discharge from

springs

Percent of days when discharge equaled or exceeded

2 springs in Ordovician rocks

2 springs in Silurian rocks

Discharge Probability Plots

Hydrograph for karst spring

Discharge as function of time

recharge recession recharge recession recharge recession

Vertical fractures and faults

Karst systems and biodiversity

Blind Cave Fish Blind Salamander

Cave Ecosystems

Modeling Flow in Karst Conduits• Porous Aquifer, Darcy:

• Conduit, Manning:

1

;

dx

dh

n

Kv

dx

dhKq

exx

2/13/2

dx

dh

n

Hv r

x

Fundamental difference in

physics of flow

Hr: hydraulic radius=x-section area/wetted perimeter

n = wall roughness

Conduit geometry and wall roughness highly variable—how to determine in the field for an aquifer?

Ozark Plateau Aquifer System

Stratigraphy of the St. Francois and Ozark

Aquifers

caves typically underlie sandstone

Pb-Zn

Geology

Thickness of Springfield Aquifer Thickness of

Ozark Aquifer

Regional potentiometric surface on Ozark Plateau and Western Interior Aquifer System

•

Cross-section on NW side of Ozark Plateau. Fresh water mixes with saline water in laterally equivalent units deeper in basin.

Potentiometric surface in Ozark Plateau in Missouri

330 Mgpd

Lead and zinc mining districts in Ozark Plateau

Biggest producer of Pb,Zn in the world in 1920s

Viburnum Trend Active

Site Mining area

Lead Zinc

Water(µg/L)

Bedsediment(µg/g)

Tissue(µg/g)

Water(µg/L)

Bedsediment(µg/g)

Tissue(µg/g)

Center Creek Tri-State <1 370 0.3 67-270 5,600 770Big River Old Lead Belt <1 2,300 134 8-19 670 514Meramec River Old Lead Belt -- 180 12.2 -- 140 296West Fork ofBlack River

Viburnum Trend <1-11 10-95 0.5-8.3 13-33 12-46 70-110

Strother Creek Viburnum Trend <1-3 20 0.7 33-148 120 150Background -- <1-20 15-28 <0.1-0.6 <1-44 43-140 57-230

Pb and Zn concentrations in water, sediment and tissue